GE D60 Instruction Manual page 466

5.7 CONTROL ELEMENTS
Generally, this scheme uses an overreaching zone 2 distance element to essentially compare the direction to a fault at all
terminals of the line. Ground directional overcurrent functions available in the D60 can be used in conjunction with the zone
2 distance element to key the scheme and initiate operation. This increases the coverage for high-resistance faults.
The scheme is intended for three-terminal and two-terminal applications with weak-infeed conditions. As a long reach of the
overreaching distance element may be required for three-terminal applications, transient blocking logic is provided for both
distance and ground directional overcurrent elements. In order to cope with weak-infeed conditions an echo feature is
made available.
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 the zone 4.
For proper operation, the zone 2 and 4 phase and ground distance elements must be enabled, configured and set per rules
of distance relaying. The line pickup element should be enabled, configured and set properly to detect line-end-open/weak-
infeed and undervoltage conditions. If used by the scheme, the selected ground directional overcurrent function(s) must be
enabled, configured, and set 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 (
) that are used to transmit the signal to the remote terminal(s). Choices of communications channel
HYBRID POTT TX4
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. When used with
telecommunications facilities the output operands should be assigned to operate output contacts connected to assert the
individual bits at the interface.
To make the scheme fully operational as a stand-alone feature, the scheme output operands must be configured to inter-
face with other relay functions, output contacts in particular. Typically, the output operands should be programmed to initiate
a trip, breaker fail, and autoreclose, and drive a user-programmable LED as per user application.
5
When used in conjunction with the trip output element, the scheme is pre-configured to initiate trip, breaker fail and single-
pole autoreclose actions.
• HYB POTT BLOCK: This setting allows the user to assign any FlexLogic operand to block the scheme. Contact inputs
from a pilot cut-out switch are typically used for this purpose.
• HYB POTT PERMISSIVE ECHO: If set to "Enabled", the scheme sends a permissive echo signal to the remote end(s)
using a pre-programmed logic (refer to the logic diagram below). If set to "Custom", the echo signal is sent if a condi-
tion selected via the
for the time specified by the
Operation of the overreaching protection elements (distance zone 2 or
• HYB POTT ECHO COND: This setting specifies a user-selected echo condition and applies only if the
is set to "Custom".
MISSIVE ECHO
• HYB POTT WEAK INFEED: If this setting is set to "Enabled", the scheme activates both the keying and operating
paths using a pre-programmed weak infeed logic (refer to the logic diagram below). If this setting is set to "Custom",
the weak infeed condition is to be specified by the user via the
• HYB POTT W/I COND: This setting specifies user-selected weak infeed condition and applies only if the
is set to "Custom".
WEAK INFEED
• HYB POTT RX PICKUP DELAY: This setting enables the relay to cope with spurious received signals. The delay
should be set longer than the longest spurious
The selected delay will increase the response time of the scheme.
• TRANS BLOCK PICKUP DELAY: This setting defines a transient blocking mechanism embedded in the hybrid POTT
scheme for coping with the exposure of both the over-reaching zone 2 and ground directional overcurrent function to
current reversal conditions.
The transient blocking logic applies to both operate (trip) and send (transmit) paths. Identifying the fault as a reverse
fault prevents the scheme from both operating and keying the channel. If the reverse fault condition prevails for
BLOCK PICKUP DELAY
. This allows riding through current reversal conditions.
DELAY
However, if distance zone 1 picks up during the transient blocking condition, the blocking action is removed. This is to
cope with evolving faults when an external fault is followed by an internal fault. Without the zone 1 feedback, the trip
would be delayed unnecessarily.
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setting is satisfied. The echo is sent only once and then the logic locks out
HYB POTT ECHO COND
setting. The duration of the echo pulse is settable as
ECHO LOCKOUT
TX
, the blocking operation will be extended by the transient blocking timer for
D60 Line Distance Protection System
GND DIR O/C FWD
HYB POTT W/I COND
signal that can be received simultaneously with the zone 2 pickup.
5 SETTINGS
through
HYBRID POTT TX1
ECHO DURATION
setting) inhibits the echo.
HYB POTT PER-
setting.
HYB POTT
TRANS
TRANS BLOCK RESET
GE Multilin
.