# Cut Off Frequency in three phase LC filter

Good afternoon all

My question is what will be the formula to calculate cut off frequency of attached LC filter.

Its a three phase LC filter.

$(L1=L2=L3= 6.1 \mathrm{mH}) \;\mathrm{and} \;(C1=C2=C3=29\mathrm{uF}).$

I know formula for single phase LC filter is $\dfrac{1}{2 \pi \sqrt{LC}}$.

What wondering same will apply to three phase system or its different. Please Help. Also what is doffrence between cut off frequency and resonance frequency.

• The $1 \over {2 \pi \sqrt{LC}}$ gives the resonant frequency which is different from the cutoff. At resonant frequency gain is maximum whereas at cutoff frequency the output power is half of the input power. I think a good start would be to convert the delta arrangement of capacitors to a Y one but I'm not too sure of this. Are you sure this is a filter?; as its looking more of a power-factor correction bank than a filter. Jul 7, 2015 at 8:33
• Thanks for answer, Its a harmonics Filter , also it will help to improve power factor. Jul 8, 2015 at 8:35