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PSA Overcurrent Coordination

PSA Overcurrent Coordination Guide

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230 views74 pages

PSA Overcurrent Coordination

PSA Overcurrent Coordination Guide

Uploaded by

Terry
Copyright
© © All Rights Reserved
We take content rights seriously. If you suspect this is your content, claim it here.
Available Formats
Download as PDF or read online on Scribd
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PSA ELECTRICAL ENGINEERING POWER SYSTEM STUDY APPLICATION GUIDE Overcurrent Coordination Setting Guidelines REPRODUCTIONS REPRODUCTION OF THIS MATERIAL, IS PERMITTED PROVIDED PROPER. ACKNOWLEDGEMENT IS GIVEN TO POWER SYSTEMS ANALYSIS. ‘Soroen Goran seg Scere Introduction ‘The proper selection and coordination of protective devices is mandated in article 110.10 of the National Electrical Code, To full this requirement an’ overcurrent ‘coordination study is required, The electrical engineer is always responsible for this ‘analysis. It's an unfortunate fact of life that many times the engineer who specified and purchased the equipment will not set the devises. Therefore, compromises. are Inevitable. ‘There are three fundamental aspects to overcurrent coordination that engineers should keep in mind while selecting and setting protective devices, The fists life safely. Life safety requirements are met if protective devices are rated to carry and interrupt maximum available oad currents, @s well as, withstand and interrupt maximum available fault curents. Life safety requirements are never compromised. The second ‘aspect is equipment protection. Protection goals ére met if overcurrent devices are set ‘above load operating levels and below equipment damage curves. Feeder and {transformer damage curves are defined in applicatie equipment standards. Motor and ‘Generator damage curves (points) are machine secific, and are normally provided in the vendor data submittal package. Based on system operating and equipment sizing Practices equipment protection is not always possible. The last aspect is protective 20 seconds. Capacitor coz soist Short Time Residual Neutral CO-8 5 Inverse Neutral Ground COB st Inverse Ground ir 50 Instantaneous 4. The CO-5is more commonly used on a moter ekeltthan the CO. LV Power Circuit Breaker Trip Function Chart Description Lona Time Short Time Instantaneous Ground Fault Main Y Y N Y Te Y Y N y Motor Feeder Y N y y ‘Transformer Feeder Y Y Y Y Generator Feeder Y Y y y MCC Feeder Y Y N Y ‘Switchboard Feeder Y v N Y Panelboard Feeder y y N Y ‘OvrcuenCordnaon Sting Gans Coordinating Time Intervals Between Series Devices Upstream ownstraam Disk Deve Devise Quervavel_ Tolerance SIRolay —S1Relay ot 04 04 04 on S1Rolay SO Relay NIA NA NA NA NA NA SiaticRelay Static Relay NA NA NA NA NA NA S1Rely Wee. NA NA StRelay Fuse NA NA Fuse, SORelay NIA NA NA NA NA NA Fuse Fuse NA Lvea@) —LvCB() NA Notes: “otal ime st maximum caren seen by bon devices, ‘Test and ealvated ly, [Natoste an eabrted rly Relay 0.07 @ 007 @) 007 @) 0.178) 047) 017) 0.07 2) 0.07 2) 0.07 0.76) 017) 017) 0.072) 0.07 2) 0.07 @) 0.417 8) 0.17 6) 0.178) 47 @) 0.178) 0.07 2) 0478) 0.07 2) 0.07 (a) 0.07 (2) 0.17.3) 0.17 3) 0473) NA NA Operating Total(1) Tmeid) (Seconds) 005 022 008028 0130.30 005. 032 008035 013° O40 005 02 0088 043-020 005 oe 003025 013 030 005% 0-2 008045 013 020 005 022 008025 013 030 NA oor NA oa7 NA oor NAS Oz, 005 oa 00s as 013 oz 005 oe 008 25 013030 NA © NA 0 Average 04 02 02 02 02 o ” ‘Downstream beaker operating tne 3-oy(0.08 seconds), yc (0.08 seconds) and cycle (0.13 ssconas. Cocrinating tine intervals not applicable. Maintsin published fuse aos. ow votage molded case or power cet breaker. (Crdinatng te tere rt appicsbe. Pubshed tmecurent curves should ot overap, ‘Ovecuret oaraton Stig Gates MV Motor Switchgear Feeder Unit Industry standard overcurrent protection schemes for MV induction and synchronous ‘motors fed from switchgear circuit breakers include an instantaneous overcurrent relay \Covice 50/51). The 50151 relay characteristics are plotted on a phase time-current ‘curve (TCC) along with the motor starting and damage curves, and the feeder damage “The purpose of the 50/51 relay Is to allow the motor to start and run, and to protect the ‘motor and cable from overloads and faults. ‘To accomplish this the relay characteristics ‘must be above and to the right ofthe mctor starting curve, and tothe let and below the ‘olor, stator and cable damage curves, and the amp rating of the cable, ‘Suggested margins are listed bolow that have historically alowed for safe operation of ‘the motor and cable while reducing instances of nuisance trips. Device Function Recommendations Comments CT Size 125-150% of FLA 51 Pickup 115-125% of FLA Set below motor stator damage curve, ‘Set at or below cable ampacity. 