Hi John and Tania:
Actually, the harmonic current problem is no
different between Europe and North America.
The basic problem is that the harmonic currents
generated in the load equipment are dissipated
in the delta primary of a delta-wye distribution
transformer. If the harmonic content is large,
then the primary winding can overheat, resulting
in transformer failure.
In North America, distribution transformers are
relatively small. Three-phase is not used in
the home, so the problem only shows up in
commercial and industrial sites. The distribution
transformers are largely owned by the business,
not by the power company. North America has
incurred such transformer failures. The problem
has been publicised, and transformers are now
designed using a "K" factor which indicates how
much harmonic current the transformer can safely
handle.
In Europe, the distribution transformers are
relatively large. Three-phase is distributed
to homes. A single transformer can supply up
to 600 homes and businesses. (In North America,
the transformer supplies 8 homes maximum.) It
is relatively rare for the business to own the
distribution transformer. Failure of such a
transformer can be quite disruptive.
So, in Europe, rather than replace the very large
distribution transformers, the power supply
industry is imposing harmonic current emission
limits on electrical products.
Harmonic currents can cause other problems. But,
this is my understanding of the reason behind
EN 6100-3-2.
Best regards,
Rich
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