Transformers are protected by fuses or circuit-interrupting devices such as breakers or circuit switchers with relays detecting faults and providing trip signals to the circuit-interrupting devices. A Buchholz relay is a gas-actuated relay installed between the transformer tank and conservator. Overheating Protection Thermal protection prevents insulation damage from excessive temperature: Fiber-optic sensors can directly measure temperature in the transformer. This guide focuses primarily on application of protective relays for the protection of power transformers. But when a transformer overheats, faces a sudden fault, or experiences overload-even for a few seconds-the entire system feels the impact. Machines slow down, production stops, and repair costs rise quickly.