© 2019 Caterpillar and SEL
Compensator Ground Fault Coverage Through a Delta-Wye Transformer –
A Case Study
Dustin HohenberyCaterpillar
Ryan McDaniel, Harish Chaluvadi, and Michael J. ThompsonSchweitzer Engineering Laboratories, Inc.
• Case study• Initial analysis• Dynamic compensator characteristic• Transformer connection effects on distance elements• Case study using dynamic compensator characteristic• Summary
Overview
• Ground fault on Line L1
• Breaker 1 relay trips
• Breaker A relay does not trip
• BT trips
Case Study Overview
B
Main B Relay
Bus-Tie RelayA
Main A Relay
13
4
Utility Sub X Utility Sub Y
2
Line L1
Line L2
Line L2Line L1
Bus BBus A
51N51
21C51 51N21C51 51N
BT
Breaker 1 Event Report
Breaker A Event Report
Initial Compensator Distance Analysis
PPCOMP AB AB R
PPCOMP BC BC R*
TORQUE
S1 V I • Z1S2 V I • Z1
PPCOMP IM • (S1• S2 )
= −
= −
=
PPCOMPTORQUE
Reach
VA
PPCOMP Balance
0 10 20 30 40 50 60
8000600040002000
0–2000–4000–6000–8000
Initial Mho Distance Analysis
PPMHO(SELF) PP PP R
PPMHO(SELF) PP
*TORQUE
S1 V I • Z1
S2 V
PPMHO(SELF) RE • (S1• S2 )
= −
=
=
MHO(SELF) Torque
Reach
VA
MHO(BC) BalanceMHO(CA)MHO(AB)
15000100005000
0-5000
–10000–15000–20000–25000–30000
0 10 20 30 40 50 60
• Compensator includes two relays Three-phase relay (3PCOMP)
Phase-to-phase relay (PPCOMP)
• PPCOMP evaluates V1 / V2 at relay reach point
Compensator Review
R R R
R R R
V1 I1 • Z1 V1C= = 1< V2 I2 • Z1 V2C
−θ
−
Compensator PerformanceEvaluate Without and With Transformer (YD11)
Z1S Z1RZ1L
ES ER
S R
Z1R
Fault Point
Z1S Z1R
ES ER
S R
Z1R
Fault Point
Z1L
Dynamic Compensator CharacteristicBC Fault With No Transformer
PPCOMPMHO(BC)MEM
Dynamic Compensator CharacteristicBC Fault With Transformer
PPCOMPMHO(BC)MEM
Dynamic Compensator CharacteristicBCG Fault
PPCOMPMHO(BC)MEM
No transformer With transformer
Dynamic Compensator CharacteristicBCG Fault With Transformer
PPCOMPMHO(BC)MEM3PCOMP
Dynamic Compensator CharacteristicCG Fault With Transformer
PPCOMPMHO(BC)MEM3PCOMP
Dynamic Compensator CharacteristicFault With Transformer
BCG fault – no load CG fault – heavy load
PPCOMPMHO(BC)MEM3PCOMP
Revisit Case Study
PPCOMPMHO(BC)MEM3PCOMP
Revisit Case Study
MHO(PP)COMP
• PPCOMP offers unreliable performance for close-in ground faults, including PPG
• Excessively long reach settings hinder performance• Lines with tapped loads require special attention• Compensated mho elements offer more reliability for
close-in ground faults through a transformer
Summary
Dynamic Compensator CharacteristicBC Fault With No Transformer
PPCOMPMHO(BC)MEM
Compensator Ground Fault Coverage Through a Delta-Wye Transformer – �A Case StudyOverviewCase Study OverviewBreaker 1 Event ReportBreaker A Event ReportInitial Compensator Distance AnalysisInitial Mho Distance AnalysisCompensator ReviewCompensator Performance�Evaluate Without and With Transformer (YD11) Dynamic Compensator Characteristic�BC Fault With No TransformerDynamic Compensator Characteristic�BC Fault With TransformerDynamic Compensator Characteristic�BCG FaultDynamic Compensator Characteristic�BCG Fault With TransformerDynamic Compensator Characteristic�CG Fault With TransformerDynamic Compensator Characteristic�Fault With TransformerRevisit Case StudyRevisit Case StudySummaryDynamic Compensator Characteristic�BC Fault With No Transformer