Westek Electronics supplies the Schaffner FN 5040/5045 output filters designed for variable speed drives to provide trouble-free operation for motors and motor cables.
Schaffner output filters consist of a series of line inductors and filtering capacitors arranged in star form or delta-wired, depending on the exact variation selected as well as current rating.
The output filters are suitable for inverters with switching frequency selection ranging from 2 kHz to 4 kHz.
Inverters employed in variable speed drives use pulse width modulation to provide a 3-phase drive.
The voltage envelope is a series of rectangular pulses of variable width corresponding to the sine function. The pulses are characterised by very high dv/dt rise and fall times, which can damage the motor drive cable and the motor.
The cable is subjected to high voltage stress because of pulse reflection at the motor terminal impedance mismatch. The motor stator insulation is also stressed simultaneously while capacitive current from the windings flowing through earth imperils bearing life.
Schaffner FN 5040/5045 output filters provide a smooth sinusoidal set of line voltages so that irrespective of cable length to a large degree, voltage build-up due to pulse reflection is avoided.
For PWM frequencies of 2 kHz, cable length can be as high as 2000 metres. A screened cable should be employed with screen bonds at both the motor and the output of the filter with the latter being connected to the protective earth terminal of the filter.
Key features of Schaffner FN 5040-5045 series output filters:
- Suitable for line voltages up to 500 volts, motor frequencies to 70 Hz, and to 200 Hz with suitable derating (50% at 200 Hz)
- Rated motor current filters are available from 4.5 amps to 1200 amps
- IP rating of IP00 for Schaffner FN 5040 series and IP20 rating for FN 5045 series
- Optional NEMA 1 protection cover is also available