VFD Output Filters

SPQ-ED3dU du/dt choke

SPQ-ED3dU du/dt Chokes

A du/dt limiting choke is commonly used to protect motor insulation against the high rate of rise of voltage from PWM VFDs.  These chokes are effective on installations with short cable lengths and relatively low (<4kHz) switching frequencies. du/dt limiting chokes maximise the motor insulation life and assist in reducing electro-magnetic interference (EMI).

SPQ-EF3LC sinewave filter in IP00 format. 55kW, 400V, 50Hz for VFD 5.5kHz switching frequency

SPQ-EF3LC Sinewave Filters

SPQ-EF3LC sinewave output filters are utilised to resolve a number of problems, particularly associated with higher VFD IGBT switching frequencies and long cable lengths (>25-50m) which can result in a phenomenon called “standing waves” (i.e. cable resonance which can trip the VFD and damage the motor).

Voltage and current waveforms after the application of a sinewave filter.

In addition to prevent cable resonance (standing waves), the SPQ-EF3LC sinewave filter reduces RFI emissions and can, on occasion, negate the requirement for special VFD rated cable between the VFD and the motor.  Motor audible noise, motor temperature and winding insulation stress are all considerably attenuated.

Both SPQ-ED3du du/dt chokes and SPQ-EF3LC sinewave filters are available from 4kW to 2600kW in voltages from 400V to 690V, 50Hz or 60Hz in ambient temperatures to 55 deg C. Both products can be supplied in IP00 format plus IP23, IP44, IP54 and IP66 enclosures for oilfield, industrial or marine use.

For further information please click here – du/dt Chokes & Sinewave Filters