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Whilst writing a recent article on the basics of climate control and monitoring using temperature and humidity measurement it dawned on me that my touching on the subject of lightning/surge protection, required for protection of pumps and cables etc., was unfinished and that I only scratched the surface of the subject.

Some facts and trivia:

Speed of a lightning strike through air is 60,000 Meters/Second (or 216,000 KPH)

Typical temperature inside a lightning “bolt” is 30,000°C

Lightning storms per year, world-wide – 16,000,000 (equivalent to 30/second)

Strike current is excess of 200,000 Amps (250,000 Amps have been recorded in SA)

Power in a strike is equivalent to 1,000,000MW and last for 30 millionths of a second

Statistics prove that 80% of damaged electrical equipment is associated directly/indirectly with lightning, its effects and/or other electrical surges

After a brief (hopefully) introduction we shall move on to the subject of “how you can protect your equipment against the effects”.

“Lightning only strikes once in the same place” – ever heard of that expression? Trust me it is a myth. Why if a “streamer” that starts the lightning strike in the place (from the ground up) is emanating from a good source then why should it not do it again and again. Sure, the chance of it being “exactly” in the same place are remote, but what about being 50M away? Is that considered to be the same place?

The concept of lightning damage and its subsequent effects is a huge subject and there are plenty of white papers written and published on the internet. Some are written by people who think that they know what they are talking about and others are written by people who have first hand experience in the problem and write “from the heart”. The latter is such an article here as, unless one specialises 100% of your business in the subject of surge protection, you too are just scratching the surface.

I worked in the industry for two years, for a company that specialised in the R&D and manufacturing of surge protection devices (SPD’s for short), and so I feel that I have some in-depth knowledge, that I am prepared to share with interested parties. Previous to my industrial exposure I spent 10-years in Swaziland where the effects being at “the coal face” where very obvious, more so as I was involved with radio communication that required repeater stations to be located on mountain tops – some kilometres away from the highest lightning strike area in South Africa (ref CSIR).

The generation of the huge voltage potentials found during electrical storms is a mixture of cloud formation, ice particle (hail) collision, winds and friction of such across the ground, these voltages can extend to many millions of volts. High humidity and temperatures contribute to the overall conditions.

Typically the voltage breakdown of normal air (the voltage required to “jump’ through air at normal pressure and temperature) is about 10,000 volts/cm thus a nice cloud full of charge at say 5,000M ASL could well produce a strike to ground of 5,000 x 100 x 10,000 or 5,000,000V !!!. Although this doesn’t often happen in practise a typical voltage of 250,000 V might well be measured, and at HUGE currents.

Direct strikes often hit trees, as they offer a low resistance path to ground, and the subsequent energy dissipation is enormous. The temperature of a direct strike inside a tree, at 3 times the surface temperature of the sun, causes total destruction.

A “strike” occurs when the up-going “positive streamer” meets a charged air pocket or “negative leader” and the voltage potential now finds and easy path to ground through the ionised air.

Striking the ground the lightning “bolt” is similar to that effect when one throws a stone into a large pond or dam in that the ripples, from where the stone hits the water, radiate out from that point in little waves (wavelets). The distance between the ripples/wavelets is actually proportional to the size of the disturbance in the first place. Try the above using a small stone and again with a larger object, you will see what I mean. In lightning terms the “water ripples” are equivalent to voltage wave-fronts, the larger the distance between the wave the higher the voltage.

Dead Cows?

In real terms, after this lightning strike, this voltage wave-front is equivalent to about 10,000V/M that is, you could measure 10KV across every meter of ground. This might not seem to be too relevant but how many dead cows have you seen after a major electrical storm? The reason, take one cow whose legs are about typically 1.5M apart (front to back) the body of the cow thus experiences a voltage of 15,000 V across its major organs, with dire consequences.

Golfers Corner:

The same is applicable to all those golfers out there who when playing a storm erupts striking the trees, or highest point around. These voltage “ripples” now travel through the ground, same as is in the “pond” effect, and your feet would then be in a similar situation, and be subjected to the same type of voltage.

Most golfers, not actually playing at the time, are normally seen standing with one leg crossed over the other whilst leaning on the golf club as a prop. This is a really great scenario to get those high voltage wave-fronts, moving through the round and radiating out from the tree, to have an effect on the golfer. A friend of mine lost his hand when he was standing like this in a storm and subsequently died when the surge finished coming up the club and continued to travel through his heart and down his leg!!!

The Solution:

Having covered some of the alarming aspects of lightning we can now move on to the effects on the man-machine interfaces, but keep in mind our “ripple” or “wave-front” effect.

Not only does the voltage wave-front travel through the ground but, as it always finds the easiest path to ground, it can and does travel through overhead lines like telephone cables, power lines and or anything strung in the air, or indeed along computer network cables. The resistance to a flow of electrical energy through a cable like this is obviously significantly less than the ground thus your equipment could be damaged even if a strike occurs many kilometres away.

Lightning has many side effects that can damage equipment but these all fit into the categories of electrical spikes and surges on any line entering ones premises – telephone, power and data cables are typical. If you operate a tunnel, or agricultural operation, in a remote area you are probably more vulnerable than if you were in a heavily built-up city.

The “general” solution to preventing equipment damage is to fit “surge protection devices” often referred to as SPD’s (not to be confused with any similar sounding disease).

SPD’s come in a plethora of qualities from many manufacturers, and, for obvious reasons, it is NOT worth saving any money by buying cheap “imitations” or low quality “Chinese” copies. Spend your hard earned bux wisely here as it will pay off in the long run.

I might be biased, and I am not getting any commission from anyone for writing this article, but I have been using products from Surge Technology for many years and have never had a problem with any equipment using their products.

Simply put the “entry level” SPD would be a device fitted to the “entry point” to a building or structure. As most of the damage occurs from a electrical mains related issue the SPD must then be fitted at the distribution board point.

Surge Technology manufacture a product that offers a simple but effective solution, namely a DEHNguard 275. This Class-2 product comes in a wide range of derivatives but a DEHNguard S 275FM is what most of our clients opt for. Each unit will set you back about R450.00 (excluding installation) and remember that you will need two such devices – one to protect the live mains line the other for the neutral mains line, with 3-phase users requiring four such devices – L1, L2, L3 and Neutral that Surge Technology conveniently package into one device.

A useful feature of the DEHNguard product is that is has a window on the front of it that shows green when the device is working and shows black when the unit needs to be replaced. The module can be replaced in a live situation as it plugs in to its base. It also has a contact output that can be interfaced to your GSM telemetry unit and so you can even receive an SMS alarm on your cellphone when the device is ready for replacement.

Internally these devices will “shunt” the “over voltage” caused by the lightning, or other sources, to ground at the source and such any electrical equipment connected down-stream from these devices will be protected. You will obviously need a good earth but your electrician can advise you at the time of installation.

I mentioned it in the previous article about the basics of GSM telemetry but, in completion of this article, I will mention it again.

We recently had a client who was spending approximately R10,000.00 per month on the repairs and/or replacement of electrical equipment at one of his key sites. We supplied and installed a 3-phase SPD and for the last 6-months we have not heard from them again since !

Given the above please, no injured golfers or dead cows, just implement a relatively simple solution to a problem that seems not to be getting any better! We live in Durban and the electrical storms frequency and its associated energy has increased 5 fold over the last 10-years.

Article supplied by CMR Projects.