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© 2017 City of College Station and SEL

Utility Implements Communications-Assisted Special Protection and Control

Schemes for Distribution Substations

Michael R. DuffCity of College Station

Payal Gupta, Dharmendra Prajapati, and Alex LangsethSchweitzer Engineering Laboratories, Inc.

• Provides electric power to residential and commercial customers

• Is composed of ~20 miles of transmission lines

~458 miles of distribution lines

7 substations

City of College Station (COCS)College Station Utilities (CSU)

© OpenStreetMap contributors

• 138 kV ring bus

• Two 138 kV / 13.8 kV power transformers

• Two buses electrically connected via normally open tie breaker

• Four feeders per bus supplied from main breaker

• Electromechanical relays

• No bus differential protection

• No breaker failure backup

• No automatic source transfer

• Challenge coordinating for simultaneous fault conditions

Traditional 13.2 kV Distribution Substation

13.2 kV Distribution

Substation for Special Protection

and Control Scheme (SPCS)

Information Flow Diagram

Communications Link Supervision for High-Speed Data Bits

IEDs Status DescriptionROK = 1 Communications channel goodROK = 0 Communications channel bad

Inverse (NOT) of ROK is used to create digital alarm bit to alert operations of

communications failure

TB1TB2

...

TB8

RB1RB2

...

RB8

TB1TB2

...

TB8

RB1RB2

...

RB8

Tran

smit

Rec

eive

Transmit

Receive

01

0

11

0

......

11

0

01

0

......

Communications Link Supervision for High-Speed Data Bits

Communications link supervision in logic processors only allows received data bits of good

quality to be considered in algorithms

Logic Processors Status DescriptionCOM = 1 Communications channel goodCOM = 0 Communications channel bad

IED-COMRB-IED

IED-RB

• Fast bus tripping scheme for significantly reduced bus fault-clearing time

• Breaker failure protection scheme for shorter breaker failure clearing time

• Double-circuit feeder trip scheme for faster clearing of simultaneous faults without causing substation outage, and stall reclose logic for system availability

• Automatic source transfer scheme (ASTS) for higher power system availability

Different Schemes Implemented

SCPS Six Major Design Criteria

Dependability Security Selectivity

Resilience Speed Cost

Limitation of traditional bus protection philosophy Bus fault is cleared with time-delayed transformer

backup protection

Typical fault-clearing time is between 0.6 and 1.0 seconds

Solution Bus differential protection is fast and secure,

but has added cost

Fast bus tripping scheme is fast and cost-effective

Fast Bus Tripping Scheme

Fast Bus Tripping Scheme

Fault on Bus 1

Fast Bus Tripping Scheme

Fault on F1 Feeder Circuit

Limitation of traditional breaker failure protection philosophy Fault is cleared with upstream inverse-time overcurrent

protection

Long fault-clearing times lead to equipment damage or reduced equipment lifespan

Solution Dedicated, fast breaker failure protection scheme using existing

IEDs and communications backbone

Low implementation cost with minimal wiring

Breaker Failure Protection Scheme

RB

-BF

RB

-BF

RB

-BF

RB

-BF

RB

-BF

RB-BF

Breaker Failure Protection Scheme

Fault on Bus 1 Bus 1

R

RRRR

Logic Processor T1

R

T1

F1 F2 F3 F4

TIE

M1

11

21

R

Breaker Fails

F1 F2 F3 F4

TB-BF

M1

11

Limitation of traditional system Simultaneous faults may cause coordination issues

Main breaker 51 element may misoperate

IED overcurrent pickup and time-dial settings must be adjusted (resulting in slower tripping)

Solution Double-circuit feeder trip scheme with low implementation cost

Fast 51 element setting and improved service reliability

Double Circuit Feeder Trip Scheme and Stall Reclose Logic

RB

-PU

RB

-PU

RB

-PU

RB

-PU

RB

-PU

RB

-PU

RB

-PU

RB

-PU

RB-PU

TB-P

U

TB-P

U

Double Circuit Feeder Trip

Simultaneous FaultBus 2

M2

R

M1

Bus 1TIE

F5

R

F6

R

F7

R

F8

R

F4

R

F3

R

F1 F2

RR

Logic Processor T2Logic Processor T1

F1 F2

TB-S

R

Stall Reclose Logic

Bus 2

M2

R

M1

Bus 1TIE

F5

R

F6

R

F7

R

F8

R

F4

R

F3

R

F1 F2

RR

Logic Processor T2Logic Processor T1

RB

-SR

F1 F2

Limitation of traditional system Less power system availability with more disruption

Long restoration times

Solution ASTS that automatically switches from primary source

to alternate source

Short restoration times to improve power system availability

ASTS

RB

-CLO

SE TB

-NO

FA

ULT

TB-F

AU

LT

SCADA ASTS ENABLE

TB-5

2ATB

-52A

TB-5

2A

ASTSTransformer Fault

Bus 1TIE

11

M1

R

R

Bus 2

22

M2

R

R

Logic Processor T2Logic Processor T1

F2 F3 F4F1 F5 F6 F7 F8

T2T1R

11

M1

F2 F3 F4F1

TIETIE

F2 F3 F4F1

M1

• Multiple SPCSs run in parallel and coordinate with each other as complete, integrated solution

• Other control logic is implemented to improve system availability and dependability Hot-line mode

IED health alarm

Other Schemes

Questions?