Electrical Network Design

Transcript

873 13. Electrical network design methodology and application example Publication, traduction et reproduction totales ou partielles de ce document sont rigoureusement interdites sauf autorisation écrite de nos services. The publication, translation and reproduction, either wholly or partly, of this document are not allowed without our written consent. Industrial electrical network design guide T&D 6 883 427/AE 874 13. ELECTRICAL EXAMPLE NETWORK DESIGN DESIGN METHODOLOGY METHODOLOGY AND APPLICATION APPLICATION The profitability of an industrial installation is directly linked to the availability of the production tool. Electrical networks supply the energy required for the production tool to operate. Thus, continuity of supply to loads is studied when the network is being designed and especially when the preliminary choices for the single-line diagram are being made. The aim of designing an electrical network is to determine the electrical installation which will meet the requirements of the industrial process for the least investment, operation and failure cost. The design methodology of a network has six main stages. n collection of data (stage 1) This involves: - identifying identifying problems, problems, needs needs to be met a and nd obligator obligatory y requireme requirements nts - collecting collecting the the elements elements required required for designing designing the network network and and de defining fining equipment. equipment. n preparation of the preliminary single-line diagram (stage 2) This involves preparing a single-line diagram which meets needs and obligatory requirements and which takes all the data into account. n technical studies and single-line diagram validation (stage 3) This involves a validation and technical/economic optimisation study of the planned structure taking into account all the data and hypotheses. It requires network calculations (short-circuit currents, load flows, etc.) to be carried out. n choice of equipment (stage 4) Once the single-line diagram has been validated, the equipment is chosen and sized using the results of the calculations carried out during the previous stage and the data collected during stage 1. Publication, traduction et reproduction totales ou partielles de ce document sont rigoureusement interdites sauf autorisation écrite de nos services. The publication, translation and reproduction, either wholly or partly, of this document are not allowed without our written consent. Industrial electrical network design guide T&D 6 883 427/AE 875 n choice and setting of protection devices (stage 5) This involves defining the protection devices allowing faults to be detected and cleared and protection settings to be determined. n choice and installation of a control and monitoring system (stage 6) This involves choosing the structure of the control and monitoring system that will enable users to control and monitor the network and which will include automatic processes optimising the cost and availability of energy: - sour source ce cha chang ngeo eove vers rs - load load-sh -shed eddi ding ng/re /resto stora rati tion on - aut automa omatic tic recon reconfigu figurat ration ions s of distri distributi bution on loops loops - etc. Publication, traduction et reproduction totales ou partielles de ce document sont rigoureusement interdites sauf autorisation écrite de nos services. The publication, translation and reproduction, either wholly or partly, of this document are not allowed without our written consent. Industrial electrical network design guide T&D 6 883 427/AE 876 13.1. Collection of of da data (stage 1) The maximum amount of data enabling the network to be designed and equipment to be defined must be collected. 13.1 13.1.1 .1.. Envi Enviro ronm nmen enta tall cond condit itio ions ns The characteristics of equipment are given for standard environmental conditions. Knowing the parameters relating to the real conditions of the site will enable the designer to introduce correction or derating factors for equipment. From among the environmental conditions, the designer will be concerned by: - risks of of explosion explosion in in the p presence resence of gas or atmosphereatmosphere-inflam inflammable mable products, products, which which determines the degree of equipment protection - ea eart rthq hqua uake ke risk risks s - altitude - aver averag age e an and d ma maxi ximu mum m temp temper erat atur ures es - soil soil therm thermal al and and elec electri trical cal resist resistivi ivity ty - prese presenc nce e of of fr frost ost,, wi wind nd and and s sno now w - lightning lightning density density level level of the region for the protecti protection on of the installation installation against against lightning lightning (see § 5.1.3) - atm atmosp ospher heric ic pollut pollution ion (dust (dust,, corrosio corrosion, n, humidi humidity ty rate) rate) - site regulations regulations (building (building frequented frequented b by y pu public, blic, high building, building, e etc.) tc.) . 13.1 13.1.2 .2.. Clas Classi sifi fica cati tion on of load loads s This involves listing the installation's loads by classifying them per type: - motor lighting h ea t i n g etc. for which the following must be known: - nomina nominall power powers s (activ (active, e, reacti reactive ve a and nd a appa pparen rent) t) powe powers rs act actua uall lly y abso absorb rbed ed cosϕ efficiency operati ope rating ng tran transie sients nts (motor (motor startin starting, g, etc.) etc.) emitted and tolerated tolerated disturbance disturbance levels levels (harmonic (harmonics, s, unbalance, unbalance, flicker, interruptions, interruptions, etc.). Publication, traduction et reproduction totales ou partielles de ce document sont rigoureusement interdites sauf autorisation écrite de nos services. The publication, translation and reproduction, either wholly or partly, of this document are not allowed without our written consent. Industrial electrical network design guide T&D 6 883 427/AE 877 13.1.3. 13.1.3. Geogra Geographi phical cal or functi functiona onall atta attachm chment ent of loads loads It is necessary to record loads in relation to the factory layout plan and their respective roles in the industrial process. Indeed, through their geographical position in the factory, or their attachment to a functional assembly, loads can be grouped together naturally. For example: - a chemical unit - a prod produc ucti tion on wo work rksh shop op - a st steam ge generat rator - a waterworks - etc. Once they have been grouped together, it is necessary to determine the environmental conditions linked to the operation of these loads. Note: 13.1 13.1.4 .4.. load load group grouping ings s may be be impose imposed d in orde orderr to carr carry y out ener energy gy subsub-met meter ering ing.. Load Load oper operat atin ing g con condi diti tion ons s To carry out a power analysis, it is necessary to specify the operating conditions of different loads. There are three main operating cases: - load loads s whi which ch op ope erate rate continuously throughout installation operation time - load loads s whi which ch op oper erat ate e intermittently in relation to installation operation time - load which do n not ot op operate erate during normal circumstances circumstances and which back up loads whose operation is vital for safety reasons and possibly for the industrial process. Publication, traduction et reproduction totales ou partielles de ce document sont rigoureusement interdites sauf autorisation écrite de nos services. The publication, translation and reproduction, either wholly or partly, of this document are not allowed without our written consent. Industrial electrical network design guide T&D 6 883 427/AE 878 13.1.5. 13.1.5. Distur Disturban bances ces genera generated ted and toler tolerate ated d by by loads loads Some loads cause disturbances on the internal network, if not on the utility network. The designer must therefore record the level of disturbances caused by each load (see § 3) in order to plan the means of reducing them to an acceptable level for the entire electrical installation. The level of disturbance tolerated by electrical equipment must therefore be recorded. These levels are not always known or supplied by manufacturers. On the other hand, IEC standard 1000-2-4 defines the electromagnetic compatibility level on industrial networks (see table 3-1). It provides the disturbance level generally acceptable for medium and low voltage equipment. 13.1 13.1.6 .6.. Futu Futurre exte xtensio nsions ns The exact knowledge of extension possibilities of all or part of the installation allows the designer to take them into account notably: - for sizing sizing cable cables, s, transfo transforme rmers, rs, circui circuit-b t-brea reaker kers, s, etc. - for choo choosin sing g the distrib distributi ution on ne netwo twork rk struc structure ture - for estimati estimating ng the the surfa surface ce area areas s of premise premises. s. 13.1.7 13.1.7.. Clas Classi sifi fica cati tion on of of load loads s by imp impor orta tanc nce e The consequences of a supply interruption with respect to safety of persons and equipment and production may be serious. Thus, it is important to define the maximum interruption time for each category of loads and as a result choose the appropriate supply restoration mode. Loads can be placed in three large families: - loads loads una unable ble to with withstan stand d an any y interr interrupti uption on - loads requiring requiring restorat restoration ion times times which which cannot cannot be be met by human human interven intervention tion - loads having having restoratio restoration n ti times mes compati compatible ble with human intervention intervention Publication, traduction et reproduction totales ou partielles de ce document sont rigoureusement interdites sauf autorisation écrite de nos services. The publication, translation and reproduction, either wholly or partly, of this document are not allowed without our written consent. Industrial electrical network design guide T&D 6 883 427/AE 879 For the first category of loads, it is necessary to have a highly reliable autonomous source: - an unint uninterr errupt uptibl ible e power power suppl supply y (UPS) (UPS) (see (see § 1. 1.6.3 6.3)) - a no no-b -brea reak k ge gene nera rator tor set set (see (see § 4.1.2 4.1.2). ). This is the case of loads such as: - autom automat atic ic pro proce cess ss con contro troll syste system m - comp comput uter er syst system ems. s. For the second category, the maximum interruption time may vary from several tenths of a second to several dozen seconds. In this category there are: - loads which only tolerate tolerate short supply supply interruptions interruptions or fast source changeover; changeover; which which corresponds to the time required for switching to a back-up source or permanent internal source ( t < 1 s) - loads which tolerat tolerate e supply supply interruption interruptions s compatible compatible with with delayed delayed automati automatic c reclosing reclosing or automatic starting of a back-up source (automatic load-shedding/restoration system: t < 20 s ). For the third category, the interruption time is generally greater than one minute, which remains compatible with manual intervention for network reconfiguration or starting of a backup source. 13.1 13.1.8 .8.. Publ Public ic net netwo work rk req requi uire reme ment nts s At the take-over point, the public network imposes certain requirements which may be decisive for the preliminary choices for the factory internal network structure. n short-circuit power and supply voltage available from the utility The short-circuit power required at the take-over point depends on the installation power, the power of large loads and the disturbances generated and tolerated by the installation. The short-circuit power greatly depends on the take-over voltage level. Because of this, it plays a determining role in the choice of factory internal network structure. Publication, traduction et reproduction totales ou partielles de ce document sont rigoureusement interdites sauf autorisation écrite de nos services. The publication, translation and reproduction, either wholly or partly, of this document are not allowed without our written consent. Industrial electrical network design guide T&D 6 883 427/AE 880 n utility power supply characteristics characteristics The main characteristics of the voltage supplied by a medium and low voltage public distribution network in normal operating conditions are defined by European standard EN 50160. The purpose of this standard is to define and describe the values characterising the supply voltage, i.e. (see table 4-1): - frequency magnitude wave form symm symmetr etry y of the thre threee-ph phas ase e volta voltage ges. s. Publication, traduction et reproduction totales ou partielles de ce document sont rigoureusement interdites sauf autorisation écrite de nos services. The publication, translation and reproduction, either wholly or partly, of this document are not allowed without our written consent. Industrial electrical network design guide T&D 6 883 427/AE 881 13.2. 