Rockwell Automation 7000 PowerFlex Medium Voltage Air-Cooled (B Frame) Installation - ForGe Control - Manual (Page 81)

Rockwell Automation Publication 7000-IN007E-EN-P - June 2014 81
Meggering Appendix B
Output Grounding Network
b. Remove the ground connection on the OGN (if installed). Lift this
connection at the OGN capacitor rather than the grounding bus, as the
grounding cable is only rated for 600V.
Note: Injecting a high voltage on the ground cable during a Megger test
will degrade the cable insulation.
3. 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 are 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.
a. Confirm the marking matches the connections, and disconnect the
ribbon cables and move them clear of the VSB. If you do not remove
these ribbon cables from the VSB, then high potential applies directly
to the low voltage control through the SCBs, causing immediate
damage to those boards.
Note: The VSB ribbon cable insulation is not rated for the potential
applied during a Megger test. You must 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 not only protects them from damage, but
removes 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.
Surge Arrestors
Drives supplied after 2009 will have surge arrestors instead of a TSN.
Surge arrestors can remain in the circuit during the meggering procedure.