Atec Zimmer-CEtest61k - Manual (Page 5)

5
Disturbances to the public power system
caused by current harmonics in the frequency
range from 2 kHz to 9 kHz
Current harmonics caused by home appliances are measured
and evaluated up to the 40th harmonic (2 kHz for a line
frequency of 50 Hz) according to EN 61000-3-2 and -12. For
frequencies of 9 kHz and higher the common EMC standards
apply. The frequency range from 2 kHz to 9 kHz is, however,
to a large extent not standardized so far. Distortions in this
frequency range originate for example from decentralized
sustainable energy sources such as photo voltaic or wind
power stations. Therefore these effects in the frequency
range from 2 kHz to 9 kHz are already existent and will
certainly increase in future, necessitating appropriate mea-
surement methods.
The standard EN 61000-4-7, Annex B, describes a process to
measure the parts of the signal above the 40th harmonic
and to cluster the output. In summary, the standard stipu-
lates the fulfillment of the following points:
• DFT with 200ms rectangular window
•
No gaps, no overlapping
•
Groups of 200 Hz, each with 40 lines in intervals of 5 Hz:
- In 50 Hz systems, the first group begins at 2005 Hz,
the 35th group finishes at 9 kHz.
- In 60 Hz systems, the first group begins at 2405 Hz,
the 33rd group finishes at 9 kHz.
- The groups are named by their center frequency.
For example the current of the first group at a line
frequency of 50 Hz is called I
2100
and the voltage
of the last group U
8900
The system ZES ZIMMER CE-Test61k allows measurements
in the frequency range from 2 kHz to 9 kHz in full compli-
ance with this standard. Future updates for software and
firmware will enable the system to remain compliant. In
comparison with the fundamental oscillation, the signals to
be measured in the above frequency range usually have a
very low level. The high precision of both the precision
power analyzers
ZES ZIMMER LMG95 and LMG500 and our
power and voltage sensors come to an advantage here by
offering a direct measurement of these signals.
Type of sensor
Nominal
value
Error at 9 kHz
Current clamp LMG-Z406 40 A 1%
High Current Wideband AC
Measuring Transformer WCT100
100 A 0.25%
Precision Wideband High
Voltage Divider HST12
12 kV 0.2%
Precision Wideband High
Voltage Divider HST30
26 kV 0.5%
Available ZES ZIMMER Current- and Voltage Transformers,
each with nominal value and error rate at 9 kHz
In order to improve the reproducibility of tests, the line
impedance viewed by the EUT (equipment under test) must
be exactly defined. An artificial-mains network with a imped-
ance in the frequency range from 2 kHz to 9 kHz according to
the standard above needs to be inserted between the device
under test and the power source. Not mandatory – but highly
recommended – is the use of a programmable AC power
source (see page 8).
However, for currents in the range of 16A to 75A the con-
struction of an artificial power line is quite complex, hence,
the testing devices are normally being connected directly to
the power system. If users also want to analyze the voltage
harmonics, they can use a wide-band precision high voltage
divider of the series
ZES ZIMMER HST to directly measure at
the medium-voltage grid.
CE-Test61k: Current harmonics measurement result of a 200 ms time frame in the frequency range from 2 kHz to 9 kHz.
Please note the distinct perturbation at 5 kHz.