322 D90
PLUS
LINE DISTANCE PROTECTION SYSTEM – INSTRUCTION MANUAL
CONTROL ELEMENTS CHAPTER 7: PROTECTION
The loss-of-guard operation picks up if all of the following conditions hold:
• The directional comparison unblocking scheme is enabled and not blocked (that is, the
scheme is active)
• Any loss-of-guard signal is received without its associated RX signal
• A fault is seen in the forward zone 2 distance elements or ground directional forward
function (if configured)
• The reverse zone 4 distance elements or ground directional reverse function (if
configured) did not pickup to set the transient blocking
If all of these conditions are met, then the timer specified by the
Loss Of Guard Pickup
Delay
setting is started. After this timer times out, the trip table is run, operating the
scheme and asserting the DCUB OP FlexLogic operand. The trip table, with the aid of the
local phase selector and loss-of-guard signals, determine which tripping operands
operate. The timer specified by the
Loss Of Guard Pickup Delay setting allows for any and
all channels to transition from guard to permissive before operating due to loss-of-guard in
the presence of a forward fault. The time window of allowing the scheme to operate when
no DCUB RX signal is received when any loss-of-guard was received is the difference
between the timers specified by the
Loss of Guard Trip Window and Loss Of Guard Pickup
Delay
settings. For the default settings, this value is 150 – 8 = 142 ms. This means the
scheme is unblocked and can trip during this time window if a forward fault is sensed.
The keying signals, which allows the relay to key the permissive channel during normal
permissive scheme operation by means of the DCUB TX1 through DCUB TX4 signals, are
established when all of the following conditions hold:
• The directional comparison unblocking scheme is enabled and not blocked (that is, the
scheme is active)
• A fault is seen in the forward zone 2 distance elements or ground directional forward
function (if configured)
• The reverse zone 4 distance elements or ground directional reverse function (if
configured) did not pickup to set the transient blocking
If all of these conditions are met, then the directional comparison unblocking scheme keys
the channels by means of asserting transmit signals DCUB TX1 through DCUB TX4 with the
aid of the local phase selector or zone 2 distance elements.
The echo signal, which allows the D90
Plus
to key the permissive channels through the DCUB
TX1 through DCUB TX4 transmit operands during echo conditions when the local breaker
opened, keys the carrier(s) if all of the following conditions hold:
• The directional comparison unblocking scheme is enabled and not blocked (that is, the
scheme is active)
•The
Permissive Echo setting is “Enabled”
•The LINE PICKUP LEO PKP operand that detects the local breaker to be open picks up for
the time specified by
Line End Open Pickup Delay setting
• Any permissive signal DCUB RX1 through DCUB RX4 is received and any DCUB LOG1 to
DCUB LOG4 signal is received
• A fault is not seen in the forward zone 2 distance elements or ground directional
forward function (if configured) for at least 100 ms
• The reverse zone 4 distance elements or ground directional reverse function (if
configured) did not pickup to set the transient blocking
If all of these conditions are met, then the directional comparison unblocking scheme
echoes (transmits the DCUB TX1 through DCUB TX4 operands) the received permissive DCUB
RX signals back to the remote relay based on the echo table.
The keying or transmit signals DCUB TX1 through DCUB TX4 consist of all normal keying or
echo keying conditions.
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