Study on the Causes and Countermeasures of High Lightning Trip-Out Rate on Electric Transmission Lines

Abstract

Trip faults are obviously increased by frequent lightning strikes, and increasing lightning trip-out seriously affects a system’s stability and power supply reliability. In this paper, the reasons for high lightning trip-out rates in electric power transmission lines are analyzed in detail from three perspectives, as follows: the substandard lightning resistance level, lightning complexity at a mid-point between towers, and the complexity of first and subsequent lightning stroke conditions. Experiments and simulations demonstrate that the solid-phase gas arc-extinguishing method has a strong ability to extinguish power–frequency continuous-current arcs and to protect against first and subsequent lightning strokes. Since the time taken by gas arc-extinguishing is much less than the response time of relay protection, trip accidents caused by lightning strikes can be avoided and the trip rates of lightning strikes can be reduced using this method. The case analysis and practical operation results show that the solid-phase gas arc-extinguishing lightning protection method can reduce the lightning trip-out rate by more than 90%, completely solve the problem of high lightning trip-out rates, and significantly improve the reliability of power supply.

1. Introduction

Lightning disasters are natural phenomena that occur frequently. On average, there are approximately 8 million lightning strikes worldwide each day, and the number of lightning strikes in China’s power grid is as high as 350,000 annually.

According to statistics, China has more than 1.1 million kilometers of electric power transmission lines and more than 50 million power transmission towers. According to a tripping analysis performed by the China Southern Power Grid Corporation on transmission lines 110 kV and above in 2016, lightning strikes are the main cause of line tripping, accounting for 66.81% of the total [1]. On a rainy night in Donguan, a city in southern China, lightning-induced trips were found to occur as many as 2000 times.

With the development of industrial technology, such as petrochemical, aerospace and smelting technologies, high-precision enterprises and other important loads increase. These power loads predominantly consist of numerous computers, electronic control systems, motor groups, and other essential components. The reliability of the power supply is crucial for these loads; once the line trips, the impact on these important loads can be disastrous.

In the recently published “power failure loss and emergency strategy for important power consumers of power distribution network”, the China Electric Power Research Institute (CEPRI) investigated the power failure loss of 10 important power consumers. The post-power-outage restart time of a considerable number of important loads is more than 3 h, and the maximum restart time can even be as high as 50 h. The economic impact of power failures is substantial. For instance, in the aviation sector, the total economic loss can exceed CNY 60 million, leading to severe consequences.

In order to reduce the huge loss caused by lightning trips, this paper will first analyze the causes of the frequent lightning trips suffered by transmission lines. They mainly include the substandard lightning resistance level, the complexity of lightning at a mid-point between towers, and the complexity of first and subsequent lightning stroke conditions. Subsequently, the focus shifts to solid-phase gas arc-extinguishing lightning protection technology [2,3,4]; this paper shows the effectiveness of a solid-phase gas arc-extinguishing device by simulation, case analysis, and experiments. The solid phase device is used to solve the problem of frequent lightning-induced trips of transmission lines, and to avoid the huge losses caused by lightning trips.

2. The Causes of High Lightning Trip-Out Rate

The reasons for the high trip-out rates caused by lightning strikes mainly relate to substandard lightning resistance levels, the complexity of lightning at a mid-point between towers, and the complexity of first and subsequent lightning strike conditions, which will be explained in detail below.

2.1. Sub-Standard Lightning Withstand Level

According to the Chinese national standard, the levels of anti-lightning counterattacks should not be lower than those shown in

Table 1. The levels of anti-lightning counterattacks in transmission lines.

System Voltage (kV)	35	66	110	220	500	750
Single-circuit line (kA)	24~36	31~47	56~68	87~96	158~177	208~232
Double-circuit transmission lines (kA)	——	——	50~61	79~92	142~162	192~224

.

As can be seen in Table 1 above, the level of anti-lightning counterattack achievable each voltage level has certain limitations. For example, the level of anti-lightning counterattack achievable by a 110 kV single-circuit line is only about 56–68 kA. According to the lightning monitoring information shown in

Table 2. Lightning monitoring information report.

