Copyright © Lower Colorado River Authority and SEL 2016

A Current Story –When Primary Met Secondary

Genardo CorpuzLower Colorado River Authority

Swagata Das and Ariana HargraveSchweitzer Engineering Laboratories, Inc.

1 2I IIRT

k+

=1 2IOP I I= +

Percentage-Restrained Differential

IOP

IRTExternal

Internal

Slope

Restrain

Operate

Minimum Operate Current

Unrestrained Pickup

Protected Zone

87I1 I2

Know Equipment Being Protected

Bϕ

H3J1 J2

Aϕ

H2

Cϕ

H1

Control Cabinet

Digital Relay

CT Secondary Wiring at Junction Box

One-Line Diagram

Internal Inspection Reveals Damage onH3 Bushing and Its CT Secondary Wiring

Pitting and Carbon

Deposits From Arc

Junction Box J1 Scorched

Fault Root Cause

Why Did Bus Relay Operate for External Fault?

Transformer Relay Filtered Event Report 200100

0–100–200

531

–1–3–5503010

–10

87UTRIP

Current (A secondary)

Current (A secondary)

Operate Current (pu of tap)

2.0 3.2 4.4 5.6 6.8 7.0 8.2 9.4 10.6 11.8Time (cycles)

IAW1IBW1ICW1

IAW2IBW2ICW2

IOP1_PUIOP2_PUIOP3_PUU87P

Backup Overcurrent Relay Raw Event Report300

200

100

0

–100

–200

–300 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0Time (cycles)

Cur

rent

(A s

econ

dary

)

IA_SECIB_SECIC_SEC

A/D Limit

A/D Limit

Bus Relay Raw Event Report2010

0–1015

5

–5–15300

100

–100

–30087U

TRIP12 3 4 5 6 7 8 9 10

Time (cycles)

IAW4IBW4ICW4

IAW3IBW3ICW3

CB1 Current (A secondary)

CB2 Current (A secondary)

T1 High-Side Current

(A secondary)

IAW1IBW1ICW1

IB Phasors at Cycle 3, Current In = Current Out

IB Phasors at Cycle 4, Current In ≠ Current Out

10,500∠–98.1°

Bus Relay Operate and Restraint Quantities70

50

30

10

–10453525155

–5

87U87U2

TRIP12 3 4 5 6 7 8 9

Time (cycles)

Operate Current (pu of tap)

Restraint Current (pu of tap)

IOP1IOP2IOP3U87P

IRT1IRT2IRT3

300

200

100

0

–100

–200

–30011.27 11.29 11.31 11.33 11.35 11.37

Time (seconds)

IB_TransformerIB_Bus

Cur

rent

(A s

econ

dary

)

True Sequence of Events

Top Gear Towing Challenge

Primary Currents Can Cause Thermal DamageCurrent Input Ratings

• 15 A continuous

• 500 A for 1 second

• 625 A / 1,250 A for 1 cycle

Primary Voltages Can Cause Dielectric Failure

Current inputs rated to withstand

2,500 Vac

“Spark Gap Effect” Saves the Day

Ground Wire

80 kV

• Respect power system• Request visual inspection during installation• Analyze event reports, even if root cause is known Download all event types

Implement automatic event retrieval system

Synchronize all relays to GPS time source

Recommendations

• Primary system exposure can damage relays Inspect for damage, perform meter and dielectric tests

• Settings expertise alone is not enough Know equipment you are protecting

Recommendations

Questions?