From the outset, a lightning seems far removed from an electrical system. Yet the protection from lightning strikes and from the damages caused by surges due to lightning strikes is an integral part of any electrical installation.
Men since the ancient times believed that a lightning strike was a demonstration of God's power, which He used as a weapon to punish those who commit great sins on earth.
Whatever the truth is, men today has developed a far more advanced knowledge and technology with regard to the lightning strikes and their effects than their ancient ancestors. Yet throughout the world the lightning strikes cause countless fatalities and material damages. Either through ignorance or an insufficient understanding of the principles underlying the theory and the practice of lightning protection.
Seen from the perspective of a building structure, lightning protection generally consist of 3 sections: aerial conductor network, the down conductors, and the earthing system. By design, the function of the aerial conductor network is to present at the highest point of the structures an area that will attract the lightning strike away from other parts of the building. The current of the strike will then be routed down through the down conductors to the earth grounding rod at the ground level or the lowest level in multiple basement structures.
The purpose of the earthing part is to help dissipate the discharge of the 200 kilo-ampere electrical energy into the earth mass as quickly as possible. This is very critical to the performance of the whole system, because a lower rate of dissipation will expose a higher risk of injuries or fatalities due to gradient voltage. Also damage to properties from flashover to ungrounded nearby metal parts.
Aerial Conductor Network
The aerial conductor network is designed to basically attract the lightning strikes. It is supposed to be where the lightning will strike when they attack a building structure. Therefore the aerial conductor network must be installed at the highest floor of the building structure.
Basically the intention is to create a network of conductors so that no point on the roof is more than five meters away from the nearest conductor of the network. Where a structure is raised above the roof level of a building (eg. lift motor room) then that part of the structure shall have their own aerial network conductor which shall be properly bonded to the overall buildings lightning protection scheme.
With the popularity of the new technology of lightweight all-metal roofing system, questions often arises whether the whole metal roofing system can be bonded to and form part of the lightning protection system without the need for a separate aerial conductor network.
Theoretically "Yes", these metal roofing system scan be used as the aerial conductor network and they have been practically installed to also serve that puspose for a while. Even though in many cases the aerial conductor network are still installed as a precaution.
However the development in the metal roofing system has resuled in the use of very thin roofing sheets that they require some form of metal parts to hold them together and to the roof structure. The effect is basically a complete isolation of a sheet fro the adjacent one, and to the roof structure. In these cases it is absolutely necesary to install a separate aerial conductor network.
Down conductors
The down conductor carries the 200kA electrical surge straight down to the earth mass. Due to the magnitude and the extremely steep front of the electrical surge, the current must be carried to the ground by the shortest possible route. Failure to do so will increase considerable the risk of side flashover.
The down conductor should be arranged to spread as uniformly as possible around the perimeter of the building at approximately 20 m spacing. They must follow the most direct path to the ground with a minimum number of bends. In difficult situations like at parapet walls, a loop-around turn must be avoided to prevent flashover. At 1.5 meter above ground, a test point must be provided at each down conductor. Here a bimetallic connector must also be installed if aluminum is used as the down conductor and the conductor below the test point to earth is copper.
Below the 1.5m test points, until terminations at the earth terminals inside the earth chambers, the down conductors must be installed inside a PVC pipe to protect it from the effects of corrosion and damage. Also to prevent a person or other metal parts from touching the conductors during lightning strike.
Copper used to be the conductor of choice for the whole lightning protection system including the down conductor in this country. But in the last ten years many engineers turn to aluminum for all parts above the test points. Parts of the reasons are the rising cost of copper materials. The other reason is vandalism. The vandalism factor is highly dangerous to the integrity of a lightning protection. This is due to the fact that it operates in silence and it is generally maintenance-free. A missing part at a few down conductors may not be noticed until the damages have been done.
This brings us to the very reason a lightning protection system must be regularly inspected. It will also ensure i is providing optimum protection. This will also check if there are other metal works within the flashover distance that is not properly bonded to the system.
Earth electrodes
The down conductors are routed along the most direct path to the ground and terminates to the lightning protection earthing system. These earthing systems usually steel reinforced copper rod half an inch in diameter, and driven a few feet deep into the ground.