Object Scope	110 kV Line of Power Supply Bureau of a City, Guangxi Province, China
Time Range	11 June 2016 00:00:01~11 June 2016 03:00:00
Seq. No.	Time	Longitude	Latitude	Current (kA)	Tower Number
1	11 June 2016 01:31:20.6833	109.422	21.5869	−88.3	3
2	11 June 2016 01:37:15.1388	109.4788	21.5559	−82.9	27~28
3	11 June 2016 01:38:22.5563	109.4765	21.5039	−70.2	19~20
4	11 June 2016 01:39:01.2319	109.4775	21.5411	−138.2	23~24
5	11 June 2016 01:39:33.5190	109.4569	21.5238	−86.1	14

, in many cases, the magnitude of the lightning current significantly exceeds 68 kA.

Because the size of impact of grounding resistance is restricted by topography, and especially soil resistivity, the impulse grounding resistance is high, and the reduction in impulse grounding resistance achievable by regular grounding grid modifications is limited. Therefore, the level of anti-lightning counterattack is difficult to improve.

According to reference [5], more than 60% of the lightning trip-out failures in lines of 110 kV voltage or above are related to lightning shielding failure. In the lightning trips of 500 kV transmission lines, the proportion of lightning shielding failure is more than 90%. For high-voltage transmission lines, lightning shielding failure has become the main factor leading to lightning trips. On one hand, this indicates that the probability of interception of overhead ground wires is not high; on the other hand, it also indicates that once a lightning shielding failure occurs, due to the low lightning resistance level caused by the lightning shielding failure, insulation flashover can occur with relative ease, presenting a significant threat to the safe and reliable power supply of transmission lines.

2.2. Lightning Complexity at a Mid-Point Between Towers

The existing theory, technology and regulations of lightning protection only put forward the requirements for lightning protection near poles and towers, but pay insufficient attention to the protection of the middle section. The following is a detailed analysis of the lightning shielding failure witnessed at the midpoint between towers.

In practice, most transmission lines are built between high mountains, with much located in canyons and across rivers. As a canyon is much deeper than a tower’s height, the ground shielding effect is seriously weakened, which increases the probability of lightning shielding failure in the midpoint between towers. This reality is not taken into account in current national standards [5].

Based on this, this paper introduces an electrical geometric model that considers the depth of a canyon, as shown in Figure 1, and which is different from the classical electrical geometric model (EGM) [6,7] proposed by Whitehead-brown et al.

The area abc is the area of lightning shielding failure about the flat land, and the area aed is the area of lightning shielding failure about the canyon. The classical electrical geometry model only considers the plain ground as the datum line, and the overhead ground wire, wire and ground are all at an equal strike distance. Considering the depth of the canyon, the analysis and calculation of the model show that the area and probability of lightning shielding failure are increased greatly. The area of lightning shielding failure of the large canyon is about 15 times that of the plain, and the probability of lightning shielding failure of the canyon is about 5 times that of the plain.

2.3. The Complexity of First and Subsequent Lightning Strike Conditions

A lightning flash contains several lightning strokes; in a lightning flash, the first stroke is called the first stroke. The second, third and later strokes are called subsequent strokes. Sometimes, the time interval between two lightning strokes is milliseconds, and sometimes it is microseconds [8]. Existing lightning protection methods do not offer protection against the first and subsequent lightning strikes.

In 1997, the U.S. defense air force standard «MIL-STD-464» confirmed the existence of first and subsequent lightning strokes. According to statistics given by the international large power grid conference (CIGRE), more than 80% of lightning strikes are first and subsequent lightning strokes [8]. The time interval of lightning strokes is between 10 and 200 ms, and sometimes the time interval of subsequent lightning strokes is between 50 and 1000 µs. Lightning observation towers have been established in countries around the world, and measurement data of first and subsequent lightning strokes have been collected in Germany, Sweden and Austria [9,10,11,12].

