Lightning and Lightning Protection in Power Systems
Lightning and Lightning Protection in Power Systems
Search Description: Learn what lightning is, how lightning discharge occurs, types of lightning strokes, harmful effects on power systems, and protection methods in simple language.
Lightning is one of the most dangerous natural causes of overvoltage in electrical power systems. A single lightning stroke can produce a very high voltage surge and damage overhead lines, transformers, generators, substation equipment, and insulation systems. That is why every electrical engineering student and power system learner should understand lightning and its protection methods clearly.
What is Lightning?
Lightning is an electric discharge that can occur between a cloud and the earth, between two clouds, or between different charged parts of the same cloud. It happens when the electrical potential difference becomes so high that the surrounding air loses its insulating property and breaks down.
In simple words, air normally behaves like an insulator. But when the voltage becomes extremely high, air becomes ionized and starts conducting electricity. This sudden discharge of electricity is called lightning.
How Clouds Become Charged
During stormy weather, warm moist air rises upward from the earth. Inside the cloud, water droplets, ice particles, and air currents move rapidly and collide with each other. Due to friction and collision, charges start separating inside the cloud.
Generally, one region of the cloud becomes negatively charged and another region becomes positively charged. When the charge becomes very large, the cloud may discharge either to another cloud or to the earth. The sound we hear as thunder is produced because lightning heats the surrounding air suddenly and causes rapid expansion.
Mechanism of Lightning Discharge
When a charged cloud passes over the earth, it induces an opposite charge on the surface below it. For example, a negatively charged cloud induces positive charge on the earth. As the potential difference between cloud and earth increases, the electric field in the air also increases.
When the electric field becomes strong enough to break down the air, the lightning discharge begins.
1. Leader Streamer
The first stage is the formation of a leader streamer, also called a pilot streamer. It starts from the cloud and moves toward the earth. This streamer carries charge and creates an ionized path in the air.
If the cloud can supply enough charge, the leader continues moving downward. If not, the streamer stops before reaching the earth and no complete lightning stroke occurs.
2. Stepped Leader
In many cases, the leader moves in steps. These are called stepped leaders. They travel downward in jumps and create the first visible stage of the discharge. The path is not always straight because air breakdown depends on local conditions.
3. Return Stroke
When the leader reaches close to the earth, a return streamer rises from the ground or from a tall object. When both paths meet, a high current flows through the ionized path. This bright flash is what we see as lightning.
Types of Lightning Strokes
In power systems, lightning strokes are mainly classified into two types:
- Direct lightning stroke
- Indirect lightning stroke
1. Direct Lightning Stroke
A direct stroke occurs when lightning directly hits power system equipment such as an overhead line, tower, substation structure, or transformer yard. This type of stroke can produce very high overvoltages and may cause flashover across insulators.
Stroke A
In Stroke A, the lightning discharge occurs directly from the cloud to the object, such as an overhead transmission line. Tall objects are more likely to receive this type of stroke because they provide a shorter discharge path.
Stroke B
In Stroke B, the discharge may be caused due to interaction between charged clouds, and the resulting discharge may strike earth or power equipment. This type is harder to predict and protect against.
2. Indirect Lightning Stroke
Indirect strokes occur due to electrostatic induction. A charged cloud can induce opposite charges on nearby conductors. When the cloud suddenly discharges, the induced charge on the line is released and travels along the conductor as a surge wave.
Most lightning-related surges in transmission lines are caused by indirect strokes.
Harmful Effects of Lightning on Power Systems
Lightning can create a steep-fronted voltage wave on the transmission line. Such a voltage surge may rise to a very high value within a very short time. These travelling waves can move along the line and damage connected equipment.
- It may puncture or shatter insulators.
- It may damage poles, towers, and line hardware.
- It may cause insulation failure in transformers and generators.
- It may initiate arcs in power system equipment.
- It may produce oscillations and disturb nearby equipment.
Protection Against Lightning
Lightning surges are among the most dangerous transient overvoltages in power systems. Protection is required for power stations, substations, transmission lines, transformers, generators, and other expensive electrical equipment.
