Rockwell Automation 7000L PowerFlex Medium Voltage AC Drive (C-Frame) - ForGe Control - Manual (Page 424)

424 Rockwell Automation Publication 7000L-UM301D-EN-P - June 2014
Appendix C Meggering
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. 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.
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.
5. Reconnecting Connections between Power Circuit and Low Voltage
Control
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
Voltage Sensing Boards
Securely reconnect the two ground conductors on the VSBs.
The two ground connections on the VSB provide a reference point for the
VSB and enable the low voltage signal to be fed to the SCBs. If the ground
Type of Drive Minimum Megger Value
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
TIP 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.
TIP 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.