Quiwen substation structure and its equipment: indoor power distribution, 220KV high-voltage room (upstairs): Pingdingshan High Voltage Switchgear Factory GIS, 110KV high-voltage room equipment (downstairs in the middle): Xi'an High Voltage Apparatus Research Institute Limited Liability Company products, 10KV high-voltage room (downstairs on the south side): Wuxi ABB products, 1 main transformer and ventilated room (downstairs on the north side).
Summary of the contents of the spring inspection in 2009: 110KV GIS internal gas pressure drop, equipment, low pressure alarm, indicating that the annual gas leakage rate does not meet the standard; 110KV GIS, 220KV GIS gas chamber micro-water exceeds the standard; 1 main variable body oil seepage. Overhaul report has been given by Weifang Power Supply Company Repair and Inspection Field. Inspection and maintenance tasks by the Weifang Power Transmission Engineering Company (not out of the project warranty period, is the scope of elimination), manufacturers and Weifang Electricity Bureau repair and inspection field **** with the undertaking.
(A) fully enclosed SF6 combined insulated appliances within the gas chamber gas pressure drop failure analysis and preventive measures
1, the problem: the problem all appeared in the production of fully enclosed SF6 combined insulated appliances produced by the West High, including a number of outgoing intervals, PT intervals. Mainly concentrated in the equipment on the inlet air chamber and disconnecting switch air chamber.
2, fault detection means: Quiwen station equipment for the gas density standards for the circuit breaker gas chamber 0.52MPa, the other no arc-breaking function of the gas chamber 0.42MPa. When the gas chamber gas pressure drops, on the one hand, the gas pressure gauge on the equipment will appear unreasonable decline, that is, more than the national standard gas annual leakage rate (detection of low credibility, mainly in the measurement error, and by the ambient temperature). (the low reliability of the test is mainly due to the high measurement error and the high influence of ambient temperature changes). On the other hand, the equipment can send protection signals such as telemetry and telecommunication through the relay protection device (gas density relay), and the gas density can be monitored in time through the backend machine. When the instrumentation and other mechanical strength of the weaker parts of the equipment damage caused by a large number of SF6 gas leakage, installed in the high-voltage chamber of the gas alarm device will act to send an alarm signal.
3, GIS gas pressure is not normal may bring the consequences:
(1) SF6 gas as a high electrical insulation strength of the insulating medium, is the main component of the equipment insulation, when the gas pressure drops, the insulation strength of the equipment will drop. Cause the GIS to withstand overvoltage ability to decline. When the gas pressure drops beyond a certain threshold, GIS can not even guarantee the insulation strength of the frequency voltage (due to the role of automatic protection devices, unless the extreme case, this situation will not occur), the internal conductors of the equipment will be discharged to the equipment shell resulting in a short-circuit fault ground. If the relay protection device does not act to remove the faulty portion in time, the fault may develop into a phase-to-phase fault, resulting in an internal system shock and a huge electromotive force destroying the electrical equipment.
(2) SF6 gas is not only an important part of the equipment insulation, but also the main arc extinguishing medium of the GIS circuit breaker gas chamber. When the circuit breaker gas chamber gas pressure drop, its arc extinguishing ability to fall, if the circuit breaker gas chamber gas pressure drop more than a certain threshold, the gas arc extinguishing ability is seriously reduced. Relay protection device at this time will block the circuit breaker closing function, resulting in the loss of switching circuit capacity. If the protection device does not block the circuit breaker closing function and at this time and the operation of the circuit breaker, due to the effective time and space can not cut off the arc, if the arc contacts the equipment shell, will cause the corresponding electrical equipment failure.
4, the relevant theoretical analysis: (1) on the SF6 gas high pressure analysis: by Paxing's law curve can be seen, the use of high pressure, the density of the gas increases, the average free range of electrons to shorten the average collision between the two adjacent collision, the probability of electrons accumulate enough energy to reduce, that is, increasing the difficulty of ionization makes the discharge voltage rise. (2) the use of SF6 as an insulating medium: SF6 has a strong electronegativity, easy adsorption of electrons with strong activity to form a stable negative molecules, weakening the gas power process, increase the discharge voltage; chemical stability, has a high electrical insulation strength; SF6 gas has excellent arc extinguishing properties, its arc extinguishing capacity is 100 times that of air.
