During operation, oil leakage in the hydraulic mechanism of the circuit breaker is unavoidable. If the hydraulic mechanism does not need to be repressurized more than twice in 24 hours under the rated gauge pressure (open or closed state), it can be considered that the hydraulic mechanism is leak-free. Otherwise, it indicates that the hydraulic mechanism is leaking. Hydraulic mechanism leakage is usually divided into two categories: external leakage and internal leakage. Internal leakage can be further divided into: leakage when closed, no leakage when open; leakage when open, no leakage when closed; leakage when both open and closed. [b]1 Causes and treatment of external leakage[/b] 1.1 Main causes of external leakage (1) Insufficient tightening torque of pipe joints, resulting in loose joints; (2) Damage, burrs, and cracks in the joint sleeves; (3) Deformation or damage to the sealing rings and gaskets; (4) Improper installation causing stress on the joints, resulting in deformation and damage. 1.2 Main treatment methods (1) Tighten the joint; (2) Remove burrs or replace the ferrule; (3) Replace the sealing ring and gasket (for copper gaskets, pay attention to annealing to soften them. It is best to install them successfully in one go, otherwise the copper gasket is prone to new leakage points after several installations and removals). [b]2 Causes and treatment of internal leakage[/b] 2.1 Main causes of internal leakage (1) Damage and aging of dynamic and static sealing rings and gaskets of hydraulic components; (2) Damage to cone valve and valve seat seals, damage to ball valve and valve line, and valve line width greater than 0.2 mm; (3) Loose internal joints of hydraulic components. 2.2 Key parts for judging possible oil leakage points (1) Internal leakage phenomenon is leakage when closing and no leakage when opening a. The self-holding cavity ball valve and valve line of the secondary valve of the control valve are not sealed well. When the switch is in the closed position, the cavity pressure is insufficient due to the poor sealing of the self-holding cavity ball valve. a. Incomplete closing of the A-cone valve causes a leak in the secondary valve's drain valve, allowing high-pressure oil to escape from the drain valve and return to the low-pressure tank via the control valve's low-pressure return line, resulting in internal leakage. b. Poor sealing of the A-cone valve's sliding combination seal and valve line. During the opening and closing operations, the A-cone valve's sliding combination seal moves up and down with the valve. Therefore, the sliding combination seal ring is prone to wear and aging, causing high-pressure oil in the self-holding cavity to leak to the secondary valve's drain valve port when the switch is closed, returning to the low-pressure tank via the control valve's low-pressure oil line, causing leakage. Furthermore, impurities in the oil, especially metallic impurities, can damage the A-cone valve's valve line or cause metallic impurities to remain on the valve line, resulting in poor sealing. As the switch ages, the valve wire of the A-cone valve thickens, causing a leak in the seal between the A-cone valve and the secondary valve's drain valve when the switch is in the closed position. This allows high-pressure oil to leak directly from the secondary valve's drain valve and return to the low-pressure tank via the low-pressure return pipe. c. Poor sealing of the tertiary valve's drain valve, the sliding combination seal of the tertiary valve's cone valve, and the drain valves for supply and discharge. When the switch is in the closed position, the instantaneous high-pressure oil in the tertiary valve can leak into the low-pressure return pipe due to the poor sealing of the tertiary valve's cone valve, returning to the low-pressure tank and causing internal leakage. Similarly, poor sealing of the tertiary valve's drain valve and the drain valves for supply and discharge will also directly cause high-pressure oil to leak into the low-pressure return pipe via the drain valve, resulting in leakage. d. Poor sealing of the control valve's static combination. When the switch is in the closed position, poor sealing of the control valve's static combination can cause high-pressure oil in the secondary valve's internal cavity to leak directly into the control valve space and return to the low-pressure tank via the low-pressure return pipe. (2) Internal leakage occurs when the switch is open but not when it is closed. a. The oil supply valve of the secondary valve of the control valve is not properly sealed. When the switch is in the open position, due to the poor sealing of the oil supply valve of the secondary valve of the control valve, the constant high pressure oil in the secondary valve will leak out from the oil drain valve of the secondary valve and return to the low pressure oil tank through the low pressure return oil pipe. b. The oil supply valve of the tertiary valve and the oil supply and drain valve are not properly sealed. When the switch is in the open position, due to the poor sealing at the above-mentioned