Can one and the same non-linear load cause different levels of harmonic dissipation under equal operating conditions?

Answer by Stefan Fassbinder

As far as different states of operation are concerned, such as busy / standby, full power / save mode, yes, but that is trivial.

However, the harmonic content of input current on one and the same device under the same internal operating conditions will vary as external operating conditions vary, say the parameters of the feeding network are different. Mind that these parameters already alter with the number and types of the other loads applied! Even though a »stiff« network with low internal impedance provides less scope for current harmonics to cause voltage harmonics, the harmonic content of input currents will be higher! Especially the reactive (inductive) component of the network’s inner impedance will »smooth« the current a bit by suppressing harmonic currents (and thereby generating harmonic voltage drops). It can therefore not be said of a specific device to have a specific harmonic content of input current. Rather, this needs consideration of the entire system. Unfortunately this circumstance is not taken into account in the metering conditions of the EN 61000-3-2. The maximum harmonic content of supply voltage for carrying out the tests is specified but not the parameters of the feeding network.

20/12/2006

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