The Relationship Between kW and A When Calculating Contactor Power

kW (kilowatt) is a unit of power, and A (ampere) is a unit of current. They cannot be directly converted; a connection must be established through voltage (V) and power factor (PF).

Basic Relationship Formula

The basic relationship between power (P), voltage (U), and current (I) is:

P = U × I (Power = Voltage × Current)

From this formula, the following can be derived:

I = P / U (Current = Power / Voltage)

P = I × U (Power = Current × Voltage)

Specific Conversion Formulas

1. DC (Direct Current) Circuits

A = (kW × 1000) / V

– Example: For a power of 1 kW and a voltage of 100 V, the current I = (1×1000)/100 = 10 A

2. AC (Alternating Current) Single-Phase Circuits

A = (kW × 1000) / (V × PF)

– PF (Power Factor): The ratio of real power to apparent power in an AC circuit, ranging from 0 to 1.

– Example: For a power of 1 kW, a voltage of 220 V, and PF = 0.8, the current I = (1×1000)/(220×0.8) ≈ 5.68 A

3. AC (Alternating Current) Three-Phase Circuits

A = (kW × 1000) / (V × √3 × PF)

– √3 ≈ 1.732

– Example: For a power of 10 kW, a voltage of 380 V, and PF = 0.9, the current I = (10×1000)/(380×1.732×0.9) ≈ 16.99 A

Why Direct Conversion Is Not Possible?

kW measures the rate of energy conversion, while A measures the rate of charge flow—they describe different physical quantities.

– 1 kW = 1000 W = 1000 V·A (1 kilowatt = 1000 watts = 1000 volt-amperes)

– For the same power, the higher the voltage, the lower the current, and vice versa.

Practical Conversion Examples

Summary

The relationship between kW and A is determined by the formula P = U × I. To convert between them, you must know the voltage and (for AC circuits) the power factor.

Remember: Power = Voltage × Current—this is a fundamental formula for understanding electrical systems.