GE D90 Plus Instruction Manual page 327

CHAPTER 7: PROTECTION
Directional comparison blocking application guidelines
PLUS
D90 LINE DISTANCE PROTECTION SYSTEM – INSTRUCTION MANUAL
The output operand from the hybrid POTT scheme
Plus
interface with other D90
fully operational. The output operand should typically be programmed to initiate a trip,
breaker failure, and autoreclose, as well as drive a user-programmable LED as per user
requirements.
For additional application recommendations refer to
(POTT) application guidelines
The directional comparison blocking scheme typically compares the direction to a fault at
both ends of the line. Unlike the permissive schemes, the absence of a blocking signal
permits operation of the scheme. Consequently, the scheme is biased toward
dependability and requires an "on/off" type of signaling.
By default the directional comparison blocking scheme uses only a forward-looking
overreaching zone 2 distance element to identify forward faults. Ground directional
overcurrent functions available in the D90
distance element to increase the coverage for high-resistance faults.
By default the directional comparison blocking scheme also uses only a reverse-looking
zone 4 distance element to identify reverse faults. Ground directional overcurrent functions
Plus
available in the D90 can be used in conjunction with the zone 4 distance element for
better time and sensitivity coordination.
For proper operation of the directional comparison blocking scheme, the zone 2 and 4
phase and ground distance elements must be enabled, configured, and specified as per
the standard rules of distance relaying. If used by this scheme, the selected ground
directional overcurrent functions must be enabled, configured, and specified accordingly.
The directional comparison blocking scheme generates two output operands
and STOP) that are used control the transmission of signals to the remote
INIT DIR BLOCK TX
end. Choices of communications channel include remote inputs and outputs and
telecommunications interfaces. When used with telecommunications facilities, the output
operand should be assigned to operate an output contact connected to key the
transmitter at the interface.
The directional comparison blocking scheme may be preferred over a hybrid POTT scheme
because of shorter reach settings for the zone 2 elements. This follows from the
fundamental difference that all zone 2 elements are required to see an internal fault for the
POTT approach, under all system conditions, which in turn means that the reversed zone 4
block initiate elements must also have an increased reach. On the other hand, a directional
comparison blocking scheme can have much shorter zone 2 reach settings if sequential
clearance can be accepted. The simple rule to ensure that all faults can be cleared is for
each terminal to have a reach setting equal to the distance to the tap plus twice the
distance from the tap to the remote terminal.
The zone 2 element must have a coordinating timer specified by the
setting to ensure that the blocking signal is received for all external faults that
Pickup Delay
are within the set reach of the local overreaching zone 2.
Transient blocking logic is implemented via the timer specified by the transient blocking
timer. This timer continues to send a blocking signal for the time specified by the
setting if it was being sent for at least 30 ms during the initial reverse
Block Reset Delay
fault specified via the
Transient Block Pickup Delay
The output operand from the directional comparison blocking scheme
be configured to interface with other D90
make the scheme fully operational. the output operand should typically be programmed to
initiate a trip, breaker failure, and autoreclose, as well as drive a user-programmable LED
as per user requirements.
(HYBRID POTT
functions (output contacts in particular) to make the scheme
Permissive overreaching transfer trip
on page 315.
Plus
can be used in conjunction with the zone 2
setting.
Plus
functions (output contacts in particular) to
CONTROL ELEMENTS
OP) must be configured to
(DIR BLOCK TX
RX Coordination
Transient
(DIR BLOCK OP) must
317