Created on:2021-07-15 14:03

Pressure failure fault of low oil circuit breaker in Substation

Pressure failure fault of low oil circuit breaker in Substation

During the spring inspection of a sw7-1101 oil less circuit breaker (equipped with CY4 hydraulic operating mechanism) in a 110kV substation, the non switch maintenance team performs the oil change task. Because we don't know the basic structure and operation principle of the switch and the operation principle and operation precautions of the hydraulic mechanism, blind operation results in the failure of the hydraulic mechanism after the oil change of the switch.

(1) Fault analysis

In the process of oil injection, the maintenance personnel carried out the following operations before the pressure failure of the mechanism.

① Because the oil through base of the switch porcelain sleeve is separated from the oil in the arc extinguishing chamber, the check valve at the top of the arc extinguishing chamber is removed and the oil is injected from the top of the cap. The oil in the porcelain sleeve of the arc extinguishing chamber flows downward through the check valve, and the gas is discharged upward through the exhaust pipe. In order to speed up the oil filling process, continuous quick closing and opening operations were carried out for many times to make the gas discharged outwards. After the oil in the cap flows out, top it up again. Repeat this. But the filling speed is very slow, as long as five or six hours.

② In the manual quick closing and opening operation, clap the closing and opening electromagnet top rod with hand.

③ The operation cycle time interval from opening to closing to opening is too short, especially the time interval from closing to opening to closing to opening is too short.

Under normal conditions, there are five requirements for the oil injection process.

① The check valve at the top of the arc extinguishing chamber should be removed during oil injection. The normal oil injection time is 2-3 hours, otherwise the oil injection speed is very slow.

② In order to speed up the oil injection, slow closing and slow opening operations should be carried out for many times in the oil injection process.

③ When the switch has no oil, fast closing and opening operation is forbidden, otherwise the mechanical and transmission parts will be damaged easily.

④ During the manual quick closing and quick opening operation, you should hold the top rod of the closing and opening electromagnet with your palm, hold the lower yoke of the electromagnet with your four fingers and press down, and keep enough closing and opening time to make the closing and opening to the end. If the push rod of the electromagnet is patted by hand, the push rod can be bent, deformed or broken.

⑤ It should be operated in strict accordance with the rated operation cycle: opening → 0.3s → closing and opening → 180s → closing and opening. In order to make the oil in the expander fully flow back to the oil tank of the hydraulic mechanism, the time interval between every two recloses should not be less than 3 min. If the time interval is too short, and the oil in the expander has not finished flowing and is filled with new oil, the expander will burst after full operation.

Therefore, it can be preliminarily determined that the failure of the mechanism is related to the operation error of the maintenance personnel in the process of oil injection.

The pressure principle of hydraulic mechanism: start to change the low pressure oil into high pressure oil, and charge it to the accumulator, high pressure oil drain valve, the ball valve closing the first stage valve, and the opening end of the second stage valve, working cylinder and signal cylinder.

Principle of closing and opening action of hydraulic mechanism: the closing valve rod moves downward to open the steel ball of closing primary valve and close the oil drain port of primary valve at the same time. High pressure oil is charged to the middle valve cavity through primary valve cavity. Under the action of differential pressure, the middle valve moves downward to open the valve port of secondary valve and close the air drain valve of secondary valve. The normal high pressure oil is charged to the closing end of working cylinder and signal cylinder through the valve port of secondary valve, Push the piston to close the switch; Under the action of normal high pressure, the valve port of the secondary valve is closed to push the intermediate valve upward, and the closing ends of the secondary air drain valve, working cylinder and signal cylinder are opened. The high-pressure oil is connected with the low-pressure oil tank through the secondary air drain valve for pressure relief. Under the action of normal high pressure at the opening end, the secondary air drain valve is opened, The reverse movement of the piston makes the switch open.

When the switch and hydraulic mechanism are in the opening position, the oil pressure can not be established, which can be analyzed and judged from the following aspects:

① Electrical circuit fault;

② The pipe joints of working cylinder, expander, pressure gauge and signal cylinder have serious leakage;

③ The nitrogen leakage of accumulator is serious;

④ High pressure oil drain valve failure, high pressure oil and low pressure oil tank connected and pressure relief;

⑤ The opening position of the steel ball of the closing primary valve is stuck (the seal of the primary valve is invalid), and the high-pressure oil is connected with the low-pressure oil tank through the discharge port of the primary valve, so it can not be pressurized;

⑥ The opening of the secondary valve is stuck (the seal of the secondary valve is invalid), and the secondary valve is connected with the secondary air drain valve without pressure;

⑦ High pressure hydraulic pump failure, no pressure;

⑧ The hydraulic oil is seriously dirty.

After investigation and analysis, the above items (1), 2, 3 and 8) can be basically excluded. In order to further analyze the cause of the failure, open the low pressure oil tank cap, discharge the oil in the tank close to the filter screen, and expose the seal of each pipe joint of the valve system. Open the high-pressure oil drain valve and jog the hydraulic pump. Oil flows out from the oil drain port connected between the high-pressure oil drain valve and the low-pressure oil tank, and the hydraulic pump works normally; Close the high-pressure oil drain valve and jog the hydraulic pump. It is observed that there is no oil outflow from the oil drain port of the high-pressure oil drain valve and there is no oil seepage from the oil drain port of the primary closing valve. It can be seen that the high-pressure oil drain valve is well sealed and the steel ball of the primary closing valve is well sealed; But there is oil overflow in the air drain valve between the inner cavity of the secondary valve and the low pressure oil tank, which indicates that the secondary valve seal is invalid.

It can be judged that the direct reason for the failure of the hydraulic mechanism is that the manual closing operation method of the maintenance personnel is wrong. When closing, tap the top rod of the closing electromagnet by hand. Because of the extremely fast speed and short time, the high-pressure oil supply into the upper chamber of the intermediate valve is insufficient. The pressure difference is not enough to overcome the friction between the valve body and the wall, causing the valve body not to move or to move slightly. The abnormal action of the secondary valve leads to the middle position of the valve, that is, the air drain valve has not been closed, the secondary valve has been opened, the high-pressure oil flows through the port of the secondary valve, the inner cavity of the secondary valve to the port of the secondary air drain valve and the low-pressure oil tank, and the valve body remains stuck, and the mechanism fails to work.

(2) Troubleshooting

Open the high pressure oil drain valve and remove the plug on the upper part of the intermediate valve. Lift the secondary valve stem to close the secondary valve port. Restore the original state of the low-pressure oil tank, close the high-pressure oil drain valve, and pressurize normally.

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