Types of Lightning Arresters

What is a lightning arrester?

     A lightning arrester, also known as a surge arrester, is a device that is used to protect electrical equipment and circuits from damage due to high voltage surges, such as those caused by lightning. It is typically placed very close to the electrical equipment that it is protecting, and its main function is to divert the high-voltage wave of lightning to the ground, thereby protecting the equipment from damage.

     The selection of a lightning arrester depends on several factors, including the voltage and current levels that the arrester will be exposed to, as well as the level of reliability that is required. Different types of lightning arresters are designed to handle different levels of voltage and current, so it is important to choose the appropriate type of arrester for a particular application. Other factors that may be considered when selecting a lightning arrester include the type of electrical equipment being protected, the location of the arrester, and the environmental conditions in which it will be used.

Types of Lightning Arresters

1. Rod Gap Arrester
2. Sphere Gap Arrester
3. Horn Gap Arrester
4. Multiple-Gap Arrester
5. Impulse Protective Gap Arrester
6. Electrolytic Arrester
7. Expulsion Type Lightning Arrester
8. Valve Type Lightning Arresters
9. Thyrite Lightning Arrester
10. Auto valve Arrester
11. Oxide Film Arrester
12. Metal Oxide Lightning Arrester

1. Rod Gap Arrester

     A rod-gap lightning arrester is a simple device that is used to protect electrical and electronic equipment from damage due to lightning strikes and other high voltage transients. It consists of two rods that are placed a small distance apart, with one end of the arrester connected to the transmission line and the other end connected to the ground.

     When a high voltage transient, such as a lightning strike, occurs on the transmission line, the voltage across the gap between the rods increases, causing the air to ionize and create a low resistance path for the current to flow through. This safely directs the lightning current to ground, protecting the equipment from damage.

     However, the rod-gap arrester has some limitations. After the spark has occurred, it may continue for some time even at low voltages. To prevent this, a current-limiting reactor can be placed in series with the rods to limit the current. Additionally, the high temperature of the arc caused by the spark can damage the rods, causing them to melt. To avoid this, the gap setting of the arrester must be carefully chosen to break before the equipment is damaged.

Advantages of rod gap arresters:

• Rod gap arresters are relatively simple and inexpensive to install and maintain.
• They are effective at intercepting and conducting lightning strikes to the ground, which can help to protect a building and its occupants from the damaging effects of lightning.
• Rod gap arresters can be installed on a variety of structures, including buildings, towers, and poles.

Disadvantages of Rod Gap Arrester:

• Inability to interrupt power frequency following current: When a rod gap arrester intercepts a lightning strike, it conducts the electrical current to the ground. However, after the initial surge has passed, there may still be a residual current flowing through the arrester, known as a "follow current." This follow current can cause damage to the arrester itself, as well as to other electrical components in the system. In some cases, the follow current may be strong enough to trigger a circuit breaker, causing the circuit to de-energize and potentially interrupt power to the protected building.
• Damage to the rods due to heat: When a rod gap arrester intercepts a lightning strike, it creates a spark between the gaps in the rods. This spark can generate a significant amount of heat, which can cause damage to the rods over time. The rods may become weakened or even break, reducing the effectiveness of the arrester.
• Performance affected by polarity and atmospheric conditions: The effectiveness of a rod gap arrester can be influenced by the polarity of the transient overvoltage and atmospheric conditions. For example, if the polarity of the overvoltage is such that it favors the rod gap arrester, it may be more effective at intercepting and conducting the lightning strike. However, if the polarity is not favorable, the arrester may be less effective at protecting the structure. Similarly, atmospheric conditions such as humidity and temperature can affect the performance of the arrester.
• Used as backup protection: Due to the limitations and potential drawbacks of rod gap arresters, they are often used as a backup protection system rather than the primary means of lightning protection. Other types of lightning protection systems, such as air terminals and down conductors, may be used as the primary means of protection, with the rod gap arrester serving as an additional layer of protection in case the other systems fail or are not effective.

2. Sphere Gap Arrester

     A sphere-gap lightning arrester is a type of device that is used to protect electrical and electronic equipment from damage due to lightning strikes and other high voltage transients. It consists of two spheres that are placed a small distance apart, with one sphere connected to the transmission line and the other sphere connected to the ground. A choking coil is inserted between the phase winding of the transformer and the spheres to help limit the current.

