Abnormality of hydraulic operating mechanism of th

Abnormal analysis of the hydraulic operating mechanism of LW6 series SF6 circuit breakers

LW6 series SF6 circuit breakers are manufactured with technology imported from French mg company. Since the early 1990s, our company has gradually used them. The following is an analysis of the hydraulic operating mechanism failure of the circuit breaker in our company, and puts forward fault handling methods and preventive measures

1 common faults

1.1 the oil pump starts frequently

under the condition of no operation, according to the manufacturer's requirements and relevant regulations, the oil pump should be started and pressurized 1 ~ 2 times a day, about 6 times should attract operating attention, strengthen monitoring, and more than 10 times should be arranged for power outage maintenance

the frequent starting of the oil pump is caused by the leakage of the hydraulic mechanism, which can be divided into external leakage and internal leakage

external leakage is due to the loosening or deformation damage of the high-pressure connecting pipe joint between the mechanism components. This kind of fault is easy to observe from the appearance of the mechanism with the naked eye, and the treatment is relatively simple. Tighten the nut of the high-pressure connecting pipe joint. If there is still leakage in the tightening nut, the joint nut, ferrule and sealing washer must be replaced

internal leakage is caused by the lax sealing of the valve between the high-pressure area and the low-pressure area inside the mechanism component, which is manifested in the marking, deformation or damage of the valve line, the damage of the valve seal, the fatigue and aging of the safety valve spring, and the impurities in the hydraulic oil stuck at each valve or sealing ring. This kind of fault is difficult to observe with the naked eye from the appearance of the mechanism. The leakage point can only be found according to the sound made by the high-pressure oil leakage, and the leakage position can also be comprehensively judged according to the oil pipe temperature and the opening and closing conditions of the switch. Finding out the location of internal leakage largely depends on the experience of maintenance personnel in this regard, and the treatment is also complex. The discharge of a large amount of waste causes heavy metals to enter the soil through various ways. It is necessary to install and disassemble components, grind valve lines, replace damaged valve needles, fatigue springs, damaged sealing washers, filter or replace hydraulic oil with impurities. The process requirements are high, and performance tests are also required. Internal leakage is a difficult fault to deal with

frequent starting of the oil pump will generally have no direct impact on the opening and closing operation of the circuit breaker, which will launch a new TPE product. However, if it is not handled for a long time, the fault will continue to develop. When the oil pump is started more than 20 times a day, the opening and closing speed of the circuit breaker will gradually decrease, affecting the breaking performance

1.2 the oil pump fails to apply oil pressure for a long time

after the normal operation of the circuit breaker, the pressure of the hydraulic system decreases and the oil pump starts, but after a long time of pressure (more than 3min), the oil pressure still cannot reach the rated pressure

the causes of this failure include various factors of frequent start-up of the oil pump, but the degree is more serious than it. It is often the serious leakage of valves at all levels. Common failures also include: the oil drain valve and control valve are not tightly closed or the secondary valve is half opened and half closed; The oil suction pipe of the oil pump is flattened and the oil inlet is not smooth; There is gas or leakage on the low-pressure side of the oil pump. To find out the fault point, we must comprehensively analyze the condition of the mechanism. It may be caused by one or more of the above factors, and the oil drain valve, control valve, oil pump or oil suction pipe need to be repaired or even replaced. This kind of fault is difficult to deal with and requires high technology

1.3 abnormal pressure of the hydraulic operating system

the normal oil pressure range of the hydraulic operating system is 31.6 ~ 32.6 MPa (temperature is 15 ℃), beyond this range, it belongs to abnormal pressure. Note that under other ambient temperatures, the oil pressure can be converted by the following formula:

pt=p15 ℃ + 0.09 (T-15)

failure of the oil circuit or electrical circuit of the hydraulic operation system will cause abnormal increase or decrease of the oil pressure of the system. The specific failure causes and corresponding treatment methods are as follows:

(1) the stop contact of the control motor is damaged, and the microswitch and contactor should be checked and repaired

(2) the contactor of the control motor malfunctions, which can remove the dirt and oil dirt on the contactor

(3) if nitrogen leaks from the pressure accumulator or oil enters the nitrogen side, check the roughness of the inner wall and replace the sealing ring. If it is serious, replace the pressure accumulator

(4) the pressure gauge fails or has errors, and the pressure gauge switch is closed, which cannot correctly reflect the oil pressure. Replace the pressure gauge or turn on the gauge switch

(5) if the intermediate relay is "stuck" or the contactor is stuck, and the oil pump motor has been running, the faulty intermediate relay or contactor should be replaced

1.4 common troubleshooting precautions

(1) the circuit breaker must be in the off position before maintenance, disconnect the power supply of the energy storage motor, and release the oil pressure to zero gauge pressure before it can work, otherwise it will damage the mechanism components

(2) after the removal and disassembly of the primary and secondary valve components, the internal valve needle and valve ball are extremely small and cannot collide or squeeze with hard objects to avoid deformation

