Wenzhou Korlen Electric Appliances Co., Ltd.
A circuit breaker is a switching device that can close, carry and break current under normal circuit conditions and can close and carry current under the abnormal loop conditions within a specified time. Circuit breakers are divided into high-voltage circuit breakers and low-voltage circuit breakers according to their use range. The division of high and low voltage lines is relatively vague. Generally, 3kV or more is called high-voltage electrical equipment.
Circuit breakers can be used to distribute electrical energy, start asynchronous motors infrequently, protect power lines and motors, and automatically cut off circuits when they are severely overloaded or short-circuited or under-voltage faults. Their functions are equivalent to fuse switches. Combined with over-heat relays and the like. Moreover, it is generally not necessary to change parts after breaking the fault current. At present, it has been widely used.
Power generation is an extremely important part of the generation, transmission and use of electricity. The power distribution system includes transformers and various high and low voltage electrical equipment, and the low voltage circuit breaker is a kind of electrical appliance with a large amount of use.
Circuit breaker working principle
The circuit breaker is generally composed of a contact system, an arc extinguishing system, an operating mechanism, a trip unit, a casing, and the like.
When short-circuited, the magnetic field generated by a large current (generally 10 to 12 times) overcomes the reaction force spring, the trip unit pulls the operating mechanism, and the switch instantaneously trips. When overloaded, the current becomes larger, the heat is increased, and the bimetal is deformed to a certain extent to push the mechanism (the larger the current, the shorter the action time).
If there is an electronic type, the current of each phase is collected by using a transformer, and compared with the set value, when the current is abnormal, the microprocessor sends a signal to cause the electronic trip unit to drive the operating mechanism.
The function of the circuit breaker is to cut off and close the load circuit, and cut off the fault circuit to prevent accidents from expanding and ensure safe operation. The high-voltage circuit breaker is to break 1500V, the current is 1500-2000A arc, these arcs can be extended to 2m and continue to burn without extinguishing. Therefore, arc extinguishing is a problem that must be solved by high voltage circuit breakers.
The principle of arc-extinguishing arc is mainly to cool the arc to attenuate the heat release. On the other hand, the arc is used to stretch the arc to enhance the recombination and diffusion of the charged particles, and at the same time, the charged particles in the arc gap are blown off, and the dielectric strength of the medium is quickly restored.
Low-voltage circuit breakers, also known as automatic air switches, can be used to switch the load circuit on and off, as well as to control motors that are not frequently started. Its function is equivalent to the sum of all or all of the functions of the knife switch, over current relay, voltage loss relay, thermal relay and leakage protector. It is an important protection device in the low voltage distribution network.
Low-voltage circuit breakers are widely used because of their various protection functions (overload, short circuit, under voltage protection, etc.), adjustable action values, high breaking capacity, easy operation and safety. Structure and working principle The low-voltage circuit breaker is composed of operating mechanism, contacts, protection devices (various trip units), arc extinguishing system and so on.
The main contacts of the low voltage circuit breaker are manually operated or electrically closed. After the main contact is closed, the free trip mechanism locks the main contact in the closed position. The coil of the overcurrent release and the thermal element of the thermal trip are connected in series with the main circuit, and the coil of the undervoltage release is connected in parallel with the power supply. When the circuit is short-circuited or severely overloaded, the armature of the overcurrent release pulls in, causing the free trip mechanism to act and the main contact to open the main circuit. When the circuit is overloaded, the heat element of the thermal tripper generates heat to bend the bimetal and push the free trip mechanism. When the circuit is under voltage, the armature of the undervoltage release is released. The free trip mechanism is also actuated. The shunt release is used for remote control. In normal operation, the coil is de-energized. When distance control is required, the start button is pressed to energize the coil.Breaker symbol
The picture above shows: the symbol of the circuit breaker
The figure is the graphical symbol of the circuit breaker in GB4728
The meaning of the breaker symbol
Inm - Circuit breaker frame class current A, which means the maximum switch and trip unit current value that can be installed in this circuit breaker.
In——The rated current A of the circuit breaker, which means the current value of the rated thermal release type selected in the circuit breaker, In=Ir1 in the non-adjustable fixed thermal release.
Ir1——The long delay setting current A of the circuit breaker, which means the current value set by the overload protection release of the circuit breaker.
Ir2——The short-delay setting current A of the circuit breaker, which means the current set by the short-delay trip of the circuit breaker. Its value is about 2~12Irl in the electronic adjustable trip unit. Tune.
Ir3——The instantaneous setting current A of the circuit breaker, which means the current set by the instantaneous release of the circuit breaker. Its value is in the non-adjustable fixed release, and the power distribution type is 5Irl and 10Irl. The motor protection type is 12Ir1, and in the electronic adjustable type, it is adjustable from 4 to 16Irl.
Ir4——The single-phase grounding setting current A of the circuit breaker, which means the current value of the grounding protection release when the single-phase grounding fault occurs in the circuit or equipment protected by the circuit breaker. Its value is 0.2~ 0.6Irl is adjustable left and right.
Ire——The leakage current A of the circuit breaker, which means the current value of the leakage protection tripping when the circuit or equipment protected by the circuit breaker has abnormal leakage current. Its value is several 0.03/0.1/0.3/0.5A.
Ir0——The circuit breaker pre-alarm action current A, which means that when the load current of the circuit breaker exceeds the preset current, the pre-alarm device sends an alarm indication signal, and its value is adjustable from 0.5 to lIr1.
Ir2——The tripping time setting value s of the short-delay trip unit is adjustable from 0.05 to 0.45s.