Rockwell Automation 7000A PowerFlex Medium Voltage AC Drive (A Frame) - ForGe Control - Manual (Page 184)

184 Rockwell Automation Publication 7000A-UM200C-EN-P - June 2014
Appendix E Meggering
Meggering the Drive
Verify the drive and any connected equipment is clear of personnel and tools
prior to commencing the Megger test. Barricade off 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 are connected together
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.
The Megger must be discharged prior to disconnecting it from the equipment.
Connect the Megger to the drive following the specific instructions for that
model. 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. 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 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.
The DC Link reactor may have to be completely isolated from the drive, at which
point all four of its power cables must disconnected. It is imperative to ensure the
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.
Table 12 - Minimum Megger Values
Note: T he 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.
Type of Drive Minimum Megger Values
Liquid Cooled Drive 200 M Ohms
Air Cooled Drive 1k M Ohm
Drive with input/output Caps Disconnected 5k M Ohm
Isolation Transformer 5k M Ohm
Motor 5k M Ohm