IEC 61000-4-13: Synthesising Distortion on Command — and the Tables We Do Not Reprint

Standards & compliance · 4 min read · 20 cited facts

Most immunity tests ask an AC source to make something clean and then disturb it. IEC 61000-4-13 asks it to make something defined and dirty: a fundamental carrying commanded harmonics and interharmonics, held as a composite waveform, out to 2 kHz on a 50 Hz mains and 2.4 kHz on a 60 Hz mains. Controlled impurity is a different engineering problem from purity, and it disqualifies instruments that look qualified on paper.

Say the awkward part first: the per-class harmonic percentage tables — which order, at what percentage of the fundamental, for which equipment class — sit inside the paywalled IEC document, and we deliberately do not reproduce them. Not because they are unimportant, but because a republished number with no provenance is exactly what a compliance plan must not be built on. If you are testing to 61000-4-13, the levels come from the document you buy, not from a vendor page — ours included.

What is sourceable without the paywall

Parameter	Value	Clause
Harmonic range	to 2 kHz (50 Hz mains) / 2.4 kHz (60 Hz mains)	61000-4-13
Voltage fluctuation	Class 2 ΔU ±8% U_n; Class 3 ΔU ±12% U_n	61000-4-14
Scope — equipment current	Up to 16 A per phase; above that, IEC 61000-4-34 applies	61000-4-11 §1

Publishable boundaries from the IEC 61000-4 family

The range row is the one that sizes the instrument. Synthesis to 2 kHz or 2.4 kHz is a statement about the source's usable bandwidth with the distortion applied — not about the fundamental range printed on its datasheet. A source specified to generate a 40–500 Hz fundamental may or may not be able to place a controlled component at 2 kHz on top of that fundamental; the datasheet line that answers 61000-4-13 is arbitrary waveform synthesis, per phase, with independent amplitude and phase control of each harmonic and interharmonic component.

Interharmonics are the harder half

A harmonic is phase-locked to the fundamental by definition. An interharmonic is not — it sits between the integer multiples and slides through the fundamental's phase continuously. Generating one on command means the synthesis engine cannot be a single stored cycle played on repeat; it has to run components at independent frequencies simultaneously and hold amplitude control over each of them for the duration of the dwell. This is where sources that pass a casual harmonics demonstration quietly stop.

A clean-output THD figure answers the wrong question

A THD specification describes what a source refuses to emit into a resistive load. It is a purity promise. 61000-4-13 needs the opposite promise — that the source will emit precisely the distortion it is told to. The two are not correlated, and our own catalogue shows it: the AFC line is a double-conversion frequency converter specified at THD below 2%, optionally below 1%, and it holds that figure because it is built to scrub distortion out — which is exactly why it is the wrong instrument for this test. Clean bulk power and commanded distortion are different products, and we sell both.

What the source has to show

Per-phase arbitrary waveform synthesis with independent harmonic and interharmonic amplitude and phase control — not stored-cycle playback
Usable bandwidth for commanded components to 2 kHz on a 50 Hz mains and 2.4 kHz on a 60 Hz mains
Sequencing that can step through the class levels of the purchased document, since the levels themselves are not public
Enough current headroom that the composite waveform survives contact with a real rectifier input stage rather than flattening against it

Testing to 61000-4-13?

Tell us the equipment class your plan names and the DUT's per-phase current — and bring the document. We will match synthesis capability to it honestly, including telling you when a clean converter is the wrong tool.

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