Circuit breaker

Circuit breakers are used in electrical engineering to automatically switch off electrical circuits or individual consumers in the event of fault currents or when the permissible current or voltage values are exceeded (overcurrent, fault current, electric arc, ...).

Basics

A circuit breaker automatically disconnects the circuit as soon as its rated current is exceeded by a certain factor. This protects the consumer located in the line behind this switch or the line from damage or destruction by the thermal effect of the current. So that the circuit breaker can fulfill its task, it consists of several function blocks: the current measurement, the contact system and the switching mechanism.

Circuit breaker types

For the protection of lines , see miniature circuit breaker

For the protection of devices, see motor protection switch

Protection against fault currents see ground fault circuit interrupter (GFCI) , formerly protection against dangerous contact voltage see fault voltage protection circuit

Protection against arcing and thus fire protection see arc fault protection device (AFDD circuit breaker)

Named after the type of current measurement and tripping, a distinction is made between thermal, magnetic or electronically controlled circuit breakers. All types have certain advantages and disadvantages, so there are also combinations of the processes in order to combine the best properties for the respective application (thermomagnetic circuit breaker and its combination, the FI circuit breaker or the AFDD circuit breaker).

Thermal release

This has a bimetallic strip or a concave bimetallic disk through which the current flows. The bimetal heats up depending on the current strength. This bends the bimetal and triggers the switching mechanism against the pressure of a spring - the circuit is disconnected.

Magnetic release

Here the current flows through a coil (electrical engineering) which, depending on the strength of the current flowing in it, generates a magnetic field . As soon as this magnetic field reaches a certain strength, the switching mechanism is triggered and the current flow is interrupted.

There is a hydraulic element in the coil so that the circuit breaker does not switch off in the event of brief starting currents, such as with motors or transformers. Depending on the viscosity of the oil, this causes a short or long delay, from a fraction of a second to a few minutes. In the event of a short circuit, e.g. B. 10 times the nominal current, however, this does not result in a delay: The magnetic field of the coil is strong enough to trigger the circuit breaker immediately and interrupt the current. This principle is called hydraulic-magnetic .

The residual current circuit breaker also uses magnetic tripping.

Electronically controlled release

The electronically controlled tripping is used for the intelligent detection of arcs or other complex types of fault currents.

literature

Günter Springer: Expertise in electrical engineering. 18th edition, Verlag - Europa - Lehrmittel, Wuppertal, 1989, ISBN 3-8085-3018-9
Günter Boy, Horst Flachmann, Otto Mai: The master's examination in electrical machines and control technology. 4th edition, Vogel Buchverlag, Würzburg, 1983, ISBN 3-8023-0725-9