GE D90 Plus Instruction Manual page 328

CONTROL ELEMENTS
Directional comparison unblocking (DCUB) application guidelines
318
The directional comparison unblocking (DCUB) 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 D90
output contact when the permissive frequency is received. This output should be wired to
any other contact input of the D90
The directional comparison unblocking scheme allows a window of opportunity for fast
tripping of the breaker if the permissive signal gets attenuated by the fault to a level less
than the receiver's threshold. The guard signal is monitored and relay allowed to trip for a
loss-of-guard without receipt of the permissive signal if the D90
forward and not reverse direction by means of the forward looking distance zone 2 and
ground directional forward function (if configured) and reverse looking distance zone 4 and
ground directional reverse function (if configured).
The directional comparison unblocking scheme is active and ready for operation when the
Block setting is "Off" and the
block the scheme by assigning any FlexLogic™ operand to the
can consist of any pre-defined logic equation, including a pilot cutout switch connected to
any contact input of the D90
switch and the pre-defined logic state on and assigned to the
comparison unblocking scheme supervises the operation and keying of all scheme
functions. The lockout feature also supervises all scheme functions. All timers are fully
adjustable, with typical values shown as defaults.
Lockout of the scheme is started for a time duration specified by the
setting if all of the following conditions hold.
Window
• The directional comparison unblocking scheme is enabled and not blocked (that is, the
scheme is active).
• No permissive RX signal is received.
• 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 the
scheme will remain blocked during longer loss-of-guard or channel conditions for any of
the configured channels. The time specified by the
ensures that the scheme remains locked out slightly longer after the loss-of-guard signal is
reset. This allows for all channel 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 operation.
Normal 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 permissive signal is received with its associated loss-of-guard signal (for example,
and
DCUB RX1 DCUB LOG1).
• 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.
Plus
. The power line carrier should also provide an
Plus
.
Scheme Function setting is "Enabled". The user can disable or
Plus
. As such, the scheme can be disabled with this pilot cutout
Guard Healthy Reset Delay
Guard Healthy Reset Delay
PLUS
D90 LINE DISTANCE PROTECTION SYSTEM – INSTRUCTION MANUAL
CHAPTER 7: PROTECTION
Plus
sees the fault in the
setting. This operand
Block
setting. The directional
Block
Loss of Guard Trip
timer. The
timer