MIL-HDBK-1003/3
APPENDIX D (Continued)
(1) True rms multimeter capable of reading AC/DC
voltages up to 750 volts.
(2) True rms clamp-on ammeter capable of reading
the VFD's maximum current output.
(3)
Photo tachometer to verify shaft output speed
at load.
(4) Current/voltage signal generator to generate a
reference analog signal to VFD (4 to 20 milliamperes or 0 to 5
volts). (This is extremely useful on HVAC applications where the
building automation system designed to control the VFD is not
ready at time of start-up.)
(5) Oscilloscope to check wave shapes of VFD
output to motor. These wave shapes can be compared to those
provided in the start-up manual, or recorded (via Polaroid
camera) for future comparison during troubleshooting or
maintenance. The scope also can be used to check volts/hertz
ratio.
e) Make up a complete final check, via a check-off
list, of electrical and mechanical components to be sure that
they are set correctly. This includes valves, dampers, limit
switches, steady-state voltage, and current valves.
f) Station people at key locations (motor, controller
panel, load(s), etc.).
g) A proper start-up can be considered complete only
when the VFD is operated at full load. This is important because
you then can make meaningful drive adjustments. You can verify
this by actually checking the FLA and comparing the value to that
on the motor nameplate.
h)
When the start-up command is given, watch, listen,
and smell for
anything unusual. Once start-up has been
accomplished,
allow the system to run a few hours before taking
test readings
for future comparison.
D-1.12
VFD Generated EMI and Harmonic Distortion Concerns.
Harmonics are generated by nonlinear devices which rectify the
incoming AC voltage to DC and then invert it back to AC, as is
the case with a VFD running a motor. Harmonics from nonlinear
devices are odd multiples of the fundamental frequency (third,
fifth, seventh, etc.). Some parts of the electrical distribution
200
Previous Page
