What Is a Main Breaker?

The main circuit breaker refers to the main switch used to switch on and off the power of electric locomotives and electric units. When the main circuit has a short circuit or a ground fault, the main circuit breaker can be quickly opened to protect it. At present, the main circuit breaker is generally an air circuit breaker, which is composed of an arc extinguishing chamber, an isolation switch, a control operation mechanism, and a compressed air supply system. When disconnected, the compressed air enters the arc extinguishing chamber, and the active contact is first disconnected, and the arc is extinguished at the same time. Then the compressed air opens the disconnector. The opening is performed under no power, and then the active contact is reset. Preparation for closed cooperation. When the main circuit breaker is closed, the compressed air closes the disconnector. The closing is performed under power. In order to suppress the over-voltage, there is also a set of non-linear resistors between the active static contacts of the arc extinguishing chamber. ^[1]

On the upper side, there is an arc extinguishing chamber, a parallel resistor, a supporting porcelain bottle, a rotating porcelain bottle, and an isolating switch gate; the lower side has a storage cylinder, a main valve, a start valve, a closing solenoid, a switching solenoid, a time delay valve, a transmission cylinder, Positioning mechanism, auxiliary switch interlock, etc. A cavity is formed inside the part.

Circuit breakers are generally composed of contact systems, arc extinguishing systems, operating mechanisms, trip units, and housings.

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Working principle of air circuit breaker Working principle of air circuit breaker Working principle of air circuit breaker

The air switch is also a circuit breaker, which is used to make, break, and carry the rated working current in the circuit, and can reliably protect the circuit and the motor from overload, short circuit, and under voltage. The dynamic and static contacts and contact rods of the circuit breaker are designed in parallel, and the dynamic and static contacts are disconnected by the electric repulsive force generated by the short circuit, with high breaking capacity and strong current limiting characteristics. During a short circuit, the aromatic insulation around the static contacts vaporizes, plays a cooling arc extinguishing role, and the arcing distance is zero. The arc extinguishing chamber of the circuit breaker uses a metal grid structure, and the contact system has a repulsive current limiting mechanism. Therefore, the circuit breaker has a high breaking capacity and a current limiting ability. With double release. The inverse time limit action is that the bimetal is heated and bent to make the tripper actuate, and the instantaneous action is that the iron core street iron mechanism drives the tripper action. There are three tripping modes: thermal, electromagnetic and multiple. . The air switch is more precise inside, but the principle is very simple. It has 10 to 20 turns of inductor in series between the incoming and outgoing wires. When the current is enough, the mechanical lever is pulled in for protection. It is safer without changing insurance, which is a good recommendation. Automatic air switches, also known as low-voltage circuit breakers, can be used to switch on and off load circuits, and can also be used to control motors that start infrequently. Its function is equivalent to the sum of the functions of some or all electrical appliances such as gate knife switches, overcurrent relays, voltage loss relays, thermal relays and leakage protectors. It is an important protective electrical device in low-voltage distribution networks.

Automatic air switch has a variety of protection functions (overload, short circuit, under voltage protection, etc.), adjustable action value, high breaking capacity, convenient operation, safety and other advantages, so it is currently widely used.

Structure and working principle

Automatic air switch consists of operating mechanism, contacts, protection devices (various trip units), arc extinguishing system, etc. .

The characteristics of the circuit breaker are: rated voltage Ue; rated current In; tripping current setting range of overload protection (Ir or Irth) and short circuit protection (Im); rated short circuit breaking current (industrial circuit breaker Icu; household circuit breaker Icn) )Wait.

Rated operating voltage (Ue): This is the voltage at which the circuit breaker operates under normal (uninterrupted) conditions.

Rated current (In): This is the maximum current that the circuit breaker equipped with a special overcurrent trip relay can withstand under the ambient temperature specified by the manufacturer, and will not exceed the temperature limit specified by the current bearing component.

Short-circuit relay trip current setting value (Im): The short-circuit trip relay (instantaneous or short delay) is used to quickly trip the circuit breaker when a high fault current value occurs, and its trip limit Im.

Rated short-circuit breaking capacity (Icu or Icn): The rated short-circuit breaking current of the circuit breaker is the highest (expected) current value that the circuit breaker can break without being damaged. The current value provided in the standard is the root mean square value of the AC component of the fault current. When calculating the standard value, the DC transient component (which always appears in the worst case short circuit) is assumed to be zero. Industrial circuit breaker ratings (Icu) and household circuit breaker ratings (Icn) are usually given in kA rms.

