The Guangxi 500kV power grid, which holds an important strategic position in the middle of China’s West-to-East China Southern Passage, has been officially put into operation for the past 11 years from 1992 to the present day. Nearly 4 000 km long, the transmission of electrical energy capacity of 5.2 million kW, put into operation 500kV substation and booster station up to 10, the number and size of the country's forefront.
The types and types of ultra-high voltage electrical equipment in operation in Guangxi are numerous, and domestic and imported parts account for a considerable part, and the equipment quality and operation conditions have their merits. This article summarizes and analyzes the experience of operation, maintenance, and accident analysis of these 500kV equipment for 11 years.
1 Transformer equipment 1.1 Transformer transformers 38 sets, of which 8 sets of three-phase transformers are mainly used as booster transformers and liaison transformers for Tianshengqiao Class 2 hydropower plant and Yantan Hydropower Plant, and Tianshuiqiao Class 2 hydropower plant for liaison (Mitsubishi, Japan). The company's 750MVA shell-type transformer has the largest capacity, separable phase transportation, on-site assembly, independent magnetic circuit but connected to the oil road, suitable for the transportation of inconvenient hydropower stations; 30 single-phase transformers are mainly used for 500kV substations, and the main manufacturers are ABB Italy. Company, Changzhou Toshiba, Shenyang and Baoding Transformer Factory.
At present, all transformers are in good condition. However, the three 500kV single-phase transformations of the subsidence have abnormal chromatograms of oil chromatograms at different initial stages (1993). When the A-phase is highest, C2H270X1 (T6, total hydrocarbon 13X1 (T3. Observed load current and voltage) Changes in chromatograms in oil are diagnosed as faults appearing on the magnetic circuit instead of the circuit, and will not immediately lead to insulation accidents, avoiding the peak of power transmission in June and systematically inspecting the three transformers on the spot during the dry season at the end of the year. The fault was found on the magnetic circuit, namely the magnetic shield of the fuel tank and the upper yoke clamp parts: the magnetic shield fixed on the fuel tank by the insulating cardboard was damaged in the board, causing a potential difference between the clamp parts and discharging; the coil pressure board pressed the bolt and The loosening of the cover caused the suspension potential to discharge, and the three transformers have been operating normally for 10 years after being inspected and handled by the on-site hanging cover.
1.2 High-voltage shunt reactors More than 60 reactors, single-phase, core or shell type, single unit capacity is 50MVA, the main manufacturers are Japan's Mitsubishi, ABB, Xi'an, Shenyang, Baoding Transformer Factory. Through the implementation of insulation technology supervision and operation and maintenance work, all current high-resistance operations are running well. However, ABB's high resistance in the Tianguang 500kV two-circuit line has an abnormal noise, vibration, and high oil temperature at the initial stage of operation. In addition, the H2 and total hydrocarbons in the oil chromatogram are very long, and they are often alarmed by the high oil temperature. As a result, the circuit breaker was jumped. Eventually, a major insulation accident occurred at the B-phase high-resistance point on the Pingguo Substation. The high-pressure relief valve was operated to inject fuel, and the flange of the 500kV bushing was fractured half the circumference. The neutral point was low. Cracks appear in the casing, and light and heavy gas and differential protection operate correctly. Jump the switch on both sides of the line.
Hanging inspection analysis is as follows: 1 high vibration during operation, resulting in iron core through the eccentric core and touch the core wall, insulation damage, short-circuit core and clip parts; 2 clamp clip anchor bolt is not tight, because Vibration exacerbates loosening. In addition, the equipotential connecting piece of the upper iron yoke is inserted too deeply and the gap between the silicon steel pieces is large, which is one of the causes of vibration and noise. 3 The rising of H2 and CH4 in the fault gas is judged from the characteristic gas analysis. Low-energy discharge, accompanied by low-temperature overheating, is analyzed as follows: First, the iron core short-circuits the clip and then acts as a whole in the magnetic field. Since each lead wire is grounded, it is equivalent to two points of ground, thereby generating a circulating current and causing low-temperature overheating. The second is that the iron yoke of the reactor has a defective installation quality. The edge of the silicon steel sheet is not completely aligned. Under abnormal conditions, some core sheets cause excessive pressure and localized slight deformation, causing weak discharge and local overheating.
