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Sulfur hexafluoride circuit breaker is a circuit breaker that uses sulfur hexafluoride (SF6) gas as arc extinguishing medium and insulating medium. Referred to as SF6 circuit breaker.
The use of sulfur hexafluoride as an arc extinguishing medium in circuit breakers began in the early 1950s. Due to the excellent characteristics of this gas, the single-break of this circuit breaker is much higher than the compressed air circuit breaker and the oil-less circuit breaker in terms of voltage and current parameters, and does not require high air pressure and a considerable number of series-connected breaks.
In the 1960s and 1970s, SF6 circuit breakers have been widely used in ultra-high voltage large-capacity power systems. In the early 1980s, SF6 circuit breakers with 363 kV single break, 550 kV double break and rated breaking currents of 80 and 100 kA were successfully developed.
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Sulfur hexafluoride circuit breaker is an oil-free switchgear that uses SF6 gas as the insulating medium and arc extinguishing medium. Its insulation performance and arc extinguishing characteristics are much higher than those of oil circuit breakers.
Due to its high price and high requirements for the application, management and operation of SF6 gas, it is not widely used in medium voltage (35, 10kV), and is mainly used in voltage levels above 110kV.
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LW type Outdoor Sulfur Hexafluoride Circuit Breaker is a porcelain-column structure with a rated voltage of 500 kV and a maximum working voltage of 550 kV. The circuit breaker consists of three independent single phases and a hydraulic and electrical control cabinet. Each phase consists of four arc extinguishing chambers (fractures) of two pillar porcelain sleeves connected in series. Two-unit arc extinguishing chambers are installed on the top of each pillar porcelain sleeve, which are arranged in a V-shaped arrangement with an included angle of 120 degree , and the two voltage equalizing shunt capacitors are arranged horizontally.
This structural arrangement not only takes into account the mechanical stress state of the structure, but also takes care of the insulation requirements. The arc extinguishing chamber and the pillar porcelain sleeve are filled with SF6 gas of rated pressure.
②Tank-type structure:
It adopts the advantages of box-type multi-oil circuit breaker, and integrates the circuit breaker with the transformer. It has a compact structure and strong anti-earthquake and anti-fouling capabilities, but the series is poor.
Sf6 tank-type SF6 circuit breaker circuit breaker is a three-phase split type. The single-phase consists of a base, an insulating porcelain bushing, a current transformer and a shell with a single-break arc extinguishing chamber.
Each phase is equipped with a hydraulic mechanism and a control cabinet, which can be operated independently and can be operated three-phase through electrical control. The circuit breaker adopts a two-way vertical blowing arc extinguishing chamber. When opening, the cylinder and the moving contact are driven to move through the crank arm box transmission mechanism. The arc extinguishing chamber is filled with SF6 gas with a rated pressure of 6 gauge (20 degree ).
Give full play to the arc blowing effect of the airflow, the arc extinguishing chamber is small in size, simple in structure, large in breaking current, short in arcing time, no re-ignition or re-ignition of the breaking capacitor or inductor current, and low overvoltage.
The 50kA full capacity can be broken continuously for 19 times, the cumulative breaking current can reach 4200kA, the maintenance cycle is long, and it is suitable for frequent operation.
The sulfur hexafluoride gas has passed various insulation tests and has a large margin when the pressure is {{0}}.3MPa. After the cumulative breaking current is 3000kA, each fracture can withstand a power frequency voltage of 250kV for 1 min under a pressure of 0.3MPa, and can withstand a power frequency voltage of 166.4kV for 5 min when the sulfur hexafluoride gas is reduced to zero gauge pressure.
Sulfur hexafluoride gas has low water content; the arc extinguishing chamber, resistors and pillars are divided into independent gas partitions, which do not need to be opened during on-site installation, and are connected with automatic connectors after installation; easy installation and maintenance, and can prevent dirt and moisture from entering the inside of the circuit breaker.
The signal cylinder in the hydraulic mechanism can realize the self-protection of the circuit breaker: a density relay monitors the leakage of sulfur hexafluoride gas; a pressure switch and a safety valve monitor the pressure of the hydraulic mechanism to protect the safety of the hydraulic system. The hydraulic mechanism adopts a valve system that can prevent "loss of pressure and slow separation", and the mechanism can be locked on the body to ensure safe operation. Two sets of opening electromagnets and anti-jump protection are used in the control loop to ensure accurate operation.
The transmission ratio of the mechanism working cylinder and the arc extinguishing moving contact is 1:1, and the mechanism characteristics are stable. The stability of the mechanism characteristics can reach 3,000 times, the mechanism life research test can be completed for 10,000 times, and the operating noise is less than 90dB.
