Zinc oxide surge arresters have gradually replaced the old valve arresters due to their superior overvoltage protection characteristics and have been widely used in power systems. However, the aging of zinc oxide surge arrester and the damage caused by heat and shock will cause failure. In severe cases, it may lead to explosion. Breakdown of lightning arrester will also cause short-circuit in busbar of substation, which will affect the safe operation of the system. Therefore, it is necessary to carry out strict and effective detection and regular preventive tests on the zinc oxide surge arresters in operation and carry out on-line monitoring of zinc oxide surge arresters. As the zinc oxide arrester pre-test (especially the main transformer three-side surge arrester) must stop the main equipment, it will affect the operational reliability of the equipment, and sometimes the main equipment cannot be stopped due to the limitation of the operating mode, resulting in the arrester not being able to pre-test on time. Therefore, the live test and on-line monitoring of the zinc oxide surge arrester are particularly important. First, the working principle of zinc oxide arrester Zinc Oxide ZnO Arrester is a new arrester developed in the 1970s. It is mainly composed of zinc oxide varistors. Each varistor has its own certain switching voltage (called varistor) when it is manufactured. Under normal working voltage (ie, less than varistor voltage), the varistor has a large value, which is equivalent to the insulation state, but Under the impact voltage (more than the varistor voltage), the varistor is punctured at a low value, which is equivalent to a short-circuit condition. However, when the varistor is hit, it can be recovered; when the voltage above the varistor is removed, it returns to a high-impedance state. Therefore, if a zinc oxide surge arrester is installed on the power line, when lightning strikes, the high voltage of the lightning wave breaks down the varistor, and the lightning current flows into the earth through the varistor so that the voltage on the power line is controlled within a safe range. Protect the safety of electrical equipment. Second, the theoretical basis of the zinc oxide arrester charged test 1. The importance of the live test of zinc oxide surge arresters Zinc Oxide Arrestors can easily cause faults due to their aging, dampness and other factors during operation. This will result in the main equipment being unprotected. In severe cases, an explosion may occur and affect the safe operation of the system. The Zinc Oxide Arrester Pretest must stop the main equipment, which will affect the operational reliability of the equipment. At times, the main equipment cannot be stopped due to the limitation of the operating mode, and the arrester cannot be pre-tested on time. Therefore, the live test and on-line monitoring of the zinc oxide surge arrester are particularly important. 2. Purpose of the Zinc Oxide Arrester Charge Test Using the live measurement of the zinc oxide arrester, the ratio of the arrester's resistive current to the total leak current is measured, that is, the resistive current component of the zinc oxide arrester to determine the moisture and aging conditions of the arrester. When the zinc oxide surge arrester ages in the valve plate and is subjected to heat and impact damage and internal moisture, the active loss of the zinc oxide arrester is intensified, that is, the resistive current component in the arrester leakage current is significantly increased, and thus is generated inside the zinc oxide surge arrester. The heat causes the zinc oxide surge arrester valve to further deteriorate, creating a vicious circle and destroying the internal stability of the zinc oxide arrester. The oxidized lightning arrester is used to measure the active component lively, and the problematic zinc oxide surge arrester is found in time to prevent equipment failure in the bud. 3. Impact of zinc oxide arrester electrification test factors There are many factors affecting the live test of zinc oxide surge arresters, including inter-phase interference, test methods, and surface contamination. The surface contamination can be solved at the scene by cleaning the surface of zinc oxide surge arresters. Here, the interphase interference within the interval and the influence of the test method on the measurement are mainly excluded. Three, zinc oxide arrester charged test 1. Selection of test methods Zinc oxide arrester on-line detection test, using the ZD1 test instrument, the instrument has three functions, namely: secondary voltage reference method, induction method and harmonic analysis method, in which the harmonic analysis method is rarely used in the actual test . Induction plate method is often used because of safety, convenience, and speed. However, this test method is greatly affected by the electric field interference, and the signal taken by the sensor plate is also greatly influenced by the position of the sensor plate, so the test data is highly volatile. The secondary voltage method requires the secondary reference voltage to be taken from the PT corresponding to the lightning arrester. This test method needs the cooperation of other team members. The data obtained by this test method is very stable, and the data during arrester shutdown are comparable. Therefore, it should become the most important method for on-line detection of zinc oxide surge arresters. The following is the data comparing the induction board method with the secondary voltage method (Note: The comparison data is the data measured under the power frequency reference voltage of the arrester before the operation): Through the comparison of the above table, it can be found that the data measured by the secondary voltage method is more accurate, and the data of the sensing plate method is relatively large, and the errors of the A and C phases are relatively large. 