Because hydraulic operating mechanisms have advantages such as small size, large operating force, small energy required for control, smooth and noiseless operation, inherent hydraulic lubrication and protection, simple opening and closing buffer, and short operation time, they are widely used in circuit breakers above 110 kV. Most of the domestic 220 kV and 110 kV circuit breakers in our bureau use the CY series hydraulic mechanism, including models such as CY, CY3, CY5, and CY12, with CY3 and CY5 being the most common. However, due to its complex process and numerous parts, the possibility of failure increases. The following discussion will focus on how to improve the reliability of the mechanism in disassembly and repair, fault handling, and technical transformation projects, taking CY3 and CY5 as examples. [b]1 Disassembly and Repair of Hydraulic Mechanisms[/b] During the overhaul of hydraulic mechanisms, they should be disassembled and repaired. For the disassembly steps, you can refer to the specific repair process guidelines. The following discussion will focus on some details that should be paid attention to during repair, based on actual work. (1) Preparation before repair. If the maintenance work is carried out outdoors, attention must be paid to the weather. There should be no wind, sand, dust, or high humidity. After depressurizing, venting, and draining the oil from the mechanism, special tools can be used to disassemble each connecting pipeline. All disassembled parts should be placed in an oil pan filled with clean hydraulic oil. Each disassembled pipeline should be recorded to prevent incorrect installation. (2) Disassembly and maintenance of the valve system. After disassembling each valve connecting pipeline, the opening and closing gate valves and the secondary valves should be placed in the oil pans respectively. 1) Assembly and disassembly of the opening and closing electromagnets: The opening and closing coils should be marked to prevent the opening coil from being installed on the closing valve. The coil must be tested for insulation, and its insulation resistance should not be less than 5 MΩ. The valve stem should be straight and free from deformation. After assembly in the opposite direction of disassembly, the core should move flexibly. 2) Disassembly and assembly of the first-stage valve: Check that the valve needle is not bent or shortened; check the wear of the valve seat end face and the steel ball. If there is slight leakage, use a copper rod to push against the steel ball and gently tap to press out the sealing line, which is about 0.1 mm wide; check whether the spring is deformed; after replacing the seal, the following should be noted during assembly: Assembly should be carried out in oil. The sealing ring should not be twisted or cracked on the surface. Also, prevent the valve body from cutting the sealing ring. After assembly, the valve needle and valve ball should move flexibly. 3) Disassembly and assembly of the second-stage valve: Check the sealing condition of the second-stage valve and the valve body, and the self-holding valve and the valve body. If the wear is serious, it should be replaced; during assembly, pay attention to the fact that the replacement sealing rings should be of the same model and installed in place. When installing the self-holding valve, pay attention to the fact that its sealing ring should not be scratched by the lower valve body. (3) Disassembly and assembly of the pressure tank. To prevent the copper sleeve from scratching the piston rod surface and causing sealing leakage; check the inner wall of the pressure storage cylinder. If there is slight wear, it can be treated with 800 grit wet sandpaper; check the piston rod surface. If there is deformation, scratches, bending, etc., it should be replaced; pour 20 mL of high hydraulic oil into the cylinder before assembly for sealing lubrication. (4) Oil pump inspection. When checking the plunger clearance, block the valve port with your hand. If there is spring force when pushing the plunger, it is normal; check the sealing condition of the low-pressure suction check valve and the high-pressure discharge check valve; before assembly, hydraulic oil should be added to the plunger and plunger cavity (to prevent the oil pump from not being pressurized). The assembly method of adding oil while turning the eccentric wheel and tightening the bolts should be adopted to exhaust the gas in the oil pump (otherwise the oil pump pressurization time will be long). Do not turn the eccentric wheel when there is no oil. (5) Working cylinder overhaul. Check the inner wall of the cylinder. If there are scratches, they should be treated. Assemble and replace all the sealing rings. After assembly, pull the piston rod by hand. There should be no jamming or free movement. The gland nut should be 0.1-0.5 mm lower. If it does not meet the requirements, it should be adjusted. (6) Assembly of the operating mechanism. When connecting the oil pipe, adding oil and charging air, pay attention to the following: The assembly of the mechanism should be carried out in the reverse order of disassembly. All parts should be clean. All valves must be tightly assembled and there should be no oil leakage. The oil added should be free of impurities and water and meet the standards. After the mechanism is assembled, after checking the micro switch, auxiliary switch, contactor, heater, pressure gauge, etc., air can be added to the pressure storage tank. The pre-charged nitrogen pressure should match the ambient temperature. According to actual working experience, the pre-charged pressure should preferably be 0.5 MPa higher than the theoretical value. (7) Adjustment and testing of the mechanism. The hydraulic pipeline venting process should be circulated 3 to 4 times until the gas is completely vented; check that the piston rod stroke and micro switch position correspond to the pressure value; check that the oil pump pressurization time does not exceed the standard; cooperate with the circuit breaker to perform slow opening and slow closing tests; perform holding and anti-slow opening tests, coordinate the mechanism with the circuit breaker to the opening and closing positions, pull off the power control switch, and check whether the stroke rod sliding distance exceeds the standard within 24 hours. [b]2 Troubleshooting[/b] In actual work, domestic hydraulic mechanisms are relatively easy to malfunction in power equipment. The following are some common troubleshooting methods: (1) Frequent oil pump starts indicate leakage inside (outside) the hydraulic system. If there is no obvious external oil leakage, the main defects are: (a) poor sealing between the valve body and seat of the first-stage