AMETEK MX CTSL - Manual (Page 22)

User Manual MX-CTSL Compliance Test System
California Instruments Revision J 22
approach outlined in IEC 868, was devised to correlate voltage fluctuations to a human perceptibility factor
(P). The EN 61000-3-3 standard sets limits for voltage fluctuations caused by electrical apparatus with a
current level up to 16 Amps per phase. The standard describes a human flicker perceptibility curve that
defines the upper limit for acceptable flicker. This curve plots the percentage of voltage fluctuation against
the amount of voltage fluctuations per minute.
As is the case for the Harmonics standards, the Flicker standard dates back several years and was rooted
in the IEC 555.3 specification. Today however, the EN 61000-3-3 standard should be used to evaluate
equipment. Note that low power equipment generally does not cause Flicker and therefore often can be
exempted from this requirement. The standard permits the equipment manufacturer to prove via analysis
that their products are unlikely to cause voltage fluctuations. This analysis becomes part of a Technical
Construction File (TCF) which in turn may be used to obtain product certification.
2.5.1 EN 61000-3-3 Flicker Test AC Source Requirements
As is the case with Harmonics testing, the IEC 61000-3-3 standard imposes requirements on the AC source
that is used. Some of these requirements are similar and less severe than those imposed under IEC
61000-3-2. For example, total harmonic distortion of the voltage can be 3 % for Flicker testing as opposed
to only 1.25% for harmonics testing. The voltage regulation needs to be better than 2 % which is not
a problem for most AC sources. In rare cases, the line voltage may even be used for this purpose. More
often than not, however, the use of an AC source with well-defined specifications is recommended to obtain
repetitive test data and eliminate the possibility of flicker caused by line fluctuations, not load current
fluctuations. The CTS system uses the MX Series and RS Series power sources, which meets these
requirements.
To simulate the resistance and inductance of the low voltage distribution systems, the IEC 61000-3-3
requires a specific AC source output impedance to be used. This reference impedance, as specified in IEC-
725, is defined in such a way that it approximates a typical distribution network impedance. Individual
countries may require the use of a different reference impedance that more closely resembles the actual
impedance of that countries’ specific distribution network. Most European countries use the specified
reference impedance value however.
The CTS uses a test impedance with a the impedance values specified in IEC 725. The test impedance is
provided by the OMNI-3-37MX unit, which is connected between the output of the MX/RS power source
and the PACS-3-75 measurement system. Note that this impedance is restricted to 37 A RMS per phase
while the MX power source can deliver more current than that. High power EUT’s should be tested to IEC
61000-3-11 using the OMNI-3-75 instead.
Note that the OMNI-3-37MX test impedance for the CTS system is matched to the California
Instruments’ MX/RS power source output impedance. Do not use third party reference impedance
networks with the CTS system as the combined AC source and network impedance may not match the
IEC 61000-3-3 requirement.
2.5.2 When to Test for EN 61000-3-3
As mentioned, it may not be necessary to test every product for EN 61000-3-3. If it can be shown that
maximum power consumption of the unit under test is low, and the surge current level at turn-on is limited,
it can be shown that the product causes insignificant Flicker levels across the reference impedance. For
loads having an rms current draw of more than 5 Amps, it is generally recommended to verify conformance
to EN 61000-3-3 however.
2.6 EN 61000-4-11p Voltage Dips and Variations
The EN 61000-4-11 is an immunity test for low voltage equipment to ensure reliable operation when
connected to the public distribution system. This test requires an AC source that is capable of generating
specific voltage variations and voltage dips. The unit under test must not sustain any damage from such
occurrences nor cause unsafe conditions.
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