Difference between Conventional and ESE Air Terminals

Difference between Conventional and ESE Air Terminals

Lightning, a natural phenomenon with immense power, can wreak havoc on structures and electrical systems. To mitigate the potential damage caused by lightning strikes, air terminals play a crucial role. In this blog, we will delve into the world of lightning protection and explore the key differences between conventional air terminals and the more advanced Early Streamer Emission (ESE) air terminals.

Basics of air terminals

Before diving into the differences, let’s understand the fundamental purpose of air terminals. A lightning strike generates a powerful surge of voltage that, if unchecked, can damage the wiring and electrical systems of a facility. Air terminals act as a defense mechanism for the power system, diverting these high voltage surges to the ground. The primary goal is to provide a low-impedance path for the lightning strike, allowing it to reach the ground without adversely affecting the structure or its electrical components.

 Conventional air terminals

Structure and Working Principle

Convertional air terminals typically consist of Franklin rods strategically placed at elevated points on a structure. The effectiveness of these rods depends on factors such as their position, morphology, materials used, and their reaction to the electrostatic field during a lightning event.

The placement of conventional air terminals involves positioning the rods at dominant heights, making them favorable points for lightning strikes. The positive charge rises to the tip of the lightning rod. When a lightning strike occurs, the device allows the lightning leader from the cloud to reach the ground safely through the grounding system. As a result, the current discharge is evenly distributed throughout the ground, protecting the structure.

Characteristics

Conventional air terminals have been a reliable method for lightning protection for many years. However, their efficiency depends on factors like proper installation, maintenance, and the specific characteristics of the structure they are protecting.

Early Streamer Emission (ESE) Technology

The key innovation in ESE air terminals lies in their Early Streamer Emission technology. These devices are also known as active lightning rods. Unlike conventional lightning rods, ESE air terminals are designed to emit a stream of ions into the air.

Working Mechanism

During a storm, when conditions in the propagation field are favorable, an ESE air terminal generates an upward leader. This upward leader, originating from the ESE tip, propagates toward the downward leader from the cloud at an average speed of 1 m/µs. The emission of this early streamer to a lightning event offers a beneficial triggering time compared to a single rod air terminal exposed to the same conditions.

Basis of Design

An early streamer emitter (ESE) is an air terminal that is equipped with a device or formed in such a manner that allegedly creates an upward propagating streamer faster than a standard air terminal or other building elements. This streamer connects with a downward propagation leader of a lightning stroke, thereby completing the circuit and carrying the current to ground. The design and layout of an ESE air terminal system is based on the Collection Volume Method (CVM) which commonly requires only a single ESE air terminal for protection of an entire structure.

History

The basis for the ionizing method of lightning protection was theorized in a paper submitted to the Academy of Science in Paris by J.B Szillard in March of 1914. It was theorized that by increasing the amount of ionization that occurred around the air terminal, the efficacy of the air terminal would increase. Early ESE air terminals were filled with Radium-226 or Americium-241. The intention was to generate massive amounts of ionized air without the presence of storm conditions. It is estimated that Hélita (French manufacturer)manufactured more than 230,000 of these radioactive air terminals between 1936 and 1986.

In the post radioactive era of ESE air terminals, manufacturers now base the design of their ESE air terminals on the theory that certain designs or shapes of air terminal tips can generate the substantial upward leaders required to “reach out and grab” the lightning stroke before other conductive, grounded objects.

Collection Volume Method

The Collection Volume Method (CVM) was developed in the late 1970’s as an attempt to replace the industry standard Electrogeometric Model (EGM). Both of these models allow designers to mathematically calculate and accurately locate strike termination devices on or around a structure. The CVM was not originally designed as the basis for ESE air terminal systems,rather it attempted to address incorrectly perceived shortcomings of the EGM.

Response Time

One of the significant differences between conventional and ESE air terminals is the response time (ΔT). The response time refers to the time taken to ground the lightning strike through the lightning protection system. According to NFC 17-102, the ΔT for an ESE should be at least 10μs. This rapid response time is achieved by storing energy from the ambient electromagnetic field or static charges at the time of the lightning.

Protection Radius

ESE air terminals have the advantage of covering a larger radius compared to traditional air terminals. This broader protection radius is a critical factor, especially in scenarios where extensive coverage is required.

Comparative Analysis

Speed of Response

The most notable distinction between conventional and ESE air terminals is the speed of response. ESE air terminals, with their early streamer emission technology, can detect and respond to lightning strikes more rapidly than their conventional counterparts. The ability to emit streamers earlier provides an added layer of protection by intercepting lightning before it gets too close to the protected structure.

Coverage Area

ESE air terminals excel in protecting larger areas. The broader protection radius makes them ideal for applications where extensive coverage is essential, such as in open spaces, sports grounds, or solar parks. This characteristic makes ESE air terminals a cost-effective solution for lightning protection in scenarios where traditional lightning rods might fall short.

Triggering Mechanism

Conventional lightning rods rely on their elevated position to attract lightning strikes. In contrast, ESE air terminals are more proactive. They create a path for lightning by emitting ions into the air, providing an earlier triggering mechanism. This proactive approach contributes to their faster response time and enhanced effectiveness.

Standards and Testing

Both conventional and ESE air terminals need to adhere to specific standards to ensure their reliability and performance. Testing protocols, such as those defined in Annex C of the French standard NF C 17-102 (2011 Version), are essential to validate the efficiency of ESE air terminals. Conventional air terminals, while proven over time, also require adherence to installation and maintenance standards for optimal performance.

Conclusion

In the realm of lightning protection, the choice between conventional and ESE air terminals depends on various factors, including the specific requirements of the structure, the desired coverage area, and the need for rapid response. While conventional lightning rods have been stalwarts in the field, ESE air terminals bring innovation with their early streamer emission technology, offering a faster and more proactive approach to lightning protection.

Understanding the differences between these two types of air terminals allows stakeholders, including architects, engineers, and facility managers, to make informed decisions when implementing lightning protection systems. Whether safeguarding homes, high-rise buildings, factories, or expansive open spaces, the right choice of lightning arresters can make a significant difference in minimizing the risks associated with lightning strikes and ensuring the safety of structures and occupants alike.