Slider

Science

SCITECH

AMAZING FACTS

NATURE SPACE

Psychology

Corrosion Types Encountered With Power Cables

Posted date: 11:25 AM / comment : 0 , ,

Corrosion Types Encountered With Power Cables

Corrosion Types Encountered With Power Cables

Introduction

There are numerous types of corrosion, but the ones that are discussed here are the ones that are most likely to be encountered with underground power cable facilities.
In this initial explanation, lead will be used as the referenced metal. Copper neutral wire corrosion is not discussed here.
Stray DC currents come from sources such as welding operations, flows between two other structures, and –in the days gone by — street railway systems.
Anodic corrosion is due to the transfer of direct current from the corroding facility to the surrounding medium, usually earth. At the point of corrosion, the voltage is always positive on the corroding facility.
In the example of lead sheath corrosion, the lead provides a low resistance path for the DC current to get back to its source. At some area remote from the point where the current enters the lead, but near the inception point of that stray current, the current leaves the lead sheath and is again picked up in the normal DC return path.
The point of entry of the stray current usually does not result in lead corrosion, but the point of exit is frequently a corrosion site.
Clean sided corroded pits are usually the result of anodic corrosion. The products of anodic corrosion such as oxides, chlorides, or sulfates of lead are camed away by the current flow. If any corrosion products are found, they are usually lead chloride or lead sulfate that was created by the positive sheath potential that attracts the chloride and sulfate ions in the earth to the lead.
In severe anodic cases, lead peroxide may be formed. Chlorides, sulfates, and carbonates of lead are white, while lead peroxide is chocolate brown.
Cathodic Corrosion
Corrosion of Metal
Corrosion of Metal - Indicative of current movement between Anodic and Cathodic Areas through the Electrolyte. The more conductive the Electrolyte, the higher rate of current movement and more accelerated the rate of corrosion.

Cathodic corrosion is encountered less fiequently than anodic corrosion, especially with the elimination of most street railway systems.
This form of corrosion is usually the result of the presence of an alkali or alkali salt in the earth. If the potential of the metal exceeds -0.3 volts, cathodic corrosion may be expected in those areas.
In cathodic corrosion, the metal is not removed directly by the electric current, but it may be dissolved by the secondary action of the alkali that is produced by the current. Hydrogen ions are attracted to the metal, lose their charge, and are liberated as hydrogen gas.
This results in a decrease in the hydrogen ion concentration and the solution becomes alkaline. The final corrosion product formed by lead in cathodic conditions is usually lead monoxide and lead / sodium carbonate. The lead monoxide formed in this manner has a bright orange / red color and is an indication of cathodic corrosion of lead.
Galvanic Corrosion
Galvanic corrosion occurs when two dissimilar metals in an electrolyte have a metallic tie between them.
One metal becomes the anode and the other the cathode. The anode corrodes and protects the cathode as current flows in the electrolyte between them. The lead sheath of a cable may become either the anode or the cathode of a galvanic cell.
This can happen because the lead sheath is grounded to a metallic structure made of a dissimilar metal and generally has considerable length.
Copper ground rods are frequently a source of the other metal in the galvanic cell. The corrosive force of a galvanic cell is dependent on the metals making up the electrodes and the resistance of the electrolyte in which they exist. This type of corrosion can often be anticipated and avoided by keeping a close watch on construction practices and eliminating installations having different metals connected together in the earth or other electrolyte.
Chemical Corrosion
Chemical corrosion is damage that can be attributed entirely to chemical attack without the additional effect of electron transfer.
The type of chemicals that can disintegrate lead are usually strong concentrations of alkali or acid.
Examples include alkaline solutions from incompletely cured concrete, acetic acid from volatilized wood or jute, waste products from industrial plants, or water with a large amount of dissolved oxygen.
AC Corrosion
Until about 1970, AC corrosion was felt to be an insigruficant, but possible, cause of cable damage.
In 1907, Hayden reporting on tests with lead electrodes, showed that the corrosive effect of small AC currents was less than 0.5 percent as compared with the effects of equal DC currents. Later work using higher densities of AC current has shown that AC corrosion can be a major factor in concentric neutral corrosion.
Local Cell Corrosion
Local cell corrosion, also known as differential aeration in a specific form, is caused by electrolytic cells that are created by an inhomogenious environment where the cable is installed.
Examples include variations in the concentration of the electrolyte through which the cable passes, variations in the impurities of the metal, or a wide range of grain sizes in the backfill. These concentration cells corrode the metal in areas of low ion concentration.
Differential aeration is a specific form of local cell corrosion where one area of the metal has a reduced oxygen supply as compared with nearby sections that are exposed to normal quantities of oxygen.
The low oxygen area is anodic to the higher oxygen area and an electron flow occurs through the covered (oxygen starved) material to the exposed area (normal oxygen level).
Differential aeration corrosion is common for underground cables, but the rate of corrosion is generally rather slow. Examples of situations that can cause this form of corrosion include a section of bare sheath or neutral wires that are laying in a wet or muddy duct or where there are low points in the duct run that can hold water for some distance.
A cable that is installed in a duct and then the cable goes into a direct buried portion is another good example of a possible differential aeration corrosion condition.
Differential aeration corrosion turns copper a bright green.
Other Forms of Corrosion
There are numerous other forms of corrosion that are possible, but the most probable causes have been presented. An example of another form of corrosion is microbiological action of anaerobic bacteria which can exist in oxygen-fiee environments with pH values between 5.5 and 9.0.
The life cycle of anaerobic bacteria depends on the reduction of sulfate materials rather than on the consumption of free oxygen. Corrosion resulting fiom anaerobic bacteria produces sulfides of calcium or hydrogen and may be accompanied by a strong odor of hydrogen sulfide and a build-up of a black slime.
This type of corrosion is more harmful to steel pipes and manhole hardware than to lead sheaths.
Resource: Electrical Power Cable Engineering – William A. Thue

