Question

Analyze the implications of using a hard magnetic material in the stator of an electric motor instead of a soft magnetic material.

• A. Increased energy efficiency due to better magnetic saturation.
• B. Reduced electrical losses due to lower coercivity.
• C. Increased energy losses due to higher coercivity.
• D. Enhanced mechanical strength and durability of the motor.

Hint:

Magnetic Materials for Motors/Transformers. Cores subjected to changing flux require Soft Magnetic Materials (low coercivity, narrow hysteresis loop) to minimize energy losses (hysteresis + eddy currents). Hard Magnetic Materials (high coercivity) are used for Permanent Magnets.

Answer 1

The Correct Option is C

The stator core of most electric motors carries a time-varying magnetic flux (due to AC currents in the windings).
To minimize energy losses associated with this changing flux, the core material should be easily magnetized and demagnetized.
This requires a *soft* magnetic material, characterized by: - Low coercivity (H\(_c\)): Easy to demagnetize.
- Low retentivity (B\(_r\)): Low residual magnetism.
- Narrow hysteresis loop: Minimizes energy loss per cycle (hysteresis loss).
- High permeability: Easy to magnetize.
- High electrical resistivity: Reduces eddy current losses.
A *hard* magnetic material (used for permanent magnets) has high coercivity and high retentivity, resulting in a wide hysteresis loop and significant energy loss when subjected to magnetization cycles.
Using a hard magnetic material in the stator core would lead to very large hysteresis losses, drastically reducing the motor's efficiency.
Option (3) correctly identifies increased energy losses due to higher coercivity as the main negative implication.
Option (2) describes the benefit of *low* coercivity (soft magnets).
Option (1) is incorrect; efficiency would decrease.
Option (4) is irrelevant to the magnetic material choice for the core's primary function.