Rockwell Automation 7000A PowerFlex Medium Voltage AC Drive - Air-Cooled (A Frame) - Manual (Page 385)

Appendix
C
7000 “A“ Frame 7000A-RM001A-EN-P – January 2011
Meggering
Drive Meggering
When a ground fault occurs, there are three zones in which the
problem may appear: input to the drive, the drive, output to the
motor. The ground fault condition indicates a phase conductor has
found a path to ground. Depending on the resistance of the path to
ground, a current with magnitude ranging from leakage to fault level
exists. Based on our experiences in drive systems, the highest
probability for the source of the fault exists in either the input or
output zones. The drive itself rarely has been a source of a ground
fault when it is properly installed. This is not to say there will never
be any ground fault problems associated with the drive, but the
chances are the fault is outside of the drive. Also, the procedure for
meggering the drive is more complex than meggering outside the
drive.
With these two factors, it is recommended to first megger the input
and output zones when encountering a ground fault. If the location
of the ground fault can not be located outside the drive, the drive will
need to be meggered. This procedure must be performed with due
care as the hazards to drive exist if the safety precautions in the
procedure are not followed. This is due to the fact the megger
procedure applies high voltage to ground: all the control boards in
the drive have been grounded and if not isolated, they will have high
potential applied to them causing immediate damage.
Meggering the
PowerFlex 7000A
A T T E N T I O N A T T E N T I O N Use caution when performing a Megger test.
High voltage testing is potentially hazardous and
may cause severe burns, injury or death. Where
appropriate, the cause of the test equipment
should be connected to ground.
It is recommended that the insulation levels be checked before
energizing power equipment. Performing a Megger test will provide
a resistance measurement from the phase to phase and phase to
ground by applying a high voltage to the power circuitry. This test is
performed to detect ground faults without damaging any equipment.
This test is performed by floating the drive and all connected
equipment to a high potential while measuring the leakage current to
ground. Floating the drive implies temporary removal of any
existing paths to ground necessary for normal operation of the drive.