Conversion Table

http://www.mpoweruk.com/conversion_table.htm

1 KiloWatthour (kWh)	=	3.6 MegaJoules (MJ)
1 Joule (J)	=	1 Watt Second
1 Calorie (cal)	=	4.19002 Joules (J)
1 Watt (W)	=	1 Joule/Second (J/s)
1 MegaWatt (MW)	=	1000 Watts (W)
1 Horse Power (hp)	=	746 Watts (W)
Speed of Light (c)	=	300 X 106 metres/second (m/s)

Coulomb force

http://www.britannica.com/EBchecked/topic/140084/Coulomb-force

Coulomb force, also called electrostatic force or Coulomb interaction,  attraction or repulsion of particles or objects because of their electric charge. One of the basic physical forces, the electric force is named for a French physicist, Charles-Augustin de Coulomb, who in 1785 published the results of an experimental investigation into the correct quantitative description of this force.

Two like electric charges, both positive or both negative, repel each other along a straight line between their centres. Two unlike charges, one positive, one negative, attract each other along a straight line joining their centres. The electric force is operative between charges down to distances of at least 10^-16 metre, or approximately one-tenth of the diameter of atomic nuclei. Because of their positive charge, protons within nuclei repel each other, but nuclei hold together because of another basic physical force, the strong interaction, or nuclear force, which is stronger than the electric force. Massive, but electrically neutral, astronomical bodies such as planets and stars are bound together in solar systems and galaxies by still another basic physical force, gravitation, which though much weaker than the electric force, is always attractive and is the dominant force at great distances. At distances between these extremes, including the distances of everyday life, the only significant physical force is the electric force in its many varieties along with the related magnetic force.

The magnitude of the electric force F is directly proportional to the amount of one electric charge, q₁, multiplied by the other, q₂, and inversely proportional to the square of the distance r between their centres. Expressed in the form of an equation, this relation, called Coulomb’s law, may be written by including the proportionality factor k as F = kq₁q₂/r². In the centimetre–gram–second system of units, the proportionality factor k in a vacuum is set equal to 1 and unit electric charge is defined by Coulomb’s law. If an electric force of one unit (one dyne) arises between two equal electric charges one centimetre apart in a vacuum, the amount of each charge is one electrostatic unit, esu, or statcoulomb. In the metre–kilogram–second and the SI systems, the unit of force (newton), the unit of charge (coulomb), and the unit of distance (metre), are all defined independently of Coulomb’s law, so the proportionality factor k is constrained to take a value consistent with these definitions, namely, k in a vacuum equals 8.98 × 10⁹ newton square metre per square coulomb. This choice of value for k permits the practical electrical units, such as ampere and volt, to be included with the common metric mechanical units, such as metre and kilogram, in the same system.

Neodymium magnet

http://en.wikipedia.org/wiki/Neodymium_magnet

A neodymium magnet (also known as NdFeB, NIB or Neo magnet), the most widely used type of rare-earth magnet, is a permanent magnet made from an alloy of neodymium, iron and boron to form the Nd₂Fe₁₄B tetragonal crystalline structure.

Developed in 1982 byGeneral Motors and Sumitomo Special Metals, neodymium magnets are the strongest type of permanent magnet commercially available.They have replaced other types of magnet in the many applications in modern products that require strong permanent magnets, such as motors in cordless tools, hard disk drives and magnetic fasteners.

Description

The tetragonal Nd₂Fe₁₄B crystal structure has exceptionally high uniaxial magnetocrystalline anisotropy (HA~7 teslas - magnetic field strength H in A/m versus magnetic moment in A.m²).^[4] This gives the compound the potential to have high coercivity (i.e., resistance to being demagnetized). The compound also has a high saturation magnetization (J_s ~1.6 T or 16 kG) and typically 1.3 teslas. Therefore, as the maximum energy density is proportional to J_s², this magnetic phase has the potential for storing large amounts of magnetic energy (BH_max ~ 512 kJ/m³ or 64 MG·Oe). This property is considerably higher in NdFeB alloys than in samarium cobalt (SmCo) magnets, which were the first type of rare-earth magnet to be commercialized. In practice, the magnetic properties of neodymium magnets depend on the alloy composition, microstructure, and manufacturing technique employed.

History

In 1982, General Motors (GM) and Sumitomo Special Metals discovered the Nd₂Fe₁₄B compound. The research was initially driven by the high raw materials cost of SmCopermanent magnets, which had been developed earlier. GM focused on the development of melt-spun nanocrystalline Nd₂Fe₁₄B magnets, while Sumitomo developed full-densitysintered Nd₂Fe₁₄B magnets.

GM commercialized its inventions of isotropic Neo powder, bonded Neo magnets, and the related production processes by founding Magnequench in 1986 (Magnequench has since become part of Neo Materials Technology, Inc., which later merged into Molycorp). The company supplied melt-spun Nd₂Fe₁₄B powder to bonded magnet manufacturers.

The Sumitomo facility became part of the Hitachi Corporation, and currently manufactures and licenses other companies to produce sintered Nd₂Fe₁₄B magnets. Hitachi holds more than 600 patents covering neodymium magnets.

