GE 845 Instruction Manual page 411

CHAPTER 4: SETPOINTS
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845 TRANSFORMER PROTECTION SYSTEM – INSTRUCTION MANUAL
SUPERVISION
Range: Current, 52b & Current, 52b
Default: Current
The setpoint specifies the type of supervision of the Breaker Failure element. There are
three options: current only, breaker status only, or both.
BREAKER CLOSED
Range: Off, Any operand from the list of FlexLogic operands
Default: Off
The setpoint selects the FlexLogic operand, digital input, virtual input or remote input
(auxiliary switch contact) to indicate that the circuit breaker is closed.
T1 PICKUP DELAY
Range: 0.000 to 6000.000 s in steps of 0.001 s
Default: 0.120 s
The setting provides a delay for Timer 1 logic which is supervised with current
supervision only. The timer is set to the expected opening time of the circuit breaker, plus
a safety margin intended to overcome the relay measurement and timing errors as well
as relay processing time and current supervision reset time. In a microprocessor relay
this time is not significant. In the 845 relay, the current magnitude ramps-down to zero
in ¾ of a power cycle after the current is interrupted.
In bulk oil circuit breakers, the interrupting time for currents less than 25% of the
interrupting rating can be significantly longer than the normal interrupting time.
T2 PICKUP DELAY
Range: 0.000 to 6000.000 s in steps of 0.001 s
Default: 0.120 s
The setting provides a delay for Timer 2 logic which is supervised with current
supervision and breaker status (52b indication). The timer is set to the expected opening
time of the circuit breaker, plus a safety margin intended to overcome the relay
measurement and timing errors, relay processing time, current supervision reset time,
and the time required for the breaker auxiliary contact to open.
T3 PICKUP DELAY
Range: 0.000 to 6000.000 s in steps of 0.001 s
Default: 0.120 s
The setting provides a delay for Timer 3 logic which is supervised with breaker status
only (52b indication). The timer is set to the expected opening time of the circuit breaker,
plus a safety margin intended to overcome the relay timing errors, and the time required
for the breaker auxiliary contact to open.
PHASE HIGHSET PICKUP
Range: 0.050 to 30.000 x CT in steps of 0.001 x CT
Default: 1.000 x CT
The setpoint specifies the phase current output supervision level. The setting detects the
lowest expected fault current on the protected circuit.
NEUTRAL HIGHSET PICKUP
Range: 0.050 to 30.000 x CT in steps of 0.001 x CT
Default: 1.000 x CT
The setpoint specifies the neutral current output supervision level. The setting detects
the lowest expected fault current on the protected circuit. Neutral current supervision is
used to provide increased sensitivity.
CONTROL
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