Excessive temperature rise, insulation aging, and institutional wear are the three main forms of switchgear failure.
Temperature rise and insulation are closely related, one of the main purposes of limiting the temperature rise is to avoid insulation problems, air insulated metal-enclosed switchgear, long term use, due to increased temperature leading to thermal runaway, accelerated insulation aging, which in turn leads to failure of the insulation system. Low-voltage circuit breaker temperature rise standard is based on the material’s heat-resistant temperature level to determine the temperature rise, which is reasonable, the use of high-level heat-resistant insulating materials, the maximum temperature of the circuit breaker connecting end is 150 ℃, the temperature rise can be up to 115 k. For the high-current low-voltage cabinets can be reduced to reduce the copper row of materials, to solve the temperature rise problem. Medium voltage due to the widespread use of epoxy resin, and epoxy resin glass transition temperature is only 115 ℃, which is still good, some lower, high glass transition temperature means high high temperature resistance performance is good.
In addition, the high temperature will also accelerate the oxidation of metal materials, especially in the case of high humidity, high temperature and high humidity will cause metal corrosion and rust. Especially the contact part, the temperature rises, the oxidation of the contact surface increases with it, the contact temperature is greater than 80 ℃, the contact metal surface is subject to thermal expansion, the contact surface of the surface of the contact surface of the subtle displacement, thus accelerating the oxidation. Resulting in increased contact resistance.
High temperature will accelerate the lubricant dry. High temperature will cause the mechanical strength of the material becomes low, elasticity aging and deformation of the material, resulting in the mechanism of hysteresis, affecting the mechanical function.
High temperature will also have an impact on the instrumentation, affecting the stability and reliability of the relay protection performance, affecting the accuracy of measurement.
Other insulation problems
Or due to moisture, dust and pollution on the insulating surface, resulting in the surface of the insulating parts scarring.
Partial discharge activity in components such as epoxy resin insulators, voltage transformers, current transformers, contact boxes, bushings, etc., and unshielded cables in switchgear.
Insufficient clearance between the voltage transformer and the frame results in excessive local air field strengths, triggering breakdown. Solid insulations such as solid-sealed poles also have this problem. If the solid insulation wall thickness is similar to the air gap, the air gap field strength is stronger than that of the unsolidified insulation layer due to capacitive partial pressure, causing breakdown.
Insulation board and the distance between the charged body is too close, resulting in local air electric field strength is too large, more than the air allowed field strength, coupled with the insulation board to absorb moisture, dirt, etc. caused by the reduction of insulation performance, thus triggering breakdown.
Due to the design and installation problems, resulting in cable terminal faults, cable lap is not good, connected to the switchgear caused by other high-voltage charged body insulation distance is not enough, after the operation triggered by overheating, creepage flashover and even arc faults.
Mechanical problems
Mechanical problems mainly include the refusal of the operating mechanism to operate, or the operating force is too large, difficult to operate, stuck, and the failure of mechanical interlocking.
Circuit breaker operating mechanism life is short, spring operation hundreds of times collapse, connecting rod pin and other fracture, and other failure modes, need to be verified by the mechanical life test, if necessary, reliability test, through a number of circuit breakers, each for more than the required number of times of operation without failure, you can get a higher level of reliability, and availability. Such as the availability of foreign products 99.9999%, the average time to failure MTBF time to 5000 years, which are based on theoretical calculations.
Circuit breaker operating mechanism for a long time in the operation of the closing state, received the breaking signal can not be tripped, half-axis lap is too large, plastic deformation of the material, high temperature, dirt and so on will cause the phenomenon of refusal to split, the need for reasonable design, half-axis hardness in line with the requirements of the use of the environment is safe and relevant tests, especially for high temperature, sand and dust impact of large environments.
Similarly for other switches, there is also a long time in the closed state, can not open the problem, such as grounding switch, contact pressure is very high, contact design is not reasonable, the material is softer, etc. will not be able to separate, affecting the use of, and in some cases, even cause damage to the operating system of the problem, causing damage.