Utility Implements Communications- Assisted Special Protection and Control Schemes for Distribution Substations Michael. Duff City of College Station Payal Gupta, Dharmendra Prajapati, and Alex Langseth Schweitzer Engineering Laboratories, Inc. 2017 City of College Station and SEL
Provides electric power to residential and commercial customers Is composed of City of College Station (COCS) College Station Utilities (CSU) ~20 miles of transmission lines ~458 miles of distribution lines 7 substations OpenStreetMap contributors
Traditional 13.2 kv Distribution Substation 138 Electromechanical kv ring bus relays Two No bus 138 differential kv / 13.8 kv power protection transformers Two No breaker buses electrically failure backup connected via normally No automatic source open tie breaker transfer Four feeders per bus Challenge coordinating supplied from main breaker for simultaneous fault conditions
13.2 kv Distribution Substation for Special Protection and Control Scheme (SPCS)
Information Flow Diagram
Communications Link Supervision for High-Speed Data Bits Transmit eceive TB1 TB2... TB8 B1 B2... B8 0 1... 0 1 1... 0 1 1... 0 0 1... 0 TB1 TB2... TB8 B1 B2... B8 Transmit eceive IEDs OK = 1 OK = 0 Status Description Communications channel good Communications channel bad Inverse (NOT) of OK is used to create digital alarm bit to alert operations of communications failure
Communications Link Supervision for High-Speed Data Bits IED-B IED-COM B-IED Logic Processors COM = 1 COM = 0 Status Description Communications channel good Communications channel bad Communications link supervision in logic processors only allows received data bits of good quality to be considered in algorithms
Different Schemes Implemented 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
SCPS Six Major Design Criteria Dependability Security Selectivity esilience Speed Cost
Fast Bus Tripping Scheme 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 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 Breaker Failure Protection Scheme Dedicated, fast breaker failure protection scheme using existing IEDs and communications backbone Low implementation cost with minimal wiring
B-BF 1 2 11 T1 Breaker Failure Protection Scheme Fault on Bus 1 Breaker Fails Bus 1 M1 TB-BF TIE F1 F2 F3 F4 B-BF B-BF B-BF B-BF B-BF Logic Processor T1
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 and Stall eclose Logic Double-circuit feeder trip scheme with low implementation cost Fast 51 element setting and improved service reliability
Double Circuit Feeder Trip Simultaneous Fault M1 M2 Bus 1 TIE Bus 2 F1 F2 F3 F4 F5 F6 F7 F8 TB-PU B-PU TB-PU B-PU B-PU B-PU B-PU B-PU B-PU B-PU Logic Processor T1 B-PU Logic Processor T2
Stall eclose Logic M1 M2 Bus 1 TIE Bus 2 F1 F2 F3 F4 F5 F6 F7 F8 TB-S B-S Logic Processor T1 Logic Processor T2
ASTS 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
11 22 T1 T2 ASTS Transformer Fault TB-FAULT M1 Bus 1 TB-52A Bus 2 TIE TB-52A B-CLOSE M2 F1 F2 F3 F4 F5 F6 F7 F8 TB-52A TB-NO FAULT SCADA ASTS ENABLE Logic Processor T1 Logic Processor T2
Other Schemes 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
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