Rockwell Automation 7000 PowerFlex Medium Voltage Air-Cooled (B Frame) Installation - ForGe Control - Manual (Page 82)

82 Rockwell Automation Publication 7000-IN007E-EN-P - June 2014
Appendix B Meggering
4. Megger the drive.
Note: Verify the drive and any connected equipment is clear of personnel
and tools prior to commencing the Megger test. Barricade any open or
exposed conductors. Conduct a walk-around inspection before
commencing the test.
All three phases on the line and machine sides of the drive connect
through the DC Link and snubber network. Therefore, a test from any
one of the input or output terminals to ground will provide all the
sufficient testing required for the drive.
a. Connect the Megger to the drive following the specific instructions for
that model.
b. If the Megger has a lower voltage setting (normally 500V or 1000V),
apply that voltage for five seconds as a precursor for the higher voltage
rating. This may limit the damage if you forgot to remove any grounds.
If the reading is very high, apply 5 kV from any drive input or output
terminal to ground.
c. Perform a Megger test at 5 kV for one minute and record the result.
The test should produce a reading greater than the minimum values
listed below. If the test results produced a value lower than these values,
segment the drive system into smaller components and repeat the test
on each segment to identify the source of the ground fault. This implies
isolating the line side of the drive from the machine side by removing
the appropriate cables on the DC Link reactor.
You may need to completely isolate the DC Link reactor from the drive, at
which point you must disconnect all four power cables. Ensure all
electrical components to be meggered are electrically isolated from ground.
Items that may produce lower than expected readings are surge capacitors
at the motor terminals, motor filter capacitors at the output of the drive.
The meggering procedure must follow a systematic segmentation of
electrical components to isolate and locate a ground fault.
ATTENTION: Discharge the Megger prior to disconnecting it from the
equipment.
Type of Drive Minimum Megger Value
Liquid-cooled Drive 200 M

Air-cooled Drive 1k M

Drive with input/output Caps Disconnected 5k M

Isolation Transformer 5k M

Motor 5k M
