5.2.6.1 General
In order to determine the immunity of industrial equipment in the frequency band 2 kHz to 9 kHz, various equipment has been tested with a 2 kHz, 5 kHz or 9 kHz voltage superimposed on the fundamental frequency with amplitude of 2 %, 5 % and 1 0 % of the fundamental.
The following equipment has been investigated:
• industrial power supplies with following topologies: single phase industrial power supply 230 Va.c./24 Vd.c., without PFC; single phase industrial power supply 230 Va.c./24 Vd.c., with PFC; three phase industrial power supply 400 Va.c./24 Vd.c.;
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• EMI filters (common-mode and differential mode);
• transformers;
• power drive systems with following topologies: no inductors and large d.c. capacitance;
line inductors: d.c. inductors.
The immunity against disturbances in the 2 kHz to 9 kHz range was observed from a functional and thermal point of view. The effect of resonances was not considered in industrial power supply networks.
Distortion in the 2 kHz to 9 kHz frequency band cause additional currents caused by the EMI filter capacitors. At 9 kHz and 1 0 % amplitude the current can reach values up to ten times the rated current of the power supply. This can cause tripping of the internal or branch fuses.
The internal thermal losses in the capacitors have not been found significant, although this cannot be generally ruled out (see B.1 .3).
Increase of the d.c. link voltage is possible in resonant conditions. The control of the voltage is not affected by distortion in this frequency band. No significant changes in the efficiency of the power supply have been observed.
Multiple zero-crossing commutations can be observed in the diode rectifier. These may lead to temperature increase at amplitudes of 5 % or 1 0 %.
5.2.6.2 EMI filters
The capacitors used in EMI filters may cause additional capacitive currents if distortion in the frequency band 2 kHz to 9 kHz is present. The amplitude of the capacitive currents can reach values that exceed the nominal current of the installed equipment. This may cause tripping of fuses or circuit breakers (see also B.1 .3).
Resonances may also occur but these have not been investigated because various EMI filters have different resonance frequencies.
5.2.6.3 Transformers
The transformer in the test was not susceptible to disturbances in the inspected frequency band between 2 kHz to 9 kHz with amplitudes up to 1 0 %. No significant additional iron losses could be measured. No significant acoustic noise could be measured. This cannot be generally ruled out, because the behavior of the transformer depends on its design. Some audible noise emissions in other transformers have been noticed even with low amplitude between 2kHz and 9kHz due to mechanical resonances (see 5.4).
5.2.6.4 Power drive systems
Three different power drive system (PDS) topologies using IGBT semiconductor switches have been investigated:
• PDS with large d.c. capacitance (Figure 28),
• PDS with large d.c. capacitance and line inductors (Figure 29),
• PDS with large d.c. capacitance and inductors in the d.c.link (Figure 30).
IEC TS 62578:201 5 IEC 201 5 – 43 –
Figure 28 – PDS with large d.c. capacitance
Figure 29 – PDS with large capacitance and line inductor
Figure 30 – PDS with a large d.c. capacitance and inductors in the d.c. link 5.2.6.5 PDS with a large capacitance
The d.c. link voltage can be slightly boosted, the maximum boost being observed at 2 kHz and 1 0 % amplitude: 9 % boost of the d.c.-link voltage.
Multiple zero crossing commutation of the rectifier is observed. This effect is attenuated at higher frequencies and is not observed anymore at 9 kHz.
The current through the capacitors of the EMI filter is increased by the disturbance, as explained in Clause A.6.
5.2.6.6 PDS with a large capacitance and line inductors
When line inductors are used the immunity of the PDS is increased in loaded conditions.
However, for the measured example in stand-by mode the d.c.-link voltage was boosted by the distortions in the 2 kHz to 9 kHz frequency band. The worst case was observed at 2 kHz
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with 1 0 % distortion. In these conditions the d.c.-link voltage is boosted by 28 %. At 2 % distortion the d.c.-link voltage has been boosted by 4,8 % (see also Clause A.5).
5.2.6.7 PDS with a large capacitance and d.c.-link inductors
In the case of the observed PDS with a large capacitance and d.c.-link inductors the d.c.-link voltage is slightly boosted.
The worst-case has been observed in this special case at 2 kHz and 1 0 % amplitude. In this case the d.c.-link voltage has been boosted by 5,9 %.