First and subsequent lightning strokes not only have high incidence, but are also difficult to prevent. When the line installed with the arrester is subjected to first and subsequent lightning strokes, the superimposed current flowing through the resistance of the valve plate is likely to cause excess residual voltage. In addition, due to the strict sealing of the arrester, the heat accumulation generated by the superimposed current is likely to cause the thermal breakdown of the arrester, and make it explode. The standard lightning arrester test only considers the case of one single lightning strike, which is inconsistent with the fact that the first and subsequent lightning strokes occur with a probability of up to 80%. China’s lightning protection standards specify that the interval between the two impulse currents of the arrester is 50 s to 60 s. Therefore, the existing standard test does not consider the actual situation of the first and subsequent lightning strokes.

Lightning overvoltage causes the circuit breaker to trip. Before the automatic reclosing action, if the circuit is struck by lightning again, the resulting overvoltage of lightning superposition will cause the circuit breaker to break down again, resulting in a reclosing failure. Under first and subsequent lightning strokes, the circuit breaker’s frequent action will lead to a cumulative short-circuit fault. In the process of frequent breaking, the arc will constantly abate the contacts, which will cause the circuit breaker to refuse to move, and then cause an explosion accident. Frequent automatic reclosing under first and subsequent lightning strokes can easily cause transformer faults.

3. Solution to the Problem of High Lightning Trip-Out Rate

The solid-phase gas arc-extinguishing lightning protection device (abbreviated as the solid-phase device) is an innovative lightning protection device that was recently developed, which can solve the problem of the high lightning trip-out rate. In the following research, based on reference [13], the latest high-voltage test and mathematical formula will be used to further assess the reasons why the installation of a solid-phase device can quickly extinguish power frequency continuous arc, and new engineering cases will prove that the installation of a solid-phase device can avert lightning-induced trips, thereby reducing the lightning trip rate.

3.1. Working Principle of Solid Phase Gas Arc Extinguishing Device

The solid-phase gas arc-extinguishing device is a gap device with an active arc-extinguishing function (as shown in Figure 2 below).

When the lightning current passes through the lightning pulse collecting device (3 in Figure 3 of this paper) on the upper part of the solid-phase device, voltage is generated by electromagnetic induction, which triggers an explosion of the built-in gas pill and generates a strong gas flow.

A schematic diagram of the arc-extinguishing is shown in Figure 3. Please refer to references [2,3,4] for the detailed working process.

The lightning current (yellow) breaks through the lightning gap and forms the initial power frequency continuous current arc (red).

The lightning current (yellow) is used to trigger the solid-phase device, in which the gas pill explodes, and this produces a strong gas flow (blue).

When the initial power frequency arc is in its vulnerable period, it will be extinguished by the strong gas flow.

In the power grid, the relay protection response time is about 20 ms [14]. The whole arc-extinguishing process of the solid-phase gas arc-extinguishing device is about 3 ms, which is far less than the response time of relay protection, thus avoiding lightning trip-out and greatly reducing the tripping rate.

3.2. Experiment on the Capabilities of a Fast Quenching Power Frequency Continuous Current Arc

In practice, the power frequency continuous current that is cut off by the strong gas flow produced by the solid-phase gas arc-extinguishing device is far less than 20 kA. In order to verify the arc-extinguishing ability of the solid-phase gas arc-extinguishing device, several high-voltage and high-current arc-extinguishing experiments were conducted in a high-voltage laboratory in China.

At present, it is possible to obtain shock pulses similar to lightning at different time intervals by use of experimental devices [15], but it is difficult to obtain both shock pulses and power frequency continuous currents in high-voltage laboratories around the world.

In the experiment, a 0.01 mm fuse was used for arc ignition, that is, the upper and lower electrodes were connected to a fuse with a diameter of 0.01 mm. The distance between the upper and lower electrodes was 88 cm, as shown in Figure 4 below.

The experimental circuit voltage was 66 kV, and the experimental current was 20 kA.

