Overview
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AC motors that drive PWM inverters are widely used in household appliances.
Motors used for PWM inverter power supplies are known to produce shaft
voltage which reduces the reliability and life span of the motors.
It is advantageous to investigate the stray capacitance using an analysis
in advance because the shaft voltage is produced by the stray capacitance
of the motor.
This example presents the use of an electric field analysis to obtain the
stray capacitance between the IPM motor's coil and stator core, rotor core
and stator core, and inner and outer rings of the bearing. |
Electric Field Distribution
The electric field distribution when the electric potential difference
is applied between the motor's coil and stator core, rotor core and stator
core, and inner and outer rings of the bearing are indicated in Fig. 1,
Fig. 2, and Fig. 3.
A large electric field is produced in the air of the slots close to the
coil and stator core when the electric potential difference is applied
between the coil and stator core as well as in the air gap when the electric
potential difference is applied between the rotor core and stator core.
A large electric field is also produced through the balls which are conductors
when the electric potential difference is applied between the inner and
outer rings. |
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Stray capacitance
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The stray capacitance between the coil and stator core and rotor core and
stator core of the motor as well as the inner and outer rings of the bearing
are indicated in Table 1.
The stray capacitance is produced by the shaft voltage. |
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