IEC 61000-4-13: Testing and measurement techniques - Harmonics and interharmonics including mains...

The basic immunity test for harmonic and interharmonic distortion of 50Hz or 60Hz mains supplies is IEC 61000-4-13, which has been adopted unchanged as the harmonized European standard EN 61000-4-13.

The ideal mains voltage is a pure sine wave at the fundamental frequency (usually either 16.67, 50, 60 or 400 Hz), but non-linear leads and injection of signaling voltages cause the waveform to be distorted. The techniques of Fourier analysis are used to describe the distortion in terms of one or more frequencies superimposed on the pure sine wave fundamental. These added frequencies are classified as harmonic -when they are an integer multiple of the fundamental, and as interharmonic - when they are any other frequency.

What are harmonics and interharmonics?

Harmonics are split into two main types: odd-numbered (3, 5, 7, 9, ...39, etc) and even-numbered (2, 4, 6, 8, ...40, etc), because they can cause different problems and as a result may need to be treated differently. Odd-numbered harmonics are often called odd-order harmonics, and the same for even-numbered harmonics. They are further divided into those that are a multiple of 3 times the fundamental because, in three-phase power systems, triplens can be canceled out whereas other odd-order harmonics cannot be.

When nonlinear loads are connected to a pure sine wave source at the fundamental frequency, they draw non-sinusoidal currents. As these non-sinusoidal currents flow in the inevitable impedance of the power supply network, they cause non-linear voltage drops that distort the waveform of the supply, so it is no longer a pure sine wave. The lower the impedance of the mains power supply, the less will be the voltage distortion created by a given non-linear load.

The outputs from the test generator are simply connected to the mains input of the EUT. Because this test does not use RF it is possible to perform it anywhere, with almost any variety of physical arrangements, and still achieve correct results. This makes it a test that is easy and low-cost for a manufacturer to perform since it does not need shielded rooms, anechoic chambers, costly RF test gear, or test engineers who have RF skills.

For example, the length of the cable from the power amplifier (mains synthesizer) to the EUT is not specified. In practice, to accurately control the levels of harmonics applied to an EUT it would be wise to keep this cable length to less than one-fiftieth of the wavelength of 2.4kHz in a PVC mains cable - about 1500m. So mains cable lengths of up to 1 km between power amplifiers and are perfectly acceptable as fewer manufacturers will need longer cables.