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Q. Why doesn’t the motor have a neutral connection as a return to the inverter?
A. The motor theoretically represents a “balanced Y” load if all three stator
windings have the same impedance. The Y connection allows each of the three
wires to alternatively serve as input or return on alternate half-cycle.
Q. Does the motor need a chassis ground connection?
A. Yes, for several reasons. Most importantly, this provides protection in the event
of a short in the motor that puts a hazardous voltage on its housing. Secondly,
motors exhibit leakage current that increase with aging. Lastly, a grounded
chassis generally emits less electrical noise than an ungrounded one.
Q. What type of motor is compatible with the Hitachi inverters?
A. Motor type – It must be a three-phase AC induction motor. Use an inverter-
grade motor that has 800V insulation for 200V class inverters, or 1600V
insulation for 400V class.
Motor size – In practice, it’s better to find the right size motor for your
application; then look for the inverter to match the motor.
NOTE: There may be other factors that will affect motor selection, including heat
dissipation, motor operating speed profile, enclosure type, and cooling method.
Q. How many poles should the motor have?
A. Hitachi inverters can be configured to operate motors with 2, 4, 6, or 8 poles.
The greater the number of the poles, the slower the top motor speed will be, but
it will have higher torque at the base speed.
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