Discussion on Application of generator circuit breaker in large generator set

Development overview of 1 generator circuit breaker

This century since the beginning of 40s, with the increase of manufacturing industry, and enhancing the level of power demand, production of large capacity generator is not only possible, but also to meet the market demand become power. With the increase of the capacity of generator short-circuit current increases rapidly, the medium voltage switch has been unable to meet the general requirements of the breaking capacity, at the same time in order to improve the safety and reliability, resulting from the rapid development phase closed bus and generator transformer unit is widely used. By the middle of 60s, more and more experts believed that the use of generator circuit breakers was necessary to simplify the operation of power plants, increase the availability of nuclear power plants and meet the needs of nuclear power technology. It was this demand that led BBC to develop the first DR type air circuit breaker that could be operated directly on a large generator terminal in 1969. The circuit breaker is off phase type full closed structure, with compressed air as quenching medium, actuator using compressed air, rated current up to 50000A, the breaking capacity of 250kA, the circuit breaker rated current is below 11000A using natural air-cooled, 11000 ~ 20000A by forced water circulation cooling, 20000 ~ 50000A for water. Since the first DR type circuit breaker was put into operation, BBC/ABB has produced about 600 units in the market, and its failure rate has been reduced to about 0.5%, and gradually stabilized. The operation failure rate is 20 * 10-6, which is equivalent to 50000 operation failures. This index is about 20 times lower than that of high voltage circuit breaker. In 1984, ABB introduced the first HE type SF6 generator circuit breaker, using SF6 gas as the arc extinguishing medium, and the actuating mechanism was still pneumatic. It uses the SF6 gas sparklet (Selt - extinguishing) principle, the arc generated by the contact part for heating SF6 gas, the expansion, formation of gas quenching required, while the fixed contact in the current through the coil produces a magnetic field, the arc of rotation, so that the contact burns is reduced to a minimum, and load contact independent and arcing contact, ensure the continuous current carrying capacity. In March 1996, ABB developed the HEC 8 type generator circuit breaker by Holland KEMA test, the circuit breaker rated current is 24000A, the breaking capacity of 160kA, the SF6 circuit breaker for 600MW generator is possible. Because of the adoption of SF6, the structure of the whole circuit breaker is more compact and the failure rate is lower. The failure rate of the 1200 HE (HEC and HEK) generator circuit breakers of ABB company is less than 0.3%. Now the generator circuit breaker is not only a circuit breaker, but integrated voltage transformer, current transformer, isolation switch, grounding switch between generator and main transformer equipment, a combined electrical appliance has a variety of functions.

In addition to ABB company, the French GEC - ALSTOM company, Japan MITSUBISHI and other companies have also developed a SF6 generator circuit breaker. GEC - ALSTOM has a long history of manufacturing generators. Although it also produces SF6 generator breakers, it is known for producing air generator circuit breakers. Its SF6 generator circuit breaker developed slowly and with little capacity. The maximum parameters of the air generator circuit breaker are rated voltage 36kV, rated current 37500A, and breaking current 275kA. Air generator circuit breaker is the use of compressed air as insulation medium and arc extinguishing medium, as well as circuit breaker operation and cooling gas. Although the air generator circuit breaker is a series of strong, universal products, but its large size, covers an area of many, expensive, and the need to set up compressed air system. Japan's Mitsubishi Co began producing generator breakers in 1977. The insulating medium used is SF6 gas. The maximum breaking current is 110kA, the number of turns is 10 times, and the breaking time is 50 times when the rated current is 42000A. A generator circuit breaker with a current break of 125kA is being manufactured.

In addition to the SF6 gas and air as an insulating medium SF6 generator circuit breaker and air generator circuit breaker, at the end of 80s and early 90s the use of vacuum technology to develop the vacuum generator circuit breaker, the generator circuit breaker is produced by the German company SIEMENS and development. 8BK40, 8BK41 series vacuum generator circuit breaker is produced by SIEMENS, the rated voltage of 7.2 ~ 17.5kV, the current rating of 8BK40 5000A, breakingcurrent 63kA; 8BK41 rated current of 4000 ~ 12000A, the maximum breaking current for 80kA. Vacuum generator circuit breaker due to the limit in the breaking level, open the vacuum breaker manufacturing fault current more than 63kA has been very difficult, but the price is more expensive, so the vacuum generator circuit breaker in small capacity units use more, in the limited unit.

The development level of domestic generator breaker relatively low, at present only Shenyang high voltage switch factory a production of generator circuit breaker, in 80s, the introduction of the French GEC ALSTOM manufacturing technology, the development of PKG2 type generator circuit breaker, the breaker from 1986 to 1988 has been put into operation 14 sets of Gezhouba hydro power station, operation the overall situation is good, but the product of large volume, high noise, large maintenance workload. Gezhouba hydropower plant with understanding, the 14 circuit breakers are replaced with SF6 circuit breaker ABB company. At present, Shenyang High Voltage Switchgear Factory is actively developing SF6 generator circuit breaker.

Due to the unique nature of generator circuit breaker, generator breaker needs to meet the existing switch manufacturing standards, such as IEC56 - 1987 (High - voltage, altemating - current - circuit - brea)