Harmonics and flicker testing

In IEC61000-3-2 (harmonic current emission limits), equipment is sorted into four classes based on what it is and how it’s powered.

• Class A covers balanced three-phase equipment and most other electronics you would see day-to-day, e.g., household appliances and audio equipment.
• Class B covers portable electric tools and non-professional arc welding equipment.
• Class C covers lighting equipment, including dimmers for discharge lamps.
• Class D covers equipment that draws current in a narrow pulse clustered near the peak of the voltage waveform. Examples include PCs, monitors and TVs.

From A to D, each class has stricter harmonic limits.

IEC 61000-3-2 limits the current harmonic emissions that the device injects into the AC mains, while IEC 61000-3-3 limits the voltage fluctuations and flicker caused by the equipment.

Flicker severity is measured using standardized flickermeters that follow IEC 61000-4-15 (and the equivalent IEEE 1453 in North America). Flickermeters are the standard instruments for regulatory/compliance measurement of Pst and Plt, but in practice, flickers is also characterized with power analyzers and oscilloscopes.

Classification is based on the equipment type and its input current waveform:

• Class A covers balanced three-phase equipment and most other electronics you would see day-to-day, e.g., household appliances and audio equipment.
• Class B covers portable electric tools and non-professional arc welding equipment.
• Class C covers lighting equipment, including dimmers for discharge lamps.
• Class D covers equipment that draws current in a narrow pulse clustered near the peak of the voltage waveform. Examples include PCs, monitors and TVs.

If none of the specific classes apply, the default class is Class A.

Power the DUT with a clean AC power supply and measure the input current waveform with the power analyzer. The power analyzer splits the current into harmonic components (up to the 40th) and compares each against the applicable class limit to determine pass/fail.

The process and test setup for EN 61000-3-3 flicker testing is roughly as follows:

1. Connect the equipment under test to a reference impedance network that simulated the public supply impedance.

2. Power the reference impedance from a stable voltage source at rated voltage/frequency.

3. Feed the equipment’s current into a flickermeter connected across the reference impedance’s output terminals, which mimics the voltage fluctuation a real installation would see.

Under the EU’s EMC Directive, most electrical and electronic equipment connected to the public low-voltage supply must be tested for harmonics and flicker before it can carry the CE mark.

• Harmonics testing follows EN 61000-3-2 (or EN 61000-3-12 for higher-current equipment). This standard limits the harmonic currents a device feeds back into the mains.
• Flicker testing follows EN 61000-3-3 (or EN 61000-3-11 for higher-current equipment). This standard limits voltage fluctuations that can cause visible flicker in lighting.

Flickermeters are the standard instruments for regulatory/compliance measurements of flicker, but in practice, flickers is also characterized with power analyzers and oscilloscopes.

Harmonics testing is done using power analyzers, oscilloscopes, AC power supplies and loads.

Most failures come down to how a device draws current from the AC line. For example, devices with simple rectifier-and-capacitor power supplies pull current in short, sharp pulses near the peak of the voltage waveform rather than drawing it smoothly. This generates strong harmonics that exceed regulatory limits.