GE L90 Instruction Manual page 613

CHAPTER 5: SETTINGS
Generally, the scheme compares the direction to a fault at all terminals 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. Also by default, 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, 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 functions must be enabled,
configured, and programmed accordingly.
In single-pole tripping applications, the scheme uses local fault type identification provided by the phase selector together
with information received from the remote terminal.
The scheme generates output operands
the transmission of signals to the remote end(s). When used with telecommunications facilities, assign the output
operands to operate output contacts connected to key the transmitter at the interface.
The output operands from the scheme
output contacts in particular, in order to make the scheme fully operational. Typically, you program the output operand to
initiate a trip, breaker fail, and autoreclose, and drive a user-programmable LED as per user application.
When used in conjunction with the trip output element, the scheme is pre-configured to initiate trip, breaker fail, and
single-pole autoreclose actions.
— This setting allows the user to assign any FlexLogic operand to block the scheme. Contact inputs
BLOCK SCHEME BLOCK
from a pilot cut-out switch are typically used for this purpose.
L90 LINE CURRENT DIFFERENTIAL SYSTEM – INSTRUCTION MANUAL
TRANS BLOCK PICKUP

DELAY: 0.030 s
TRANS BLOCK RESET

DELAY: 0.090 s
BLOCK SCHEME SEAL-IN

DELAY: 0.010 s
GND DIR O/C FWD:

Off
GND DIR O/C REV:

Off
BLOCK SCHEME NO OF

COMM BITS: 1
BLOCK SCHEME RX1:

Off
BLOCK SCHEME RX2:

Off
BLOCK SCHEME RX3:

Off
BLOCK SCHEME RX4:

Off
BLOCK SCHEME TARGET:

Self-Reset
BLOCK SCHEME EVENT:

Disabled
(DIR BLOCK TX INIT and
DIR BLOCK TX1 STOP
(DIR BLOCK A, B, C, and 3P) must be configured to interface with other relay functions,
Range: 0.000 to 65.535 s in steps of 0.001
Range: 0.000 to 65.535 s in steps of 0.001
Range: 0.000 to 65.535 s in steps of 0.001
Range: FlexLogic operand
Range: FlexLogic operand
Range: 1, 2, or 4
Range: FlexLogic operand
Range: FlexLogic operand
Range: FlexLogic operand
Range: FlexLogic operand
Range: Self-Reset, Latched, Disabled
Range: Disabled, Enabled
through
DIR BLOCK TX4
CONTROL ELEMENTS
5
STOP) that control
5-389