After the high-resistance was returned to Italy for dissection and X-ray analysis, it was found that there was an arc-induced micro-hole in the high pressure casing pressure sphere. Pressure equalization ball surface in the manufacture of the formation of the trachoma can not be distinguished, the operation of the 1. arrester in the domestic three-kilo structure majority of major manufacturers in Xi'an blishing stadium strong distortion, resulting in partial discharge and continuous development, small holes continue to expand, so that the electric field distortion Severe, eventually leading to breakdown of the main insulation and discharge to the inner wall of the tank. The situation on the site is basically consistent with the above analysis.
1. Current transformer (TA) step analysis believes that this type of TA suddenly exploded in the normal operation of the system and normal test detection, mainly due to the manufacturer's problems in the selection of insulating materials and manufacturing processes, and these Accidental hazards are difficult to detect by routine preventive testing of dielectric loss. In response, Southern Company has replaced more than 100 sets of Tianguang First Cycle Transmission Project with more than 40 sets of TA (Shenyang Instrument Transformer Factory Type LB-500) selected earlier in this type of TA. In 1997, it was found that dielectric loss was generally exceeded. The results of the two thermal stability tests performed by the Institute and the Shen-Yuan Group on the two products were basically the same. The tangential loss reached approximately 3.6% after it was basically stable without any final breakdown. Based on this, it is believed that although these TAs have exceeded the dielectric loss, they will not immediately jeopardize the safety of the equipment. They can be arranged in batches to return to the factory for overhaul in dry season. More than 40 TA major repairs have performed well so far.
1. There are more than 100 CVT CVTs, and the main manufacturers are ABB, Guilin, and Xi'an Power Capacitor Plants. In the early days of ABB CVT, local capacitor breakdown caused a high secondary voltage. Later, in the full-voltage ratio error test, it was found that the internal discharge of the device was increased to approximately 60kV when boosted, and the main capacitance became large, causing partial pressure. The capacitive reactance becomes larger and the secondary voltage is higher.
The test voltage of the traditional pre-test is too low to detect such failures. It was found that the insulation margin of this type of CVT design is small, and that the electric valley single pole is easy to break down. After the batch of products are all replaced.
Domestic CVTs have also experienced some failures during operation, such as the breakdown of small surge arresters in the internal medium-voltage transformers, and the occurrence of abnormal noises when the reactors are loosened. One of the CVTs had a pre-test intermediate loss of 0.2% and a breakdown occurred three months later, causing the line to trip. Therefore, we must pay enough attention to the CVT with large dielectric loss.
2 arrester electric porcelain factory and Fushun arrester factory. The overall operation of the arrester is good. In the pretest, the DC voltage is less unqualified each year. The main problem is that the base insulation resistance is low, and most of them have undergone technological transformation. However, two explosions still occurred during the operation.
Together, a group of lightning arresters in the Liuzhou Shatang 500kV substation exploded during operation. There were flashes of burns inside the valve plate, and the entire phase (total of 3 knots) penetrated from top to bottom. The reason was that the lightning current amplitude was too high to exceed the lightning arrester resistance. The internal components of the lightning arrester that are affected by the ability but are damp and defective are flash-through breakdown under the lightning overvoltage.
Another is the 500kV line lightning arrester of the Tianshengqiao secondary power plant (two-phase structure produced by Mitsubishi). The leakage current at the DC voltage is high (130MA) since it was put into operation, which is more than double the domestic equivalent, but the annual value. No change, and the charged current measured every year will remain unchanged and the three phases will remain balanced. Because there was no corresponding Japanese Mitsubishi product standard, it was not processed and finally exploded during operation.
