Rockwell Automation 7000L PowerFlex Medium Voltage AC Drive (C-Frame) - ForGe Control - Manual (Page 423)

Rockwell Automation Publication 7000L-UM301D-EN-P - June 2014 423
Meggering Appendix C
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 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.
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.
4. Meggering the Drive
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.
Connect the Megger to the drive following the specific instructions for
that model. If the Megger has a lower voltage setting (normally 500V or
TIP 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.
TIP 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.
TIP Be sure the Megger is discharged prior to disconnecting it from the
equipment.