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

S6 Current Elements

Short Circuit Trip

SHORT
CIRCUIT TRIP
WARNING
GE Multilin
S6 Current Elements
PATH: SETPOINTS S6 CURRENT ELEM.
[ ] SHORT CIRCUIT
TRIP: Off
SHORT CIRCUIT TRIP
MESSAGE
OVERREACH FILTER: Off
ASSIGN TRIP RELAYS:
MESSAGE
Trip
SHORT CIRCUIT TRIP
MESSAGE
PICKUP: 10.0 x CT
INTENTIONAL S/C TRIP
MESSAGE
DELAY: 0 ms
SHORT CIRCUIT TRIP
MESSAGE
BACKUP: Off
ASSIGN BACKUP
MESSAGE
RELAYS: Auxiliary2
SHORT CIRCUIT TRIP
MESSAGE
BACKUP DELAY: 200 ms
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 assigned to
an auxiliary relay and connected such that it trips an upstream device that
is capable of breaking 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 the time specified by
feature may also be enabled. The
than the
INTENTIONAL S/C TRIP DELAY
is "On" and a Short Circuit trip has initiated, a second trip occurs
CIRCUIT TRIP BACKUP
if the motor phase current persists for a time exceeding the
. It is intended that this second trip be assigned to 2 Auxiliary or
BACKUP DELAY
3 Auxiliary which would be dedicated as an upstream breaker trip relay. Whenever
the output relay assigned to backup trip operates, it will remain latched regardless
of how the trip relay is configured for the Short Circuit Trip element.
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
SHORT CIRCUIT TRIP PICKUP
is adjustable in 10 ms increments. This delay can be fine
INTENTIONAL S/C TRIP DELAY
tuned to an application so it still responds very fast but rides through normal
operational disturbances. Normally, the
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
TRIP PICKUP
that there would be nuisance trips during motor starting. A rule of thumb has been
developed over time that short circuit protection at least 1.6 times the symmetrical
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 of fault. This eliminates overreach; however, the response
time slows slightly (10 to 15 ms) but remains within specification.
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Motor Management Relay
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,
Auxiliary3
Range: 10 to 2000 ms in steps of 10
INTENTIONAL S/C TRIP DELAY
SHORT CIRCUIT TRIP BACKUP DELAY
plus the breaker clearing time. If the
level for a very short period of time. The
INTENTIONAL S/C TRIP DELAY
469
Aux2 & Aux3,
. A backup trip
should be greater
SHORT
SHORT CIRCUIT TRIP
is set as quick as
SHORT CIRCUIT
5–49