Causes of damage to metal oxide arresters:
According to the damage of gapless metal oxide arresters, good quality has less damage and poor quality has more damage; there is less damage in sunny days and more damage in thunderstorms; there is less damage in no operation and more damage in operation; there is less damage in normal operation and more damage in abnormal operation.
Metal oxide arrester
1.1 Get damp
Metal oxide arresters use silicone rubber as the arrester. The quality of the silicone rubber sleeve is poor. This is mainly caused by fake products from small factories with imperfect technology, or the sealing material has unstable anti-aging properties, large temperature differences, or the operating time is close to the end of the product life, resulting in poor sealing. The two ends of the lightning arrester are roughly processed and soaked in water or moisture, causing damage to the internal insulation, accelerating the deterioration of the resistor, and causing damage.
It can be seen from the remains of the arrester after the accident that there are no traces of flow through the valve plate, and no traces of discharge after the passage of large currents are found on the aluminum-sprayed surfaces at both ends of the valve plate. However, there are obvious flashover marks on the inner wall of the silicone rubber sleeve or on the side of the valve plate, and there are rust spots or zinc white on the metal accessories, which are affected by moisture.
1.2 The rated voltage and continuous operating voltage are low.
The rated voltage of a metal oxide arrester is an important parameter indicating its operating characteristics and is also an indicator of its ability to withstand power frequency voltage.
The ability of metal oxide arrester valves to withstand power frequency voltage is closely related to the duration of the operating voltage. (Electrical World www.dgjs123.com) Continuous operating voltage is also an important characteristic parameter of metal oxide arresters, which has a great impact on the reliability of metal oxide arresters. The effective value of the power frequency voltage that is allowed to be continuously applied to the terminals of the arrester during operation covers the highest value of the power frequency voltage that may be continuously applied to the metal oxide arrester during the operation of the power system.
1.3 Grid voltage fluctuations.
Distribution network voltages fluctuate over a wide range. For metal oxide arresters, thermal collapse may result if large amounts of energy need to be absorbed in steady state. When using gapless metal oxide arresters, the system operating voltage fluctuation range must be met. Otherwise, due to the excessive steady-state voltage, the arrester will not be damaged, but many arresters will be damaged at the same time.
1.4 Aging problem.
The gapless metal oxide arrester valve plate has poor uniformity, resulting in uneven potential distribution. After running for a period of time, some valve plates will deteriorate first, causing the reference voltage of the arrester to drop and the resistance current and power loss to increase. Since the grid voltage remains unchanged, the charge rate of other normal valves in the metal oxide arrester increases (the charge rate is the ratio of the maximum operating phase voltage peak of the metal oxide arrester to the peak value of the DC reference voltage or power frequency reference voltage), resulting in accelerated aging, forming a vicious cycle, and ultimately leading to the thermal collapse of the metal oxide arrester. The aging speed of the lightning protection valve plate is a key factor affecting its service life.
The oxide arrester operates at the end of the product life, and the deterioration of the valve plate leads to an increase in leakage current and even internal discharge. When the discharge is severe, the gas pressure and temperature inside the arrester increase sharply, causing the breakdown of the oxide arrester body. When the internal discharge is not too severe, the system can be grounded on a single phase.
1.5 harmonics
The application of large-tonnage electric arc furnaces, large-scale rectification and frequency conversion equipment in metallurgical enterprises and the impact load of steel rolling production have a greater impact on the power grid, seriously exceeding the high harmonic values on the power grid. Due to the nonlinearity of the valve plate, there is a series of high harmonics under the action of sinusoidal voltage. Under the action of high harmonics, the valve plate deteriorates faster.
1.6 Poor impact resistance.
Oxide arresters mostly cause accidents under overvoltage or lightning conditions. The reason is that during the manufacturing process of the valve plate, due to the lax control of each process quality control point, the valve plate's ability to withstand impulse voltage is not strong, which accelerates the deterioration and damage of the valve plate in the process of frequently absorbing overvoltage energy. When the power grid is disconnected, grounded or otherwise causes resonance, its amplitude can reach 3 times the phase voltage, which may cause damage to the metal oxide arrester.
1.7 Metal oxide arresters have poor overvoltage protection capabilities.
For overvoltages with limited energy, such as lightning overvoltage and operating overvoltage, arrester leakage can play a role in voltage limiting protection. For overvoltages with infinite energy (supplementary energy), such as transient overvoltage (general term for power frequency overvoltage and resonant overvoltage), the frequency may be an integer multiple or a fractional multiple of the power frequency to form a transient overvoltage. The power frequency power supply can automatically supplement the overvoltage energy so that the arrester leakage overvoltage range does not attenuate or weakly attenuate. If the transient overvoltage enters the arrester protection action area, it will inevitably last for a long time until thermal collapse. Therefore, transient overvoltage is fatal to gapless metal oxide arresters.
