Compliance Measurements With The Ha1600; Overview Of Harmonics Measurements - AimTTi HA1600A Instruction Manual

Overview of Harmonics Measurements

The standard defining the limits for harmonic current emissions, for equipment with input current
≤ 16A per phase, is EN61000–3–2. This standard is an essential document that should be read
before any compliance quality measurements are attempted. There have been multiple versions
of it, each with a succession of Amendments. This standard (which defines the required
characteristics of the equipment being tested) refers to EN61000–4–7 for measurement
methods. The present version of the instrument firmware supports both the current issue,
EN61000–3–2:2014 (using the test methods from EN61000–4–7:2002 as amended, which
include inter-harmonics and grouping – see below) and also the earlier version EN61000–3–
2:2000 (using the test methods of EN61000–4–7:1993, which did not include inter-harmonics and
grouping); the latest methods are preferred. All these documents should be available for
purchase from National Standards Organisations worldwide (BSI in the UK).
The firmware of the HA1600 is stored in FLASH memory and can be updated from a PC. This
capability enables the manufacturer to implement all the changes to the standards as software
updates, which can be installed by users without the need to open the instrument or return it to
the factory. See the Firmware Updates section for details of the upgrade process.
Aspects of the measurements
The following points are a quick guide to some aspects of the measurement requirements,
particularly where confusion might arise from the changes made to the standards. As always,
users should read the full standards for exact details.
Interharmonics
EN61000–4–7 uses the term interharmonics for spectral components of the current waveform
that fall between two harmonic frequencies. The 2002 version introduced a process known as
grouping which requires the amplitude of interharmonics to be rms summed into the magnitude
of the nearest harmonic before comparing that value with the limit. The 1993 requirements
exclude interharmonics.
Equipment classification
All classification is now by equipment type; class D does not depend on a special waveform test.
Basis of limits
For classes A and B the limits are absolute; for classes C and D the limits are now based on a
rated consumption declared by the manufacturer. This figure must be within ±10% of the value
obtained during the test. It is also possible to base the limits on the maximum consumption that
occurs during the test. Dynamic limits that vary continuously during the test, as the consumption
of the load changes, are no longer used.
Basis of measurement
The comparisons of measured harmonic currents against the limits are now made using the
arithmetic average of all the results of the 1.5 second filtered results of every transform in the
measurement interval.
Fluctuating harmonics – the "POHC rule" and the "200%/90%" rule
The assessment of fluctuating harmonics has completely changed. A "10% of 2½ minutes" rule,
which was applied for a limited set of harmonics in the first issue of the standard, is no longer
used. There are now two sets of rules:
The first, commonly known as "the POHC rule", allows any harmonic to fluctuate up to a
maximum of 150% of its limit, provided that its average value is below 100% of the limit. In
addition, some trade-off between harmonics is allowed for odd harmonics of order 21 to 39 based
on a value called the Partial Odd Harmonic Current; this is the rms sum of all the odd harmonics
between 21 and 39. This rms sum is compared to the Partial Odd Harmonic Limit, which is the
rms sum of the limits for the same set of harmonics.

Compliance Measurements with the HA1600

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