Hot Motor; Breaker Failure; Ground Current - GE 239 Instruction Manual

CHAPTER 4: PROGRAMMING
4.5.7

Hot Motor

4.5.8

Breaker Failure

4.5.9

Ground Current

239 MOTOR PROTECTION RELAY – INSTRUCTION MANUAL
Courtesy of NationalSwitchgear.com
• THERMAL CAPACITY USED: This feature is used to signal a warning when the thermal
capacity has exceeded a level set in this setpoint. Once the set level is exceed the
alarm relay will activate immediately and the "THERMAL CAPACITY USED ALARM"
message will be displayed.
• BREAKER FAILURE FUNCTION: This feature is used to activate the selected relay, if the
current continues to flow after a trip has occurred. If the feature is assigned to
or ALARM & AUX , the "BREAKER FAILURE ALARM" message will be displayed and the
assigned output relay will be active. If the function is assigned to
auxiliary output relay will be active but, no message will be displayed.
• BREAKER FAILURE PICKUP: If a trip is present and the current is still flowing (breaker
failed to open) and the level of the average three phase current is equal to or greater
than the setting in the
BREAKER FAILURE PICKUP
will operate.
• BREAKER FAIL PICKUP DELAY: If all other conditions are met, the breaker failure
feature will operate after the delay programmed in this setpoint has elapsed. See
Section 1.2: Specifications on page –8 for BREAKER FAILURE timing specifications.
• BREAKER FAIL DROPOUT DELAY: If the breaker opens or if the average three phase
current falls below the
BREAKER FAILURE PICKUP
will not clear until the delay programmed in this setpoint has elapsed. See Section 1.2:
Specifications on page –8 for BREAKER FAILURE timing specifications.
• GROUND TRIP: Aging and thermal cycling can eventually cause a lowering of the
dielectric strength of the winding insulation in the stator winding. This can produce a
low impedance path from the supply to ground resulting in ground currents which can
be quite high in solidly grounded systems. These could quickly cause severe structural
damage to the motor stator slots. In resistance grounded systems there is a
resistance in series with the supply ground connection to limit ground current and
allow the system to continue operating for a short time under fault conditions. The
fault should be located and corrected as soon as possible, however, since a second
fault on another phase would result in a very high current flow between the phases
through the two ground fault paths. In addition to damaging the motor, a ground fault
can place the motor casing above ground potential thus presenting a safety hazard to
personnel.
On the occurrence of a ground fault caused by insulation breakdown, a motor will
usually have to be taken out of service and rewound. However an unprotected motor
could suffer mechanical damage to the stator slots making repair impossible. The
fault could also cause the power supply bus to which the faulty motor is connected to
trip in order to clear the fault resulting in unnecessary process shutdowns. Ground
faults can occur in otherwise good motors because of environmental conditions.
Moisture or conductive dust, which are often present in mines, can provide an
ALARM
AUXILIARY , the
setpoint, the breaker failure feature
setpoint, the breaker failure feature
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