Several wiring methods of metal zinc oxide arrester manufacturers in parallel capacitor devices and their main technical parameters and model selection
Metal oxide arrester, the English name is Metal Oxide Arrester, referred to as MOA. Gapless metal oxide arrester refers to an arrester composed of only metal oxide non-linear resistors connected in series and/or parallel, without parallel or series discharge gaps. It is a protective device used to protect electrical equipment from various overvoltage hazards. Power system overvoltage is caused by lightning strikes, switching operations or failures, etc., and can be divided into three major categories: temporary overvoltage, operating overvoltage, and lightning overvoltage (or atmospheric overvoltage). MOA is a new type of lightning arrester developed in the 1970s. It is mainly composed of zinc oxide varistor. Each varistor has a certain switching voltage (called a varistor) when it is made. Under normal operating voltage (i.e., less than the varistor voltage), the varistor has a large value, which is equivalent to an insulation state. However, under the action of an impulse voltage (greater than the varistor voltage), the varistor has a low value and is broken down, which is equivalent to a short-circuit state. However, the varistor can recover after being hit; when the voltage higher than the varistor voltage is removed, it returns to the high resistance state. Therefore, if an MOA is installed on a power line, when an overvoltage occurs, the high voltage will cause the varistor to breakdown, and the current will flow into the ground through the varistor, controlling the voltage on the power line within a safe range, thereby protecting the safety of electrical equipment. In order for the arrester to reliably protect electrical equipment, the volt-ampere characteristics of the arrester are required to be below the volt-ampere characteristics of the electrical equipment. When the system generates overvoltage, the voltage across the capacitor increases and the arrester operates, limiting the voltage across the capacitor below the arrester protection level. At present, the main component of the oxide arrester valve is zinc oxide, so it is often called zinc oxide arrester.
Currently, there are two types of arresters used by manufacturers: porcelain jacket type and composite jacket type. The main material used for the jacket material of composite jacket arresters is methyl vinyl silicone rubber.
Compared with porcelain jacketed arresters, composite jacketed arresters have the following characteristics:
(1) Light weight and small size;
(2) The arrester has good dirt resistance. The hydrophobicity of the silicone rubber jacket is used to improve the external insulation performance of the arrester and reduce the maintenance workload of the device;
(3) The arrester has good explosion-proof performance. It uses a composite jacket made of epoxy glass fiber cylinder and silicone rubber material, which is beneficial to releasing the internal pressure when the arrester fails and avoids the harm to other equipment caused by the explosion of the arrester.
Therefore, composite jacket oxide arresters are often used now.
Product type:
Y—Porcelain jacketed oxide arrester YH—Composite jacketed oxide arrester
Structural features:
W—no gap C—series gap B—parallel gap
Place of use:
S—Distribution type Z—Power station type B—For parallel capacitors D—For motors T—For electrified railways X—Line type
Additional features:
W - Anti-pollution type G - Plateau type TH - For use in humid tropical areas. According to the pollution situation in the area where the arrester is installed, the pollution level of the external insulation of the arrester is selected according to the standard GB/T5582. Pollution levels are divided into four levels, which stipulate the requirements for the minimum nominal creepage distance of jackets: Level I light pollution areas are 17mm/kV; Level II moderate pollution areas are 20mm/kV; Level III heavy pollution areas are 25mm/kV; Level IV extremely heavy pollution areas are 31mm/kV.
Terminology for lightning arrester:
Continuous operating voltage (Uc), the effective value of the power frequency voltage that is allowed to be permanently applied between the arrester terminals.
Rated voltage (Ur), the maximum allowable effective power frequency voltage applied between the arrester terminals.
Nominal discharge current (In), used to classify arrester levels, has a lightning impulse current peak value of 8/20 waveform.
Residual voltage (Ures), the maximum voltage peak between the terminals of the arrester when the discharge current passes through it. DC 1mA reference voltage (U1mA), the voltage on the arrester measured at 1mA DC reference current. Generally not less than the rated voltage peak value of the arrester. The DC 1mA voltage is often called the breakover voltage. When the terminal voltage is less than U1mA, the current through the arrester is very small and is dominated by the capacitive component. When the terminal voltage is greater than U1mA, the arrester current increases rapidly and is dominated by the resistive component.
Charge rate (η), the percentage of the peak value of the continuous operating voltage and the DC 1mA reference voltage. The high or low charging rate directly affects the aging speed of the arrester, which is generally less than 80%. The nominal discharge current In of the arrester is an important parameter with a waveform of 8/20μs to classify its class.