Other methods are also used instead of the deep driven steel rods to provide the best possible contact with the earth mass. The choice depends on the prevailing ground conditions: the soils resistivity and the soil moisture content.In urban areas, a few earth rods are installed first and their combined resistance is measured. More rods are driven and connected until the 10-ohm requirement is met. However in locations away from recent developments, the soil conditions are not known. So the soil resistivity tests must be carried out to determine the earthing method most suitable and the extent of the work required.
At times when the soil is sitting on rocky subsoil below ground, a hole has to be drilled down 100 m or more and a long copper rod inserted deep into the hole to get the 10-ohm requirement. In more extreme cases, even this is not enough and soil conditioning agents like Bentonite or conductive cement need to be used. These compounds are prepared as a slurry or mix, and poured down the vertically drilled hole, creating a lower resistance between the embedded copper earth electrode and the surrounding soil.
The performance of a lightning protection is only as good as it weakest link. Any weakness along the flow path of the surge from the aerial conductor network down to the earth chamber can cause a side flashover to the building structure. A flashover means the surge current has taken an un-controllable path to the ground, causing damage to properties and possibly injuring persons along the way.Therefore it is vital that a lightning protection system is inspected properly and regularly. Recording of the tests must be done according to the latest international standards.
By the very nature of lightning strikes, no international standard can guarantee a total protection from their strikes. However, by obeying the latest international standards, we can ensure that the risk of damage and danger to human lives has been reduced to minimal.
Showing posts with label Home. Show all posts
Showing posts with label Home. Show all posts
Monday, July 6, 2009
How Does Electricity Produce Light
In order to understand how a home electrical installation works, one need to understand the basics of electricity itself. In this article I will try to explain in an easy to understand way how electricity is produced, and how it is utilized by the simplest equipment, the light bulb, to produce light. This article is not for technicians or engineers. It is for those people who have been using electricity all their lives without knowing at all how it works, how it causes fire or how it kills people.
a) How is Electricity Produced?
The discovery of electricity is one of the most important discoveries of our world. It is from electricity that many of the wonderful modern inventions have been created. The refrigerator, the electric bulb, radio and telephone have all been invented after the discovery of electricity.
Two things have allowed the production of useful electricity: magnetic field and electrons. Magnetic field is an invisible force and it has always been around us. The earth itself produces magnetic field. That is why we can use a compass to tell a direction correctly and consistently. The needle of a compass always align itself with the earth's magnetic field. In other words, the earth magnetic field forces the compass needle to align itself. This means the magnetic field can exert an invisible force on some things.
The second is something that scientists call electrons. Actually electrons are present in all matters. But it is the electrons within metal materials that were found useful for the production of electricity. The electrons within a length of metal can easily travel along the length of the metal when it is moved within a magnetic field. The magnetic field used to produce electricity is not the earth's magnetic field, but from magnets. When it was first discovered magnets were just natural materials found in the environment, but later development of knowledge and technologies allow it to be artificially produced.
Electricity that we use in our homes comes from power plants. In order to produce electricity, metals in the form of wires are continuously moved at high speed within a strong magnetic field. The energy to keep moving the wires within the magnetic field comes from coals, nuclear fuels or even the wind energy. The continuous movement creates a continuous flow of electrons along the metal wires.This electron flow is what we call electric current.
By having cables (i.e. metal wires insulated by materials that cannot conduct electrons) connecting the power plant to our houses, the flow of electrons is channeled to our homes. Of course we can buy our own power plant if we want, that is the small electric power generator. In that case we can actually disconnet the cables from the power company and connect the small electric generator with cables directly to the house distribution board. I will post some articles on these small electric generators later, but for now let's just concentrate on the basics of electricity first.
b) How Does a Bulb Produce Light
At the power plant, coal or other sources of energy is used to power machines that force huge numbers of electrons to continuously flow along the inside electrical wires and cables into our houses. When inside a house, the electrons continue flowing along the inside the house wiring cables into the electric bulbs and other electrical appiances.
The light bulb itself has two insulated cables connected to it. One is the live cable, and the other is the neutral or "return" cable. The electrons flow from the power plant to the light bulb inside the house through the live cable and flow back to the power plant through the neutral cable. That is why it is also called the "return" cable.
