1 Development trend and existing problems of vacuum circuit breakers The advantages of vacuum circuit breakers are not only oil-free equipment, but also its long electrical life, mechanical life, high breaking capacity and continuous breaking capacity. The utility model has the advantages of small volume, light weight, frequent operation, no fire, low operation and maintenance, low failure rate, and the like, and is an ideal electrical equipment for an unattended substation. At present, it is widely developed and used at home and abroad, and has a tendency to completely replace oil arc extinguishing media. At present, most of the substations use multi-functional microcomputer (electronic) protection devices, and the degree of comprehensive automation has also increased, and the requirements for unattended operation have been basically met. Therefore, the main electrical equipment is required to have a certain on-line detection (self-test) function, and vacuum circuit breakers should not be an exception. The main faults of vacuum circuit breakers are mainly manifested in two parts:
(1) Mechanical failure. Since this type of failure rate is less likely to be compared with the electrical failure rate, it is still necessary to implement the online inspection to further unify the plan in terms of structure, size, and combination.
(2) Electrical failure. This type of failure is a major problem that directly threatens the long-term stable operation of the grid, and its probability cannot be ignored. As far as the electrical fault of the vacuum circuit breaker is concerned with the mechanical fault, not only the fault is serious but also has a large concealment, suddenness, randomness, and difficulty in timely forecasting. Therefore, it is also common for manufacturers to remind users to observe the arc-breaking physical phenomenon of the vacuum interrupter in the factory report. Therefore, such failures not only threaten the safety of the power grid, but also cause major problems in personal and national economic losses.
2 Solving the online detection method of vacuum circuit breaker At present, there are many online detection methods for vacuum circuit breakers. The following are common ones: 1 capacitive sensing method; 2 artificial neutral point method; 3 high voltage electric field induction method; 4 resistance capacity Partial pressure method; 5 photoelectric remote sensing method.
In addition to this, there is an online measurement method for vacuum circuit breakers constructed using the Penning discharge principle (electromagnetic wind).
In summary, each has its own characteristics. Although they can also obtain the signal that the vacuum interrupter has a broken breaking capacity due to air leakage under certain circumstances, the electricizing process can achieve the purpose of alarming and blocking. There are still many questions to discuss in order to fully promote the use.
It does not have much impact on the entire system under normal working conditions. It is reasonable and characteristic to use the high-voltage potential and the N (ground) point reference to check whether the vacuum circuit breaker is in good condition. If such methods are used in large quantities, and some vacuum circuit breakers are overhauled or faulty, it is obvious that they are a virtual grounding point formed between the main system and the ground. Therefore, in the calculation of safe work and relay protection, the operation of the distribution network Organizational programs cannot be ignored. As for other solutions, there are also large-volume, complicated structures, poor anti-interference, low seismic resistance, difficult data transmission, and effective vacuum circuit breakers that can only be used for glass casings or for easy observation. Therefore, these methods must be carefully considered for practical impact and feasibility in terms of popularization and actual adoption.
In fact, the online detection of vacuum circuit breakers can also be achieved by other methods, and it is not very complicated. The interest in this topic is to measure the negative pressure changes in the vacuum interrupter. Its main point is that the online detection device itself not only has better electrical insulation capacity, small volume, reliable operation performance, but also has safety specifications, reasonable standards, convenient use, minimum maintenance, and stable cycle. In addition, it must have the dual functions of data remote transmission and local notification. Communication must also have standard transmission characteristics, which cannot be distinguished by relay protection.
To do a good job in the online detection of the vacuum interrupter arc-breaking chamber must comply with the current grid operating mechanism and feedback requirements, otherwise the result of a willingness can only solve a local problem and bring some unnecessary repetitive work or cumbersome.
3 The basic method for realizing the realization of the specific method is to use mechanical sensors to change the refraction angle and conduction amount of the optical signal transmitted by the optical fiber, to change the transmission amount of the optical fiber at the receiving end, and then to perform discrimination, processing, and communication through a subsequent processing circuit. Thereby achieving the purpose of online detection. The benefits of using this method are:
(1) It can solve the problem of insulation of high voltage electrical equipment to the ground.
(2) Detection sensitivity is not only practical but also high.
(3) Strong resistance to optoelectronics, magnetic fields, radiation, vibration and environmental pollution.
(4) Simple structure and self-contained with vacuum interrupter (5) It is very convenient to use and basically requires no maintenance.
(6) Basic conditions for real-time and remote monitoring.
(7) Long-lasting life, basically the same life as the vacuum interrupter.
(8) Low cost.
In the top or ground cover of the vacuum interrupter, there is a pressure detecting component--a sensor (corrugated tube, elastic film or other elastic component), and an auxiliary tensioning element is provided inside to enhance the anti-fatigue of the detecting device. ability. An adjustment device and an information transmission element are also provided on the top of the detection device to form an information sensor. Under normal conditions, the pressure detecting member (which exhibits a high vacuum inside the vacuum interrupter) exhibits a highly compressed state by the action of the natural atmospheric pressure. When there is a leak in the vacuum interrupter (the outside atmosphere enters), the internal vacuum pressure of the vacuum interrupter will be changed, forcing the pressure detecting component to change its compression state, activate the information sensor, and change the light source transmission of the transmitting and receiving fibers. Bonding portion; changing the amount of exposure of the optical fiber B to the optical fiber A. The photoelectric converter G1 of the subsequent processing circuit (see FIG. 2) changes the output parameter of the IC1 (operational amplifier) ​​as the amount of transmission of the optical fiber B changes. Then, the subsequent processing circuit performs another processing on the parameter to finally achieve the purpose of alarming and blocking.
The feasibility of the method not only has the advantages of convenient material selection, reasonable overall design structure and high electrical insulation capability, but also simple implementation method and no additional impact on the power grid due to the presence of the detection device even in the case of a serious accident of the circuit breaker. The reasons this method can be implemented are:
(1) Test devices made of special materials have a good degree of free recovery and a measurement capability of 10-7.
(2) Organic fibers have better light guiding properties (short distance) and their own conversion characteristics have a certain linearity.
(3) Organic optical fibers have good electrical insulation capability and can reach an average of more than kV/cm.
(4) Organic optical fibers do not need to perform special photoelectric conversion work to transmit signals within a short distance.
(5) The flexibility, corrosion resistance and flame retardancy of organic optical fiber are better, which is more suitable for this project.
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