Shocking Revelations in the OSP
Naturally, our lightning journey begins in the clouds.
As you may recall, warm air is thinner (less dense) and rises toward the sky. Colder air is denser and sinks toward ground level.
Clouds contain dust, dirt, debris, ice crystals, maybe snow, hail particles, etc. and perhaps, some level of local pollutant chemicals.
All objects (metal or not) have a constant static charge of very near zero. The majority of objects in our world are neutral in static charge. All the positive/negatives charges cancel and the object therefore carries a neutral charge.
Chasing Highly Charged Clouds
In clouds there are large areas, maybe hundreds of miles across, where the hot air and colder air differ greatly in temperature. As a direct result of the air temperature differences, there is MUCH upward and downward movement of air inside the cloud.
Ever notice that just before or during a local storm there is much wind and intermittent very high gusts of wind? The storm is bringing hotter air and forcing the local cooler air out of its path. This is wind.
As hot air gets to the top of the cloud, it cools and falls to the bottom of the cloud. Cold air at the bottom of the cloud warms and rises to the top of the cloud. This cycle will continue until the cloud dissipates.
As all these different particles are traveling up and down great distances and at great speeds inside the cloud, they physically collide into each other. As a direct result of these billions and billions of high-speed collisions, the negative charges are literally knocked loose.
This means that a particle of ice, for example, physically loses its negative charge as a result of a collision. By definition, when the positive charges outnumber the negative charges that item becomes positively charged. The loose negative charge is now free floating around in the air by itself, attached to nothing.
As a result of billions and trillions of collisions in the cloud, as described above, the top of the cloud becomes highly positive and the bottom of the cloud becomes highly negative.
The static voltage differences from the top to the bottom of the cloud could easily exceed tens of millions of volts. Easily!
Lightning is created by the buildup of very high levels of static electricity caused by friction among colliding particles inside the cloud.
In nature, anything that has a positive charge attracts anything that has a negative charge. Different charges are physically drawn towards each other.
Static energy particles encountering the same charge physically repel each other. When positive meets positive charges or negative meets negative charges they physically repel each other.
The bottom of the nearby cloud is now highly negative and becoming more so every second. The cloud is approaching the top of the building where lightning will strike. The negative charge of the cloud forces the negative static charge of the entire building into the surrounding dirt. (Reminder: Like charges repel.) As a consequence again, the entire building is at a positive static charge. Yes, the entire building and everything within is at a positive static charge.
The highly charged negative cloud keeps moving closer and closer and forces even more negative charges of the building into the surrounding dirt. The building is even more positive than it was a few minutes ago! Do you see where this is going?
Eventually, the building becomes so positive and the negative cloud charge is so strong and so close they begin to strongly attract each other. (Reminder: Opposite charges attract.)
At this point, the positive charge of the building and the negative charge of the cloud have built up differences that are so great that something has to give. The building’s sharpest shaped surface launches a POSITIVE visible arc into the air toward the cloud. At the same time the cloud launches a NEGATIVE visible arc toward the building. The positive visible arc of the building and the negative visible arc from the cloud meet about 150 feet above the building.
Now the circuit is complete. The highly negative charged cloud is connected to Earth’s surface. The intense flashes of lightning and very loud clap of thunder occur. Now the heavily negative charged cloud begins to discharge into the surrounding dirt, through the building, of course. This is a lightning strike.
The average lightning strike is about 25,000 amps and the voltage is in the millions. Power in watts is determined by simply multiplying volts times amps. Do the math. You can see that a direct lightning strike generates very, very high power levels indeed.
Let’s look at an example for 1 hypothetical lightning strike. As an average, that means 25,000,000 volts strikes the building. This means until the full energy of that strike is dissipated into the surrounding dirt, the entire building and its entire contents are also at the 25,000,000 volts. As you might guess, this much energy passing from the top to the bottom of the building in unpredictable directions can easily create much lightning-related damage to people, electrical devices, and wiring.