13.2. Prepa Preparat ration ion of the prelim prelimina inary ry single single-li -line ne diagra diagram m (stage 2) Using the data collected, a first single-line distribution diagram can be drawn up. 13.2 13.2.1 .1.. Power analysis This is the first essential stage in studying the design of a network. It must assess and geographically locate the active and reactive power values. Depending on the size of the site, the installed powers and the way they are shared, the installation will be divided into several geographical zones (3 to 8 zones). The analysis of active and reactive powers will thus be carried out for each zone with the utilisation factors for each load (see § 6.1.2.) and the coincidence factor for the group of several loads or circuits being applied to the installed powers (see tables 6-1 and 6-2) . 13.2 13.2.2 .2.. n Choi Choice ce of volt voltag age e lev level els s choice of utility supply voltage The choice of supply voltage depends on: - the the ins insta tall llat atio ion n pow power er - the minimu minimum m short short-ci -circu rcuit it powe powerr requi required red - the distur disturban bances ces gener generated ated and and tolerate tolerated d by the instal installati lation on - the voltag voltage e level levels s avail availabl able e ne near ar the the site. site. n choice of voltages The choice of voltages inside the site depends on: - the the s site ite size size and and pow power er shar sharin ing g - whe whether ther or or not there there are are MV loads loads such such as motors motors,, furnace furnaces, s, etc. etc. The choice of two or three voltage levels results in a technical/economic optimisation study which takes into account the advantages and drawbacks of each alternative. Publication, traduction et reproduction totales ou partielles de ce document sont rigoureusement interdites sauf autorisation écrite de nos services. The publication, translation and reproduction, either wholly or partly, of this document are not allowed without our written consent. Industrial electrical network design guide T&D 6 883 427/AE 882 In general, experience shows that: - for power powers s up to 10 MVA, MVA, two volt voltage age leve levels ls (MV, (MV, LV) are are chose chosen n - for powers powers over 10 10 MVA, choosin choosing g three voltage voltage levels may may prove prove to be more economic economic (HV, MV, LV). 13.2 13.2.3 .3.. Energy sources The main source of energy is generally constituted by the public distribution network. For reasons of safety or service continuity, the main source of an industrial installation is often accompanied by a replacement source. The different replacement sources possible are listed below. n second utility power supply This solution is advantageous when this second power supply comes from a different utility substation from the one which feeds the first. It may nevertheless also be worth using in the case where the two power supplies come from the same utility substation if the outgoing feeders are allocated to different busbars or transformers. n permanent internal source This solution may be chosen for reasons of safety or service continuity depending on the level of quality available on the public distribution network. It may also prove to be a good economic choice: - the factory has has residual residual fuel fuel at a marginal marginal cost (incinera (incinerating ting plant, plant, paper paper mill, mill, iron and and steel industry, petrochemical industry) - the factory factory produces produces steam for for the industr industrial ial process process which which can can be recovere recovered d to produce produce electrical energy (urban centralised heating). Generally, permanent internal sources are used connected with the public distribution network. The connection arrangement must nevertheless enable rapid disconnection of the sources and balance of the loads attached to each one of them respectively. Publication, traduction et reproduction totales ou partielles de ce document sont rigoureusement interdites sauf autorisation écrite de nos services. The publication, translation and reproduction, either wholly or partly, of this document are not allowed without our written consent. Industrial electrical network design guide T&D 6 883 427/AE 883 Connection can be carried out at any level of the distribution network structure, in relation to the following criteria: - intern internal al source source pow power er in rela relation tion to the tota totall power power - presence presence of this this source linked to specific specific needs needs which have or have not not been located located - concen concentrat tration ion or or dispersi dispersion on of load loads s to be save saved, d, etc. etc. The generator of these internal sources may be driven by: - a gas turbine - back back pres pressu sure re steam steam turb turbin ine e - cond conden ensi sing ng ste steam am tur turbi bine ne - diesel motor - etc. n back-up source This equipment allows the vital parts of the installation to be backed up in the event of a utility failure. It is also used to reduce the energy bill by being used during periods when the kWh cost is high. Generally speaking, these sources do not operate connected to the utility network. Depending on the size of the installations and the powers to be backed up, they may either be installed locally near the loads or centralised in such a way that source multiplication is avoided. In the latter case, these sources are connected to the distribution MV side, if not the HV side. The generators of these back-up sources may be driven by diesel motors or by gas turbines. Publication, traduction et reproduction totales ou partielles de ce document sont rigoureusement interdites sauf autorisation écrite de nos services. The publication, translation and reproduction, either wholly or partly, of this document are not allowed without our written consent. Industrial electrical network design guide T&D 6 883 427/AE 884 n power supply sources of substation auxiliaries These are the loads which are linked to the electrical distribution such as: - pro protect tectiv ive e rel relay ays s - operating operating mechanis mechanisms ms carrying carrying out out opening opening and closing closing of circuit-br circuit-breakers eakers,, switches switches and isolators - cont contac actt coil coils s of con conta tact ctor ors s - switchgear switchgear which is linked linked to to the substation substation control control and monitor monitoring ing system system - air condition conditioning ing systems systems of electric electrical al rooms rooms or switchboar switchboards ds and anti-cond anti-condensati ensation on resistors resistors - elec electr tric ical al room room vent ventililato atorr - elec electr tric ical al roo room m ligh lighti ting ng - coolin cooling g radiato radiators, rs, fans fans and and tap chang changers ers of of transfor transformer mers. s. These loads must be supplied by specific sources having a high level of reliability. If these sources are lost, two operating principles are used: - substation substation tripping; tripping; this this principle principle makes the the safety of persons persons and equipment equipment a priori priority ty - non-trippin non-tripping; g; this this princip principle le makes makes service service co continui ntinuity ty a priority. priority. Monitoring the state of these sources is essential. They generally come from: - a speci specific fic substat substation ion auxili auxiliary ary transfo transforme rmerr - stor storag age e ba batt tter erie ies s - an uninte uninterrup rruptib tible le pow power er supply supply (UPS). (UPS). Publication, traduction et reproduction totales ou partielles de ce document sont rigoureusement interdites sauf autorisation écrite de nos services. The publication, translation and reproduction, either wholly or partly, of this document are not allowed without our written consent. Industrial electrical network design guide T&D 6 883 427/AE 885 13.2 13.2.4 .4.. n Choi Choice ce of eart earthi hing ng sys syste tems ms choice of MV network earthing systems The choice of earthing system in medium voltage is a compromise between the following parameters (see § 2.12.2): - serv servic ice e cont contin inu uity ity - leve levell of overv overvol oltag tages es gen gener erate ated d - equ equipm ipment ent pha phasese-ear earth th insulati insulation on level level - the therma rmall stress stress relat relating ing to to the earth earth faul faultt curren currentt value value - comp comple lexi xity ty of of prot protec ecti tion ons s - ope operat ration ion and mainten maintenanc ance e requ require iremen ments ts - network si size. n choice of earthing systems in LV networks The choice of earthing system in low voltage is a compromise between the following parameters (see § 2.11.2): - serv servic ice e cont contin inu uity ity - leve levell of overv overvol oltag tages es gen gener erate ated d - risk risk of of an ele elect ctric rical ally ly cau cause sed d fi fire re - level level of electro electromag magnet netic ic disturb disturbanc ances es - desi design gn and and opera operati tion on requ requir irem emen ents. ts. There may be a high number of low voltage networks (several dozen); the appropriate earthing system must be determined for each one. Publication, traduction et reproduction totales ou partielles de ce document sont rigoureusement interdites sauf autorisation écrite de nos services. The publication, translation and reproduction, either wholly or partly, of this document are not allowed without our written consent. Industrial electrical network design guide T&D 6 883 427/AE 886 13.2 13.2.5 .5.. Choi Choice ce of netw networ ork k str struc uctu ture re The choice of network structure is a determining stage for energy availability. Among the different possible structures, it is important to base this choice notably on the requirements of availability, on limiting disturbances (voltage dips, unbalance, harmonics, flicker) and on operation and maintenance requirements. The different structures are described in paragraph 1. n HV/MV utility substation structure Depending on the size of the installation and the availability required, the following arrangements are used: - sing single le pow power er sup suppl ply y (see (see fig fig.. 1-2) 1-2) - dual dual powe powerr supp supply ly (se (see e fig. fig. 1-3 1-3)) - dua duall fe fed d do doubl uble eb bus us syste system m (see (see fig. fig. 1-4). 1-4). n MV network structure MV distribution inside the site is designed in relation to the availability required for each zone. Thus, a distinction is made between the following: - single single fed radial radial network network (see (see fig. 1-17). 1-17). This is is used when when the availab availability ility required required is low. It is often chosen for cement plant networks. - dual fed fed radial radial network network (with (with or without without coupler coupler - see fig 1-18 1-18 and 1-19). 1-19). This This is often often used used (with coupler) in the iron and steel industry and in the petrochemical industry for its good availability. - loop system system (open (open or closed - see fig. fig. 1-20-a 1-20-a and 1-20-b). 1-20-b). This is is well suited to widesprea widespread d networks with large future extensions. The closed loop has a better performance than the open loop. It is, on the other hand, more costly. - parallel parallel feeder feeder system system (see fig. fig. 1-21). 1-21). This is is well suited suited to widespread widespread networks networks with with limited limited future extensions and requiring very good availability. Publication, traduction et reproduction totales ou partielles de ce document sont rigoureusement interdites sauf autorisation écrite de nos services. The publication, translation and reproduction, either wholly or partly, of this document are not allowed without our written consent. Industrial electrical network design guide T&D 6 883 427/AE 887 n structure of low voltage networks Depending on the level of availability required, LV switchboards may be fed by several sources, a back-up generator set or an uninterruptible power supply (see § 1.6). The parts of the installation that must be fed with a specific earthing system must be fed through a specific transformer (see § 2). Sensitive or highly disturbing loads may require a specific transformer to feed them (see § 3). 13.2.6. 