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Contents : g GE Power Management Technical Notes Overcurrent Elements for Feeder Protection in the F60 GE Publication No. GET-8394 Copyright 2002 GE Power Management Introduction F60 FEATURES The GE Power Management F60 Feeder Protection Relay is intended for feeder protection and includes numerous features required to provide complete feeder protection against all types of faults in different system conditions. The relay includes several overcurrent elements for protection against phase-to-phase and phase-to-ground faults in solidly grounded impedance grounded or ungrounded systems. For protection against high impedance phase-to-ground faults (associated or not with a down conductor) in a solidly grounded system a high impedance (Hi-Z) element is provided. The element requires a special DSP that must be ordered if this feature is desired. The relay also includes various under and overvoltage elements under and overfrequency elements breaker failure protection autorecloser and synchrocheck schemes and additional specific functions such as Breaker Arcing Current Cold Load Pickup and VT Fuse Failure. This document is a guide for setting the F60 overcurrent elements for feeder protection. OVERCURRENT ELEMENTS OVERVIEW A number of instantaneous and inverse time delay overcurrent elements (phase neutral ground/sensitive ground and negative sequence) are available in F60. Ideally overcurrent settings must be sensitive to short circuit/overload currents coordinate with upstream and downstream devices and be set above maximum load (or maximum unbalance current). The phase TOC elements include voltage restraint capability for situations where the fault to load ratio is low. For detecting unbalanced faults and for more sensitive protection against phase-to-phase faults instantaneous and time delay negative sequence overcurrent elements are available. All instantaneous overcurrent elements can be used as instantaneous elements with no intentional time delay or as definite time elements (when necessary for coordination purposes). 1 GET-8394: Overcurrent Elements for Feeder Protection in the F60 All overcurrent elements can be assigned up to 8 different settings according to the setting group designation 1 to 8. Multiple setting groups provide the capability to automatically change settings for different system conditions (cold load pickup changing settings between autorecloser shots etc.). To establish overcurrent elements settings the following data are necessary: a single line diagram including equipment significant characteristics: lines cables generators motors transformers circuit breakers CTs VTs relays fuses normal and emergency operating conditions a short circuit study for the system maximum expected load on feeders and transformers maximum expected unbalance current existing settings on adjacent equipment Phase Overcurrent Elements PHASE INSTANTANEOUS OVERCURRENT (50P) Two instantaneous overcurrent elements are available in the F60. Typical applications for these elements includes: A high set instantaneous overcurrent intended to operate for close faults with high short circuit current. In some applications this element can be used to block the autorecloser. The setting applied is usually higher than the maximum short circuit current beyond the closest downstream device (breaker or fuse) and above the feeder inrush current. This setting should prevent the high-set overcurrent from unselectively tripping the feeder breaker for faults on taps which will normally be cleared by the tap fuse (unless a fuse-saving scheme is preferred). A low-set instantaneous element is used for further coordination with the downstream devices for enhanced equipment protection against the damaging effect of the fault currents and used in fuse-saving schemes. PHASE INVERSE TIME OVERCURRENT (51P) Two inverse time overcurrent elements are available in F60. The settings of these elements must be coordinated with the downstream and upstream devices be above the feeder maximum load current and be sensitive to the end feeder short circuit current. To satisfy these conditions the appropriate pickup time delay reset characteristic (fast or induction disc emulation) and curve type settings should be selected. When coordination with electromechanical relays is required the induction disc reset must be considered. Neutral/Ground Overcurrent Elements DESCRIPTION Several neutral and ground overcurrent elements are provided for protection against phase to ground faults. The neutral overcurrent elements respond to the calculated neutral (residual or unbalance) current as the sum of the phase currents: I n I a + Ib + I c . 2 GE Power Management GET-8394: Overcurrent Elements for Feeder Protection in the F60 The ground elements respond to the current connected to the relay ground current terminals (IG) typically from a ground current source (core-balance CT or a CT

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