GE Multilin D60 Line Distance Protection System 9-9
9 APPLICATION OF SETTINGS 9.3 PROTECTION SIGNALING SCHEMES
9
9.3.7 DIRECTIONAL COMPARISON UNBLOCKING
a) OVERVIEW
The directional comparison unblocking scheme is used with a frequency shift keying (FSK) PLC that produces a loss-of-
guard output during an actual loss-of-guard signal condition and during reception of the permissive keyed frequency when
the received carrier signal changed from guard to permissive frequency. The loss-of-guard signal should preferably be a
normally-closed contact, allowing the scheme to get this signal if the communications equipment failed. This loss-of-guard
output should be connected to a contact input of the D60. The power line carrier should also provide an output contact
when the permissive frequency is received. This output should be wired to any other contact input of the D60.
The directional comparison unblocking scheme allows a window of opportunity for tripping the breaker fast if the permissive
signal gets attenuated by the fault to a level below the receiver's threshold. The guard signal is monitored, and the relay is
allowed to trip for a loss of guard without receipt of the permissive signal, if the relay sees the fault in the forward, and not
reverse direction by means of the forward looking distance zone 2 and ground directional forward, if configured, and
reverse looking distance zone 4 and ground directional reverse, if configured.
The scheme is active and ready for operation when the
DCUB BLOCK setting is “Off” the DCUB SCHEME FUNCTION setting is
“Enabled”. The user can disable or block the scheme by assigning any FlexLogic operand to the DCUB BLOCK setting. This
operand can consist of any pre-defined logic, including a pilot cutout switch connected to any contact input of the D60. With
this pilot cutout switch and the pre-defined logic state on and assigned to
DCUB BLOCK, the scheme will be disabled. The
directional comparison unblocking scheme supervises the operation and keying of all scheme functions. The lockout fea-
ture of the scheme also supervises all scheme functions. All timers are fully adjustable, with typical values indicated.
Lockout of the directional comparison unblocking scheme is established as follows. Lockout of the scheme is started for a
time duration set by
DCUB LOG TRIP WINDOW setting if:
• The scheme is enabled and not blocked (that is, the scheme is active), and
• no permissive
RX signal is received, and
• any loss-of-guard signal is received.
Lockout is sealed-in through an AND gate with the directional comparison unblocking scheme active and any loss-of-guard
through GUARD HEALTHY RESET DELAY timer. The scheme will thus remain blocked during longer loss-of-guard or channel
conditions for any of the configured channels. The GUARD HEALTHY RESET DELAY timer ensures that the scheme will remain
locked out slightly longer after the loss-of-guard signal(s) is reset. This allows for all channel(s) stabilizing and contact
denouncing. This timer determines how long the logic waits before enabling the directional comparison unblocking scheme
when the communications channel is restored.
Operating of the directional comparison unblocking scheme consists of two parts: normal operation and loss-of-guard oper-
ation.
b) NORMAL OPERATION
Normal operation picks up under the following conditions:
• The scheme is enabled (
DCUB FUNCTION is “Enabled” and DCUB BLOCK is “Off”), and
• any permissive signal is received with its associated loss-of-guard signal (e.g. DCUB RX1 and DCUB LOG1), and
• a fault is seen in the forward zone 2 distance elements or ground directional forward function (if configured), and
• the reverse zone 4 distance elements or ground directional reverse function (if configured) did not pickup to set the
transient blocking, and
• the scheme is not locked out.
If these conditions are met, the trip table is run, operating the scheme and asserting
DCUB OP FlexLogic operand. The trip
table with the aid of the local phase selector and received
RX signals will determine what tripping operands will be oper-
ated. During normal operation, the loss-of-guard signal will be seen momentarily before the permissive
DCUB RX signal is
received for each channel being operated, as the channel transitions from guard to permissive frequency, but the scheme
operates instantaneously after any
DCUB RX signal is received.
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