Hi, I'm new to this Forum. I have a question that most supplier will print in their catalogue that a detuned reactor will generate over-voltage in capacitor series connected, thus a higher voltage capacitor has to used. Thus, if I have a system with 380V AC operated voltage, I was suggested to use a rated 440V AC capacitor. Do this means the actual voltage measured in capacitor terminal is 440V ? If the capacitor unit is 50kVAR in rated voltage 440V, this value also true for 380V operation voltage ?

Hello stccs

Welcome to the forum.

Detuning reactors are strongly recommended in environments where there are high harmonic currents.
The issue is that the capacitor appears as a very low impedance to the higher frequencies and therefore carries a higher current if there are harmonic voltages present. The impedance of the capacitor reduces with the inverse of the frequency, so the higher the harmonic, the lower the impedance and the higher the harmonic current through the capacitor.

For example if we have a capacitor that carries 10 Amps at 230V 50 Hz, and we have 2.3 volts at 500Hz (1%), then the current due to the 500Hz will be 1 Amp (10%).
The detuning reactors are put in series to ensure that the total impedance does not fall for increasing frequencies and therefore reduces the harmonic current that flows through the capacitors.

When you have a series reactor capacitor circuit, you have a resonant circuit. It is important that the reactors match the capacitors. These are specially sized to ensure that the series resonant circuit is well away from any likely harmonic frequencies.
Because of the resonance, transients will cause ringing voltages in the capacitors and these can be well above the supply voltage. It is recommended that the capacitors should be capable of withstanding 525 volts for an average supply or even higher for a bad supply.
When the KVAR rating for a capacitor is given, it is given at a particular voltage and frequency. This is because the current through the capacitor changes with voltage and frequency. The KVAR for a fixed frequency, increases with the square of the voltage.
Many manufacturers of power factor correction capacitors manufacture a range of capacitors for use with detuing reactors. These capacitors are designed for the higher voltage, but are given KVAR ratings at the nominal supply voltages.

Best regards,

1. The actual measured capacitor terminal voltage is higher. How much
higher depends on the size of the reactor. The 440 V you were recommended
might be a conservative capacitor rating.

2. Adding a detuned reactor does make the apparent size of the capacitor bank
increase. See my earlier post on "Detuned Reactors".

Thanks,
Submonkey

hello this is bt pagar i'm new to this forum , i'm doing project for engineering on power factor improvement/energy management i've read various leaflets of pf controller manufacturers indicating 7% detuned reactors in series with capacitors .
why 7% reactors are used ? how harmonics are improved in single phase loads ? what is a low pass filter ?
waiting for ur reply

thanking you

bt pagar

Hello bt pagar

Welcome to the forum.

Connecting an inductor in series with a capacitor creates a series tuned circuit.
It important to ensure that the series resonant circuit does not resonate at the line frequency or harmonics of it.
Using a 7% reactor ensures that the resonant frequency is well away from supply harmonics.

The use of detuning reactors reduces the harmonic currents flowing into the capacitors if the supply voltage is disorted.
Detuning reactors do not improve the haromincs in the connected load.

Best regards,
Mark.

Hi all,

Why %7 why not %14 or 5,6 what is criteria of choosing harmonic filter ?

Thanks.