What if the return wire is broken, and the electrons cannot flow back to the power plant? Then the electrons cannot flow (i.e. no current flow) and the light bulb will not light up. This is to say that the the electrons must keep flowing continuously from the power plant to the house and back to the power plant, and then back again to the the house, again and again. In other words they move back and forth in circle, or in a "loop".
This is one of the most important requirements of an electrical installation for it to work properly and safely: the electrons must be able to keep flowing inside the live and the neutral cables in a "loop".
If the loop is broken (i.e. the wire or the cable is broken somewhere along its path), then what will happen to the electricity? The electrons inside the live cable just before the wire break are still there, and they are still under the force of the the magnetic field at the power plant. If a person accidentally touch the metal wire or the metal part of the insulated cable, that person will get electrocuted. This is because the electrons are still under force or under pressure, just like the the water under pressure in a water pipe. When come into contact, the electrons inside the wire will try to flow through the human body to go into the earth mass. They will try to do this in order to flow back to the power plant to complete the "loop".
As explained above, when the loop is broken the bulb will not light up, but the electron under pressure are still there unless the power plant is shut down. This is one of the common scenarios very dangerous to home users. But it is a topic suitable for a separate article by itself.
So how does the light get produced inside a bulb? Inside the bulb is a length of a very thin metal wire that lets the electrons flow through. However this wire is very thin, and when huge quantities of electrons flow through it continuously, the electrons keep knocking on each other while flowing through at the thin section. This electron behaviour releases a lot of heat energy, making the wire so hot that it glows, releasing heat and light. That is how we get the light from the bulb.
That's it for now. In future articles we will continue our journey along the flow path of the electrons so we can better understand their behaviour. This is very important in order to understand how the home electrical installation works and how to ensure the safety of our families and properties.
a) How is Electricity Produced?
The discovery of electricity is one of the most important discoveries of our world. It is from electricity that many of the wonderful modern inventions have been created. The refrigerator, the electric bulb, radio and telephone have all been invented after the discovery of electricity.
Two things have allowed the production of useful electricity: magnetic field and electrons. Magnetic field is an invisible force and it has always been around us. The earth itself produces magnetic field. That is why we can use a compass to tell a direction correctly and consistently. The needle of a compass always align itself with the earth's magnetic field. In other words, the earth magnetic field forces the compass needle to align itself. This means the magnetic field can exert an invisible force on some things.
The second is something that scientists call electrons. Actually electrons are present in all matters. But it is the electrons within metal materials that were found useful for the production of electricity. The electrons within a length of metal can easily travel along the length of the metal when it is moved within a magnetic field. The magnetic field used to produce electricity is not the earth's magnetic field, but from magnets. When it was first discovered magnets were just natural materials found in the environment, but later development of knowledge and technologies allow it to be artificially produced.
Electricity that we use in our homes comes from power plants. In order to produce electricity, metals in the form of wires are continuously moved at high speed within a strong magnetic field. The energy to keep moving the wires within the magnetic field comes from coals, nuclear fuels or even the wind energy. The continuous movement creates a continuous flow of electrons along the metal wires.This electron flow is what we call electric current.
By having cables (i.e. metal wires insulated by materials that cannot conduct electrons) connecting the power plant to our houses, the flow of electrons is channeled to our homes. Of course we can buy our own power plant if we want, that is the small electric power generator. In that case we can actually disconnet the cables from the power company and connect the small electric generator with cables directly to the house distribution board. I will post some articles on these small electric generators later, but for now let's just concentrate on the basics of electricity first.
b) How Does a Bulb Produce Light
At the power plant, coal or other sources of energy is used to power machines that force huge numbers of electrons to continuously flow along the inside electrical wires and cables into our houses. When inside a house, the electrons continue flowing along the inside the house wiring cables into the electric bulbs and other electrical appiances.
The light bulb itself has two insulated cables connected to it. One is the live cable, and the other is the neutral or "return" cable. The electrons flow from the power plant to the light bulb inside the house through the live cable and flow back to the power plant through the neutral cable. That is why it is also called the "return" cable.
What if the return wire is broken, and the electrons cannot flow back to the power plant? Then the electrons cannot flow (i.e. no current flow) and the light bulb will not light up. This is to say that the the electrons must keep flowing continuously from the power plant to the house and back to the power plant, and then back again to the the house, again and again. In other words they move back and forth in circle, or in a "loop".
