Weather Protection. (Published article in the Cyprus living magazine)
1st published in november 2007
The theory of lightning
Benjamin Franklin (1707-1790) is generally considered to be the father of modern lightning protection theory. His celebrated kite experiment proving for the first time that storm clouds generate, hold and discharge static electricity.
Here in Cyprus we witness thunderstorms throughout the year but especially as the cooler months arrive bringing fantastic light shows and clearing the humidity. We recently witnessed some immense thunderstorms in the middle of October a few years ago
For most people it was a welcome change from the long hot summer bringing the thought of cooler nights and pleasant days. The parched island has begun its rejuvenation, flowers and plants are springing back to life and the dams are beginning to fill once again. But to many people it brought devastation. With Fires, flooding and severe damage to property structure and electrical appliances.
Many of the storms in Cyprus begin in the Atlantic Ocean. This cool air travels into the Mediterranean region meeting warm air and forming thunderclouds they then pass over the eastern Mediterranean region and generally dissipate in the Middle East
Formation of storm clouds
There are two types of storm cloud which generate static electrical energy these are Heat storms and Frontal storms.
On a hot day, warm air rises from warm ground and is replaced by cooler air drifting down. The convection process progressively cools the rising air to form clouds, first as water droplets and then at greater heights as ice crystals. In this way, a single cloud ‘cell’ is formed, the top of which may reach a height of 12 km, quite often they resemble the shape of a anvil.
Frontal storms which predominate in temperate regions are caused by the impact of a front of cold air, which hits a mass of warm moist air. The warm moist air is then lifted above the advancing cold front. As the warm air rises the Cooler air moves down to take its place. A convection process begins and progressively cools the rising air to form clouds but the resulting cumulous - nimbus clouds may, in this case extend over hundreds of kilometers. They may contain a large number of cells with heights of 7.5km to18km.
A typical thunderstorm produces a brief period of heavy rain and lasts anywhere from 30 minutes to an hour. However, not all thunderstorms produce rain that reaches the ground. These dry thunderstorms are most common across the western USA and often spawn wildfires. They often form high above the ground with a large layer of very dry air between the base of the cloud and the ground. As rain falls from the cloud into the dry air, the rain drops evaporate before they reach the ground. Warm, humid conditions are very favorable for thunderstorm development. This helps create the strong updrafts that feed warm, moist air into thunderstorms. If the air is very unstable, severe thunderstorms with damaging winds, large hail, and sometimes tornadoes erupt.
The characteristics of lightning
As a thunderstorm grows, electrical charges build up within the cloud. Oppositely charged particles gather in the ground below. The attraction between positive and negative charges quickly grows strong enough to overcome the air's resistance to electrical flow. Racing toward each other, they connect and complete the electrical circuit. Charge from the ground then surges upward at nearly one-third the speed of light and we see a bright flash of lightning. This happens in 4 steps as follows;
Stepped leader, Within the cloud, Electrons which have a negative charge begin zigzagging downwards seeking the positive earth this is called a stepped leader.
Attraction, As the stepped leader nears the ground, it draws a streamer of positive charge upwards this is called a streamer.
Flowing charge, as the stepped leader and the streamer come together a powerful electric current begins to flow
Contact, An intense wave of positive charge travels upward at 60,000 miles per second this is called a stroke.
Air resistance splits lightning into fingers
Some of the more spectacular and scary displays of lightning feature forked lightning bolts. The same general process described above creates the lightning flash. But, a single stepped leader might separate and create multiple channels of charge on its way to the ground. Here's how it happens in less than a second:
The stepped leader is a stream of weakly charged particles. It's not very bright because so little charge flows from the cloud.
The stream moves downward out of the cloud in fits and starts, traveling from just inches to 150 feet before stopping, and quickly starting again.
Since the atmosphere is a good insulator, this weak charge snakes its way downwards, often branching, trying to find the path of least resistance toward oppositely charged particles.
When each branch of a stepped leader forking from the cloud meets a rising streamer, multiple return strokes are generated.
Each return stroke travels from the ground to the cloud in less than a half second, so all the channels appear to light up at the same time as forked lightning.Forked lightning is sometimes referred to as "branch lightning."
Multiple strokes make lightning flicker
In many cases, lightning seems to flicker. After the initial return stroke, several flashes can occur along the same path. A new dart leader, dimly lit, because it's comprised of such little charge will travel quickly downward through the previously made path toward the Earth. When it reaches the ground, another return stoke occurs. This may happen several times in a second or two. Between return strokes the lightning path is dark, which makes the lightning appear to flicker. The slower this process happens the more noticeable the flicker will appear.
Lightning discharges are awesome and are claimed to have currents of up to 530,000 amps and produce voltages in the magnitude of millions of volts it has be suggested that the energy from 1 strike could light millions of 100watt light bulbs
Were lightning to strike a building without a structural lightning scheme, this energy would seek a path to earth through the fabric of the building in an erratic and un predictable manner. The building is likely to be damaged and may even catch fire.
When lightning strikes it brings a massive energy field surrounding the actual visible strike, this invisible energy then induces into any conductive substance capable of producing thousands of volts which will seek a path to earth, this includes the wiring of your property putting all your delicate electronic equipment at risk.
With switching events, transient overvoltage’s are caused when current flowing through a circuit is cut off suddenly, especially with inductive components like transformers or electric motors.
When these components are energized they are surrounded by an electromagnetic field and when the current is switched off either manually or by a power cut the electromagnetic field collapses inducing a very high voltage within its windings, this is similar to a car ignition system, and this high voltage energy then tries to seek a path to earth.
The national grid system supplying our power has hundreds of transformers, when then power supply is cut, transient overvoltages are induced onto the power supply lines. Other common causes can be the local switching of fridge and machinery motors.
Transient overvoltage’s are very short duration increases in voltage, between two or more conductors. Though short, the effects they can have on components and solid state circuitry of modern electronic systems can be, quite literally, devastating.
Most modern electronic systems are sensitive to the effects of transient over-voltages: computers, telecommunications equipment, PBX, control and instrumentation systems, telemetry, programmable logic controllers and closed circuit TV systems. In fact any piece of equipment, incorporating sensitive electronic components is at risk - and this includes many uninterruptible Power Supplies (UPS).
Written By Steve Holloway for cyprus living magazine 2007
Information Courtesy of Keison international limited.
And USA today.com