1) It is used to protect electrical equipment from high transient over-voltage and limit the freewheeling time and the freewheeling amplitude. This term includes any external clearance necessary for the normal function of the appliance during operation and installation, regardless of whether it is a part of the whole.
Note 1: The lightning arrester is usually connected between the grid conductor and the ground wire, but sometimes it is also connected near the electrical winding or between the conductors.
Note 2: Lightning arrester is sometimes called overvoltage protector or overvoltage limiter.
2) Arrester is another important equipment often used to prevent communication cables from being damaged by lightning. The following describes the relevant knowledge of lightning arrester.
definition
Arrester: an electrical appliance used to protect electrical equipment from the harm of high transient overvoltage during lightning stroke, and to limit the freewheeling time and the freewheeling amplitude. Lightning arrester is sometimes called overvoltage protector or overvoltage limiter.
Applied discipline: information communication
Features: High transient, overvoltage, electrical appliances, lightning protection
Scope of application
AC gapless metal oxide arrester is used to protect the insulation of AC power transmission and transformation equipment from lightning overvoltage and switching overvoltage. It is applicable to overvoltage protection of transformers, transmission lines, distribution panels, switch cabinets, power metering boxes, vacuum switches, parallel compensation capacitors, rotating motors and semiconductor devices.
Features and principles
AC gapless metal oxide surge arresters have excellent nonlinear volt ampere characteristics, good response characteristics, no freewheeling, large current capacity, low residual voltage, strong ability to suppress overvoltage, pollution resistance, anti-aging, free from altitude constraints, simple structure, gapless, tight sealing, long life and other characteristics.
Under normal system working voltage, the arrester presents a high resistance state, and only microamp current passes through. Under the action of over-voltage and large current, it presents low resistance, thus limiting the residual voltage at both ends of the arrester.
classification
There are many types of surge arresters, including metal oxide surge arresters, line type metal oxide surge arresters, gapless line type metal oxide surge arresters, fully insulated composite sheathed metal oxide surge arresters, and removable surge arresters.
The main types of lightning arresters are pipe type, valve type and zinc oxide type. The main working principle of each type of lightning arrester is different, but their work essence is the same, which is to protect communication cables and communication equipment from damage.
Tubular arrester
The tubular arrester is actually a protective gap with high arc extinguishing capacity. It is composed of two series gaps. One gap is in the atmosphere, called the outer gap. Its task is to isolate the working voltage and prevent the gas pipe from being burned by the power frequency leakage current flowing through the pipe; The other one is installed in the gas pipe, which is called internal gap or arc extinguishing gap. The arc extinguishing capacity of tubular arrester is related to the power frequency continuous current. This is a kind of protective gap type arrester, which is mostly used for lightning protection on power supply lines.
Valve type arrester
Valve type arrester is composed of spark gap and valve resistance, which is made of special silicon carbide. The valve resistance made of silicon carbide can effectively prevent lightning and high voltage and protect the equipment. When there is high lightning voltage, the spark gap is broken down, the resistance value of the valve resistance drops, and the lightning current is introduced to the ground, which protects the cable or electrical equipment from the harm of lightning current. Under normal conditions, the spark gap will not be broken down, and the resistance value of the valve blade resistance is high, which will not affect the normal communication of the communication line.
Zinc oxide arrester
Zinc oxide arrester is a lightning protection equipment with superior protection performance, light weight, pollution resistance and stable performance. It mainly makes use of the good nonlinear volt ampere characteristics of zinc oxide to make the current flowing through the arrester very small (micro ampere or milliampere level) under normal working voltage; When over-voltage acts, the resistance drops sharply, and the over-voltage energy is released to achieve the protection effect. The difference between this arrester and the traditional arrester is that it has no discharge gap and uses the nonlinear characteristics of zinc oxide to discharge current and disconnect.
Several types of lightning arresters are introduced above. Each type of lightning arrester has its own advantages and characteristics. It needs to be used in different environments to achieve good lightning protection effect.
effect
The lightning arrester is connected between the cable and the earth, usually in parallel with the protected equipment. The lightning arrester can effectively protect communication equipment. Once abnormal voltage occurs, the lightning arrester will act to protect. When the communication cable or equipment is operating under normal working voltage, the arrester will not work and will be regarded as open circuit to the ground. Once high voltage occurs and endangers the insulation of the protected equipment, the arrester acts immediately to guide the high voltage impulse current to the ground, so as to limit the voltage amplitude and protect the insulation of communication cables and equipment. When the over-voltage disappears, the lightning arrester quickly recovers to the original state, making the communication line work normally.