It is important to note that the 88 cm fuse was a one-off; it is not designed to carry power frequency current, and was quickly destroyed during the experiment when the power frequency arc was successfully guided.

The moment at which the solid-phase gas arc-extinguishing device is triggered is shown in Figure 10. Due to the extremely rapid reaction of the test product, the pressure peak generated by the strong gas flow at the entrance of the solid-phase device at about 10 µs is shown in the simulation (Figure 12). Although the arc was not extinguished, at 10 µs, the power frequency continuous current was cut off. Since this time is very short, the oscilloscope did not detect anything. The A-phase current displayed on the oscilloscope was 0, and there was no sinusoidal current wave with an effective value of 20 kA. The current waveform displayed on the oscilloscope is shown in Figure 5 below.

The voltage waveform displayed on the oscilloscope is a complete sinusoidal voltage wave. The A-phase voltage waveform is shown in Figure 6.

Here, the authors carried out experiments on power frequency voltage at different phase angles. The current and voltage waveforms obtained are consistent with those in Figure 5 and Figure 6.

It is proven by these experiments that the power frequency continuous arc can be extinguished within 3 ms after a strong lightning strike. The state of a power frequency short circuit can last up to 3 ms, which is far less than the response time of relay protection. The power failure caused by the circuit breaker being tripped can be avoided, and the power supply’s reliability can be greatly improved

After this experiment, the external surface of the solid-phase device was pictured, as shown in Figure 7.

If the arc-extinguishing unit in the solid-phase device was removed and the above experimental process was repeated, referred to as the non-arc-extinguishing unit test. After this test, the external surface of the solid-phase device was assessed as follows.

Following the two experiments, the outer surface of the solid-phase device showed almost no ablative phenomenon as induced by the arc-extinguishing experiment with an arc-extinguishing unit (as shown in Figure 7, different from Figure 8).

In the non-arc-extinguishing unit experiment, because the device had no arc-extinguishing function, it was seriously overheated by the arc; the surface was almost completely charred, and the arc-extinguishing chamber even more so, with a large area of carbonization on the indoor wall (see Figure 8 above). The importance of the arc-extinguishing unit is thus proven.

The protective effect of a solid-phase device against first and subsequent lightning strokes is thus further verified by this modeling and simulation.

3.3. Modeling and Simulation Process for Protecting Against First and Subsequent Lightning Strokes

3.3.1. Mathematical Model of Power Frequency Continuous Current Arc

The mathematical model of the electric arc can be used to predict the change trend of the electric arc, as verified by the simulation. There are two models of arc, one of which is a physical–mathematical model based on various physical processes and mathematical characteristics of the arc [16]

The other is a black box model limited to the external volt–ampere characteristics of the arc [17].

The derivation of the physical–mathematical model is complicated, and the determination of the boundary conditions requires a large amount of experimental data, which is difficult to achieve. However, the mathematical equation of the black box model is simple, the physical meaning is clear, and it is easy to make contact with the external circuit in order to solve the arc’s changing trend.

The Mayr model [18] used in this paper is a type of black box model. The Mayr arc model has a clear physical meaning and simple form, making it suitable for simulating the change law of a power frequency continuous current arc.

An electric arc has both electrical and thermal characteristics, which are determined by both electrical and thermal processes. Under certain assumptions, according to the energy balance principle,

Q = uit − P

(1)

where u is the arc voltage, I is the arc current, Q is the heat content of the arc, and P is the dissipation power.

The Mayr arc model is thus further deduced,

$${\displaystyle \frac{1}{g}}{\displaystyle \frac{dg}{dt}}={\displaystyle \frac{1}{\tau }}({\displaystyle \frac{ui}{P}}-1)$$

(2)

Using the relational equation I = gu, the equation above can be written as

$${\displaystyle \frac{dg}{dt}}={\displaystyle \frac{1}{\tau }}({\displaystyle \frac{i^2}{P}}-g)$$

(3)

Then, Formula (3) is further simplified as

$$g=g_0{e}^{\int {\displaystyle \frac{1}{\tau }}({\displaystyle \frac{ui}{P}}-1)}$$

(4)

$g_0$ in the equation above is the initial value of $g$.

