Mechanical Jam; Undercurrent Protection - GE MM300 Instruction Manual

CHAPTER 5: SETPOINTS

Mechanical jam

Undercurrent
protection
MM300 MOTOR MANAGEMENT SYSTEM – INSTRUCTION MANUAL
After the motor has started and reached a running state, the mechanical jam element (if
enabled) produces a trip when the magnitude of Ia, Ib, or Ic reaches or exceeds the pickup
level for the time specified by the
used to indicate a stall condition when running. Not only does it protect the motor by
taking it off-line faster than the thermal model (overload curve), it may also prevent or limit
damage to the driven equipment if motor starting torque persists on jammed or broken
equipment.
The
Mechanical Jam Level
operation, but lower than the motor stall level. Normally the delay is set to the minimum
time delay or to avoid nuisance trips due to momentary load fluctuations.
The following setpoints are available for the mechanical jam element.
Mechanical Jam Level
Range: 1.01 to 4.50 × FLA in steps of 0.01 or OFF
Default: OFF
This setpoint specifies the current pickup level. Set this value to "OFF" to disable
mechanical jam protection.
Mechanical Jam Delay
Range: 0.1 to 30.0 seconds in steps of 0.1
Default: 0.1 seconds
This setpoint specifies the time that the motor current must reach or exceed pickup to
generate a mechanical jam trip.
When the motor is in the running state, a trip or alarm will occur should the magnitude Ia,
Ib, or Ic fall below the pickup level for the time specified by the
The pickup levels should be set lower than the lowest motor loading during normal
operations.
The following setpoints are available for the undercurrent protection element.
Undercurrent Trip Level
Range: 1 to 100% of FLA or OFF
Default: OFF
This setpoint specifies the undercurrent trip pickup level. A value of "OFF" disables the
undercurrent trip function.
Undercurrent Trip Delay
Range: 1 to 60 seconds in steps of 1
Default: 1 second
This setpoint specifies the time that the motor current must exceed pickup to generate a
trip.
Undercurrent Alarm Level
Range: 1 to 100% of FLA or OFF
Default: OFF
This setpoint specifies the undercurrent alarm pickup level. A value of "OFF" disables the
undercurrent alarm function.
Undercurrent Alarm Delay
Range: 1 to 60 seconds in steps of 1
Default: 1 seconds
This setpoint represents the time that the motor current must exceed pickup to generate
an alarm.
For example, if a pump is cooled by the liquid it pumps, loss-of-load may mean that the
pump overheats. In this case, the undercurrent feature is enabled. To prevent motor
loading from falling below 0.75 × FLA, even for short durations, the
Mechanical Jam Delay
should be set higher than motor loading during normal
PROTECTION ELEMENTS
setpoint. This feature may be
Undercurrent Alarm Delay
Undercurrent Trip Level
.
5–43