A circuit breaker is a switching device capable of turning on, carrying and breaking the current in normal circuit conditions and of turning on, carrying and breaking the current in abnormal circuit conditions within a specified period of time. Circuit breaker according to its use range is divided into high voltage circuit breaker and low voltage circuit breaker, high and low voltage line division is more fuzzy, generally referred to as high voltage electrical appliances above 3kV.
Circuit breakers can be used to distribute electric energy, start asynchronous motors infrequently, protect the power line and motor, and automatically cut off the circuit when they occur serious overload or short circuit and undervoltage faults, its function is equivalent to the combination of fuse switch and overheat and underheat relay. And there is generally no need to change the parts after breaking the fault current. It has been widely used.
Electricity distribution is a very important link in the generation, transmission and use of electricity. Distribution system includes transformer and various high and low voltage electrical equipment, low voltage circuit breaker is a kind of use of a wide range of electrical equipment.
Working principle
The circuit breaker is generally composed of contact system, arc extinguishing system, operating mechanism, trip device, shell, etc.
When short circuit, the magnetic field generated by the large current (generally 10 to 12 times) overcomes the reaction spring, and the trip device pulls the operating mechanism to move, and the switch trips instantaneously. When overloaded, the current becomes larger, the heat is intensified, and the bimetallic sheet deforms to a certain extent to promote the mechanism action (the greater the current, the shorter the action time).
Electronic type, use the transformer to collect the current size of each phase, compared with the set value, when the current is abnormal, the microprocessor sends a signal, so that the electronic trip to drive the operating mechanism action.
The function of the circuit breaker is to cut off and switch on the load circuit, and cut off the fault circuit, prevent the expansion of the accident, ensure the safe operation. However, the high-voltage circuit breaker needs to break the 1500V arc with the current of 1500-2000A. These arcs can be stretched to 2m and still continue to burn. So arc extinguishing is a problem that high voltage circuit breaker must solve.
The principle of arc blowing is mainly to cool the arc to weaken the thermal ionization, on the other hand, by blowing the arc to lengthen the arc to strengthen the compound and diffusion of charged particles, while blowing the charged particles in the gap, quickly restore the dielectric insulation strength.
Low-voltage circuit breakers, also known as automatic air switches, can be used to switch on and off load circuits or to control infrequently started motors. Its function is equivalent to the partial or total function of knife switch, overcurrent relay, voltage loss relay, thermal relay and leakage protector and so on. It is an important protection appliance in low-voltage distribution network.
Low voltage circuit breaker has a variety of protection functions (overload, short circuit, undervoltage protection, etc.), adjustable action value, high breaking capacity, easy to operate, safety and other advantages, so it is widely used. The low-voltage circuit breaker consists of operating mechanism, contact, protection device (all kinds of trip device), arc extinguishing system, etc.
The main contact of the low-voltage circuit breaker is manually operated or electrically closed. After the main contact is closed, the free trip 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 to the main circuit in series, and the coil of the undervoltage release is connected to the power supply. When the circuit occurs short circuit or serious overload, the armature of the overcurrent trip device closes, making the free trip mechanism operate, and the main contact disconnects the main circuit. When the circuit is overloaded, the heat element of the thermal release makes the bimetallic sheet bend and pushes the free release mechanism to operate. When the circuit is under voltage, the armature of the undervoltage trip is released. Also allows the free trip mechanism to operate. Shunt trip is used as a remote control, in normal operation, the coil is off, in the need of distance control, press the start button, make the coil energized.
Main characteristics
The circuit breaker has the following characteristics: rated voltage Ue; Rated current In; Setting range of trip current for overload protection (Ir or Irth) and short circuit protection (Im); Rated short-circuit breaking current (industrial circuit breaker Icu; Home circuit breaker Icn, etc.
1.Rated Operating voltage (Ue) : This is the voltage at which the circuit breaker operates in normal (uninterrupted) condition.
2.Rated current (In) : This is the maximum current that a circuit breaker equipped with a special overcurrent trip relay can withstand indefinitely at the ambient temperature specified by the manufacturer and does not exceed the temperature limit specified by the current bearing part.
3.Short-circuit relay trip current setting (Im) : Short-circuit trip relay (instantaneous or short delay) is used to make the circuit breaker trip quickly when high fault current value occurs, its trip limit Im.
4.Rated short-circuit Breaking capacity (Icu or Icn) : The rated short-circuit breaking current of the circuit breaker is the maximum (expected) current that the circuit breaker can break without damage. The current value provided in the standard is the root mean square value of the AC component of the fault current, and the DC transient component (which always occurs in the worst-case short-circuit) is assumed to be zero when calculating the standard value. Industrial circuit breaker ratings (Icu) and domestic circuit breaker ratings (Icn) are usually given in the form of kA root mean square values.
Main classification
According to the number of poles: a single pole, two poles, three poles and four poles;
Divided by installation mode: insert type, fixed type and drawer type, etc.
Connection mode
The wiring modes of circuit breakers are in front of the board, after the board, insert type, drawer type, if the user has no special requirements, they are supplied according to the front of the board, the front of the board wiring is a common wiring mode.
Working condition
1. Ambient air temperature: upper ambient air temperature +40℃; ○ Lower limit of ambient air temperature -5℃; The average ambient air temperature for 24h does not exceed +35℃.
2. Elevation: The elevation of the installation site does not exceed 2000m.
3. Atmospheric conditions: the relative humidity of the atmosphere does not exceed 50% when the ambient air temperature is +40℃; It can have higher relative humidity at lower temperature. The monthly mean maximum relative humidity of the wettest month is 90%, while the monthly mean minimum temperature of the month is +25℃, taking into account the condensation that occurs on the product surface due to temperature changes.
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