The given question is related to the behavior of a short line under load conditions. A short transmission line is generally considered as a line with a length less than 250 km. In this case, the resistance and reactance of the line are equal. Let's analyze the behavior of the load under these conditions.

Resistance and Reactance of a Short Line

A short transmission line can be represented by an equivalent circuit consisting of resistance (R) and reactance (X). The resistance represents the real component of the line impedance, which is caused by the resistance of the conductors and losses in the line. The reactance represents the imaginary component of the line impedance, which is caused by the inductive and capacitive effects of the line.

Equal Resistance and Reactance

When the resistance and reactance of the line are equal, it means that the line impedance has an equal real and imaginary component. Mathematically, this can be represented as:

Z = R + jX

where Z is the line impedance, R is the resistance, and X is the reactance.

Load at Zero Regulation

Zero regulation refers to the condition where the voltage at the load end of the line remains constant, regardless of the load current. In other words, the voltage regulation is zero.

Under zero regulation, the power factor at the load end is unity (1), which means the load is purely resistive. However, in this case, the load is not purely resistive since the resistance and reactance of the line are equal.

- When the resistance and reactance of the line are equal, the load power factor will be 0.707 lead or lag.
- The load power factor is given by the angle between the resistance and reactance components of the line impedance.
- In this case, since the resistance and reactance are equal, the load power factor angle will be 45 degrees.
- A power factor angle of 45 degrees corresponds to a power factor of 0.707 lead or lag.

Therefore, the correct answer is option D: 0.707 lead.