5, the basic method of treatment: As the strategy used is still preventive maintenance. So the method is also relatively traditional, that is, the GIS shell leakage point to find out, and then the leakage point can be repaired. In the overhaul process, the use of traditional bandaging method of combined electrical leakage gas chamber to determine the area of the leakage point, to determine the area after the SF6 leak detector probe on the emergence of the leakage of the region to scan, to find out the leakage point (in the basic confirmation of the location of the leakage point of the general situation, can be used to apply soap bubbles to further confirm the method). The leaks are mainly located at the joints of the gas chambers, which are more likely to be marked with green tape (the joints of the two connected gas chambers). This point is physically easier to understand, the metal surface out of the installation of the sealing ring and sealant sealing, if the sealing ring quality is not good or sealant is not evenly coated, or tightening screws on the torque is not uniform, may trigger the generation and development of leaks. Another place where leaks are easier to find is at the interface of the instrument, where the self-sealing valve is connected to the pipe body. This is caused by the mechanical structure. In addition, in the maintenance process, found in a gas chamber of the cable terminal leaks, and another gas chamber to the cylinder wall found leaks. After the leakage point leakage is found, for the interface of the leakage point is often used to re-tighten, change the sealing ring and other measures can be eliminated leakage point; cable terminal leakage due to 110KV high-voltage cables, it requires manufacturers to re-produce the cable terminals; for the leakage point on the wall of the cylinder to find a specialized manufacturer of leakage welding repair (welding is completed by specialists, to prevent the inner side of the cylinder wall of the GIS due to high temperatures to produce rational changes, resulting in cylinder), and the leakage point leakage is found. Decomposition of impurities, serious damage to the gas chamber internal insulation environment).
6 Knowledge and insights on the monitoring methods of GIS gas leakage faults and the measures to prevent such faults from occurring.
The use of gas density relay, the gas density signal transmitted to the relay protection equipment can be regarded as a monitoring method. But this monitoring method has certain limitations, which is mainly because the density and activity of the gas is affected by temperature or vibration. In particular, the circuit breaker gas chamber, the action mechanism in the moment of opening and closing the release will trigger a great deal of vibration circuit breaker; and the temperature is different at the same time, the gas activity and expansion coefficient is also different. It has been pointed out that the installation position of the gas density relay has a certain impact on the measurement accuracy. I think, for the monitoring of gas leakage, should focus on the following aspects of all kinds of considerations:
(1) Consider the outside world vibration or the impact of the split for the measurement error and its correction of this interference method. The most basic such as the use of multiple circuit breakers, the relevant parameter comparison of the inoperative circuit breaker.
(2) Consider the changes in gas density and pressure when the temperature is different, consider the temperature distribution of the gas inside the circuit breaker at different locations; seasonal and weather changes, consider the gas density distribution.
(3) a combination of other signals to determine the gas leakage: for example, the size of the current through the conductor (resistance to heat) as a factor for consideration; the internal occurrence of partial discharge, the local discharge signal and the combination of gas density signal. Of course, these depend on the signal processing and its intelligent analysis process.
(4) Detection and monitoring of both methods: now there has been the existence of laser camera type SF6 gas leakage detector, it is said that the existence of a high degree of sensitivity. From an economic point of view, it can be used as a supplement to online monitoring. In addition, the weak points of the gas chamber are also characterized, which provides a quick way to deal with this means of detection.
(5) the most important I think should be the rapid leakage of gas may lead to a serious failure of the diagnosis of the situation, this diagnosis must be fast, accurate. For example, if there is a rapid leakage of gas and the conductor is already discharged (change in temperature) and the equipment is not equipped with highly sensitive fast-acting protection (e.g., longitudinal differential protection).
On the prevention of such failures, I believe that focuses on the following 2 aspects:
(1) Improvement of the processing accuracy of power system equipment, improve the materials used in GIS equipment. Such as the use of ultra-low temperature for electrical assembly.
(2) Improve the operation standard of the electrical construction and operation personnel, and work strictly according to the perfect regulations.
(2) totally enclosed SF6 combined insulated electrical appliances internal gas chamber gas micro-water fault analysis and preventive measures
1, the problem: the problem is more serious in the 110KV GIS produced by Xigaozhuang, and Pingdingshan high-voltage switchgear factory also has an interval of PT gas chamber micro-water exceeds the standard.
2, fault monitoring means: micro-water standards in different types of gas chamber has different provisions, you can refer to the relevant regulations. This site is tested by the repair yard, through the micro-water tester to obtain the micro-water situation in the gas chamber. From the configuration of relay protection telecommunication, there is no telecommunication signal of micro water quantity. Therefore, in this overhaul and the normal operation of this station, the monitoring of micro-water has been used off-line monitoring method. (Note: in accordance with the regulations, the new injection of gas micro-water detection should be carried out 24 hours after the completion of the filling)
3, micro-water exceeds the standard hazards: under normal conditions, SF6 gas has good insulation and arc extinguishing performance, and when the atmospheric moisture intrusion of the gas chamber or the gas chamber wall of the medium of the water escaped, the water in the SF6 gas will increase. The consequence is a significant reduction in the electrical strength of the gas. Especially circuit breakers, such as the presence of arc gas chamber, SF6 gas in the arc and moisture *** with the role of physical and chemical reactions will occur, and ultimately generate highly corrosive hydrofluoric acid, sulfuric acid and other highly toxic chemicals, etc., on the circuit breaker's insulating materials or metal materials caused by corrosion, so that the insulation degradation. In addition, when the micro-water seriously exceeds the standard, it may even cause the conductor to discharge to the barrel wall and flashover along the surface of the inside of the barrel wall. In the absence of timely treatment, eventually leading to electrical accidents.
