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Likely
Cause:
Motor takes too long to accelerate:
A.
Motor leads are not connected correctly.
Supply voltage has dropped or become
B.
severely unbalanced.
C.
Load exceeds motor capability.
D.
Faulty start capacitor (Single Phase)
E.
Mechanical Failure.
Motor rotates in the wrong direction:
A.
Incorrect wiring connection at motor.
Motor overheats or overload protector repeatedly trips
A.
Driven Load is excessive.
B.
Ambient temperature too high.
Motor cooling fins and/or vent openings
C.
blocked.
D.
Insufficient Air Flow.
E.
Motor is started too frequently.
Supply voltage too low, too high, or
F .
unbalanced.
Motor Vibrates
A.
Motor misaligned to load.
Load out of balance (Direct drive
B.
application).
C.
Uneven tension on multiple belts.
Driven load operating at resonant point /
D.
natural frequency.
E.
VFD torque pulsations.
Corrective Action:
Match motor lead wiring to nameplate diagram.
1. CAUTION! Ensure that steady state supply voltage at motor terminals is
within limits (see section 4.6). Correct as needed.
2. Obtain correct motor to match actual supply voltage.
Determine correct motor size and contact motor representative to obtain
replacement motor.
Motor may be too small for load. Record acceleration time.
Start capacitors may fail if acceleration time exceeds 3 seconds.
1. Check to make sure motor & load turn freely.
2. Disconnect motor from load & ensure motor turns freely.
For Single Phase, reconnect motor according to wiring schematic provided.
NOTE: Some motors are non-reversible.
1. If motor current exceeds nameplate value, ensure that driven load has not
increased. Correct as needed.
2. If new motor is a replacement, verify that the rating is the same as the
old motor. If previous motor was a special design, a general purpose
motor may not have the correct performance.
Most motors are designed to operate in an ambient up to 40˚C.
(See section 7 .3 Hot Surface Caution)
Remove foreign materials – clear vent openings, fan guard air inlets and
frame fins (TEFC motors).
TEAO (Totally Enclosed Air Over) motors: Measure airflow next to motor
surface and obtain minimum requirements from motor manufacturer.
Do not start more than twice in succession under full load. Repeated
starts and/or jogs of induction motors can cause overheating and
immediate failure. Contact the motor manufacturer if it is necessary to
repeatedly start or jog the motor.
1. CAUTION! Ensure that steady state supply voltage at motor terminals is
within limits (see section 4.6). Correct as needed.
2. Reconnect motor per input voltage.
3. Obtain correct motor to match power supply.
Realign load.
1. Ensure that load is dynamically balanced.
2. Remove motor from load and inspect motor by itself. Verify that motor shaft
is not bent. It is recommended that a 50 micron runout for shaft extension
lengths up to 76mm (2 thou for 3'' extension length). Add 12.7 micron for
every 25.4mm (0.5 thou for every 1") shaft length beyond 76mm.
Mixing new with used belts. Replace multiple belt applications with a
complete set of matched belts.
1. De-energize motor and record vibration as load coasts from 100% speed
to 0 RPM. If vibration drops immediately, vibration source is electrical. If
levels do not drop immediately, source is mechanical
2. Redesign system to operate below the resonant point.
3. On VFD-driven loads, program skip frequencies to bypass resonant points.
4. Increase carrier frequency to obtain <3% THD current.
5. On variable torque loads reduce volts/hertz below base speed.
1. Adjust VFD to obtain <3% THD current at rated motor current.
2. Adjust VFD stability for smooth operation. Vector drives may be unstable
at light load.
©2019, 2020 Regal Beloit Corporation, All Rights Reserved. MCIM2022E • Form# SB0250E
13
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