The classification of arresters and the advantages and characteristics of various types of arresters
Surge arrester is one of the main maintenance machinery and equipment to ensure the optimal operation of power engineering systems. It is mainly used for lightning strike overvoltage of limited route or internal structure overvoltage caused by actual operation.
The arresters include pipeline arresters, gate valve arresters and active zinc oxide arresters. The specific principle of each arrester is different, but the essence of the work is the same, so as to maintain the communication optical cable and communication equipment from being damaged.
The tubular arrester is composed of inner and outer gaps connected in series. Bronchial tubes are made of fibrous tubes, vertical raw material tubes, or hard plastic, with rods and inner gaps of annular electrodes in the tube. The material of the bronchus cannot bear the working voltage for a long time, and it must be protected by external clearance and route during normal operation. When the overvoltage exceeds the maintenance equipment, the external gap will be raised first, and then the internal structural gap will be charged and discharged immediately, introducing the lightning current into the earth. The bronchus forms a lot of vapor under the effect of electric isolation, which is ejected from the opening orifice of the annular electrode. When the power frequency freewheeling current crosses 0 for the first time, the electric isolation can be extinguished.
The use period of the bronchi is relatively limited, and part of the wall thickness raw material is consumed after each posture. The gas production volume is less than once, and the arc extinguishing capacity is reduced, which cannot ensure reliable arc extinguishing. The bronchus should be selected according to the rated voltage of the system software and the short-circuit capacity value of the installation point. For example, the pipeline arrester marked with the words 10/0.5~0.7 on the factory nameplate has a rated voltage of 10kV, and the short-circuit capacity of the installation point cannot be lower than 0.5ka or 7ka. The limiting current is determined by the tube diameter and impact toughness of the arc extinguishing tube, and the minimum value current is determined by the nominal diameter of the arc extinguishing tube and the gas production and supply volume. Due to the over-consideration of its after-flow specifications, the gas is not enough to extinguish the arc; if the after-flow is too large, the flatulence is too large, and the working pressure of the pipeline is too high, resulting in the explosion of the pipeline arrester. Because of the multiple changes in the operation method of the power grid, the transition area of the power frequency freewheeling value passing through is relatively large, resulting in the inability to extinguish the arc safety accident. Whether it is an explosion of the arrester or a short-circuit fault of the power grid, the pipeline arrester is rarely used.
The tubular arrester is actually a maintenance gap with high arc extinguishing ability. It consists of 2 serial gaps, one gap in the air, called the outer gap. Its goal is to protect the working standard voltage and prevent the bronchus from being burned by the power frequency leakage current flowing through the pipeline; the other is installed in the respiratory tract, which is called the inner gap or arc extinguishing gap. The arc extinguishing capacity of the tubular arrester is related to the size of the power frequency freewheeling current. This is also a lightning arrester with a maintenance gap, which is mainly used for lightning protection maintenance of distribution lines.
The valve arrester is composed of a flame gap and a valve plate resistor, which is made of a unique carbon-carbon composite material. Hair chip resistors made of carbon-carbon composite materials can effectively avoid lightning strikes and high voltages, and maintain machinery and equipment. When there is a high lightning working voltage, the flame gap is penetrated, the resistance of the valve resistor is reduced, and the lightning current is introduced into the earth to protect the cable or electrical equipment from the damage of the lightning current. Under normal circumstances, the flame gap is not easily penetrated, and the resistance of the valve plate resistor is high, which is not easy to endanger the normal communication of the communication network.
The key components of the valve arrester are the gap and the perforated plate (optimum control resistor plate). The perforated plate assists in arc extinguishing in the gap to limit the power frequency freewheeling current after the lightning strike. Generally, the freewheeling current of the earrings in the valve arrester is 50A (the highest value); such a small amount of current can reliably disconnect the freewheeling current when the freewheeling current crosses 0 for the first time. When the working voltage is high, the optimal control resistor is particularly small, which can introduce a lot of lightning current into the ground to maintain electrical equipment. When a lightning strike occurs, it can exhibit a high resistance to limit the value of the power frequency freewheeling, which is beneficial to the arc extinguishing of the gap.
The expression for the optimal control resistor of the valve plate is:
U-pressure drop on the valve plate, V;
I - the amount of current passing through the valve plate, KA;
The C parameter is related to the relative height and total area of the valve plate;
a-optimal control index, the smaller the a, the better the optimal control, generally a=0.2 or so.
Because UZY=ILL (lightning current) R; arc extinguishing working voltage UBY=IBL (freewheeling) R.
This ratio is called the maintenance ratio of the valve arrester, which is the main parameter in the design. The smaller the maintenance ratio, the better the protection characteristics.
Gap characteristics: several small gaps with uniform electrostatic field are connected in series, and the arc extinguishing characteristics of several gaps in series are much better than that of long gaps with the same spacing alone. When the freewheeling current is 0 for the first time, the breakdown voltage that can be repaired immediately for each gap is about 700V (starting to repair the compressive strength), so increasing the total number of gaps is very beneficial to arc extinguishing; because the gap between each small gap is not Large (about 1mm), the electrostatic field is more uniform, and the dispersion of charge and discharge is also smaller. Too many gaps consume raw materials, and if the inter-pole spacing is too small, it is very easy to cause gap short-circuit failures.
Several gaps are used in series, the current distribution of each gap is uneven, and there is a working voltage problem, which is caused by the harmful influence of the electric level on the stray resistance of the road capacitor and the high-voltage bearing end cover. The working voltage is uneven and unfavorable for arc extinguishing (the gap with higher working voltage is separated out again, and other gaps share the working voltage of the original shared resource before the allocation of the gap, which is likely to cause all valve arresters to reignite and fail to extinguish the arc), reduce The working voltage of power frequency charging and discharging (power frequency charging and discharging current is low, the arrester is likely to operate when the power is in normal operation, such as the FS arrester power frequency charging and discharging working voltage is seriously reduced), therefore, the arrester uses a voltage equalizing resistor, Making the working voltage evenly distributed can improve the actual effect of voltage equalization.
Active zinc oxide arrester.
Activated zinc oxide arrester is a lightning protection machine and equipment that maintains performance, light weight, environmental pollution resistance and characteristic stability. The key is to use the excellent optimal control volt-ampere characteristic curve of active zinc oxide, so that the current amount of the arrester is not large (micro safety or mAh level) under normal working standard voltage; Release the kinetic energy of overpressure to maintain the actual effect. The difference between this arrester and the traditional arrester is that it has no charge-discharge gap, and the optimal control feature of active zinc oxide has the effect of discharge and button.
In recent years, metal oxide arresters with rated voltages of 110kV and above have been selected. Because of its many advantages, especially its light weight, it has been widely used in power supply systems and has a tendency to replace gate valve arresters. In recent years, the total amount of funds invested in the operation of the power grid for non-gap active zinc oxide arresters with rated voltages of 110kV and above has been increasing. In terms of operating conditions, most of them operate well, but explosions also occurred during the entire operation. Analysis of explosion accidents, whether it is Chinese or foreign products, all are the product quality problems of the arrester itself, some of which are poor valve characteristics, unscientific design of the main parameters, and some internal structures The insulation layer material is not very good, the arrester The whole process of assembling leads to the defect of sealing, and the operation is wet and cold.
Post time: Apr-30-2022