13.2.6. Energy Energy manag managem ement ent - Choic Choice e of optimu optimum m tarif tarifff ratin rating g Electrical energy utilities offer tariff rating which is adapted both to their production cost and the specific characteristics of users. The user often does not fully understand his real energy needs and his contract with the utility is often badly adapted to his needs. A tariff optimisation study always proves to be profitable and allows up to 10 to 20 % to be gained on the energy bill if real "energy management" is implemented, notably with the help of a high performing control and monitoring system (see § 12). n tariff components Electrical utilities offer their customers supply contracts whose basic characteristics are in essence identical (see § 11). The energy tariff comprises: - a standing standing charge charge related related to the the subscribed subscribed demand demand (not (not to be exceeded). exceeded). The lower lower the the subscribed demand, the lower the standing charge. - a ch charg arge e fo forr active active ene energy rgy consump consumption tion in kWh. kWh. - any penalty penalty payments payments related related to power power consumption consumption exceeding exceeding the subscrib subscribed ed demand. demand. - an eventual eventual charge for reactive reactive power power consumpt consumption, ion, in units of kvarh, kvarh, once its value value exceeds the utility's uninvoiced consumption threshold during certain tariff periods (see § 11.4.4). The different energy cost components vary according to the month of the year, the day of the week and the hour of the day or night, i.e. the tariff periods. n reactive energy compensation To get over costs relating to an excessive consumption of reactive energy, the designer determines the compensations to be installed (see § 7). 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Industrial electrical network design guide T&D 6 883 427/AE 888 n load curves Daily and seasonal load curves representing the installation's variations in active and reactive power allow: - tariff tariff rating rating and and reactive reactive ener energy gy compen compensati sation on to be optim optimise ised d - the decision decision whether whether or or not to put the back-up back-up supply supply into service, service, notably notably during during peak tariff tariff periods, to be taken - the power power to be shed shed an and d the shedding shedding times times to be be determined determined in relation relation to the tariff period. n identifying loads that can be shed This is a question of identifying loads which can be shed without this having repercussions on the industrial process and the possible load-shedding time. advantage of installing a generator set to supply the installation during peak tariff periods n The load curve runs, load-shedding possibilities and tariff ratings may be used to determine whether it is useful or not to install a utility supply replacement generator set. In general, the installation of a replacement generator set is accompanied by an advantageous change in the type of tariff. The energy cost must be simulated and the following compared: - ann annual ual cost cost of ener energy gy witho without ut the the ge gener nerator ator set - ann annual ual cost cost of energy energy with with the generat generator or set operat operating ing during during peak peak tariff tariff periods periods.. The energy cost difference will be used to determine whether it is preferable or not to invest in the purchase of a replacement generator set. The designer must include the maintenance costs of the generator set. It must be added that the replacement generator set can also, in certain cases, provide the installation with a back-up supply. The investment will thus be all the more worthwhile. Publication, traduction et reproduction totales ou partielles de ce document sont rigoureusement interdites sauf autorisation écrite de nos services. The publication, translation and reproduction, either wholly or partly, of this document are not allowed without our written consent. Industrial electrical network design guide T&D 6 883 427/AE 889 n advantage of installing a cogeneration plant In installations simultaneously consuming electrical and thermal energy, a cogeneration plant may prove to be highly profitable. Indeed, recovering the thermal energy produced by a diesel set greatly improves energy efficiency. This can reach 80 to 90 % instead of 35 to 40 % without a recovery system. In some cases, part of the electrical energy is sold back to the utility. A technical/economical study must be carried out and it must notably take into account: - cost of of purchasing purchasing and selling selling electrical electrical energy energy from and and to the utility utility - cogene cogenerati ration on plant plant inve investme stment nt and mainten maintenanc ance e costs costs - gains gains made made th throu rough gh th the e recove recovery ry of elect electrica ricall energy energy - advanta advantage ge of bene benefiti fiting ng from from a repl replace acement ment source. source. Note: another another type type of of cogener cogeneration ation exists, exists, i.e. i.e. inciner incinerating ating plants plants and and heating heating stations. stations. These have thermal energy at a lower cost which can be used to produce electrical energy. Publication, traduction et reproduction totales ou partielles de ce document sont rigoureusement interdites sauf autorisation écrite de nos services. The publication, translation and reproduction, either wholly or partly, of this document are not allowed without our written consent. Industrial electrical network design guide T&D 6 883 427/AE 890 13.3. technical studies and single-line diagram validation (stage 3) At this stage of the design study, the previously defined structure must be validated using calculations. This is a repetitive stage insofar as certain pre-defined parameters may be modified to comply with certain standard conditions or provisions. In this case, the calculations concerned will be revised each time to match the changed parameters. 13.3.1. Nominal current calculation On the basis of the power analysis carried out in paragraph 13.2.1., the nominal currents that flow in each wiring system, transformers and other network elements will be determined. 13.3 13.3.2 .2.. Choi Choice ce of tran transf sfor orme mers rs The transformer is chosen on the basis of the maximum power which corresponds to the most heavily loaded day in the year. This power is the result of a power analysis, taking into account the utilisation and coincidence coefficients (see § 13.2.1). A more accurate method can be used to determine the transformer power based on the installation load curves and transformer overload curves (see IEC 76-2). Note: 13.3 13.3.3 .3.. it is someti sometimes mes worth worth installing installing a range range of transform transformers ers of of the same powe powerr in order order to facilitate facilitate maintenance and interchangeability. interchangeability. Choic hoice e of of ge genera nerato torrs The power of the generators will be determined in relation to the replacement power required or the power to be shed during peak tariff periods. For use continuously connected to the public distribution network, it may be worthwhile installing an asynchronous generator (see § 4.3) Publication, traduction et reproduction totales ou partielles de ce document sont rigoureusement interdites sauf autorisation écrite de nos services. The publication, translation and reproduction, either wholly or partly, of this document are not allowed without our written consent. Industrial electrical network design guide T&D 6 883 427/AE 891 13.3.4. 13.3.4. Determ Determinin ining g conduc conductor tor cross cross-se -secti ctiona onall areas areas The detailed conductor cross-sectional area determination method is described in paragraph 6. The method consists in: - calcul calculati ating ng the maximu maximum m desi design gn curren currentt - determining determining the the overall overall correction correction factor factor relating relating to the the installation installation method method and conditions conditions - determining determining the the cross-secti cross-sectional onal area area necessary necessary for the flow flow of the the maximum maximum design design current current in normal operating conditions - checking checking thermal thermal withstand withstand in the event event of a short short circuit, circuit, with respect respect to the protectiv protective e device - checking checking voltage voltage drops drops during during normal normal operating operating conditio conditions ns and during during starting starting of large motors - for low voltage, voltage, checking checking maximum maximum wiring wiring system lengths lengths for the protecti protection on of persons persons against indirect contact, with respect to the protective device and the earthing system - checking checking the thermal thermal withstand withstand of cable cable screens screens during during earth faults in MV - det determ ermini ining ng the earth earthing ing cond conditi itions ons of cabl cable e screens screens in in MV - determining determining neutral, neutral, protecti protective ve and equipote equipotential ntial bonding bonding conducto conductorr cross-section cross-sectional al areas. areas. The cross-sectional area to be chosen is the minimum area meeting all these conditions. It may be worhtwhile to determine the economic cross-sectional area (investment, joule losses - see § 6.3) on the basis of an economic analysis. 13.3.5. 13.3.5. Study Study of earth earth circui circuits ts and earth earth electr electrode odes s The values of earth circuit and earth electrode impedances determine the overvoltage levels in relation to earth which may appear on electrical equipment (see § 5 and § 2). It is notably useful to make equipotential bonding zones at the bottom of the trench to reduce overvoltages between equipment and earth. Publication, traduction et reproduction totales ou partielles de ce document sont rigoureusement interdites sauf autorisation écrite de nos services. The publication, translation and reproduction, either wholly or partly, of this document are not allowed without our written consent. Industrial electrical network design guide T&D 6 883 427/AE 892 13.3.6 13.3.6.. Calc Calcul ulat atin ing g shor shortt-ci circ rcui uitt curr curren ents ts (see § 4 of the Protection guide ) All electrical installations must be protected against short circuits every time there is an electrical connection, which is generally when there is a change in conductor cross-sectional area. The short-circuit current value must be calculated at every stage of installation for different possible network configurations. This is done to determine the characteristics of the equipment that must withstand or switch the fault current. In order to choose the appropriate switching devices (circuit-breakers or fuses) and set the protection functions, three short-circuit values must be known: n the root mean square value of the maximum short-circuit current (symmetrical threephase short circuit) This determines: - the brea breakin king g capaci capacity ty of the the circuit circuit-bre -breake akers rs and and fuses fuses - the ther thermal mal stres stress s that that the equi equipme pment nt must must withst withstand and.. It corresponds to a short circuit in the immediate vicinity of the downstream terminals of the switching device. It must be calculated taking into account a good margin (maximum value). n the peak value of the maximum short-circuit current (value of the first peak of the transient period) This determines: - the ma makin king g capacit capacity y of the circu circuit-b it-brea reakers kers and and switch switches es - the e electro lectrodynami dynamic c withstand withstand of the wiring systems and switchgear. switchgear. n the minimum short-circuit current This must be known in order to choose the tripping curve of the circuit-breakers or fuses or set the thresholds of the overcurrent protections, especially when: - the cables cables are are long long or when when th the e source source has a relatively relatively high interna internall impedance impedance (e.g. generators or inverters) - protection protection of persons persons relies relies on the the phase phase overcurrent overcurrent protective protective devices devices operatin operating. g. This is essentially the case in low voltage for TN or IT earthing systems. The use of calculating software programs * in compliance with IEC 909 is extremely advantageous as they both speed things up and provide reliable results. (*) SELENA SELENA (Schneider (Schneider ELEctrical ELEctrical Network Analysis) Analysis) Publication, traduction et reproduction totales ou partielles de ce document sont rigoureusement interdites sauf autorisation écrite de nos services. The publication, translation and reproduction, either wholly or partly, of this document are not allowed without our written consent. Industrial electrical network design guide T&D 6 883 427/AE 893 13.3 13.3.7 .7.. Starting mo motors Starting is a delicate part of using electric motors. The starting devices described in this paragraph should be able to solve most of the cases with which the installation designer is confronted: - high lo load to torque - limi limite ted d cur curre rent nt inru inrush sh - fre frequent sta starts rts. On energization, the impedance of the motor is very low. A violent current inrush (4 to 10 times the nominal current) may follow if no specific device is provided to limit it. Since the power supply network is never of infinite power, this current inrush may cause a drop in voltage on the network which is likely to disturb other users. This voltage drop may also cause the motor to operate in operating zones which are not recommended, due to the resulting excessive temperature rise, or a speed build-up of the machine which is too slow, or even a slowing down or stopping of