Directional Comparison Blocking - GE D60 Instruction Manual

9.3 PROTECTION SIGNALING SCHEMES 9 APPLICATION OF SETTINGS
If used by this scheme, the selected ground directional overcurrent function(s) must be enabled, configured, and set
accordingly.
The scheme generates an output operand (HYBRID POTT TX) that is used to transmit the signal to the remote end.
Choices of communications channel include Remote Inputs/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.
For more application recommendation refer to the POTT scheme.
The output operand from the scheme (HYBRID POTT OP) must be configured to interface with other relay functions, output
contacts in particular, in order to make the scheme fully operational. Typically, the output operand should be programmed to
initiate a trip, breaker fail, and auto-reclose, and drive a user-programmable LED as per user application.

9.3.6 DIRECTIONAL COMPARISON BLOCKING

Generally, the scheme 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 this scheme uses only a forward-looking over-reaching Zone 2 distance element to identify forward faults.
Ground directional overcurrent functions available in the relay can be used in conjunction with the Zone 2 distance element
to increase the coverage for high-resistance faults.
By default the scheme uses only a reverse-looking Zone 4 distance element to identify reverse faults. Ground directional
overcurrent functions available in the relay can be used in conjunction with the Zone 4 distance element for better time and
sensitivity coordination.
For proper operation of the scheme the Zone 2 and 4 phase and ground distance elements must be enabled, configured
and set per rules of distance relaying.
If used by this scheme, the selected ground directional overcurrent function(s) must be enabled, configured and set accord-
ingly.
The scheme generates output operands (BLOCKING SCHEME TX INIT and BLOCKING SCHEME TX STOP) that are
used control the transmission of signals to the remote end. Choices of communications channel include Remote Inputs/
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.
A blocking scheme may be preferred over a Hybrid POTT scheme, because of shorter reach settings for the Zone 2 ele-
ments. 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. A blocking scheme on the other hand, 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 , to ensure that the blocking signal is
BLOCK RX CO-ORD PKP DELAY
received for all external faults that are within the set reach of the local overreaching Zone 2.
Transient blocking logic is implemented via the timer, which continues to send a blocking signal for a settable
TRANS BLOCK
time , if it was being sent for at least 30 ms during the initial reverse fault set via
TRANS BLOCK RESET DELAY TRANS BLOCK
.
PICKUP DELAY
The output operand from the scheme (BLOCKING SCHEME OP) must be configured to interface with other relay functions,
output contacts in particular, in order to make the scheme fully operational. Typically, the output operand should be pro-
grammed to initiate a trip, breaker fail, and auto-reclose, and drive a user-programmable LED as per user application.
9
9-8 D60 Line Distance Relay GE Multilin