A Lightning Rod Offers Invaluable Protection for a Home During Storms

Thunderstorms strikes are a scary experience. Around the nation, there are hundreds of stories of objects or people being hit by a bolt of lightning, especially during the summer. According to research from the National Weather Service, there is an average of 47 reported fatalities per year and hundreds of accounts of people being severely injured.

Additionally, according to National Geographic, cloud-to-ground bolts strike the Earth’s surface nearly 100 times every single second. And each bolt can bring with it up to one billion volts of electricity. While seeking shelter indoors offers greatly increased safety, these powerful bolts can also strike property, cars, and more.

There is usually costly damage done to inanimate objects that get hit by bolts. Despite the common myth, lightning can and often does strike the same place twice, especially tall and isolated buildings. Depending on the damage to things like buildings and cars, the cost of repair can be thousands of dollars. Additionally, with buildings, the large electrical currents from the bolt can cause dangerous fires.

So how can homeowners and business owners avoid some of this damage? Scientists agree that an easy preventative method to avoid damage is to install a lightning rod.

Why Use a Lightning Rod?

The lightning rod, also known as a finial, acts as a tool to negate the positive power of a bolt, according to Richard Orville, a professor of atmospheric sciences at Texas A&M who has studied lightning for more than 35 years. In an interview with Texas A&M Today, Orville says that the key is to place the rod at the highest point of a structure. The rod is then connected to a series of conductors and electrodes that provide a specific path for the electric current to travel and become safely grounded.

Many new residential construction sites, especially in more prone areas, include some form of finial as a preventative measure. All tall buildings, which are very attractive to bolts, include finials. The National Weather Center notes that the Empire State Building in New York City, for example, has been struck thousands of times since it was finished in 1931. But there has never been an issue because it was built with rods.

Choosing to spend money to install a finial is a tough decision that each property owner has to consider. Homeowners should determine if their home insurance plan includes lightning protection. In areas of frequent thunderstorms, such as Tornado Alley across the Midwest and areas of Florida, it can be an especially worthwhile investment. While lightning strikes are rarer for smaller structures like homes, it offers an added element of safety and peace of mind.

The Problems Encountered With Photographing Lightning

Lightning results when charges are separated in a cloud, and induce a charge on the ground. When the charges are large enough, the electrons travel from the negative region to the positive charges in a discharge. Discharges can be between the cloud and the ground, or between the cloud and another portion of the cloud. When a discharge occurs, an enormous number of electrons move, and literally rip other electrons from their molecules as the lightning passes through the atmosphere. The recapture of electrons by the charged molecules gives off light.

Since the cloud sends many electrons through the air at one time, they overwhelm the area they strike, giving that area has an excess of negative charges. Many return via the original charged air column where some charged molecules have yet to capture electrons. This process repeats, with a flickering of lightning that lasts for some time.

Photographing lightning requires overcoming several obstacles. Although lightning may last for some time, it is not a long enough duration to allow a photographer to focus a camera and to open the aperture. One must have the camera set for distant objects, and have it aimed in advance. But that is difficult, since we never know where the next lightning bolt will be. So, it becomes a process of set, aim, and hope.

Even if the camera happens to be properly aimed, the reaction time in opening the aperture is determined by reaction of the photographer, and is usually to long to capture the image.

Leaving the aperture open using a time exposure requires the surroundings be dark, or light from the surroundings will flood the image, rendering it unusable. Setting up with a street light to the side is not acceptable for night time exposures. The incidental light will flood a time exposure photographic attempt. A second problem is the brilliance of the lightning. If the aperture is open too long the image may itself flood too much light into the camera. This is more of a problem with digital cameras, since slow film designed for such events cannot be used in them. Yet many people have now gone to digital. Too fast of a camera speed may catch the flickering lightning at the instance it is dark, missing the opportunity. This is also a problem.

Still another concern is safety. Lightning must be photographed from in front of the storm, since photographing through rain is impractical. But lightning may strike ahead of the storm, and frequently does. Keeping the photographer safe is a necessity. But photographing from indoors has a drawback. The brilliance of the flash of lightning often illuminates the interior of a room, and that light reflects off of everything within the room illuminating the glass window from the inside. This causes the same problem as using a flash to tale a picture at night through a window, the image of everything inside the room reflects from the window into the lens and is caught in the photograph as an aberration looming.

This article is provided by Henry M. Smith of Black Spaniel Gallery. Please visit us at blackspanielgallery.8m.com

Principles of Lightning and Surge Protection

Lightning strokes, which amount to 200 kA or 300 kV, cause hazards to the equipment or location, so lightning protection is crucial for operation.

Let us start with the initial note as to what is lightning and why lightning protection is so important. The basic phenomenon behind lightning is that charges accumulated from the cloud and the earth are equal and opposite. This forms a non-uniform potential gradient surface in the air. When the gradient is greater than the potential of the surface, the breakdown occurs and a “streamer” flows from the cloud towards the earth.

A direct stroke occurs when the lightning hits the power systems directly that the immense potential will cause destruction of the equipment or the facility. In contrast, an indirect stroke occurs from the lightning discharges in the proximity of the power line or from electrostatic discharge on the conductor due to the charged clouds.

The main power system elements requiring lightning protection are power feeds, security systems, telephone lines, data and control systems and RF cables.

Methods of Lightning Protection
The rolling sphere method is used for identifying the exact placement of the lightning and surge protection devices near the equipment under operation.

Protection of the power line against direct strokes is through a ground wire or protector tube. The former produces electrostatic screening, which is affected by the capacitances of the cloud to line and the line to ground. The latter forms an arc between the electrodes, causing gas deionisation.

Rooftop/Frame Protection
It is interesting to note that the building and rooftop frame or cladding is preferably metal than insulation type.

Installation of a finial at the top of the power tower should have a minimum distance of 1.5 m above the highest antenna or lights. Such a rooftop or building frame is made of reinforced steel for protection purpose.

Wooden towers without downconductors may cause a fire hazard, as they route the incoming charges to ground. In principal, for non-metallic roofs, proper downconductors should be installed at the appropriate location and height.

Device Protection
Antenna lightning protection is provided through spark gap, the gas discharge tube and quad-wavelength shorted stub. The first method uses ball points so that if a strike occurs, high potential forms between them and the ground. The second method causes gas deionisation through arc formation between the electrodes. The last method uses a coax transmission line across the transmission line so that system bandwidth is narrow.

A lightning arrester is a device offering lightning protection by regulating spark gaps. The device classification may range from rod gap, horn gap and valve type to metal oxide lightning arresters.

Earthing and Bonding Solutions
Now let us discuss how earthing and bonding solutions for lightning protection should be afforded. The design of earth rods, terminals or clamps should be in a way to route the incoming transients to earth to minimise step and touch potentials. The geometric measurements chosen should comply with the IEEE and NFPA standards. Any earthing system should have proper bonding, as ground potential rise cannot be compensated. Again, the number of interconnects and spacing should be designed per the lightning standards.

Surge Protection
The device ideal for protection against travelling waves is a surge diverter, connected between line and earth at the substation. Its purpose is to divert the excessive incoming voltage to ground by developing low impedance between the line and earth. Surge protection is essential as the overvoltage may damage the lightning protection devices and others across the line. Surge measurement can be performed based on the Faraday principle or remote monitoring with sensors.

If there are overvoltage devices, they are placed between surge arresters or diverters and the control equipment.

Surge protection for telephone cables is through a setup of a gas arrester, metal oxide varistors and suppressor diodes.