Temperature Limiter

Transformers must be suitably protected against impermissibly high temperatures in the event of overload or short circuit. A number of protective devices (fuses, magnetic and thermo-magnetic switches, overload releases, temperature limiters, etc.) are possible and suitable depending on the application.

A temperature limiter cannot be adjusted by the user and, if a transformer is not used as specified, limits its temperature by opening the circuit or reducing the current.
A self-resetting temperature limiter (“temperature monitor”) restores the current flow as soon as the transformer has cooled down. A temperature limiter that does not reset automatically also requires manual intervention.
A “thermal fuse” or “temperature fuse” must be replaced after it has responded once. Usually, this involves replacing the entire transformer.

Small transformers – especially small print transformers – in a conditionally short-circuit-proof design are often equipped with thermal fuses permanently built into the transformer. After an overload or short circuit, the transformer must be replaced.
Alternatively, automatically resetting bimetal thermal switches (“temperature monitors”) can be installed, but these require a minimum size for space reasons and a certain unit value for commercial reasons.

Temperature monitors, for example bimetal normally open or normally closed contacts, can be installed in the windings and their contacts routed to terminals. After installing the transformers in a system or equipment, the user has an easy-to-handle signal for control or warning purposes or for emergency shutdown.

See also: Short-circuit strength