36 Megawatt of Electricity can be produced from Iceland Deep Drilling Project(Volcano)

Posted date: 7:02 PM / comment : 0 , ,


Why volcanoes are the energy source of the future



What's good for Mordor is good for America. AP Photo/Binsar Bakkara
In Iceland, scientists have just completed a successful experiment in harnessing energy directly from a volcano.
+

But first, a little background: In early 2009, I wrote about an audacious project. Scientists in Iceland were going to attempt to drill into a reservoir of water so much hotter than anything tapped before that the water it contained was thought to exist in a fourth state of matter distinct from liquid, solid and steam. This super-heated water, which is in a state known as “supercritical,” that is beyond the point at which a substance can be either a liquid or a gas, exists only under conditions of extreme heat and pressure. Scientists can generate it in the lab, but no one knew if it existed in nature. Researchers believed that in Iceland’s water-logged subterranean depths, close to the fire-breathing hearts of its many volcanoes, they might find supercritical water.
1

It would be a world-changing discovery, because if you can get supercritical water to the earth’s surface and into a power plant, you can extract ten times as much energy from it as you can from typical steam or hot water. The government of Iceland, various engineering firms and foreign partners were so excited about the potential of supercritical water (also called supercritical steam, since in some ways it behaves like steam) that they envisioned pockmarking Iceland with advanced geothermal power plants with wells extending down into the country’s volcanoes like steel-clad straws, generating so much surplus energy that Iceland could lay power cables to Europe and help its friends on the Continent kick their fossil fuel habit.
+

But then disaster struck: In June of 2009 (pdf) scientists on what was known as the Iceland Deep Drilling Project struck magma—actual liquid rock—with their drill. That, I was told at the time, was the end of their quest to find a reservoir of supercritical water flowing in the bowels of a volcano. Hitting magma before the supercritical water meant no more drilling to a target depth of 4.5km (2.8 miles) below the earth’s surface—everyone assumed that the project was a failure.
+

Fast forward to the present day, and a surprising result has been just announced in the journal Geothermics: Rather than give up when their initial plan failed, the engineers decided to see whether the hole they drilled would form a reservoir of usable hot water on its own, as water from the surrounding, fractured rock flowed past the magma. Astonishingly, it worked. Two years later, the scientists were able to draw water from their well at 450°C (842°F), a world record.
+

While 450°C is not hot enough at atmospheric pressure to be supercritical, it still contains an enormous amount of usable energy. As a result, engineers estimated they could use the well to create a power plant capable of generating 36 megawatts of electricity. That’s 20 times less than what a typical coal-fired power plant can generate, but it’s often the case that a geothermal power plant will have more than one well. Plus, geothermal power doesn’t come with any fuel costs or appreciable carbon emissions.
+

So can the Icelandic Deep Drilling project ultimately be judged a success? While it didn’t achieve its stated and rather outlandish original goal, the engineers involved did manage a world first: tapping directly into a volcano and transforming the molten rock into a source of power. It’s been estimated that only a small fraction of Iceland’s geothermal resources have been tapped, and the potential to drill directly into volcanoes could mean that the country could become the renewable power plant for Europe, after all. Unlike wind and solar, geothermal power never switches off.

