CSLB C-10 Electrical ContractorElectrical Theory and CalculationsMedium
A client is installing a new 240V, 3-phase motor with a full-load current of 50 amps. If the motor has a power factor of 0.85, what is its approximate real power consumption?
- A20.8 kW
- B26.0 kW
- C17.6 kW
- D15.3 kW
Show answer & explanationAnswer & explanation
Correct answer: C. 17.6 kW
To find the real power for a three-phase motor, use the formula P = (√3 × V × I × PF) / 1000. Plugging in the given values, P = (√3 × 240V × 50A × 0.85) / 1000 = 17.66 kW.
Why the other options are wrong
- A. This might represent apparent power or an incorrect power factor application.
- B. This is likely the apparent power (S = √3 × V × I) without considering the power factor.
- D. This value would be incorrect, possibly from a calculation error or using a single-phase formula.
Three-Phase Real Power
Real power in a three-phase system is the actual power consumed by the load and is measured in watts (W) or kilowatts (kW). It accounts for the power factor.
- Formula: P = √3 × V_L × I_L × PF
- V_L is line-to-line voltage, I_L is line current, PF is power factor.
- Measured in Watts (W) or kilowatts (kW).
Memory trick: Real Power is Root-3 times Volts, Amps, and Power Factor.