SF6 gas leakage from circuit breakers is a serious problem, affecting not only the safe operation of the equipment but also causing environmental pollution (SF6 is a potent greenhouse gas). The following are the main causes of leakage and standard handling procedures:
1. Causes of SF6 Gas Leakage:
(1) Inadequate Sealing. Studies have shown that the causes of inadequate sealing are as follows:
① Loose bolts securing the sealing surface. Poor installation quality or vibration may cause the bolts securing the sealing surface to loosen, leading to inadequate sealing and gas leakage.
② Aging of the sealing ring. Field experience shows that the sealing ring ages relatively quickly, generally hardening, deforming, or even corroding within 8-10 years, thus losing its sealing effect. From this perspective, the maintenance cycle of SF6 circuit breakers should be shorter than the specified maintenance cycle of 15-20 years; the actual maintenance cycle should be determined by the aging life of the rubber sealing ring.
③ Inappropriate machining method of the sealing surface. After detailed research on the machining method of the sealing surface, foreign countries believe that turning with the machining marks consistent with the O-ring sealing line is more suitable. It is pointed out that under experimental conditions, the critical roughness of turning is about 25μm. Considering safety factors, the roughness limit should be less than 5μm.
④ Dust falling into the sealing surface. Dust particles larger than 20μm in diameter falling onto the sealing surface will cause gas leakage. Therefore, measures must be taken to strictly prevent dust from falling onto the sealing surface. SF6 circuit breakers should be assembled in a dust-proof room.
(2) Weld leakage. The main reason for weld leakage is incomplete weld penetration, coupled with inaccurate weld inspection methods, thus bringing hidden dangers to the site and causing gas leakage.
(3) Damage to the sealing gasket. Damage to the sealing gasket, especially at the joint, can cause leakage.
(4) Porcelain bushing damage. During transportation and installation, external forces may damage the porcelain bushing, leading to gas leakage.
In addition, poor bonding at the joint between the porcelain bushing and the flange, and aging or misalignment of the gasket at the connection between the porcelain bushing and the gasket, can also lead to air leakage.
(5) Poor product quality. Essentially, leakage and moisture intrusion occur simultaneously. Poor product quality creates tiny gaps that allow SF6 gas to leak, thus allowing moisture to enter.
2. Handling Methods
(1) Detect leaks according to the prescribed cycle and methods. Once a leak is identified, appropriate measures should be taken based on the causes of the leak, such as tightening bolts or replacing seals; preventing dust intrusion; and, if necessary, carrying out major repairs.
(2) Careful welding and strict inspection. Using penetration welds is the fundamental solution to weld leakage. To achieve penetration, the following must be ensured:
① The weld section must conform to relevant standards and specifications;
② Special attention must be paid to the continuity of the weld. In areas of layered welding or where welding must be stopped, the slag must be thoroughly cleaned before continuing welding to ensure no slag inclusions in the weld;
③ From a design perspective, the weld direction should be as simple and smooth as possible to improve the welding processability;
④ Operators must possess a pressure vessel welding technical qualification certificate and strictly follow standard and specification procedures.
In addition to the above reliable and stable technological foundation, improving weld quality also requires correct inspection methods, which are indispensable guarantees. Currently, one of the most thorough methods for inspecting the internal quality of welds is flaw detection. Only welds that pass flaw detection can be transported to the site for installation.
(3) Replacement. Leaking pressure gauges and damaged porcelain bushings should be replaced promptly.
(4) Improve product quality and strictly control the "input" of welds.
Safety Precautions
Ventilation and Protection: Ventilate for at least 15 minutes after a leak. Personnel entering the area must wear protective equipment.
Gas Handling: SF6 gas and its decomposition products must be professionally recovered and must not be released.
Records and Reports: Record the leak location and handling process in detail and report to the management department for record-keeping.
In summary, handling SF6 leaks requires a combination of detection, maintenance, and preventative measures. The core principles are accurate leak location, standardized sealing processes, and strict gas management. For equipment with frequent leaks or that is old, it is recommended to consider complete replacement or upgrading to new, environmentally friendly alternatives (such as vacuum circuit breakers, SF6/N2 mixed gas switches, etc.).
Shaanxi Huadian, with its superior vacuum circuit breakers and SF6 circuit breakers, builds a reliable, efficient, and intelligent safety barrier for the modern power grid. We are not only a manufacturer of switchgear, but also a guardian of the stable operation of the power system. Please contact us if you are interested.
Email:pannie@hdswitchgear.com.
Whatsapp/Wechat:+8618789455087