2. Angle correction of live test of zinc oxide arrester Three-phase zinc oxide surge arresters are generally arranged in a straight line. The three-phase zinc oxide surge arresters in operation interact with stray capacitances to cause phase changes in the total leakage currents at the bottom of the arresters on both sides. The phases are oxidized due to interphase interference. A change in the leakage current of the zinc arrester will cause the measured phase zinc oxide surge arrester voltage fundamental current and the total current fundamental wave φU-Ix to change, and the zinc oxide surge arrester will operate normally under the continuous operating voltage because IR/IX is less than or equal to 25%. Therefore, φU-Ix is 80° to 85°. If φU-Ix deviates, the measured parameter will deviate from the true value, which will bring errors to the measurement. A, B, C (edge, middle, side) three-phase zinc oxide surge arresters are arranged in a straight line, the current and voltage vectors during operation (see Figure 1), and the roles of A and C phases relative to phase B are symmetrical and cancel each other out. . Therefore, when measuring the B phase zinc oxide surge arrester, the current probe takes the total current IX signal from the B phase zinc oxide surge arrester leakage current monitor, and the voltage probe is connected with the B phase PT secondary winding to perform measurement. When measuring phase-A zinc oxide surge arresters, due to the effect of phase B zinc oxide surge arresters on phase-A zinc oxide surge arresters, consider entering a correction angle φ0 before testing to make φU-Ix close to the real value during the test. First, the voltage takes A phase PT secondary signal, the current takes C phase zinc oxide surge arrester current signal, measured φU-Ix is denoted as φC, then the current takes the A phase zinc oxide surge arrester current signal, and the measured φU-Ix is denoted as φA. All readings are for uncorrected readings of zinc oxide surge arresters. The angle between IA and IC is 120°. The influence of B relative to phase C and the influence of phase B relative to phase A is symmetric, so φOC=-φOA (see Figure 1). To: Correction angle φOA = (φC-φA - 120°)/2 The test data before and after the angle correction is compared as follows: According to Jiangsu Provincial Electric Power Corporation, "Procedures for the Handover and Preventive Testing of Electric Power Equipment in Jiangsu Province," "If there is a marked change in the measured group current compared with the initial value, monitoring should be strengthened. When the resistive current increases by 1 time, the power should be cut off. Check." "The measured value of the active component of the leakage current shall be less than or equal to 25% of the full current." Without the introduction of angle correction data, the phase C of the outgoing line 1 is already close to the critical value, while the phase C of the outgoing line 2 has exceeded the standard, and the outgoing line Phase 1 of Phase 1 and Phase A of Line 2 are significantly smaller than the corresponding data. The two groups of Zinc Oxide Arrester need to be monitored and one set must be deactivated. The introduction of angle corrected data shows that the two sets of zinc oxide surge arresters are in good condition. IV. Technical Management of Zinc Oxide Surge Arrester Strengthen the technical management of zinc oxide surge arresters, that is, establish a technical file for each zinc oxide surge arrester that operates on the Internet, and store technical reports on the factory reports, periodic test reports, and online monitor operation records until the arrester Exit the run. According to the statistics of foreign technical data, the reason for the damage of the zinc oxide surge arresters is lightning and operating over-voltage, moisture, pollution flash, system conditions, and their own faults, but there is still a certain proportion of the reasons for damage is unknown, so it is still in operation The cause of the accident is not clear. Because of the dispersion of the deterioration rate of zinc oxide surge arresters, and the randomness of lightning, operating overvoltage, harmonics, and operating environment, they all determine the reliability of the safe operation of zinc oxide surge arresters. Therefore, they must be used in future work practices. To study, experiment, explore and summarize, so that its insecurity in the operation can be prevented and improved. in conclusion When the zinc oxide surge arrester is charged, the secondary voltage method and the introduction angle correction can effectively provide accurate basis for the operation status of the zinc oxide arrester, especially when the IR/IX is close to the critical state of the standard, the zinc oxide arrester can be determined. Can you continue to use it and avoid misjudging the status of the zinc oxide arrester? When the zinc oxide surge arrester is charged by the above method, there are a lot of devices that need to be carried. If the device can be simplified, it has even more field use value.
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