Short-circuit breaking capacity (Ics): The rated breaking capacity of the circuit breaker is divided into two types: rated limit short-circuit breaking capacity and rated operating short-circuit breaking capacity. The national standard "Low Voltage Switchgear and Control Equipment Low Voltage Circuit Breakers" (GB14048.2-94) explains the rated limit short-circuit breaking capacity and rated operating short-circuit breaking capacity of the circuit breaker as follows:

1. The rated short-circuit breaking capacity of the circuit breaker: According to the conditions specified in the prescribed experimental procedure, the breaking capacity of the circuit breaker to continue to carry its rated current capacity is not included;

2. The rated short-circuit breaking capacity of the circuit breaker: according to the conditions specified in the prescribed experimental procedures, including the breaking capacity of the circuit breaker to continue to carry its rated current capacity;

3. The test procedure for rated ultimate short-circuit breaking capacity is O-t-CO.

The specific test is: adjust the line current to the expected short-circuit current value (such as 380V, 50kA), and the test button is not closed, the circuit breaker under test is in the closed position, press the test button, the circuit breaker passes the 50kA short-circuit current, The circuit breaker opens immediately (open for short), the circuit breaker should be intact and can be closed again. t is the intermittent time, generally 3 minutes, at this time the line is still in the hot standby state, the circuit breaker is once again closed (C for short) and the next open (O), Electrical and thermal stability at current). This procedure is called CO. If the circuit breaker can be completely opened, its limit short-circuit breaking capacity is qualified.

4. The test procedure for the rated operating short-circuit breaking capacity (Icn) of the circuit breaker is O-t-CO-t-CO. It has one more CO than Icn's test procedure. After the test, the circuit breaker can completely break and extinguish the arc, and its rated short-circuit breaking capacity is deemed to be qualified.

Therefore, it can be seen that the rated limit short-circuit breaking capacity Icn refers to the low-voltage circuit breaker that can operate normally after breaking the maximum three-phase short-circuit current at the outlet end of the circuit breaker and break this short-circuit current once again. The circuit breaker is not guaranteed to make and break; the rated operating short-circuit breaking capacity Ics means that the circuit breaker can be normally opened multiple times when the maximum three-phase short-circuit current at its outgoing end occurs.

The IEC947-2 "Low-voltage switchgear and control equipment low-voltage circuit breakers" standard stipulates that the Ics of Class A circuit breakers (referring to circuit breakers with only overload and long delay and short-circuit transient) can be 25%, 50%, 75% and 100%. The Ics of Class B circuit breakers (three-stage protection circuit breakers with overload long delay, short circuit short delay, and short-circuit transient) can be 50%, 75%, and 100% of Ics. Therefore, it can be seen that the rated short-circuit breaking capacity is a breaking current value smaller than the rated limit short-circuit breaking current.

Generally speaking, a circuit breaker with three functions of overload long delay, short short delay and short-circuit transient protection can achieve selective protection. Most trunk lines (including the outlet of the transformer) use it as the main protection switch. . Circuit breakers without short-circuit and short-delay functions (only overloaded long-delay and short-circuit instantaneous two-stage protection) cannot be used for selective protection. They can only be used in branch circuits. IEC92 "Ships Electric" points out that a circuit breaker with three stages of protection is biased towards its operating short-circuit breaking capacity value, while a circuit breaker used in a branch line should ensure that it has a sufficient limit short-circuit breaking capacity value.

No matter what kind of circuit breaker, although there are two important technical indicators of Icu and Ics. However, as a circuit breaker used on a branch line, it only needs to meet the rated limit short-circuit breaking capacity. The more common bias is to take the big one rather than the right one. However, if it is too large, it will cause unnecessary waste (the same type of circuit breaker, its H type-high breaking type, is 1.3 times to 1.8 times more expensive than the S type-ordinary type). Therefore, the circuit breaker on the branch line does not need to blindly pursue its operation short-circuit breaking capacity index. As for the circuit breaker used on the main line, not only must it meet the requirements of the rated limit short-circuit breaking capacity, but it must also meet the requirements of the rated operating short-circuit breaking capacity. Will bring hidden danger to users.

The circuit breaker is a basic low-voltage electrical appliance. The circuit breaker has overload, short circuit and under voltage protection functions, and has the ability to protect the line and power.

The main technical indicators are rated voltage and rated current. Circuit breakers have different functions according to different applications, there are many varieties and specifications, and there are many specific technical indicators.

Breaker free trip: At any time during the closing of the circuit breaker, if the protection action is connected to the trip circuit, the circuit breaker can be completely and reliably opened, which is called free trip. The circuit breaker with free tripping can ensure that the circuit breaker can be quickly opened when the circuit breaker is closed and short-circuited, which can avoid expanding the scope of the accident.