It can be seen from Equation (4) above that when the arc current I decreases rapidly, the arc conductance will decrease rapidly. The arc temperature will then drop rapidly, and the arc will soon be extinguished.

When the solid-phase device is triggered by a lightning current, the built-in gas pill explodes, and this generates a high-speed gas flow. The high-speed gas flow quickly cuts off the initial power frequency current and quickly extinguishes the power frequency continuous current arc. The law can be proven by simulations and experiments.

3.3.2. Simulation of Protection Against First and Subsequent Lightning Strokes

As mentioned above, sometimes, the time interval between the two lightning strokes is milliseconds, and sometimes it is microseconds. No matter what kind of lightning strike occurs, it is assumed that a strong lightning strike can break down the gap in the solid-phase gas arc-extinguishing device and generate a power-frequency continuous current arc, as shown in Figure 3. Before the lightning current enters the ground, the gas pill in the solid-phase arc-extinguishing device is triggered to explode, and this produces a strong arc-extinguishing gas. It is then necessary to quickly extinguish the power frequency continuous current arc, so as to prevent the power frequency continuous current arc from lasting too long, causing a tripping accident. This process is reproduced by simulation.

In this paper, the theoretical basis of the simulation is taken from references [19,20,21].

Please refer to the user’s manual (ANSYS FLUENT User’s Guide, ANSYS Inc. of Pittsburgh, PA, USA) for detailed information about the simulation process.

According to the steps of the ANSYS simulation software, the process of the power frequency continuous arc being extinguished by strong gas flow several times is simulated under ideal conditions. The plane simulation model of the arc extinguishing chamber of the solid-phase gas arc-extinguishing device is shown in Figure 9—that is, the red-circled part in Figure 10.

At the same time, three temperature-monitoring points—A, B and C—are set up in the arc-extinguishing chamber.

The materials for the simulation include ceramics, graphite electrodes, air and explosives. The initial conditions of the simulation are as follows: the environmental temperature is 300 K, the melting point of the graphite material is 3773 K (which is set as the temperature boundary condition for the electrode), and the initial temperature of the arc is set as 20,000 K.

Following actual measurement, the velocity of the arc-extinguishing gas produced after the explosion was shown to be an exponential function. This important function will be embedded in the simulation program. The average speed at the entrance of the arc-extinguishing chamber was about 200 m/s.

After the derivation of an iterative solution with 10 microseconds set as the time interval step, a pressure cloud diagram and temperature curve diagram for the arc-extinguishing chamber in a solid-phase device can be obtained. From the distribution of the pressure cloud diagram, we can clearly infer the development process of the arc-extinguishing gas flow generated by the explosion of the gas pill in the solid-phase device, triggered by the lightning current. In the 0–5 µs stage, the lightning current triggers a gas pill explosion, and then enters the ground, forming the initial power frequency continuous current arc. During the 5–10 µs stage, the arc-extinguishing gas flow generated after the explosion of the gas pill was concentrated at the entrance of the arc-extinguishing chamber, and the gas flow pressure reached its peak, as shown in Figure 12, before developing along the axis.

At 0.1 ms, the line was hit by a subsequent lightning stroke lasting microseconds, and after 10 µs, at 0.11 ms, the flow pressure peaked, as shown in the Figure 14, and then developed along the axis.

At 3 ms, the line was subjected to one subsequent lightning stroke lasting milliseconds; the lightning current triggered the second gas pill to explode, producing a strong arc-extinguishing gas. After 10 µs, at 3.01 ms, the pressure of the arc-extinguishing gas reached another peak, as shown in Figure 18, and developed along the axis.

The pressure development process of the whole arc-extinguishing chamber is shown in Figure 11, Figure 12, Figure 13, Figure 14, Figure 15, Figure 16, Figure 17, Figure 18, Figure 19, Figure 20 and Figure 21.

