Before installs of capacitor
kVAri = kW*tan(thetai) ……… (1)
After installs of p.f.correction
kVArf = kW*tan(thetaf) …….. (2)
The value of capacitor, kVAr = kVAri – kVArf
equation (1) – (2)
kVAri – KVArf = kW*tan(thetai) – kW*tan(thetaf)
kVAr = kW*(tan(thetai) – tan(thetaf)) …… (3)
i = initial
f = final
theta = angle of power factor
kVAr = reactive power = 117.6
kW = real power = 100
assume that,
cos(thetai) = 0.85, therefore tan(thetai) = 0.6197
cos(thetaf) = 1, therefore tan(thetaf) = 0.0000
where
thetai = initial angle
thetaf = final angle
kVAri = initial reactive power
kVArf – final reactive power
kW = real power of electrical load
The reduction in current after installs of capacitor, Ir is:
Ir = [kVAi – kW*cos(thetai)]/(sqrt(3)*V) ……. (4)
where V in kV = nominal voltage supply from supply authority = 0.415kV
The reduction of power in cable = Ir^2*resistance of cable ………… (5)
assume that resistance of cable 0.005 ohm
From equation (3): kVAr = 100*(0.6197 – 0)
= 61.97
From equation (4): Ir = [117.6 – 100*0.85]/(1.732*0.415)
= 32.6/0.7188
= 45.4 Amperes
From equation (5): The reduction in power = 45.5^2*0.005
= 10.4 Watts