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  • Writer's pictureFlorent Giraudet

Current Limiting Gaps (CLGs) : An alternative to Metal-Oxide Line Surge Arresters (MO LSAs) ?

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1. Introduction

Have you ever heard of Current Limiting Gaps (CLGs)? They may not be well-known, but these devices are commonly applied in preventing lightning-induced outages on distribution lines. It should be noted that Japan uses CLGs also on transmission lines up to 154kV system. Officially described in the CIGRE Technical Brochure 855 published in 2021, CLGs are considered a type of Line Surge Arrester, but their technology significantly differs from the Metal-Oxide Line Surge Arresters (MO LSA) traditionally used on transmission systems. CLGs are not resistor valve types of arresters made of Silicon Carbide elements and series gaps. CLGs are not designed to protect valuable equipment in substations, such as power transformers. CLGs utilize an innovative approach involving one or several arc quenching chambers. This design offers follow current quenching capabilities, tested and verified similarly to Externally Gapped Line Arresters (EGLA). Though the first CLG applications emerged in the 1990s, they have since gained popularity in various countries. This is largely due to their attractive lifecycle costs and ability to withstand high charge transfer ratings on unshielded overhead lines. Today, CLGs are an increasingly popular choice for distribution networks worldwide, offering a promising solution for reducing lightning-related outages on medium and high voltage lines.

2. Current Limiting Gaps versus Metal Oxide Line Surge Arresters

Both Current Limiting Gaps (CLGs) and Metal Oxide Line Surge Arresters (MO LSAs) serve the same purpose in electrical power systems – to prevent lightning-induced outages. They are installed on overhead lines in parallel to the tower insulation. However, there are key differences between these two technologies that can influence the choice between them.

Although MO LSAs are a proven and established technology commonly used on transmission lines, their adoption on distribution lines has been relatively limited. Several reasons contribute to this moderate acceptance:

• Financial impact: Outages on distribution lines are not as financially critical as those on transmission lines, reducing the urgency to adopt MO LSAs in distribution networks.

• Initial investment: The cost of MO LSAs can be a barrier to adoption, as the solutions and experiences offered by manufacturers are often not convincing enough for system operators to justify the investment.

• Lightning charge transfer: Distribution lines are mostly unshielded, leading to a higher expected lightning charge transfer than the standard Qrs ratings of distribution class arresters.

• Temporary Overvoltage (TOV) stress: Isolated or impedance neutral systems can cause high TOV stress, which might exceed the standard voltage ratings of MO LSAs.

• Failure rates: Failures in MO LSAs have been reported due to issues with sealing systems, such as moisture ingress resulting from manufacturing flaws or aging during operation. These failures have not been effectively addressed in the technology.

Therefore, CLGs have become an interesting alternative to address some of the limitations of MO LSAs.

3. How do CLGs Work?

To better understand CLG technology, let's delve into its inner workings. At the core of a CLG is an arc quenching chamber, which extinguishes an electric arc struck between two electrodes. The chamber provides a path for electrical current to flow through, dissipating the arc's energy and extinguishing it. Unlike interrupter units in circuit breakers, which use active extinction mechanisms and insulation mediums like SF6 gas or vacuum, arc quenching chambers are static components with extinguishing capabilities by design, without any active mechanisms.

CLGs come in various designs, featuring one or several arc quenching chambers:

1. Multi-chamber design: These designs dissipate the arc's energy by dividing it into a series of smaller power arcs, which are eventually extinguished.

Credit Streamer Electric

2. Single-chamber design: Single-chamber designs extinguish the arc differently, using two holes at the extremities of the active part. These holes project the arc onto the insulator string's horns, where it is extinguished.

Credit CRIEPI Report

4. Operation and Limitations of CLGs

While CLGs are effective in preventing lightning-induced outages, it is essential to recognize their limitations regarding fault currents. System parameters must be carefully considered when implementing CLGs on the line.

