A lightning arrester (also called a lightning diverter) is a device used in electrical systems and telecommunications systems to insulate systems and protect conductors from the harmful effects of electricity.
The common lightning arrester has a high-voltage terminal and a ground terminal. Lightning (or very similar switching surge) travels to the arrester along the power line. In most cases, the currents from the earth grow through the arrester.
In telegraphy and telephone, an electrical arrester is placed where the wire enters a structure, preventing damage to electronic devices within it and ensuring the safety of nearby people.
Smaller versions of lightning arresters also called amplifier protectors, connect power and communication systems and every electrical conductor on earth. These resist general power or signal currents on the ground but provide a pathway that conducts high-voltage electricity bypassing connected equipment.
Their objective is to limit voltage spread when a contact or power line is struck by lightning or near lightning. If certainty fails or is missing, the lightning that beats the electrical system introduces thousands of kilovolts that can harm the transmission line and cause severe damage to transformers and other electrical or electronic devices.
The final voltage spikes generated by electricity can damage or even cause electrical home appliances’ death in the incoming power line. Lightning arrests are used to protect electric fences. These have a spark gap and sometimes a series indicator. Such devices are also used to protect the transmitters feeding the mast radiator.
Bringing a series for this type of device usually has a twist. Lightning can make a part of large electrical transformers and can break into pieces when the transformer explodes. High-voltage transformer fire barriers require small-to-small ballistic as well as transformer bushings and projectiles from lightning generators per NFPA 850.
Potential targets for lightning strikes, such as an outdoor television antenna, are connected to a terminal labeled in the photograph. The terminal is connected to a long rod buried in the ground. Normally no current will flow between the antenna and the ground because there is ultimate resistance between B and C and between C and D. The voltage of the lightning strike is many times greater than the need to move electrons through two air gaps.
The result is that electrons travel through the television set through lightning instead of destroying it. An electric amplifier may have a spark gap or a semiconductor material block such as silicon carbide or zinc oxide.
“Thyrite” is the trade name used for Silicon Carbide compounds used by General Electric for their arrest and Verister products. Some spark gaps are open to the air. Still, most modern varieties are filled with the perfect gas mixture and contain very little radioactive material to encourage the gas to ionize when the voltage across the gap reaches a certain level.
Other designs of lightning generators use a glow-discharge tube (basically like a neon glow lamp) connected between a protected conductor and ground or use voltage-activated solid-state switches called varistors or MOVS.
Lightning rods used in power substations are large devices, consisting of a porcelain tube several feet long and several inches in diameter, usually filled with a disc of zinc oxide. A safety port on the device’s side occasionally causes an internal explosion without breaking the porcelain cylinder.
Lightning arresters move by what they can withstand, how much energy they can absorb, and the break-over voltage that they set to start driving. Lightning arresters move by what they can withstand, how much energy they can absorb, and the break-over voltage that they set to start driving.
Types of Lightning Arresters
Lightning arresters protect electrical equipment from lightning. It is placed very close to the equipment and when the thunderstorm occurs, the arrester diverts the high voltage wave of electricity to the ground. Alaster selection depends on various factors such as voltage, current, reliability, etc. Lightning arresters are classified into twelve types. Such are;
- Rod Gap Arrester
- Sphere Gap Arrester
- Horn Gap Arrester
- Multiple-Gap Arrester
- Impulse Protective Gap
- Electrolytic Arrester
- Expulsion Type Lightning Arrester
- Valve Type Lightning Arresters
- Thyrite Lightning Arrester
- Auto valve Arrester
- Oxide Film Arrester
- Metal Oxide Lightning Arresters
Their types are explained below in detail.
1. Rod Gap Arrester
It is the simplest form of an extended diverter with two 12 mm dia or square facing each other, one connected to the line and the other to the earth. These are usually attached across the bushing of different tools.
To avoid cascading across the insulating surface of very steeply covered waves, the rod’s gap should be set at a thickness of about 20% below the insulation impulse spark where it is installed.
To protect the insulator from pressure, the distance between the rod gap and the insulator should be more than one-third of the rod gap length. The spacing of the rod depends on the operating voltage of the system.
The typical figures are given below:
The rod gap site has the advantage of low cost and easy adjustment.
