In recent years, the number of defects found in vacuum switches and accidents has increased. Although the proportion is low, the problems are quite prominent, mainly manifesting as vacuum bubble chronicity, air leakage, mechanical jamming, etc. This requires strengthening the comprehensive quality management of vacuum switches in terms of selection, installation, operation, and maintenance. The common faults of 11KV vacuum circuit breakers are mainly divided into electrical circuit faults and mechanical faults, mainly manifesting as: vacuum interrupter air leakage, insulation faults, failure to open or close, and inconsistent timing of switching.
During the use of the 11KV vacuum circuit breaker, the vacuum degree of the interrupter tube must be checked regularly. The current inspection methods are:
① For glass-shell vacuum interrupters, regular visual inspections can be carried out. Under normal conditions, the surfaces of internal components such as the shield should be very bright, and pale blue arc will be emitted when breaking the current. When the vacuum degree drops significantly, the internal color will become gray, and a dark red arc will be emitted when breaking the current.
② Conducting a power frequency withstand voltage test (42 KV) approximately every three years. If the power frequency withstand voltage is not lower than the rated withstand voltage under the condition that the movable and stationary contacts maintain the specified gap, the vacuum degree meets the usage requirements. If continuous breakdown or glow discharge occurs inside the vacuum interrupter during the voltage increase, it indicates that the vacuum degree of the vacuum interrupter has significantly dropped and can no longer be used.
Ensuring that the overtravel and contact travel of the high-voltage 11KV vacuum circuit breaker are within the specified range and reasonably selecting the usage and storage environment are important measures to solve the vacuum interrupter air leakage problem.
When installing or overhauling the 11KV vacuum circuit breaker, the measurement of the contact overtravel must be strictly adjusted according to the product installation manual requirements. The contact surface of the vacuum interrupter will gradually wear electrically after multiple current breaks, increasing the contact travel, which increases the operating travel of the bellows and rapidly decreases its lifespan. The maximum allowable contact electrical wear is usually around 3mm. When the cumulative wear value reaches or exceeds this value, the breaking performance and conductive performance of the vacuum interrupter will decrease, indicating that the vacuum interrupter's lifespan is over.
To accurately control the electrical wear value of each vacuum interrupter contact, it is necessary to accurately measure the gap and overtravel during each preventive test or maintenance from the start of the interrupter's installation and use, and make comparisons. The cumulative reduction in value after contact wear is the cumulative contact electrical wear value.
Before putting new circuit breakers into operation, measure the opening and closing speed. This not only establishes the original technical data but also identifies some product quality issues timely to take measures. When the vacuum degree decreases, it is necessary to replace the vacuum tube or the 11KV vacuum circuit breaker and conduct travel, timing, and bounce characteristic tests.
Insulation accident prevention mainly involves the following aspects:
One is to consider the operating environment and maintenance conditions when selecting the 11KV vacuum circuit breaker and choose products with reliable quality.
Two is to ensure proper process and tooling during installation, commissioning, and maintenance to prevent the damage to insulators caused by mechanism movement during operation.
Three is to ensure the operating environment is fully guaranteed, reduce the impact of dust and moisture on the equipment, shorten maintenance cycles, and regularly clean and visually inspect the insulation parts, including insulating rods, of the switch.
Four is to follow procedures and standards for regular insulation testing.
Additionally, enhancing insulation life prediction is of significant importance for reducing insulation accidents. Once an insulation accident occurs, the principle of identifying the accident cause and taking corresponding measures should be followed, damaged insulation components should be replaced, and insulation testing should be carried out.
Refusal and mis-operation faults of 11KV vacuum circuit breakers are mainly caused by faults in the operating mechanism and control circuits. The prevention and handling of these faults should focus on the following aspects:
① Prevent loosening and tightness. The mechanism may experience impact and vibration during operation, so all fastening points should have anti-loosening measures. Some heavily loaded pins should not only use cotter pins for positioning to prevent tightness due to the unbalance of forces on various connecting plates during operation, which may shear off cotter pins;
② Prevent rust and dirt. Rust and dirt significantly reduce the reliability of the mechanism's operation, deteriorate the mechanical characteristics of the operating system, and even cause refusal to open or close accidents. The friction coefficient can increase up to 0.3 due to rust and dirt on sliding bearings. Even if roller and roller bearings are used, rust and dirt may increase their friction coefficient to 0.1, which is an order of magnitude higher than normal conditions, causing instability in the toggle and tripping mechanisms' operation. Keeping the environment of the mechanism clean, regularly removing dirt (especially for rotating and sliding fits), and regularly lubricating by applying molybdenum disulfide solid lubricant on axes and pins can achieve good results;
③ Prevent water ingress into the mechanism. Water ingress can cause the insulation parts of the mechanism to become damp, accelerating the rusting of metal parts;
④ Improve the reliability of the control circuit. Ensure reliable wiring, so that it does not fall off due to vibration after a certain number of operations, ensure proper insulation of insulating parts, firmly fix auxiliary switches so that they do not move or drift during operation, adjust linkage mechanisms in place and prevent changes, and protect auxiliary switch contacts from rust.
To ensure that the 11KV vacuum circuit breaker can work reliably and normally, operators should enhance operational inspections, strengthen daily maintenance and testing, observe for any anomalies during operation, eliminate defects promptly upon identifying potential problems, strictly adhere to the preventive testing procedures of electrical equipment, ensure proper maintenance, guarantee the quality of repair and testing, thus improving equipment health, and avoid any negligence on the operating 11KV vacuum circuit breaker to prevent accidents.
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