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Decide if I need to use a REO Output Choke or Sinewave filter with a Drive

Decide if I need to use a REO Output Choke or Sinewave filter with a Drive image #1

The nature of a Variable Speed drive and the PWM (Pulse Width Modulated) output it applies to a motor creates a number of potential issues.

Either a REO Motor Choke (CNW854) or a REO SineWave Filter (CNW933) will help to reduce the effects of the following:-

dv/dt, this is basically the rate of change of the voltage that appears at the motor terminals. This can cause a degradation of motor insulation, especially if the motor cable is beyond 10m

Reduced reflected wave phenomena, this is when the rise time of the PWM pulses is shorter than the time the pulse takes to propagate along the motor cable. In this case the voltages can be additive and there is a resultant increase in motor terminal voltage. This can damage drive insulation and cause the drive to trip.

Most drive switching frequencies are within the frequency range which is audible to humans – approximately 20 Hz – 20 kHz. In some instances, depending on motor mountings or characteristics, the motor will emit audible noise at the same frequency as the switching frequency.

Conducted EMC is reduced by fitting these products, especially in the case of the SineWave filter, CNW933.

In general the beneficial effects of a Sinewave filter will normally be greater than those for a motor choke in a given application, but a motor choke should be considered first as it usually represent the lowest cost option for most applications.

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