3 circuit breaker high-voltage circuit breakers several hundred units, more imported products than domestic, the main manufacturers are Japan's Mitsubishi, France Alstom, Germany's Siemens, Xi'an high-voltage switch factory, Pingdingshan switch factory. There are 4, 3, 2 fractures, etc. from the switch fracture. There are mainly hydraulic, pneumatic, and spring-operated mechanisms from the steering mechanism. All switches are SF6 gas insulated switches. The main problem of the switch in operation during the annual pre-test is that the disconnected shunt capacitor dielectric loss is mostly exceeded (they are generally replaced after discovery). Another problem is that the low-voltage operation test of the switch is often unqualified. In the past 10 years, the overall operation has been sound and no malignant explosions have occurred. However, a vicious explosion accident occurred during the commissioning of Guiguang Transmission Project this year. The switch is a double-break SF6 circuit breaker of Hangzhou Siemens Company. When the power is turned on, the arc extinguishing chamber has flashed and the line protection action trips. When the cause is not clear, the switch in the opening position is charged again, causing a comminuted explosion after the charge is instantaneously grounded, causing damage to the surrounding equipment.
After the accident, the insulation lifting rod has penetration flashover marks, which may be a problem in the production, transportation, preservation, or installation of the switch. Before the operation, lift rods and fracture pressure tests have not been performed. To ensure that no similar accident occurs. The 500kV circuit breaker that requires new production must be tested for DC leakage and AC withstand voltage.
4 Conclusion Manufacturing quality of domestically produced 500kV power transmission and transformation equipment has been greatly improved. It is not worse than imported equipment. It fully meets the engineering needs and is reflected in the lower accident rate than imported equipment, but its appearance quality is inferior to that of imported products.
Doing a good job in insulation technology supervision is a prerequisite for safe production.
Adherence to the annual preventive testing work will promptly detect and deal with operational equipment defects and hidden accidents, reduce the accident rate to a minimum, and ensure safe operation in the future.
The rod and the club contact 3 are in an open state, and the A phase is turned on after a slight touch (see discharge point 1).
Table 3 megohmmeter measurement results DC measurement voltage / kV breakdown 1.3 After the test phase C plum blossom contacts 2 and 3 between the conductive rod and the three connections after the three-phase measurement of normal data, discharge phenomenon eliminated.
1.4 Part of the fault analysis process phenomenon 1.4.1 GIS quasi-homogeneous field SF6 breakdown field strength is much higher than atmospheric pressure, the external performance of the discharge (voice, interference, etc.) must be very different. Therefore, when the voltage is applied to 50 kV, a clear discharge sound can be heard under the condition that the air chambers 1 and 2 are inflated, and no clear discharge sound is heard when the air chamber 2 has no SF6 gas. Comparing the test data of Tables 1 and 2, it can be concluded that when the gas chamber is filled with SF6 gas, the C-phase discharge is the intermittent breakdown in the case of Table 1, and when the gas chamber is opened, the C-phase discharge is the continuity in the case of Table 2. The stable discharge.
The discharge point in 1.4.2, which is the discharge point of the C-phase MOA low-voltage lead at the clamp (non-metallic grounding), is not the real cause of data anomalies during the handover test. Because there is no gap discharge between the high-voltage leads, the voltage of the low-voltage lead to ground is so small that it does not cause discharge at all.
1.43A phase MOA high voltage conductive rods have only a slight contact failure. When the continuous current is measured, the continuous current is discharged after the low voltage discharge. The test data is normal. However, if the partial discharge caused by poor contact is not treated, it will seriously affect the safe operation of GIS.
2 Conclusions Under the same gap conditions, the discharge voltage when charging SF6 gas is much higher than the discharge voltage in the air. At the same time, external discharge sound, discharge current and other phenomena are also very different, so look for the conduction left during installation. In the case of failures such as rod gaps, it is necessary to consider whether the air chamber is inflated or not, and it is not possible to judge whether the fault exists or is reduced merely by eliminating or weakening the discharge phenomenon after discharging the SF6 gas.
When measuring the continuous current of M0A, poor contact of the high-voltage lead leads to severe discharge (large gap or excellent dielectric insulation performance), which will make the measurement result unstable or even interfere with the normal operation of the measuring instrument.
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