| Abstract |
This paper presents the voltage stresses on a
squirrel-cage motor when the motor is supplied by a
frequency converter with modern insulated gate bipolar
transistors (IGBT) and where there is a long cable between
the motor and the frequency converter. Voltage stresses
occur with frequency converter drives when the output
voltage of the frequency converter consists of pulses. These
pulses cause voltage stresses on the motor when they are
reflected from an impedance boundary. Voltage stresses are
a well-known problem with frequency converter drives, but
numerous articles in the literature about them address cases
in which the peak voltage in the motor terminal is twice the
DC bus voltage, or less. In practice, the peak voltage in the
motor terminal may be even more than that: for example,
three times the DC bus voltage. These voltage peaks are very
harmful to the insulation of the motor, especially in older
motors that are not designed for frequency converter drives.
This paper reports on the measurements, research and
results of this phenomenon in crane applications. |