All CLGs are certified to extinguish follow currents within half a cycle. This interruption prevents the breaker operation and subsequent lightning-induced outage. Generally, the current interrupting capability can reach up to 10 kA for specific designs. However, large energy dissipation is expected when interrupting power arcs in the active part, which limits the follow current interrupting capability and the allowable number of operations. As a result, CLGs are best suited for systems or locations where the prospective fault current is lower than the interrupting capability.

The Maximum Prospective Fault Current is influenced by the distance to the power transformer feeding the fault point. Essentially, the closer the CLG is to the transformer, the higher the current will be. It is crucial to verify and ensure a minimum distance between the CLG and the transformer to prevent exceeding the device's operational limitations.

5. Terminology and Designations

In the technical literature, you might find different terminologies. It could be confusing but all of these terms refer to the same technology.

6. Global Market Overview

The global deployment of CLGs is estimated at approximately 3 million units, predominantly in networks with voltage levels up to 77kV, although there are instances of usage beyond this range. The increasing significance of CLGs within distribution networks can be attributed to the limitations of MOSA manufacturers in catering to the diverse market demands. Over the past 25 years, CLGs have been widely adopted across distribution networks worldwide, primarily to address lightning-related challenges:

• In Japan, over 120,000 units have been installed up to 77kV since 1994. Notably, the country has also implemented the technology in their 154kV network.

• In the CIS region, including Russia and Kazakhstan, around 2.5 million units are operational up to 35kV since 1999, with some pilot projects executed at higher voltage levels.

• China has embraced the technology with more than 200,000 units installed up to 35kV since the initial deployment in 2012.

• Other countries, such as Vietnam and Indonesia, account for an estimated 100,000 CLG installations since 2012.

• In summary, it can be asserted that approximately 3 million units are currently in operation globally. Please note that these figures are rough estimates and may deviate slightly from the actual numbers.

7. Japan: A Pioneer in CLG Adoption and Innovation

Japan boasts over 25 years of experience with CLGs, demonstrating its early commitment to embracing this innovative technology. The country has not only successfully implemented CLGs to address lightning performance challenges but has also found additional applications for this versatile technology, such as bird protection equipment. By replacing conventional arcing horns on insulator strings with CLGs, the electrical hazard posed to animals is significantly reduced or even completely eliminated, as CLGs function as insulated horns. This dual-purpose application of CLGs showcases Japan's ingenuity in finding creative solutions to unique challenges.

Furthermore, Japan has a long history of utilizing Line Surge Arresters (LSAs) for the past 40 years, with claims of the first installation dating back to this period. As of today, over 120,000 CLG units are installed across the country. According to an official report from 2009, there have only been nine reported failures, highlighting the reliability and effectiveness of CLGs in the Japanese power distribution network. This impressive track record underscores Japan's role as a pioneer in the adoption and continuous development of CLG technology.

8. Russia: A Trailblazer in CLG Technology Adoption

With over 20 years of experience, Russia has been a pioneer in adopting CLG technology since its first installation in 1999. This early commitment highlights Russia's recognition of CLGs' potential in addressing lightning-related issues and improving network efficiency. Russia's ongoing investment and expertise in CLGs have positioned the country as a leader in the global CLG market, contributing to its own power distribution infrastructure and encouraging broader global adoption.

9. China: Rapid Standardization and Growth

Since the first installation of CLGs in 2012, China has quickly standardized the technology, recognizing its value in improving the performance and reliability of distribution networks. The country has witnessed a surge in CLG installations, and new manufacturers are entering the market to meet the growing demand. Chinese standardization efforts are exemplified by the establishment of the Chinese Society for Electrical Engineering (CSEE) standard T/CSEE 0082-2018, which outlines the general technical requirements for multi-chamber gap (MCG) lightning protection devices used in medium-voltage distribution lines. This standard highlights China's commitment to ensuring the quality and safety of CLG technology while promoting its widespread adoption throughout the nation's power distribution infrastructure. As a result, China has become a significant player in the global CLG market, driving innovation and growth in this evolving industry.