51 Time Dial_ 2-10 seconds abeve Set below motor rotor damage curve, knee of motor cure Set below cable damage curve. 50 Pickup 200% of LRA. Set below cable damage curve, Cable damage curve must be above the maximum fault current at 0.1 seconds. ig 1. Mv motor sutengear eed nt ane Ho ‘verre Cordnnton—Seting Quine CURRENT IN AMPERES. 1000 100 t 0.10 | oot 05 1 10 tj 400 1K 10K MVMSFU.tce Ret. Voliage: 4160 Current Scale x10" Fg.2. MV moter sntchasar feeder unt- pas ToC. oo ‘SQNOO3S NI SNL. nme Gornnon- sexing Gucetnes MV Motor Fused Starter Feeder Unit Industry standard overcurrent protection schemes for MV induction and synchronous ‘motors fed from fused starters include an overcurrent relay (device 51), and a set of R= ‘ated fuses (device 50). R rated fuses met at 100 times the R rating and 20 seconds, Both the fuse and relay characteristics are plotted on a phase TCC along with the motor starting and damage curves, and the feeder damage curve. ‘The purpose of the fuse-relay vommbizaon fs fo allow the motor to start an run, ard to protect the motor and cable from overloads and faults. To accomplish this the fuse- ‘lay characteristics must be above and tothe right of the motor staring curve, and to the left and below the rotor, stator and cable damage curves, and the amp rating of the cable. ‘Suggested margins ae listed bolow that have historically allowed for safe operation of the motor and cable while reducing instances of nuisance tips, Device Function Recommendations Comments cr Size 125-150% of FLA 51 Pickup 115-125% of FLA Set below motor stator damage curve, ‘Set at or below cable ampacity. 51 Time Dial 2-40 seconds above Set below motor rotor damage curva. knee of motor eume ‘Set below cable damage curve. 50 Fuse Size Rang? 11LRAYO0 Set blow cable damage curve. ANPrams> FLA Cable damage curve must be above the ‘maximum faut curent a 0.01 seconds SPT © Ez 7h | { pie rees7'y ade, & ve sO SZENT VALS 7 he omer) | + op DAMAGE cvbves [ + ST8E (VIE Pade qf h mer tmtsnmt cy a Co a The & rer 4 Fu (setts) 0 WAKE sete ok 1 OF sa. TRS. 0.01 CURRENT IN AMPERES 05 1 MVMFSFU.toc Ref. Voltage: 4180 Current Scale x10" Fig. 4. MV motor used starter feeder unt phage TCC. ‘SaNOO3S NI WL MV Generator Switchgear Feeder Unit with Voltage Controlled 51V Industry standard backup overcurrent protection schemes for NIV generators fed from ‘switchgear circuit breakers include elther a voltage controlled or voltage restrained ‘overcurrent relay (device 51V). The voltage controlled overcurrent relay wil be covered Inthis section. The 51V relay characteristics are plotied on a phase TCC along with the {enerator decrement curve and damage point, andthe feeder damage curve. ‘The purpose of the rely isto allow the generator to operate, and to provide backup ‘fault protection forthe generator and cable, To accomplish this the relay pickup must be tothe left of the generator armature steady stale current. Also, the relay time delay ‘characteristics must be above and to the right of the generator decrement curve with ‘constant excitation, and to the left and below the generator damage point, cable ‘damage curve and the amp rating of the cable. ‘The time delay must also be set to be ‘selective with downstream feeder relays. ‘Suggested margins are listed below that have historically alowed for safe operation of the generator and cable while reducing instances of nuisance trips Device Function Recommendations Comments cr Size 125-180% of FLA SIV Pickup 80-90% of l= 11K, ‘Assume X= 1.5.0 pu if Xsunknown. 