Wireless Transmission of Electricity

Posted date: 11:42 AM / comment : 0 ,

Wireless Transmission of Electricity

Intel recently announced a display of some new technology which looks like another step along the way to a good proof of concept of efficient wireless electricity.
Building on Marin Soljacic’s work at MIT (it’s unclear to me whether Intel is actually building on top of the work of Marin’s group or if they’re working in parallel) the group from Intel is displaying the transfer of energy without wires from a transmitter to a receiver separated only by air which in result lights a light bulb.
Intel’s demonstration was covered by Gizmodo and has a nice description and some great pictures.Two years ago Marin Soljacic’s group out of MIT made their first announcements of their plans to use electromagneticinduction (the transfer of energy through the conversion of electric charge to magnetism and vice-versa) to transfer energy through the air from a sending device to a receiving device. The trick to keeping everything safe for humans and electronic devices sharing the air in between was to use a very low power signal and to then use the principle of resonant energy transfer.

This is essentially pushing on a wave at a frequency that in result magnifies the strength of the wave. In plain English, think about pushing someone swinging on a play groun dswing. If you push them at the right time during their swing you will increase the speed at which they swing and the distance they cover. Push at the wrong time and you slow them down. The same concept allows your standard AM/FM radio to tune into a radio wave frequency..

How Wireless Power Works

Unless you are particularly organized and good with tie wrap, you probably have a few dusty power cord tangles around your home. You may have even had to follow one particular cord through the seemingly impossible snarl to the outlet, hoping that the plug you pull will be the right one. This is one of the downfalls of electricity. While it can make people's lives easier, it can add a lot of clutter in the process.
For these reasons, scientists have tried to develop methods of wireless power transmission that could cut the clutter or lead to clean sources of electricity. While the idea may sound futuristic, it isn't particularly new. Nicola Tesla proposed theories of wireless power transmission in the late 1800s and early 1900s. One of his more spectacular displays involved remotely powering lights in the ground at his Colorado Springs experiment station.
Tesla's work was impressive, but it didn't immediately lead to widespread, practical methods for wireless power transmission. Since then, researchers have developed several techniques for moving electricity over long distances without wires. Some exist only as theories or prototypes, but others are already in use. If you have an electric toothbrush, for example, you probably take advantage of one method every day.
The wireless transmission of energy is common in much of the world. Radio waves are energy, and people use them to send and receive cell phone, TV, radio and WiFi signals every day. The radio waves spread in all directions until they reach antennae that are tuned to the right frequency. A similar method for transferring electrical power would be both inefficient and dangerous.
For example, a toothbrush's daily exposure to water makes a traditional plug-in charger potentially dangerous. Ordinary electrical connections could also allow water to seep into the toothbrush, damaging its components. Because of this, most toothbrushes recharge through inductive coupling. See the next page to learn more about how inductive coupling works.

Inductive Coupling

Inductive coupling uses magnetic fields that are a natural part of current's movement through­ wire. Any time electrical current moves through a wire, it creates a circular magnetic field around the wire. Bending the wire into a coil amplifies the magnetic field. The more loops the coil makes, the bigger the field will be.
If you place a second coil of wire in the magnetic field you've created, the field can induce a current in the wire. This is essentially how a transformer works, and it's how an electric toothbrush recharges. It takes three basic steps:
Current from the wall outlet flows through a coil inside the charger, creating a magnetic field. In a transformer, this coil is called the primary winding.
When you place your toothbrush in the charger, the magnetic field induces a current in another coil, or secondary winding, which connects to the battery.
This current recharges the battery.
You can use the same principle to recharge several devices at once. For example, the Splash power recharging mat and Edison Electric's Power desk both use coils to create a magnetic field. Electronic devices use corresponding built-in or plug-in receivers to recharge while resting on the mat. These receivers contain compatible coils and the circuitry necessary to deliver electricity to devices' batteries.
 

A newer theory uses a similar set-up to transmit electricity over longer distances.

Subscribe to: Posts (Atom)
Copyright © 2014 Science and Nature
⬆
Top