258 / 2018-09-24 22:33:22

Analysis on Breakdown of Two Single-Break 330kV GIS Circuit Breakers with Same Type

circuit breaker,single-break,electric field simulation,insulation margin

GIS has been widely used, in which circuit breaker has been replaced by single-break structure from double-break structure, and some problems have arisen. This paper takes two breakdown faults of single-break 330 kV GIS circuit breaker with the same type as an example, analyzes the causes and puts forward corresponding preventive measures combined with the disintegration of the plant, electric field simulation, process simulation test and insulation margin verification test.
Both faults occurred during the operation of GIS with single-phase grounding resulted in protective action. The SO2 content in the interrupter of circuit breaker was detected by gas decomposition test. The two breakers were the same type of equipment manufactured by a manufacturer. They consisted of three poles. The arc extinguishing chamber was arranged horizontally with a single break. The principle of pneumatic arc extinguishing was adopted. Each pole was equipped with a hydraulic operating mechanism, which was connected horizontally and directly. Significant black burning marks were found on the flange and shielding cover of insulating cylinder on the moving side of arc extinguishing chamber of circuit breaker after disintegration. However, the results of AC withstand voltage, partial discharge and X-ray flaw detection are all normal after the treatment of related insulating cylinders.
In order to further explain the reasons for the two faults, it is necessary to explain: 1) whether the metal debris found in the fixed bolt hole of the moving side shield cover is the cause of the faults; 2) the type of circuit breaker is a miniaturized product, which evolves from a double-fracture to a single-fracture, considering the structural design, whether there are defects leading to the faults should be investigated.
For this purpose, the possible foreign body source of this type of circuit breaker was inspected and simulated. The metal scraps found when returning to the factory and disintegrating belong to the normal phenomenon of bolt loosening of shield cover, not the cause of the accident. However, it cannot be ruled out that other foreign bodies, such as parts in the manufacturing, assembly of offset or sharp burr, or in the field installation process introduced in the sand and dust particles. The electric field simulation of the single fracture was carried out, and the results were compared with those of the double fracture. The simulation results show that the maximum field strength increases slightly from double fracture to single fracture. In order to further verify that the structure of this type of circuit breaker can meet the operational insulation margin, the insulation margin verification test was carried out according to the requirements of the national standard medium type test, including full voltage power frequency withstanding voltage, lightning impulse withstanding voltage, operating impulse withstanding voltage and 80% power frequency withstanding voltage, lightning impulse withstand voltage test after 100 mechanical operations.
The results show that the single-break structure can operate normally without foreign particles, and the insulation margin meets the requirements. The two breakdown faults are mainly caused by foreign particles in the circuit breaker, which need to be controlled from assembly to site installation.