Lightning arrester is an electrical device that can release lightning or release the power system operating overvoltage energy, protect electrical equipment from instantaneous overvoltage (lightning overvoltage, operating overvoltage, power frequency transient overvoltage impact), and cut off the continuous current, and do not cause system grounding short circuit.
The role of the lightning arrester: The lightning arrester is the equipment that protects the substation equipment from the lightning shock wave. When the lightning shock wave of the incoming substation along the route exceeds the protection level of the arrester, the arrester first discharges, and the lightning current is safely introduced to the earth through a good conductor. The grounding device is used to limit the lightning voltage amplitude below the lightning impact level of the protected equipment, so that the electrical equipment is protected.
(1) When the power grid has an instantaneous pulse voltage due to lightning strikes, the lightning arrester is switched on within nanoseconds.
(2) The lightning arrester is switched on within nanoseconds, the pulse voltage is short-circuited to the ground, and then restored to a high resistance state, so as not to affect the power supply of the user equipment.
Several indicators of power arrester:
(1) Volt second characteristics: refers to the corresponding relationship between voltage and time.
(2) power frequency continuous current: refers to the end of the lightning voltage or overvoltage discharge, but the power frequency voltage still acts on the arrester, so that it flows through the power frequency short-circuit grounding current.
(3) self-recovery ability of insulation strength: the relationship between the insulation strength of electrical equipment and time, that is, the speed of recovery to the original insulation strength.
(4) The rated voltage of the arrester: after the power frequency continuous current passes zero for the first time, the gap can withstand the maximum power frequency voltage that will not cause arc reignition, also known as arc voltage.
Classification of lightning arrester:
Commonly used arresters are: valve type, tube type, protection gap, metal oxide and so on.
1, valve arrester: valve arrester is mainly divided into ordinary valve arrester and magnetic blow valve arrester two categories, ordinary valve arrester FS and FZ two series. Magnetic blow valve arrester has FCD and FCZ two series. The meaning of the lightning arrester symbol: F-valve type lightning arrester, S- with (variable) electrical action, Z- for power station, Y- for line, D- for rotary motor, C- with magnetic blow discharge gap.
Structure:
The valve is composed of discharge gap and non-linear resistance valve, and is sealed in porcelain tube.
② The discharge gap is formed by a number of standard single discharge gaps (gap capacitors) in series, and a group of equalizing resistors in parallel can improve the recovery ability of the gap insulation strength.
(3) The non-linear resistance valve plate is also made of many single valve plates in series. The spark gap consists of several disc-shaped copper electrodes, each pair of gaps separated by 0.5 ~ 1mm thick mica sheet (washer type).
Valve type arrester working process: Valve type lightning arrester in the normal power frequency voltage under the spark gap is not broken down, but in the lightning wave, overvoltage, the spark gap of the lightning arrester is broken down, the resistance value of the nonlinear resistance suddenly becomes larger with the voltage resistance becomes smaller, the overcurrent flows through the resistance into the earth, the resistance valve to the power frequency voltage with the lightning current presents a large resistance, thus the power frequency current is blocked by the spark gap. The line returns to normal operation, the spark gap and the resistance valve plate work closely together, opening and closing like a valve, so it is called a valve arrester.
Equivalent circuit of valve arrester:
Valve arrester application:
FS series is generally used to protect power distribution equipment and circuits due to the small arrester valve plate and low flow capacity.
SZ series is generally used for 35KV and above electrical equipment because the valve plate is large, and the spark gap is connected with silicon carbide resistance, and the flow capacity is large.
2, protection gap: Protection gap is the simplest lightning protection equipment, generally made of galvanized round steel, with the main gap and auxiliary gap composition. The main clearance is angular and installed horizontally to quench the arc. In order to prevent the main gap from being short-circuited by foreign objects and causing misoperation, auxiliary gaps are arranged in series under the main gap. Because the protection gap arc extinguishing ability is weak, it is generally required to be equipped with automatic reclosing devices to improve the reliability of power supply.
Structure:
① It is composed of main gap and auxiliary gap.