     The air gap between the spheres is set so that a discharge does not occur under normal operating conditions. However, when a high voltage transient occurs on the transmission line, the voltage across the gap increases, causing the air to ionize and create a low resistance path for the current to flow through. The arc travels up the sphere as the heated air near the arc tends to rise upward, lengthening until it is interrupted automatically. This safely directs the lightning current to ground, protecting the equipment from damage.

Advantages of sphere gap arresters:

• Cost: One advantage of sphere gap arresters is that they are typically less costly than some other types of lightning protection devices, such as air terminals and down conductors. This makes them a more affordable option for protecting electrical systems.
• Impulse ratio: The impulse ratio of a sphere gap arrester is unity, which means that it is able to withstand transient over voltages of the same magnitude as the rated voltage of the system. This makes it a reliable protection device for electrical systems.

Disadvantages of sphere gap arresters:

• Arc does not quench: One disadvantage of sphere gap arresters is that the arc created by the overvoltage does not quench (extinguish) on its own. Instead, it requires an external means of quenching, such as a circuit breaker. This can cause an interruption in the electrical supply, which may not be desirable in some applications.
• Circuit breaker tripped: In order to quench the arc and protect the system, a circuit breaker may need to be tripped, or opened, to interrupt the flow of electricity. This can cause an interruption in the electrical supply, which may not be desirable in some applications.

3. Horn-gap arrester 

     A horn-gap lightning arrester is a simple and inexpensive device that is used to protect electrical and electronic equipment from damage due to lightning strikes and other high voltage transients. It consists of two horn-shaped pieces of metal rods that are separated by a small distance and connected in parallel between each conductor and the ground. The gap between the horns is smaller at the bottom and larger at the top.

     Under normal operating conditions, the breakdown strength of the gap is greater than the normal power frequency voltage, so the gap does not conduct. However, when an overvoltage with a value greater than the breakdown strength of the gap occurs, the gap conducts and a spark or flash takes place across the gap. The heated air around the arc and the electromagnetic action of the arc cause the arc to travel up the gap. When the gap becomes wide enough at a certain point, the voltage is insufficient to maintain the arc, so the arc is extinguished. This process takes only a few seconds.

     A resistor is placed in series with the horn gap to reduce the flow of current to a safe value. The horn gap can only handle currents up to 10 amperes. A choke coil is also included in the circuit, connected between the system to be protected and the ground of the horn gap. This helps to reduce the sharpness of the incident wave and prevent transients from entering the protected system. The impulse ratio of this type of arrester is typically 2 to 3.

Advantages of horn gap arresters:

• Arc quenches on its own: One advantage of horn gap arresters is that the arc created by the overvoltage quenches (extinguishes) on its own, without the need for an external means of quenching, such as a circuit breaker. This can help to prevent interruptions in the electrical supply.
• Decrease in following current: Another advantage of horn gap arresters is that the magnitude of the following current (the residual current that flows through the arrester after the initial surge has passed) decreases due to the series resistance of the arrester. This can help to reduce the risk of damage to the system.

Disadvantages/limitations of horn gap arresters:

• External objects can short the horns: One limitation of horn gap arresters is that the horns can become shorted by external objects, such as branches of trees or wires. This can reduce the effectiveness of the arrester and increase the risk of damage to the system.
• Performance affected by corrosion and pitting: The setting of the horns (the gap between them) can be affected by corrosion and pitting over time, which can reduce the performance of the arrester. This can increase the risk of damage to the system.
• Long operating time: Horn gap arresters have a relatively long operating time, typically around 3 seconds. This can be a disadvantage in some applications where a fast response is required to protect the system.

4. Multi Gap Lightning Arrester:

     It consists of a series of small metal cylinders that are insulated from one another and separated by an air gap. The first and last cylinders in the series are connected to the ground, while the other cylinders are connected to the transmission line. The number of gaps required depends on the line voltage.

     It consists of a series of metallic cylinders that are insulated from one another and separated by small air gaps. The first cylinder is connected in series with the transmission line, while the last cylinder is connected to the ground through a series resistance.

     Under normal operating conditions, the voltage between the first and last cylinders is not sufficient to break down the series gap. However, when an overvoltage occurs due to a fault, the breakdown between the first and second gaps occurs and a large fault current flows through the shunt resistance. After the surge is over, there is no arc between the second and third gaps, and the remaining power follows the path through the shunt and series resistances to the ground.