There are five levels: 1.5, 2.5, 5, 10, and 20kA. The first three levels correspond to the neutral point, motor arrester, and capacitor arrester respectively. The power station arrester is divided into the last three levels.
Protective features:
The protective characteristics of MOA are completely determined by its residual pressure. Generally, the residual voltage is proportional to the rated voltage of the arrester. For a MOA with a certain rated voltage, its residual voltage is a function of the current through the arrester.
Protective properties are a combination of:
a) Residual voltage under steep wave current impact;
b) Residual voltage under lightning impulse current;
c) Residual voltage under operating surge current.
The operating impulse protection level of the arrester is the maximum residual voltage under the specified operating impulse current. The metal zinc oxide arrester in the shunt capacitor device mainly limits the operating overvoltage. The 8/20μs lightning impulse residual voltage of the system bus arrester mainly limits the protective characteristics of the atmospheric overvoltage arrester under operating overvoltage. Residual voltage tests under operating impulse current are required. , the apparent wave front time of the experiment is 30 μs but less than 100 μs, and the apparent wave tail half-peak time is about twice the apparent wave front time and the discharge current peak value. Because the wave front time of the operating impulse current is in the range of 30 to 100 μs, it has no obvious impact on the residual voltage value. The current amplitude specifies different values according to different voltage levels.
(The peak value of surge current in Table 14 of Table 14 of 8.3.3 of GB11032-2000 for parallel compensation capacitors operated by lightning arresters is 125A and 500A).
The operating overvoltage of the capacitor bank may be:
(1) Closing overvoltage;
(2) Non-synchronous closing overvoltage;
(3) The contact bounces over voltage when closing;
(4) When opening, there is a single-phase ground fault on the power supply side or a single-phase slamming through voltage without a single-phase ground fault;
(5) When the gate is opened, the two phases hit the through voltage;
(6) Multiple blow-through voltages generated by one operation of the circuit breaker;
(7) Other overvoltages related to operating capacitor banks.
It can be seen from the test data that the overvoltage during the opening operation is the main one. The opening overvoltage mainly occurs during single-phase re-breakdown. The chances of two-phase re-breakdown and multiple re-breakdown during one operation are very small.
Selection of main parameters of lightning arrester manufacturers, European cable joints, and cold shrink cable terminals:
GB50227-1995 Design Specifications for Parallel Capacitor Devices: The operating overvoltage protection and arrester wiring methods of high-voltage parallel capacitor devices should comply with the following regulations:
1. For group circuits of high-voltage parallel capacitor devices, operating overvoltage protection should be set.
2. When the circuit breaker only undergoes single-phase re-breakdown, the neutral point arrester wiring method or the phase-to-ground arrester wiring method can be used.
3. When the probability of two-phase re-breakdown of the circuit breaker is extremely low, the two-phase re-breakdown fault protection does not need to be set. When it is necessary to limit the overvoltage between the capacitor poles and the power supply side to ground, the protection method should comply with the following regulations:
(1) When the reactance rate is 12% and above, parallel connection of arrester and reactor and neutral point arrester wiring can be used
(2) When the reactance rate is not greater than 1%, the arrester and capacitor can be connected in parallel and the neutral point arrester can be connected.
(3) When the reactance rate is 4.5% to 6%, the arrester wiring method should be determined through simulation calculation research.
3~66kV is an ungrounded system, and the neutral points of the capacitor banks connected to this system are not grounded. Therefore, if a single-phase rebreakdown occurs when the capacitor bank is disconnected, the power supply side (high-voltage end) of the capacitor bank may have an overvoltage to the ground that exceeds the insulation level of the equipment to the ground. For example, when the reactance rate K=0, the theoretical maximum value is 5.87 times the phase voltage, and as the K value increases, the overvoltage shows an upward trend; when there is a single-phase ground fault on the power supply side, the single-phase strike through voltage is much higher than the situation without grounding. Therefore, the single-phase slam-through voltage should be limited. For vacuum circuit breakers that operate more frequently, the possibility of single-phase re-breakdown should be considered.
Yichang Hengyuan Technology Co., Ltd. specializes in the production of European cable joints, plug-and-pull heads, cable branch boxes, American elbows, high-voltage vacuum circuit breakers, high-voltage load switches, lightning arresters, zinc oxide arresters, tank arresters, overvoltage protectors, counters, monitors, heat-shrinkable cable accessories, Manufacturer of cold shrink cable accessories, T-heads, wall bushings, European cable accessories, American cable joints, transformer neutral point protection devices, fuses, isolating switches, PT cable heads, elbow cable joints, 10kV outdoor terminals, switch cabinets, cable intermediate joints, cable accessories and other products