The commonly used devices for lightning protection are:
- Earthing screen
- Overhead ground wires
- Lightning arresters or surge diverters
1. Earthing Screen
An earthing screen is generally used in power stations and substations. It consists of a network of conductors connected to earth and placed above the equipment. If lightning strikes, the earthing screen provides a low-resistance path to ground and protects the equipment below it.
2. Overhead Ground Wires
Overhead ground wires are installed above transmission line conductors. Their main purpose is to intercept direct lightning strokes and conduct the lightning current safely to ground through towers.
The effectiveness of ground wires depends on the shielding angle. A smaller shielding angle generally gives better protection to the phase conductors.
3. Lightning Arresters or Surge Diverters
Lightning arresters are connected between the line and earth. Under normal voltage, they do not conduct. But when a high-voltage surge arrives, they conduct and divert the surge current to earth. After the surge disappears, they return to their normal non-conducting state.
| Protection Device | Main Use | Where It Is Used |
|---|---|---|
| Earthing Screen | Protects against direct strokes | Substations and power stations |
| Overhead Ground Wire | Intercepts lightning before it reaches phase conductors | Transmission lines |
| Lightning Arrester | Diverts surge current to earth | Substations, transformers, feeders, and equipment terminals |
Modern Power System View
In modern power systems, lightning protection is even more important because networks now include smart substations, renewable energy plants, digital relays, power electronic converters, communication systems, and sensitive monitoring equipment.
Solar power plants, wind farms, EV charging stations, and grid-connected inverters can also be affected by lightning surges. Therefore, surge protection devices, proper earthing, shielding, and insulation coordination are essential parts of modern electrical design.
Student Notes
- Lightning is a high-voltage discharge caused by breakdown of air.
- The return stroke carries the major current of lightning.
- Indirect strokes are a major cause of travelling waves on transmission lines.
- Lightning arresters protect equipment from surge voltages.
- Ground wires mainly protect overhead lines from direct strokes.
Interview Questions and Answers
What is lightning?
Lightning is a sudden electric discharge between charged regions, such as cloud-to-earth, cloud-to-cloud, or within the same cloud.
What is a direct lightning stroke?
A direct stroke occurs when lightning directly hits a power line, tower, substation, or other equipment.
What is an indirect lightning stroke?
An indirect stroke occurs due to induced charges on power lines caused by nearby charged clouds or lightning discharge.
Which devices are used for lightning protection?
Earthing screens, overhead ground wires, and lightning arresters are commonly used for lightning protection in power systems.
Frequently Asked Questions
Why is lightning dangerous for power systems?
Lightning produces high-voltage surges that can damage insulation, transformers, generators, transmission lines, and substation equipment.
What is the difference between thunder and lightning?
Lightning is the electrical discharge, while thunder is the sound produced due to sudden heating and expansion of air caused by lightning.
What is the role of a lightning arrester?
A lightning arrester diverts surge current safely to earth and protects electrical equipment from overvoltage.
Why are ground wires used on transmission lines?
Ground wires are installed above phase conductors to intercept lightning strokes and carry the current safely to earth through towers.
Can lightning damage transformers?
Yes. Lightning surges can travel through power lines and damage transformer insulation if proper surge protection is not provided.
Conclusion
Lightning is a natural electrical discharge that can create serious overvoltage problems in power systems. Direct and indirect strokes can produce travelling waves, flashover, insulation failure, and equipment damage. To reduce these risks, power systems use earthing screens, overhead ground wires, and lightning arresters. A clear understanding of lightning protection helps students, technicians, and engineers design safer and more reliable electrical networks.
Suggested URL Slug: lightning-protection-power-system
Focus Keywords: lightning protection, lightning in power system, lightning arrester, direct lightning stroke, indirect lightning stroke, overhead ground wire, surge protection, electrical power system protection
Posts
Very useful , thanks!
ReplyDeleteSubsequent to playing with the $1,000 esteem soon after the New Year, Bitcoin has been consistently exchanging at around $950 on the Mt. Gox trade in the course of the last fortnight and is in effect pleasantly upheld by the multi day moving normal demonstrating Bitcoin is still positively bullish. bitcoin mixer
ReplyDelete