What are the functions of circuit breakers? Detailed explanation of the working principle of circuit breakers
When a fault occurs in the system, the protection of the fault element acts and its circuit breaker fails to trip, the protection of the fault element acts on the adjacent circuit breaker of the substation to trip, and if conditions permit, the channel can be used to make the related circuit breakers at the remote end at the same time. The tripped wiring is called breaker failure protection.
Generally, after the phase current element judged by phase separation operates, two sets of starting contacts are output, which are connected in series with the external action protection contacts to protect the starting failure when the line, bus tie or sectional circuit breaker fails.
What are the functions of circuit breakers
Circuit breakers are mainly used in motors, large-capacity transformers and substations that frequently break loads. The circuit breaker has the function of breaking the accident load, and cooperates with various relay protections to protect electrical equipment or lines.
Circuit breakers are generally used in low-voltage lighting and power parts, which can automatically cut off the circuit; circuit breakers also have many functions such as overload and short-circuit protection, but once there is a problem with the load at the lower end, maintenance is required. The role of the circuit breaker, and the creepage distance of the circuit breaker is not enough.
Now there is a circuit breaker with isolation function, which combines the functions of an ordinary circuit breaker and an isolation switch. The circuit breaker with isolation function can also be a physical isolation switch. In fact, the isolation switch generally cannot be operated with load, while the circuit breaker has protection functions such as short circuit, overload protection, undervoltage and so on.
Detailed explanation of the working principle of circuit breakers
Basic: The simplest circuit protection device is the fuse. A fuse is just a very thin wire, with a protective sheath attached to the circuit. When the circuit is closed, all current must flow through the fuse – the current at the fuse is the same as the current at other points on the same circuit. This fuse is designed to blow when the temperature reaches a certain level. A blown fuse can create an open circuit that prevents excess current from damaging the house wiring. The problem with a fuse is that it only works once. Whenever the fuse is blown, it must be replaced with a new one. A circuit breaker can perform the same function as a fuse, but can be used repeatedly. As long as the current reaches a dangerous level, it can instantly create an open circuit.
Basic working principle: The live wire in the circuit is connected to both ends of the switch. When the switch is placed in the ON state, current flows from the bottom terminal, through the electromagnet, the moving contactor, the static contactor, and finally the top terminal. The current can magnetize the electromagnet. The magnetic force produced by an electromagnet increases as the current increases, and if the current decreases, the magnetic force decreases. When the current jumps to dangerous levels, the electromagnet generates enough magnetic force to pull a metal rod attached to the switch linkage. This tilts the moving contactor away from the static contactor, breaking the circuit. The current is also interrupted. The design of the bimetal strips is based on the same principle, the difference is that instead of powering the electromagnets, the strips are allowed to bend on their own under high current, which in turn activates the linkage. Other circuit breakers are filled with explosives to displace the switch. When the current exceeds a certain level, the explosive material is ignited, which in turn drives the piston to open the switch
Enhanced: More advanced circuit breakers do away with simple electrical devices in favor of electronics (semiconductor devices) to monitor current levels. A ground fault circuit interrupter (GFCI) is a new type of circuit breaker. This circuit breaker not only prevents damage to the wiring in the house, but also protects people from electric shocks.
Enhanced working principle: The GFCI constantly monitors the current on the neutral and live wires in the circuit. When all is well, the current should be exactly the same on both wires. Once the live wire is directly grounded (like someone accidentally touches the live wire), the current on the live wire will suddenly spike, but the neutral wire will not. The GFCI immediately shuts down the circuit upon detecting this condition to prevent electric shock injuries. Because the GFCI doesn’t have to wait for the current to rise to dangerous levels to take action, it reacts much faster than traditional circuit breakers.
Post time: Mar-30-2023