Evolving Transmission Line Faults While Single

Phase OpenWestern Protective Relaying Conference 2014

Charles HenvilleHenville Consulting Inc, and

Tony JiaoBC Hydro

Evolving faults are rare… And even more rare under single phase

open conditions…but they do happen!What are the problems associated with

them during single phase open (SPO)? Two recent cases in BC Hydro are

presented And protection performance is analyzed

Single phase open

Directional relays have some difficulties during SPO

is like an LLG fault

BC Hydro transmission (part)

12 August 201314:28 hours lightning strike

Followed by another strike 90 ms after first strike.

AG Fault followed by correct single phase trip in 3 cycles

BG Fault followed by correct (but slow) 3 phase trip in 24 cycles

Line manually reclosed OK

REV Terminal

Zoom

Zoomed AreaFault plasma ionizes air Second fault

on B Phase

Arc from second fault is close to the ionized air from first

REV Terminal

REV Zone 1 Quad sees initial fault

SPO Blocks all quads

MG2 No Op.51S1T Trips 3P and Key 3P DTT

Check relay response to faults

ACK Trips from A PH DTT Received

ACK Terminal

Modeled Response

REV Zone 1 Quadoperates

ACK All distance elements restrain

11

5L72

SYA Series Capacitor Station

12

Shield wire

13

February 4th, 2014 - 6:48amSC controller issued auto isolation command (OCT supervision logic mis-operation)

With 5BP2 not electrically closed,5D3 and 5D4 tried to interrupt 600A load current. Arcs start across open contacts

5CB2 and 5BP2 closed automatically by isolation sequence. But 5BP2 did not close electrically

14Snow on 5BP2 contact

Arcs rise due to heat

Source More Arcs 'n Sparks! http://205.243.100.155/frames/longarc.htmWith permission from Bert Hickman, http://www.capturedlightning.com

16

Seymour Arm Series Capacitor Station

A phase arcing to shield wire

5L72 tripped 3-phase at both ends in 3 cycles.

5L72 tripped A-phase at both ends in 3 cycles.

16 cycles later, C phase arcing to shield wire

5L72 reclosed 3-phases successfully 80 cycles later, and initiated arcing on 5BP2, arcing melted snow between MOD main contacts and eventually 5BP2 fully contacted. 5BP2 RFI ball and corona ring damaged.

17

Burn mark on 5D3

18

5BP2 Corona Ball gone!

19

5BP2 Corona Ring burned!

5L72 current before SC bypass, 800A 5L72 current after SC bypass, 600A

SYA 5CB2 closed, SC2 bypassed

21MCA Terminal

87LQ/87LG detected A-G fault in less than 1 cycle

87LC detected C-G fault in less than 1 cycle

A phase trippedAll 3 phases tripped

SYA 5D3 A-Phase arcing to shield wire

16 cycles after a phase open, SYA 5D3 C-Phase arcing to shield wire

NIC Terminal

87LQ/87LG detected A-G fault in less than 1 cycle 87LC detected C-G fault in less than 1 cycle

A phase tripped All 3 phases tripped

A – G fault 16 cycles after a phase open, C – G fault

ConclusionsPOTT Line Differential

PN Speed(Normal)

1 cycle 1 cycle

PN for GND FLT (during SPO)

Ground mho & 51NT

Blocked PN:67G2, 67Q2 and

All Quads

87LA, 87LB, 87LC

87LG and 87LQBlocked PN:

NonePN Speed

(SLG during SPO)

1 cycle to 1 second

1 cycle

Simulating the event in Fault Study model

Series of events Prefault load flow SLG on A phase A phase open at both ends LLG on A and B phases (A ph. Still open) No fault

Create a bus for line side VTs Create a relay test file in Comtrade format Repeat until satisfied

Some differences between real and simulated events

Conclusions Some quadrilateral and directional protection

may be degraded during open phase condition Phase and ground mho elements on unfaulted

phases will still clear low impedance faults (at both ends)

Ground time overcurrent is useful during open phase period.

Line current differential protection is more robust during single pole open conditions

P&C Planning 27

Questions?