Therefore, the main function of the lightning arrester is to cut the amplitude of the intrusion flow wave and reduce the voltage value of the protected equipment through the effect of the parallel discharge gap or nonlinear resistance, so as to protect the communication lines and equipment.
Arrester can be used not only to protect the high voltage generated by lightning, but also to protect the operating high voltage.
Type of arrester
The function of lightning arrester is to protect various electrical equipment in the power system from lightning overvoltage, switching overvoltage and power frequency transient overvoltage. The types of arrester mainly include protective gap, valve type arrester and zinc oxide arrester. The protection gap is mainly used to limit atmospheric overvoltage, and is generally used for protection of power distribution system, lines and incoming section of substation. The valve type arrester and zinc oxide arrester are used for the protection of substations and power plants. In 500KV and below systems, they are mainly used to limit atmospheric overvoltage. In ultra-high voltage systems, they are also used to limit internal overvoltage or as backup protection for internal overvoltage.
Seven characteristics:
1、 Large current carrying capacity of zinc oxide arrester
This is mainly reflected in the lightning arrester's ability to absorb various lightning overvoltage, power frequency transient overvoltage and switching overvoltage. The current carrying capacity of the zinc oxide arrester produced by Chuantai fully meets or even exceeds the requirements of the national standard. The line discharge level, energy absorption capacity, 4/10 nanosecond high current impulse withstand, 2ms square wave current carrying capacity and other indicators have reached the domestic leading level.
2、 Excellent protection characteristics of zinc oxide arrester
Zinc oxide arrester is an electrical product used to protect various electrical equipment in the power system from overvoltage damage, with good protection performance. Because of the excellent non-linear volt ampere characteristics of zinc oxide valve slice, only a few hundred microamps of current can pass through under the normal working voltage, which is convenient to design a gapless structure, making it have the characteristics of good protection performance, light weight and small size. When the overvoltage intrudes, the current flowing through the valve plate increases rapidly, at the same time, the amplitude of the overvoltage is limited, and the overvoltage energy is released. After that, the zinc oxide valve plate returns to the high resistance state, making the power system work normally.
3、 The sealing performance of zinc oxide arrester is good
High quality composite jacket with good aging performance and air tightness is used for arrester elements. Measures such as controlling the compression amount of sealing ring and adding sealant are adopted. Ceramic jacket is used as sealing material to ensure reliable sealing and stable performance of arrester.
4、 Mechanical properties of zinc oxide arrester
The following three factors are mainly considered:
⑴ Seismic force;
(2) Maximum wind pressure acting on the arrester
(3) The top of the arrester bears the maximum allowable tension of the conductor.
5、 Good decontamination performance of zinc oxide arrester
The gapless zinc oxide arrester has high pollution resistance.
The specific creepage distance specified in the current national standard is:
⑴ Grade II medium pollution area: specific creepage distance 20mm/kv
(2) Grade III heavily polluted area: specific creepage distance 25mm/kv
(3) Grade IV extremely polluted area: specific creepage distance 31mm/kv
6、 High operation reliability of zinc oxide arrester
The reliability of long-term operation depends on the quality of products and the rationality of product selection. Its product quality is mainly affected by the following three aspects:
A Rationality of overall structure of arrester;
Volt ampere characteristics and aging resistance of B zinc oxide valve plate
C. Sealing performance of lightning arrester.
7、 Power frequency tolerance
Due to various reasons in the power system, such as single-phase grounding, long line capacitance effect and load rejection, the power frequency voltage will rise or the transient over-voltage with high amplitude will occur. The arrester has the ability to withstand a certain power frequency voltage rise within a certain period of time.
use
1. It shall be installed near the distribution transformer side
The metal oxide arrester (MOA) is connected in parallel with the distribution transformer during normal operation, with the upper end connected to the line and the lower end grounded. When over-voltage occurs in the line, the distribution transformer at this time will bear three parts of voltage drop generated when over-voltage passes through the arrester, lead and grounding device, which is called residual voltage. In the three overvoltage parts, the residual voltage on the arrester is related to its own performance, and its residual voltage value is certain. Residual voltage on the grounding device can be eliminated by connecting the grounding downlead to the distribution transformer housing and then to the grounding device. How to reduce the residual voltage on the lead becomes the key to the protection distribution transformer. The impedance of the lead is related to the frequency of the current passing through. The higher the frequency, the stronger the inductance and the greater the impedance of the lead. It can be seen from U=IR that to reduce the residual voltage on the lead, the lead impedance must be reduced. The feasible way to reduce the lead impedance is to shorten the distance between MOA and the distribution transformer, so as to reduce the lead impedance and lead voltage drop. Therefore, the lightning arrester should be installed near the distribution transformer.
