GE Multilin L90 Line Current Differential System 10-1710 APPLICATION OF SETTINGS 10.5 PROTECTION SIGNALING SCHEMES1010.5PROTECTION SIGNALING SCHEMES 10.5.1 OVERVIEWThe L90 includes six common pilot-aided schemes:• direct under-reaching transfer trip (DUTT)• permissive under-reaching transfer trip (PUTT)• permissive over-reaching transfer trip (POTT)• hybrid permissive over-reaching transfer trip (Hybrid POTT)• directional comparison blocking• directional comparison unblocking10.5.2 DIRECT UNDER-REACHING TRANSFER TRIP (DUTT)This scheme uses an under-reaching Zone 1 distance element to key a transfer trip signal to the remote end(s), where onreceipt, the DUTT pilot scheme operates without any additional supervision.For proper operation of the scheme the Zone 1 phase and ground distance elements must be enabled, configured and setper rules of distance relaying.The scheme generates an output operand (DUTT TX) that is used to transmit the signal to the remote end. Choices of com-munications channel include Remote Inputs/Outputs and telecommunications interfaces. When used with telecommunica-tions facilities the output operand should be assigned to operate an output contact connected to key the transmitter at theinterface.Note that the same protection signaling may be used by a breaker failure scheme, in which case the signal can be sealedin by breaker fail for a time longer than the auto-reclose “reclaim” time which then prevents auto-reclose when not required.A provision for an optional seal-in of the send signal is made to cover those situations where PLC (Power Line Carrier) sig-naling is used and the signal must be transmitted in a potentially noisy situation due to the fault.The scheme output operand (DUTT OP) must be configured to interface with other relay functions, output contacts in par-ticular, in order to make the scheme fully operational. Typically, the output operand should be programmed to initiate a trip,breaker fail, and auto-reclose, and drive a user-programmable LED as per user application.10.5.3 PERMISSIVE UNDER-REACHING TRANSFER TRIP (PUTT)This scheme uses an under-reaching Zone 1 distance element to key a transfer trip signal to the remote end where it issupervised by the over-reaching Zone 2 distance elements.For proper operation of the scheme the Zone 1 and 2 phase and ground distance elements must be enabled, configuredand set per rules of distance relaying.The scheme generates an output operand (PUTT TX) that is used to transmit the signal to the remote end. Choices of com-munications channel include Remote Inputs/Outputs and telecommunications interfaces. When used with telecommunica-tions facilities the output operand should be assigned to operate an output contact connected to key the transmitter at theinterface.The PUTT RX PICKUP DELAY timer can be used to ride through spurious PLC receive signals.The scheme output operand (PUTT OP) must be configured to interface with other relay functions, output contacts in partic-ular, in order to make the scheme fully operational. Typically, the output operand should be programmed to initiate a trip,breaker fail, and auto-reclose, and drive a user-programmable LED as per user application.10.5.4 PERMISSIVE OVER-REACHING TRANSFER TRIP (POTT)This scheme is intended for two-terminal line applications only.This scheme uses an over-reaching Zone 2 distance element to essentially compare the direction to a fault at both the endsof the line.