② The main gap is angular, so that the power frequency continuous arc is easy to rise and be stretched and self-extinguished under the action of its own electric power and hot air flow.
③ The role of the auxiliary gap: in order to prevent the main gap from being short-connected by foreign objects, resulting in a grounding short-circuit accident.
Insufficient protection gap and application:
(1) The main drawback is that the strong impulse current will cause damage to the insulation between phases of the three-phase transformer.
(2) The application is often used in distribution networks where the neutral point is not directly grounded below 10KV, and is generally installed on the inside of the high-voltage fuse to reduce the number of trips of the substation line breaker.
3, tubular arrester: The basic element of tubular arrester (exhaust arrester) is the spark gap installed in the production pipe, and the gap is composed of rod and ring electrodes. The tubular arrester is composed of internal gap and external gap. Arc extinguishing tubes are generally made of materials such as fiber bakelite that can produce gas at high temperatures. When the lightning wave and overvoltage come, the internal and external gaps of the tubular arrester are broken down, and the overcurrent flows into the earth through the ground wire. The ensuing power frequency current produces a strong arc, which burns the tube wall and produces a large amount of gas ejected from the tube mouth, which quickly blows out the arc. At the same time, the external gap is restored insulation, arc extinguishing tube or arrester is separated from the system, and the power is restored to operation. See the figure below for details.
Tube arrester shortage and application:
(1) It can cut off large current and is suitable for installation in the inlet section of the substation and some weak insulation locations on the line. However, due to the inherent structural characteristics of the exhaust arrester, its spark gap is exposed to the atmosphere, and the electrical performance is not stable enough. So this type of lightning arrester is rarely used.
(2) Because the tubular arrester relies on the power frequency current to produce gas arc extinguishing, if the short-circuit current is too large to break, and the gas is generated too much to exceed the mechanical strength of the arc extinguishing tube, it will crack or explode, so it is generally installed outdoors.
4, metal zinc oxide arrester: (1) No gap metal zinc oxide arrester (pressure sensitive arrester), is a new type of arrester that began to appear in the 1970s. Compared with conventional arresters, gackless metal oxide arresters have no spark gap and use zinc oxide instead of silicon carbide in valve arresters. In the structure of the valve plate made of varistor stack, the valve plate in the power frequency voltage, the maximum resistance, effective suppression of power frequency current, and in the case of overvoltage and small resistance, can be a good release of overcurrent, protect the equipment.
(2) There is a series gap type metal oxide arrester, in the composite jacket metal oxide arrester resistor and a gap in series, suitable for non-neutral ground system. Serious long-term transient overvoltage may occur when the single phase is grounded, and it is difficult for the gassless zno arrester to withstand this overvoltage. The zinc oxide arrester with series gap does not act under the overvoltage with low amplitude of single-phase grounding, so the arrester is isolated from the system. When the voltage is higher than the above, the gap is on and the arrester is discharged. Effective protective equipment and lightning arrester.
Advantages of metal oxide arrester:
(1) Excellent protection performance. MOA has good nonlinear characteristics.
(2) Large flow capacity. It has good ability to absorb lightning overvoltage and transient overvoltage.
(3) High operational reliability. The normal working state is close to the insulation state, the power frequency continuous current is only microamperage, the energy release quickly restores the high resistance state, the operation reliability is high, and the anti-pollution ability is strong.
Arrester inspection and maintenance:
A, newly installed or overhauled lightning arrester
1, the new installation or overhaul of the arrester, the high voltage test should be qualified, and should be from the installation or maintenance personnel to obtain the following data, not lower than the standard:
(1) insulation resistance value;
(2) conductivity current value;
(3) Main technical parameters.
2, porcelain and flange clean, no damage.
3, connecting wire, grounding wire and cable should be firm.
4, the body is not inclined, the pressure balancing ring is firmly connected and complete.
5, the discharge recording device should be complete, and record its indication value.
