Preventive test of common zinc oxide arresters

Preventive test of common zinc oxide arresters
1. Measurement of insulation resistance of arrester

The measurement of the insulation resistance, for the FS type arrester, is mainly to check the sealing situation, if the sealing is not strict, it will inevitably cause internal moisture, so the insulation resistance is significantly reduced. According to the requirements of the pre-test procedures, the measurement should be carried out with a 2500V megohmmeter. The insulation resistance should be no less than 2500MΩ. Wipe the surface of the arrester porcelain sleeve before testing, otherwise the accuracy of the test will be affected by the leakage current on the surface of the jacket. To this end, the surface of the porcelain sleeve should be wiped clean with a clean cloth with good water absorption before the test. Use a thin metal wire to make a circle around the lower part of the first shed of the jacket and then connect it to the MIG "shield" terminal. Eliminate the effects of. In the test, the connection between the megohmmeter and the arrester should be as short as possible, and the electrical contact should be good. The megohmmeter should be placed horizontally during the test, and the shaking speed should be uniform, and 120 rpm should be used to obtain good measurement results.

For the FZ type arrester, in addition to checking whether the internal moisture is affected, it is also necessary to check whether the parallel resistance is broken or aged. If the parallel resistance is aged and broken, the insulation resistance will increase due to poor contact. To ensure that the measurements are worthy of accuracy, measure twice and compare the data for changes. Measurements should be made using the same megohmmeter of the same voltage class, otherwise they cannot be compared.

2. DC 1 mA reference voltage test

During the test, 0.75 times 1 mA DC voltage is applied across the arrester (DC voltage pulsation rate is not more than ±1.5%), and the current through the arrester is stabilized at 1 mA. The voltage across the arrester should be no less than 25 kV.

3. DC leakage current test

During the test, after applying 0.75 times 1 mA DC voltage across the arrester, the leakage current through the arrester should be no more than 50μA. During the test, when the leakage current reaches 30μA, the voltage will continue to rise. At this time, the leakage current will increase sharply. At this time, the voltage should be slowly increased. If the voltage is too fast, the measurement will be inaccurate. In order to prevent the influence of leakage current on the surface of the porcelain sleeve, the outer surface of the porcelain sleeve should be wiped clean with a water-absorbent cloth before the test to eliminate the influence.

4. Measurement of electrical current flow with parallel resistance arrester

The micro-ampere meter used for measuring the electric current flow with the parallel resistance arrester shall have an accuracy of not less than 1.5, and the connecting wire shall be thick and short to reduce the influence of the wire resistance on the measurement. Also pay attention to the effects of corona current and stray capacitance around high voltage. It is not advisable to measure with an electrostatic voltmeter. Test equipment away from equipment that is prone to disturbing magnetic fields, or set shielding measures.

When measuring the electrically conductive current, the application of the DC test voltage should start from a sufficiently low value and then slowly rise, apply the voltage in sections and read the electrically conductive flow value in sections. After the voltage to be tested is kept for a specified time, if the pointer of the micro-ampere meter does not swing greatly, the displayed value is the value of the electrical conductivity of the voltage.

If the parallel resistance is aging and the contact is poor, the electrical conduction current drops significantly. If the parallel resistance is broken, the electrical conduction current drops to zero. If the parallel resistance itself is wetted by water, the electrical conductivity will increase sharply, generally up to 1000μA.

In order to ensure the safety and accuracy of the test number, the electrical conductivity values ​​measured at different temperatures are compared and converted to electrical conductivity values ​​at the same temperature. Experience has shown that for every 10 °C increase in temperature, the electrical conductivity increases by about 3% to 5%.

5. Power frequency discharge test without parallel resistance arrester

Testing the power-frequency discharge voltage of the arrester is a necessary item for checking the protection performance of the arrester. For each arrester, three power frequency discharge tests shall be performed. The average value of the three discharge voltages in parallel shall be used as the power frequency discharge voltage of the arrester. When the actual interval of each test is not less than 1 min.

The power frequency discharge test is similar to the general withstand voltage test except that the voltage of the power frequency discharge is not constant but rises to the arrester discharge. The speed of the boosting is preferably 3~5 kV per second, and the power supply is cut off within 0.5s of the gap discharge, so the flow loop protection should be installed in the test circuit.

6. Test of zinc oxide arrester

MOA is a new type of overvoltage protection device, which has superior protection performance than silicon carbide arrester and is widely used in lightning protection of power systems. Test items, cycles and requirements are specified in the preventive test procedures for electrical equipment. In the test of the zinc oxide surge arrester, in addition to the conventional test items such as the insulation resistance, the base insulation resistance, and the discharge counting operation, the leakage current of the DC 1μA voltage and 0.75 times 1μA DC voltage is also measured.

The DC leakage current is measured at 0.75 times DC voltage. The purpose is to detect the change of the allowable operating current for a long time. The leakage current should be no more than 5μA. This current value is closely related to the service life of the arrester. At the same time, this value should be compared with the manufacturer's specified value, the change should be no more than ± 5%. If it is too high, the insulation margin of the protection equipment will be reduced; if it is too low, the MOA may be transient in various operations and faults. An explosion occurs under voltage. If the surface of the MOA porcelain sleeve is severely damp, it will also affect the measured value. Therefore, the surface leakage should be eliminated during the test to affect the test.

Measurement of the AC leakage current of the operating voltage. The test measures total current, resistive current and power loss. If the measured full current value is more than 20% higher than the initial value, or exceeds the manufacturer's specified value, immediate attention should be paid and operational monitoring should be strengthened. If the measured full current value is increased by more than 50% from the initial value, the operation should be exited for exclusion. If the measured resistive current is more than doubled than the manufacturer's specified value, it should also be withdrawn from operation. If the cause is to be eliminated or replaced, it must not be operated with fault.

When conducting the above tests on the MOA, the ambient temperature, relative humidity and operating voltage should be recorded at the time, and the effects of the relevant disturbances should be noted, and the test should be eliminated.

7. Other tests

With the emergence of new equipment and new test methods, the arrester is both capable of conducting live test electrical conduction current and charged infrared temperature measurement test. In order to ensure the reliable and safe operation of the arrester, the new arrester shall be put into operation within 3 months and the annual autumn inspection, and a general survey shall be carried out according to the regulations, and the general survey data shall be recorded and archived for comparison in the next test. Conducive to the inspection found that the problem of stability.

The temperature is measured by an infrared thermal imager, that is, a small temperature change can be measured, and the difference in surface temperature of the lateral flange or the porcelain sleeve can be compared. If the temperature deviation is large, it indicates that the arrester may have defects, and further inspection is required. After the cause is removed or replaced, the network can be operated.

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