1.8 Unqualified grounding resistance leads to counterattack.
The grounding body of the arrester is the first channel for leakage of lightning current. The grounding resistance is too high or the grounding device is unqualified. When lightning intrudes, the lightning current leaks greatly through the lightning arrester and through the ground. Due to the high ground resistance and the inability to discharge, part of the lightning current reversely impacts the arrester or distribution transformer, causing the counterattack to damage the arrester and sometimes even damage the distribution transformer.
1.9 installation error.
Due to the small size of the gapless metal oxide arrester, the shed is not obvious. In addition, the technical level of individual electricians is not high and the sense of responsibility is not strong. The direction of the arrester is reversed. Rainwater makes the shed water, causing discharge arc creeping. Over time, the silicone rubber jacket of the metal oxide arrester is damaged due to arc creeping discharge. When inspecting the variable oxide arresters, the author found that some were scrapped because the shed was reversed and the silicone rubber jacket had arc creeping discharge.
High voltage arrester
2. Measures to prevent damage to metal oxide arresters.
Correctly choose high voltage surge arrester.
The main difficulty in selecting a surge arrester is to determine the range of temporary overvoltage, not only to ensure safe and reliable operation under high operating overvoltage and atmospheric overvoltage, but also to ensure that the valve plate does not operate under temporary overvoltage. At this stage, the selection and design of the arrester must ensure that when a single phase is grounded for 2 hours, the system's highest overvoltage occurs and the metal oxide arrester does not move, otherwise the oxide arrester will undergo thermal collapse.
In terms of design selection, choose products that have been operating stably for many years. When selecting a manufacturer, you should choose a manufacturer with advanced process equipment and complete detection methods to ensure that the selected metal oxide arrester has high aging resistance and impact resistance, so that it can operate stably during the product life cycle.
Use series gap metal oxide arresters. The valve plates of gapless metal oxide surge arresters are subjected to grid voltage for a long time and have severe working conditions, low inflection point voltage, and high operating frequency. They may suffer transient overvoltage and temperature thermal damage, accelerate the aging of the valve plates, and some have a shorter service life than silicon carbide arresters.
The gap of the series gap metal oxide arrester can ensure that the valve plate only withstands high voltage during the overvoltage protection process and the time is very short. In other cases, the valve plate is in a low potential state (composite gap resistance voltage division), which greatly improves the long-term working conditions of the valve plate.
The protective action of the series gap metal oxide arrester only discharges lightning current, flows discontinuously, and has a light operating load. The gap does not require arc extinguishing and cutting off the continuous flow capability. The 10kV metal oxide arrester has only one gap, and its operating characteristics can operate stably for a long time. 2.2 Install the disconnector.
In order to prevent the accident from expanding when the metal oxide arrester is damaged, it is recommended to install a disconnector at the bottom of each arrester so that the arrester can be separated from the operating grid in time when the voltage is abnormal. The main characteristic of arrester failure is an increase in leakage current, which is difficult to detect during operation. It may be ill for a long time, thereby expanding the accident. Therefore, it is necessary to monitor its operating status. Metal oxide surge arresters are equipped with disconnectors. When it fails and is damaged, the disconnector will run automatically (no more than 8 minutes at 30ma) to avoid causing greater losses and accidents and improve operational safety and reliability. It can reduce the trouble of regularly conducting various electrical performance tests or online monitoring of metal oxide arresters.
2.3 Strengthen power grid harmonic control.
Strengthen the control of harmonics in the power grid and add dynamic reactive power compensation or harmonic elimination devices in the harmonic source line segments to control the high harmonic values of the power grid within the range allowed by national standards.
2.4 Strengthen the management of metal oxide arresters.
Strengthening monitoring is one of the important measures to ensure the safe and reliable operation of metal oxide lightning devices. Metal oxide surge arresters must be inspected and tested before operation, and the test results must be recorded in the technical file. A technical profile should be established for each metal oxide surge arrester operating on the distribution network. Factory reports, periodic test reports and online monitoring operation records should be stored in technical files as a reference for periodic inspections until the arrester is removed from operation.
Strengthen the professional and technical training for electricians and enhance their sense of responsibility. Each unit will set up full-time (part-time) administrators for the management of metal oxide arresters and conduct strict assessments.
2.5 The grounding resistance should meet the specified requirements.
The grounding body of the arrester should be considered durable and should be made of φ16mm hot-dip galvanized round steel. (Plain areas) 7~8m into the ground, 10.
Lightning arrester manufacturer