6, FCD type arrester to check the parallel resistance on and off and contact, 6KV or 15.7KV arrester, insulation resistance should be measured using 2500V shake meter, resistance value should not be less than 150 MΩ, 220KV arrester should not be less than 500 MΩ, and compared with the previous data, there should be no significant change, If it is infinite, it may be a parallel resistance fracture.
- Lightning arrester in operation
In addition to the inspection in accordance with the above articles, the lightning arrester in operation should also check:
1, there is no sound inside;
2, there is no discharge phenomenon;
3, after a thunderstorm, whether the discharge recorder operates, and record the indicating value;
4, strong winds, check the swing of the arrester lightning rod, lead, wire should be firm and undamaged.
- In case of any of the following situations, the operation shall be suspended immediately
1, insulation sleeve explosion, rupture or serious discharge.
2, the connection is loose, there is a risk of falling off;
3, internal discharge sound.
Operation and maintenance of valve type arrester:
1) Normal patrol and inspection in the operation of valve type arrester
① Check the surface of the arrester porcelain sleeve. In daily operation, the pollution status of the porcelain jacket surface of the arrester should be checked, especially for the arrester operating in serious pollution areas or coastal areas. Because when the surface of the porcelain sleeve is seriously polluted, the voltage distribution will be very uneven. In a shunt resistor arrester, when the voltage distribution of one of the components increases, the current through the 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 the valve type arrester, and reduce the protection characteristics of the arrester. Therefore, when the porcelain sleeve surface of the arrester is found to be seriously polluted, it must be cleaned in time.
② Check the lead and ground lead of the arrester, whether there are burn marks and broken strands, and whether the discharge recorder is burned out.
Through this inspection, it is most easy to find the invisible defect of the arrester. Because under normal circumstances, after the action of the arrester, the ground lead line and the recorder only pass the lightning current and the power frequency continuous current with a small amplitude (generally below 80A) and a short time (about 0.01S), so in addition to the indication of the action recorder, it generally does not produce traces of burn damage. If, when the internal valve plate of the arrester is defective or cannot extinguish the arc, the amplitude and time of the continuous current through the power frequency will increase, then the connection point of the ground lead line will produce burn marks, or the internal discharge recorder will burn black or burn out. When the above situation is found, try to disconnect the arrester immediately and carry out a detailed electrical inspection to avoid accidents.
③ Check whether the top lead of the arrester is sealed properly. The poor seal of the arrester will cause water and moisture easily cause accidents, so it is necessary to check whether the cement joint at the joint of the porcelain sleeve and the flange is tight. A waterproof cover can be installed on the lead line of the 10kV valve type arrester to avoid rainwater infiltration.
④ Check whether the electrical distance between the arrester and the protected electrical equipment meets the requirements. The arrester should be as close as possible to the electrical equipment being protected.
2) Abnormal phenomenon and fault treatment of valve type arrester
Abnormal phenomena and faults often occur in the operation of the valve type arrester. The personnel on duty should analyze and judge the abnormal phenomena and take timely measures to deal with the faults.
If cracks are found in the porcelain sleeve of the arrester in the thunderstorm, the arrester should not be removed from operation as much as possible, and then handled after the thunderstorm. If the flash is caused by a crack in the porcelain sleeve of the arrester, but the system is not grounded, the fault phase arrester should be disabled if possible.
When it is found that there is abnormal sound inside the arrester or the casing has exploded and cracked, and the system grounding fault is caused, the operation duty officer should avoid being near, at this time, the circuit breaker or artificial grounding transfer can be used to disconnect the fault arrester.
If the valve type arrester suddenly explodes during operation, but the system is not permanently grounded, pull the isolation switch of the fault phase to disable the arrester after the thunderstorm, and replace the qualified arrester in time. If the system is permanently grounded after the explosion, do not use the isolation switch to disable the faulty arrester.
If it is found that the valve type lightning arrester action indicator is burned or burned inside, and there is a burn mark or burning phenomenon on the ground lead down connection point, there may be internal defects such as valve plate resistance failure, spark gap arc extinguishing characteristic deterioration, causing the power frequency continuous current increase, etc., should be timely electrical test or disassembly inspection of the arrester.