The power rating of given on the name plate of a transformer indicates the

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Apparent power which it can supply

Explanation: The power rating of a transformer is expressed in kVA (kilovolt-amperes), which represents the apparent power. This rating is defined by the thermal limitations of the transformer (winding insulation and cooling capabilities) rather than the real power, which is dependent on the connected load power factor.

Working Principle: The internal losses in a transformer consist of copper losses (I^2R) and iron losses (hysteresis and eddy current). Copper losses depend on the current flowing through the windings, and iron losses depend on the voltage applied to the core. Since both current and voltage are independent of the load's power factor, the maximum safe capacity is constrained by the combination of voltage and current, i.e., $S = V 	imes I$.

Key Formulas: $S = V_{rms} \cdot I_{rms}$ — The formula for apparent power.; $P = S \cdot \cos(\phi)$ — The relation between real power (P) and apparent power (S), where $\cos(\phi)$ is the load power factor.

Key Points: Transformer rating is independent of the load's power factor.; Copper losses are proportional to the square of the current ($I^2R$).; Iron losses are primarily a function of the supply voltage and frequency.; Rating in kVA allows the manufacturer to specify a limit that covers both voltage and current stress.

Advantages: Simplifies transformer selection for diverse loads.; Provides a clear thermal capacity limit for engineers.

Disadvantages: Can lead to confusion if the user conflates kVA with kW.; Requires knowledge of power factor to calculate the actual useful real power.

Applications: Distribution transformers; Power grid infrastructure; Industrial motor drive supply

Additional Info: If a transformer is rated at 100 kVA, it means it can handle a combination of voltage and current such that their product does not exceed 100,000 VA.. Option A and D are incorrect because true power depends on the load's power factor, which is external to the transformer's design constraints.. Option C is incorrect because the transformer does not 'draw' power based on its rating; it supplies power based on the connected load.

Answer: B is correct — The kVA rating indicates the apparent power capacity of the transformer, which is determined by the maximum allowable voltage and current before thermal insulation damage occurs.

Exam Tip: Always remember that machines are rated by their physical limits (current for copper, voltage for insulation/core), leading to kVA ratings for transformers/alternators and kW ratings for motors (as they perform mechanical work).

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