What does a potential transformer primarily measure?

A potential transformer is designed specifically to measure high voltage levels and to step down these high voltages to a lower, more manageable level for measurement and monitoring purposes. This functionality enables accurate voltage readings while ensuring the safety of equipment and personnel.

In power systems, potential transformers play a crucial role in transferring high voltage signals from the transmission lines to instruments or control systems that can work with lower voltage, thus facilitating the measurement of voltage for protection, control, or metering purposes.

This makes high voltage the primary focus of potential transformers, whereas the other choices, such as low voltage, medium voltage, and direct current, do not align with their intended use. Potential transformers are not typically used for low or medium voltage measurements, nor are they suited for measuring direct current, which is an entirely different process that often involves different types of sensors or transformers.