Correct option is A
The efficiency of a transformer is given by the ratio of the output power to the input power, and it is affected by both core (iron) losses and copper (I²R) losses.
The core losses are constant regardless of the load, while the copper losses vary with the square of the load current.
For maximum efficiency, the total losses should be minimized. In a transformer, the condition for maximum efficiency is when the core losses equal the copper losses.
This condition is independent of the power factor of the load.
However, the power factor affects the load current for a given amount of power delivered to the load. At unity power factor (where the load is purely resistive), the load current is at its minimum for a given load power.
This minimizes the copper losses for the same amount of power delivered, leading to higher efficiency.
Considerations for Different Power Factors: Unity power factor (a): At unity power factor, the load current is minimum for a given power output. This minimizes the copper losses, helping achieve maximum efficiency.
Lagging power factor (b, c): At lagging power factors (like 0.6 or 0.8), the load current increases for the same power output because the power factor is less than 1. This increased current causes higher copper losses, reducing efficiency.
Leading power factor (d): Similarly, at a leading power factor of 0.6, the load current is higher than at unity power factor for the same power output, leading to increased copper losses and lower efficiency.
Therefore, the correct answer is:
(a) unity power factor