At about 10 µs, after each lightning stroke, although the initial power frequency continuous arc had not been extinguished at this time, the pressure of the arc-extinguishing gas reached its peak, and the power frequency arc current had been basically cut off, conforming to Formula (4) above. The conductance and energy of the arc will decrease rapidly, and the arc will be extinguished very quickly.

The process of development of the arc-extinguishing gas can be clearly seen in the pressure cloud diagram. In order to better elucidate the arc-extinguishing process, the temperature change process in the arc-extinguishing chamber is further analyzed.

Since the arc-extinguishing chamber is a semi-closed space, the arc-extinguishing gas can act on the power frequency continuous current arc to the greatest possible extent, thus accelerating the dissipation of arc energy and reducing the arc temperature. When the temperature in the arc-extinguishing chamber drops to below 3000–4000 k, the arc can be determined to have been extinguished, according to the temperature criterion of arc-extinguishing [22,23].

The temperature curve of each observation point is shown in Figure 22. At 0 ms and 0.1 ms, they were subjected to a main lightning strike and a subsequent stroke, respectively, and each generated a power frequency continuous current arc at the same time. The highest temperature in the arc-extinguishing chamber reached up to 20,000 K. At the time of 0 ms, the gas pill in the device exploded, triggered by the lightning current, producing a strong arc-extinguishing gas. Under the action of the strong arc-extinguishing gas, the temperatures of the three test points dropped to below 3000 K at 3 ms, and the average temperature of the whole arc-extinguishing chamber was much lower than 3000 K, so the arc can be judged to have been extinguished. At the same time, at 3 ms, it was struck again by a subsequent lightning strike, and this triggered the power frequency continuous current arc to reinitiate, but this was also extinguished within 3 ms.

If the time interval of subsequent strokes is in the range of microseconds, the intensity will be weak. Through calculation, we see that a strong gas flow can last for tens of milliseconds in the arc-extinguishing chamber, which can extinguish the multiple power frequency continuous arcs generated by the subsequent strokes. If the time interval of subsequent strokes is millisecond, the intensity will be strong, and each strike can trigger the explosion of the gas pill, producing strong arc-extinguishing gas.

The modeling and simulation process above shows that the current is cut off at approximately 10 microseconds. The conductance slows down, the thermal dissociation rapidly weakens, and the arc will soon be extinguished. The mathematical model of the arc is thus proven to be correct.

By repeating the simulation process shown above, it can also be found that only when the diameter of the lower arc-extinguishing chamber is 3–6 cm will the gas pressure change and temperature change in the arc-extinguishing chamber be consistent with those in the process above. When the diameter of the arc-extinguishing chamber is less than 3 cm or more than 6 cm, the gas pressure and temperature therein will change irregularly, leading to the failure of arc-extinguishing. This provides a basis for the establishment of standard dimensions for the solid-phase device’s arc-extinguishing chamber.

4. Case Analysis

Currently, the solid-phase gas arc-extinguishing device is mainly installed in 35 kV, 110 kV and 220 kV transmission lines, as a result of which the lightning trip-out rates have dropped by more than 90%.

A 35 kV line in Guangxi, China, with a total length of about 48 km and a total of 152 base poles and towers, reaching across plains and some mountainous areas, was here assessed. The average annual thunderstorm days in the region reached 59.8 d, and the average lightning trip-out rate in the plain and mountainous areas reached 8.528 times/(100 km·a) and 9.742 times/(100 km·a), respectively, denoting areas with severe lightning damage.

After installing the solid-phase gas arc-extinguishing device on the whole line in 2016, according to the operation data, the average lightning trip-out rate in the plain and mountain areas decreased to 0.1263 times/(100 km·a) and 0.1297 times/(100 km·a), respectively.

