10kv and sf6 load switchgear has the advantages of safety, convenient installation, less maintenance, small size and low price, and has won the favor of users. Since the adoption of 10kv load switch in China, the products of sfg switch of abb company and sm6rm6 of Schneider company have occupied most of the domestic market. With the domestic manufacturers gradually mastering the manufacturing technology of 10kv and sf6 load switches, the number of domestic 10kv and sf6 load switches is increasing. At present, more than a dozen domestic manufacturers are producing different types of sf6 load switches.
Our company is one of a dozen manufacturers. In the process of producing sf6 load switch, we learned a lot of good experiences from our brothers. In order to get more help and guidance from experts, scholars and peers, the technical measures for quality control of 10kv and sf6 load switches in our company in recent two years are briefly described as follows. Please give your comments.
A, epoxy resin insulation shell:
Epoxy resin has become the first choice for manufacturing high-quality insulation parts because of its good mechanical, insulation, aging resistance and manufacturing process performance, and the glue pressing process has fully exerted the various performance advantages of epoxy resin. The insulation shells of sf6 load switches of various brands at home and abroad are made of epoxy resin by glue pressing process. The process flow is as follows:
Because the switch shell has the functions of insulation, air tightness and mechanical support at the same time, its structure is complex, and its mechanical performance and accuracy are high, which undoubtedly puts forward strict requirements for material selection and manufacturing technology.
1. Material selection
1. 1 epoxy resin:
Basic epoxy resin (that is, epoxy resin produced by a large resin factory with an annual output of thousands of tons) and curing agent can not be directly used to produce insulation parts, especially the epoxy resin and curing agent used in the insulation shell of sf6 switch need special modification to improve its mechanical strength, toughness, cold and hot impact resistance and processability. Different manufacturers' modification technologies have their own advantages, which are suitable for different product requirements. As a supporting part, the insulation shell of sf6 switch is subjected to certain impact during the switch opening and closing process, which puts forward higher requirements for the strength of epoxy resin. In order to fill sf6 gas into the switch housing and ensure a very low leakage rate, higher requirements are put forward for the adhesion between epoxy resin and plug-in. In recent years, cracks have appeared in the shell of sf6 load switch during production or work. After testing, the tensile strength and bending strength of the cracked shell are not low, but the impact strength representing the toughness of the material is low. It can be seen that the impact strength of sf6 switch insulation shell is the most important among all performance indexes. After our repeated screening, the domestic he2082-hh2082 material is especially suitable for producing sf6 switch insulation shell. The measured glass transition temperature of the system is 104℃, which meets the requirements of an internationally renowned brand. From 100℃ to10℃, the impact strength reaches 15kj/m2, which exceeds the average value.
12 silicon micropowder:
Adding silicon powder to epoxy resin can improve the heat resistance, hardness and dimensional stability of cured products and reduce the production cost. Due to the different mineral sources and production processes, silicon micropowder has a great influence on the properties of cured epoxy resin. In the production of general products, the viscosity of the mixture or the amount of silica fume can be used as the main index to measure the quality of silica fume. However, as a formula system for producing important thermal insulation parts, the high performance of cured products is the first choice to measure the quality of silicon micropowder. After adding high-quality silicon powder into epoxy resin, the viscosity is high, which makes the addition amount low. It is considered that the high content of needle-like particles in silicon micropowder just improves the mechanical strength of epoxy resin.
1.3 dye:
The dyes used in epoxy resin are nothing more than organic dyes and inorganic dyes, and organic dyes have no obvious effect on the electrical insulation performance of epoxy resin reinforcement; Inorganic dyes are mostly metal oxides with iron oxide as the main component. Adding epoxy resin will increase the dielectric loss of cured products, so in order to ensure the electrical insulation performance of products, inorganic dyes should not be added to the formulation system as much as possible.
In order to ensure the electrical insulation performance, the technical index of fe2o 3 content of electrical grade silicon micropowder is required to be ≤0.0 1, and adding 1.5 iron oxide red powder in the formula system is equivalent to increasing the fe2o 3 content of silicon micropowder to 0.5, which is 50 times of the basic content, thus affecting the electrical insulation performance.
