Magnetic Levitation Train

Maglev (derived from magnetic levitation) is a system of transportation that uses magnetic levitation to suspend, guide and propel vehicles with magnets rather than using mechanical methods, such as wheels, axles and bearings. With maglev a vehicle is levitated a short distance away from a guide way using magnets to create both lift and thrust. High-speed maglev train solutions promise dramatic improvements for human travel if widespread adoption occurs.

Maglev Trains work with an electro magnet, Maglev trains move more smoothly and somewhat more quietly than wheeled mass transit systems. Their non-reliance on friction means that acceleration and deceleration can surpass that of wheeled transports, and they are unaffected by weather. The power needed for levitation is typically not a large percentage of the overall energy consumption ^.most of the power is used to overcome air resistance (drag), as with any other high-speed form of transport. Although conventional wheeled transportation can go very fast, maglev allows routine use of higher top speeds than conventional rail, and this type holds the speed record for rail transportation. Vacuum tube train systems might hypothetically allow maglev trains to attain speeds in a different order of magnitude, but no such tracks have ever been built.
Compared to conventional wheeled train’s differences in construction affect the economics. With wheeled trains, at very high speeds, the wear and tear from friction along with the concentrated pounding from wheels on rails accelerates equipment deterioration and prevent mechanically-based train systems from routinely achieving higher speeds.^[3] Conversely, maglev tracks have historically been found to be much more expensive to construct, but require less maintenance and have low ongoing costs.


Despite decades-long research and development, there are presently only two commercial maglev transport systems in operation, with two others under construction. In April 2004, Shanghai began commercial operations of the high-speed Tran rapid system. In March 2005, Japan began operation of the relatively low-speed HSST "Linimo" line in time for the 2005 World Expo. In its first three months, the Linimo line carried over 10 million passengers. South Korea and the People's Republic of China are both building low-speed maglev lines of their own design, one in Beijing and the other at Seoul's Incheon Airport. Many maglev projects are controversial, and the technological potential, adoption prospects and economics of maglev systems have often been hotly debated. The Shanghai system has been accused of being a white elephant.

analog electronics , semiconductors, Drift current, Diffusion current

ANALOG ELECTRONICS:

SEMICONDUCTORS:

intrinsic semiconductors:

An intrinsic semiconductor, also called an undoped semiconductor or i-type semiconductor, is a pure semiconductor without any significant dopant species present. The number of charge carriers is therefore determined by the properties of the material itself instead of the amount of impurities. In intrinsic semiconductors the number of excited electrons and the number of holes are equal: n = p.

The electrical conductivity of intrinsic semiconductors can be due to crystallographic defects or electron excitation. In an intrinsic semiconductor the number of electrons in the conduction band is equal to the number of holes in the valence band. An example is Hg_0.8Cd_0.2Te at room temperature.

Extrinsic semiconductror:

An extrinsic semiconductor is a semiconductor that has been doped, that is, into which a doping agent has been introduced, giving it different electrical properties than the intrinsic (pure) semiconductor.

Doping involves adding dopant atoms to an intrinsic semiconductor, which changes the electron and hole carrier concentrations of the semiconductor at thermal equilibrium. Dominant carrier concentrations in an extrinsic semiconductor classify it as either an n-type or p-type semiconductor. The electrical properties of extrinsic semiconductors make them essential components of many electronic devices.

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	Intrinsic semiconductor	Donor atoms	Acceptor atoms
Group IV semiconductors	Silicon, Germanium	Phosphorus, Arsenic	Boron, Aluminium
Group III-V semiconductors	Aluminum phosphide, Aluminum arsenide, Gallium arsenide, Gallium nitride	Selenium, Tellurium, Silicon,Germanium	Beryllium, Zinc, Cadmium, Silicon,Germanium

N-type semiconductors

Main article: N-type semiconductor

Band structure of an n-type semiconductor. Dark circles in the conduction band are electrons and light circles in the valence band are holes. The image shows that the electrons are the majority charge carrier.

Extrinsic semiconductors with a larger electron concentration than hole concentration are known as n-type semiconductors. The phrase 'n-type' comes from the negative charge of the electron. In n-type semiconductors, electrons are the majority carriers and holes are the minority carriers. N-type semiconductors are created by doping an intrinsic semiconductor with donor impurities. In an n-type semiconductor, theFermi energy level is greater than that of the intrinsic semiconductor and lies closer to the conduction band than the valence band.

