What primarily affects the operating speed of a protective relay?

The operating speed of a protective relay is primarily influenced by spring tension. This is because many mechanical relays use springs to operate their contacts, and the force exerted by these springs determines how quickly the relay can respond to changes in system conditions. When a fault occurs, the relay must operate rapidly to disconnect the faulty section of the circuit and prevent damage. Increased spring tension can lead to a faster operation because it reduces the time it takes for the relay’s mechanism to activate.

Other factors, such as temperature, voltage level, and current capacity, may impact the performance and reliability of the relay but do not directly dictate its speed of operation in the same way that spring tension does. For instance, extreme temperatures can affect the materials' properties but won't necessarily cause a direct change in the speed of operation, while voltage and current levels primarily relate to the relay's ability to handle fault conditions rather than how fast it actuates.