Divided by the number of poles: unipolar, dipolar, tripolar, and quadrupole;

According to the installation method: there are plug-in, fixed and drawer.

Product introduction A9 / EC65 miniature circuit breaker: lighting distribution circuit, short circuit and overload protection.

Circuit breaker picture

A9LE / EPNLE earth leakage circuit breaker: short circuit overload and earth leakage protection in grounding system. Normal operation fault protection of the circuit breaker keeps the phase line and the neutral line in the disconnected state when the circuit breaker is in the disconnected position, to avoid being charged when the neutral line fails. When making and breaking operations, the neutral line is given priority and the breaking lags. With short circuit current limiting function, high rated short circuit breaking capacity. With overload protection short circuit leakage and voltage protection device, complete protection functions, convenient and reliable wiring.

Over-voltage and under-voltage release: Full-automatic over-voltage and under-voltage delay protector is a new-generation product developed by our company according to market needs. The protector has a reasonable design and is assembled with imported components and domestic brand-name components. The product can quickly and reliably switch power under high-voltage shock and under-voltage conditions to protect household appliances. When the voltage returns to the normal value, the circuit can be automatically connected and the power supply can be restored after a delay, which can effectively protect the electrical equipment from the impact of instantaneous power supply. All functions are fully automated, no special operation is required, and bi-color light-emitting diode instructions are used, which is safe and fast.

EC100 miniature circuit breaker: industrial power distribution system, short circuit and overload protection. Rated current 63A-125A, high rated short-circuit breaking capacity, short-circuit current limiting structure. Complete protection functions, with overload and short circuit protection devices, safe and reliable wiring, using "frame type" wiring structure, simple and easy function expansion, safe and reliable. Can be equipped with a variety of accessories: leakage current release, auxiliary contacts, alarm contacts, shunt release, undervoltage release, bus.

EPD surge protector: EPD plug-in uses the same working principle and selection criteria as fixed surge protection. Protects against indirect lightning and direct lightning effects or other transient overvoltage surges.

EIC1 AC contactor: mainly used for AC 50Hz or 60Hz rated voltage to 660V and below, for long-distance connection and disconnection of the circuit, and can be combined with the corresponding specifications of the thermal relay or electronic protector into electromagnetic or electromechanical integration Motor starter.

ENS plastic case circuit breaker: Plastic case circuit breaker is one of the new circuit breakers designed and developed by the company using international advanced technology. Used to divide the circuit breaker's rated insulation voltage 800V, suitable for AC 50Hz and 60Hz, rated operating voltage to 690V, rated operating current from 6A to 1250A in the distribution network circuit, used to distribute electrical energy and protect lines and power equipment from Damage of overload, short circuit, under voltage and other faults can also be used as infrequent starting of the motor and under voltage protection of overload short circuit. This circuit breaker has the characteristics of small size, high breaking capacity, short flashover (or no flashover), etc. It is an ideal product for users. The circuit breaker is installed vertically (that is, vertical installation) or horizontally (horizontal).

ENSLE plastic case leakage circuit breaker: It is used to provide indirect contact protection for people. It can also prevent fire danger caused by equipment insulation damage and ground fault current. It can also be used to distribute electrical energy and protect the wire and overload short circuit of power equipment. It can be used for infrequent switching of the line and infrequent starting of the motor. The working power of the conventional leakage protection module with residual current protection circuit breaker is sampled as two phases. This series of circuit breakers are three phases. If any one phase is missing, the circuit breaker The leakage protection module can still work normally, the rated residual operating current and the maximum disconnection time can be adjusted on site according to the actual situation.

EGL-125 isolating switch: Isolating switch is one of the most used electrical appliances in high-voltage switchgear, which is used to isolate the circuit. Its working principle and structure are relatively simple, but due to the large amount of use and high reliability requirements, it has a greater impact on the design, establishment and safe operation of substations and power plants. The main feature of the knife gate is that it has no arc extinguishing capability, and can only open and close the circuit without load current. EGL-125-4000A is suitable for switching between two low-voltage circuits or switching or safety isolation of two load devices.

EATS3 dual power transfer switch: two power sources are used to ensure the reliability of power supply, and a product can reliably switch between the two power sources. This product has two switching functions: self-returning and self-returning. This is a manual transfer switch. Novel design, safe and reliable, high degree of automation and wide range of use.

