Directional Comparison Unblocking - GE L90 Instruction Manual

10.5 PROTECTION SIGNALING SCHEMES
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 L90. 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 L90.
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
"Enabled". The user can disable or block the scheme by assigning any FlexLogic™ operand to the
This operand can consist of any pre-defined logic, including a pilot cutout switch connected to any contact input of the L90.
With this pilot cutout switch and the pre-defined logic state on and assigned to
The directional comparison unblocking scheme supervises the operation and keying of all scheme functions. The lockout
feature 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
• The scheme is enabled and not blocked (that is, the scheme is active), and
• no permissive
RX
• 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
conditions for any of the configured channels. The
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 (
• any permissive signal is received with its associated loss-of-guard signal (e.g.
• 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
trip table with the aid of the local phase selector and received
ated. During normal operation, the loss-of-guard signal will be seen momentarily before the permissive
received for each channel being operated, as the channel transitions from guard to permissive frequency, but the scheme
operates instantaneously after any
10
10-20
setting if:
DCUB LOG TRIP WINDOW
signal is received, and
timer. The scheme will thus remain blocked during longer loss-of-guard or channel
is "Enabled" and
DCUB FUNCTION
signal is received.
DCUB RX
L90 Line Current Differential System

10.5.7 DIRECTIONAL COMPARISON UNBLOCKING

setting is "Off" the
DCUB BLOCK
GUARD HEALTHY RESET DELAY
is "Off"), and
DCUB BLOCK
signals will determine what tripping operands will be oper-
RX
10 APPLICATION OF SETTINGS
DCUB SCHEME FUNCTION
DCUB BLOCK
, the scheme will be disabled.
DCUB BLOCK
timer ensures that the scheme will remain
and
DCUB RX1 DCUB LOG1
FlexLogic™ operand. The
DCUB OP
DCUB RX
setting is
setting.
), and
signal is
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