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AMETEK MX CTSH User Manual

Page 20

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California Instruments

Revision H

20

User Manual

MX Series CTSH Compliance Test System


2.5

IEC 61000-3-11 Flicker

Flicker standards are imposed to limit voltage variations caused by loads connected to the low voltage
supply network that would cause lights connected to the same circuit to flicker. A complex measurement
approach outlined in IEC 868, was devised to correlate voltage fluctuations to a human perceptibility factor
(P). The IEC 61000-3-11 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 IEC 61000-3-11 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

IEC 61000-3-11 Flicker Test AC Source Requirements

As is the case with Harmonics testing, the IEC 61000-3-11 standard imposes requirements on the AC
source that is used. Some of these requirements are similar and less severe than those imposed under
IEC 61000-3-12. 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 MXCTS system uses the MX Series power source, which meets these requirements.

To simulate the resistance and inductance of the low voltage distribution systems, the IEC 61000-3-11
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.

Since the actual reference impedance values would result in very how power dissipation at currents up to
75 A per phase, the CTS uses a test impedance with a value recommended by the IEC 61000-3-11
standard. The flicker data is automatically scaled based on the value of the test impedance (Ztest to Zref).
This provides for a lower level of dissipation, which makes the impedance more cost effective.

The test impedance is provided by the OMNI-3-75 which is housed in its own cabinet and needs to be
placed directly next to the MX/RS Series power source to keep power cable lengths as short as possible.

Note that the OMNI-3-75 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 61000-3-11
requirement.

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