Chinese manufacturers have become a dominant force in neodymium magnet production, based on their control of much of the world's sources of rare earth ores.

The United States Department of Energy has identified a need to find substitutes for rare earth metals in permanent magnet technology, and has begun funding such research. TheAdvanced Research Projects Agency has sponsored a Rare Earth Alternatives in Critical Technologies (REACT) program, to develop alternative materials. In 2011, ARPA-E awarded 31.6 million dollars to fund Rare-Earth Substitute projects.

Electric Motor

http://www.britannica.com/EBchecked/topic/182667/electric-motor

electric motor, any of a class of devices that convert electrical energy to mechanical energy, usually by employing electromagnetic phenomena.

Most electric motors develop their mechanical torque by the interaction of conductors carrying current in a direction at right angles to a magnetic field. The various types of electric motor differ in the ways in which the conductors and the field are arranged and also in the control that can be exercised over mechanical output torque, speed, and position.

Induction motors

The simplest type of induction motor is shown in cross section in the figure. A three-phase set ofstator windings is inserted in slots in the stator iron. These windings may be connected either in a wye configuration, normally without external connection to the neutral point, or in a delta configuration. The rotor consists of a cylindrical iron core with conductors placed in slots around the surface. In the most usual form, these rotor conductors are connected together at each end of the rotor by a conducting end ring.

The basis of operation of the induction motor may be developed by first assuming that the stator windings are connected to a three-phase electric supply and that a set of three sinusoidal currents of the form shown in the figure flow in the stator windings. This figure shows the effect of these currents in producing a magnetic field across the air gap of the machine for six instants in a cycle. For simplicity, only the central conductor loop for each phase winding is shown. At the instant t₁ in the figure, the current in phase a is maximum positive, while that in phases b and c is half that value negative. The result is a magnetic field with an approximately sinusoidal distribution around the air gap with a maximum outward value at the top and a maximum inward value at the bottom. At timet₂ in the figure (i.e., one-sixth of a cycle later), the current in phase c is maximum negative, while that in both phase b and phase a is half value positive. The result, as shown for t₂ in the figure, is again a sinusoidally distributed magnetic field but rotated 60° counterclockwise. Examination of the current distribution for t₃, t₄, t₅, and t₆ shows that the magnetic field continues to rotate as time progresses. The field completes one revolution in one cycle of the stator currents. Thus, the combined effect of three equal sinusoidal currents, uniformly displaced in time and flowing in three stator windings uniformly displaced in angular position, is to produce a rotating magnetic field with a constant magnitude and a mechanical angular velocity that depends on the frequency of the electric supply.

The rotational motion of the magnetic field with respect to the rotor conductors causes a voltage to be induced in each, proportional to the magnitude and the velocity of the field relative to the conductors. Since the rotor conductors are short-circuited together at each end, the effect will be to cause currents to flow in these conductors. In the simplest mode of operation, these currents will be about equal to the induced voltage divided by the conductor resistance. The pattern of rotor currents for the instant t₁ of the figure is shown in this figure. The currents are seen to be approximately sinusoidally distributed around the rotor periphery and to be located so as to produce a counterclockwise torque on the rotor (i.e., a torque in the same direction as the field rotation). This torque acts to accelerate the rotor and to rotate the mechanical load. As the rotational speed of the rotor increases, its speed relative to that of the rotating field decreases. Thus, the induced voltage is reduced, leading to a proportional reduction in rotor conductor current and in torque. The rotor speed reaches a steady value when the torque produced by the rotor currents equals the torque required at that speed by the load with no excess torque available for accelerating the combined inertia of the load and the motor.

The mechanical output power must be provided by an electrical input power. The original stator currents shown in the figure are just sufficient to produce the rotating magnetic field. To maintain this rotating field in the presence of the rotor currents of the figure, it is necessary that the stator windings carry an additional component of sinusoidal current of such a magnitude and phase as to cancel the effect of the magnetic field that would otherwise be produced by the rotor currents in thefigure. The total stator current in each phase winding is then the sum of a sinusoidal component to produce the magnetic field and another sinusoid, leading the first by one-quarter of a cycle, or 90°, to provide the required electrical power. The second, or power, component of the current is in phase with the voltage applied to the stator, while the first, or magnetizing, component lags the applied voltage by a quarter cycle, or 90°. At rated load, this magnetizing component is usually in the range of 0.4 to 0.6 of the magnitude of power component.

A majority of three-phase induction motors operate with their stator windings connected directly to a three-phase electric supply of constant voltage and constant frequency. Typical supply voltages range from 230 volts line-to-line for motors of relatively low power (e.g., 0.5 to 50 kilowatts) to about 15 kilovolts line-to-line for high-power motors up to about 10 megawatts.

Except for a small voltage drop in the resistance of the stator winding, the supply voltage is matched by the time rate of change of the magnetic flux in the stator of the machine. Thus, with a constant-frequency, constant-voltage supply, the magnitude of the rotating magnetic field is held constant, and the torque is roughly proportional to the power component of the supply current.

