【Knowledge Sharing】VCB breaker

This article tells you the difference between VCB, VCS, and ACB of high-voltage circuit breakers. What does a VCB circuit breaker do? 5 reasons for using VCB, the structure of the vacuum circuit breaker, the internal pressure range of the arc extinguishing chamber of the vacuum circuit breaker, the application range, and the structural requirements of the vacuum circuit breaker, so that you can understand the relevant knowledge.

FKN12A-12D air-blast load break switch

What is the difference between VCB breaker, VCS, and ACB of high voltage circuit breaker?
The main difference is that the rated voltage of the work is different, and the corresponding insulation level is also different; the universal circuit breaker is an air circuit breaker, but the air circuit breaker is not necessarily a universal circuit breaker, it may also be a molded case and a micro-break.
VCB breaker: vacuum circuit breaker, vacuum arc extinguishing, can break fault current, widely used in substations.
VCS: Vacuum isolating switch, used for isolating fractures, cannot break load current and fault current.
ACB: air circuit breaker, the air is used as the arc extinguishing medium, which can break the fault current.

ZN28G side mounted indoor vacuum circuit breaker

What does a VCB circuit breaker do?
The vacuum circuit breaker is designed to cut off the overcurrent quickly, safely, and reliably when the traction transformer fails in the circuit after the secondary side. The moving and static contacts of the VCB are set in a vacuum environment, and the current is broken by using the insulation resistance in the vacuum and the diffusion of the arc.

ZW8-12/C intelligent outdoor high-voltage vacuum circuit breaker

5 reasons to use VCB breaker
(1) Small size and lightweight, suitable for breaking capacitive load current.
(2) The arcing time is short and has nothing to do with the switching current, generally only half cycle.
(3) After the arc is extinguished, the recovery speed of the contact gap medium is fast, and the performance of breaking near-field faults is better.
(4) The contact opening distance is small, the contact opening distance of the 10KV vacuum circuit breaker is only about 10mm, the operating power of the operating mechanism is small, the stroke of the mechanical part is small, and its mechanical life is long.
(5) Since the dredger wears less when breaking the current, the electrical life of the contract is long, the full capacity breaking can reach 30-50 times, the rated current breaking can reach more than 5000 times, and the noise is small, which is suitable for frequent operation.

ZUW1 fixed type air circuit breakers

Structure of Vacuum Circuit Breaker
A vacuum circuit breaker mainly consists of three parts: vacuum interrupter, electromagnetic or spring operating mechanism, bracket, and other components. The following is a brief sharing of relevant knowledge by vacuum circuit breaker manufacturers.
(1) Vacuum interrupter

According to different switch types, there are outer shield-type ceramic vacuum interrupters, intermediate sealed cup-shaped longitudinal magnetic field miniaturized vacuum interrupters, and inner sealed glass bubble interrupters. The basic structure is as follows:
1) Airtight insulation system (housing)
The airtight insulation system consisting of an airtight insulating cylinder made of ceramics, glass or glass-ceramic, a moving end cover, a fixed end cover, and stainless steel bellows is a vacuum-tight container. In order to ensure airtightness, in addition to the strict operation process in the sealing type, it is also required that the material itself has a small amount of air permeability and internal gas release.

2) Conductive system
It consists of a fixed conductive rod, a fixed running arc, a fixed contact, a moving contact, a moving running arc, and a moving conductive rod. There are generally three types of contact structures: cylindrical contact, transverse magnetic field contact with spiral groove arc surface, and longitudinal magnetic field contact. At present, the longitudinal magnetic field technology is adopted, and this kind of arc extinguishing chamber has a strong and stable arc-breaking ability.

3) shielding system
The shield is an indispensable component in the vacuum interrupter, and there are many kinds of the main shield surrounding the contact, the bellows shield and the shield for voltage equalization. The function of the main shielding cover is: a. Prevent the arc products from splashing to the inner wall of the insulating shell during the arcing process, thereby reducing the insulating strength of the shell. b Improving the uniformity of the electric field distribution inside the arc extinguishing chamber is conducive to reducing the local field strength and promoting the miniaturization of the vacuum interrupting chamber. c Condensate the arc products, absorb part of the arc energy and help restore the dielectric strength of the back-arc gap.

(2) Operating mechanism
According to different types of circuit breakers, different operating mechanisms are used. Commonly used operating mechanisms include spring operating mechanisms, CD10 electromagnetic operating mechanisms, CD17 electromagnetic operating mechanisms, CT19 spring energy storage operating mechanisms, and CT8 spring energy storage operating mechanisms.

(3) Other components
Bases, insulating supports, insulators, etc.

ZW7-40.5 outdoor HV vacuum circuit breaker

The internal pressure range of the arc extinguishing chamber of the vacuum circuit breaker
Rough vacuum: the vacuum pressure range is 1.01105Pa~1.33102Pa
Low vacuum: the vacuum pressure range is 1.33102Pa~1.33101Pa
0 High vacuum: the vacuum pressure range is 1.33101Pa~1.33106Pa
Ultra-high vacuum: the vacuum pressure range is 1.33106Pa~1.331010Pa
A large number of studies have shown that the breakdown of the vacuum gap is not caused by the collision and ionization of gas molecules in the gap, but is mainly determined by the electrode phenomenon. As the temperature of the electrode surface and the strength of the applied electric field increase, the current density of electron emission from the electrode surface also increases. Experiments have shown that when the current density reaches a certain critical value, the vacuum gap is broken down.
If only the electric field effect is considered, the electric field strength must reach more than 109V/m in order to produce gap breakdown. However, the value of the electric field strength in actual situations is much smaller. For example, the breakdown voltage of a 1cm-long high-vacuum gap is about 100kV, and the corresponding electric field strength is 107V/m.

Application range of vacuum circuit breaker
It is used for the protection and control of electrical equipment in industrial and mining enterprises, power plants, and substations. It is especially suitable for places that require oil-free, less maintenance, and frequent operations. The circuit breaker can be configured in central cabinets, double-layer cabinets, and fixed The cabinet is used to control and protect high-voltage electrical equipment.

Structural requirements for vacuum circuit breakers
1. The vacuum switching tubes used in vacuum circuit breakers of the same type are interchangeable.
2. There is a counter for recording the number of operations on the front panel of the circuit breaker.
3. The circuit breaker is equipped with opening and closing buttons and opening and closing indicators.
4. The circuit breaker should be equipped with a spring energy storage indicator.
5. The metal box of the circuit breaker should have a grounding bolt with a diameter of 12mm that is anti-rust and good in conductivity, and a grounding symbol should be marked near the grounding point.
6. The secondary circuit of the circuit breaker should be connected with wires and terminals, and the secondary circuit should be isolated from the main circuit.
7. The insulation rod of the vacuum circuit breaker must apply a DC voltage of 20kV to test the leakage current.