The spark over operates at a very high voltage due to the lightning, but it cannot flashover at the normal power supply voltage. The problem with the rod gap arrester is that once the spark has occurred, the low supply voltage may continue for some time.
To avoid this, a current limiting resistance is used in series with the rod, limiting the current to such an extent that it is sufficient to maintain the pressure. Another disadvantage is that the rock gaps are responsible for the damage caused by the high temperature of the pressure, which can cause the rods to melt.
The rod gap’s performance is badly affected due to climate change and the polarity of the resistance. Thus, rod spacing cannot be relied upon as major protection in a very low-quality type of diverter and high voltage power systems where supply continuity and equipment protection are also given priority. It could, of course, employ a second-line defense, given its low cost.
2. Sphere Gap Arrester
This is similar to the device’s sphere is supplied by the air gap – and the other is connected to a line basis. The distance between the two spheres is very small compared to their diameter and can be adjusted with gauges’ help. A suffocating coil is inserted between the sphere phase’s windings connected to the transformer and the line.
This is done to reflect any overvoltage surges that may tend to enter the transformer winding. The minimum air gap is set so that discharge does not occur at normal operating voltages but the pressure is created at predefined excess voltages. This pressure will travel to the spheres as the nearby heated air continues to rise.
The arc will continue to travel upwards and longer until it is automatically interrupted. When the voltages source continues, a sound pressure follows until the first voltage’s normal condition is achieved. It has the advantage of the ratio of unity to inspiration, i.e., if the instrument is protected against 50 cycle waves, it is protected against waves.
Unfortunately, when the spacing of the sphere is elongated, the electric pressure maintains the arc, requiring very little voltage to maintain it, and the pressure is not self-extinguishing. Circuit breakers have to intervene to interrupt the RK current and, therefore, supply continuity is interrupted. This is why the sphere gap is not effective.
3. Horn Gap Arrester
It was one of the earliest types of diverters to be developed and is still used to a certain extent in low-voltage lines due to its great simplicity. It consists of two horn-shaped pieces of metal separated by a small air gap and connected disconnected between each conductor and the earth.
The distance between the two electrodes is that the normal voltage gap between the line and the earth is insufficient to jump. Still, abnormally high voltages (twice less than the normal operating voltage) will break the gap and find their way. As a result of heated air and electromagnetic action, the pressure thus created will rise in the horn and extinguish itself, thus preventing the following pressure.
The time taken for a complete operation is usually between 3 and 5 seconds. A suffocating coil consisting of several turns of blank copper wire is attached to the line between the arrester and the machine to protect it from reflecting travel waves on the ladder.
The choke is without effect on the low-frequency power wave because its response is negligible at normal power frequency. In practice, 20 or 30 turns with a diameter of about 0.3 m seem quite effective. The line arrester should be located close to the transmission line’s end as possible for maximum protection of the terminal equipment.
Also, the choke coil’s connections to the arrester and from the arrester to the earth should be as short and direct as possible. The horn gap cannot break the current in more than ten arcs and the pressure needs to be limited to a small value of current as a dead short circuit. This is accomplished by inserting a non-inductive resistance between the line and the horn on its side.
The efficiency of horn spacing is severely reduced by resistance. Therefore, selecting a value for resistance is a matter for compromise; Commonly used values such as limiting kinetic current between 1 and 5 A by applying normal voltage. Resistance is made to a water column, oil-immersed metal wire, carbon rod, or carborundum, and as non-inductive as possible.
i. The breakdown that occurs during the transfer of voltage depends on the perceived ratio of the gap.
ii. The value of breakdown voltage is also affected by atmospheric conditions such as temperature and air pressure.
iii. The thunderbolt performance is also affected by any roughness of the horn gap and frequent settings need to be made for the gap.
iv. A long air gap is required at altitude because it depends on the air density and is inversely proportional to it.
It can be seen that in low-voltage installations, the gap has to be fixed very close, as insects or other objects reduce the gap as a result of accidental currents. Permutation change can also occur due to the formation of small globules of corroded or molten metal.
These problems are overcome in the user shown in Figure 9.21:
The main gap is set for a voltage at the top to be protected (1 cm for 2,000 V). The auxiliary gap, which is supplied with an electronically connected platinum point but is set for discharge, is said to be above 25% of the normal voltage.
