With direct current, the electrical power is the product of voltage and current. With AC voltage, current and voltage fluctuate. The product of voltage and current describes the apparent power. This is divided into active power (used power: U*I* cosϕ) and reactive power (unused power: U*I* sinϕ / or apparent power minus active power). For three-phase current, the chaining factor must still be taken into account. So the calculation for the apparent power is U*I*.