points, the constant high pressure oil of its hydraulic components will leak through the oil drain valve to the low pressure return oil pipe and return to the low pressure oil pipe, resulting in internal leakage. (3) Internal leakage occurs when both the switch is open and closed. a. Leakage in the constant high pressure system. Leakage in both the open and closed positions indicates that the common constant high pressure part of the open and closed systems is leaking. For example, if the oil supply valve of the primary valve of the closing position is not properly sealed, the constant high pressure oil will leak out through the oil drain valve of the primary valve when the switch is open or closed, leak into the control valve, and return to the low pressure oil tank through the low pressure oil pipe. b. Oil drain valve leakage. Because the oil drain valve is frequently used during maintenance, a loose valve core, improper closure due to negligence, or damage to the valve line can all cause high-pressure oil to leak into the low-pressure tank, resulting in internal leakage. c. Safety valve not closing tightly. When the safety valve does not close tightly or the valve line is damaged, high-pressure oil can backflow into the low-pressure oil pipe through the low-pressure return pipe. 2.3 Determining the specific leak point mainly involves: based on the observed phenomena, setting the switch to either open or closed, establishing the rated oil pressure, and "touching," "listening," and "looking" at the key areas where leakage is likely. Touching refers to using your hand to check if the suspected leak area is hot or if the temperature is significantly higher than other areas; listening refers to using a stethoscope to detect leaking sounds in the hydraulic components; looking refers to observing whether oil is leaking from the hydraulic components and inspecting the low-pressure return pipe. 2.4 Handling. Once the specific leak point is found, handling it is easy. If the dynamic or static seals or gaskets are damaged or aged, replace the seals or gaskets. If the valve line is damaged, it can be polished with 400-600 grit polishing compound, but the width of the valve line must not exceed 0.2 mm. If it exceeds this, it must be replaced. If the ball valve is damaged, a qualified ball valve can be replaced and the sealing line can be re-tapping. When assembling hydraulic components, attention must be paid to the assembly quality and the cleanliness of the workpiece before assembly, otherwise leakage will be difficult to handle. [b]3 Typical Cases of Leakage Handling[/b] 3.1 Oil Leakage Handling of Circuit Breaker No. 31 (Yang 31) at Yangluo Power Plant Phenomenon: "Yang 31" leaks when both open and closed, and pressure is replenished every half hour. There are no external leakage points. Judgment: Leakage in the constant high pressure system or leakage in the drain valve. Handling: Set the switch to open, set it to the rated pressure, drain the oil in the low pressure tank, and turn off the motor power. No leaks were found by touch or listening. After about 20 minutes, the low-pressure oil tank was cleaned again, residual oil was wiped off, and the return oil pipe of the low-pressure oil tank was observed. An abnormal return oil was found in the low-pressure return oil pipe of the control valve. The sealing cover of the three-phase control valve was opened, and it was found that oil was leaking at the constant high-pressure pipe joint of the B-phase closing primary valve. The oil pressure of the hydraulic mechanism was released, the pipe joint was tightened, and the pressure holding of the opening and closing circuits was qualified. 3.2 Oil leakage treatment of Yangluo Power Plant No. 38 circuit breaker (Yang 38): During the 0-30 s closing time of "Yang 38", a clear "squeaking" sound was heard from the A-phase control valve. After several closings, the "squeaking" sound was intermittent and of varying lengths. There was no "squeaking" sound when opening. The pressure holding during closing was not qualified, while the pressure holding during opening was qualified. Judgment: Since the oil leakage sound was always within 0-30 s, the hard seal (valve line) was unlikely to be damaged. The sliding combination seal and static combination seal of the A cone valve were more likely to be damaged. The rubber sealing ring, which was not damaged, may have gradually sealed the high-pressure oil under the action of high-pressure oil. Troubleshooting: With the switch in the closed position and the oil pressure at the rated pressure, drain the oil from the low-pressure oil tank, turn off the motor power, and remove the sealing cover of the A-phase control valve for inspection. Oil leakage was found at the lower drain valve of the secondary valve. The hydraulic pressure was released, and the sliding combination seal ring of the A-cone valve and the static combination seal ring of the control valve were replaced. Pressure holding was successful during both opening and closing operations, and there was no leakage sound when closing. "Yang 38" was then resolved.