the energized motor. The network short-circuit power is a very important parameter. A motor starts more quickly, heats less and causes a smaller voltage drop if the short-circuit power at the connection point of the motor is high. We may consider that it is high if it is above 100 times the motor power. Paragraph 3.3.4. explains the different motor starting methods and the current and torque characteristics. Publication, traduction et reproduction totales ou partielles de ce document sont rigoureusement interdites sauf autorisation écrite de nos services. The publication, translation and reproduction, either wholly or partly, of this document are not allowed without our written consent. Industrial electrical network design guide T&D 6 883 427/AE 894 13.3.8 13.3.8.. Netw Networ ork k dyn dynam amic ic stab stabil ilit ity ys stu tudy dy The dynamic stability of a network is its ability to recover normal operation following a heavy disturbance. The state of the network is determined by the spreading of loads and the current and voltage values in steady-state conditions. This state is subject to variations following load fluctuations, electrical incidents and network configuration modifications. The progressive or sudden modification of one or several parameters changes the network state. It may then develop towards a new steady state or its behaviour may become unstable. It is then impossible for it to recover an acceptable steady state. This results in the loss of synchronous machine synchronism and the slowing down of the asynchronous motors to such a point that they may stop. For example, when a short circuit occurs in a network having a more or less large amount of synchronous machines (alternators or motors) and asynchronous machines (generators or motors), all the machines supply this short circuit, the motors slow down and the generators accelerate (the generators no longer supply active power but remain nevertheless driven by the turbines or Diesel motors). A stability study st udy (see § 9) consists therefore in analysing the electrical and mechanical behaviour of the machines between the moment when the disturbance occurs and the moment when, once the disturbance has been cleared, the network either recovers or does not recover its normal operating state. There are too many parameters involved for it to be possible to give an intuitive estimate of the influence of such and such a factor and roughly foresee the consequences of a variation in one of them. The study is carried out by computer calculations as the number of calculations to be done is too great for them to be carried out "by hand". The MGSTAB software program developed by Schneider Electric to carry out calculations provides direct and economic processing of all industrial network cases, regardless of the number of cables and machines. Publication, traduction et reproduction totales ou partielles de ce document sont rigoureusement interdites sauf autorisation écrite de nos services. The publication, translation and reproduction, either wholly or partly, of this document are not allowed without our written consent. Industrial electrical network design guide T&D 6 883 427/AE 895 13.3.9 13.3.9.. Reac Reacti tive ve ener energy gy comp compen ensa sati tion on (see § 7) In general, electrical energy utilities charge consumers having a high tan ϕ value. For example, in France: - customers customers subscribing subscribing to a power power above above 250 kVA kVA pay for for reactive reactive energy energy above above 40% of of the active energy consumed (during certain periods). - customers customers subscri subscribing bing to to a power power between between 36 36 and 250 kVA pay a standing standing charge charge which which depends on the subscribed apparent power. Reactive energy compensation allows the standing charge to be reduced by decreasing the subscribed apparent power. Thus, reactive power compensation enables savings to be made on the energy bill. Furthermore, it allows joule losses and voltage drops in conductors and transformers to be reduced. n search for optimum compensation After having calculated the global reactive power to be installed (see ( see § 7.6.), the t he optimum places to install the capacitors and the type of capacitor bank (fixed or automatic) must be determined in order to obtain as short a return on investment as possible. First of all, it is necessary to determine the value of the reactive power and if possible the load curve for different places where the capacitors may be installed. Using these curves, information about the minimum, average and maximum reactive power required at these different places is obtained. The compensation mode depends on the value of the minimum reactive power consumed by the installation compared with the global power to be installed. o case where the minimum reactive power consumed by the installation is greater than the planned compensation power Compensation may be global as there is no risk of overcompensating during normal operation, which would cause abnormal rises in voltage. However, when the installation is stopped, the capacitors must be disconnected so that no steady-state overvoltages are caused on the public distribution network due to overcompensation. Publication, traduction et reproduction totales ou partielles de ce document sont rigoureusement interdites sauf autorisation écrite de nos services. The publication, translation and reproduction, either wholly or partly, of this document are not allowed without our written consent. Industrial electrical network design guide T&D 6 883 427/AE 896 o case where the minimum reactive power consumed by the installation is lower than the planned compensation power When the reactive power consumed is minimum, there would be overcompensation with global compensation which would cause an abnormal rise in voltage. For example, experience has shown that overcompensation at the terminals of a transformer must not exceed 15 % of its nominal power. To avoid overcompensation, it is possible to: - install install an automatic automatically-co ally-controll ntrolled ed stepped stepped capacitor capacitor bank which which enables enables the the load curve to be respected - install, install, at the origin of the installa installation, tion, compensa compensation tion equal equal to the minimum minimum power consumed consumed and locally compensate loads or sectors consuming a large amount of reactive power, as long as capacitor switching is controlled by the load or sector. - in the case of of an installation installation containing containing several several MV/LV transformers, transformers, transfer transfer part of of the compensation of a transformer to another transformer. n selection criteria Compensation may be: - carried carried out in MV and/or and/or in LV; LV; it is more more economical economical to install install medium medium voltage voltage capaci capacitors tors for power greater than roughly 800 kvar. - glob global al,, by sect sector or,, indi indivi vidu dual al.. - carried out by fixed bank or automatically-controlled stepped capacitor bank; in the case where the stepped bank is selected, it may be preferable to install sections of different powers in order to obtain better adjustment. For example, with sections of 800, 400, 200 and 100 kvar, it is possible to obtain all powers from 0 to 1 500 kvar in steps of 100 kvar. To determine the optimum solution, the following criteria must be taken into account: - avoidance avoidance of of reactive reactive energy energy costs or reduction reduction of subscribe subscribed d po power wer - reducti reduction on of Joule Joule losse losses s in conduc conductors tors and and in trans transform formers ers - regula regularr voltag voltage e at any point point of the install installatio ation n - cost of investmen investment, t, installati installation on and maintenance maintenance of every every solution. solution. Publication, traduction et reproduction totales ou partielles de ce document sont rigoureusement interdites sauf autorisation écrite de nos services. The publication, translation and reproduction, either wholly or partly, of this document are not allowed without our written consent. Industrial electrical network design guide T&D 6 883 427/AE 897 n energization of capacitor banks and protections Energizing capacitor banks causes considerable overcurrents and overvoltages in the network. These pose a problem for capacitor switching devices and for protections (especially in MV). These problems are studied in paragraph 10.6. of the Protection guide . n problems relating to capacitors in the presence of harmonics In the presence of harmonics, installing capacitors is likely to cause an amplification of harmonic currents and voltages and related problems. In this case, it is necessary to carry out an analysis. These problems are studied in paragraph 8. Publication, traduction et reproduction totales ou partielles de ce document sont rigoureusement interdites sauf autorisation écrite de nos services. The publication, translation and reproduction, either wholly or partly, of this document are not allowed without our written consent. Industrial electrical network design guide T&D 6 883 427/AE 898 13.3.1 13.3.10. 0. Stud Study y of of harm harmon onic ics s (see § 8) Non-linear loads such as arc furnaces, lighting systems, convertors, rectifiers, etc., absorb non sinusoidal currents which flow through the network impedances and hence cause deformation of the supply voltage sinusoid. The wave form deformation is characterised by the occurrence of harmonic voltage frequencies. The disturbances generally observed are: - heat heatin ing g or bre break akdo down wn of of capa capacit citors ors - heat heatin ing g of moto motors rs or or tran transfo sform rmer ers s - abnormal operation of regulators, regulators, converters, permanent permanent insulation insulation monitors, protective relays, etc. The purpose of a harmonic study is to define the means enabling disturbances to be reduced to an acceptable level: - for site site equi equipme pment, nt, an an overal overalll distort distortion ion rate rate < 5 to 10 10 % - for the public distribution distribution network network (see table 8-23 for the case case of France). France). The means generally implemented are: - installation installation of capacitor capacitor banks banks with with antiharmoni antiharmonic c inductors inductors which which reduce reduce resonance resonance phenomena between the capacitors and the power supply inductance - installation installation of of shunt filters filters which which reduce reduce harmonic harmonic voltages voltages by "trapping" "trapping" harmon harmonic ic currents currents - increase increase of of short-circu short-circuit it power power at at the location location of disturbing disturbing loads loads - electricall electrically y moving moving away disturbing disturbing loads from sensitive sensitive equipm equipment ent - inst instal alla latio tion n of of acti active ve filte filters rs - restric restricting ting the gen genera eratio tion n of of harm harmoni onics. cs. A harmonic study is generally essential in the presence of capacitors which amplify the distortion rate through resonance phenomena. The harmonic study consists in: - determining pre-existing voltage harmonics on the utility network - defining defining power powers s and harmon harmonic ic current current value values s for each each non-line non-linear ar load load - calculating calculating the the voltage voltage distortion distortion rate, rate, at different different points of of the installati installation on and for all possible network configurations - simulating simulating possible possible solution solutions s where the the acceptable acceptable limits limits for equipme equipment nt or the utility utility network network are overstepped. Publication, traduction et reproduction totales ou partielles de ce document sont rigoureusement interdites sauf autorisation écrite de nos services. The publication, translation and reproduction, either wholly or partly, of this document are not allowed without our written consent. Industrial electrical network design guide T&D 6 883 427/AE 899 13.3. 