Formulas and rule of thumb 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)

Prolouge

The purpose of this blog is to share my experience and learning with others in the industry. I hope some of this information may be useful to someone out there who is trying to find out some technical information through a web search.

This blog is trying to give few technical information regarding distribution system design, with particular reference to Buildings. The information contained herein is generally based on practices followed as per British Standards(BS), IET Regulations 16th Edition and Indian Standards.

Disclaimer:

The information provided herein is given with the good intention of sharing of knowledge and the author is not responsible for any damage or loss whatsoever arising out of using the information contained herein.