Underpower (37) - GE 339 Instruction Manual

S3 PROTECTION

Underpower (37)

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The Underpower element responds to total three-phase real power measured from the
phase currents and voltages.
When the motor is in the running state, a trip or/and alarm will occur once the magnitude
of three-phase real power falls below the pickup level for a period of time specified by the
Delay. The pickup levels are based on Motor Nameplate Rated Power (MNR) and should be
set lower than the lowest motor loading during normal operations.
For example, underpower may be used to detect loss of load conditions. Loss of load
conditions will not always cause a significant loss of current. Power is a more accurate
representation of loading and may be used for more sensitive detection of load loss or
pump cavitations. This may be especially useful for detecting process related problems.
The Underpower element is blocked if the VT Fuse Fail element is active; indicating which
valid voltage inputs are not available due to fuse failure.
A Block Underpower on Start feature is available to the user. The Block Underpower
element is active only when the motor is running and is blocked upon the initiation of a
motor start for a period of time defined by the setting BLK U/P ON START. This block may
be used to allow pumps to build up head before the underpower element trips or alarms.
Blocking this unit via the Block setting is highly recommended if "VFD Not Bypassed" is
asserted.
PATH:
SETPOINTS > S3 PROTECTION > UNDERPOWER
U/POWER ALARM FUNC
Range: Disabled, Enabled
Default: Disabled
For details see Common
BLK U/P ON START
Range: 0 to 60 s in steps of 1 s
Default: 0 s
This setting specifies the length of time to block the underpower function when motor is
starting. The underpower element is active only when the motor is running and is
blocked upon the initiation of a motor start for a period of time specified by this setting.
A value of 0 specifies that the feature is not blocked from start.
U/POWER ALARM PKP
Range: 1% to 100% MNR
Default: 70% MNR
This setting specifies a pickup threshold for the Alarm stage. The alarm pickup threshold
should be less than the motor load during normal operation.
U/POWER ALARM DLY
Range: 0.1 to 60.0 s in steps of 0.1 s
Default: 0.1 s
This setting specifies a time delay for the alarm stage. The time delay should be long
enough to overcome any short lowering of the load (e.g. during system faults).
U/POWER TRIP FUNC
Range: Disabled, Enabled
Default: Disabled
This setting enables the Underpower Trip functionality.
setpoints.
339 MOTOR PROTECTION SYSTEM – INSTRUCTION MANUAL
CHAPTER 6: SETPOINTS