The microprocessor-based relay shall provide a combination of functions including protection, monitoring, control, and automation. Relay self-checking functions shallbe included. Specific requirements are listed below:➤Current Differential Protection.The relay shallcompare local and remote phase and sequence currents to provide operation in less than one cycle.The relay shall operate for unbalanced faults withcurrents below line charging current. MismatchedCTs shall be accommodated by relay setting. Distortion caused by CT saturation of one or both endsshall not cause misoperation.➤Distance Protection.The relay shall incorporatefour zones of phase and ground mho distance andquadrilateral ground distance protection for use ifpotentials are available. Two zones shall be settablefor either forward or reverse direction. Both positive-sequence memory polarized and compensatordistance phase distance elements shall be available.The relay shall detect CCVT transients and blockthe operation of underreaching Zone 1 distanceelements during the transient period. The relayshall detect stable and unstable power swings.➤Overcurrent Fault Protection.The relay shallincorporate phase, residual ground, and negativesequence overcurrent elements. These shall havedirectional control available for use if potentialsare available. A system to automatically select themost stable polarizing source for ground directional elements shall be included.➤Channel Requirements.The relay shall haveoptions for a direct or IEEE C37.94 single- or multimode fiber-optic interface, or EIA-422 or G.703operating at 56 kb or 64 kb. The relay shall accommodate up to 5 ms of channel asymmetry.➤Dual Channel Capability.The relay shall operatewith one or two communications channels. Whentwo channels are used as hot standby, the relayshall switch to the unfaulted channel with no protection interruption.➤Two- or Three-Terminal Application.The relayshall be suitable for two- or three-terminal lines.For three-terminal protection the relay system shallbe capable of protecting the line with dual channelsat each relay or with dual channels on only one ofthree relays.
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