MIL-HDBK-1003/3
APPENDIX D (Continued)
system designed for 60 Hz can have significant losses at harmonic
frequencies, which causes higher operating temperatures and
shortened component life. The harmonics generated by a VFD
affect not only the load it serves (the motor), but are also
reflected back into the power distribution system, thus affecting
other devices connected to the distribution system. Reference 13
addresses the motor heating and life expectancy concerns. The
physical location of the VFD and its interface point with the
power system within the facility are important. Do not locate
the VFD near other electronic equipment, including radar
equipment, radio equipment, computers, hospital diagnostic and
life support equipment, or telecommunications equipment.
Minimize the length of line and load power leads as much as
possible. Always run line and load conductors in a grounded
continuous metallic conduit system. Since most mechanical
systems and controls now include solid-state electronics, take
precautions to prevent their damage or malfunction due to VFD
generated harmonics. Filters can be added to the VFD input
circuit when the VFD does not include adequate filtering
internally for the specific application. Consult the electrical
design engineer for help with resolving interference and harmonic
distortion concerns.
D-1.13
VFD-Driven Premium Efficiency Motor Concerns. Although
beyond the scope of this handbook, it should be noted that not
all premium efficiency motors are suitable for control by VFD's.
During the design stage, contact both VFD manufacturers and
premium efficiency motor manufacturers to ensure compatibility
for the application at hand.
D-1.14
Troubleshooting VFD Problems. Although important in
ensuring long-term successful VFD operation, it is beyond the
scope of this handbook to cover troubleshooting of VFD problems.
The subject of troubleshooting VFD's during their operating
lifetime is well covered in References 6 and 7.
REFERENCES
1.
Understanding Variable Speed Drives - Part 1, S. S. Turkel,
Electrical Construction and Maintenance (EC&M), February 1995.
2.
Understanding Variable Speed Drives - Part 2, S. S. Turkel,
EC&M, March 1995.
3.
Understanding Variable Speed Drives - Part 3, S. S. Turkel,
EC&M, April 1995.
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