Reliability comparison between electrical and mechanical linkage of high voltage switch
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1 Introduction
The high-voltage circuit breaker plays a role of control and protection in the power system, and its reliability is related to the safe and stable operation of the power system. In order to reduce the occurrence of non-full phase closing, some places need to use three-phase mechanical linkage. Some users more intuitively judge that the reliability of three-phase mechanical linkage breakers is much greater than that of electrical linkages, but the actual situation requires specific analysis.
2 Circuit breaker failure probability statistics
According to CIGRE's reliability survey of 66kV and above single-pressure SF6 circuit breakers put into operation from 1978 to 1991 in CIGRE, a total of 70,708 years, the failure caused by the failure of the operating mechanism accounted for 64.8% of the total failures. Among them, the secondary electrical control and auxiliary circuit failure accounted for 21%, and the mechanical failure of the operating mechanism accounted for 43.8%.
From 1989 to 1997, the national power system 110, 220, 330kV and 500kV SF6, the breakdown of the operating mechanism of the circuit breaker is shown in Table 1. The operating mechanism comprises two parts, one is a mechanical transmission part; the other is a control circuit and an auxiliary circuit including a control part of the mechanical part, such as a terminal, a contactor, an auxiliary switch, a closing and closing coil, a micro switch, Secondary components such as motors and gas relays. A total of 458 faults were counted and 304 faults occurred.
CIGRE report WGl3.06, the breakdown of faults according to the type of operating mechanism is shown in Table 2.
It can be seen that the number of failures of the spring operating mechanism is much lower than that of the hydraulic and pneumatic mechanisms, and its reliability is relatively high. In order to avoid the influence of different types of mechanism on the analysis results, this paper selects the spring mechanism SF6 high voltage circuit breaker.
3 Analysis of failure rate of electrical linkage and mechanical linkage
3.1 Electrical and mechanical linkage
The three-phase electric linkage high-voltage circuit breaker generally adopts three independent operating mechanisms, and the three-way linkage is realized by electrical connection between the mechanisms through the communication control box, and the output shaft of each phase mechanism is directly connected with the pole; on the protection device The trip is initiated by a three-phase position inconsistency relay.
The three-phase mechanical linkage high-voltage circuit breaker generally adopts an operating mechanism, and the three poles of the circuit breaker and the operating mechanism are connected by an operating rod.
According to SDJ5-85 "Technical Regulations for Design of High-voltage Power Distribution Devices", the phase-to-phase distance of the outdoor power distribution devices is not lower than the requirements of A2 in the regulations, that is, 110J, 220J, 330J, and 500J are 1000mm, 2000mm, 2800mm, and 4300mm, respectively.
3.2 Failure probability analysis
The possibility of failure of the three-phase electrical and mechanical linkage operating mechanism is analyzed according to Table 3.
For both insulation breakdown and failure of the circuit breaker to open or operate, the probability of electrical or mechanical linkage should occur the same. The difference is the difference in mechanical failure inside the spring mechanism and the difference in mechanical failure between the spring mechanism and the body, namely P3 and P50 in the table.
3.3 Failure Analysis
3.3.1 Possible failure between the organization and the ontology
Mechanically linked circuit breakers are much more difficult to install than electrical linkages. It requires an accurate adjustment between the three poles to ensure that the mechanical connection between the three poles is within the tolerance and guarantees its synchronicity. Under normal circumstances, due to the relatively simple construction conditions on the site, the circuit breaker base and bracket size will also be biased, coupled with the different technical qualities of the construction personnel, it is difficult to meet the installation requirements. It can also be seen from Table 1 that the proportion of mechanical part deformation damage in the partial failure of the mechanism reaches 23%. If the influence of the type of hydraulic and pneumatic mechanism is deducted, the ratio will be larger, which indirectly reflects the on-site installation. The difficulty of debugging increases, which will increase the number of faults after operation. Since the electric linkage operation mechanism is directly connected to the pole of the circuit breaker, the probability of occurrence of the failure is much less.
Secondly, for the mechanical linkage mechanism, the transmission of force and energy at each pole is different, and the pole closest to the mechanism will withstand relatively large mechanical stress; the vibration between the poles is also different, the closest to the mechanism Extremely, the vibration is the most serious. In addition, due to changes in atmospheric temperature, the metal will expand and contract, and the change in the length of the connecting rod will change the position of the circuit breaker when it is closed and closed, and the consequences of this change are serious.
Finally, the stress inside the mechanical link increases as the distance between the phases changes. Generally proportional to dA (1 ≤ A ≤ 2). When linear deformation (such as deformation or elongation), A = 1; when nonlinear deformation (such as: expansion), A = 2. Tests have shown that when the interphase distance is less than 2.5 m, the stress is still within an acceptable range. However, when the phase distance exceeds 2.5 m, stress and deformation have an impact on the reliability and stability of the circuit breaker. Moreover, since the opening distance of the SF6 circuit breaker is much smaller than that of the oil-less circuit breaker, the slight difference in the mechanical transmission has a great influence on the performance of the circuit breaker. This is one of the most important reasons why all circuit breaker manufacturers in the world are unwilling to produce three-phase mechanical linkage breakers of 300kv and above.
3.3.2 The possibility of failure of the organization itself
It can be seen that the number of failures of the spring mechanism circuit breaker is much lower than the number of failures of the hydraulic and pneumatic mechanism circuit breaker. However, compared with the electric linkage mechanism, the three-phase linkage mechanism requires much more operation work than the latter, and the generated stress and vibration are large, and the damage to the mechanism is large. Of course, for each manufacturer, its product performance has a lot to do with its manufacturing quality and process level. Users can choose the manufacturer with low average failure rate and reliable quality to reduce the failure rate, but in general, three-phase. The failure rate P4 of the linkage mechanism is much larger than the failure rate P3 of the electrical linkage mechanism.
4 Summary
The failure rate of three-phase mechanical linkage is greater than that of three-phase electrical linkage mechanism. In the absence of special requirements, the circuit breaker of the electric linkage mechanism should be selected as much as possible; the distance between the circuit breakers of 1l0kV and below is generally less than 2000mm, and the three-phase mechanical linkage method is adopted. More suitable; 220kV and above circuit breakers, the phase distance is generally 3000 ~ 4000mm, the use of three-phase electrical linkage mechanism is more appropriate.