If a foreign company misses the auxiliary gap, the result is that the series’s high resistance causes the current to die quickly. On the other hand, a pressure created by the rise of a voltage remains constant and ions the air in the main gap, resulting in a similar side pressure and the line is relieved.
This is another variation of the simple horn gap arrester. It symbolizes the triangular choke coil wound feature from the copper strip, being used as one of the horns on one side of the coil.
The arrangement is illustrated in Figure 9.22. It can be seen that the line current moves around the triangular reaction coil and moves to the load from the center of the north. The main gap has a series of resistance and also has a support spacing that is directly connected to the ground.
Severe over-voltages flash across the main and auxiliary gaps and go directly to the ground. Simultaneously, the resistance then limits less severe voltages only flashover the main gap and the current. The ohmic value of resistance is such that it limits the kinetic current with normal voltage from 4A to 3.3 kV at 66A kV to 2A.
It is claimed that this type of arrested choke coil has a magnetic blow-out effect, causing the pressure to rise rapidly above the horn. Furthermore, a wave traveling along the line from the first sharp ward upward bend of the triangle meets its first obstacle against which the grounded horn is mounted.
This accumulates the voltage and allows the use of a wide enough gap without reducing the device’s sensitivity compared to other types of horn arrestors. There are several other types of arresters that have varying degrees of horn and resistance devices. Classified-resistance horn arresters, for example, have a threaded or step gap.
A medium discharge occurs across a narrow part of the interval in the continuity of which it has a high resistance. If the current flow is not enough to remove the line, the arc crosses the next ‘larger gap,’ Then, the continuous gaps have lower and lower resistance. In the most severe conditions, the discharge will occur at intervals where there is no series resistance.
4. Multiple-Gap Arrester
Such an arrest consists of a series of small metal cylinders heated from each other and separated by an air gap of about 1 mm wide. The first of the series is connected to the line, and from the end to the ground and the number of gaps required depends on the line voltage.
The cylinders are made of an alloy of zinc known as a non-arcing metal to help suppress the arc and to prevent dynamic currents from flowing through the arrester through it. The vapor formed by an arc between these cylinders has a rectifying effect similar to mercury vapor, causing the arc to suppress every other half cycle.
It is a common practice to normalize the cylinders’ surface so that the cooler surface can be presented as much as possible; this helps in emitting dynamic currents. There is a certain capacitance between successive cylinders and between each of these cylinders and the ground. This leads to a non-uniform distribution of potential between different gaps – it is the largest of the last lines of arrest and gradually decreasing towards the gaps on the ground.
The result is that when the voltage between the arrestors achieves a certain critical value, a breakdown occurs between the first and second cylinders. The second cylinder is first connected to one utilizing an arc so that its probability increases until there is a breakdown between the second and third cylinders; Etc.
The dynamic current follows the discharge. As a result, a potentially equal fall along the line of cylinders results in that the maximum PD in the cylinders is less than required for the initial breakdown. Dynamic current continues to flow through the line voltage zero until the next half cycle when the metal electrodes’ pressure is multiplied by the selected quality.
Some zinc evaporates with the heat of the discharge and when the current in the gap phalf-cycleugh the zero points of the wave, the zinc vapor prevents its regeneration from the opposite direction. Before the voltage is reversed again, the arc vapor in the gap is cooled to a non-conducting state by isolating other currents of current.
In the case of horn arresters, there is such a current limit, yet it is higher, beyond that it will be maintained despite the action of refinement, so in most cases, limited restraint measures must be used. Such resistors are usually graphite alloys or metals connected in series with the gap group described in Figure 9.23.
Their value is that he can limit the dynamic flow to less than 20A. Such arresters are unsatisfactory for use in systems with a line voltage greater than 33 kV. The increase in the number of gaps required to prevent arcing by the normal voltage is beyond all voltage increase proportions.
There is also a lot of uncertainty about the number of intervals required, depending on the arches’ position relative to the surrounding ground objects. To get a more even distribution of the arresters’ potential and reduce the number of gaps required, sometimes a metal earth shelter or antenna is placed near the gaps at the high-potential end of the arrest to the line conductor.
