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Waltec Elecronic Engineering

Project Motor Surge Filter

Variable Frequency Drives (VFD) or Frequency Inverters are used to control the speed of large Electric motors.

They do this by generating a 3 phase Pulse Width Modulated (PWM) sinusoidal signal. This signal contains very fast rising and falling edges of the PWM signal.
When connecting these fast rising and falling edges to a long motor cable large voltage spikes will occur at the motor terminals. These surge voltages (up to 1300 V) can be larger than the isolation of the motor windings will allow. Specially when the motor runs hot.

Waltec has developed a special filter to prevent these large voltage spikes at the motor terminals and reducing Conducted Emissions generated by the VFD.

Compare Waltec surge filter with conventional solutions here

Oscilloscope image of PWM motor voltage

Motor Surge filter

Frequency inverters and long motor cables.

Problems resulting from voltage surges.

A number of problems can occur with voltage surges on the motor terminals.

1. Winding isolation can be damaged (read more).

2. The motor bearings can be damaged. (read more)

3. Conductive emissions are increased. The drive system may not be compliant with EMC regulations. (read more)

4. Filter performance. (read more)

For size: A 5.5 kW motor with filter.

Advantages of Motor Surge filter (MSF).

 No voltage peaks

 No EMC problems

 Low power loss in filter.

 All drive function available (like vector control PG feedback etc)