Those magnetic materials are best suited for making armature and transform cores which have ........

Question

Those magnetic materials are best suited for making armature and transform cores which have ...........permeability and ...........hysteresis loss

Examoogle · Accepted Answer

High, low

Explanation: Magnetic materials for cores must have high permeability to allow easy flux concentration and low hysteresis loss to minimize energy dissipation during rapid magnetic field reversals. Materials like Silicon Steel are typically used for this purpose to ensure efficiency in transformers and rotating machines.

Working Principle: The hysteresis loss in a magnetic material is proportional to the area enclosed by the B-H loop. A material with high permeability and low coercivity results in a 'narrow' B-H loop, reducing the energy wasted as heat ($W_h = \oint H dB$) per cycle. Consequently, this keeps the machine operating at maximum efficiency by reducing core losses.

Key Formulas: $W_h = \eta B_{max}^{1.6} f V$ — Steinmetz hysteresis loss formula; $\mu_r = \frac{B}{\mu_0 H}$ — Relative permeability definition

Key Points: High permeability minimizes the magnetizing current requirement.; Low hysteresis loss is achieved by using soft magnetic materials.; Silicon steel is the industrial standard for transformer cores to keep these parameters optimal.; Eddy current losses are further reduced by using laminated cores.

Advantages: Improved energy efficiency of the electrical machine; Reduction in core temperature rise during operation

Disadvantages: High permeability materials often have lower saturation flux density; Increased manufacturing complexity due to lamination requirements

Applications: Power and Distribution Transformers; Armature cores of DC machines and Induction motors

Additional Info: The area of the B-H loop is directly proportional to the hysteresis loss in Joules per cycle.. Option A is incorrect because high hysteresis loss leads to excessive heating; Option C and D are incorrect because low permeability would require much larger magnetizing currents to produce the same flux.

Answer: B is correct — Magnetic cores must have high permeability for efficient flux paths and low hysteresis loss to minimize thermal waste.

Exam Tip: Always remember: 'Soft' magnetic materials (e.g., Silicon Steel) are for cores (High $\mu$, Low loss), while 'Hard' magnetic materials (e.g., Alnico) are for permanent magnets (High coercivity).

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