GE Masoneilan 469 Series, Instruction Manual

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5–66 469 MOTOR MANAGEMENT RELAY – INSTRUCTION MANUAL
CHAPTER 5: SETTINGS
NOTE
Note
Care must be taken when turning On this feature. If the interrupting device (contactor or
circuit breaker) is not rated to break ground fault current (low resistance or solidly
grounded systems), the feature should be disabled. Alternately, the 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.
Various situations (e.g. contactor bounce) may cause transient ground currents during
motor starting that may exceed the Ground Fault pickup levels for a very short period of
time. The Ground Fault time delays are adjustable in 10 ms increments. The delay can be
fine tuned to an application such that it still responds very fast, but rides through normal
operational disturbances. Normally, the Ground Fault time delays are set as quick as
possible, that is, 0 ms. Time may have to be increased if nuisance tripping occurs.
Special care must be taken when the ground input is wired to the phase CTs in a residual
connection. 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. This momentary DC
component will cause each of the phase CTs to react differently and the net current into
the ground input of the 469 will not be negligible. A 20 ms block of the ground fault
elements when the motor starts enables the 469 to ride through this momentary ground
current signal.
The overreach filter removed 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.
5.7.7 Phase Differential
PATH: SETTINGS

S6 CURRENT ELEM.

PHASE DIFFERENTIAL
These settings program the differential element when the differential feature is in use. This
feature consists of three instantaneous overcurrent elements for phase differential
protection. Differential protection may be considered first line protection for phase to
phase or phase to ground faults. In the event of such a fault, differential protection may
limit the damage that may occur.

PHASE [

]
DIFFERENTIAL
PHASE DIFFERENTIAL
TRIP: Off
Range: Off, Latched, Unlatched
MESSAGE
ASSIGN TRIP RELAYS:
Trip
Range: Trip, Trip & Auxiliary2, Trip &
Aux2 & Aux3, Auxiliary2, Aux2
& Aux3, Auxiliary3
MESSAGE
STARTING DIFF.
TRIP PICKUP: 0.10 x CT
Range: 0.05 to 1.00 x CT in steps of
0.01
MESSAGE
STARTING DIFF.
TRIP DELAY: 0 ms
Range: 0 to 60000 ms in steps of 10
MESSAGE
RUNNING DIFF.
TRIP PICKUP: 0.10 x CT
Range: 0.05 to 1.00 x CT in steps of
0.01
MESSAGE
RUNNING DIFF.
TRIP DELAY: 0 ms
Range: 0 to 1000 ms in steps of 10