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CHAPTER 5: SETTINGS
Note
469 MOTOR MANAGEMENT RELAY – INSTRUCTION MANUAL
MESSAGE
MESSAGE
MESSAGE
MESSAGE
MESSAGE
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.
Care must be taken when enabling this feature. If the interrupting device (contactor or
circuit breaker) is not rated to break potential faults, 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. A low level
differential fault can develop into a short circuit in an instant.
A trip occurs once the magnitude of either I
differential) exceeds the Pickup Level × Differential CT Primary for a period of time specified
by the delay. Separate pickup levels and delays are provided for motor starting and
running conditions.
The Differential trip element is programmable as a fraction of the rated CT. The level may
be set more sensitive if the Differential CTs are connected in a flux balancing configuration
(3 CTs). If 6 CTs are used in a summing configuration, the values from the two CTs on each
phase during motor starting may not be equal since the CTs are not perfectly identical
(asymmetrical currents may cause the CTs on each phase to have different outputs). To
prevent nuisance tripping in this configuration, the
have to be set less sensitive, or the
ride through the problem period during start. The running differential delay can then be
fine tuned to an application such that it responds very fast to sensitive (low) differential
current levels.
ASSIGN TRIP
RELAYS:
STARTING DIFF.
TRIP PICKUP: 0.10
STARTING DIFF.
TRIP DELAY: 0 ms
RUNNING DIFF.
TRIP PICKUP: 0.10
RUNNING DIFF.
TRIP DELAY: 0 ms
-I
, I
aIN
aOUT
bIN
STARTING DIFF. TRIP PICKUP
STARTING DIFF. TRIP DELAY
Range: Trip, Trip & Auxiliary2, Trip &
Aux2 & Aux3, Auxiliary2, Aux2
& Aux3, Auxiliary3
Range: 0.05 to 1.00 x CT in steps of
0.01
Range: 0 to 60000 ms in steps of 10
Range: 0.05 to 1.00 x CT in steps of
0.01
Range: 0 to 1000 ms in steps of 10
-I
, or I
-I
(phase
bOUT
cIN
cOUT
level may
may have to be extended to
5–65
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