A circuit breaker is a switching device that can close, carry and break current under normal circuit conditions and can close, carry and break current under abnormal circuit conditions within a specified 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 boundaries is relatively vague. Generally, those above 3kV are called high-voltage electrical appliances.circuit breaker pattern

 

A circuit breaker is an electrical safety device used to protect the circuit from overcurrent (overload and short circuit) damage; its basic function is to manually open and close (close and open) the circuit, and automatically cut off the faulty circuit to protect the equipment (circuits in the circuit) Electrical appliances) and prevent fire risks, widely used in industrial production and daily life.

 

The main function of the circuit breaker is to disconnect the current flow in the circuit. When the current in the circuit exceeds the preset value, the circuit breaker will quickly cut off the circuit to protect electrical equipment and wires from damage. A circuit breaker usually consists of an electromagnetic trigger and a switching mechanism. The trigger senses a change in current and triggers the switching mechanism, thereby breaking the circuit.

 

Depending on their current rating and breaking capacity, circuit breakers are used in different types of circuits, including low and high voltage power systems, residential and commercial buildings, industrial equipment, and more. They are usually resettable or non-resettable and can be manually or automatically reset as required.

 

Ⅰ. Structure of circuit breaker

 

When the handle is pulled up by hand, the starting current will be executed. When the circuit is overloaded or short-circuited, it will automatically trip. After eliminating the cause of the accident, pull it down and then up again, otherwise it will not be able to close the circuit again.

 

The difference from ordinary power switches is the addition of springs and arc suppression devices. The spring function is to open or close (CLOSE) the operation process, after the pre-stored spring force reaches the critical point, it springs away instantly and quickly connects or jumps off the contact, so its operating speed is not affected by the hand operating speed. Influence.circuit breaker box

 

The arc-extinguishing device is an arc-extinguishing chamber for eliminating the sparks generated by the internal contacts of the operation. Any contact opening and load current will generate an arc (that is, a spark). Because the arc itself is a conductor formed by the dissociation of an extremely high-temperature air column, it uses Ampere's right-hand rule to form a strong magnetic field between the iron sheets in the arc-extinguishing chamber, and then uses Fleming's right-hand rule to divide the arc. The rapid bending of the air conductor lengthens the arc, causing the spark to extinguish more quickly.

 

If the load is a motor, there will be a sudden high current during normal startup, so a circuit breaker with 1.5 to 2 times the rated current should be selected.

 

Ⅱ. Working principle of circuit breaker

 

A circuit breaker is generally composed of a contact system, an arc extinguishing system, an operating mechanism, a trip unit, and a housing.
When short-circuited, the magnetic field generated by the large current (generally 10 to 12 times) overcomes the reaction force spring, the release pulls the operating mechanism to act, and the switch trips instantaneously. When overloaded, the current becomes larger, the heat generation is intensified, and the bimetal sheet is deformed to a certain extent to push the mechanism to move (the greater the current, the shorter the action time).

 

The function of the circuit breaker is to cut off and connect the load circuit, and cut off the faulty circuit, so as to prevent the expansion of the accident and ensure safe operation. The high-voltage circuit breaker needs to break 1500V, and the current is 1500-2000A arc, and these arcs can be stretched to 2m and still continue to burn without extinguishing. Therefore, arc extinguishing is a problem that must be solved for high voltage circuit breakers.

 

The principle of arc blowing and arc extinction is mainly to cool the arc and weaken the thermal ionization. On the other hand, the electric arc is elongated by blowing the arc to strengthen the recombination and diffusion of charged particles, and at the same time, the charged particles in the arc gap are blown away to quickly restore the dielectric strength of the medium.

 

1. Circuit interruption: Once the circuit breaker detects a fault in the circuit, it will quickly cut off the circuit to protect electrical equipment and wires from damage.

 

2. Fault detection: When an overcurrent, short circuit or other fault occurs in the circuit, the circuit breaker needs to be able to detect these abnormal conditions.

 

Ⅲ. Main characteristics of circuit breakers

 

1. Rated Current: The rated current of the circuit breaker refers to the maximum current value that the circuit breaker is designed to withstand. Choosing an appropriate rated current can ensure that the circuit breaker operates under normal load and can accurately detect and cut off the overload current in the circuit.