(3) before replacing new components and sealing rings, clean with clean No. 10 aviation oil, dry the hydraulic pipe with pure nitrogen, and clean the hands of staff to ensure that hands, tools, components and parts are clean and free of impurities. The newly replaced No. 10 aviation hydraulic oil must be filtered to maintain purity

(4) after maintenance, the circuit breaker should be stationary at the closing position for more than 2h, so as to check the sealing of each high-pressure hydraulic pipe, closing command pipe, closing hold valve, etc

2 serious fault

2.1 zero gauge pressure caused by voltage loss during operation

when the circuit breaker is in the static state of closing, the pressure loss is caused by serious leakage of the hydraulic system, and the oil pressure quickly drops to zero gauge pressure. Zero gauge pressure caused by pressure loss during operation is generally caused by internal leakage of hydraulic mechanism, including various initiating factors. The degree of oil leakage is much more serious than the fault of "oil pump can't turn on oil pressure for a long time", which is the most serious manifestation of abnormal pressure of hydraulic operation system. When the fault occurs, the circuit breaker is strictly prohibited from any opening/closing operation, and must immediately exit the operation

2.2 disconnection fault

during the closing/opening process of the circuit breaker, when the flexible packaging gradually becomes the main role of food packaging materials, its normal high-voltage pipe or closing command pipe falls off, a large amount of high-pressure oil ejects, and the closing/opening action of the circuit breaker is abnormal. The reasons for this failure are:

(1) the installation process of the normal high-voltage pipe or the closing command pipe is poor, and the fastening is insufficient to withstand the impact of the closing/opening operation and fall off

(2) due to the long operation time of the circuit breaker, the joint of the normal high-voltage pipe or the closing command pipe is aging and loosened (especially the pipe that has been tightened for many times due to oil leakage of the joint), and the ability to withstand high voltage decreases

this is the most serious fault that has occurred in our company so far. When it occurs, it must be immediately out of operation. Before repair, the circuit breaker is strictly prohibited from any opening/closing operation

2.3 emergency troubleshooting steps

(1) disconnect the power supply of the circuit breaker energy storage motor

(2) switch the "local"/"remote" operation handle of the circuit breaker to the "local" position

(3) report scheduling

(4) exit the operating power supply and relevant protection, reclosing and automatic switching devices of the circuit breaker

(5) in case of zero gauge pressure fault, use the special anti slow opening fixture to block the lower part of the closing indicating disc of the operating transmission rod, and tighten it with screws

(6) isolate the circuit breaker from the system through switching operation

(7) in case of pipe failure, replace the fallen hydraulic pipe, Supplement No. 10 aviation hydraulic oil, pressurize and exhaust until the circuit breaker is repaired

(8) in case of zero gauge pressure fault, deal with the leakage part of the mechanism according to the treatment method of frequent starting of the oil pump, Supplement No. 10 aviation hydraulic oil, pressurize and exhaust until the circuit breaker is repaired

2.4 precautions for serious fault handling

(1) after the fault occurs, the operator should cut off the power supply of the oil pump in time and place the circuit breaker in the local operation position in time. Never force the pressure artificially, that is to say, when completing the first and second steps of the above fault handling steps, the action should be rapid, otherwise it will be very easy to cause the circuit breaker to open (or close) slowly, causing a serious accident of circuit breaker explosion

(2) in case of such failure of the circuit breaker, it is strictly prohibited to carry out any closing/opening operation

(3) after adding hydraulic oil, exhaust for many times

(4) during the closing/opening test after the maintenance of the circuit breaker, it is advisable to operate remotely, and the staff should stay away from the circuit breaker to ensure personal safety

3 preventive measures

3.1 carry out various maintenance and inspection work according to the specified cycle

(1) re filter No. 10 aviation hydraulic oil every 2 years

(2) No. 10 aviation hydraulic oil, cleaning valve system and hydraulic pipeline must be replaced every 4 years

(3) calibrate the pressure gauge and pressure safety valve of the hydraulic system every 1 ~ 3 years to prevent abnormal pressure rise of the operating mechanism

(4) if the operation time is within 10 years, in principle, if there is a problem with a certain element, the element should be replaced. If the main valve elements in the hydraulic operating mechanism are generally in bad condition, the whole hydraulic operating mechanism should be replaced

(5) if there is a problem with the main valve in the high-pressure oil system with an operation time of more than 10 years, replace the whole hydraulic operating mechanism. If there is a problem with the components of the low-pressure oil system, only replace the components

(6) after overhaul, measure the travel, speed characteristics, time parameters, the minimum operating voltage of synchronization and opening/closing of the circuit breaker, and the operating pressure drop value of the operating mechanism under opening/closing and reclosing

(7) when the number of mechanical operations reaches 3000, carry out temporary maintenance and replace the hydraulic oil

3.2 the planned maintenance should strengthen the comprehensive work

(1) in addition to replacing the damaged parts in time, the condition of each component of the mechanism should be comprehensively inspected to eliminate the defects in the bud, improve the reliability of the equipment and avoid repeated maintenance

(2) check the pressure value corresponding to each contact of the microswitch

(3) clean all components in the operating mechanism box regularly