New Method of Capacitors Failure Detection and

Location in Shunt Capacitor Banks

Hesam Jouybari-Moghaddam – Western Universit y

Tarlochan Sidhu –Universit y of Ontario Inst itute of Technology

Ilia Voloh –GE Grid Solut ions

Mohammad Zadeh - ETAP

2018 Texas A&M Protective Relaying Conference

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 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 ambiguousfailures, live reporting of number of failedelements helps for preventive maintenanceand thus reducing unscheduled outages

3

• Ungrounded (a)

• Grounded (b and c)

Different Grounding Configurations

N

XA XB XC

ABC

VN

VP

IG

RXN VN VR

N N

(a)(b) (c)

4

Estimate the neutral voltage assuming a A-phase failure (apply Kirchhoff’s Current Law to the neutral node)

Ungrounded banks

5

Ungrounded banks

Superimposed Reactance (SR)

Rewrite and use simplifying terms (calibrating factors)

6

and are calibrating factors pλpγ

• For self-tuning we need to update and factors • Two unknowns, two equations (real and imaginary)

• For the faulted phase SR angle has to be near approach zero value

• SR magnitude indicates the number of failed elements

p: phase p (A, B or C)pf: phase p after failure

Ungrounded banks

( ) ( )A AB N B C N C N AV V K V V K V V− + − = −

1p p pfSpup

pf pf

X X XX

X X−

= − =

ACKA

BK

7

• Adjustments for direction of change in reactance

𝐾𝐾𝑎𝑎𝑎𝑎𝑎𝑎 = +1−1

𝑓𝑓𝑓𝑓𝑓𝑓𝑓𝑓𝑓𝑓𝑓𝑓𝑓𝑓𝑓𝑓𝑖𝑖𝑖𝑖𝑖𝑖𝑓𝑓𝑖𝑖𝑖𝑖𝑎𝑎𝑓𝑓𝑓𝑓𝑖𝑖 𝑓𝑓𝑓𝑓𝑓𝑓𝑓𝑓𝑎𝑎

Ungrounded banks: capacitors types

Fusing TypeInternally Fused Reactance Mag.

Fuseless,Externally fused

Reactance Mag.

Spuadj pK XDecision making quantity

8

Self-tuning process: periodic and after failure

Update the k-factors(supervised)

K-factor Calculations

Update the calibrating factors

Balance out (reset) the SR

Failure Detection Calculations

Calibrating Factors Calculations

( ) ( )A AB N B C N C N AV V K V V K V V− + − = −

1 A AA B CK Kλ = + +

0 0( 1)( ) ( 1)( )A AA B B C CK V V K V Vγ = − − + − −

0( )Spu A A NA

N A

V VXV V

γ λ− −=

−

9

• 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

Capacitor Failure Dependent Self-tuning

Time

Angle Zone

Magnitude Threshold

Capacitor Element(s) Failure

Fault Location Determined; SR Reset Applied

Counting Scheme Angle

Mag.

10

• Self-tuning prevents misoperation by resetting the SR and thus its magnitude and angle value

• Supervised for gradual changes compensation

• Arrows Show Periodic Self-tuning Moments (note the time scale)

• Possible update period: One hour

Periodic Self-tuning

11

Superimposed Reactance method flowchart

Blockk-factor Updates

Report Affected Phase

Report Number of Fai led Element s

Re-calculate the k-factors

Phase Angle Evaluation

Count ing Scheme

Calculat ion of

Magnitude Thresholds

Unbalance Protection

Inputs

Sett ing Calibrat ing

Factors

Time Stamped Events Sequence

HMI/SCADA

Multifunctional Numerical SCB Relay

Annunciators

12

Simulation Model

Internally Fused bank

Fuseless

62 ...

...

...14

3

1.36µF

2

.....

Unit

12

5

...

1

6

60.8µF

.........

...

...

Unit

100 MVA

230 KV 50 km 50 km

SCB

Feeder

13

• Unbalance load

• Pre-existing inherent unbalance

• Harmonics

• Measurement noise

• Impact of temperature (could be shading) or aging

Validation: PSCAD and Relay models

The PSCAD model has considered:

• Anti-aliasing filter

• Decaying DC removal

• Full cycle DFT

The Relay model applies:

14

Ungrounded banks: Method Evaluation

0.2 0.25 0.3 0.35 0.4-180

0

180(a) Phase A

Ang

le (D

eg.)

