In order to meet the European directive 89/336/EEC Electro-Magnetic Compatibility (EMC)

The equipment manufacture, systems integrator and installer shall comply with the requirements of the directive.

Electrical & Electronic equipment shall be constructed such that:-

  • The levels of emission shall be such that the equipment does not affect safe and intended operation of other equipment.
  • The equipment has an adequate immunity to emissions from other sources in order to function safely and as intended.

Compliant equipment shall carry the CE mark.

Electromagnetic interference problems associated with VSD’s:-

  • Supply side
  • VSD output
  • Motor
  • Cabling

Supply side:-

Need to consider the mains interference and harmonic distortion. Harmonics are a sinusoidal component of the mains fundamental frequency (50 Hz). Harmonics are generated by equipment such as, power electronics, drives, transformers and arc welders.

Distortion caused be harmonics on the mains supply effects the correct operation of other equipment on the supply system. (Overheating problems, causing failure).

Therefore this is an important issue for the electricity authorities. Hence legislation, level. Requiring the reduction of harmonics level.

VSD Ouput Slide:-

The high frequency voltage rises (dv/dt) travels along the cable to the motor, stresses the motor insulation causing insulation deterioration and premature ageing.


  • Increased losses generating increased heat.
  • Radiated noise.
  • Leakage and current loops through the motor shaft and bearings.


Earth and Shield (screen) cables have to be installed according to the instruction manual and the relevant EMC guidelines. Correct screening and earthing is very important in reducing the effects of interference to other equipment and also correct and safe installation of VSD & filters.

EMC Solution


  • Harmonics filter
  • EMI/RFI filters
  • Line reactors


  • Motor protection chokes
  • dv/dt filters
  • Sinusoidal output filters


1) EMI. Causes distortion of the mains 50 hz waveform.

2) RFI. High frequency signal superimposed on mains 50 hz waveform. Generated by communication equipment and high frequency electronic equipment.

Up to 10 Mhz is usually conducted.

Above 30 Mhz is radiated.

3) Filter leakage current must be taken into account in terms of safety and its effect on RCD devices.

Line Reactor

Line Reactor

Line reactors:-

  • Reduction of harmonics
  • Limits Inrush & peak currents
  • Improvements of power factor

RFI filters:-

Attenuation up to 30 Mhz.

Harmonics filters:-

Output filters:-

  • Motor operates as if powered by the mains
  • Improve motor life
  • Reduces motor noise.
  • Can use unshielded motor cable.
  • Need to consider power loss due to filter

dv/dt Choke:-

  • Protects motor insulation,
  • Reduces motor noise.
  • Enable longer cable runs

EMC Solution. Cabling

Supply Transformer

Supply Transformer

RFI Filter

RFI Filter

Supply Cabling

Supply Cabling