 

2. Isolation: The circuit breaker should have good circuit isolation ability when it is in the open state to ensure the safe maintenance and operation of electrical equipment.

 

3. Environmental Adaptability: Circuit breakers need to work under various environmental conditions, including temperature, humidity, vibration and pollution. A high-quality circuit breaker should have good environmental adaptability to ensure its reliability and durability.

 

4.Breaking Capacity: The breaking capacity of a circuit breaker refers to the maximum short-circuit current that it can safely cut off. Circuit breakers need to have sufficient breaking capacity to ensure that the circuit can be reliably interrupted in the event of a short circuit or other fault, preventing further damage or hazard to electrical equipment.

 

5.Resetting Method: The circuit breaker can have manual reset or automatic reset function. Manual reset circuit breakers require human intervention to return them to the closed state. The automatic reset circuit breaker will automatically return to the closed state after the fault is removed, without manual operation.

 

6. Arc Extinction: When the circuit breaker cuts off the circuit, arcing may occur. The circuit breaker should have good arc extinguishing ability, that is, to extinguish the arc quickly, so as to reduce the risk of fire and damage to electrical equipment. Different types of circuit breakers use different arc extinguishing technologies, such as air arc extinguishing, oil immersion arc extinguishing, vacuum arc extinguishing or gas arc extinguishing, etc.

 

7.Tripping Characteristics: The triggering characteristics of the circuit breaker define the time and current conditions required to trigger the circuit breaker action. Common trigger features include overload protection, short circuit protection, and instantaneous overcurrent protection, among others. Different trigger characteristics are suitable for different types of circuits and application requirements.

 

Ⅳ. Components of circuit breaker

 

1. Internal accessories

Alarm contact: the alarm contact used for circuit breaker accidents, and this contact will only act when the circuit breaker is tripped and broken, and the circuit breaker will trip freely when the load of the circuit breaker is overloaded, short-circuited or under-voltage. The original normally open position is converted into a closed position, and the indicator light, electric bell, buzzer, etc. in the auxiliary circuit are connected to display or remind the fault tripping state of the circuit breaker.

 

Since the probability of free tripping of the circuit breaker due to load failure is not too much, the life of the alarm contact is 1/10 of the life of the circuit breaker. The working current of the alarm contact generally does not exceed 1A.

 

Undervoltage release: The undervoltage release is a release that makes the circuit breaker disconnect with or without delay when its terminal voltage drops to a certain range. When the power supply voltage drops (even slow down) to the range of 70% to 35% of the rated operating voltage, the undervoltage release should operate, and the undervoltage release should operate when the power supply voltage is equal to 35% of the rated operating voltage of the release. It can prevent the circuit breaker from closing; when the power supply voltage is equal to or greater than 85% of the rated operating voltage of the undervoltage release, it should be able to ensure the reliable closing of the circuit breaker under thermal conditions.

 

Auxiliary contact: contact mechanically linked with the opening and closing mechanism of the main circuit of the circuit breaker, mainly used for displaying the opening and closing state of the circuit breaker, connected to the control circuit of the circuit breaker through the opening and closing of the circuit breaker, to its Relevant electrical appliances are controlled or interlocked.

 

Shunt release: The shunt release is a release that is excited by a voltage source, and its voltage has nothing to do with the main circuit voltage. The shunt release is an accessory for remote control of the opening. When the power supply voltage is equal to any voltage between 70% and 110% of the rated control power supply voltage, the circuit breaker can be reliably broken. The shunt release is a short-time working system, and the coil energization time generally cannot exceed 1S, otherwise the wire will be burned.

 

2. External accessories

Extended handle: It is an external extended handle, which is directly installed on the handle of the circuit breaker. It is generally used on large-capacity circuit breakers of 600A and above for manual opening and closing operations.

