Active Harmonic Filtration
Active Harmonic Filtration
(OP)
We are looking at installing Active Filters to mitigate enhanced harmonic propagation due to the addition of non linear loads to our network. We are experiencing about 2.8% Voltage THD at the 11kV point of common coupling which can peak at around 7% when differnet switching configurations are requireded (maintenance load sharing etc). As a result we are looking to add Active filters on 2 Large 2.7MW 12 pulse drives. We have calculated that we will need about 200amps per bridge. Has anyone experience of active filtration as this would be a first for us, and any information on manufacturers and or suppliers





RE: Active Harmonic Filtration
But, at those levels, will it really be necessary? Is your 11 kV used internally? Or are there other consumers connected to it?
Gunnar Englund
www.gke.org
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Half full - Half empty? I don't mind. It's what in it that counts.
RE: Active Harmonic Filtration
Skogs, my initial thought.
yorgi, perhaps you should investigate a phase shifting transformer to feed one of the drives. Turn the site, or at least the drives part, into a 24 pulse system. I haven't looked at pricing of any active harmonic filters at 11 kV, so don't know what the price difference there will be between an active harmonic filter, and a phase shifting transformer; but I do know which of the two will be more reliable and need far less maintenance.
RE: Active Harmonic Filtration
RE: Active Harmonic Filtration
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RE: Active Harmonic Filtration
RE: Active Harmonic Filtration
A switching filter is connected between the output bridge and the supply to attenuate the switching frequency curents, but depending on the attenuation of the switching filter and the impedance of the supply, there can be significant levels of the switching voltage appearing on the supply.
The switching frequency is above the 31st harmonic, so these voltages do not appear when checked with a power quality meter, but we hve many experiences where power factor correction capacitors and lighting circuits are badly affected by these switching voltages.
Where the supply impedance is very low, this is not an issue, but if the reactive impedance is high, then it can become a problem.
Phase shifting transformers are useful at reducing 5th and 7th harmonics by cancellation, but some higher order harmonics are actually additive rather than subtractive, so not a perfect solution. Additionally, because it is a subtractive method, it requires identical harmonic loads on each transformer to give best results.
A good broad band filter such as the Lineator is an efficient solution.
Mark Empson
Advanced Motor Control Ltd