With the induction motor shown in the foregoing figures, the magnetic field rotates through one revolution for each cycle of the supply frequency. For a 60-hertz supply, the field speed is then 60 revolutions per second, or 3,600 per minute. The rotor speed is less than the speed of the field by an amount that is just enough to induce the required voltage in the rotor conductors to produce the rotor current needed for the load torque. At full load, the speed is typically 0.5 to 5 percent lower than the field speed (often called synchronous speed), with the higher percentage applying to smaller motors. This difference in speed is frequently referred to as the slip.

Other synchronous speeds can be obtained with a constant frequency supply by building a machine with a larger number of pairs of magnetic poles, as opposed to the two-pole construction of thefigure. The possible values of magnetic-field speed in revolutions per minute are 120 f/p, where f is the frequency in hertz (cycles per second) and p is the number of poles (which must be an even number). A given iron frame can be wound for any one of several possible numbers of pole pairs by using coils that span an angle of approximately (360/p)°. The torque available from the machine frame will remain unchanged, since it is proportional to the product of the magnetic field and the allowable coil current. Thus, the power rating for the frame, being the product of torque and speed, will be roughly inversely proportional to the number of pole pairs. The most common synchronous speeds for 60-hertz motors are 1,800 and 1,200 revolutions per minute.

Permanent-magnet motors

The magnetic field for a synchronous machine may be provided by using permanent magnets made of neodymium-boron-iron, samarium-cobalt, or ferrite on the rotor. In some motors, these magnets are mounted with adhesive on the surface of the rotor core such that the magnetic field is radially directed across the air gap. In other designs, the magnets are inset into the rotor core surface or inserted in slots just below the surface. Another form of permanent-magnet motor has circumferentially directed magnets placed in radial slots that provide magnetic flux to iron poles, which in turn set up a radial field in the air gap.

The main application for permanent-magnet motors is in variable-speed drives where the stator is supplied from a variable-frequency, variable-voltage, electronically controlled source. Such drives are capable of precise speed and position control. Because of the absence of power losses in the rotor, as compared with induction motor drives, they are also highly efficient.

Permanent-magnet motors can be designed to operate at synchronous speed from a supply of constant voltage and frequency. The magnets are embedded in the rotor iron, and a damper winding is placed in slots in the rotor surface to provide starting capability. Such a motor does not, however, have means of controlling the stator power factor.

Reluctance motors

Reluctance motors operate on the principle that forces are established that tend to cause iron poles carrying a magnetic flux to align with each. One form of reluctance motor is shown in cross section in the figure. The rotor consists of four iron poles with no electrical windings. The stator has six poles each with a current-carrying coil. In the condition represented in the figure, current has just been passed through coils a and a′, producing a torque on the rotor aligning two of its poles with those of the a-a′ stator. The current is now switched off in coils a and a′ and switched on to coils band b′. This produces a counterclockwise torque on the rotor aligning two rotor poles with stator poles b and b′. This process is then repeated with stator coils c and c′ and then with coils a and a′. The torque is dependent on the magnitude of the coil currents but is independent of its polarity. The direction of rotation can be changed by changing the order in which the coils are energized. Reluctance motors can have other pole configurations, such as eight stator poles and six rotor poles.

The currents in the stator coils are usually controlled by semiconductor switches connecting the coils to a direct voltage source. A signal from a position sensor mounted on the motor shaft is used to activate the switches at the appropriate time instants. Frequently a magnetic sensor based on theHall effect is employed. (The Hall effect involves the development of a transverse electric field in a semiconductor material when it carries a current and is placed in a magnetic field perpendicular to the current.) The overall system is known as a self-synchronous motor drive. It can operate over a wide and controlled speed range.

The share of Oil and Coal.

http://en.wikipedia.org/wiki/World_energy_consumption

Oil remained the largest energy source (33%) despite the fact that its share has been decreasing over time. Coal posted a growing role in the world's energy consumption: in 2009, it accounted for 27% of the total.

Oil and coal combined represented over 60% of the world energy supply in 2008.

At this rate of consumption world reserves of coal will last for another 150 years only.

Energy Consumption

http://en.wikipedia.org/wiki/World_energy_consumption

It is estimated that between 100 and 135 billion tonnes of oil has been consumed between 1850 and the present.

The United States Energy Information Administration regularly publishes a report on world consumption for most types of primary energy resources. According to IEA total world energy supply (consumption) was 102,569 TWh (1990); 117,687 TWh (2000); 133,602 TWh (2005) and 143,851 TWh (2008). World power generation (electricity) was 11,821 TWh (1990); 15,395 TWh (2000); 18,258 TWh (2005) and 20,181 TWh (2008). Compared to power supply 20,181 TWh the power end use was only 16,819 TWh in 2008 including EU27: 2 857 TWh, China 2 883 TWh and USA 4 533 TWh.

World annual coal production increased 1,905 Mt or 32% in 6 years in 2011 compared to 2005, of which over 70% was in China and 8% on India. Coal production was in 2011 7,783 Mt, and 2009 6,903 Mt, equal to 12.7% production increase in two years.

If production and consumption of coal continue at the rate as in 2008, proven and economically recoverable world reserves of coal would last for about 150 years.