Co-ordination of directional overcurrent protection with load current for parallel feeders

Conference · Mon Nov 01 04:00:00 EST 1999

OSTI ID:697233

Wright, J W; Lloyd, G; Hindle, P J ^[1]

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1. Alstom, Inc., Stafford (United Kingdom). T and D Protection and Control

Directional phase overcurrent relays are commonly applied at the receiving ends of parallel feeders or transformer feeders. Their purpose is to ensure full discrimination of main or back-up power system overcurrent protection for a fault near the receiving end of one feeder. This paper reviews this type of relay application and highlights load current setting constraints for directional protection. Such constraints have not previously been publicized in well-known text books. A directional relay current setting constraint that is suggested in some text books is based purely on thermal rating considerations for older technology relays. This constraint may not exist with modern numerical relays. In the absence of any apparent constraint, there is a temptation to adopt lower current settings with modern directional relays in relation to reverse load current at the receiving ends of parallel feeders. This paper identifies the danger of adopting very low current settings without any special relay feature to ensure protection security with load current during power system faults. A system incident recorded by numerical relays is also offered to highlight this danger. In cases where there is a need to infringe the identified constraints an implemented and testing relaying technique is proposed.

• Research Organization: Illinois Inst. of Tech., Chicago, IL (United States)
• OSTI ID: 697233
• Report Number(s): CONF-990410--PROC.-Vol.1
• Country of Publication: United States
• Language: English

Related Subjects

32 ENERGY CONSERVATION, CONSUMPTION, AND UTILIZATION
DESIGN
ELECTRICAL FAULTS
EQUIPMENT PROTECTION DEVICES
OPERATION
OVERCURRENT
POWER DISTRIBUTION SYSTEMS