What is the purpose of a voltage relay?

A voltage relay is designed primarily to monitor electrical systems and respond when voltage levels deviate from predetermined thresholds. Its main function is to detect power loss or significant drops in voltage. When such a condition occurs, the voltage relay activates a switchover mechanism, which typically entails switching to an alternative power source, such as a backup generator or another power grid. This automatic response helps maintain continuous service and prevents system outages during a power failure.

In the context of the question, the option that describes the purpose of a voltage relay aligns with its main role of ensuring that power supply remains stable and uninterrupted by managing switchover protocols. Other functions such as regulating pressure or increasing voltage supply do not relate to what a voltage relay specifically does. Protection against electrical surges is generally managed by surge protectors and voltage clamping devices, which serve a different purpose than that of a voltage relay.