Thumb rules

Here I am giving few thumb rules for electrical calculations:

kVA to Current

Current= 1.443 x kVA ( 3 phase 400 Volts)

Current= 1.39 x kVA ( 3 phase 415 Volts)

Eg:- 1000 kVA Transformer’s Full load current on LT side

1.443 x 1000= 1443 Amperes ( 3 phase 400 Volts)

1.39 x 1000 = 1390 Amperes ( 3 phase 415 Volts)

kW to Current ( power factor assumed as 0.8)

Current= 1.8 x kW (3 phase 400 Volts)

Current= 1.74 x kW (3 phase 415 Volts)

Power in 3 Phase circuit

kW= \/ 3 x V x I x cos φ

V= Line voltage ( 400 or 415 Volts)

I = Per phase current (Ampere)  

Power factor correction Capacitor 

Capacitor size=  kW * (tan θ 2 - tan θ1)   (kVAR)  

cos θ1 = system power factor(say 0.8)

cos θ2 = Desired power factor( say 0.9)

Capacitor current

Ic = kVAr / \/ 3 x V   ( V= 0.400 or 0.415 kV )

Breaker and Cable size for capacitor = 1.35 x Capacitor current (Minimum)