10. Interesting Use Case: Malaysia's Approach

Malaysia presents a insightful use case for the adoption of CLGs in power distribution networks. Initially, Metal Oxide Line Surge Arresters (MO LSAs) were installed on distribution lines following the IEEE 1410 Guide. However, several failures were reported due to factors such as grounding conditions, soil resistivity, and surge arrester requirements. These challenges led the Malaysian Distribution System Operator to seek alternative solutions, and CLGs emerged as a more compelling choice. The adoption of CLGs in Malaysia has provided a more reliable and effective solution, addressing the unique challenges faced by the country's power distribution infrastructure. This approach showcases the adaptability and value of CLGs, highlighting their potential to meet diverse market requirements and improve the resilience of power distribution networks. Malaysia's experience serves as an essential case study for other countries exploring the implementation of CLGs as part of their power distribution strategies.


Mohd Faris Ariffin, Muhammad Fazli Nozlan, Noradlina Abdullah

11. Summary and Future Outlook

In conclusion, Current Limiting Gap (CLG) technology has proven to be a valuable and effective solution for improving lightning performance mainly on distribution overhead lines but also on transmission systems. With a track record of more than 25 years in Japan and growing adoption worldwide, CLGs demonstrate reliability and effectiveness in addressing diverse power stability challenges.

Key advantages of CLGs include their high charge transfer ratings compared to typical Qrs ratings for MO LSAs, making them an ideal choice for ungrounded systems with high soil resistivity. Furthermore, their compact and lightweight design facilitates easy integration and installation, providing a user-friendly solution for system operators.

While CLG manufacturers primarily focus on addressing distribution network needs, MOSA manufacturers cater to the broader industry, which may have led to missed opportunities to showcase the full potential of MO LSAs. Despite their niche focus, CLGs have demonstrated promising lifecycle cost advantages over MO LSAs, though a comprehensive comparative study between the two technologies has yet to be published.

Existing standards, such as those established in China, and national specifications in countries like Japan, demonstrate the growing recognition of CLGs' importance in power systems infrastructure. However, there is a need for standardization at the international level (IEC/IEEE) to incorporate industry standards already applied to MO LSAs. This would further promote the widespread adoption and development of CLG technology, ensuring its continued role in enhancing power distribution networks globally.

In light of the increasing demand for reliable and efficient power distribution systems, it is crucial for industry stakeholders to consider the proven advantages of CLGs. By carefully evaluating network parameters, such as the Maximum Prospective Fault Current, and adopting international standardization, the global power distribution industry can continue to benefit from the innovation and versatility offered by CLG technology.

12. References

To develop the subject in detail, here are some reference documents which have been used for this article.

CIGRE TECHNICAL BROCHURE 855 - Effectiveness of line surge arresters for lightning protection of overhead transmission lines (2021)

CRIEPI Report H17001 – Development of Low-Cost High-Strength Fault Current Interrupting Arcing Horns for 77kV Overhead Transmission Lines (2018)

Development of Arcing Horn Device for Interrupting Ground-Fault Current of 77 kV Overhead Lines (IEEE, Chino 2005)

LLPD Line lightning protection devices for medium-voltage networks- Streamer Catalogue 2022

Application Guide for EasyQuench Technology, Basic Knowledge on Streamer’s EasyQuench Technology for MV networks from 6 to 40 kV


Multi-Chamber Arrester Field Test Experience in Asia High Lightning Density Area (Zinck, Streamer)

Distribution Network Modernization in TNB with the application of line lightning protection onto the 33KV OHL with High Soil Resistivity – CIRED 2021

Research on Structure and Experiment of Multi-series-gap Lightning Protection Device for 10 kV Distribution Lines (China - ICLP 2018)

363 views2 comments


May 09

How to decide the gap between both the horns of arcing horn

Florent Giraudet
Florent Giraudet
May 10
Replying to

As part of the insulation coordination verification (consistent with the EGLA standard), we need to ensure that the gap withstands power-frequency and switching overvoltages, and that it operates safely under the gap for lightning impulse sparkover voltages. At a later stage, the manufacturer should demonstrate such performance during the acceptance tests if not available at an earlier stage.

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