EW45 universal intelligent circuit breaker: mainly used to distribute electrical energy and protect lines and power equipment from overload, short circuit, under voltage, single-phase grounding and other faults. The circuit breaker has a variety of intelligent protection functions and can be selectively protected. , And the action is accurate, avoid unnecessary power outages, and improve power supply reliability and safety.

In order to make the main circuit breaker in good working condition, it is necessary to strengthen maintenance management.

1. Keeping the air moist or dirty, or the pipes being dirty, may have the following consequences:

(1) Humid gas decomposes into a mixed gas such as hydrogen and oxygen under the action of an arc, which destroys the insulation between the fractures after the main contact is broken. It is difficult to re-ignite the arc or the arc will reignite. In severe cases, the arc-extinguishing chamber will burst.

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(2) The insulation strength of the supporting porcelain bottle and the arc extinguishing chamber is reduced, causing creeping discharge.

(3) Foreign objects such as paint skin and rust residue in the pipeline may block the air port, causing the main circuit breaker to malfunction and causing jamming.

(4) If foreign matter enters the arc extinguishing chamber, it may cause poor contact of the main contact, causing the non-linear resistor to burn out due to long-term energization. In severe cases, the non-linear resistor porcelain bottle will burst.

Therefore, an oil-water separator is installed on the air inlet pipe of the main circuit breaker storage cylinder, and a water drain valve is provided at the lower part. During use and maintenance, water should be drained regularly to keep the air circuit clean.

2. Replace rubber parts regularly

The main circuit breaker is a kind of complicated pneumatic electrical equipment. Each component has high requirements for sealing performance. To ensure good sealing performance, the rubber parts should be replaced regularly.

3 Regular inspection of major components

Every major component should be checked regularly to maintain good technical condition.

(1) Arc-extinguishing chamber

Regularly detect the state of the main contact overtravel and the moving contact recovery spring. Due to the frequent opening and closing of the moving and static contacts, they will wear due to friction with each other, resulting in reduced overtravel and reduced contact pressure. When the overtravel is reduced to a certain extent, the moving and static contacts must be replaced. When the deformation of the moving contact restoration spring exceeds a certain limit, it must be replaced in time.

(2) Non-linear resistance

Keep the internal resistance of non-linear resistance porcelain bottles clean and well sealed. Replace the desiccant in non-linear resistance porcelain bottles regularly. Detect the resistance value of the non-linear resistor. If the resistance value changes beyond a certain limit, it must be replaced in time.

(3) the main valve

Regularly check the size of the fit between the piston and the valve body. If the size does not meet the requirements, it should be replaced in time.

Properly adjust the buffer of the transmission air cylinder to ensure that the disconnector works well. Regularly check the accuracy of the fit between the piston and the cylinder, and ensure its good performance by trimming or replacing parts. (4) Transmission air cylinder

(5) Ventilation plug door

The packing in the plug must be replaced regularly, the ventilation of the plug should be checked and adjusted to within the allowable range.

The solenoid is not energized and compressed air enters the cavity of the starter valve and main valve. When closing, the closing solenoid is activated, the compressed air enters the transmission cylinder from the closing valve of the starter valve, and the piston is moved to the left through the lever to push the porcelain bottle to rotate. Shut off the closing solenoid power immediately. When opening, the opening solenoid operates, and the compressed air is discharged from the main valve cavity to the atmosphere through the starter valve; under the action of the compressed air in the storage cylinder, the main valve piston moves to the right, and the compressed air enters the extinction via the main valve and the cavity supporting the porcelain Arc chamber, push the moving contact to open the main circuit breaker; compressed air then enters the moving contact nozzle, extinguishes the arc, and discharges to the atmosphere through the exhaust port of the cover. Compressed air entering the main valve, and at the same time entering the transmission cylinder through the time-delay valve, the piston is moved to the right, thereby pushing the rotating porcelain bottle to rotate, the isolator switch blade is opened, and the auxiliary switch interlocking contact immediately cuts off the power of the opening solenoid.

The main circuit breaker has both control and protection purposes, and has a higher mechanical life than ordinary circuit breakers. The main work of the main circuit breaker is to cut off the small load current (including no-load excitation current) of the traction transformer. The strong air current can quickly cut off such small inductor current, which causes a large overvoltage due to the interception. In order to suppress the over-voltage, a group of non-linear resistors are connected in parallel between the dynamic and static contacts of the arc extinguishing chamber. The amount of compressed air is directly used as the arc extinguishing medium, so it must be filtered and dried before being sent to the main circuit breaker. In order to adapt to complex environmental conditions, the main circuit breaker is gradually being improved to a vacuum circuit breaker with a sealing element, which can improve reliability and reduce maintenance workload.