Which device is not classified as an electromagnetic relay?

The Buchholz relay is indeed not classified as an electromagnetic relay. This type of relay is specifically used as a protection device in oil-filled transformers and is designed to detect gas accumulation and oil flow. It operates based on the principles of gas detection and oil movement rather than electromagnetic forces.

In contrast, other types of relays, such as solid-state relays, electromechanical relays, and thermal relays, all operate based on electromagnetic principles. Solid-state relays use semiconductor devices to perform switching functions without moving parts, while electromechanical relays rely on physical movement of a mechanical armature influenced by an electromagnetic field. Thermal relays also utilize thermal effects, often linked to electrical currents, to break or make connections in an electrical circuit. Each of these devices has electromagnetic characteristics, distinguishing them from the Buchholz relay’s operation mechanism.