Rockwell Automation 7000L PowerFlex Medium Voltage AC Drive (C-Frame) - ForGe Control - Manual (Page 421)

Rockwell Automation Publication 7000L-UM301D-EN-P - June 2014 421
Appendix
C
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 7000
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.
ATTENTION: 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.
ATTENTION: There exists the possibility of serious or fatal injury to personnel if
safety guidelines are not followed.