GE D90 Plus Instruction Manual page 329

CHAPTER 7: PROTECTION
PLUS
D90 LINE DISTANCE PROTECTION SYSTEM – INSTRUCTION MANUAL
POTT scheme is to recognize that a permissive signal has been received and then allow the
time specified by the
Transient Block Pickup Delay
directional element to pick up.
The POTT scheme generates an output operand
to the remote end. Choices of communications channel include remote inputs and outputs
and telecommunications interfaces. When used with telecommunications facilities the
output operand needs to be assigned to operate an output contact connected to key the
transmitter at the interface. Power line carrier (PLC) channels are not recommended for
this scheme because the PLC signal can be interrupted by a fault.
For proper operation of the POTT scheme, the zone 2 phase and ground distance elements
must be enabled and configured per the standard rules of distance relaying. The line
pickup element also needs to be enabled and configured to detect line-end open and
weak-infeed conditions.
If used by the POTT scheme, the selected ground directional overcurrent functions must be
enabled and configured accordingly. The output operand from the scheme
be configured to interface with other D90
make the scheme fully operational. Typically, you program the output operand to initiate a
trip, breaker failure, and autoreclose, as well as to drive a user-programmable LED as per
user requirements.
Hybrid permissive overreaching transfer trip (hybrid POTT) application guidelines
The hybrid permissive overreaching transfer trip (hybrid POTT) scheme typically uses an
overreaching zone 2 distance element to essentially compare the direction to a fault at
both ends of the line. Ground directional overcurrent functions available in the D90
be used in conjunction with the zone 2 distance element to key the scheme and initiate its
operation. This increases the coverage for high-resistance faults.
The hybrid POTT scheme is intended for three-terminal applications and for weak-infeed
conditions. As a long reach of the overreaching distance element can be required for
three-terminal applications, transient blocking logic is provided for both distance and
ground directional overcurrent elements. An echo feature is made available to cope with
weak-infeed conditions.
By default the scheme uses the reverse-looking zone 4 distance element to identify reverse
faults. Additionally, reverse-looking ground directional overcurrent functions can be used
in conjunction with zone 4.
For proper operation of the scheme, the zone 2 and zone 4 phase and ground distance
elements must be enabled and configured per the standard rules of distance relaying. The
line pickup element also needs to be enabled and configured to detect line-end-open,
weak-infeed, and undervoltage conditions.
If used by the hybrid POTT scheme, the selected ground directional overcurrent functions
must be enabled and configured accordingly.
The hybrid POTT scheme generates an output operand
transmit the signal to the remote end. Choices of communications channel include remote
inputs and outputs and telecommunications interfaces. When used with
telecommunications facilities the output operand needs to be assigned to operate an
output contact connected to key the transmitter at the interface.
The output operand from the hybrid POTT scheme
Plus
interface with other D90
fully operational. Typically, you program the output operand to initiate a trip, breaker
failure, and autoreclose, as well as drive a user-programmable LED as per user
requirements.
For additional application recommendations, see the
(POTT) application guidelines
setting for the local forward looking
(POTT TX) that is used to transmit the signal
Plus
functions (output contacts in particular) to
(HYBRID POTT
functions (output contacts in particular) to make the scheme
Permissive overreaching transfer trip
on page 318.
CONTROL ELEMENTS
(POTT OP) must
(HYBRID POTT TX) that is used to
OP) must be configured to
Plus
can
319