Harmonic currents emission limits

Most electronic devices use switching power supplies that generate non-sinusoidal waveform currents and consequent harmonics of the 50Hz/60Hz fundamental frequency. This results in harmonic currents being injected back into the public power system. The level of harmonics must therefore be controlled on all CE-marked devices to avoid excessive distortion caused to the power system.

The standard IEC/EN 61000-3-2 divides equipment into four classes:

Class A: Balanced three-phase equipment and all other appliances, excluding those specified as belonging to Class B, C, or D.

Class B: Portable appliances.

Class C: Lighting equipment including brightness control devices.

Class D: Personal computers and computer monitors, television receivers.

compatibilità elettromagnetica

Based on the class and cycle time, harmonic currents must be analyzed over precisely defined time periods and comply with the specified limits in the standards. To achieve the required accuracy up to the 40th harmonic, it is essential to automate the testing procedure.

The test requires:

  • A dedicated AC power source with adjustable voltage and frequency and low distortion.
  • A specific analyzer whose characteristics are described in standard IEC 61000-4-7.
  • Acquisition and processing software.

The applicable standards depend on the maximum current drawn and the use of the device under test:

EN 61000-3-2
Electromagnetic Compatibility (EMC) - Part 3-2: Limits - Limits for harmonic current emissions (equipment with input current <= 16 A per phase).

EN 61000-3-12
Electromagnetic Compatibility (EMC) - Part 3-12: Limits - Limits for harmonic currents produced by equipment connected to low-voltage public power supply systems with input currents > 16 A and <= 75 A per phase.