Rockwell Automation 7000 PowerFlex Medium Voltage AC Drive (B Frame) - ForGe Control - Manual (Page 188)

188 Rockwell Automation Publication 7000-UM202B-EN-P - June 2014
Appendix D Meggering
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 5 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 5kV from any drive input or output
terminal to ground.
c. Perform a Megger test at 5 kV for 1 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
start segmenting the drive system down 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. You must ensure
that you have electrically isolated all electrical components to be meggered
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.
The motor filter capacitors and line filter capacitors (if applicable) may
result in the Megger test result being lower than expected. These capacitors
have internal discharge resistors designed to discharge the capacitors to
ground. If you are uncertain of the Megger test results disconnect the
output capacitors.
5. Reconnect connections between power circuit and low voltage control.
a. Reconnect the ribbon cables “J1”, J2” and “J3” in all the VSBs. Do not
cross the cable connections. Mixing the feedback cables may result in
serious damage to the drive.
6. Reconnect the power circuit to the system ground.
Type of Drive Minimum Megger Value
Liquid Cooled Drive 200 M Ω s
Air Cooled Drive 1k M Ω
Drive with input/output Caps Disconnected 5k M Ω
Isolation Transformer 5k M Ω
Motor 5k M Ω
IMPORTANT Humidity and dirty standoff insulators may also cause leakage to ground
because of tracking. You may have to clean a 'dirty' drive prior to commencing
the Megger test.