valve, poor sealing between the valve seat and the first-stage ball valve, poor sealing between the valve body and the piston of the second-stage valve, poor sealing between the valve body of the first-stage valve and the second-stage valve, poor sealing between the valve body of the first-stage valve and the second-stage valve, damage to the piston seal of the working cylinder, wear of the piston rod seal of the pressure storage cylinder, poor sealing of the high-pressure safety valve, poor sealing between the ball (cone) valve and the rifling of the valve seat, unclean hydraulic oil, impurities stuck in the sealing parts, etc. These problems can be solved by replacing the seal, re-rifling, filtering the hydraulic oil, etc. (2) Abnormal increase in oil pressure. During the emergency repair of the switches of Cixi Substation and Tunshan Substation, after on-site inspection, two of them were caused by wear of the piston seal or cylinder wall of the pressure storage cylinder, which caused the hydraulic oil to enter the nitrogen. One was caused by the failure of the micro switch to control the pump stop, which caused the motor to not stop when the piston of the pressure storage cylinder reached the specified position, resulting in abnormally high pressure. This can be solved by replacing the seal and repairing the micro switch. (3) Abnormally low oil pressure is mainly due to nitrogen leakage. Soap water can be used to check for leaks. After plugging the leak, gas can be added. It may also be a problem with the pressure gauge and micro switch. The cause can be found and dealt with accordingly. (4) If the oil pump cannot pressurize or takes a long time to pressurize, and there is no obvious oil leakage on the outside, it may be due to a blockage of the low-pressure oil filter, air in the oil pump, excessive clearance between the plunger and the cylinder seat, a broken seal of the oil pump inlet (outlet) check valve, or leakage in the high-pressure oil circuit. It can be solved by repairing or replacing the oil pump check valve and plunger, cleaning the low-pressure oil filter, and removing air from the oil pump. According to on-site emergency repair experience, the most likely cause is air in the oil pump. (5) The mechanism refuses to open or close, which may be due to the broken wire of the opening (closing) coil, the stuck opening (closing) electromagnet push rod or the opening (closing) valve needle being too short or bent, poor contact in the secondary circuit or the auxiliary switch not being in place, the pressure of the accumulator being too low causing the electrical circuit to be locked, the operating power supply fuse being blown, the transmission system being stuck, etc. The first emergency repair inspection of Tunshan substation confirmed that the auxiliary switch was not reset in the open state, causing the closing circuit to be blocked and thus refusing to operate. Therefore, the main focus should be on checking the secondary circuit. (6) The circuit breaker opens again after closing, mainly due to oil leakage in the holding circuit, which prevents the holding pressure from being established. This includes the closing holding check valve steel ball not being sealed properly, the sealing ring of the opening primary valve seat being damaged, and dirt at the opening valve port causing seal damage. This can be solved by filtering the hydraulic oil, cleaning the valve system, replacing the sealing ring, and re-pressing the rifling. [b]3 Improvement of the hydraulic mechanism[/b] (1) Improvement of the oil tank. (1) For CY5 oil tank, a clear sign indicating the direction of opening and closing should be added next to the manual operating lever; for CY3 oil tank, a filling hole should be provided on the top cover; and an oil level line that changes with temperature can be marked on the oil level gauge of the oil tank. (2) Prevent oil leakage in the low-pressure system. There are too many oil level gauge seals on CY3, which can easily cause oil leakage. It can be changed to a flat embedded type; the low-pressure oil pipe of CY5 should be changed to an oil-resistant rubber pipe, and its joint should be changed to a clamp joint. (3) Improvement of the mechanism box. The intermediate box door of the CY3 mechanism is fixed, which is not conducive to maintenance work, especially when dealing with micro switches, there is no place to insert tools. It is advisable to use a movable door; lighting equipment should be added to the CY5 mechanism to facilitate emergency repair work at night. (4) Improve the working reliability of the pressure storage cylinder. The gas charging check valve of the pressure storage cylinder of the CY5 mechanism should be further improved. Its sealing material is easily damaged. The manufacturer can be asked to improve the performance of the material; the piston rod of the pressure storage cylinder of the CY3 mechanism is made of copper with chrome plating. During maintenance, it is easy to be scratched by the copper sleeve. Its material should be changed to steel. (5) Improve the reliability of the valve system. In actual troubleshooting, valve system failures are the most common, especially the sealing rings. Manufacturers should improve the manufacturing process and materials used for the sealing rings. (6) Improve the reliability of the secondary circuit. A slide rail device should be added to the middle part of the connecting plate of the auxiliary switch of the CY3 mechanism to improve the working flexibility of the auxiliary switch. When the control switch is in the on position, it is often found to be loose and flipped down. The clamping force of the copper snap ring should be increased. (7) Improve the high-pressure oil discharge valve. The oil discharge valve of CY3 can be arbitrarily unscrewed and removed. A limit device should be added so that it cannot be arbitrarily removed when it is unscrewed. (8) Add a protective device to the piston rod of the working cylinder. Although the exposed part of the piston rod is in the protective box, there is still rust. It is advisable to add a sealing ring to the square top cover. In the technical renovation project, in addition to the factors of the maintenance personnel, it is recommended that the manufacturer strive to improve the structural design, improve the processing accuracy and processing quality, and use special equipment for the processing of important parts to improve their processing accuracy, improve the quality of materials, improve surface treatment, and improve the wear resistance of parts. [b]References[/b] ［1］Electric Power Company, Ministry of Energy. SW2-110220 Oil-Less Circuit Breaker Maintenance Technology [M]. Beijing: Water Resources and Electric Power Press, 1992.