2. Low voltage side of distribution transformer shall also be installed
If MOA is not installed at the low voltage side of the distribution transformer, when the lightning arrester at the high voltage side discharges lightning current to the ground, a voltage drop will be generated on the grounding device, which will act on the neutral point of the winding at the low voltage side through the distribution transformer housing. Therefore, the lightning current flowing through the low-voltage side winding will make the high-voltage side winding induce a very high potential (up to 1000 kV) according to the transformation ratio. This potential will be superimposed with the lightning voltage of the high-voltage side winding, causing the neutral point potential of the high-voltage side winding to rise and breaking down the insulation near the neutral point. If MOA is installed on the low-voltage side, when the MOA discharge on the high-voltage side increases the potential of the grounding device to a certain value, the MOA on the low-voltage side starts to discharge, reducing the potential difference between the low-voltage side winding outlet terminal and its neutral point and the housing, so that the influence of the "reverse transformation" potential can be eliminated or reduced.
3. MOA grounding wire shall be connected to the distribution transformer housing
The earth wire of the MOA shall be directly connected to the distribution transformer enclosure, and then the enclosure shall be connected to the earth. It is wrong to connect the grounding wire of the arrester directly to the ground, and then lead another grounding wire from the grounding pile to the transformer shell. In addition, the grounding wire of the arrester shall be shortened as much as possible to reduce the residual voltage.
4. Carry out regular maintenance and test in strict accordance with the requirements of the regulations
The insulation resistance and leakage current of MOA shall be measured regularly. Once the insulation resistance of MOA is obviously reduced or broken down, it shall be replaced immediately to ensure the safe and healthy operation of the distribution transformer.
Operation and maintenance
In daily operation, check the pollution condition of the porcelain bushing surface of the arrester, because when the porcelain bushing surface is seriously polluted, the voltage distribution will be very uneven. In an arrester with shunt resistance, when the voltage distribution of one element increases, the current through its shunt resistance will increase significantly, which may burn out the shunt resistance and cause a fault. In addition, it may also affect the arc extinguishing performance of valve type arrester. Therefore, when the surface of arrester porcelain bushing is seriously polluted, it must be cleaned in time.
Check the lead wire and grounding down lead of the arrester, if there are burn marks and broken strands, and if the discharge recorder has passed this inspection, it is easy to find the hidden defects of the arrester; Check whether the lead at the upper end of the arrester is well sealed. If the arrester is poorly sealed, water will enter and become damp, which may easily cause accidents. Therefore, check whether the cement joint at the connection between the porcelain sleeve and the flange is tight. Install a waterproof cover on the lead of the 10kV valve type arrester to avoid rainwater infiltration; Check whether the electrical distance between the lightning arrester and the protected electrical equipment meets the requirements. The lightning arrester should be as close to the protected electrical equipment as possible, and the action of the recorder should be checked after the thunderstorm; Check the leakage current. If the power frequency discharge voltage is greater than or less than the standard value, conduct maintenance and test; Overhaul the discharge recorder if it operates too many times; Cracks are found at the joint of porcelain bushing and cement; If flange plate and rubber pad fall off, maintenance shall be carried out.
The insulation resistance of arrester shall be checked regularly. 2500 V insulation megger shall be used for measurement. The measured value shall be compared with the previous result. If there is no obvious change, it can continue to be put into operation. When the insulation resistance drops significantly, it is generally caused by damp due to poor sealing or short circuit of spark gap. When it is lower than the acceptable value, the characteristic test shall be conducted; When the insulation resistance increases significantly, it is generally caused by poor contact or fracture of internal parallel resistance, spring relaxation and separation of internal components.
In order to find the hidden defects in the valve type arrester in time, a preventive test should be carried out before the thunderstorm season every year.