Static charges are more intense on objects on the ground that are pointed/sharp in shape rather than rounded. Lightning will likely strike the top of a building and hit the corner of the building or a narrow pole pointed tip antenna first. The tops of buildings usually have sharper points and are also much closer to the cloud.
Again, statistically, lighting will strike at the closest object to its cloud having the sharpest point.
If you are anywhere and suddenly there is intense increase in static electricity all around, you will notice your hair is on end and you may be getting zapped by touching other nearby objects.
You already understand that this static negative side of a cloud is very intense and nearby, and a lightning strike is imminent any second! What can you do to prevent injury and possible death? If possible, immediately get inside a structure. If not, do not be the tallest or sharpest pointed object around. Immediately drop anything in your hands.
One of the most dangerous places to be is very near the base of trees and towers that are likely to take the direct brunt of the imminent stroke. Standing near a tree will likely get you killed or seriously injured, twice. The lightning energy traveling down the tree toward the dirt will turn the water inside the tree to steam. That severe explosion alone can kill you.
Next, as the lightning’s energy travels down the tree into the nearby dirt, the millions of volts from the strike must be measured differently.
The dirt area near an object that has just been struck with lightning also has severe electrical energy all around, literally in the dirt. The unit of measure of that lightning voltage is volts per meter. It is possible during the stroke’s duration to have 5,000 to 10,000+ volts per meter between your right and left feet. This is what could really kill you! That is exactly how four-legged animals die from lightning strikes.
Immediately squat down, do not touch anything, and keep your arms and head down. Keep both feet touching firmly together. Never lie prone during a storm. If you have the time and presence of mind, to protect your hearing, put your fingers in your ears as the loud clap of thunder is certainly going to be very nearby.
The Striking Bottom Line
If you want to be more lightning savvy, remember these 4 points:
1. Lightning favors striking the object nearest to its cloud having the sharpest pointed objects.
2. Sudden static buildup means a lightning strike is imminent. Your life is at risk.
3. At the lightning strike location, reduce the volts per meter in the dirt by putting your feet together.
4. Get as low to the ground as possible without lying prone or touching anything.
AC/DC Electricity Primer
The truly immense negative static charge in the cloud that eventually caused the lightning strike in the building we described earlier will now begin to flow in/on/around/through all metals in that building. Yes, the immense static charge of the cloud, once the lightning strike occurs, converts, if you will, to electricity when encountering metals. (See Figures 3 and 5.) That's why we need to understand a few characteristics of electricity.
Electricity is divided into 2 types. First is Direct Current, commonly called DC. Figure 1 shows that the value of the DC voltage never changes over time. In DC, the current and voltage values are always at their peak values at the same time. In DC, the value of the resistor (Drawing 5 Fig. A) never changes, ever. It is that simple. DC usually applies to all batteries and the DC voltage power applied to electronic devices. One way or another, all electronic devices require DC to operate.
The resistance to electricity working on DC circuits is called resistance, abbreviated R. Its unit of measure is called ohms.
The second type of electricity is Alternating Current, or AC. Figure 2 shows that AC is the exact opposite of DC. In AC electricity, the value of the voltage is ALWAYS changing. The changing AC voltage never stops changing, ever. Hence the word alternating. As you can see, the AC voltage swings from zero at A to +60 to zero to –60 at B during 1 cycle; this cycle repeats 60 times per second.
The critical key point to remember is that lightning is an AC voltage not a DC voltage! This is why using a typical DC ohm meter surrounding lightning situations is virtually useless.
This is a fundamental fact in preventing or stopping lightning damage. Again, lightning is an AC voltage. It has an alternating component and its frequency is in the range of 1 MHz to 10 MHz
In Figure 7, you see how AC traveling down a wire creates a magnetic field. This field is created because the wire has a property called natural inductance, abbreviated L.It is the nature of inductance to resist AC frequency (Figure 3) and NOT a AC voltage. (See Figure 5.) This "AC resistance" of L to AC frequencies is DIRECTLY related to its alternating frequency (NOT the AC voltage level). Example: 500 cycles presents more "AC resistance" than, say, 60 cycles, even though the applied voltages are identical.
