# How to Calculate Power of A Motor?

Question: In our life, we often need to calculate the power of a

**motor**. If the power of a**motor**is 11KW, then P = UI, does it mean that the**motor**voltage is 380V and the current is 28.9? How to calculate the electricity used by the**motor**per hour?Answer: The rated voltage U and the rated current I on the nameplate of the

**motor**are normally incoming line voltage and current.Derivation:

P single-phase active power circuit = Up * Ip * cos phi, active three-phase circuit P = 3 * Up * Ip * cos phi, where Up is the phase voltage, Ip is the phase current, cos phi power factor, Phi is the current lag voltage angle.

On the

**motor**nameplate, if it's a star connection, the line current I = phase current Ip, the line voltage U = 1.732 * Up, so P = 3 * (U / 1.732) * I * cosphi * efficiency = 1.732 * U * I * cosphi * efficiency.If it's a delta connection, the line voltage U = phase voltage Up, the line current I = 1.732 * Ip, it is P = 3 * U * (I / 1.732) * cosphi * efficiency = 1.732 * U * I * cosphi * efficiency.

So regardless Star connection and delta connection, electrical power equals to P = 1.732 * U * I * cosphi * efficiency.

Energy = power * time, commonly used energy units: degrees (kWh) = Power (kW) * Time (h).