New Method of Capacitors Failure Detection and Location in Shunt Capacitor Banks

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1 New Method of Capacitors Failure Detection and Location in Shunt Capacitor Banks Hesam Jouybari-Moghaddam West ern Universit y Tarlochan Sidhu University of Ontario Institute of Technology Ilia Voloh GE Grid Solutions Mohammad Zadeh - ETP 218 Texas &M Protective Relaying Conference

2 Outline Introduction Superimposed Reactance method -Ungrounded wye banks -Grounded wye banks Self-tuning process: periodic and during failures Method Flowchart Simulation model and method evaluation for different configurations Conclusions 2

Introduction Transient over voltages, temperature changes, manufacturing defects can cause internal failures of capacitor units The search of the faulty capacitor can in a large high voltage

3 Introduction Transient over voltages, temperature changes, manufacturing defects can cause internal failures of capacitor units The search of the faulty capacitor can in a large high voltage capacitor bank can take significant time and should be reduced to expedite the repair process Fuseless and internally fused designs do not have any visual indication for the failures Unbalance methods are the most sensitive methods used to detect capacitors failures. Detecting consecutive and ambiguous failures, live reporting of number of failed elements helps for preventive maintenance and thus reducing unscheduled outages 3

4 Different Grounding Configurations B C X X B X C Ungrounded (a) Grounded (b and c) N V N V P (b) (a) (c) N N I G X N V N R V R 4

5 Ungrounded banks Estimate the neutral voltage assuming a -phase failure (apply Kirchhoff s Current Law to the neutral node) 5

6 Ungrounded banks Rewrite and use simplifying terms (calibrating factors) Superimposed Reactance (SR) γ p and λ p are calibrating factors 6

7 Ungrounded banks For self-tuning we need to update and factors Two unknowns, two equations (real and imaginary) ( V V ) K + ( V V ) K = V V B N B C N C N For the faulted phase SR angle has to be near approach zero value SR magnitude indicates the number of failed elements X p X Spu p X pf X p = 1 = X X pf pf K B K C p: phase p (, B or C) pf: phase p after failure 7

8 Ungrounded banks: capacitors types djustments for direction of change in reactance KK aaaaaa = +1 1 ffffffffffffffff iiiiiiiiiiiiiiiiiiii ffffffffff Internally Fused Reactance Mag. Fusing Type Fuseless, Externally fused Reactance Mag. Decision making quantity K adj X Spu p 8

9 Self-tuning process: periodic and after failure K-factor Calculations ( V V ) K + ( V V ) K = V V B N B C N C N Update the k-factors (supervised) Calibrating Factors Calculations λ = 1+ K + K B C γ = ( K 1)( V V ) + ( K 1)( V V ) B B C C Balance out (reset) the SR Failure Detection Calculations X γ λ ( V V ) = V V Spu N N Update the calibrating factors 9

10 Capacitor Failure Dependent Self-tuning Self tuning is applied (updating the k-factors) once a failure is detected SR would be reset upon detection Method is ready for detection of subsequent failures ngle Zone Capacit or Element(s) Failure Counting Scheme Time ngle Mag. Fault L ocat ion Det ermined; SR Reset pplied M agnit ude T hreshold 1

time scale) Possible update period: One hour Self-tuning

11 Periodic Self-tuning Supervised for gradual changes compensation rrows Show Periodic Self-tuning Moments (note the time scale) Possible update period: One hour Self-tuning prevents misoperation by resetting the SR and thus its magnitude and angle value 11

12 Superimposed Reactance method flowchart Multifunctional Numerical SCB Relay Unbalance Prot ecti on Inputs Sett ing Calibrat ing Fact ors Calculat ion of Magnit ude T hresholds Block k-fact or Updates Phase ngle Evaluation Report ffect ed Phase Report Number of Failed Element s Count ing Scheme Re-calculat e t he k-fact ors Time Stamped Events Sequence HMI/ SCD nnunciators 12