00.20.40.60.8

% M

agni

tude

Angle Magnitude

0.2 0.25 0.3 0.35 0.4-180

0

180Phase B

Ang

le (D

eg.)

00.20.40.60.8

% M

agni

tude

0.2 0.25 0.3 0.35 0.4-180

0

180Phase C

Ang

le (D

eg.)

00.20.40.60.8

% M

agni

tude

0.2 0.25 0.3 0.35 0.40

1

2

3(b)

Num

ber

Time (s)

A B C

Failure in phase A

1

Double failure in phase B

2

Consecutive failure in phase A

3

Double failure in phase C

4

15

• A third K-factor shows up

• It is much larger than phase K-factors• It has trivial changes upon capacitor failures in

each phase• As a result, it will have a constant value in the

algorithm (IEEE C37.99)

Grounded banks (via capacitor)

ppN

N

XK

X=

0 0( ) pp p N NSpu

pN p

V V K VX

V Vγ λ− − −

=−

16

Grounded Bank via Cap: Method Evaluation

0.2 0.25 0.3 0.35 0.4 0.45-180

0

180(a) Phase A

Ang

le (D

eg.)

00.20.40.60.8

% M

agni

tude

Angle Magnitude

0.2 0.25 0.3 0.35 0.4 0.45-180

0

180Phase B

Ang

le (D

eg.)

00.20.40.60.8

% M

agni

tude

0.2 0.25 0.3 0.35 0.4 0.45-180

0

180 Phase C

Ang

le (D

eg.)

00.20.40.60.8

% M

agni

tude

0.2 0.25 0.3 0.35 0.4 0.450123

(b)

Num

ber

Time (s)

A B C

Capacitor Failure in Phase A1

Phase A Open Pole due to external faut

2

3 Phase A reclosed

17

• The phase reactance shows up

• Phase reactance has minor changes after element failures

• Can be considered as the rated value (IEEE C37.99)

Grounded banks (via CT)

A ASpu A B B C C RA

A

V V K V K jXVXV

+ + +=

−

18

Grounded Bank via CT: Method Evaluation

• A noticeable failure (Unit) and a subsequent minor (Element) failure detected

• Verifying the applicability of constant rated reactance assumption in detection principle (SR)

0.2 0.25 0.3 0.35 0.4 0.45-180

0

180(a)

Ang

le (D

eg.)

0

2

4

6

8

% M

agni

tude

Angle Magnitude

0.2 0.25 0.3 0.35 0.4 0.450

2

4

6

8(b)

Num

ber

Time(s)A Capacitor unit fails in Phase A

1

AC System Fault2

AC Fault cleared4

A Capacitor Element fails in Phase A3

19

• Externally fused units are more susceptible tocascadingcapacitor element failures

• An intact or blown fuse does not always meanhealthy or failed capacitor unit

• Failed elements remain as short circuits

• Superimposed Reactance can provide advancealarms for preventive maintenance

Application to Externally Fused Banks

2000 MVAX/R=5.0

138 kV 138kV / 33kV

25 MVar

20 Ω

0.008 H

20

Application to Externally Fused Banks

0.2 0.25 0.3 0.35 0.4-180

0

180(a) Phase A

Ang

le (D

eg.)

00.150.30.450.6

% M

agni

tude

Angle Magnitude

0.2 0.25 0.3 0.35 0.4-180

0

180 Phase BA

ngle

(Deg

.)

00.150.30.450.6

% M

agni

tude

0.2 0.25 0.3 0.35 0.4-180

0

180 Phase C

Ang

le (D

eg.)

00.150.30.450.6

% M

agni

tude

0.2 0.25 0.3 0.35 0.40123

(b)

Num

ber

Time (s)

A B C

One element fails in phase A

1

Two elements fail in phase C2

3 Consecutive failure in phase C

Consecutive failure in phase A4

21

Validation

PSCAD, NI cDAQ and LabVIEW were used to apply waveforms to the relay

• 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

Conclusions

23

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 quantityare used to detect capacitor element failures, makingmethod robust even during external disturbancessimultaneously with internal failures.

• Method is immune to external disturbances, noise,bank inherent unbalance, measurementinaccuracies.

• Real time report of number of failed elements andlocation enables quick response for repair

Conclusions

24

Thank You

Questions?

25