- General Electric Computer Accessories User Manual

GEH-6385 Reference and Troubleshooting, 2300 V Drives Chapter 3 Paramters/Functions •
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Diagnostic variables
The following table specifies the diagnostic variables of the Motor Ground
Protection function.
Variable Description
Gnd flt warning This variable is for external use to indicate that the alarm,
Ground flt alm, LP is present.
Gnd flt trip This variable is for external use to indicate that the fault, Gnd flt
trip is present.
Faults and alarms
The following table specifies the faults and alarms of the Motor Ground Protection
function.
Fault/Alarm Description
Ground flt alm, LP The alarm is present when Gnd cur signal >= Gnd signal alarm
on and is not present when when Gnd cur signal < Gnd signal
alarm off.
Gnd flt trip The trip fault occurs if Gnd cur signal >= Gnd signal trip lvl.
Function description
The VATF-MID voltage feedback board provides a direct measure of the DC bus
neutral voltage to the control. This signal is filtered and conditioned to eliminate the
effects of bridge modulation and then monitored.
With no motor ground fault condition, the voltage will be nearly zero. With a fault
to ground, the voltage will be at a maximum. For a partial ground fault condition,
which could be caused by damaged motor insulation, the voltage increases almost
linearly between zero and the maximum voltage. The ground fault voltage, variable
Gnd cur signal is compared to thresholds to create the alarm or trip fault. Variable
Gnd cur signal is most sensitive at higher motor voltages. When a ground fault
condition exists, the alarm may be present at maximum motor voltage but may
disappear under other operating conditions.