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Vol. 2.6 © 2020 Hanbell Precise Machinery Co., Ltd. All rights reserved
2.
Ensure power supply wiring and output motor wiring are connected to the proper
terminals. Failure to do so will cause catastrophic failure of the motor.
5.4.4 Limitation of power supply
a. Voltage limitation b. Frequency:
1. Long term running: Low voltage±5%; High voltage±2%1. Rated frequency±2%
2. Instant running: Low voltage±10%; High voltage±4%
3. Unbalanced: Low voltage±3%; High voltage±2%
Power of some areas is unstable. Install an additional voltage protector with mentioned
voltage limitation above to ensure safe operation of the compressor.
1.
Unbalanced voltages :
Unbalanced voltages occur because of variations in load. When load on one or more of
the phases are different from the other(s), unbalanced voltages will appear. This can be
due to different impedances, type, and value of load on each phase. Unbalanced voltages
can cause serious problems, particularly for the motor.
National Electrical Manufacture Association (NEMA) defines voltage unbalance as below:
voltage
average
voltage
average
from
deviation
voltage
maximum
100
voltage
unbalanced
of
Percentage
×
=
NEMA states that poly-phase motors shall operate successfully under running
conditions at rated load when unbalanced voltage at the motor terminals does not exceed
1%. Furthermore, operation of a motor under above 5% unbalanced condition is not
recommended. It probably results in motor damage.
Unbalanced voltages at motor terminals cause unbalanced phase current. This causes
excessive heat to shorten motor life. If unbalanced voltage is too high, thereduced torque
capability might not be adequate for the application and the motor will not attain rated
speed and.
Some more common causes of unbalanced voltages are:
●
Unbalanced utility supply
●
Unequal transformer tap settings
●
Transformer failure
●
Open delta connected transformer banks
●
Large single phase distribution transformer in the system
●
Heavy reactive single phase loads such as welding machine
●
Open phase on the primary of a 3-phase transformer in the distribution system
●
Blowout fuse on the 3-phase bank of power factor improvement capacitors
●
Unequal impedance in conductors of power supply wiring
●
Unbalanced distribution of single phase load, such as lighting
A 3-phase unbalanced voltage protector is an optional accessory. Please contact Hanbell
for more details.
