Useful Electrical Formulas for Determining Amperes, Horsepower, Kilowatts and Kilovolt Amperes
|To Find||Direct Current||Single Phase||Three Phase|
|Amperes when Horsepower is known||(HP x 746)/(V x Eff)||(HP x 746)/(V x Eff x PF)||(HP x 746)/(1.73 x V x Eff x PF)|
|Amperes when Kilowatts are known||(KW x 1000)/V||(KW x 1000)/(V x PF)||(KW x 1000)/(1.73 x V x PF)|
|Amperes when Kilovolt Amperes are known||(KVA x 1000)/V||(KVA x 1000)/V||(KVA x 1000)/1.73 x V|
|Kilowatts||(I x V)/1000||(I x V x PF)/1000||(I x V x 1.73 x PF)/1000|
|Kilovolt Amperes||(I x V)/1000||(I x V)/1000||(I x V x 1.73)/1000|
|Horsepower (Output)||(I x V x Eff)/746||(I x V x Eff x Pf)/746||(I x V x 1.73 x Eff x PF)/746|
Legend: I = Amperes; V = Phase-to-Phase Volts; Eff. = Efficiency expressed as a decimal (95% = 0.95); PF = Power Factor expressed as a decimal (85% = 0.85); KW = Kilowatts; KVA = Kilovolt Amperes; HP = Horsepower.
Fundamentals of Power Factor Correction
Power factor correction: A optimum PFC is designed based on the required demand on reactive power. The best method is to measure active and reactive power for a typical day and night time load.
Active Power: P(W) = √3 x V x I x cosΦ
Reactive Power: Q(var) = √3 x V x I x sinΦ
Apparent Power: S(VA) = √3 x V x I
Power Factor: COSΦ: = W/VA : active power (P) / apparent power (S)
Reactive Power Compensation: QC = P x (tanΦ1 – tanΦ2). tanΦ1 is derived from cosΦ1 which is the existing power factor. tanΦ2 is from cosΦ2 which is the desired power factor as recommended by the utility company.