# Reactor for Capacitor Bank

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### #1 Guest__*

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Posted 28 August 2005 - 03:20 PM

Hi, as we known reactor commonly have 5%, 7% and 11%. How's the difference and criteria for we to select ? If I install a 5% reactor with a 300kVar capacitor, will its rating being decreased by 300kVar - 300kVar x 5% = 285kVar ?

Do we need to first calculate the tuned frequency of capacitor with detuned reactor before we choose the percentage of reactor ?

Some manufacturer catalogue written the tuned order is "2.3, 2.8 and 3.2" (not sure for the exact value), is it referring to those 5%, 7% and 11% ?

Also, I have a case, user previously installed a capacitor bank but found the system with high harmonic content later. Is it possible for we to add the reactor afterwards by series connect the reactor with other brand to the capacitor bank?

Peter

### #2 marke

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Posted 28 August 2005 - 07:06 PM

Hello Peter

Detuning reactors are used to reduce the resonant frequency of the capacitors and supply inductance to a frequency well below the harmonics that are likely to be present and to reduce the effect of harmonic currents flowing into the capacitors.

Harmonic current flowing into the capacitors causes excess heat and reduces the lifetime of the capacitors.
If the capacitors resonate with the reactance of the supply at any harmonic frequencies, there can be very large harmonic currents and associated voltages.

The percentage (typically 5%, 7% or 11%) of the reactor is the effective reduction in the reactance of the capacitors by putting the reactors in series. The higher the percentage, the lower the tuned frequency and the higher the impedance to harmonic currents.
Above the resonant frequency, the series L-C circuit looks inductive rather than capacitive and so the impedance rises with frequency rather than falls.
The 7% option is a good compromise. If harmonics are particularly high, then look at the 11% option. If harmonics are a very minor problem, then you could consider a 5% reactor.

Best regards,

### #3 Guest__*

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Posted 29 August 2005 - 02:38 PM

Dear Marke,