S6 Current Elements; Short Circuit Trip - GE 469 Instruction Manual

4.7 S6 CURRENT ELEMENTS

4.7S6 CURRENT ELEMENTS
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PATH: SETPOINTS S6 CURRENT ELEMENTS
n SHORT CIRCUIT TRIP
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4
Care must be taken when turning On this feature. If the interrupting device (contactor or circuit breaker) is
not rated to break the fault current, this feature should be disabled. Alternatively, this feature may be
WARNING
assigned to an auxiliary relay and connected such that it trips an upstream device that is capable of break-
ing the fault current.
If turned on, the Short Circuit element functions as follows.
A trip occurs once the magnitude of either Ia, Ib, or Ic exceeds the Pickup Level × Phase CT Primary for a period of time
specified by
INTENTIONAL S/C TRIP DELAY
should be greater than the
DELAY
is "On", and a Short Circuit trip has initiated, a second trip occurs if the motor phase current persists for a period of
BACKUP
time exceeding the
SHORT CIRCUIT TRIP BACKUP DELAY
would be dedicated as an upstream breaker trip relay.
Various situations (e.g. charging a long line to the motor or power factor correction capacitors) may cause transient inrush
currents during motor starting that may exceed the
INTENTIONAL S/C TRIP DELAY
responds very fast but rides through normal operational disturbances. Normally, the
quick as possible, 0 ms. This time may be increased if nuisance tripping occurs.
When a motor starts, the starting current (typically 6 × FLA for an induction motor) has an asymmetrical component. This
asymmetrical current may cause one phase to see as much as 1.6 times the normal RMS starting current. If the
was set at 1.25 times the symmetrical starting current, it is probable that there would be nuisance trips
CUIT TRIP PICKUP
during motor starting. A rule of thumb has been developed over time that short circuit protection at least 1.6 times the sym-
metrical starting current value. This allows the motor to start without nuisance tripping.
The overreach filter removes the DC component from the asymmetrical current present at the moment a fault occurs. This
results in no overreach whatsoever, however, the response time slows slightly (10 to 15 ms) but times still remain within
specifications.
4-42
Courtesy of NationalSwitchgear.com
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SHORT CIRCUIT TRIP

ð
SHORT CIRCUIT
ENTER
ESCAPE TRIP: Off
SHORT CIRCUIT TRIP
ESCAPE
OVERREACH FILTER: Off
MESSAGE
ASSIGN TRIP RELAYS:
ESCAPE
Trip
MESSAGE
SHORT CIRCUIT TRIP
ESCAPE
PICKUP: 2.0 x CT
MESSAGE
INTENTIONAL S/C TRIP
ESCAPE
DELAY: 0 ms
MESSAGE
SHORT CIRCUIT TRIP
ESCAPE
BACKUP: Off
MESSAGE
ASSIGN BACKUP
ESCAPE
RELAYS: Auxiliary2
MESSAGE
SHORT CIRCUIT TRIP
ESCAPE
BACKUP DELAY: 200 ms
MESSAGE
. A backup trip feature may also be enabled. The
INTENTIONAL S/C TRIP DELAY
. It is intended that this second trip be assigned to R2 or R3 which
SHORT CIRCUIT TRIP PICKUP
is adjustable in 10 ms increments. This delay can be fine tuned to an application so it still
469 Motor Management Relay
4.7.1 SHORT CIRCUIT TRIP
Range: Off, Latched, Unlatched
Range: On, Off
Range: Alarm, Auxiliary2, Auxiliary3, Alarm & Aux2,
Alarm & Aux3, Aux2 & Aux3, Alarm & Aux2 &
Aux3
Range: 2.0 to 20.0 x CT in steps of 0.1
Range: 0 to 1000 ms in steps of 10
Range: On, Off
Range: Auxiliary2, Aux2 & Aux3, Auxiliary3
Range: 10 to 2000 ms in steps of 10
SHORT CIRCUIT TRIP BACKUP
plus the breaker clearing time. If the
level for a very short period of time. The
INTENTIONAL S/C TRIP DELAY
4 SETPOINTS
SHORT CIRCUIT TRIP
is set as
SHORT CIR-
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