     The two resistances work together to limit the remaining power, so that only a small amount of current is left. This current is not enough to maintain the arc between the first and second gaps, so the system returns to its normal condition. Multiple gap arresters are commonly used in systems with voltage levels up to 33 kV to protect against lightning strikes and other high voltage transients.

Advantages of multi gap arresters:

• Simple construction: One advantage of multi gap arresters is that their construction is relatively simple, which makes them relatively easy to install and maintain.
• Arc does not persist: Another advantage of multi gap arresters is that the arc created by the overvoltage does not persist (continue to burn) after the normal voltage is restored. This can help to prevent damage to the system.

Limitations of multi gap arresters:

• Comparatively costly: One limitation of multi gap arresters is that they are generally more expensive than some other types of lightning protection devices, such as rod gap arresters.
• Proper gap must be adjusted: In order for a multi gap arrester to function properly, it is important that the proper gap be adjusted between the cylinders. If the gap is too small, the arrester may not be able to conduct the electrical current to the ground effectively. On the other hand, if the gap is too large, the arrester may not be able to withstand the transient overvoltage, increasing the risk of damage to the system.
• Limited voltage range: Another limitation of multi gap arresters is that they are typically only useful up to 33 kV. For higher voltage systems, other types of lightning protection devices may be needed.

5. Expulsion Type Lightning Arrester

     An expulsion-type lightning arrester, also known as a protector tube or expulsion gap, is a device used to protect electrical and electronic equipment from damage due to lightning strikes and other high voltage transients. It is typically used in systems operating at voltages up to 33kV.

     The arrester consists of a fibre tube that contains an isolating spark gap and an interrupting spark gap. The interrupting spark gap is in series with the rod gap and is enclosed within the fibre tube. The upper electrode of the interrupting spark gap is connected to the rod gap, while the lower electrode is connected to the ground. There is one expulsion arrester under each line conductor.

     When a surge voltage occurs on the line, the rod gap length increases and an arc is produced between the electrodes in the tube. The heat of the arc vaporizes the fibre of the tube walls, producing neutral gas in the tube. The gas builds up high pressure in a short period of time and is expelled from the tube. At the lower electrode, the gas carries ionized air around the arc, which is extinguished at current zero due to the strong deionizing effect. The arc will not re-establish. As soon as the gases are expelled and the arc is extinguished, the tube is ready for another operation.

Advantages of expulsion type lightning arresters:

• Lower cost: One advantage of expulsion type lightning arresters is that they are relatively inexpensive compared to some other types of lightning protection devices.
• No power frequency follow current: Another advantage of expulsion type lightning arresters is that they do not produce a power frequency follow current (the residual current that flows through the arrester after the initial surge has passed). This can help to reduce the risk of damage to the system.
• Easy to install: Expulsion type lightning arresters are relatively easy to install, making them a convenient choice for many applications.

Disadvantages/limitations of expulsion-type lightning arresters:

• Limited lifespan: One limitation of expulsion type lightning arresters is that they have a limited lifespan, as some of the insulating material is consumed each time the arrester operates. This means that the arresters will need to be replaced after a certain number of operations, which can increase the overall cost of protection.
• Gas liberation: When an expulsion type lightning arrester operates, it liberates a small amount of gas. This can be a problem in closed installations, as the gas may accumulate and create a hazardous situation.
• Poor volt-ampere characteristic: The volt-ampere characteristic of an expulsion type lightning arrester (the relationship between the voltage and current passing through the arrester) is not always ideal. This can make them less suitable for protecting expensive equipment, as they may not provide reliable protection against transient overvoltages.
• Limited voltage range: Another limitation of expulsion type lightning arresters is that they are typically only useful up to 33 kV. For higher voltage systems, other types of lightning protection devices may be needed.

6. Impulse Protective Gap

     The sphere gap is that it has an impulse ratio of unity, meaning that it is effective at protecting against high voltage transients. However, it has the drawback that the arc between its electrodes is not self-extinguishing. This means that the arc will continue to burn until the transient has passed, which can cause damage to the equipment being protected.

     On the other hand, the horn gap is a type of device that is self-extinguishing, meaning that the arc between its electrodes will extinguish automatically after the transient has passed. However, it has a higher impulse ratio of 2 or 3, unless the setting is small, as with low voltages. This means that it is less effective at protecting against high voltage transients than the sphere gap.

