CHAPTER 7: PROTECTION CONTROL ELEMENTS
D90
PLUS
LINE DISTANCE PROTECTION SYSTEM – INSTRUCTION MANUAL 293
Function
Range: Enabled, Disabled
Default: Disabled
This setting enables and disables the direct under-reaching transfer trip (DUTT) scheme.
Seal-In Delay
Range: 0.000 to 65.535 seconds in steps of 0.001
Default: 0.000 seconds
The DUTT OP FlexLogic operand is produced according to the scheme logic. A seal-in
time delay is applied to this operand for coping with noisy communication channels,
such as a power line carrier. This setting specifies a minimum guaranteed duration for
the DUTT OP pulse. As this operand activates the trip table of the DUTT scheme, the trip
operands (DUTT TRIP A, DUTT TRIP B, DUTT TRIP C, and DUTT TRIP 3P) are sealed-in for the
same period of time.
Communication Bits
Range: 1, 2, 4
Default: 2
This setting specifies the number of bits available on the communications channel. With
only one bit available, the scheme sends the direct under-reaching transfer trip
command on bit 1 (the DUTT TX1 operand) and responds to the direct trip command
received on bit 1 (the
RX1 setting). The scheme uses only local fault type identification
provided by the phase selector to assert the trip operands (DUTT TRIP A, DUTT TRIP B, DUTT
TRIP C, and DUTT TRIP 3P).
RX1, RX2, RX3, RX4
Range: any FlexLogic operand
Default: OFF
These settings allow the user to select the FlexLogic operands that represent the receive
signals for the scheme. Typically input contacts interfacing with a signaling system are
used.
The DUTT scheme requires a secure and dependable signaling system. For this reason, a
series-parallel combination of receive signal contacts is often used. This is accomplished
by using a multi-bit communications system to transmit redundant copies of the
transmit signal (often via different paths) and building appropriate security logic (such as
series (AND gate) or two-out-of-three voting logic) with FlexLogic. The
RX1 to RX4 settings
should be associated with the final (secure) transmit signals.
These settings are used in the following manner:
– Single bit applications — Only
RX1 is used
– Two-bit applications —
RX1 and RX2 must be used
– Four-bit applications —
RX1 through RX4 must be used
In multi-terminal applications, the receive signals from two or more remote terminals
need to be connected through OR gates in protection FlexLogic and the resulting signals
configured as the RX1 through
RX4 settings.
Events
Range: Enabled, Disabled
Default: Enabled
This setting enables and disables the logging of direct under-reaching transfer trip
(DUTT) scheme events in the sequence of events recorder.
The figure shows the DUTT scheme logic.
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