The annual average lightning trip-out rate of this line in the plain area decreased by

$${\displaystyle \frac{8.528-0.1263}{8.528}}=98.52\%$$

The annual average lightning trip-out rate in the mountainous areas decreased by

$${\displaystyle \frac{9.742-0.1297}{9.742}}=98.67\%$$

Whether facing first and subsequent strokes or a high-intensity lightning stroke, the solid-phase device can be successfully protected regardless of which part of the transmission line is struck by lightning. Therefore, the solid-phase gas arc-extinguishing lightning protection device can essentially solve the problem of high lightning trip-out rates.

As shown in Figure 23 below, after the solid-phase gas arc-extinguishing device on the relevant line has been operated, there will be an obvious burning phenomenon on the interior side of the arc-extinguishing chamber. This shows that the device successfully protects against complex strong lightning strikes.

At present, one solid-phase device contains about 50 gas pills. A solid-phase device installed on a high-voltage transmission line can last for 5 years. At the beginning, the clock hand points towards the starting position of the dial. If a gas pill explodes, the hand will rotate clockwise. If all the gas pills are used up, the hand will point towards the end position of the dial (as shown in Figure 24 below).

Our rule is that the operating period of the solid phase device is 5 years. Thorough inspection or replacement is required after 5 years. In areas with frequent lightning disasters, starting from the second year, the solid-phase devices will be inspected every six months with a telescope.

To date, the solid-phase device technology has made significant progress, and the combination of solid-phase devices and compression devices [24,25] can help to achieve a better lightning protection effect (as shown in Figure 25).

5. Comparison of Solid-Phase Device with Other Lightning Protection Methods

5.1. Comparison with the Traditional Lightning Protection Measures

Compared with traditional lightning protection methods, solid-phase gas arc-extinguishing technology has unique advantages in the context of lightning protection, in terms of effectiveness, operation and maintenance, as shown in

Table 3. Comparison of characteristics of different equipment.

Category	Traditional Lightning Protection Methods	Solid-Phase Gas Arc-Extinguishing Technology
Application situation	On all occasions	110 kV, 220 kV, some 35 kV lines
Lightning protection concept	Traditional lightning protection concept. It is difficult to solve the problems of the first and subsequent strokes, strong lightning strikes, lightning shielding failure on lines, and the delay of the ZnO arrester valve plate.	Lightning flashover is allowed but power frequency arc construction is not allowed, and the lightning protection process of “lightning arc dredging–rapid arc-extinguishing–power frequency strong blocking” is completed. The open “field” structure with no ZnO valve plate delays the problem. Good protection against subsequent lightning strokes. Strong lightning strikes and lightning shielding failure on lines are also completely preventable.
Technical rationality	Lightning intensity, lightning resistance level, lightning mode, etc., are uncontrollable factors.	No uncontrollable factors.
Lightning protection effect	It is difficult to reach the standard; there is no protection against subsequent lightning strokes, and the lightning trip rate is high.	The arc-extinguishing time (within 3 ms) is less than the response time of the relay protection action, which solves the problem of protection against subsequent lightning strokes, and the lightning trip rate is reduced by more than 90%.
Investment cost	The grounding grid is huge and easy to corrode, requiring huge investment and renovation projects, and the arrester has many inherent defects, along with the threat of external damage, which requires continuous additional investment.	As long as the integrity of the grounding structure is ensured, resistance reduction is not required, which saves huge investment costs in the later period, reduces the required maintenance work, and reduces the cost by 70%.
Operation and maintenance	Continuous maintenance is required.	The solid-phase unit has no vulnerable parts and is maintenance-free for 5 years.

.

5.2. Comparison with Typical Lightning-Protection Devices in Other Countries

The research into and application of the arc-extinguishing lightning protection gap in foreign countries have mainly focused on the use of the power frequency arc as the trigger energy and the use of the power frequency arc to produce the arc-extinguishing gas, after which the arc-extinguishing gas acts on the power frequency arc and extinguishes it. The main representative devices include the arc-extinguishing gap lightning protection devices used in Japan (Figure 26 below) and thermal expansion arc-extinguishing lightning protection devices used in Russia (Figure 27 below). These are now compared and analyzed, as shown in

Table 4. Characteristic comparison with typical lightning protection devices used in other countries.