13.3.11 11.. Insu Insula latio tion n coco-or ordi dina natio tion n in in an an ind indus ustri trial al elec electr tric ical al inst instal alla lati tion on Co-ordinating the insulation of an installation consists in determining the insulation characteristics necessary for the various network elements, in view to obtaining a withstand level that matches the normal voltages, as well as the different overvoltages (see § 5). Its ultimate purpose is to provide dependable and optimised energy distribution. Optimal insulation co-ordination gives the best cost-effective ratio between the different parameters depending on it: - cost cost of equi equipm pmen entt ins insul ulat atio ion n - cost cost of of over overvol volta tage ge p pro rotec tectio tions ns - cost of failures failures (loss of operation operation and and destruction destruction of equipment), equipment), taking into account account their their probability of occurrence. With the cost of overinsulating equipment being very high, the insulation cannot be rated to withstand the stress of all the overvoltages studied in paragraph 5.2. Overcoming the damaging effects of overvoltages supposes an initial approach which consists in dealing with the phenomena that generate them, which is not always very easy. Indeed, although switchgear switching overvoltages can be limited using the appropriate arc interruption techniques, it is impossible to prevent lightning strikes. Reducing the risks of overvoltages, and thus the danger that they represent for persons and equipment, is all the better if certain protection measures are respected: - limitation limitation of substati substation on earth electrode electrode resistance resistances s in order order to reduce reduce overvoltage overvoltages s on occurrence of an earth fault - reduction reduction of switchin switching g overvoltage overvoltages s by choosing choosing the app appropria ropriate te switching switching devices devices - running running lightning lightning impuls impulses es to earth earth by a first first clipping clipping device device (surge (surge arrester arrester or spark-ga spark-gap p at the substation entrance) with limitation of the earth electrode resistances and pylon impedances - limiting limiting the residual residual voltage voltage of the first first clipping clipping carried carried out out by the HV HV surge arrester arrester which is transferred to the downstream network, with a second protection level being provided on the transformer secondary - protection protection of sensitive sensitive equipment equipment in in LV (computer (computer systems, systems, telecommunic telecommunications ations,, automatic automatic devices, etc.) by adding series filters and/or overvoltage limiters to them. Publication, traduction et reproduction totales ou partielles de ce document sont rigoureusement interdites sauf autorisation écrite de nos services. The publication, translation and reproduction, either wholly or partly, of this document are not allowed without our written consent. Industrial electrical network design guide T&D 6 883 427/AE 900 13.3.1 13.3.12. 2. Depe Depend ndab abil ilit ity y stud study y Owing to the increase in costs generated by a loss of supply, designers and users of electrical networks need a set of qualitative and quantitative network dependability evaluation methods (see § 10). When designing, it is important to have methods enabling: - dep depend endabi ability lity to to be assess assessed ed in order order to meet meet speci specifica ficatio tions ns - suit suitab able le solu solutio tions ns to be be c cho hose sen n - service service continu continuity ity for for the the least least cost cost to be gu guara arante nteed ed - the o opti ptimum mum main mainten tenanc ance e polic policy y to be be determi determined ned.. Schneider Electric has developed two software programs designed to carry out dependability studies. o Adélia This is an expert system able to construct an electrical network failure tree using the diagram and carry out qualitative and quantitative analyses on it. o Micro Markov This is a software program which determines the reliability of an electrical network using the Markov graph method . The dependability study of an electrical network allows: - service continuity to be quantified by the network's unavailability being calculated. - the cost of a production loss to be estimated (to be compared with the investment costs). Publication, traduction et reproduction totales ou partielles de ce document sont rigoureusement interdites sauf autorisation écrite de nos services. The publication, translation and reproduction, either wholly or partly, of this document are not allowed without our written consent. Industrial electrical network design guide T&D 6 883 427/AE 901 13.4. .4. Choice of of eq equipment (stage 4) Once the network structure has been chosen and validated, the electrical equipment selected must comply with the following constraints. n standards in force n network characteristics These concern notably: - duty voltages voltages which must be compatible compatible with with the highest highest voltage voltage for the equipmen equipmentt - overvoltages overvoltages likely likely to occur occur in the network network and which must must be compatibl compatible e with the the equipment equipment withstand voltages (power frequency, switching impulse, lightning impulse) - no nomi mina nall curr curren ents ts - short-circui short-circuitt currents currents which which must be compatible compatible with with the breaking breaking capacit capacity, y, the making making capacity and the thermal and electrodynamic withstand of the equipment. n - n functions associated with each piece of equipment short-c short-circ ircuit uit interr interrupt uption ion (by (by circuit-b circuit-brea reaker ker or fuse) fuse) switchi switching ng opera operatio tion n during during nomi nominal nal state state (swi (switch tch)) frequen frequentt switchi switching ng opera operatio tions ns (cont (contacto actors, rs, etc.) etc.) off-l off-loa oad d switc switchi hing ng (iso (isola lato tors) rs).. service continuity requirements This determines the choice of equipment type: - fixed device - drawou drawoutt device device to facilita facilitate te mainte maintenan nance ce or replac replaceme ement. nt. n personnel qualifications The qualification level of operator and maintenance personnel determines: - whether or not it is necessar necessary y to have have interlockin interlocking g devices devices to prevent prevent erroneous erroneous switching switching operations - the choice choice of of equipme equipment nt which which is or is not not mainte maintenan nancece-free free . n requirements relating to future extensions Publication, traduction et reproduction totales ou partielles de ce document sont rigoureusement interdites sauf autorisation écrite de nos services. The publication, translation and reproduction, either wholly or partly, of this document are not allowed without our written consent. Industrial electrical network design guide T&D 6 883 427/AE 902 This determines the reserves to be provided and may lead to the choice of modular equipment. Publication, traduction et reproduction totales ou partielles de ce document sont rigoureusement interdites sauf autorisation écrite de nos services. The publication, translation and reproduction, either wholly or partly, of this document are not allowed without our written consent. Industrial electrical network design guide T&D 6 883 427/AE 903 13.5. 13.5. Dete Determ rmin inin ing g the the prot protec ecti tion on syst system em (stage 5) The basic role of the protections of an industrial electrical network is to ensure the safety of persons and equipment and improve continuity of supply to loads. The normal operation of an installation may be disturbed by a certain number of incidents: - overloads - short circuits - erro errone neou ous s switc switchi hing ng o ope pera ratio tions ns - det deteri eriora oratio tion no off insu insulat lating ing materia materials. ls. It is the purpose of the protections to prevent the consequences of these incidents, allowing: - thermal thermal and mechanical mechanical stress to whi which ch equipme equipment nt is subject subject to be be limited limited - netwo network rk sta stabi bilility ty to to be pres preser erve ved d - the duration duration of of electromagneti electromagnetic c disturbances disturbances caused to neighbouri neighbouring ng circuits circuits to be be reduced. reduced. The protection system is a coherent assembly which depends on the network structure and the earthing system. It must ensure selectivity by isolating the faulty part of the network as quickly as possible while preventing the healthy parts from deteriorating (see Industrial network  protection guide ). ). Publication, traduction et reproduction totales ou partielles de ce document sont rigoureusement interdites sauf autorisation écrite de nos services. The publication, translation and reproduction, either wholly or partly, of this document are not allowed without our written consent. Industrial electrical network design guide T&D 6 883 427/AE 904 13.6. 13.6. Choi Choice ce of a con contro troll and and moni monito torin ring g sys syste tem m (stage 6) To guarantee energy availability and reduce energy bills, industrial installations require optimal management of their electrical networks. A control and monitoring system (see § 12) enables optimisation optimis ation of network management through the use of automatic functions such as: - supp supply ly chan change geov over er - loop loop reco reconf nfig igur urat atio ion n - load load-sh -shed eddi ding ng/re /resto stora rati tion on - time-de time-depen penden dentt program programmin ming g and tari tariff ff manage managemen mentt - manage managemen mentt of intern internal al gene generato ratorr sets, sets, etc. Furthermore, it offers network supervision, remote control of equipment and maintenance planning. n network remote control and monitoring Remotely monitoring and controlling the network allows operators to: - displa display y the state state of tthe he e elec lectric trical al instal installat lation ion - mo moni nito torr the diffe differe rent nt me meas asur urem emen ents ts - carr carry y ou outt remo remote te co cont ntro roll of equ equip ipme ment nt - be inform informed ed of any any inciden incidents ts on the elec electric trical al instal installati lation. on. n improving the speed and effectiveness effectiveness of network diagnosis and intervention The speed and effectiveness of network diagnosis and intervention are improved through the following functions: - automatic automatic load-sh load-shedding edding/restora /restoration tion and supply changeover changeover management management - manage managemen mentt of automati automatic c restarti restarting ng of mediu medium m voltage voltage m motor otors s - ma manag nagem ement ent o off inter interna nall gene genera rator tor set sets s - fine fine time time stam stampi ping ng - faul faultt reco record rdin ing. g. Publication, traduction et reproduction totales ou partielles de ce document sont rigoureusement interdites sauf autorisation écrite de nos services. The publication, translation and reproduction, either wholly or partly, of this document are not allowed without our written consent. Industrial electrical network design guide T&D 6 883 427/AE 905 n optimising energy costs The following functions enable electrical energy costs to be optimised: - tari tariff ff ma mana nage geme ment nt - time time-d -dep epen ende dent nt prog progra ramm mmin ing g - inte intern rnal al gene genera rato torr set man manag agem emen entt - reac reactiv tive e ene energ rgy y com compe pens nsat atio ion n - ener energy gy mete meteri ring ng a and nd subsub-me meter terin ing. g. n optimising maintenance Using the system's recorded count of switching device operations and equipment operating times, maintenance can be optimised. Publication, traduction et reproduction totales ou partielles de ce document sont rigoureusement interdites sauf autorisation écrite de nos services. The publication, translation and reproduction, either wholly or partly, of this document are not allowed without our written consent. Industrial electrical network design guide T&D 6 883 427/AE 906 13.7 13.7.. Appl Applic icat atio ion n exa example mple Let us now study the electrical supply of an industrial production installation whose layout plan is given in figure 13-1. An analysis of the specifications sheet and the project technical file shows the constraints and basic data necessary for the design study. The aim is not to present a detailed study, but to underline the methods for resolving problems relating to design. This is the reason why certain stages are not dealt with in detail. 