This is one of the most important requirements of an electrical installation for it to work properly and safely: the electrons must be able to keep flowing inside the live and the neutral cables in a "loop".
If the loop is broken (i.e. the wire or the cable is broken somewhere along its path), then what will happen to the electricity? The electrons inside the live cable just before the wire break are still there, and they are still under the force of the the magnetic field at the power plant. If a person accidentally touch the metal wire or the metal part of the insulated cable, that person will get electrocuted. This is because the electrons are still under force or under pressure, just like the the water under pressure in a water pipe. When come into contact, the electrons inside the wire will try to flow through the human body to go into the earth mass. They will try to do this in order to flow back to the power plant to complete the "loop".
As explained above, when the loop is broken the bulb will not light up, but the electron under pressure are still there unless the power plant is shut down. This is one of the common scenarios very dangerous to home users. But it is a topic suitable for a separate article by itself.
So how does the light get produced inside a bulb? Inside the bulb is a length of a very thin metal wire that lets the electrons flow through. However this wire is very thin, and when huge quantities of electrons flow through it continuously, the electrons keep knocking on each other while flowing through at the thin section. This electron behaviour releases a lot of heat energy, making the wire so hot that it glows, releasing heat and light. That is how we get the light from the bulb.
That's it for now. In future articles we will continue our journey along the flow path of the electrons so we can better understand their behaviour. This is very important in order to understand how the home electrical installation works and how to ensure the safety of our families and properties.
Home Electrical Installation - How it works
In this article I will explain the skeleton of how a home electrical installation works. The content of this article is very basic. It is not for technicians or engineers. It is for those people who have been using electricity all their lives without knowing at all how it works, how it causes fire or how it kills people.
The electrical current that goes into our homes come from the electricity supply company's distribution network, usually in the form of overhead cables running on concrete poles or using cables buried one meter below the ground. When the cables reach a residential house, they usually enter the house through the front entrance and connect to a meter panel. Together with the meter on the panel is also a cut-out fuse. The meter and the fuse usually belong to the supply company. From the meter panel the electrical cables go to the home distribution panel. On the panel are usually an isolation switch, a leakage protection circuit breaker and a few outgoing fuses or outgoing circuit breakers. From the outgoing fuses or circuit breakers the wiring cables run above the ceiling, inside or on the surface of the wall, or concealed inside the concrete floor to go the lamps, ceiling fans, socket outlets and other equipment like the toilet exhaust fans in our homes.
When a home user connects an electrical appliance to a socket outlet, the connection is usually made by the use of an electrical cord. One end of the cord has a plug unit (sometimes the plug unit contains a fuse) that is inserted to the power socket (i.e.wall plug). The other end will be plugged to another socket already built-in on the appliance. Now and then the location of the electrical appliance need to be quite a few meters away from the wall socket outlet. The electrical cord provided with the appliance is usually between one to one and a half meters long. In these cases home users usually purchase an extension cord to connect between the wall socket and the appliance's electrical cord.
From the viewpoint of the electrical current flow, the supply uses only two wires. That is why in some countries or regions we can see only two big wires coming down from the electric pole to a house. One of them is called the live wire, "hot" wire or phase wire. It is this wire that is "dangerous". The second wire is called the neutral wire or the "return" wire. The electric current flow into the house will come out again (i.e. return) in the same magnitude and goes back into the supply company's transformer or generator. This electrical path forms a complete "loop", like a circle. The continuous and circulating flow of this electrical current is what makes the filament inside the house incandescent lamp burns and produce light that brightens our house. This behaviour of the home electrical system brighten and enrich our lives. When used and handled properly, electricity is very useful and friendly. It is however very powerful and dangerous, and therefore must be treated with respect.
With the two wires described above, we can have electricity in our home that can keep our food fresh in the refrigerator and replace the candles to light up the house during the night. However with just these two wires, it is like driving an car at high speed without the brake. Driving the car without a brake is extremely dangerous even on an empty freeway that has no traffic light for hundreds of kilometers at three in the morning. As in driving, we need to step on the brake now and then to slow down, or during an emergency.