     It is designed to have a low voltage impulse ratio, even less than one, and to extinguish the arc.The protective impulse gap consists of two sphere electrodes S1 and S2, which are connected to the line and the arrester, respectively. An auxiliary needle is placed between the two sphere electrodes.

     At normal frequency, the impedance of capacitor C1 is much larger than the impedance of resistor R. As a result, the potential of the auxiliary electrode is midway between those of S1 and S2, and the electrode has no effect on the flashover between them.

     When a transient occurs, the impedance of capacitors C1 and C2 decreases, while the impedance of resistor R becomes more effective. As a result, the entire voltage is concentrated across the gap between E and S1. The gap immediately breaks down, and the rest of the length between E and S2 follows.

     This process causes the arc to extinguish, protecting the equipment from damage. Protective impulse gaps are typically used in systems operating at high voltage levels to protect against lightning strikes and other high voltage transients. 

7. Electrolyte Arrester

      It operates by using a thin film of aluminum hydroxide deposited on aluminum plates immersed in electrolyte, which acts as a high resistance to low voltages but a low resistance to voltages above a critical value. When the voltage exceeds this critical value, the arrester allows a free flow of current to earth, protecting the equipment from damage.

     To increase the total critical voltage value of the arrester, additional films can be added on top of each other. The total critical voltage of such an arrester is equal to the product of the number of films and the critical voltage of each film.

     When the voltage exceeds this critical value, the arrester allows a free flow of current to earth, protecting the equipment from damage. The critical value of voltage for an electrolytic arrester is typically around 400 volts. When the voltage returns to its normal value, the arrester again offers a high resistance in the path, effectively stopping any leakage of current.

     One of the main drawbacks of electrolytic arresters is that they are very delicate and require daily supervision. The film must be reformed whenever it is destroyed, which can be a challenging task. Additionally, electrolytic arresters may be prone to freezing in cold climates due to the presence of electrolyte.

     In many cases, electrolytic arresters are used in conjunction with an impulse gap, which is a type of device that is designed to have a low voltage impulse ratio and to extinguish the arc. This combination provides both high discharge capacity and self-extinguishing capabilities, making it effective at protecting against high voltage transients.

Advantages of electrolyte arresters:

• High discharging capacity: One advantage of electrolyte arresters is that they have a high discharging capacity, meaning that they are able to conduct large amounts of electrical current to the ground. This makes them effective at protecting electrical systems from lightning strikes and other transient overvoltages.
• No need for series resistance: Another advantage of electrolyte arresters is that they do not require a series resistance (a resistor placed in series with the arrester to reduce the flow of current) in order to function properly. This simplifies their design and makes them easier to install and maintain.

Disadvantages/limitations of electrolyte arresters:

• Dependence on film formation: The operation of an electrolyte arrester depends on the formation of a film on the electrodes. If this film is not properly formed, the arrester may not function correctly. This can require frequent maintenance and can increase the overall cost of protection.
• Frozen electrolyte: In cold climates, the electrolyte solution used in electrolyte arresters may freeze, making the arrester less effective or even unusable. This can be a significant limitation in cold countries.

8. Valve Type Lightning Arrester

     A valve-type lightning arrester is a device used to protect electrical systems from high voltage surges. It consists of two main components: series spark gaps and nonlinear resistors. The spark gaps are formed by two electrodes with a fixed gap between them, which are connected in series and maintained at equal voltage by using grading resistors. These spark gaps remain non-conducting under normal conditions, but will spark over and allow high current to flow to the ground during high voltage surges. 

     The nonlinear resistors are made of an inorganic compound such as thyrite or metrosil, and have a low resistance to high-frequency surge currents but a high resistance to power frequency currents. When a surge voltage occurs on the line, the spark gaps spark over and the nonlinear resistors allow the surge to move quickly to the ground. After the surge is over, the nonlinear resistors offer high resistance to power frequency currents, protecting the electrical system.

Advantages of valve type arresters:

• Effective protection against overvoltages: One advantage of valve type arresters is that they provide effective protection against overvoltages, including lightning strikes.
• Rapid response time: Another advantage of valve type arresters is that they work rapidly, typically taking less than 1 second to respond to an overvoltage. This can help to minimize the risk of damage to the system.
• Impulse ratio: The impulse ratio of a valve type arrester is almost unity, which means that it is able to withstand transient over voltages of the same magnitude as the rated voltage of the system. This makes it a reliable protection device for electrical systems.

