Table of Contents
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Section 1
General Information
Special Drive Situations
Control Enclosures
Special Motor Considerations
Analog Signal Wires
5-12 Troubleshooting
For severe noise situations, it may be necessary to reduce transient voltages in the wires
to the motor by adding load reactors. Load reactors are installed between the control and
motor.
Reactors are typically 3% reactance and are designed for the frequencies encountered in
PWM drives. For maximum benefit, the reactors should be mounted in the drive
enclosure with short leads between the control and the reactors.
Motor controls mounted in a grounded enclosure should also be connected to earth
ground with a separate conductor to ensure best ground connection. Often grounding
the control to the grounded metallic enclosure is not sufficient. Usually painted surfaces
and seals prevent solid metallic contact between the control and the panel enclosure.
Likewise, conduit should never be used as a ground conductor for motor power wires or
signal conductors.
Motor frames must also be grounded. As with control enclosures, motors must be
grounded directly to the control and plant ground with as short a ground wire as possible.
Capacitive coupling within the motor windings produces transient voltages between the
motor frame and ground. The severity of these voltages increases with the length of the
ground wire. Installations with the motor and control mounted on a common frame, and
with heavy ground wires less than 10 ft. long, rarely have a problem caused by these
motor–generated transient voltages.
Analog signals generally originate from speed and torque controls, plus DC tachometers
and process controllers. Reliability is often improved by the following noise reduction
techniques:
•
Use twisted-pair shielded wires with the shield grounded at the drive end only.
•
Route analog signal wires away from power or control wires (all other wiring types).
•
Cross power and control wires at right angles (90°) to minimize inductive noise
coupling.
MN723
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Table of Contents
Troubleshooting