 

Electric operating mechanism: This is an accessory used for long-distance automatic opening and closing of circuit breakers. The electric operating mechanism has two types: motor operating mechanism and electromagnet operating mechanism. The motor operating mechanism is a molded case circuit breaker shell Frame level rated current 400A and above circuit breakers, the electromagnet operating mechanism is suitable for molded case circuit breakers frame level rated current 225A and below circuit breakers, whether it is an electromagnet or a motor, their attraction and rotation direction are the same, only Closing and opening are achieved by the position of the cam inside the electric operating mechanism. When the circuit breaker is operated by the electric mechanism, it should be able to ensure reliable closing of the circuit breaker at any voltage between 85% and 110% of the rated control voltage.

 

Handle locking device: It is to install a clip on the handle frame, punch a hole in the handle and lock it with a padlock. Mainly used when the circuit breaker is closed.

 

Rotary operating handle: suitable for molded case circuit breakers. A mechanism for rotating the operating handle is installed on the cover of the circuit breaker. The rotating shaft of the handle is installed in its mechanism matching hole. The other end of the rotating shaft passes through the door hole of the drawer cabinet. The handle is installed on the shaft head exposed on the door of the complete device, and the round or square seat of the handle is fixed on the door with screws. This installation enables the operator to turn the handle clockwise or counterclockwise outside the door to Ensure that the circuit breaker is closed or opened.

 

Ⅴ. Circuit breaker wiring

 

The wiring methods of the circuit breaker include front panel, rear panel, plug-in type, and drawer type. If the user has no special requirements, they will be supplied according to the front panel. Front panel wiring is a common wiring method.

 

1. Rear-panel wiring mode: The most important feature of the rear-panel wiring is that the circuit breaker can be replaced or repaired without re-wiring, and only the front-end power supply needs to be disconnected. Due to the special structure, the product has been equipped with a special mounting plate, mounting screws and wiring screws according to the design requirements when leaving the factory. Special attention should be paid because the contact reliability of a large-capacity circuit breaker will directly affect the normal use of the circuit breaker.

 

2. Plug-in wiring: On the mounting plate of the complete device, first install a circuit breaker mounting base, 6 plugs on the mounting base, and 6 sockets on the connecting plate of the circuit breaker. There are connecting plates on the surface of the mounting base or bolts behind the mounting base, and the power line and load line are pre-connected to the mounting base. To use, insert the circuit breaker directly into the mount. If the circuit breaker is broken, just pull out the bad one and replace it with a good one.

 

3. Drawer-type wiring: The drawer in and out of the circuit breaker is rotated clockwise or counterclockwise by the rocker.

 

4. The plug-in structure omits the isolator necessary for the fixed type, so that one machine can be used for two purposes, which improves the economy of use, and at the same time brings great convenience to operation and maintenance, and increases safety and reliability. . In particular, the main circuit contact knife seat of the drawer seat can be used in common with the NT type fuse contact knife seat.

 

Ⅵ. Common uses of circuit breakers

 

1. Overcurrent protection: The circuit breaker can also provide overcurrent protection, that is, when an abnormally large current occurs in the circuit, it will quickly cut off the circuit to prevent damage to electrical equipment and wires.

 

2. Overload protection: The circuit breaker can monitor the current in the circuit and cut off the circuit when the current exceeds the rated value, so as to prevent the electrical equipment from being overloaded and damaged.

 

3. Fault location: When a fault occurs in the circuit, the action of the circuit breaker can help locate the fault point. By triggering the circuit breaker and checking the action position, the part of the circuit where the fault is located can be determined.

 

4. Short-circuit protection: When a short-circuit fault occurs in the circuit, the circuit breaker can quickly cut off the circuit and prevent the flow of excessive current to prevent fire and damage to electrical equipment.

 

5. System control: The circuit breaker can be used as a switching device in the power system to control the on-off state of the circuit to achieve segmental control and maintenance operations of the circuit.

 

6. Earthquake protection: Some circuit breakers have an earthquake protection function. When an earthquake occurs, they can automatically cut off the circuit to protect the safety of equipment and personnel.

 

7. Equipment protection: Circuit breakers can prevent electrical equipment from being damaged by excessive current or short circuit. By cutting off the circuit in time, the circuit breaker protects the normal operation and life of electrical equipment.

