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3.3.3 PWM to Sine Filter
Plus
The KEBCO PWM to sine filter plus creates sinusoidal voltages phase to
phase and phase to ground. All problems with long motor leads are
eliminated and it is no longer necessary to use shielded motor cable. This
filter is recommended for extremely long motor cables, >300ft. Addition-
ally, these filters can be used when retrofitting older installations with
inverters. The filter allows the use of the existing motor cables instead of
requiring a new shielded cable to be installed.
With loads >150% inverter-rated current (I
N
) the next higher filter must be
used. Min. 8 kHz (better 16 kHz) carrier frequency are required. The filter
is dimensioned for a maximum output frequency of 100 Hz.
For more information consult KEBCO. Ask for our AF series output filters.
3.3.2 PWM to Sine Filter When controlling the motor with pulse width modulation (PWM), the
motor can be subject to very rapid voltage rise times, dv/dt of 5…10kV/
uSec. This rapid turn on can create many side effects with long cable runs
greater than 150 feet, the primary problem being voltage peaks either at
the motor or at the inverter. If a motor with suitable winding insulation is
used then the inverter becomes the limiting factor since the output
transistors are only rated for 1200V.
Installing a PWM to sine filter converts the PWM voltage to standard AC
sine wave voltage phase to phase. As a result all of the problems
associated with long cable runs, high dv/dt, and high voltage peaks are
eliminated. The phase to ground voltage still contains some PWM
voltage therefore shielded motor cables are still recommended. The
standard-PWM to sine filters are designed for a maximum output
frequency of 120 Hz.
For more information consult KEBCO. Ask for our AF series output filters.
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