Rockwell Automation 7000A PowerFlex Medium Voltage AC Drive (A Frame) - ForGe Control User Manual
Page 183
Rockwell Automation Publication 7000A-UM200C-EN-P - June 2014
183
Meggering
Appendix E
Output Grounding Network
Remove the ground connection on the OGN (if installed). This connection
should be lifted at the OGN capacitor rather than the grounding bus as the
grounding cable is only rated for 600V.
Note: I
njecting a high voltage on the ground cable during a Megger test will
degrade the cable insulation.
Disconnect Connections between Power Circuit and Low Voltage
Control
Voltage Sensing Boards
The connections between the low voltage control and the power circuit are made
through ribbon cable connectors. The cables will be plugged into connectors on
the Voltage Sensing Board marked “J1”, “J2”, and “J3”, and terminate on the Signal
Conditioning Boards. Every ribbon cable connection made on the VSBs should
be marked for identification from the factory. Confirm the marking matches the
connections, and disconnect the ribbon cables and move them clear of the VSB.
If these ribbon cables are not removed from the VSB, then high potential will be
applied directly to the low voltage control through the SCBs, and cause
immediate damage to those boards.
Note:
The VSB ribbon cable insulation is not rated for the potential applied
during a Megger test. It is important to disconnect the ribbon cables at the VSB
rather than the SCB to avoid exposing the ribbon cables to high potential.
Potential Transformer Fuses
A Megger test may exceed the rating of potential transformer fusing. Removing
the primary fuses from all potential and control power transformers in the system
will not only protect them from damage but remove a path from the power
circuit back to the drive control.
Transient Suppression Network
A path to ground exists through the TSN network as it has a ground connection
to dissipate high energy surges in normal operation. If this ground connection is
not isolated the Megger test will indicate a high leakage current reading through
this path, falsely indicating a problem in the drive. To isolate this ground path, all
fuses on the TSN must be removed before proceeding with the Megger test.