Solar Flare wrote:

Notch filters are always good selective units...

The R in these series RLC circuts broadens the notch and uses real power.
How much would a 4.7 uF cap in parallel with a 150 watt 277 V load
with a 10% 3rd harmonic distortion raise the power factor?

With 1/(377C) = 564 ohms at 60 Hz and 277 V and L = 1/((2Pi180)^2x4.7x10^-6)
= 0.166 henrys in series to resonate at 180 Hz, limiting 60 Hz ripple current
requires Z = sqr(R^2+(wL-1/(wC)^2) = 564, ie R^2+(377x0.166-564)^2 = 564^2,
ie R = sqr(564^2-251291) = 258 ohms. With how many real watts?

How much would that raise the power factor?

Nick