Which of the following statements about equivalent circuit with core losses of single- phase motor is/are true

Question

Which of the following statements about equivalent circuit with core losses of single- phase motor is/are true? equipment is called no load current of the motor.

Examoogle · Accepted Answer

The correct answer is Option A: The current drawn by the induction motor when it is not coupled to the driven Both 1 and 2 are true. No-load current in an induction motor is the current drawn when the shaft is not coupled to any load. It consists of the magnetizing component, required to produce the revolving magnetic field, and the core-loss component, which accounts for eddy current and hysteresis losses.

Step-by-Step Solution & Concepts:
No-load current in an induction motor is the current drawn when the shaft is not coupled to any load. It consists of the magnetizing component, required to produce the revolving magnetic field, and the core-loss component, which accounts for eddy current and hysteresis losses.

Working Principle: When voltage is applied to the stator, the no-load current $I_0$ establishes the rotating magnetic flux $\Phi$ in the air gap to induce EMF in the rotor. The magnetizing component $I_m$ lags the voltage by nearly $90^\circ$ due to the high inductance of the stator winding. The core-loss component $I_w$ is in phase with the voltage, representing the power dissipated in the stator core.

Key Formulas: $I_0 = \sqrt{I_m^2 + I_w^2}$ — Total no-load current calculation; $\Phi_m \propto \frac{V}{f}$ — Flux relation to voltage and frequency

Key Points: No-load current is typically 20\% to 50\% of the full-load current.; The power factor of an induction motor at no load is very low (lagging).; The core losses include both hysteresis and eddy current losses in the stator laminations.

Advantages: Used to determine the shunt branch parameters in the equivalent circuit.; Helps in estimating core losses and magnetizing reactance.

Disadvantages: High no-load current can lead to poor power factor in lightly loaded conditions.; Not an efficient operating point for energy consumption.

Applications: No-load test of induction motors.; Calculation of core-loss resistance $R_c$ and magnetizing reactance $X_m$.

Additional Info: The magnetizing current $I_m$ is responsible for the air-gap flux.. The core-loss current $I_w$ provides for the power consumed in the stator core due to flux changes.

Answer: A is correct — The no-load current is defined by both its mechanical state (uncoupled) and its electromagnetic function (producing the air-gap magnetic field).

Exam Tip: Always remember that the no-load current is dominated by the magnetizing current component, which is why the power factor is very poor at no load.

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Option B: The no load current produces the magnetic field in the motor. Both 1 and 2 are not true

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Option C: Only 1 is true

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Option D: Only 2 is true

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