51 Time Dial Above knee of generator Set above downstream feeder relays, decrement curve with constant excitation ‘Set below cable damage curve. ga Fig 6. MV genorat awichgear feeder unt VG SAV =e fine 1000 0.10 ot ‘Ovcinet Cardston Sting Cadena CURRENT IN AMPERES. With votage contol the curent and voltage functions ae in series ‘Therefore, curents above tho time curve will not trip the relay for votages above the setpoint oct A 05 4 0 +100 1K MVGSFUVC.toc Ref. Voltage: 12470 Current Scale x10" Fig. 6 MV gonerator switchgear feeder unt wiVC S1V- phase TCE. 10K ‘SNOO3S NI SWLL ‘Ovecarent ourdntn = Seng isos MV Generator Switchgear Feeder Unit with Voltage Restrained 51V Industry standard backup overcurrent protection schemes for MV generators fed from switchgear circuit breakers Inciude either a voltage controled of voltage restrained ‘overcurrent relay device 61V)}. The voltage restrained overcurrent relay will be covered in this section. The 5tV relay characteristics are plotd on a phase TCC along withthe "generator decrement curve and damage point, and the feeder damage curve. “The purpose of the relay is tc allow the generator to operate, and to provide backup ‘fault protection forthe generator and cable. To accomplish this the relay pickup at O% ‘restraint must be tothe left of fhe generator armature steady stale current, and at 100% restraint must be to the right o' the generator full load amps. Also, the relay time delay ‘characteristics must be above and to the right of the generator decrement curve with ‘constant excitation, and to the left and below the generator damage point, cable ‘damage curve and the cable amp rating, The time delay must also be soi to be ‘selective with downstream feeder relays, ‘Suggested margins are listed below that have historically allowed for safe operation of ‘he generator and cable while reducing instances of nuisance trip. Device Function Recommendations Comments cr Size 125-150% of FLA SIV Pickup 125-180% of FLA @ 100% Voltage Restraint ‘Set below Overload Curve 51 Time Dial Above knee of generator Set above downstream feeder relays. decrement curve with cconstent excitation ‘Set below cable damage curve, Fig. 7. MY gonororswithgoar oder unt wVR S1V one. -10- rent oro ag eben CURRENT IN AMPERES 00 22a won a Decrement Curve with ~—} Constant Exetation f= 1p. 10 | | 1 | 0.10 wor vonage resvaint curenis abovethe time curve wil tip the relay for voltages above the setpoint Shee 0.01 05 10 100 1 10K MVGSFUVR.toc Ref. Voltage: 12470 Curent Scale x10" ig. 8. MV generator swichgearfeederunt wR S1V- phase TCC me ‘SUNOOSS NI SINLL ‘ovrcuat CosrSnton=Seting Gdns MV Transformer Switchgear Feeder Unit Industry standard oversurent protection schemes for MV transformers fed from switchgear circuit breakers include an instantaneous overcurrent relay (device 50/51). The 50/51 relay characteristics are plotied on a phase TCC along with the transformer and feeder damage curves. “The purpose of the phase overcurrent rola isto allow for full use of the transformer, and to protect the transformer and cable from overioads and faults. To accomplish this ‘the relay characteristic should be to the right of the transformer FLA rating and inrush ‘point, and to the left ofthe transformer and cable damage curves and the cable amp rating ‘Suggested margins are listed bolow that have historically alowed for safe operation of ‘the transformer and cable while reducing instances of nuisance tips. Device Function Racommendations Comments, CT © — Size 200% of FLA FLA on base rating St Pickup 110-140% of FLA__Set below the transformer damage curve. Set at or below cable ampacity. 51 Time Dial lotthru current @ 1.0 Set below the transformer damage curve ‘second Sot at or above low voltage main device, 50 Pickup 200% ofetthru—_‘Set below cable damage curve, current Set above transformer inrush pont. Cable damage curve must be above the ‘maximum fault current at 0.1 seconds. Fg. 8. MV transformer swichgearfesderunt-on8 tae. a1 rece Gowrdorln = Serine Gein CURRENT IN AMPERES. 