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Procedure

4.1

What are the steps to minimize EMC issues from VFDs?

The operating function of VFDs causes electromagnetic noise. The high-speed switching of

the inverter stage can emit significant radio frequency energy. Without mitigation, this

energy can interfere with other nearby electrical equipment.

Process control and sensor instrumentation is often found in the same area of a factory or

process as VFDs. Some of this equipment can be sensitive to interference from

electromagnetic sources and this can cause performance degradation ranging from incorrect

measurements to disabled instruments. Precise and reliable measurements require careful

installation and configuration.

Some general installation recommendations will apply in all cases where instrumentation and

VFDs are mounted near each other.

• Install Electromagnetic Compatibility (EMC) filters on the line side of the drive converter.

This will prevent noise from traveling back through the mains and affecting other

equipment.

• Use shielded motor feed cables as recommended by the VFD manufacturer.

The manufacturer will know the characteristics of the energy from the drive and will know

the optimum cable specifications to keep this energy contained.

• The length of feed cables between the drive and the motor should be as short as possible.

This will reduce line losses and will also reduce cost.

• Instrumentation cables and drive components should be as far apart as possible.

Doubling the separation distance will reduce power of the radiated energy to one quarter

of its previous value.

• Avoid parallel runs of drive cables and instrumentation cables.

Cables run in parallel can allow radio frequency energy from one to be induced in the

other.

• If an instrumentation cable must cross a drive cable, it must do so at a 90º angle.

This will provide a minimum area of coupling between the cables.

• Use shielded and/or twisted pairs for instrumentation cables.

These types of cables are designed to both contain and resist Radio Frequency (RF)

emissions.

• Install cables close to metal surfaces to avoid creating an antenna effect.

Cables raised off metal surfaces can increase the amount of electromagnetic energy

transmitted or received by the cable.

Using Variable Frequency Drives and Instrumentation Without Interference

Application examples, 09/2020, AG080819