P-type semiconductors

Main article: P-type semiconductor

Band structure of a p-type semiconductor. Dark circles in the conduction band are electrons and light circles in the valence band are holes. The image shows that the holes are the majority charge carrier

As opposed to n-type semiconductors, p-type semiconductors have a larger hole concentration than electron concentration. The phrase 'p-type' refers to the positive charge of the hole. In p-type semiconductors, holes are the majority carriers and electrons are the minority carriers. P-type semiconductors are created by doping an intrinsic semiconductor with acceptor impurities. P-type semiconductors have Fermi energy levels below the intrinsic Fermi energy level. The Fermi energy level lies closer to the valence band than the conduction band in 

Drift current:

In condensed matter physics and electro chemistry, drift current is the electric current, or movement of charge carriers, which is due to the applied electric field, often stated as the electromotive force over a given distance. When an electric field is applied across a semiconductor material, a current is produced due to flow of charge carriers.

The drift velocity is the average velocity of the charge carriers in the drift current. The drift velocity, and resulting current, is characterized by the mobility; for details, see electron mobility (for solids) or electrical mobility (for a more general discussion).

                                V  = E

Here v=velocity

 =mobility,E=electric field


Diffusion current:

Diffusion current is a current in a semiconductor caused by the diffusion of charge carriers (holes and/or electrons). Diffusion current can be in the same or opposite direction of adrift current, that is formed due to the electric field in the semiconductor. At equilibrium in a p–n junction, the forward diffusion current in the depletion region is balanced with a reverse drift current, so that the net current is zero. The diffusion current and drift current together are described by the drift–diffusion equation.

What is a transformer? How does it works ?

What is a transformer? How does it works ?

Transformer is a constant power, frequency, flux device. This converts voltage from step up to step down or vice versa. This works on the principle of mutual induction.

A transformer is an electrical device which converts alternating current from one voltage to another. It can be designed to "step-up" or "step-down" voltages and works on the magnetic induction principle. A transformer has no moving parts and is a completely static solid state device which insures, under normal operating conditions, a long and trouble-free life. A transformer consists of two or more coils of insulated wire wound on a laminated steel core. When voltage is introduced into one coil (called the primary), it magnetizes the iron core. As a result, a voltage is induced into the secondary or output coil. The change of voltage (voltage ratio) between the primary and secondary depends on the turn’s ratio of the two coils.

A transformer operates on the principle of magnetic induction. Each transformer consists of two or more coils of insulated conductor (wire) wound on a laminated steel core. When a voltage is supplied to the PRIMARY (input) coil, it magnetizes the steel core, which in turn induces a voltage on the SECONDARY (output) coil. The voltage induced from the primary to the secondary coils is directly proportional to the turn’s ratio between the two coils.

For example, if a transformer's input or primary leg has twice as many turns of wire as the secondary, then the ratio would be 2:1. Therefore, if you applied 200 volts to the primary, 100 volts would be induced in the secondary. This is an example of a two winding "step-down" transformer. If the voltage is to be "stepped-up" or increased, the same transformer could be turned around and connected so that the input side would have the 100 volts and the output would be 200 volts. Standard transformers rated at 3kVA and larger can be used for either step-up or step-down service. Transformers rated 2kVA and below have compensated windings and should not be used in reverse feed applications.

Formulas:

Transformation ratio (k) = N2/N1       N1: primary turns, N2: secondary turns

                                     = E2/E1         E1: primary induced EMF, E2: secondary induced EMF

Induced EMF (RMS) E1 = 4.44 Φ fN1         Φ: Maximum flux, f = frequency, N1 = Total Turns on primary

Induced EMF (RMS) E2 = 4.44 Φ fN2         Φ: Maximum flux, f = frequency, N2 = Total Turns on Secondary

Electrical Power Systems 

Brief Definition:-

“Power system deals with generation, transmission and distribution of electrical energy.  Almost all the equipment's like generators, transformers, synchronous motors, induction machines are involved in it.”

Generation:-

Electrical energy generated in two ways

i)                     Conventional Electrical power generation

ii)                   Non – Conventional Electrical power generation

Transmission:-

Generally the power generating stations are located at very far areas from populated areas. so we need a system which transfers power from there to domestic areas, that’s called transmission system.

In transmissions system we will come across equipment's like transformers, PT s, CT s, transmission conductors, etc

Distribution:-

Finally transmitted power will get at substations, from there we need to distribute the power to houses, industries, street lighting, etc., this system is called the distribution system.

In distribution systems we come across equipment's like distribution transformers, capacitor banks, feeders, distributors, etc.