10 01 I os 1 10 100 1k 10K. MVTSFU.tec Ref. Voltage: 4180. Current Scale x10" Fig 10. MY wanton sera fader Une pie TOC, ne ‘S0NO93S NI WL ‘vera! Cerdnton- etn ees MV Transformer Fused Switch Feeder Unit E-rated power fuses are typically used in fused Switches serving MV transformers. Fuses rated 100E or less must trip in 300 seconds at currents between 200 and 240% oftheir E ratings. Fuses above 100E must trip in 600 seconds at curents between 220, ‘and 264% of their E ratings. The fuse characteristics are potted on a phase TCC along with the transformer and feeder damage curves. ‘The purpose of the fuse Is to allow for ful use of the transformer, and to protect the transformer and cable from faults. To accomplish this, the use characteristic should be {o the right ofthe transformer inrush point and to the let of the cable damege curve. ‘The fuse will always cross the transformer damage curve. The LV main device provides ‘overcurrent protection forthe circu, ‘Suggested margins are listed below that have historically allowed for safe operation of the transformer and cable while reducing instances of nuisance trips. Device Function Recommendations Comments 50 Fuse Size E-ating > FLA FLAat bop rating. Eating 250300% FLA (NEC) Set ato: below cable ampalty. eee 11504) ‘Set above transformer inush 12 x 0.1 secon, ‘Set above transformer inush 25 x0.01 ‘seconde. Cable damage curve must be above the ‘maximun fault curent at 0.01 seconds. Fg. 11. MV transformer fused such feeder unt -or in. oie CURRENT IN AMPERES 1000 saa ' ville it onllll | O05 1 10 100, 4K 10K MVTFSFU.tco Ref. Voltage: 12470 Current Scale x10" Fig. 12, MV tanstomer fused switch feeder unt phase TEC, “15 'SGKOORS NI aWLL ‘Ovcurent Corton = Satin Glos MV Capacitor Switchgear Feeder Unit Industry standard overcurent protection schemes for MV fused capacitor banks fed ‘from switchgear circut breakers include an instantaneous overcurrent relay (device '50151). The 0/51 relay characteristics are plotled on a phase TCC along with the ‘feeder damage curve, “The purpose ofthe phase overaurrent relay isto allow for fll use ofthe capacitor, and ‘to protect the capacitor and cable from overloads, and the cable from faults. The [Purpose of the fuse isto preven: a case rupture due to a fault within the capactor tank. ‘To accomplish this, the relay and fuse characteristics should be to the right of the ‘capacitor amp rating, and to the left ofthe capacitor case rupture curve, cable damage ‘curve and cable amp rating. ote, the phase relay is not fast enough to protect the ‘capacitor bank from damage. ‘Suggested margins are listed below that have historically allowed for safe operation of ‘the transformer and cable while educing instances of nuisance tps, Device Function Recommendations Comments, cr Size 190% of lomscm 51 Pickup 190-188% of lene Set at or below cable ampaciy 51 Time Dial Time Di 1 50 Pickup 200-450% of capex ‘Set below cable damage curve, Cable damage curve must be above the ‘maximum fault current at 0.1 seconds. Fuse Fuse Size 200% dllewaay Defer to manufacturer's recommendations. Set below capacitor case rupture curve, Fig. 18. MV capacitor switchgear food unt - oe ne ote CURRENT IN AMPERES. 1000 = 100 10 0.10 0.01 05 1 10 100 1K 10k MVCSFULtce Ref. Voltage: 4160 Current Scale x10%0, Fla, 4, MV capactor switchgear feeder unit-phase Too, ot ‘SONOO3S NI NIL ‘Onreutt Coaratn = eng lions MV Main Service Switchgear Feeder Unit Industy standard overcurrent protection schemes for switchgear main crcult breakers include an overcurrent relay (device 51). However, there are those who believe in ‘adding an instantaneous function (device 50). The problem with adding tis function is that the main and feeder instantaneous functions wil never be selective, Those who do ‘this, accept the risk of nuisance tripping in order to reduce tripping times for a fault on ‘the main bus. The relay characteristics are plotied on a phase TCC along with upstream and downstream protective device characteristics, “The purpose of the $1 relay isto provide overcurrent protection for the main service bus and feeder. The 51 relay must be selective with downsizeam feeder relays. ‘Suggested marghs are listed below thet have historically alowed for safs operation of ‘the main bus and cable while reducing instances of nuisance tips. Device Function Recommendations Comments CT Size» 100% Bus Rating 51 Pickup < 100% Bus Rating Do not set pickup according to load, Set above the transformer FLA. Set below the transformer damage curve, Sot at or below feeder amgacty. Set below the feeder damage curve. Do not set above main bus ampacity 51 TimeDDial_NoSpeciic Rule Set above feeder rlays, ‘Set below transformer primary relay if possible, Not necessary tc coordinate since devices are in series. Fo 1B. Vala canien sutchgerfeder unt oetne.

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