13.7.1 13.7.1.. Desc Descri ript ptio ion n of of the the inst instal alla lati tion on The industrial installation to be supplied is a production plant which is spread over a surface area of 26 hectares and is made up of several buildings: - a rrec ecep eptio tionn-pr prep epar arat atio ion n uni unitt - a pro produ duct ctio ion n pro proce cess ss - a storage un unit - a dispa spatch tch unit - a rep repai airs rs wo work rksh sho op - a wat water er puri purifi fica cati tion on unit unit - an admi admini nistr strat ativ ive e bui build ldin ing g located inside the site and two buildings located outside the site: - an extr extrac acti tion on un unit it - a wa waterworks. Publication, traduction et reproduction totales ou partielles de ce document sont rigoureusement interdites sauf autorisation écrite de nos services. The publication, translation and reproduction, either wholly or partly, of this document are not allowed without our written consent. Industrial electrical network design guide T&D 6 883 427/AE 907 Figure 13-1: installation layout plan  Publication, traduction et reproduction totales ou partielles de ce document sont rigoureusement interdites sauf autorisation écrite de nos services. The publication, translation and reproduction, either wholly or partly, of this document are not allowed without our written consent. Industrial electrical network design guide T&D 6 883 427/AE 908 13.7 13.7.2 .2.. Colle ollect ctio ion n of data ata Only data useful to the parts being studied has been given. n load power A power analysis has been carried out and the results are given in table 13-3. The characteristics of MV motors are given in table 13-1: Unit Number cos ϕ Efficiency Pm (kW) P (kW) (1) (1) Q (kvar) S (kVA) T max I st  T st  T max T  N   I n T  N  T  N  2 0.95 0.9 450 474 229 526 2.4 5.7 0.75 2.4 2 0.93 0.78 165 177 142 227 2.3 5.0 1.25 2.3 Receptionpreparation 1 0.93 0.78 165 177 142 227 2.3 5.0 1.25 2.3 Storage 1 0.93 0.78 165 177 142 227 2.3 5.0 1.25 2.3 Production (1) Pm : mechan mechanica icall power power P : electr electrica icall power power Table 13-1: MV motor characteristics  n equipment causing disturbance Two speed variators for asynchronous motors are installed at the location of the production unit and their characteristics are given in table 13-2. Type P (kW) cos ϕ S (kVA) F  p Q (kvar) F h U n (V ) Number ATV-52 V 110 0.85 204 0.54 68 0.63 400 2 Tableau 13-2: speed variator characteristics  Publication, traduction et reproduction totales ou partielles de ce document sont rigoureusement interdites sauf autorisation écrite de nos services. The publication, translation and reproduction, either wholly or partly, of this document are not allowed without our written consent. Industrial electrical network design guide T&D 6 883 427/AE 909 n requirements imposed by the industrial process o interruption time tolerated The interruption time tolerated is defined as follows: - no interruptio interruption n is tolerated tolerated for process process control control and and emergency emergency lighting; lighting; i.e. i.e. a total power of of 250 kVA - the p prod roducti uction on un unit it to toler lerates ates an interr interrupti uption on o off 10 s - the plant plant has an autonomy autonomy in raw materials materials and storage storage capacity capacity of 8 hours, hours, a long long supply supply interruption is thus authorised on the reception-preparation, storage and dispatch units. o sheddable load Loads which can be shed in the event of the public network failing, without this incurring any production problems, represent: - 60 % of the the recep receptio tionn-pr prep epar arat atio ion n un unit it - 50 % of of the the stor storag age e uni unitt - 50 % of of the the disp dispat atch ch unit unit.. n utility network constraints - shortshort-circ circuit uit p powe owerr equal equal to 200 200 MVA on a 20 20 kV overhe overhead ad netwo network rk - earth earth fau fault lt cur curre rent nt limi limited ted to 300 300 A - aver averag age e ser servi vice ce cont contin inui uity: ty: . short in interruptio tions : 50 to to 10 100 pe per ye year . long interruptions : 10 to 20 per year. - the oth other er character characteristics istics comply with European European standard standard EN 50160 50160 (see (see table 4-1). 4-1). Publication, traduction et reproduction totales ou partielles de ce document sont rigoureusement interdites sauf autorisation écrite de nos services. The publication, translation and reproduction, either wholly or partly, of this document are not allowed without our written consent. Industrial electrical network design guide T&D 6 883 427/AE 910 13.7.3. 13.7.3. n Prepar Preparati ation on of of a prelim prelimina inary ry single single-li -line ne diag diagra ram m power analysis (see table 13-3) The analysis of active and reactive powers is given for each unit on the basis of the installed power after the utilisation and coincidence factors have been applied. To determine the installation's total power, a total coincidence factor of 0.9 is applied to the sum of powers of each unit. P (kW) Q (kvar) cos ϕ S (kVA) Variators Motors Lighting Heating Total Motors Lighting Heating Total 220 300 30 300 850 150 30 150 330 136 225 69 0 430 113 69 0 182 408 375 75 300 953 188 75 150 377 0.85 0.80 0.40 1.00 0.89 0.80 0.40 1.00 0.88 Motors Lighting Heating Total Motors Lighting Heating Total Lighting Heating 120 45 100 265 192 24 100 316 30 300 90 103 0 193 144 55 0 199 69 0 150 113 100 328 240 60 100 373 75 300 0.80 0.40 1.00 0.81 0.80 0.40 1.00 0.85 0.40 1.00 Repairs workshop Total Motors Lighting Heating 330 80 20 60 69 60 46 0 337 100 50 60 0.98 0.80 0.40 1.00 Water purification Total Motors Lighting Heating 160 80 3 90 106 60 7 0 192 100 8 90 0.83 0.80 0.40 1.00 Total Motors Lighting Heating 173 128 6 50 67 96 14 0 186 160 15 50 0.93 0.80 0.40 1.00 Total 184 110 214 0.86 Total 160 2 x 474 4 x 177 120 2 x 229 4 x 142 200 2 x 526 4 x 227 0.80 0.90 0.90 Total 1 656 1 026 1 948 0.85 4 424 x 0.9  ______  3 982 2 502 x 0.9  ______  2 252 5 082 x 0.9  ______  4 575 0.87 Production process Reception Preparation Storage Dispatch Administrative building Extraction Waterworks MV motors Installation total Total coincidence factor of 0.9 Utility takeover point balance Table 13-3: plant power analysis  Publication, traduction et reproduction totales ou partielles de ce document sont rigoureusement interdites sauf autorisation écrite de nos services. The publication, translation and reproduction, either wholly or partly, of this document are not allowed without our written consent. Industrial electrical network design guide T&D 6 883 427/AE 911 n choice of voltages o utility supply voltage The public distribution network 20 kV voltage is suitable for the power required by the plant which is roughly 5 MVA. The 200 MVA short-circuit power is equal to 400 times the power of the largest load. Possible disturbances generated by the loads probably do not disturb the public distribution network. o distribution voltages The choice of a 5.5 kV MV distribution voltage is due to: - the prese presence nce of of 6 MV motors motors spread spread o over ver the the site (see (see table table 13-2 13-2)) - the the pow power er requi required red by each each unit unit - the size size of the the site, site, including including distances distances varying varying between between 300 m and 1 000 m. m. With regard to low voltage, a three-phase voltage of 400 V is sufficient for the supply to the largest loads. n energy sources o main source The plant power supply will be ensured by 2 mains/standby 20 kV lines coming from two different sources (from the same utility substation but from separate transformers). o replacement source In case the public network fails, the plant power supply will be ensured by a replacement source connected to the utility substation 5.5 kV busbar. Disconnected from the public network, this source will supply loads which cannot be shed during storms or when the 20 kV lines are unavailable. It will be connected to the public network during peak tariff periods in order to make savings on the energy bill. o safety source To ensure the safety of persons and equipment, an uninterruptible power supply (UPS) will be provided for the following vital loads: - 200 kVA kVA for the the produc production tion control control and moni monitor toring ing syste system m - 50 kVA of em emer erge genc ncy y lig lighti hting ng.. Publication, traduction et reproduction totales ou partielles de ce document sont rigoureusement interdites sauf autorisation écrite de nos services. The publication, translation and reproduction, either wholly or partly, of this document are not allowed without our written consent. Industrial electrical network design guide T&D 6 883 427/AE 912 The power supply to this UPS will be backed up by a 250 kVA generator set which supplies the production plant LV switchboard in order to overcome the limited autonomy of the storage batteries (10 to 30 min.). n choice of earthing systems o in medium voltage The presence of MV motors requires the earth fault current to be limited to 30 A on the 5.5 kV network. Limiting resistance earthing is chosen. o in low voltage - production production process: process: the service service continui continuity ty requiremen requirements ts mean that the unearthed unearthed ne neutral utral system must be chosen. For lighting, an LV/LV transformer is used to change to the TT earthing system. - for the remainder remainder of the installati installation on the TT system is chosen, chosen, notably notably so so as not not to d damage amage the motors in the event of an earth fault. n network structure The previously determined data and elements are used to draw up a preliminary single-line diagram of the network (see fig. 13-2). o utility substation The utility substation is fed by 2 x 20 kV lines connected to two 20 kV/5.5 kV transformers supplying the 5.5 kV busbar with coupler. o internal network - production production process: process: this this part of the the installation installation will will be dual dual fed with with couplers couplers on the the MV and LV sides - the receptio reception-prep n-preparation aration,, storage storage and dispatch dispatch units will be single single fed - the rest of the units units will will have an open open loop supply owing to to the considera considerable ble distances distances.. 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Industrial electrical network design guide T&D 6 883 427/AE 913 utility utility N1 U n = 20 kV S sc = 200 MVA 3 x 1500 kVA 3 x 1200 kW 20 / 5.5 kV G1 2 x 5 MVA G2 G3 U sc sc = 7.5 % BB 1 (5.5 kV) 360 m W06 W05 260 m W01 260 m W02 W03 W04 W07 500 m 530 m BB 22 BB 2 BB 23 2 x 400 kVA 5500 / 400 V 2 x 1250 kVA M M M M U sc= 6.5 % 450 kW 165 kW 165 kW M U sc = 4 % M 450 kW 165 kW 400 kVA U sc = 4 % 165 kW G4  N53 reception preparation production BB 121 250 kVA U sc sc = 4 %  N130 BB 3 250 kVA N37 N79 storage dispatch UPS 430 m W11 extraction BB 24 430 m W10 BB 131 310 m W09 BB 141 250 kVA U sc sc = 4 % 400 kVA U sc sc = 4 %  N146   N142 waterworks building 550 m W08 BB 161 BB 151 250 kVA U sc sc = 4 % 250 kVA U sc sc = 4 %  N138 repairs workshop  N134 water purification Figure 13-2: installation single-line wiring diagram  Publication, traduction et reproduction totales ou partielles de ce document sont rigoureusement interdites sauf autorisation écrite de nos services. The publication, translation and reproduction, either wholly or partly, of this document are not allowed without our written consent. Industrial electrical network design guide T&D 6 883 427/AE 914 13.7.4. 13.7.4. n Techni Technical cal studie studies s and and single single-li -line ne diagr diagram am vali validat dation ion choice of transformers If the installation load curves are not known, the transformers are chosen in relation to the installation's power analysis. The characteristics of the transformers are given in figure 13-2. n choice of generators The power to be backed up is determined by the power analysis at the utility take-over point from which loads that can be shed are subtracted by applying the total coincidence factor: 982 − 0.9 × [330 × 0.6 + 265 × 0.5 + 316 × 0,5] = 3 542 kW  P = 3 98  Q = 2 252 − 0.9 × [182 × 0.6 + 193 × 0.5 + 199 × 0.5] = 1 977 k var  575 − 0.9 × [377 × 0.6 + 328 × 0.5 + 373 × 0.5] = 4 05 056 kVA S = 4 57 Three 1 500 kVA generators having the characteristics given in table 13-4 are chosen: Type U n (V ) LSA 545A 5500 P ( kW ) Q ( k var var ) S ( kVA) 3 x 1200 = 3600 3 x 900 = 2700 3 x 1500 = 4500 ''  X d  (% ) cos ϕ n 18.4 0.8 Table 13-4: generator characteristics  n short-circuit current calculation The short-circuit current calculations are carried out using the Schneider SELENA software program for different source configurations: - netw networ ork k fe fed d by by th the e uti utilility ty onl only y - netw network ork fed fed by the gene genera rator tors s only only - net network work fed fed by the the gener generator ators s connect connected ed to the the utility utility.. The calculating method used complies with IEC standard 909. Publication, traduction et reproduction totales ou partielles de ce document sont rigoureusement interdites sauf autorisation écrite de nos services. The publication, translation and reproduction, either wholly or partly, of this document are not allowed without our written consent. Industrial electrical network design guide T&D 6 883 427/AE 915 n determining conductor cross-sectional areas The study is limited to 5.5 kV wiring wiring systems. o wiring system characteristics The wiring systems are made up of 3 XLPE-insulated copper 6/10 (12) kV single-core cables installed directly in enclosed channels at a temperature of 30°C. 30°C. The wiring systems sy stems do not comprise groupings of several circuits. The wiring system corresponds to the L4 installation method (see table 6-23). Column (3) in the current-carrying capacity tables must be used. The correction factors to be applied are: - inst instal alla lati tion on me meth thod od  f 0 = 0.8 - am ambi bien entt tempe tempera ratur ture e (see (see table table 6-24 6-24): ):  f  1 = 1 - group group of of sever several al circ circuits uits (see (see ta table ble 6-28): 6-28):  f 5 = 1 . The total correction factor is:  f  = 0.8 . o production unit: W01 and W02 wiring systems Ÿ determining the maximum design current  I  B The W01 and W02 wiring systems can back each other up and they must therefore be able to supply the entire busbar BB2. Table 13-5 gives the power analysis on BB2 assuming that the transformer has a cos ϕ = 0.85 . P (kW) Q (kvar) S (kVA) cos