CHAPTER 8: APPLICATION OF SETTINGS PROTECTION SIGNALING SCHEMESL90 LINE CURRENT DIFFERENTIAL SYSTEM – INSTRUCTION MANUAL 8-1788.5.2 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 and configured perrules of distance relaying.The scheme generates an output operand (DUTT TX) that is used to transmit the signal to the remote end. Choices ofcommunications channel include Remote Inputs/Outputs and telecommunications interfaces. When used withtelecommunications facilities, assign the output operand to operate an output contact connected to key the transmitter atthe interface.Note that the same protection signaling can be used by a breaker failure scheme, in which case the signal can be sealed inby 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 Power Line Carrier (PLC)signaling 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 inparticular, in order to make the scheme fully operational. Typically, the output operand is programmed to initiate a trip,breaker fail, and auto-reclose, and to drive a user-programmable LED as per user application.8.5.3 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 andconfigured 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 ofcommunications channel include Remote Inputs/Outputs and telecommunications interfaces. When used withtelecommunications facilities the output operand should be assigned to operate an output contact connected to key thetransmitter at the interface.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 inparticular, in order to make the scheme fully operational. Typically, the output operand is programmed to initiate a trip,breaker fail, and auto-reclose, and to drive a user-programmable LED as per user application.8.5.4 Permissive over-reaching transfer trip (POTT)This scheme is intended for two-terminal line applications.This scheme uses an over-reaching Zone 2 distance element to essentially compare the direction to a fault at both theends of the line.Ground directional overcurrent functions available in the relay can be used in conjunction with the Zone 2 distanceelement to key the scheme and initiate its operation. This provides increased coverage for high-resistance faults.Good directional integrity is the key requirement for an over-reaching forward-looking protection element used tosupplement Zone 2. Even though any FlexLogic operand can be used for this purpose, allowing the user to combineresponses of various protection elements or to apply extra conditions through FlexLogic equations, this extra signal isprimarily meant to be the output operand from either the Negative-Sequence Directional IOC or Neutral Directional IOC.Both of these elements have separate forward (FWD) and reverse (REV) output operands. Use the forward indication NEGSEQ DIR OC1 FWD or NEUTRAL DIR OC1 FWD).An important consideration is when one of the line terminals is open. It is then necessary to identify this condition andarrange for a continuous sending of the permissive signal or use a slower but more secure echo feature to send a signal tothe other terminal, which is producing the fault infeed. With any echo scheme however, a means must be provided to avoid
