Sulfur Hexafluoride Circuit Breaker (SF6 Gas Circuit Breaker)

SF6 circuit breaker, referred to as GCB for short, is an air-blown circuit breaker. Its characteristic is that the working air pressure is low. During the arc blowing process , the gas is not discharged to the atmosphere, but is recycled in the sealed system. Due to the good insulation performance and arc extinguishing performance of SF6 gas medium, GCB has the advantages of high breaking capacity , high fracture voltage, allowed for a large number of consecutive breaks, low noise and no risk of sparks. Properties of SF6 gas (1) Physical properties of SF6 gas. SF6 gas is a colorless, odorless, non-toxic, non-flammable, non-metallic compound that does not support combustion. At normal temperature and pressure, the density of SF6 gas is about 5 times that of air. Due to its large molecular weight (146.07) and large heat capacity, its thermal conductivity is far better than that of air, taking into account the natural convection effect. (2) Insulating properties of SF6 gas. After the circuit breaker is opened, the recovery of the insulation capacity of the gap between the contacts is an important factor in arc extinguishing. The number of charged particles in the gap indicates the strength of the insulation capacity. When the contacts are separated to generate an arc, the charged particles are mainly produced by thermal dissociation and collision dissociation.

Because SF6 is strongly electronegative and has a large volume, it is easy to capture electrons and can absorb their energy to generate stable negative ions with low mobility. Its free path is short, making it difficult for collision dissociation to occur in the gap, greatly reducing the amount of electrons in the gap. Charged particles. Therefore, at one atmospheric pressure (1. 01X105Pa), the insulation capacity of SF6 is more than twice that of air. When the pressure is 3 atmospheric pressure, its insulation capacity is equivalent to that of transformer oil. (3) Arc extinguishing performance of SF6 gas. Under the action of arc, SF6 receives electrical energy and generates low- fluorine compounds. However, when the arc current crosses zero, the low-fluorine compounds rapidly re -synthesize SF6. Therefore, the arc gap medium strength recovers quickly, and the arc extinguishing ability of SF6 is equivalent to 100 times that of air under the same conditions. During operation, since the gas decomposed by SF6 under the action of arc is harmful, attention must be paid to sealing the gas and taking correct treatment methods to ensure safety.

Structural forms of SF6 circuit breakers. In terms of appearance and structure, SF6 circuit breakers can be divided into two categories: porcelain pillar type SF6 circuit breakers (referred to as GCB.P.) and floor-standing tank type SF6 circuit breakers (referred to as GCB.T.). Among them, the porcelain pillar type SF6 circuit breaker is currently the most widely used form. The porcelain pillar type SF6 circuit breaker is similar in structure to the outdoor oil-less circuit breaker. It has the advantages of good serialization, high single-break voltage, large breaking current, high operational reliability and low maintenance workload, but it cannot have built-in current. transformer, and has poor earthquake resistance. The floor-standing tank type SF6 circuit breaker is developed on the basis of the porcelain column SF6 circuit breaker. It has all the advantages of the porcelain column SF6 circuit breaker, and can have a built-in current transformer. The overall height of the product is low, and its earthquake resistance is relatively improved. But the cost is relatively expensive.

Structural principle of 220kV SF6 circuit breaker

A factory uses Swiss ABB high-voltage switchgear

ELFSP4-1 circuit breaker produced by Co., Ltd.,

With AHWA single-phase transmission operating mechanism.

The circuit breaker consists of three independent columns (phases).

A circuit breaker consists of three main parts.

In the insulating epoxy housing at the bottom is the mechanical operating part,

The upper part of the mechanism is connected with an insulating tie rod moving in a hollow insulating porcelain sleeve .

The upper part is the breaking device ( i.e. arc extinguishing chamber ). The rated current is 4000A.

arc extinguishing unit in each arc extinguishing chamber porcelain bottle is composed of upper,

It consists of the lower outlet flange and the upper and lower current channels and contact systems in the middle.

The injection chamber is on the lower current channel,

The contacts installed in the upper and lower current channels are of integrated construction.

Each phase circuit breaker is mounted on a separate hot-dip galvanized bracket.

The bracket consists of two welded frames connected together with brace irons .

The ELFSP4-1 circuit breaker is operated by the AHWA type hydraulic operating mechanism.

the mechanism chamber of the pole are connected through a tie rod system.

The basic structure is shown in Figure 6-1:

Among them, 1 represents the circuit breaker column, 2 represents the operating mechanism, and 3 represents the bracket.

Figure 6-1 Basic structure of a circuit breaker The circuit breaker works according to the principle of automatic compression. The compression cylinder is divided into two parts, an automatic compression chamber and a compression chamber. When the normal operating current is cut off, SF6 gas is pressed into the compression chamber, causing its pressure to increase. When arcing occurs , the gas in the compression chamber is ejected, extinguishing the arc when the current crosses zero. When the short-circuit current is cut off, the required arc extinguishing pressure is generated in the automatic compression chamber due to the heating of the arc. In this way, the energy of the arc can be used to increase the pressure of SF6, so that no additional energy is required to operate the mechanism. When closing, the pressure cylinder moves upward, the contacts contact each other, and the pressure cylinder is refilled with gas. Operating mechanism of high-voltage circuit breaker The operating system of the circuit breaker is a system used to close, open and maintain the circuit breaker closed. The action process of the operating system is actually to obtain kinetic energy from the operating components (closing components and opening components ), and then transfer the kinetic energy to the contacts through the arm and link mechanism to achieve opening and closing. The part of the operating system that is independent of the circuit breaker body is called the operating mechanism, and the rest of the part that transmits power is called the transmission mechanism. According to the different power sources required for circuit breaker operation, the operating mechanism can be divided into manual, hydraulic, electromagnetic, and spring operating mechanisms. A mechanism that requires manpower directly as closing power is called a manual operating mechanism. Obviously, its operating power is limited by manpower, the closing time is long, reclosing cannot be achieved, and it is only used on small-capacity circuit breakers. The mechanism that uses electromagnets to convert electrical energy into mechanical energy as closing power is called an electromagnetic operating mechanism. This type of operating mechanism is simple and reliable.

But DC is required to operate the power supply. In the spring operating mechanism, the driving energy is supplied by the closing spring with pre-stored energy. Before operating the circuit breaker, another low-power power supply first stores energy in the closing spring to make it in the ready closing state. This mechanism does not require It is a large-capacity energy device and therefore widely used. The mechanism that uses high-pressure compressed gas (nitrogen) as the energy source and hydraulic oil as the energy transfer medium is injected into the working cylinder with the piston to push the piston to perform work to close and open the circuit breaker. It is called a hydraulic operating mechanism. . There is also a mechanism that uses a pre-stored closing spring as the energy source and hydraulic oil as the medium for energy transmission, which is called a hydraulic spring operating mechanism. The structural principles of the operating mechanism will not be introduced in detail here. The operating mechanism used in the ELFSP4-1 circuit breaker is a hydraulic operating mechanism.

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