 

Ⅶ. Working conditions of circuit breaker

 

1. Ambient air temperature: The upper limit of the ambient air temperature is +40°C, and the lower limit of the temperature is -5°C; the average value of the ambient air temperature for 24 hours does not exceed +35°C.

 

2. Atmospheric conditions: The relative humidity of the atmosphere does not exceed 50% when the ambient air temperature is +40°C; there can be a relatively high relative humidity at a lower temperature; the monthly average maximum relative humidity of the wettest month is 90%, and the The monthly average minimum temperature of the month is +25°C, and the condensation on the surface of the product due to temperature changes is taken into account.

 

3. Control circuit: After the closing and tripping are completed, the command pulse should be released, that is, the power supply for closing or tripping can be cut off; for equipment that may have abnormal working conditions or failures, a warning signal should be installed; spring operation The power supply of mechanism and manual operation mechanism can be DC or AC, and the power supply of electromagnetic operation mechanism is required to use DC.

 

Ⅷ. Precautions for installation and maintenance of circuit breakers

 

Install:

 

1. Safety switch: Make sure the power supply is disconnected during installation, and use suitable personal protective equipment (such as insulating gloves).

 

2. Code Compliance: Ensure that the circuit breaker is installed in accordance with applicable electrical codes and installation guidelines. Follow proper installation procedures and requirements.

 

3. Appropriate environment: According to the specifications and guidelines of the circuit breaker, install it in a suitable environment to avoid the influence of excessive temperature, humidity, vibration, etc.

 

4. Appropriate rated current: Choose a circuit breaker that meets the circuit requirements, and ensure that its rated current matches the circuit load.

 

5. Proper Wiring: Make proper wire connections, make sure the cables are properly grounded, and use the correct wire gauge.

 

Maintenance items:

 

1. Professional maintenance: For complex or special circuit breakers, maintenance and repair are required by qualified electrical professionals.

 

2. Regular inspection: Carry out regular inspection and maintenance, including checking the appearance of the circuit breaker, the status of contacts, connectors and wires.

 

3. Cleaning and dust removal: Regularly clean the circuit breaker and the surrounding area to ensure good ventilation and heat dissipation of the circuit breaker.

 

4. Replace worn parts in time: If necessary, replace worn contacts, springs or other key parts in time to ensure the normal operation of the circuit breaker.

 

Frequently Asked Questions

 

1. How to choose a circuit breaker suitable for a specific circuit?

 

Determine the load current of the circuit and select the circuit breaker's current rating to match that load current. The rated current of the circuit breaker should be greater than or equal to the load current of the circuit to ensure normal operation and provide adequate protection; understand the short-circuit current level of the circuit and select a circuit breaker with sufficient breaking capacity. The breaking capacity of the circuit breaker should be able to safely cut off the maximum short-circuit current that may occur in the circuit; consider the environmental conditions of the circuit, such as temperature, humidity, vibration, etc. Choose a circuit breaker that is suitable for the environment to ensure its reliability and durability.

 

2. How to judge whether the arc extinguishing capacity of the circuit breaker is sufficient?

 

Refer to applicable standards and codes, such as IEC, ANSI, etc. These standards usually specify the arc extinguishing capability requirements of circuit breakers. Different types of circuit breakers use different arc extinguishing media and techniques. The arc extinguishing time refers to the speed at which the circuit breaker extinguishes the arc. Shorter arc extinguishing times mean faster arc extinguishing, reducing the risk of fire and damage to electrical equipment. Therefore, make sure that the selected circuit breaker has a suitable arc extinguishing time.

 

3. What is the relationship between the rated current and breaking capacity of a circuit breaker?

 

The rated current of the circuit breaker should be greater than or equal to the load current of the circuit, and the breaking capacity should be greater than or equal to the maximum short-circuit current that may occur in the circuit. This ensures that the circuit breaker will function properly under both normal load and short circuit conditions. When selecting an appropriate circuit breaker, it is necessary to evaluate the rated current and breaking capacity of the circuit breaker based on the load current of the circuit and the possible short-circuit current level. The rated current of the circuit breaker should be able to meet the load demand of the circuit, and the breaking capacity should be able to safely cut off the maximum short-circuit current that may occur in the circuit.