ϕ 450 kW motor 2 x 474 2 x 229 2 x 526 0.9 165 kW motor 2 x 177 2 x 142 2 x 227 0.78 1 250 kVA transformer 2 x 1 063 2 x 658 2 x 1 250 0.85 BB2 total 3 428 2 058 3 998 0.86 Table 13-5: power analysis on BB2 busbar  Publication, traduction et reproduction totales ou partielles de ce document sont rigoureusement interdites sauf autorisation écrite de nos services. The publication, translation and reproduction, either wholly or partly, of this document are not allowed without our written consent. Industrial electrical network design guide T&D 6 883 427/AE 916 The maximum design current is therefore:  I B = 3998 3 × 5 50 500 = 420 A The equivalent current that the cable must be able to carry in standard installation conditions is: I   I  z =  B = 525  A  f  Table 6-31 (column (3), XLPE, copper) gives a minimum cross-sectional area of S1 = 180 mm2 which has a current-carrying capacity of  I 0 = 550 A . Ÿ checking thermal withstand The calculations carried out by the SELENA software give us the maximum short-circuit current for BB1: sc I= 8.77 kA We assume that the maximum short-circuit clearance time is t  = 1 second. The conductor cross-sectional area meeting this short-circuit requirement is: I t  S2 ≥ sc k  k  = 143 : value of the coefficient coefficient corresponding corresponding to a XLPE-insulated XLPE-insulated copper copper conductor (see (see table 6-35) whence S2 ≥ 61 mm2 The minimum cross-sectional area is therefore S2 = 70 mm2 . Ÿ cross-sectional area to be chosen S = 180 mm2 Publication, traduction et reproduction totales ou partielles de ce document sont rigoureusement interdites sauf autorisation écrite de nos services. The publication, translation and reproduction, either wholly or partly, of this document are not allowed without our written consent. Industrial electrical network design guide T&D 6 883 427/AE 917 o Ÿ reception-preparation reception-preparation unit: W05 wiring system determining the maximum design current Table 13-6 gives the power analysis on the BB22 busbar assuming that the transformer has a cos ϕ = 0.85 . P (kW) Q (kvar) S (kVA) cos ϕ 165 kW motor 177 142 227 0.78 400 kVA transformer 340 210 400 0.85 BB22 total 517 352 625 0.83 Table 13-6: power analysis on BB22 busbar  The maximum design current is therefore:  I B = 625 3 × 5 50 500 = 66 A The equivalent current that the cable must be able to carry in standard installation conditions is:  I   f  = 83  A Table 6-31 (column (3), XLPE, copper) gives a minimum cross-sectional area of S1 = 10 mm2 which has a current carrying capacity of  I 0 = 93 A . Ÿ checking thermal withstand We assume that the maximum short-circuit clearance time is the same as for wiring systems W01 and W02 ( t  = 1 second), the minimum cross-sectional area adapted to the thermal stress is thus S2 = 70 mm2 . Ÿ cross-sectional area to be chosen S2 = 70 mm2 Publication, traduction et reproduction totales ou partielles de ce document sont rigoureusement interdites sauf autorisation écrite de nos services. The publication, translation and reproduction, either wholly or partly, of this document are not allowed without our written consent. Industrial electrical network design guide T&D 6 883 427/AE 918 o other 5.5 kV wiring systems systems The maximum design currents of other 5.5 kV wiring systems are lower than or equal to that of wiring system W05. The cross-sectional area is thus imposed by the thermal stress in the event of a short circuit. The values of the maximum short-circuit currents of all the 5.5 kV cables are identical as they are attached to the same busbar. Furthermore, it is assumed that the maximum short-circuit clearance time is the same for each cable, i.e. 1 second. The cross-sectional areas to be chosen are therefore: S = 70 mm2 . o voltage drops Voltage drops during normal operating conditions are lower than 1 %, at any point of the 5.5 kV network. They are not therefore restrictive. o thermal withstand of cable screens The earth fault current is limited to 30 A, which does not impose any restriction (see table 6-37 to 6-39). n reactive energy compensation The reactive energy to be compensated is calculated so as to limit it to tan ϕ 0 = 0.4 at the take-over point. o determining the total reactive power to be compensated The power analysis in table 13-3 gives the following total powers: P = 3982 kW  252 k var var Q = 2 252 S = 4 575 575 kVA cos ϕ = 0.87 → tan ϕ = 0.567 We can deduce from this: QC  = P ( tan ϕ − tan ϕ 0 ) = 3 982 (0 .567 − 0.4) QC  = 665 665 k var var Publication, traduction et reproduction totales ou partielles de ce document sont rigoureusement interdites sauf autorisation écrite de nos services. The publication, translation and reproduction, either wholly or partly, of this document are not allowed without our written consent. Industrial electrical network design guide T&D 6 883 427/AE 919 o choice of capacitor location We assume that the minimum reactive energy required by the plant is 120 kvar; this power will be installed on the 5.5 kV side of the supply substation, on BB1. The production unit consumes the most amount of energy and the MV and LV motors have a highly irregular load curve. Stepped capacitor banks are therefore installed on the busbars supplying the motors, which will be controlled by a varmeter relay so that they match the load curve: - 6 x 50 = 300 300 kvar kvar on BB 2 - 4 x 30 = 120 120 kvar kvar on BB3. BB3. The remaining compensation is carried out by fixed banks: - 50 kvar kvar on tthe he rece recepti ptionon-pre prepar paratio ation nu unit nit - 50 kva kvarr on the the sto stora rage ge u uni nit. t. Table 13-7 provides a recap on capacitor bank location. Location Supply Production unit substation QC  ( k var) 1 50 MV LV 3 00 12 0 Receptionpreparation Storage Total 50 50 670 Table 13-7: location of capacitor banks  The power to be compensated is not very high and is essentially located on the MV side. With the MV cables not being very long, joule losses due to reactive power are almost negligible. It is therefore not useful to carry out an economic optimisation calculation. Publication, traduction et reproduction totales ou partielles de ce document sont rigoureusement interdites sauf autorisation écrite de nos services. The publication, translation and reproduction, either wholly or partly, of this document are not allowed without our written consent. Industrial electrical network design guide T&D 6 883 427/AE 919 n harmonic study The 250 kVA uninterruptible power supply is fitted with an input filter that reduces the harmonic current values enough for them to be negligible. The study consists in determining the distortion rates of current and voltage generated by the speed variators for different network configurations and determining the means of reducing them to an acceptable level. We will concentrate on the network branches connecting the utility substation to the speed variators; a model of the rest of the network is made using loads ( P,Q) connected to busbars BB1, BB2 and BB3 (see fig. 13-3). The two speed variators are identical and are connected to busbar BB3. The values of the harmonic currents which they generate are given in table 13-8. order current (%) 1 5 7 11 13 17 19 23 25 100 85 72 41 27 8 5 6 5 Table 13-8: harmonic currents generated by the ATV-52V variators  Simulations have been carried out using the Schneider "harmonic" software program for different source configurations: - UTILITY UTILITY,, plant plant fed by the utilit utility y alone alone - GENERAT GENERATORS, ORS, plan plantt fed by the the replace replacemen mentt generato generatorr sets alone alone - UTILITY AND GENERATORS, GENERATORS, plant fed by both both source sources s in parallel. parallel. Publication, traduction et reproduction totales ou partielles de ce document sont rigoureusement interdites sauf autorisation écrite de nos services. The publication, translation and reproduction, either wholly or partly, of this document are not allowed without our written consent. Industrial electrical network design guide T&D 6 883 427/AE 920 utility U = 20 kV S sc = 200 MVA  R 0.1 =  X  3 × 1500 kVA kVA "  X d  = 18.5 % G1 G2 G3 Sn TR21 U  = 5 MVA = 7.5 % BB 1 5.5 kV C1 Qc = 150 P = 1830 kW  Q = 1080 k var k var 180mm² Cu  L = 260 m BB 2 5.5 kV C2 Qc = 300 k var P = 1302 kW  Q = 742 k var Sn TR22 U  = 1250 = kVA 5.5 % BB 3 400 V C3 V  Qc V  = 120 k var P = 630 kW  Q = 294 k var ATV - 52V variator P = 2 × 110 kW ; Q = 2 × 68 k var  Figure 13-3: network model diagram  Publication, traduction et reproduction totales ou partielles de ce document sont rigoureusement interdites sauf autorisation écrite de nos services. The publication, translation and reproduction, either wholly or partly, of this document are not allowed without our written consent. Industrial electrical network design guide T&D 6 883 427/AE 921 For each case, 4 different simulations have been carried out: - A : network network befor before e compens compensati ation on (witho (without ut capaci capacitors tors). ). - B : netwo network rk with with co compe mpensa nsation tion defined defined in ta table ble 13-7. 13-7. - C : network network with with modified modified compensation compensation to move resonance resonance to an an order that that is far away away from the high value harmonic currents. To carry out this modification, 50 kvar is installed instead of 120 kvar on BB3; the difference is installed on BB1. - D : network network after an an anti-harmo ti-harmonic nic inductor inductor tuned to order order 3.8 has been been installed installed capacitor C 3 ; compensation is as in case B. on - E : network network after after resonant resonant shunts shunts tuned tuned to orders 5 and 7 have been installe installed. d. The simulation results are presented in table 13-9. Source UTILITY GENERATORS GENERATORS & UTILITY Type of voltage distortion capacitor load transformer simula- (%) (%) derating (k) tion BB 1 BB 2 BB 3 C1 C2 C3 T R2 1 TR22 A 2.6 2.6 9.0 -- -- -- 0.99 0.96 B 7.2 7.2 13 115 117 160 0.98 0.93 C 6.8 6.8 10.9 112 113 181 0.99 0.93 D 8.4 8.4 10.5 138 138 128 0.98 0.97 E 6.1 6.1 6.2 -- -- 130/150* 0.99 0.98 A 4.3 4.3 10.6 -- -- -- -- 0.96 B 13.8 14.1 21.6 148 149 224 -- 0.89 C 10.8 11.0 16.3 121 122 209 -- 0.93 D 6.8 6.8 9.1 115 115 -- -- 0.96 E 3.5 3.5 2.2 107 107 146/121* -- 0.98 A 1.8 1.8 8.3 -- -- -- 0.99 0.96 B 8.6 9.1 18.8 142 148 290 0.98 0.88 C 8.0 8.5 15.1 137 141 255 0.99 0.92 D 4.9 4.9 8.9 120 120 -- 0.99 0.96 E 3.6 3.6 5.5 114 114 149/128* 0.99 0.99 (*) both values correspond to order 5 and 7 fil ter capacitor loads respectively. Table 13-9: simulation results  Publication, traduction et reproduction totales ou partielles de ce document sont rigoureusement interdites sauf autorisation écrite de nos services. The publication, translation and reproduction, either wholly or partly, of this document are not allowed without our written consent. Industrial electrical network design guide T&D 6 883 427/AE 922 o interpreting results - the results results obtained obtained for the 3 source source configuratio configurations ns without without compensati compensation on underline underline the influence of the short-circuit impedance on the harmonic distortion rates - installing installing capacito capacitors rs increases increases the distorti distortion on rates owing owing to the the harmonic harmonic resonance resonances. s. They well exceed the compatibility levels of IEC 1000-4-2 (see table 8-20) - installing installing an anti-ha anti-harmonic rmonic induct inductor or limits limits voltage voltage distortions distortions,, capacitor capacitor overloads overloads and transformer derating factors, but not enough. - installing installing resonan resonantt shunts tuned to orders 5 and 7 greatly greatly limits limits voltage voltage distortions. distortions. The maximum rate (6.2% on BB3) is recorded on the utility and it remains acceptable. With the association of a third shunt tuned to order 11, we obtain very weak distortion rates (1.8 % on BB3), compatible with the use of very sensitive loads (class 1). o interpreting impedance curves The curves in figures 13-4 to 13-8 represent the network impedance seen from the speed variator terminals in the case of generator supply (generally the most restrictive restrictive case). They illustrate the distortion rates obtained on the busbar supplying the variators (BB3). Before compensation (case A), the network impedance is proportional to the harmonic order. Compensation (case B) causes resonance close to order 7, having a high harmonic current value. The distortion rate is thus high. Moving the capacitors (case C) reduces the resonance close to order 7, but not enough. Installing an anti-harmonic inductor (case D) reduces the impedance on order 7. On the other hand, a resonance close to order 9 appears. This is due to resonance between the MV capacitors and the upstream network. The order 5 and 7 resonant shunts (case E) decrease the resonance close to order 9. There is no high impedance on the harmonic orders supplied by the variators. The distortion rate is thus reduced to an acceptable value. Publication, traduction et reproduction totales ou partielles de ce document sont rigoureusement interdites sauf autorisation écrite de nos services. The publication, translation and reproduction, either