In a home electrical system, this braking is accomplished through a third wire, the earth wire. Many electrical terms are commonly used for this wire such as earthing wire, ground wire, chasis wire or protective wire. In a house, this earth wire is almost always colored green or green with yellow stripes. The wire connects the metal casing of the electrical appliance in our homes to the "earth body". (Really, it is actually connected to the huge mass of the earth.) When the "hot" or live wire somehow come into contact with the outer metal casing of your washing machine, for example, then the fuse at the distribution board will immediately blow, stopping the current flow to the metal casing of the washing machine so we do not get the shock, a fatal shock actually. Where the distribution board uses a circuit breaker instead , the circuit breaker immediately trips, cutting off the supply just like the fuse does.
If the green wire is broken, or it does not connect properly along its path to the earth body, then the electrical power has no brake. The person touching the washing machine's metal casing can get electrocuted.
So do treat the electrical wiring and electrical appliances in your home with respect. Safety comes first. In future articles I will explain more on the "earth wire" and I will also give more tips and techniques on how to make sure your home electrical installation is safe for you and your family.
The electrical current that goes into our homes come from the electricity supply company's distribution network, usually in the form of overhead cables running on concrete poles or using cables buried one meter below the ground. When the cables reach a residential house, they usually enter the house through the front entrance and connect to a meter panel. Together with the meter on the panel is also a cut-out fuse. The meter and the fuse usually belong to the supply company. From the meter panel the electrical cables go to the home distribution panel. On the panel are usually an isolation switch, a leakage protection circuit breaker and a few outgoing fuses or outgoing circuit breakers. From the outgoing fuses or circuit breakers the wiring cables run above the ceiling, inside or on the surface of the wall, or concealed inside the concrete floor to go the lamps, ceiling fans, socket outlets and other equipment like the toilet exhaust fans in our homes.
When a home user connects an electrical appliance to a socket outlet, the connection is usually made by the use of an electrical cord. One end of the cord has a plug unit (sometimes the plug unit contains a fuse) that is inserted to the power socket (i.e.wall plug). The other end will be plugged to another socket already built-in on the appliance. Now and then the location of the electrical appliance need to be quite a few meters away from the wall socket outlet. The electrical cord provided with the appliance is usually between one to one and a half meters long. In these cases home users usually purchase an extension cord to connect between the wall socket and the appliance's electrical cord.
From the viewpoint of the electrical current flow, the supply uses only two wires. That is why in some countries or regions we can see only two big wires coming down from the electric pole to a house. One of them is called the live wire, "hot" wire or phase wire. It is this wire that is "dangerous". The second wire is called the neutral wire or the "return" wire. The electric current flow into the house will come out again (i.e. return) in the same magnitude and goes back into the supply company's transformer or generator. This electrical path forms a complete "loop", like a circle. The continuous and circulating flow of this electrical current is what makes the filament inside the house incandescent lamp burns and produce light that brightens our house. This behaviour of the home electrical system brighten and enrich our lives. When used and handled properly, electricity is very useful and friendly. It is however very powerful and dangerous, and therefore must be treated with respect.
With the two wires described above, we can have electricity in our home that can keep our food fresh in the refrigerator and replace the candles to light up the house during the night. However with just these two wires, it is like driving an car at high speed without the brake. Driving the car without a brake is extremely dangerous even on an empty freeway that has no traffic light for hundreds of kilometers at three in the morning. As in driving, we need to step on the brake now and then to slow down, or during an emergency.
In a home electrical system, this braking is accomplished through a third wire, the earth wire. Many electrical terms are commonly used for this wire such as earthing wire, ground wire, chasis wire or protective wire. In a house, this earth wire is almost always colored green or green with yellow stripes. The wire connects the metal casing of the electrical appliance in our homes to the "earth body". (Really, it is actually connected to the huge mass of the earth.) When the "hot" or live wire somehow come into contact with the outer metal casing of your washing machine, for example, then the fuse at the distribution board will immediately blow, stopping the current flow to the metal casing of the washing machine so we do not get the shock, a fatal shock actually. Where the distribution board uses a circuit breaker instead , the circuit breaker immediately trips, cutting off the supply just like the fuse does.
If the green wire is broken, or it does not connect properly along its path to the earth body, then the electrical power has no brake. The person touching the washing machine's metal casing can get electrocuted.
So do treat the electrical wiring and electrical appliances in your home with respect. Safety comes first. In future articles I will explain more on the "earth wire" and I will also give more tips and techniques on how to make sure your home electrical installation is safe for you and your family.
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