Disadvantages/limitations of valve type arresters:

• Limited protection against steep wave fronts: One limitation of valve type arresters is that they do not provide effective protection against steep wave fronts (rapidly rising overvoltages). Other types of lightning protection devices, such as air terminals and down conductors, may be needed to provide protection against these types of overvoltages.
• Performance affected by moisture: The performance of a valve type arrester can be affected by moisture, such as humidity or rain. This can reduce its effectiveness and increase the risk of damage to the system.

Applications of valve type arresters:

• Station type lightning arresters: Station type valve arresters are used in power stations and substations up to 220 kV.
• Line type lightning arresters: Line type valve arresters are used up to 66 kV, typically for protecting transmission and distribution lines.

9. Thyrite Lightning Arrester

     A thyrite arrestor is a device used to protect electrical systems from high voltage surges, such as those that can be caused by lightning. It consists of several discs made of a special inorganic compound called thyrite, which has a high resistance to electricity at low voltages but a low resistance at high voltages. The discs are coated with a metal layer and placed inside a porcelain container.

     When a high voltage surge, like a lightning strike, occurs, the thyrite arrestor allows the surge to pass through it and discharge into the ground, protecting the electrical system from damage. After the surge has passed, the thyrite arrestor returns to its original state, offering high resistance to normal power frequency voltage. This helps to prevent damage to the electrical system from normal electrical current.

10. Auto valve Arrester

     A type of voltage arrestor (also known as a surge arrester) consists of a stack of flat discs made of a porous material, such as porcelain, that are separated by thin mica rings. The disc material is not homogenous, meaning it is not uniform in composition. Instead, it contains a mixture of conducting and non-conducting materials. When the voltage across the arrestor exceeds a certain level, a glow discharge occurs within the capillaries of the porous material. This results in a voltage drop across the arrestor, typically to about 350 volts per unit.

     The discs are arranged in such a way that, under normal voltage conditions, a discharge does not occur. However, when the voltage across the arrestor exceeds a certain level, the discharge occurs and the voltage is reduced to a safe level. This helps protect electrical equipment and circuits from damage due to high voltage surges.

11. Oxide Film Arrester

     An oxide film arrester is a type of voltage arrester that uses certain dry chemicals that change their electrical conductivity upon the application of heat. One such example is lead peroxide, which has a specific resistance of 1 ohm per inch cube at ordinary temperatures. When the temperature rises to around 150°C, the lead peroxide is converted to red lead, which has a specific resistance of around 24 million ohms per inch cube.

     An oxide film arrester consists of a number of cells, each of which is made up of two iron electrodes coated with varnish on one side. The electrodes are separated by an annular ring, and the space between them is filled with lead peroxide powder. Each cell can be used for voltages in the range of 250-300 volts.

     When an overvoltage occurs on the line, the varnish film breaks down at one or more points in each cell, causing a discharge to pass through the lead peroxide. This causes the lead peroxide to be converted to red lead due to heating, and the discharge ceases. The high resistivity of the red lead prevents the power current from flowing to ground. Over time, the whole of the lead peroxide may be converted to red lead, but the dimensions of the cell are chosen such that it takes a number of years before it becomes useless for further service.

12. Metal Oxide Lightning Arrester

     A metal oxide lightning arrester is a type of voltage arrester that is commonly used in modern power systems. It consists of a stack of series-connected metal discs made up of zinc oxide, which has a highly non-linear resistance. This high degree of non-linearity in resistance over a large current range allows the arrester to eliminate the use of a series gap, hence it is also known as a zinc oxide gapless lightning arrester.

     The metal oxide arrester is dimensioned so that the peak value of the phase-to-ground voltage under normal operating conditions (when there is no surge) never exceeds the sum of the rated voltages of the series-connected discs. This means that under normal conditions, the arrester offers a high resistance (almost infinite) to ground.

     However, when a surge voltage occurs on the line, the metal oxide arrester responds very quickly by decreasing its resistance. As the arrester is connected between the phase and ground, the large current due to the surge is discharged to the earth, safely diverting the surge voltage and absorbing the energy of the surge. Once the system returns to its normal rated voltage, the arrester offers a high resistance and acts as an open circuit, leaving the system voltage unaffected at normal conditions.

     In summary, the metal oxide lightning arrester is designed to protect electrical equipment and circuits from damage due to high voltage surges by quickly and effectively diverting the surge voltage to ground and absorbing the energy of the surge. This helps to ensure the reliable and safe operation of electrical systems.