4, the relevant theoretical analysis
From the point of view of the design of insulation, we hope that the insulation of the main equipment as uniform as possible. And for SF6 gas, its excellent insulation properties of the full play is only in the uniform electric field can be realized. When the gas contains water, by the arc and partial discharge excitation, SF6 thermal dissociation produces sulfur and fluorine, these impurities and water cracking oxygen and hydrogen produced by a series of physical and chemical reactions to generate hydrofluoric acid, sulfuric acid and metal fluoride and so on. These impurities will corrode the inner cylinder wall, destroying the uniformity of the electric field and destroying the insulation. Therefore, GIS requires very strict control of moisture and impurities.
Personal understanding: SF6 contains moisture in the analysis can draw on the theory of liquid dielectric breakdown, such as "small bridge theory" analysis. Moisture in the internal impurities caused by the original nearly uniform insulation structure in the construction of the insulation of the uneven area, looks like the insulation level to reduce the "small bridge", and this "small bridge" area is the " The "bridge" area is the short board in the "short board of the barrel".
5, micro-water exceeds the standard reason analysis:
(1) SF6 gas product quality is not qualified. That is, the new gas injected into the equipment is unqualified, which is mainly caused by the gas production plant on the new gas testing is not strict, the transportation process and storage environment does not meet the requirements, storage time is too long.
(2) The circuit breaker is filled with SF6 gas with moisture, which is mainly caused by the staff not according to the regulations and maintenance operation requirements for operation.
(3) Moisture brought in by insulation parts. Manufacturers do not dry the insulation before assembly or drying treatment is not qualified. During overhaul, the insulation is exposed to moisture in the air.
(4) Moisture penetration through the sealing connection. The moisture pressure outside is higher than inside the air chamber. Moisture seeps in through tube wall connections, etc.
(5) Moisture infiltration at leakage points. Leakage points such as filling port, pipe joints, leakage at the flange, sand holes in aluminum castings, etc., are channels for moisture to penetrate into the interior of the circuit breaker, and the water vapor in the air gradually penetrates into the interior of the device.
(6) The electrical installation process is not carried out in accordance with the temperature and humidity specified in the regulations.
(7) Moisture in the gas moisture adsorbent. This is generally less impact, because the intact adsorbent is vacuum-packed, when the vacuum packaging is found to be abnormal, this band of adsorbent will not be in use.
6, micro-water exceeds the standard treatment of the basic method: will measure the micro-water exceeds the standard gas chamber gas is discharged directly into the atmosphere (in accordance with the provisions of the regulations, should be recovered through the SF6 recovery device, but is limited to the recovery of the high cost of purification and the violation of the operation); replacement of adsorbent
agent (new intact adsorbent with vacuum packaging, the best before replacing the replacement of the oven to heat up before replacement); through the vacuum pump to extract a vacuum until the gas chamber inside the vacuum pump to extract a vacuum until the adsorbent will not be used. Vacuum pump to extract the vacuum until the negative pressure inside the gas chamber reaches the standard of the regulation (due to the use of the vacuum meter to measure the vacuum degree, so it is not very accurate, and the vacuum pump on the vacuum gauge is not very trustworthy. Therefore, the vacuum level should be larger relative to the regulation margin. In addition, when measuring the vacuum degree with the vacuum meter of Mack's, the operation should be standardized to prevent the mercury in the vacuum meter from entering the cylinder through the self-sealing valve to cause insulation accidents); further drying of the gas chamber by injecting dry nitrogen; then extract the vacuum to reach the standard; injecting a new SF6 gas (gas injection should pay attention to the brand of the gas, the gas of different manufacturers do not try to mix and fill the gas, and try not to mix and fill the new gas and the old gas).
7, the GIS micro-water fault monitoring methods and measures to prevent such failures and insights.
Limited to their own knowledge and practice, the GIS micro-water fault monitoring methodology is very little understanding. And I think: for the GIS micro water online monitoring is just borrowed similar to the transformer oil moisture detection or hydrogen cooling generator hydrogen humidity detection method. Micro-water detection, the usual offline detection means is only the use of dew point meter. Monitoring can be achieved by installing the dew point sensor of the instrument, i.e. the humidity sensor, inside the equipment, but there are also feasibility and economic considerations. These are also dependent on the development of newer sensor technology and advances in communications technology.
On the prevention of such failures, I think focus on the following two points:
(1) improve the production quality and technology of electrical products and related products, such as the use of self-sealing inflatable valves on the GIS is a good example.
(2) Improve the operation level of electric power construction personnel, which is critical.
(3) Improve the automation level of the power grid, focusing on the development of online monitoring technology for electrical equipment.
Conclusion: From this spring inspection process, the construction and operation of the power system must pay attention to the following points: 1, a reasonable choice of electrical products, in this overhaul and operation, the product quality of the West High relative to the quality of the four major high-voltage switchgear factory (Shenkai, Xikai. Pingkai, Taikai) product quality is poor; 2, improve the quality level of power system operators, strict management, many of the causes of failure are due to the construction or operation of the operators in the illegal operation of the consequences; 3, the study of the power system operation process fault detection technology, improve the automation level of power system operation.