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INTRODUCTION

WHEN IS IT NECESSARY TO INSTALL A DETUNED PFC SYSTEM?

The installation of detuned (reactor-connected) capacitors is designed to force the resonant frequency of the network below the
frequency of the lowest harmonic present, thereby ensuring no resonant circuit and, by implication, no amplification of harmonic
currents. Such an installation also has a partial filtering effect, reducing the level of voltage distortion on the supply, and is
recommended for all cases where the share of harmonic-generating loads (“non-linear loads”) is more than 10% of the rated
transformer power. The resonance frequency of a detuned capacitor is always below the frequency of the lowest harmonic pre-
sent. A close-tuned filter circuit however is tuned to a certain harmonic frequency and presents a very low impedance to the
individual harmonic current, diverting the majority of the current into the filter bank rather than the supply.

Detuned capacitors can in general be operated in any mains. In any case, they are a safer choice than non-detuned capacitors
and future-proof under the conditions of more and more deteriorating power quality in modern mains.

Attention: Non-detuned and detuned capacitors must never be combined together. »!«

We strongly advise to conduct a comprehensive mains analy- Installation of detuned
sis, including measurement of the harmonic content, before (reactor-connected)
designing and installing your power factor correction equip- L 1 L 2 L 3 capacitors
ment. In cases, however, where such analysis is not possible,
cautious and conservative assessment of the situation to be
expected shall be made by means of the general rules in
chart 3.

A detuned PFC system is also necessary
• if one or more harmonic voltages in the MV mains
are > 2 %, and/or
• if certain audio frequency control signals are used
(see page 10)

S : S T Detuning
OS
0 % ... 100 % non-detuned
> 10 % ... 50 % detuned
> 40 % ... 100 % detailed calculation needed,
installation of filter circuit if necessary

Abbreviations
S ... power of harmonic generating („non-linear“) loads
OS
in the own network
S ... rated transformer power or connection power
T
chart 3 pic. 1

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