A circuit breaker uses an electromagnet.
Explain why the current is cut off by a circuit breaker if it is larger than a certain value.
A circuit breaker is a safety device used to protect electrical circuits from overcurrent situations. It automatically cuts off the flow of current if it exceeds a certain value. This is achieved through the use of an electromagnet.
To understand why the current is cut off when it exceeds a certain value, let's go through the operation of a typical circuit breaker:
1. Bimetallic Strip: Inside a circuit breaker, there is a bimetallic strip made up of two different metals with different rates of expansion when heated. When the current passing through the circuit breaker exceeds its rated value, it causes an increase in temperature.
2. Heating Effect: Due to the heating effect of the excess current, the bimetallic strip starts bending or deforming. The extent of the deformation depends on the magnitude of the overcurrent flowing through the circuit.
3. Tripping Mechanism: As the bimetallic strip deforms, it activates a tripping mechanism. The most common mechanism is the release of a latch or lever, which is holding the contacts of the circuit breaker closed.
4. Electromagnet: Once the contacts are released, they are rapidly pulled apart by an electromagnet. The electromagnet is energized when the bimetallic strip bends and completes the circuit. The magnetic field produced by the electromagnet exerts a force on a metal armature, which aids in opening the contacts.
5. Current Interruption: When the contacts open, the circuit is broken, and the flow of current stops. This interruption of current flow protects the electrical appliances, wirings, and reduces the risk of electrical hazards like fires or damage to equipment.
In summary, when the current flowing through a circuit breaker exceeds a certain value, a bimetallic strip heats up, causing it to bend and activate the tripping mechanism. The tripping mechanism, in turn, opens the contacts with the help of an electromagnet, interrupting the current flow and cutting off the excessive current. This helps prevent damage to the electrical system and ensures the safety of the circuit.