13 Simulation Model 23 KV 5 km 5 km Feeder Internally Fused bank 1 MV SCB µF Fuseless Unit µF Unit

14 Validation: PSCD and Relay models The PSCD model has considered: Unbalance load Pre-existing inherent unbalance Harmonics Measurement noise Impact of temperature (could be shading) or aging The Relay model applies: nti-aliasing filter Decaying DC removal Full cycle DFT 14

15 Ungrounded banks: Method Evaluation ngle (Deg.) ngle (Deg.) ngle (Deg.) 18 ngle Magnitude (b) 3 B C 2 Number Time (s) Failure in phase Double failure in phase B (a) Consecutive failure in phase Double failure in phase C Phase Phase B Phase C % Magnitude % Magnitude % Magnitude 15

16 Grounded banks (via capacitor) third K-factor shows up K p N = X X p N It is much larger than phase K-factors It has trivial changes upon capacitor failures in each phase s a result, it will have a constant value in the algorithm (IEEE C37.99) X Spu p γ = λ ( V V) KV p p p N N V N V p 16

17 Grounded Bank via Cap: Method Evaluation ngle (Deg.) ngle (Deg.) ngle (Deg.) 18 ngle Magnitude Phase B (a) Phase 18 Phase C (b) 3 2 B C Time (s) Number 1 2 Capacitor Failure in Phase Phase Open Pole due to external faut 3 Phase reclosed % Magnitude % Magnitude % Magnitude 17

18 Grounded banks (via CT) The phase reactance shows up X V + V K + V K + jxv Spu B B C C R = V Phase reactance has minor changes after element failures Can be considered as the rated value (IEEE C37.99) 18

19 Grounded Bank via CT: Method Evaluation ngle (Deg.) (b) 8 Number ngle Magnitude Time(s) Capacitor 1 unit fails in Phase 2 C System Fault (a) % Magnitude 3 4 Capacitor Element fails in Phase C Fault cleared noticeable failure (Unit) and a subsequent minor (Element) failure detected Verifying the applicability of constant rated reactance assumption in detection principle (SR) 19

20 pplication to Externally Fused Banks Externally fused units are more susceptible to cascading capacitor element failures n intact or blown fuse does not always mean healthy or failed capacitor unit Failed elements remain as short circuits Superimposed Reactance can provide advance alarms for preventive maintenance 138 kv 138kV / 33kV.8 H 2 MV X/R=5. 25 MVar 2 2 Ω

21 pplication to Externally Fused Banks ngle (Deg.) ngle (Deg.) ngle (Deg.) Number ngle Magnitude (a) Phase Phase B Phase C (b) B C Time (s) % Magnitude % Magnitude % Magnitude 1 One element fails 3 Consecutive failure in phase C in phase 4 Consecutive failure in phase 2 Two elements fail in phase C 21

22 Validation PSCD, NI cdq and LabVIEW were used to apply waveforms to the relay

Conclusions Superimposed Reactance faulted phase detection method for internally fused and fuseless wye capacitor banks is presented to expedite the repair process Superimposed Reactance provides

23 Conclusions Superimposed Reactance faulted phase detection method for internally fused and fuseless wye capacitor banks is presented to expedite the repair process Superimposed Reactance provides advance maintenance alarms for externally fused banks Superimposed Reactance can be used for both grounded and ungrounded banks Superimposed Reactance faulted phase detection method applies self-tuning and auto-setting that result in: Detecting consecutive failures Detecting ambiguous failures 23

24 Conclusions Compensating for gradual capacitance change due to temperature changes or aging Compensating for errors due to the PT/CTs by initial setting (commissioning process) Both magnitude and phase angle of the SR quantity are used todetect capacitor element failures,making method robust even during external disturbances simultaneously with internal failures. Met hod is immune to external disturbances, noise, bank inherent unbalance, measurement inaccuracies. Real time report of number of failed elements and 24 location enables quick response for repair

25 Thank You Questions? 25

Fault Location in High Voltage Shunt Capacitor Banks

Western University Scholarship@Western Electronic Thesis and Dissertation Repository August 7 Fault Location in High Voltage Shunt Capacitor Banks Hessamoddin Jouybari Moghaddam The University of Western