Rockwell Automation 23P PowerFlex DC Stand Alone Regulator and Gate Amplifier - Manual (Page 45)

Rockwell Automation Publication 23P-UM001D-EN-P - July 2012 45
Gate Amplifier Installation and Wiring Chapter 3
Chassis Grounding
A ground stud is provided on the lower right corner of the chassis mounting
flange for making a ground connection. Connect the grounding wire provided to
the ground stud and the metal panel. Make sure that the lug makes a good
connection to the panel.
To provide additional grounding, with regard to noise immunity, the upper and
lower “mounting feet” of the unit have areas that are free of paint to provide a
positive connection between the unit and the enclosure mounting panel.
It is important that the panel that the Gate Amplifier is mounted to is properly
grounded to the power system ground in the customer’s plant. Ideally, the panel
that the Gate Amplifier is mounted on, as well as the associated components
should be at the same potential as the Armature Power Module and the Motor.
Each of the signals that go to/from the Gate Amplifier are bypassed to chassis
ground through small capacitors. These capacitors aid in removing noise from the
signal lines. If the Gate Amplifier or the panel that it mounts to is not properly
grounded, the bypass capacitors can actually inject noise onto the signal lines
resulting in nuisance trips.
For example, if the motor frame and the Gate Amplifier chassis are not grounded
together, the motor frame potential can fluctuate as the drive is run. If the motor
frame fluctuates in potential, the case of the feedback device, resolver or encoder
will also “see” this fluctuation. The capacitive coupling between the case of the
feedback device and the internal wiring and/or electronics can result in a
common mode noise signal being injected into the wiring. This can result in
noise on the feedback lines. Another source of noise in the feedback path are the
voltage fluctuations of the motor shaft, especially in higher hp motors (above 300
Hp). In these cases, an insulated “Thomas” coupling is recommended for
interfacing with the feedback device. The internal part number of an insulated
Thomas coupling is 406041-17, (Power Division Part Number).
For retrofit installations, lack of sufficient bonding/grounding is often the cause
of noise problems. If the regulator components are installed on a sub-panel, a 1/0
fine strand welding cable should be used to connect the panel to the ground bus.
Panels within the cabinet(s) must be bonded together. If the panels within the
cabinet are not bonded together, use 1/0 fine strand welding cable to connect the
panels. Be sure that all paint is scraped off at the connection points; a 2 milli-
Ohms connection or less is ideal. In the absence of a milli-Ohm or micro-Ohm
meter to actually measure the connection resistance, the connections should be
made suitable enough to support the “cranking current required to start a car.”
This means that the connection must be clean and free of paint and other debris.
The supply transformer frame, drive cabinet panels, and motor frame must be
bonded together to provide a “preferred path” for high frequency noise.