A circuit breaker is a switching device capable of closing, carrying, and breaking current under normal circuit conditions and capable of closing and breaking current under abnormal circuit conditions for a specified period of time. Circuit breakers are divided into high-voltage circuit breakers and low-voltage circuit breakers according to their scope of use. The division of high and low voltage boundary lines is rather vague. Generally, 3 kV or more are called high-voltage electrical appliances.

 

Circuit breakers can be used to distribute electrical energy. Asynchronous motors are activated infrequently to protect power lines and motors. When they are severely overloaded or short-circuited or under-voltage faults, the circuit can be shut off automatically. Its function is equivalent to a fuse switch. In combination with over-heat relays. In addition, it is not necessary to change parts after breaking the fault current. At present, it has been widely used.

 

Electricity is an extremely important link in the generation, delivery and use of electricity. The distribution system includes transformers and various high- and low-voltage electrical equipment. Low-voltage circuit breakers are widely used appliances.

 

Circuit breaker working principle

 

Circuit breakers generally consist of a contact system, an arc extinguishing system, an operating mechanism, a trip unit, a housing, and the like.

 

When a short circuit occurs, a magnetic field generated by a large current (typically 10 to 12 times) overcomes the reaction force spring, and the tripping device pulls the operating mechanism to actuate and the switch trips instantaneously. When overloaded, the current increases and the heat builds up. The bimetal deforms to a certain degree and pushes the mechanism (the greater the current, the shorter the operating time).

 

There are electronic type, the use of transformers to collect the current level of each phase, compared with the set value, when the current is abnormal, the microprocessor sends a signal, so that the electronic trip unit drives the operation mechanism.

 

The role of the circuit breaker is to cut off and connect the load circuit, and cut off the fault circuit to prevent accidents from expanding and ensure safe operation. The high-voltage circuit breaker to break 1500V, current 1500-2000A arc, these arcs can be extended to 2m and continue to burn without extinguishing. Therefore, arc extinguishing is a problem that high voltage circuit breakers must solve.

 

The principle of arc quenching is mainly to cool the arc to weaken the heat release. On the other hand, the arc is used to stretch the arc to reinforce the compounding and diffusion of charged particles, and at the same time, the charged particles in the arc gap are blown away, and the dielectric strength of the medium is rapidly restored.

 

Low-voltage circuit breakers, also known as automatic air switches, can be used to switch on and off the load circuit and can also be used to control motors that do not start very often. Its function is equivalent to some or all of the functions of the switch, over-current relay, voltage-loss relay, thermal relay and leakage protector, etc. It is an important protection appliance in low-voltage distribution network.

 

Low-voltage circuit breakers have a variety of protection functions (overload, short circuit, undervoltage protection, etc.), adjustable operating values, high breaking capacity, easy operation, and safety, so they are widely used. Structure and working principle Low-voltage circuit breakers consist of operating mechanisms, contacts, protection devices (various trip units), and arc extinguishing systems.

 

The main contacts of the low-voltage circuit breaker are manually operated or electrically closed. After the main contact is closed, the free tripping mechanism locks the main contact in the closing position. The coil of the overcurrent release and the thermal element of the thermal release are connected in series with the main circuit and the coil of the undervoltage release is connected in parallel with the supply. When the circuit is short-circuited or severely overloaded, the armature of the over-current release pulls in, causing the free tripping mechanism to act, and the main contact opens the main circuit. When the circuit is overloaded, the thermal element of the thermal release heats up to bend the bimetal and push the free tripping mechanism. When the circuit is under voltage, the armature of the undervoltage release releases. The free trip mechanism is also actuated. The shunt release is used for remote control. In normal operation, the coil is powered off. When distance control is required, press the start button to energize the coil.