AMETEK CTS 3.0 - Manual (Page 26)

Compliance Test System 3.0 User Manual
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minimum test time required is 2.5 minutes or 150 seconds, this means the current harmonics can
be as high as 150% of the standard limits for no more than 15 seconds in any 150 second period.
This requirement imposes more demands on the power analyzer being used than it does on the
AC power source.
Steady state harmonics are those exhibited by equipment that has a constant current draw such
as a fluorescent lighting fixture. Many pieces of equipment, such as Laser printers that have a
heating element that kicks in any time a page is printed, have fluctuating power demands and may
require transitory harmonics testing.
Note that Amendment 14 does away with the distinction between stationary and transitory
harmonics.
2.4.3 IEC 61000-4-7 Inter Harmonics Evaluation.
IEC61000-3-2 Edition 2.2 (2004-11) references measurement methods per IEC61000-4-7 and
Edition 2.0 of this measurement standard specifies the inclusion of inter harmonics. For the
assessment of harmonics, the harmonic and inter-harmonic current levels are grouped to be the
sum of squared intermediate lines between two adjacent harmonics according to the equation
below, as visualized also in the accompanying figure. The resulting harmonic group component of
order n (corresponding to the center line in the hatched area) has the magnitude C (rms value).
In these equations, “c” is the modulus of the spectral component corresponding to an output bin of
the Fourier Transform of the data obtained from the 200 ms acquisition period , and “C” is the
resulting modulus of the harmonic which is to be compared against the limits in IEC61000-3-2 for
the selected test class.
This inter harmonics measurement is not mandatory as of this writing, as the use of equipment
meeting the previous version of IEC61000-4-7 (the older Edition 1) is permitted for a short period
(until the existing IEC61000-4-7 Edition 2 has gone through its maintenance cycle). Therefore the
user has the option to either disregard inter harmonics, or to group them into the assessment by
selecting the appropriate field in the “Test Category” settings.
It should be noted that sele cting this “inter harmonics grouping” has little impact on the
measurement results for the vast majority of products. Only products with active power factor
correction AND highly fluctuating power consumption will produce inter harmonic levels that would
a
dd to the level of “C” as given above. Most products do not produce inter harmonics, and
therefore the measured harmonic currents will be the same either way.