Lightning Arrester

What Is a Lightning Arrester?

Lightning can generate voltage surges in various ways, and what you need is a device that can protect circuits at critical moments – a lightning arrester.

Lightning strikes, sparks or arcs can all bring high voltages and large currents. Lightning arresters will use low-resistance paths to quickly dissipate these dangerous energies into the ground, helping your power system stay away from damage. Lightning arresters are generally made of metals such as copper or aluminium. They rely on grounding paths to disperse lightning energy and are often installed on transmission poles, iron towers or the top of buildings to ensure that the discharge current can be safely released.

Working principle:

• When a surge generated by lightning or a switch travels along the conductor to the lightning arrester, there will be a low-impedance channel between the power line and the ground. It will immediately break through the insulation and discharge along the channel to the ground. Once the voltage drops back to the safe range, the insulation will automatically recover, and the current will immediately stop.

The characteristics of an ideal lightning arrester:

• It is completely non-conductive under normal voltage: It does not leak electricity and does not affect power transmission. Even if the voltage fluctuates slightly, the maximum system voltage cannot be lower than the breakdown voltage.
• Instantaneous response to surges: Whether from overvoltage caused by lightning strikes or from switch operations, the lightning arrester quickly establishes a low-impedance path to ground.
• It can withstand extremely high discharge currents: even under severe surge events, it can prevent system damage and repeatedly perform protection tasks.
• Immediately restore insulation after the surge ends: Once the voltage drops back to a safe range, it will immediately block the subsequent power frequency current, avoiding energy waste and ensuring the system continues to operate stably.

The Characteristics of Lightning Arresters

Structure and Material

A lightning arrester consists of three parts: the pointed metal rod, the grounding system and the grounding path. The materials are mostly copper, iron, brass or low-carbon steel. These metals have good electrical conductivity and can cover a protective range of approximately 60 meters.

To cope with the huge current caused by lightning strikes, the main body of lightning arresters is mostly made of low-carbon steel and undergoes hot-dip galvanising treatment, which has stronger corrosion resistance and can maintain stable operation for a long time even in outdoor environments.

Installation

To achieve the best effect, lightning arresters are usually installed close to the protected equipment, providing the shortest release path for voltage surges.

In an AC system, it is generally connected between the phase line and the ground line. In a DC system, it is mostly connected between the pole and the ground wire. If your system is ultra-high voltage alternating current, the lightning arrester will focus on protecting the generator, transformer, busbar, line and circuit breaker. In high-voltage direct current systems, key equipment such as converters, valve halls, busbars, and reactors all rely on lightning arresters to block surges.

In practical applications, lightning arresters are often found in the following locations:

• Overhead lines: Installed on transmission towers and utility poles, they protect transmission and distribution lines and prevent power outages and flashover in the event of voltage surges.
• Transformer: It is used to protect the low-voltage coil and ensure that related components are not damaged by surges, so that the transformer can be used continuously for a long time.
• Switchgear: It is installed on some components of a substation to limit overvoltage generated within the substation due to lightning strikes or operations.
• Electric motors and generators: Protect stator windings, bearing housings and cable interfaces.
• Building main service entrance: Prevent lightning strike energy from entering the interior along the power system and protect electrical appliances and wires.
• Communication and data lines: Install at the interface between data cables and telephones to reduce the impact of lightning surges on line equipment.

Maintenance and Testing

Basic Cleaning and Power-off Operations

Before inspection, the power supply should be cut off first, and then the lightning arrester housing should be cleaned to remove dust and dirt to avoid affecting performance.

Check the Grounding System and Connection Points

Grounding is the only way for a lightning arrester to release energy. Regularly check whether the grounding wire, terminals and conductors are firm, free from corrosion and looseness.

Surge Counting Record

Check and record the data of the surge counter to understand how much surge the surge arrester has endured and determine whether the surge arrester is approaching the end of its service life.

Regular Inspection and Component Replacement

Once the lightning protection system malfunctions, the voltage generated by lightning strikes can reach as high as 1000kV, which can damage transmission lines, transformers and various electrical equipment. Even household appliances can be affected by extreme voltage spikes.

Therefore, a reasonable test plan is of great significance:

• The structural parts of buildings should be visually inspected every six months.
• The electrical test of the lightning protection system should be conducted at least once a year.
• An insulation resistance test should be conducted once a year to check for cracks, leaks or contamination.
• After encountering a strong lightning strike or a large switching surge, a more comprehensive and strict functional test should be carried out immediately.

In terms of replacement, it is also necessary to note:

• The pressure relief valve of the storage tank-type lightning arrester should be replaced or replenished every five years.
• Even if the varistor block appears intact, it is still recommended that you replace it every ten years.

Types of Lightning Arresters

Rod Gap Arrestor

This type of lightning arrester is often used in low-voltage lines. Its structure is very simple, with the ends of two metal rods forming an air gap. One end is connected to the line, and the other end is grounded. When high voltage suddenly appears in the line, the air gap will be broken through, and the current will be immediately directed to the ground, protecting your equipment from impact.

Multi-Gap Arrestor

A multi-gap lightning arrester is composed of multiple metal cylinders connected in series. Each cylinder has an independent air gap between them and is insulated from the others. The first end of the cylinder is connected to the power cord, and the last end is grounded. The higher the line voltage is, the more gaps are required. Once there is a surge, these air gaps will conduct electricity step by step, introducing high voltage to the ground, effectively protecting your power system and ensuring the safety of electricity usage.

Horn Gap Arrestor

It consists of two metal sheets in the shape of a trumpet, leaving a very small air gap in between, which are connected in parallel between the wire and the ground wire.

When the voltage is within the normal range, the lightning arrester has not yet reached the breakdown gap. However, when the voltage abnormally rises, the air gap will be broken down, forming a path to the ground. You can understand it as a protective device that “automatically diverts high voltage”.

Sphere Gap Arrestor

In this device, an air gap is formed between two independent metal balls, with one ball connected to the circuit and the other grounded. The gap distance is very small, and a choke is added to one side of the transformer for auxiliary protection.

When a high-voltage wave emerges, the air is broken through to form an electric arc. The electric arc will move upward along the spherical surface, gradually elongating as the hot air rises, and eventually be naturally. This type of lightning arrester can effectively divert high-voltage surges and also reduce the impact on equipment.

Metal Oxide Surge Arrester (MOSA）

The most commonly used type of lightning arrester in modern power systems mainly employs metal oxide varistors (MOV) to absorb surges.

MOV components are made of zinc oxide material and encapsulated in an insulating housing filled with nitrogen or sulfur hexafluoride. It does not require an air gap, has a fast reaction speed and a long service life, and is often used in high-pressure environments.

Surge Arresters vs Lightning Arresters