The values of "AC resistance" caused by inductance to AC frequency is not called resistance. The correct term for "AC resistor" resistive values are reactance, XL, impedance, etc. The measurement unit of this "AC resistance" is not ohms! Ohms is a DC unit of resistance measurement only.
Among the 3 characteristics of electricity -- voltage, resistance and current -- there is a simple explanation as to how they interact: E = IR. This means the voltage E, equals the current I, times the resistance R. It is that simple. Applying that to lightning, E is the lightning voltage we do NOT want. What to do then? The only variable of the three is R resistance that can be adjusted. In the expression E =IR, if somehow R goes pretty close zero, the voltage E is made near zero also. That is it!
To control/manage/mitigate/prevent the damaging voltage of lightning, you must understand and grasp the existence of the "AC resistor." You must make the "AC resistor" values as low as possible to eliminate the damaging lighting voltages. The only way the "AC resistor" values can be reduced is by minimizing coiling and turns of the wire. When a wire is not straight, from slight bends to full coils, the wire total inductance value L is increased.
The true DC resistance of the wire plays a truly minor part in all lightning issues.
Let's review that one more time. The "AC resistor's" value is solely dependent on the AC frequency. It is not visible, cannot be touched nor easily measured. But, it must be made as low as possible to eliminate the damaging lightning voltage from the strike on the roof. In other words, there is zero lightning voltage across zero "AC resistance".
The inductance of wire is always present. Inductance L is a natural property of metals. What can be controlled concerning inductance is adding additional inductance through excessive lengths of wire, avoiding turns, coils, loops, and, the worst, right angle turns of wires.
Review and Not-So-Shocking Summary
Below are a dozen things to keep in mind as you work to prevent damage to sensitive electronic equipment and injury to those folks in the field.
1. Static building up of negative charges in a cloud is the birthplace of high-voltage lightning energy.
2. The negative charge of the cloud nears a building and forces the negative charges of the building into the dirt. (Remember: Like charges repel.)
3. Eventually the positive building and negative cloud attract each other, and both launch a visible arc toward each other above the building. When they meet you will get the bright flashes of light and the very loud clap of thunder. This is a lightning strike!
4. Static electricity is the initiator and cause of lightning striking a particular location.
5. All wires have natural inductance. When AC frequency encounters inductance, an "AC resistor" is created that cannot be seen, touched, nor easily measured.
6. The "AC resistors" value is directly dependent on the frequency and NOT the applied voltage's value
7. Lightning is an AC voltage that has a frequency of 1 to 10 MHz
8. As the lighting voltage travels from the top of the building to the dirt, the objective is to ensure a low "AC resistive" path so the energy will not flow through electronic equipment nor people. See Figure 4.
9. To prevent lightning damage or prevent future additional lighting damage, it is absolutely necessary to understand "AC resistors". No other choice is possible. The "AC resistor" on Figure 5 that cannot be seen, cannot be felt, nor easily measured is the single largest source of equipment damage by lightning energy. One way or another, if you have equipment that is being damaged by lighting you have an "AC resistor" value that is much too high somewhere!
10. As lightning strikes the tallest object closet to the cloud having the sharpest points, statistically lightning will strike a specific location more than once.
11. Lightning can easily strike if it is raining or not.
12. If you can hear the "boom" or see the "flash" of a lightning strike, you are in range of being harmed.
Gene Thomas has more than 30 years of experience in the communications, electronics, and power industries. His expertise is in planning, engineering, project management, general and technical management, along with installation quality standards development and enforcement. Gene has also created training materials that are used both domestically and internationally. He is a subject matter expert in AC/DC electricity, Echo Cancellers, Network Synchronization (timing), and in all matters surrounding lightning, bonding, grounding, shielding, and preventing electrocution hazards. Gene can be reached via email at firstname.lastname@example.org.
Gene's next article will address lightning damage prevention and mitigation.
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