Category	Solid-Phase Gas Arc-Extinguishing Device (Figure 2)	Expansion Arc-Extinguishing Lightning Protection Device used in Russia (Figure 27)	Arc-Extinguishing Gap Lightning Protection Device used in Japan (Figure 26)
Structural characteristics	Open, all-air structure, “field” structure.	“Road” structure.	“Road” structure.
Arc-extinguishing mechanism	“Dredging–Extinguishing–Blocking” mode. Firstly, the lightning energy is channeled into the ground, and at the same time, the arc is extinguished by the strong jet gas induced by lightning, and the power frequency component is forcefully blocked.	Dredging–Extinguishing mode. First, the lightning arc is channeled, and after being baked by the initial power frequency arc, thermal expansion occurs, and finally the arc is extinguished by air flow.	Dredging–Extinguishing mode. After lightning strikes, gap flashover occurs, and the generated high-temperature power frequency arc bakes the inner wall of the pipeline, the gas-producing material on the inner wall produces a lot of gas, and finally the power frequency arc is cut off.
Action object	Power frequency continuous arc during initial fragile phase.	Power frequency arc in full development stage.	Power frequency arc in full development stage.
Arc-extinguishing difficulty	The arc is extinguished at the initial stage of formation of the power frequency continuous arc. Low arc-extinguishing difficulty coefficient.	The power frequency continuous arc has strong energy, and it is difficult to extinguish the arc.	It is difficult to extinguish the arc when the power frequency continuous arc is fully developed.
Arc-extinguishing time	Within about 3 ms (the power frequency arc is extinguished in the initial stage), less than the relay protection action response time, the circuit breaker trip can be avoided.	For extinguishing the arc in the fully developed period, the time required in most cases is longer than the response time of the relay protection action, and the circuit breaker can be easily tripped.	The arc-extinguishing time is longer than the response time of the relay protection action, and the circuit breaker can be easily tripped.
Arc-extinguishing effect	Excellent arc-extinguishing performance, limited arc-extinguishing times, but easy to replace. Effective protection against the first and subsequent strokes and other types of lightning strikes. Full-impact arc voltage. The residual voltage shows negative resistance.	In the initial stage of power frequency, arc development is slow, and gas production energy development lags behind arc energy development. The arc is weak, the gas production level is low, and the arc-extinguishing ability is not good. If the arc is strong and the gas production level is high, it can easily reignite, and this leads to a failure in arc-extinguishing.	The gas is produced by the organic gas-producing material on the inner wall of the pipeline, and the power frequency arc is extinguished. The gas-producing material can be easily lost and is difficult to replace, and the number of operations is limited, while the arc-extinguishing effect is not good.

.

6. Conclusions

Table 3 and Table 4 show comparative analyses between the solid-phase gas arc-extinguishing device and other lightning protection devices, in order to show the differences between, novelty and originality of the solid-phase gas arc-extinguishing devices. Within 0–10 µs, the solid-phase device channels the lightning current into the ground. Following the trigger of a lightning current, the explosion of a built-in gas pill will produce huge levels of arc-extinguishing gas flow pressure. At about 10 µs, the power frequency arc current is first cut off, thus accelerating the extinction of the power frequency continuous arc. The solid-phase device can quench the power frequency continuous current arc generated by the first and subsequent strokes several times within 3 ms, which is far shorter than the response time of the relay protection action enacted to prevent the lightning strike from tripping the circuit.

Solid-phase arc-extinguishing technology represents a significant and innovative advancement, and it was entirely conceived and developed from original research. This technology effectively addresses the issue of high lightning-induced trip-out rates, and enhances the reliability of power supply systems.

The lightning protection effect of the solid-phase gas arc-extinguishing device is very good. However, due to the high initial investment required in the solid-phase device, it is only used in the electric transmission network in southern China. Furthermore, given that the solid-phase device only has an 8-year operational history, ensuring its long-term stability still requires further work.