Limits on the harmonics for electrical appliances
The growth of non-linear loads on the electricity supply system has led to an increase in the current harmonics drawn from the mains. In an attempt to limit this problem, an IEC standard IEC61000-3-2 has been published that prescribes limits on the harmonics that an electrical appliance can draw from the mains supply.
In addition, the variation in current supplied to appliances connected to the electricity supply causes local voltage drops across the impedance of the mains. This can manifest itself as a flickering of the lights. The extent to which this is annoying to people is related to the magnitude of the light change and the rate at which it changes. In an attempt to reduce this phenomenon, an international standard IEC61000-3-3, imposes limits on the levels of flicker which can be induced by a given electrical appliance.
Manufacturers of electrical appliances must satisfy the requirements of both these standards in order to sell equipment in the European Union. This is usually done by carrying out a type test on the appliance in question in which the current harmonics and flicker is measured by using a 'power analyser'. Large manufacturers often purchase their own analyser to test their appliances; others may use an accredited test laboratory.
Failure to meet the harmonic or flicker standard can prevent an appliance from gaining access to important European markets. This can lead to costly redesign and delays in marketing a new product. When a product fails, particularly in 'border-line' cases, attention is drawn to the analyser. In such cases ensuring that the analyser is calibrated in a traceable manner is very important.
Our UKAS accreditation includes the following parameters:
For sinusoidal waveforms
- Current Accuracy up to 20 A
- Current frequency response up to 20 A, 50 Hz to 2 kHz
- Voltage accuracy up to 1000 V
- Power Measurements with current up to130 A and Voltage up to 1000 V
For non-sinusoidal waveforms
- Fluctuating harmonic measurements for current waveforms up to 10 A, 50 Hz fundamental; harmonics up to 2 kHz
- Flicker (Pst) Square or sine wave modulated and complex waveforms