Introduction about Vacuum Circuit Breakers

     The main structure consists of three main parts: Vacuum arc extinguishing chamber (vacuum interrupter) , Electromagnetic or spring operating mechanism and racket, other components.

     Vacuum arc extinguishing chamber :According to the different switch type, there are external shielded ceramic vacuum arc extinguishing chamber, miniaturized vacuum arc extinguishing chamber with cup shaped longitudinal magnetic field sealed in the middle, inner sealed glass bubble arc extinguishing chamber. Its basic structure includes an airtight insulation system (shell), a conductive system, and a shielding system. As shown in the following image.

Electromagnetic or spring operating mechanism: According to the different types of circuit breakers, the operating mechanism will be different.

Common operating mechanisms include: Spring operating mechanism, CD10 electromagnetic operating mechanism, CD17 electromagnetic operating mechanism, CT19 spring energy storage operating mechanism, CT8 spring energy storage operating mechanism.

Other components: Base, Insulation support, Insulators, etc.

The working principle of vacuum circuit breaker:

When the dynamic and static contacts open under the action of the operating mechanism, arc generated between contacts, the surface of contact emits steam at high temperatures, due to the special shape of the contact design, a magnetic field is generated when current passes through it. The arc rapidly moves along the tangent direction of the contact surface under the action of this magnetic field, some metal vapor has condensed on the metal cylinder (shield), the arc extinguishes when it naturally crosses zero, then the dielectric strength between the contacts quickly recovers.

The application of vacuum circuit breakers:

High voltage vacuum circuit breakers are widely used in various aspects of the power system, such as transmission lines, substations, distribution rooms, etc. The main function of vacuum circuit breaker is to interrupt the current in the circuit to protect the safety of electrical equipment and personnel. High-voltage vacuum circuit breakers are usually used in conjunction with other protective devices in the power system, to achieve comprehensive protection of the power system, such as lightning arrest-er, isolation switches, etc.

When the vacuum circuit breaker in the closed position, its insulation to the ground is supported by insulators, once a permanent grounding fault occurs in the circuit connected to the vacuum circuit breaker, and the grounding fault point is not cleared after the circuit breaker trips, the insulation of the electrical bus-bar to the ground must also be borne by the vacuum gap of the circuit breaker fracture. When various faults break, the vacuum insulation gap between a pair of contacts at the fracture should withstand the effects of various recovery voltages without breakdown.

The functions of vacuum circuit breakers:

The reasons why vacuum circuit breakers are widely used is also because they have the following functions:

1. Improve insulation tolerance of vacuum arc extinguishing chamber.

The vacuum circuit breaker should be developed to the field of high voltage application and improve the insulation tolerance of fracture electrode in vacuum arc extinguishing chamber. The economic significance of making a separate fracture vacuum arc extinguishing chamber with higher rated voltage is enormous, not only can it reduce the number of series fractures, but it can also make the circuit breaker structure simple, so that it improves the reliability of the equipment and correspondingly reduces the cost of the equipment.

2. Improving the withstand voltage strength between contacts in the vacuum arc extinguishing chamber.

When the vacuum gap is actually broken down, there may be several mechanisms acting simultaneously, and there is always free gas present in the breakdown pathway. This is provided by the metal vapor generated after applying voltage or the gas adsorbed released by the contact. After using a vacuum circuit breaker, the voltage withstand performance of the contact gap in the vacuum arc extinguishing chamber can be improved.

3. Increase the insulation recovery speed between the contact poles after breaking the current.

After using a vacuum circuit breaker, the key to successfully breaking the current is usually the speed of insulation recovery in the contact gap after the arc current passes zero, which determines whether the arc will happen re-ignition, if the transient recovery voltage speed is faster than the contact gap, the successful disconnection can be achieved. If the insulation recovery speed between contact gaps is faster than the transient recovery voltage speed between contact gaps, there will be no re-ignition and successful disconnection will be achieved.

4. Can enhance the external insulation performance of the arc extinguishing chamber.

Insulators made of materials such as epoxy resin can wrap around the ceramic shell surface of the arc extinguishing mechanism in vacuum circuit breakers, thus achieving the effect of insulation strengthening while also improving pollution resistance performance.

The characteristics of vacuum circuit breakers:

1. The contact opening distance is small, and the contact opening distance of a 10KV vacuum circuit breaker is only about 10mm. The operating power of the operating mechanism is small, and the mechanical stroke is small, resulting in a long mechanical life.

2. The arc burning time is short, and has nothing to do with the switching current size, generally only half cycle wave.

3. After arc extinguishing, the recovery speed of the contact gap medium is fast, the fault performance is better in the near area of breaking.

4. Due to the small amount of wear on the contacts during current breaking, the electrical life of the contacts is long, with full capacity breaking up to 30-50 times and rated current breaking up to over 5000 times. The noise is low and suitable for frequent operation.

5. Small size and light weight.

6. Suitable for breaking capacitance load current.

The specification standards for vacuum circuit breakers:

1. Voltage level: Vacuum circuit breakers can usually be divided into multiple voltage levels. Low voltage type is generally used for explosion-proof electrical applications. Like coal mines and so on.

2.  The rated current :The rated current reaches 5000A, the breaking current reaches a good level of 50kA, and has developed to a voltage level of 35kV.

3. Domestic standards:JB/T 3855-2008<High Voltage AC Vacuum Circuit Breakers>; DL/T 403-2017<High voltage AC vacuum circuit breaker>. The standards for vacuum circuit breakers in China are at least higher or stricter than the IEC standards in the following aspects:

(1)  Insulation level: Test voltage IEC China

(2)  Voltage withstand level of vacuum interrupter fracture after electrical life test: 

There is no regulation in IEC56. However, according to JB3855-96 regulations in China. After completing the electrical life test, the insulation capacity between the fracture surfaces of the vacuum circuit breaker should not be lower than 80% of the initial insulation level, namely power frequency 1min 33.6kV and impact 60kV.

(3)  Contact closing and bouncing time: IEC has no regulations, while China's regulations require no more than 2ms.

(4)  Test current for temperature rise test: The test current is equal to the rated current of the product in the IEC standard. The test current specified in DL403-91 in China is 110% of the rated current of the product.

The advantages of the vacuum circuit breakers:

1. Strong breaking capacity, up to 50kA; After disconnection, the recovery speed of the medium between the fracture surfaces is fast, and the medium does not need to be replaced.

2. The contact opening distance is small, and the contact opening distance of 10kV vacuum circuit breakers is only about 10mm, the required operating power is small, the action is fast, the operating mechanism can be simplified, the service life can be extended, and generally can reach about 20 years without maintenance. 

3. Short arc extinguishing time, low arc voltage, low arc energy, low contact loss, and multiple interruptions.

4. The inertia of the moving guide rod is small, suitable for frequent operation.

5. When operating the switch, the action noise is low and suitable for use in urban areas.

6. The arc extinguishing medium or insulation medium does not require oil, and there is no risk of fire or explosion.

7. The contact part is a fully sealed structure, which will not reduce its performance due to the influence of moisture, dust, harmful gases, etc. Reliable operation and stable on-off performance. As an independent component, the arc extinguishing chamber is easy to install and debug.

8. During the service life of a vacuum circuit breaker, the contact part does not need to be repaired or inspected, and even if repaired or inspected, the required time is very short.

9. Extinguish the arc in a sealed container without exposing the arc and hot gas.

10. It has multiple re-closing functions and is suitable for application requirements in distribution networks.