2. Insert pretreatment:
In order to ensure good adhesion between epoxy resin and insert, good pretreatment of insert is also very important. Pretreatment of the insert includes sandblasting, cleaning oil and dust, accurately preheating to the same temperature as the mold, and being careful not to over-oxidize, so as to avoid the extremely low-strength copper oxide affecting the bonding strength between the epoxy resin and the insert, and to ensure that the insert is not polluted twice during the turnover process. The good adhesion between epoxy resin and insert not only ensures a very low air leakage rate, but also makes the product have a very low partial discharge. When the discharge capacity is 15kv, it is only 5pc.
3. Post-curing, setting and cooling:
The elastic modulus of epoxy resin at room temperature is very high, for example, the shear elastic modulus reaches 4000mpa, which is in a rigid state; When the temperature exceeds the glass transition temperature, its shear elastic modulus is only 40mpa, showing a high elastic state. It can be deformed under a small external force. Using this characteristic, the mating surfaces of the upper and lower casings of sf6 switch insulation casing can be set on the flat plate with a certain precision in the post-curing process. After curing, the product is cooled with the furnace at a very low cooling speed (≤5℃/h), which is not only beneficial to ensure that the flatness error of the mating surface of the upper and lower shells of the insulating shell is small, but also the internal stress of the product is very low and will not appear in the future.
After such treatment and proper selection, the mating gap between the upper and lower shells is less than ≤0.25mm, so that when the upper and lower shells are locked together, the deformation internal stress of the product is extremely small, which ensures the safe use of the switch and will not cause cracking and air leakage.
Second, the quality control of sf6 load switch leakage rate.
The leakage rate of sf6 load switch has always been the focus of manufacturers and users. The sealing test of foreign product load switch with inflation pressure of 0.04mpa hours shows that the annual leakage rate is basically about 0.05/ year and the service life of the switch is 30 years. The sf6 load switch produced by domestic enterprises has an inflation pressure of 0.045mpa, and the annual air leakage rate of 24-hour sealing test is high, both of which are about 1 ~ 0.5/ year.
What makes the annual leakage rate of similar products at home and abroad so different?
After analysis, we think that the main reason is that the material and performance of sealing rings produced in China are worse than those produced abroad. In view of the problems existing in the sealing ring, we consulted the sealing experts many times and changed the shape and material of the sealing ring. We use the patented technology of the Institute of Sealing Technology. The sealing rings used between the upper and lower shells and between the movable fittings and the shells are changed into "□"-shaped sealing rings, and the material is changed into cork rubber. In order to ensure the life of the rubber ring, a hot air aging test of 100℃×24 hours was carried out, and the hardness changed by 2 degrees. Elongation change 16, tensile strength change 15, and oil resistance test of 25# transformer. 100℃24 hours volume change 2.8, weight change-1. 1, hardness change -3 degrees, brittleness temperature change -45℃.
The test results show that the performance of the sealing ring meets the requirements. At the same time, the EPDM sealing ring used in the ventilation valve and observation window is changed into butyl rubber with good oil resistance, high and low temperature resistance and good performance. The clamping line is changed to non-sealing surface, which greatly improves the sealing effect.
We modified the assembly process of sf6 switch with "□" sealing ring, and changed the tightening sequence of bolts: the locking force of bolts was reduced from 30n/m to 22n/m, and the switch was sealed after 100 "on-off". The inflation pressure of the switch is 0.045mpa, and the basic values measured before and after 24 hours are exactly the same. This shows that the accuracy of the leak detection equipment cannot be measured at 10-7, which means that the leak rate is basically zero. Therefore, it is stipulated that the growth value measured in about 24 hours is zero, which is the testing standard of our company. If there is a change around 24 hours, the product is considered unqualified. In this type test, the leakage gas concentration increment δc=0.03μl/l, and the closed cover volume VM = 2.46 m3. Sample volume v1= 0.72m3; Inflated volume in the switch v = 0.029m3 interval Δ δt = 86400s；; Absolute atmospheric pressure p = 0.1MPa; Sf6 switch inflation pressure pr = 0.045mpa；; F = (δ c× (VM× v1)× p)/δ tfy = [(f× 31.5×106)/(v× (PRP) )×100. After calculation.
