GE 469 Instruction Manual page 211

CHAPTER 5: SETTINGS
Note
469 MOTOR MANAGEMENT RELAY – INSTRUCTION MANUAL
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.
-I , I -I
aIN aOUT bIN bOUT
STARTING DIFF. TRIP PICKUP
STARTING DIFF. TRIP DELAY
, or I -I (phase
cIN cOUT
level may
may have to be extended to
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