wholly or partly, of this document are not allowed without our written consent. Industrial electrical network design guide T&D 6 883 427/AE 923  Z  ( m ) 320 1 2 3 4 5 6 7 8 9 order 10 11 1 2 13 13 14 15 15 16 16 17 17 18 18 19 19 20 21 21 22 22 23 23 24 25 26 27 2 7 28 28 29 29 30 30 31 31 Figure 13-4: generator-fed generator-fed network, case A  Z  ( m ) 350 1 2 3 4 5 6 7 8 order 9 10 11 1 2 13 13 14 15 15 16 16 17 17 18 18 19 19 20 21 22 22 23 23 24 25 26 27 2 7 28 28 29 29 30 30 31 31 Figure 13-5: generator-fed generator-fed network, case B  Publication, traduction et reproduction totales ou partielles de ce document sont rigoureusement interdites sauf autorisation écrite de nos services. The publication, translation and reproduction, either wholly or partly, of this document are not allowed without our written consent. Industrial electrical network design guide T&D 6 883 427/AE 924  Z  ( m ) 90 2 4 5 7 8 10 1 1 13 4 1 16 7 1 19 19 0 2 22 22 3 2 25 6 2 28 28 9 3 31 rd r Figure 13-6: generator-fed network, case C   Z  ( m ) 200 1 2 3 4 5 6 7 8 order 9 10 11 1 2 13 13 14 15 15 16 16 17 17 18 18 19 19 20 21 22 22 23 23 24 25 26 27 2 7 28 28 29 29 30 30 31 31 Figure 13-7: generator-fed network, case D  Publication, traduction et reproduction totales ou partielles de ce document sont rigoureusement interdites sauf autorisation écrite de nos services. The publication, translation and reproduction, either wholly or partly, of this document are not allowed without our written consent. Industrial electrical network design guide T&D 6 883 427/AE 925  Z  ( m ) 280 1 2 3 4 5 6 7 8 order 9 10 1 1 12 12 13 13 14 15 15 16 16 17 1 7 18 18 19 19 20 21 21 22 22 2 3 24 25 26 27 27 28 28 29 29 30 30 31 31 Figure 13-8: generator-fed generator-fed network, case E  n protection selectivity study We shall study the selectivity of overcurrent protections for three MV network elements (see fig. 13-9): - produc production tion unit unit MV/L MV/LV V trans transfor former mer,, TR22 TR22 - MV motor, ASM1 - MV cable, W W0 01 . Obtaining selectivity whatever the source configuration (utility alone, generators alone, utility + generators) is sometimes difficult, if not impossible. In this case, two protection systems must be provided, one for the utility alone and the utility + generators, and another for the generators alone. A change in source configuration will cause, if necessary, the modification of the protection settings (the Sepam 2000 offers this possibility). We will limit ourselves to studying the case of the network being supplied by the utility alone. The short-circuit current calculations and selectivity curve simulations are carried out using the SELENA software program. Publication, traduction et reproduction totales ou partielles de ce document sont rigoureusement interdites sauf autorisation écrite de nos services. The publication, translation and reproduction, either wholly or partly, of this document are not allowed without our written consent. Industrial electrical network design guide T&D 6 883 427/AE 926 utility U = 20 kV TR21 Ssc = Sn 200 MVA = U sc 5 MVA = 7.5 % BB 1 fault at 2  I sc 3 max = 5.4 kA  I sc 2 min = 4.2 kA 5.5 kV wiring system W01 BB 2 2 Pn M  I st  ASM1  I n 450 kW  = = TR22 5.7 Sn  I sc 3 max = 1.6 kA fault at  I sc 2 min = 1.5 kA 1 = 1250 U sc 5.5 kV = kVA 5.5% 1 BB 3 400 V  I sc3max : maximum maximum three-ph three-phase ase short short circuit circuit  I sc2min : minimum two-phase two-phase short circuit Figure 13-9: short-circuit current values  Publication, traduction et reproduction totales ou partielles de ce document sont rigoureusement interdites sauf autorisation écrite de nos services. The publication, translation and reproduction, either wholly or partly, of this document are not allowed without our written consent. Industrial electrical network design guide T&D 6 883 427/AE 927 o TR22 transformer protection The transformer is protected by a primary side double threshold protection, the low threshold acting as back-up to the secondary side protection (see § 10.3.4.3.2 of the Protection guide ). ). See curve 1 in figure 13-10. High threshold: Ih.set ≥ 1.25 × I sc max LV  = 1.25 × 1 600 = 2 000 A I = 2 kA h.set  th.set  = 0.1 s  I sc max LV   : maximum current for a three-phase short circuit at the transformer secondary terminals Low threshold: Il .set ≤ 0.8 × I sc min LV   = 0.8 × 1500 = 1200 A  HV  I = k A 1 . 2 l.set  tl.set  = 0.4 s  I sc min LV   minimum current seen by the MV protection for a short s hort circuit at the : transformer secondary terminals The curves in figure 13-10 show that the protection is not activated when the transformer is energized. o ASM1 motor protection (see § 10.4.1 of the Protection guide ) See curve 1 in figure 13-11. The condition to be met for protection setting is:  Im.set = 1.3 I st   The starting current is: I st = 5.7 nI = 315 A whence Im.set  = 410 A we will take a time delay of t m.set  = 0.1 s Figure 13-11 shows that selectivity is ensured with the upstream part. Publication, traduction et reproduction totales ou partielles de ce document sont rigoureusement interdites sauf autorisation écrite de nos services. The publication, translation and reproduction, either wholly or partly, of this document are not allowed without our written consent. Industrial electrical network design guide T&D 6 883 427/AE 928 o W01 wiring system protection see curves in figures 13-10 and 13-11. Selectivity with the TR22 transformer and ASM1 motor protections is of the time-graded type. The conditions to be met for protection setting are: - w.set I≤ 0.8 × sc, miIn, BB2 - w.sIet ≥ 1.25 × h.sIet  = 2.5 = 0.8 × 4 200 = 3.4 kA - tw.set ≥ t h.set   + ∆t = 0.4 s kA ≥ 1.25 × m.sIet  = and w.sIet and t w.set ≥ t m.set   + ∆t = 0.4 s 0.51 kA The following settings are therefore chosen: - I = 2.5 w.set  kA - tw.set  = 0.4 s Publication, traduction et reproduction totales ou partielles de ce document sont rigoureusement interdites sauf autorisation écrite de nos services. The publication, translation and reproduction, either wholly or partly, of this document are not allowed without our written consent. Industrial electrical network design guide T&D 6 883 427/AE 929 t (s) 100 1 0 10 2 1 0,1 0,01 0,1 1 10 0 : W01 wiring wiring system system protec protection tion curve curve 1 : TR22 transfo transformer rmer protectio protection n curve 2 : TR22 transformer transformer inrush current 100 1e+003 1 e+004 1e 1 e+005 I (A) Figure 13-10: transformer selectivity curves  t (s) 100 2 1 0 10 1 0,1 0,01 0,1 1 10 0 : W01 wiring wiring system system protec protection tion curve curve 1 : ASM1 motor protection protection curve 2 : ASM1 motor starting starting current current 100 1e+003 1 e+004 1e 1 e+005 I (A) Figure 13-11: motor selectivity curves  Publication, traduction et reproduction totales ou partielles de ce document sont rigoureusement interdites sauf autorisation écrite de nos services. The publication, translation and reproduction, either wholly or partly, of this document are not allowed without our written consent. Industrial electrical network design guide T&D 6 883 427/AE 930 n study of motor starting The study has been carried out using simulations on the Schneider "Start'n Go" software: - for the install installati ation' on's s most most powe powerfu rfull mo motor tor - for the simultaneous simultaneous starting of the producti production on unit unit 's 4 MV motors using an "equivale "equivalent" nt" motor (the software allows only one motor to be studied at a time). o Ÿ study of the 450 kW motor starting motor-load assembly characteristics (see table 13-10) Elements Pn (kW) Efficiency Speed tr/min Moment of inertia (kg m²) U n (V) cos ϕ 450 0.95 1 485 135 5 500 0.9 300 -- 1 485 200 -- -- Asynchronous motor Compressor without sliding lock panels Table 13-10: motor-load assembly characteristics  Note: Ÿ the oth other er mot motor or chara characte cteris ristic tics s are are given given in tab table le 13-1. 13-1. starting diagnosis - star starti ting ng time time:: 8.9 8.9 s - star starti ting ng curr curren ent: t: 296 296 A The starting current given by the manufacturer is determined for an infinite short-circuit power and its value of 315 A. The value determined by the software program is lower since it takes into account the voltage drop at the motor connection point. - voltag tage drops: 6.26 6.26 % on busb busbar ar BB2 BB2 5.93 5.93 % on busb busbar ar BB 1 1.57 % at th the e utilit utility y take-ov take-over er point point (20 (20 kV) kV) These values are acceptable for the motor and other loads fed by BB2 and BB1, and for the utility whose voltage variation must be lower than 4% (see table 4.1, EN 50 160). Publication, traduction et reproduction totales ou partielles de ce document sont rigoureusement interdites sauf autorisation écrite de nos services. The publication, translation and reproduction, either wholly or partly, of this document are not allowed without our written consent. Industrial electrical network design guide T&D 6 883 427/AE 931 - motor heatin ting: The software program has a database of starting withstands determined using motor heating characteristics. The database provides the withstands for our motor, i.e. 992 kA2 × s when cold 298 kA2 × s when warm. The stress on starting is 602 kA2 × s . The motor will therefore be able to withstand cold starting, but not warm starting . o study of simultaneous starting of the production unit's 4 MV motors The motor characteristics are given in table 13-1. We assume that the values of the moments of inertia of each motor and each load are known. We determine an equivalent cos ϕ by weighting the cos ϕ of each motor giving them a coefficient equal to the power: 4 ∑ P cos i i =1 cos ϕ = 4 ϕi = ( 474 × 2 × 0.9) + (177 × 2 × 0.78) ∑P 2 × 474 + 2 × 177 = 0.87 i i =1 In the same way we can determine the equivalent starting current:  I st   I n = ( 474 × 2 × 5.7) + (177 × 2 × 5) 2 × 474 + 2 × 177 = 5.5 We can deduce from this the characteristics of the equivalent motor-load assembly (see table 13-11). Elements Equivalent motor Equivalent load Pn (kW) Efficiency Speed tr/min Moment of inertia (kg m²) U n (V) cos ϕ I st   I n 1 230 0.95 1 485 370 5 500 0.87 5.5 900 -- 1 485 600 -- -- -- Table 13-11: equivalent motor-load assembly characteristics  Publication, traduction et reproduction totales ou partielles de ce document sont rigoureusement interdites sauf autorisation écrite de nos services. The publication, translation and reproduction, either wholly or partly, of this document are not allowed without our written consent. Industrial electrical network design guide T&D 6 883 427/AE 932 Ÿ starting diagnosis - sta startin rting g tim time: e: 13 13.7 .7 s - star starti ting ng curr curren ent: t: 765 765 A - voltag tage drops: 16.2 16.2 % on busb busbar ar BB 2 15.4 15.4 % on busb busbar ar BB 1 Voltage drops are considerable and they may disturb the network. Furthermore, the motors are subject to considerable heating when they are started since the voltage drop causes an increase in starting time. It will thus be preferable to start the motors one by one. Publication, traduction et reproduction totales ou partielles de ce document sont rigoureusement interdites sauf autorisation écrite de nos services. The publication, translation and reproduction, either wholly or partly, of this document are not allowed without our written consent. Industrial electrical network design guide T&D 6 883 427/AE 933 CHAPTER 13 BIBLIOGRAPHY n standards o IEC 76-2: power transformers. Part 2: temperature rise o IEC 364: electrical installations of buildings o IEC 909 (1988): short circuit calculations in three-phase a.c. systems o IEC 1000-2-4 (1994): electromagnetic compatibility (EMC). Part 2: environment. Section 4: compatibility levels in industrial plants for low-frequency conducted disturbances o IEC 50160 (05.1995): voltage characteristics of electricity supplied by public distribution systems n Schneider cahiers techniques o Guide to the design of industrial H.V. systems, Cahier Technique n° 124, M. Dana o Enclosures and degrees of protection , Cahier Technique n° 166, J. Pasteau P asteau o HV industrial network design, Cahier Technique n° 169, G. Thomasset o Protection of industrial and commercial MV networks, Cahier Technique n° 174, A. Sastré S astré n Schneider publications o Industrial network protection guide, C. Prévé (05-1996), ref. 02 888 608/BE o SELENA, calculating short-circuit short-circuit currents according according to IEC 909 909 (10.1995), F. Dumas, T. Rutgé o Electrical installation guide (07.1996), ref. MD1 ELG 2E Publication, traduction et reproduction totales ou partielles de ce document sont rigoureusement interdites sauf autorisation écrite de nos services. The publication, translation and reproduction, either wholly or partly, of this document are not allowed without our written consent. Industrial electrical network design guide T&D 6 883 427/AE 934 Publication, traduction et reproduction totales ou partielles de ce document sont rigoureusement interdites sauf autorisation écrite de nos services. The publication, translation and reproduction, either wholly or partly, of this document are not allowed without our written consent. Industrial electrical network design guide T&D 6 883 427/AE