Third, the quality control of loop resistance.
Domestic sf6 load switch technical conditions generally stipulate that the main circuit resistance is ≤ 65 μ Ω, and foreign similar products are ≤ 42 μ Ω. In order to reduce the loop resistance of sf6 switch and reach the level of similar products abroad, our company made an analysis and finally came to the conclusion that one of the reasons affecting the loop resistance is the magnitude and consistency of the clamping force between the static and moving contacts. We have done a lot of experiments here, determined that the clamping force is between 160n- 190n, screened the disc springs that affect the contact clamping force, and selected the cooperative manufacturers that can guarantee the quality. Our company has made a contact clamping force tester in a professional manufacturer, and the measurement accuracy is 1n, which ensures the consistency of contact pressure. The second reason is that the spherical contact of r 13 of the static and moving contacts must be greater than 85 of the whole spherical surface, so as to ensure that the resistance value of the main circuit of the switch is below 40μω. The above two conclusions ensure the temperature rise test and loop resistance test before and after the type test life. The test results are shown in table (1), which makes the quality standard of control loop resistance of the company ≤ 42 μ Ω, and its through-flow temperature rise test margin is large. The maximum temperature increase is only about 50 of the specified value. See table (2)
Fourthly, the quality control of electrical life.
In order to test the product process quality of fln single-break sf6 load switch, our company specially entrusts the quality inspection center of electric power equipment and instruments in the electric power industry (namely the switch test station of China Electric Power Research Institute) to conduct type tests according to the technical requirements of GB/T1KLOC-0/022-1999 "High-voltage switchgear and controlgear".
In the opening and closing test of fln load switch, it was conducted as required (mode 1: "On and off" rated active load opening current of 630a, 100 times; Mode 2: "On-off" closed-loop current 630a, 10 times; Mode 3: "On-off" 5 rated active load interrupting current 3 1.5a, 20 times; Mode 4: "On-off" rated current charging current is turned off 10a 20 times; Mode 5: Turn on the peak rated short-circuit starting current of 50ka twice, and turn on the grounding switch of 50ka peak rated short-circuit starting current twice) Main circuit with mechanical life of 5000 times, grounding for 2000 times, and transfer current 1700a. After the above rigorous type test, it shows that the assembly process and inspection process of sf6 load switch in our company are correct and feasible.
On the basis of successful type test, our company dissected and analyzed the test products, and found that the high temperature resistance of insulation grid material was not ideal. After short-term withstand current of 20ka and 4s, the high temperature resistance of polycarbonate material is not very good, and the insulation grid is deformed around 100℃. Consult relevant experts, update the raw materials of the isolation barrier, and select the high insulation material polyamide that can work normally at 250℃. The type test results of our company's load switch switchgear used in other factories show that polyamide material greatly improves the performance of the isolation barrier, which makes the sf6 load switch complete the opening and closing test very smoothly, and no deformation is found after withstanding the current of 20ka for a short time.
Five, sf6 switch water content control.
According to the requirements of the national standard GB/11022-1999 "General Technical Conditions for High Voltage Switchgear" and dl/t596- 1996 "Preventive Test Regulations for Power Equipment". Our company has implemented trace moisture control for sf6 load switch. First of all, we should pay attention to the guarantee of the transformation process system in the production environment, and third, we should monitor the measuring instruments. In the transformation of production environment, a special workshop for sf6 load switch production line was built. The production line meets the requirements of dust-free, constant temperature and humidity, and its technology and process discipline are the guarantee for manufacturing qualified products. When executing the process, we check the original process. After many tests, the assembly process and baking process were modified. The requirements of baking time, baking temperature and vacuum degree, the use of desiccant and its activation treatment are formulated. At the same time, the extension system of baking, assembly, vacuumizing, filling sf6 gas and testing was established. Finally, it was tested with a precision dew point meter calibrated by National Metrology Institute. The moisture content of sf6 load switch meets the requirements of national standards.
To sum up, the main technical parameters of fln single-break sf6 load switch products produced by our company are not inferior to those of similar international products, and some indexes are higher than those of similar international products.