To calculate electrical power in a three-phase circuit, you need to consider both the active (real) power and the apparent power. Active power is the actual power consumed by the load and is measured in watts (W), while apparent power represents the total power, including both active and reactive components, and is measured in volt-amperes (VA).
In a balanced three-phase circuit, where all three phases have the same voltage and current, the formulas for calculating power are as follows:
Active Power (P) in watts (W):
P = √3 × Vph × Iph × cos(θ)
Where:
√3 ≈ 1.732 (square root of 3)
Vph is the phase voltage in volts (V)
Iph is the phase current in amperes (A)
cos(θ) is the power factor (a dimensionless value between 0 and 1)
Apparent Power (S) in volt-amperes (VA):
S = √3 × Vph × Iph
In a balanced system, the power factor (cos(θ)) is typically known or can be determined based on the load type. For resistive loads (e.g., heaters), the power factor is 1 (cos(θ) = 1) since there is no reactive power. For most other loads, such as motors or electronic equipment, the power factor is less than 1 due to the presence of reactive power.
To find the real power in an unbalanced three-phase circuit or to calculate power in a more complex scenario, you may need to use vector representations and complex numbers, but for balanced systems, the above formulas should suffice.