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Engineering Design Information

Useful Electrical Formulas for Determining Amperes, Horsepower, Kilowatts and Kilovolt Amperes

    Alternating Current  
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.

PFC Formulas
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.

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