What is Indoor High Voltage Vacuum Circuit Breaker?

What is Indoor High Voltage Vacuum Circuit Breaker?

Vacuum circuit breakers are the most commonly used type of high-voltage circuit breakers, and are mainly divided into indoor and outdoor. We mainly focus on indoor vacuum circuit breakers. (Indoor circuit breaker: a high-voltage circuit breaker that does not have the properties of wind, rain, snow, ice and thick frost, and is suitable for installation in buildings.)
The vacuum circuit breaker is named after its interrupting medium and the insulating medium of the contact gap after interrupting is high vacuum; it has the advantages of small size, light weight, suitable for frequent operation and interrupting without maintenance, and is more popularly used in the 3kV-40.5kV distribution network.

Main domestic standards
JP3855-96 “General technical conditions for 3.6～40.5kV AC high voltage vacuum circuit breakers”
DL403-91 “Technical Conditions for Ordering of 10～35kV Indoor High Voltage Circuit Breakers”
It needs to be explained here: There is no special standard corresponding to China’s JB3855 in the IEC standard, but the “IEC56 AC High Voltage Circuit Breaker” is applied. Therefore, the standards of vacuum circuit breakers in China are higher or stricter than IEC standards in at least the following aspects:
(1) Insulation level: Test voltage IEC China
1min power frequency withstand voltage (kV) 28 42 (between poles, pole to ground) 48 (between fractures)
1.2/50 impulse withstand voltage (kV) 75 75 (between poles, pole to ground) 84 (between fractures)
(2) The withstand voltage level of the vacuum interrupter fracture after the end of the electrical life test: not specified in IEC56. my country’s JB3855-96 stipulates that the insulation capacity between the fractures of the vacuum circuit breaker after completing the electrical life test should not be lower than 80% of the initial insulation level, that is, the power frequency of 1min33.6kV and the impact of 60kV.
(3) Contact closing bounce time: IEC has no regulations, while my country’s regulations require no more than 2ms.
(4) The test current of the temperature rise test: In the IEC standard, the test current is equal to the rated current of the product. my country’s DL403-91 stipulates that the test current is 110% of the rated current of the product.

The structure of vacuum circuit breaker
The components of the vacuum circuit breaker are vacuum interrupters, electromagnetic or spring operating mechanisms, brackets and other components.
The vacuum interrupter is the core component of the vacuum circuit breaker. Its main function is to quickly extinguish the arc and suppress the current after the medium and high voltage circuit is cut off through the excellent insulation of the vacuum in the tube, so as to avoid accidents and accidents.
There are two types of operating mechanisms: spring operating mechanism and permanent magnet operating mechanism.
The conductive circuit is divided into the form of insulating cylinder (the vacuum interrupter is installed in the insulating cylinder) and the form of embedded poles (the vacuum interrupter is installed in epoxy resin).

The embedded pole is formed by inserting the vacuum interrupter and the circuit breaker-related conductive parts into an easily solidified solid insulating material such as epoxy resin or thermoplastic material to form a pole, so that the entire circuit breaker pole becomes an integral part.

The role of vacuum circuit breakers
Control function: according to the needs of the power system operation, put some or all of the electrical equipment, and some or all of the lines into or out of operation
Protection function: When a certain part of the power system fails, it cooperates with protection devices and automatic devices to quickly remove the faulty part from the system, reduce the scope of power outages, prevent accidents from expanding, and protect various electrical equipment in the system from damage. , to ensure the safe operation of the fault-free part of the system.

The principle of vacuum circuit breaker
The working principle of the vacuum circuit breaker is: when the moving and static contacts are opened under the action of the operating mechanism, an arc is generated between the contacts, and the surface of the contact volatilizes at high temperature. When passing through, a magnetic field is generated, and the arc moves rapidly along the tangential direction of the contact surface under the action of this magnetic field, and part of the metal vapor is condensed on the metal cylinder (shield), and the arc is extinguished when it naturally crosses zero. The strength of the medium quickly recovered.

One sentence understanding: high vacuum, so as to achieve the effect of arc extinguishing and breaking current.

The use environment of vacuum circuit breaker
In terms of the natural environment, the circuit breaker should be able to work reliably under various conditions in the surrounding environment.

Normal use environment:
1. The ambient air temperature does not exceed 40℃, and the average value measured within 24 hours does not exceed 35℃.
2. The minimum ambient air temperature is -5°C for the “-5 indoor” class, -15°C for the “-15 indoor” class, and -25°C for the “-25 indoor” class.
3. The influence of sunlight radiation can be ignored.
4. The altitude does not exceed 1000m.
5. The surrounding air is not appreciably polluted by dust, smoke, corrosive and/or flammable gases, vapors or salt mist.

Humidity conditions
1. (Condensation may occasionally occur under such conditions):
– The average relative humidity measured within 24 hours does not exceed 95%;
– The average value of water vapor pressure measured within 24h does not exceed 2.2kPa;
– The average monthly relative humidity does not exceed 90%;
– The average monthly water vapor pressure shall not exceed 1.8kPa.
2. Vibration or ground motion from outside the switchgear and control equipment is negligible.
3. The amplitude of electromagnetic interference induced in the secondary system should not exceed 1.6kV.

Special conditions of use
When the circuit breaker is used under normal environmental conditions exceeding the standard, it shall be resolved by the user and the company through consultation. Usually the following measures will be considered:
1. When the use site exceeds 1000m above sea level, it is necessary to strengthen the external insulation level;
2. When the air temperature at the place of use exceeds the technical requirements, it is necessary to reduce the rated current or install a fan for forced heat dissipation;
3. When the place of use is high in humidity or has a sudden temperature change, measures should be taken to avoid the equipment from rusting, or electric heating should be used to eliminate condensation.

Main parameters of vacuum circuit breaker

Rated frequency: The standard value of the rated frequency is 16Hz, 25Hz, 50Hz.

(Note: In China, the standard value of the rated frequency of the high voltage circuit breaker is 50Hz.)

1. Rated current: The current value that the main circuit of the high-voltage switchgear can continuously carry under the specified normal use and performance conditions. Such as 125A, 250A, 400A, 630A, 1250A, 1600A, 2000A, 2500A, 3150A, 4000A, 5000A, etc.

Rated short-time withstand current: The rms value of the current that the switching device and control device can carry at the closing position within a specified short period of time under specified conditions of use and performance. Such as: 20kA, 25kA, 31.5kA, 40kA, 50KA, 63KA, 80KA.

2. Rated short-circuit breaking current: Under the specified conditions, the circuit breaker can guarantee the maximum short-circuit current of normal breaking.
3. Rated peak withstand current: The peak current of the first large half-wave of the rated short-time withstand current that the switchgear and control equipment can carry at the closing position under specified conditions of use and performance. Such as: 50kA, 63kA, 80kA, 100kA.

The rated peak withstand current should be equal to 2.5 times the rated short-time withstand current.

4. Rated short-circuit duration: The time interval during which the switching device and the control device can carry the rated short-time withstand current at the closing position.

The standard value of the rated short circuit duration is 2 s.

If necessary, you can choose a value less than or greater than 2s. The recommended values ​​are 0.5s, 1s, 3s and 4s.     

The current corresponds to the breaking current parameters

（Please refer to the vacuum circuit breaker catalog for the specific models and voltage circuit breaker parameter tables.）

Application of vacuum circuit breaker