The power mentioned on the nameplate of an electric motor indicates

Question

Examoogle · Accepted Answer

Option D: the output power available at the shaft

Explanation & Concepts:
The power rating specified on an electric motor nameplate represents the mechanical power output available at the shaft. This rating reflects the maximum power the motor can deliver continuously under specified operating conditions without exceeding thermal limits.

Working Principle: An electric motor consumes electrical energy ($P_{in} = \sqrt{3} V_L I_L \cos \phi$) and converts it into mechanical work at the shaft. Due to internal losses such as copper loss ($I^2R$), iron loss, and mechanical friction/windage, the mechanical output power ($P_{out}$) is always less than the electrical power input. The efficiency is defined as $\eta = \frac{P_{out}}{P_{in}}$.

Key Formulas: $P_{out} = 	au \cdot \omega$ — mechanical power output where $	au$ is torque and $\omega$ is angular velocity; $\eta = \frac{P_{out}}{P_{in}} 	imes 100\%$ — efficiency of the motor

Key Points: Motor ratings are based on the continuous duty cycle.; Mechanical power is usually expressed in kW or HP (Horsepower).; Operating above nameplate power causes excessive heating and insulation degradation.

Advantages: Ensures safe equipment operation; Prevents motor burnout due to overloading

Disadvantages: Over-dimensioning the motor leads to low power factor and poor efficiency; Under-dimensioning leads to stalling or thermal overload

Applications: Industrial drives; HVAC systems; Pump and compressor operations

Additional Info: Nameplates also specify rated voltage, current, frequency, and speed (RPM).. Option A is incorrect because kW input is typically higher than output due to losses.. Option B is incorrect as kVA represents the apparent power input, not the mechanical output.

Answer: D is correct — The nameplate rating specifies the mechanical power output available at the shaft.

Exam Tip: Always distinguish between Electrical Input (kVA/kW) and Mechanical Output (HP/kW). Efficiency is the bridge between these two.

Examoogle · Answer

Option A: the power drawn in kW

Examoogle · Answer

Option B: the power drawn in kVA

Examoogle · Answer

Option C: the gross power

Correct Answer

Discussion (0)

Correct Answer

Related Questions

Discussion (0)