Like other types of lightning archers, the multi-gap arrester tends to lose its efficiency as a discharge path for acute disturbances when supplied with series resistance. However, this difficulty can, in most cases, be overcome by dropping some gaps with resistance and using a series of resistances smaller than the un-shunted format.
The arrester with shunted gaps is known as the ‘low-equivalent arrester,’ and the construction principle is shown in Fig. 9.24:
From Figure 9.24, it is clear that point B is in the potential position under normal conditions and ‘so discharge will occur when the voltage is sufficient to break the series gaps between A and B.
The enthusiastic rush of currents after rupture, due to high frequency, will choose the straight path of land with shunt gaps between BB and C, gradually resisting instead of the alternate path through resistance, will eventually move to the ground through short series of resistance.
As soon as the emotional rush of currents is over, the arcs in the frightened gaps die, so that any dynamic current trying to follow must flow through both resistances, which are now continuous.
This current will be reduced by the high resistance in its path so much that it will not be enough to maintain the arcs in the series gaps, causing it to go out. Therefore, the effect of moving away from some gaps provides the arrester with a certain amount of selective action, as it breaks the low resistance on the way to high-frequency interruptions and high resistance on the way to low-frequency discharge.
The series resistance is fully distributed in the form of construction, the arrest consists only of a huge number of gaps in which some are closed and some are not. Compared to horn arresters, multiple-gap type arresters have the advantage of greater sensitivity to minor voltage surges.
Furthermore, it has the property of emitting any kinetic current after zero discharge instead of the maximum value in the vicinity’s horn spacing. So Arstar is not likely to be a high-frequency oscillation seat after surgery. On the other hand, multiple-gap type arresters are more expensive, especially for higher line voltages.
5. Impulse Protective Gap:
It was noted that the spacing of the sphere has an induction ratio of unity, but suffers from the error that the pressure between its electrodes is not self-extinguishing. The horn gap is self-extinguishing but it has a high tendency ratio of 2 or 3 if it is not as small as low voltage. The emotional protective gap is designed for low impulse ratios, even lower than unity k and extinguishing stress. In principle, the Emuls defensive gap is very common, as illustrated in Figure 9.25.
The spacing is precisely that of the two sphere-horn electrodes S1 and S2, connected to the line and the arrester, respectively, the latter being usually of the electrolytic type.
An auxiliary needle is placed between the electrodes S1 and S2 and is connected to them via (R, C1) and C2. The impedance of capacitance C1 at the normal line frequency is much larger than the resistive art impedance.
C1 = C2 if the potential of the auxiliary electrode is between S1 and S2 and there is no effect of flashover between the electrodes. In the case of short passing along the line, the impedance of capacitors C1 and C2 decreases, and resistance R now becomes pre-dominant. The result is that virtually the entire voltage is concentrated across the gap between E and S1.
The gap at once breaks down, the rest of the gap between E and S2 immediately following:
As a result, a high-frequency wave occurs when the length of the gap is immediately halved. On the other hand, during the initial breakdown, an electron is pointed to the fact that a slight time interval is introduced.
However, with commercial forms of the interval, an apparent emulsion ratio of 0.6 to 0.7 can be achieved. The electrolytic arrester on the side of the earth extinguishes the pressure.
Electrolytic Arresters: Electrolytic Arrester Early Arrester with greater discharge capacity. A thin film of aluminum hydroxide deposited in aluminum plates immersed in the electrolyte is important as high resistance to a low voltage but acts as low resistance to a low voltage.
A voltage greater than 400 volts (critical breakdown voltage) causes a puncture and a free flow of current to the earth. When the voltage returns to its normal value of 400 volts, the arrester again offers high resistance and the leak closes. The insulating film of hydroxide is formed by applying DC voltage to the aluminum plates’ critical value immersed in the electrolyte.
During the formation of the film, the current passes fairly smoothly but with the current stops’ formation. To increase the total critical value of the voltage, the number of films is arranged on top of each other.
The toe of the film’s formation voltage of this national arrester is equal to the number of films and each film’s critical voltage. Such arresters are very subtle, requiring daily supervision and the film needs to be reformed whenever it is destroyed. Electrolyte freezing can cause serious problems in cold countries. Electrolytic arresters are used in conjunction with a penetration interval.