3 4-3 transmission hodder kasztenny & fischer backupconsiderations

8/9/2019 3 4-3 Transmission Hodder Kasztenny & Fischer BackupConsiderations

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Copyrigh t © Hydro One Netwo rks, Inc. and SEL 2012

Backup Considerations for LineCurrent Differential Protection

Steven HodderHydro One Networks, Inc.

Bogdan Kasztenny and Normann FischerSchweitzer Engineering Laboratories, Inc.


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Outline

• Line protection redundancy• Loss of 87L protection

• 87L backup schemes♦ POTT or DCB

♦ Zone 1 extension

♦ Stepped distance♦ Overcurrent

• Backup protection strategies


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Line Protection Considerations

• Critical fault clearing time – protection type• Forced outages avoided – protection

availability

• HV / EHV applications♦ Breaker failure protection

♦ Communications-assisted schemes♦ Parallel redundancy of protection


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Hydro One Example

• Operates Ontario transmission system(500, 230, and 115 kV)

• Follows NPCC guidelines

• Categorizes BES lines♦ Impactive

♦ Nonimpactive


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Instantaneous Tripping Lost

• BES-impactive circuit♦ Independent electricity system operator

(IESO) must be notified within 5 minutes ofsecond failure

♦ Forced line outage is immediate

• Non-BES-impactive circuit♦ Line typically removed from service

♦ If removal has adverse impact on customerload, leave line in service and rely on timed

backup only


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Line Current Differential Protection

• Inherently selective• Very sensitive

• Immune tosystem conditions

• Easy to set

• Dependent oncommunications


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Loss of 87L Protection

• 87L element blocked• Relay out of service

• Problems with communications♦ Channel loss

♦ Channel brownout

• Inability to align local and remotecurrents – loss of time referencewhen using asymmetrical channels


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Loss of Time Reference

• IRIG-B connection severed• IRIG-B signal noisy

• Time source (external clock) malfunction

• Time source not locked

• GPS problems

Using IEEE C37.118-compliant clocksthat report time quality is important


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87L Adaptivity to

Channel Problems


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Primary Channel

Hot Standby Channel

Hot StandbyLogic

Hot StandbyLogic

87L 87L

87L Relay 87L Relay

Hot Standby Logic


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Primary Channel

Hot Standby Channel

Hot StandbyLogic

Hot StandbyLogic

87L 87L

87L Relay 87L Relay

Hot Standby Logic


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Channel 1

C h a n n e l 2 C h a n

n e l 3

Master Master

Master

87L1

87L2

87L

3

Three-Terminal Applications


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Three-Terminal Applications

C h a n n e l 2 C h a n

n e l 3

Slave Slave

Master

87L1

87L2

87L

3


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87L

87L

87L

Stub Bus Zone

Line ZoneMaster

Master

Master

Channel Loss Under Stub Bus


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CommunicationsRedundancy

A87LMain Path

B87L Alternate Path

SONETRing #1

A87L

Alternate Path

B87L

Main Path

SONET

Ring #2

Add / Drop

MUX

A87L B87L

DS1MUX

DS1MUX

DS1MUX

DS1MUX

Add / DropMUX


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Hydro One ProtectionPhilosophy With SONET

DS0 Protection Circuits Static (Pinned)

• Avoid complexity (e.g., testing), especiallyas SONET network grows

• Support protection scheme designed towork despite single communications failure

• Ensure channel symmetry, especially forbusiness-class SONET equipment


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SONET Path Routing forThree-Terminal Lines

1 2

3

Line

Distance

Line

Distance

LineDistance

Main1-2

Main2-1

Alternate1-3

Alternate

3-1

Alternate2-4

Main

3-4

Alternate4-2

Main

4-3


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Communications Contingencies

• Channel redundancy is preferred solutionfor POTT or DCB over SONET

• Channel redundancy is limited option for

87L schemes♦ Available for two-terminal schemes only

when direct point-to-point channels are used

♦ SONET path switching may cause problems

• 87L backup is preferred over 87L channelredundancy


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87L Backup

• Backup required for rare occasions when87L is unavailable♦ Channel problems

♦ Timing problems

• Backup integrated within multifunction 87Lrelay acceptable and beneficial

• Selectivity requirements can be relaxed if87L backup engaged only when needed


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Directional Comparison

• Not practical in many cases – requireschannel in addition to 87L channel

• More difficult to set compared with 87L

• Sensitive if 67Q / 67G used, maycause sequential tripping

• Less secure compared with 87L


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Zone 1 Extension Logic

• Substitute for extra channel atexpense of selectivity♦ Trips from overreaching Z1

♦ Reduces Z1 reach before reclosing

• Less sensitive compared with 87L

• Susceptible to load and power swings• Supplemented with 51Q / 51G and

67Q / 67G for high-resistance faults


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Stepped Distance

• Time-delayed for selectivity and coordination• Part of remote backup strategy (if used)

• More difficult to set (infeed)

• Less sensitive compared with 87L

• Susceptible to load and power swings

• Supplemented with 51Q / 51G and67Q / 67G for high-resistance faults


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87L Backup Strategies

• Fully operational backup• Backup engaged only upon loss of 87L

• Adaptive backup


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Fully Operational Backup

• Parallel with 87L scheme• Requires no information about 87L state –

standalone implementation

• Biases protection toward dependability

• Must be set conservatively to maintainsecurity – faces settings challenges

• Not justified if redundant system operational


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Backup Engaged if 87L Lost

• Does not adversely impact security• Can follow simpler operating principles –

stepped distance

• Can be biased toward dependability –Zone 1 extension

• Faces fewer settings challenges


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87L

21

87L

21

87L 21


• Master-slave mode uponfirst channel failure

• Backup remains blocked


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87L

21

87L

21

87L 21


Backup engaged whensecond channel fails


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87L

21

87L

21

87L 21


Or…

Backup engaged ifany relay is slave


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Adaptive Backup Examples

87L /21P /21G

87L /21P /21G

Z AX

Terminal A Terminal C

Zone 2 (Timed)Zone 1 (Instantaneous)

ZCX

ZBX

Terminal B

87L / 21P / 21G

X


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87L /21P /21G

87L /21P /21G

Z AX


Zone 2 (Timed)Zone 1 (Instantaneous)

ZCX

ZBX

Terminal B

87L / 21P / 21G

X

Adaptive Backup Examples


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DTT A-C-B

DTT C-B

Master-Slave Configuration

87L21P21G

87L21P21G

87L, 21P, 21G


Terminal B

DTT A-C

DTT A-B

21-1


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Stub Bus

DTT Rem2 _ Local_Rem1

DTT Rem1 _ Local_Rem2

Z2_Pickup (Rem1)Z2_Pickup (Rem2)

Local_Stub_Bus

DTT Local_Rem1

DTT Local_Rem2

Local_DTT_TX


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Conclusions

• 87L is selective, sensitive, and secure• Communications paths and equipment

affect overall 87L availability

• Communications and timing contingenciescan render 87L unavailable


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Conclusions

• 87L backup covers failures incommunications and timing, not relays

• Regulatory requirements and internal

practices impact selection of backup• Typical backup schemes include 21T,

Z1EXT, 51, and POTT or DCB


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Conclusions

• Settings backup schemes are typicallymore involved than 87L

• 87L backup elements integrated within

same protective device are prudent• Backup only engages upon loss of 87L

♦ Benefits security

♦ Simplifies settings selection


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Questions?

3 4-3 transmission hodder kasztenny & fischer backupconsiderations

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