MIL-HDBK-1003/3
APPENDIX D (Continued)
(16)
Output signals required
D-1.10
VFD Installation and Start-Up. Over half of drive
failures are a result of improper installation and start-up.
Careful planning of your VFD installation will help avoid many
problems. Be sure the VFD specification requires furnishing of
the drive's operation and maintenance manual. Important
considerations include temperature and line power quality
requirements, along with electrical connections, grounding, fault
protection, motor protection, and environmental parameters.
a) Temperature. Equipment should be located in areas
which are well within manufacturer's specified temperature limits
and are well ventilated to remove generated heat. Avoid
installing units in mezzanines, direct sunlight, or near external
heat sources to avoid unpredictable temperature rises. Provide
supplemental cooling if these areas cannot be avoided.
b) Supply Line Power Quality. The line voltage to the
drive input should vary no more than plus or minus 10 percent to
avoid tripping the unit via a protective fault. Voltage drop
calculations must take this into account when running conductors
long distances from the power source.
c) Electrical Connections.
Size VFD line and load
conductors to conform to NFPA 70.
d) Grounding. In addition to running a grounding
conductor back to the electrical service entrance, bring a
grounding conductor back from the motor to the VFD's internal
grounding terminal. This direct motor ground to the VFD is
required to minimize interference and for proper operation of the
ground-fault protection function.
e) Fault Protection. Many VFD's have short-circuit
protection (usually in the form of fuses) already installed by
the manufacturer. This is usually the case on larger horsepower
units. Smaller units (1/3 to 5 hp) normally require external
fuse protection. In either case, the selection and sizing of
these fuses is critical for semiconductor protection in the event
of a fault. The manufacturer's recommendations must be followed
when installing or replacing fuses for the VFD. Be sure to
torque-bolt fuses in place according to the manufacturer's
specification to ensure fast operation of fuses in case of a
fault.
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