Start Permissive

In order to obtain a permissive to start the LM6000, the following conditions must be met:

1. All shutdowns and alarms are cleared and reset.


2. Fire system is available and gas system is available.


3. Unit is in run mode.


4. Fuel control indicates Ready to Start.


5. Unit is stopped (XN25<300>


6. Customer permissives have been met.


7. Flame detectors indicates OK.


8. Turbine lube oil reservoir temp OK.


9. Turbine lube oil reservoir level OK.


10. Gen/GB lube oil reservoir temp OK.


11. Gen/GB lube oil reservoir level OK.


12. Start skid hydraulic reservoir temp OK.


13. Start skid hydraulic reservoir level OK.


14. Gas fuel filter skid valves in proper position.


15. Unit in start/run sequence.


16. Stop sequence not in progress.


17. Generator stator temp OK.


18. Crank cycle not in progress.


19. Water wash not enabled.


20. Unit not in calibrate mode.


21. Unit shutdowns is cleared.


22. Four-hour lockout not in progress.


23. Combustor drain valve in closed position.


24. DC lube pump in auto position.


25. Gas fuel supply pressure OK.

Laser

Laser is the acronym for light amplification by stimulated emission of radiation. It is a device that creates and amplifies electromagnetic radiation of a specific frequency through the process of stimulated emission. The radiation emitted by a laser consists of a coherent beam of photons, all in phase and having the same polarization. Lasers have many uses, such as cutting hard or delicate substances, reading data from compact disks and other storage devices, and establishing straight lines in geographical surveying.

The word light in the acronym is used in the broader sense, referring to electromagnetic radiation of any frequency, not just that in the visible spectrum. Hence there are infrared lasers, ultraviolet lasers, X-ray lasers, etc. The gain medium of a laser is a material of controlled purity, size, concentration, and shape, which amplifies the beam by the process of stimulated emission.

A laser emits a thin, intense beam of nearly monochromatic visible or infrared light that can travel long distances without diffusing. Most light beams consist of many waves traveling in roughly the same direction, but the phases and polarizations of each individual wave (or photon) are randomly distributed. In laser light, the waves are all precisely in step, or in phase, with each other, and have the same polarization. Such light is called coherent. All of the photons that make up a laser beam are in the same quantum state. Lasers produce coherent light through a process called stimulated emission.

laser contains a chamber in which atoms of a medium such as a synthetic ruby rod or a gas are excited, bringing their electrons into higher orbits with higher energy states. When one of these electrons jumps down to a lower energy state (which can happen spontaneously), it gives off its extra energy as a photon with a specific frequency. But this photon, upon encountering another atom with an excited electron, will stimulate that electron to jump down as well, emitting another photon with the same frequency as the first and in phase with it. This effect cascades through the chamber, constantly stimulating other atoms to emit yet more coherent photons.

Mirrors at both ends of the chamber cause the light to bounce back and forth in the chamber, sweeping across the entire medium. If a sufficient number of atoms in the medium are maintained by some external energy source in the higher energy state, a condition called population inversion, then emission is continuously stimulated, and a stream of coherent photons develops. One of the mirrors is partially transparent, allowing the laser beam to exit from that end of the chamber.

Solar Cell

Solar cells use sunlight to produce electricity by the photovoltaic effect, converting photons into electrons. They do this without the use of either chemical reactions or moving parts. Solar cells have many applications. Cells are used for powering small devices such as electronic calculators. Photovoltaic arrays generate a form of renewable electricity, particularly useful in situations where electrical power from the grid is unavailable such as in remote area power systems, Earth-orbiting satellites and space probes.

Solar cells, or Photovoltaic (PV) cells, are made of special materials called semiconductors such as silicon, which is currently the most commonly used. Basically, when light strikes the cell, a certain portion of it is absorbed within the semiconductor material. This means that the energy of the absorbed light is transferred to the semiconductor. The energy knocks electrons loose, allowing them to flow freely. PV cells also all have one or more electric fields that act to force electrons freed by light absorption to flow in a certain direction. This flow of electrons is a current, and by placing metal contacts on the top and bottom of the solar cell, we can draw that current off to use externally.

The photovoltaic effect was first recognized in 1839 by French physicist Antoine Cesar Becquerel, while experimenting with a solid electrode in an electrolyte solution. He observed that voltage developed when light fell upon the electrode. However, it was not until 1883 that the first solar cell was built, by Charles Fritts, who coated the semiconductor selenium with a very thin layer of gold to form the junctions. Early solar cells, however, still had energy-conversion efficiencies of less than 1 percent. This difficulty was finally overcome with the development of the silicon solar cell by Russell Ohl in 1941. In 1954, three other American researchers, G.L. Pearson, Daryl Chapin, and Calvin Fuller, demonstrated a silicon solar cell capable of a 6-percent energy-conversion efficiency when used in direct sunlight.

Modern solar cells are based on semiconductor physics. They are basically just P-N junction photodiodes with a very large light-sensitive area. The photovoltaic effect, which causes the cell to convert light directly into electrical energy, occurs in the three energy-conversion layers. The first of these three layers necessary for energy conversion in a solar cell is the top junction layer, which is made of N-type semiconductor. The next layer in the structure is the core of the device; this is the absorber layer, the P-N junction. The last of the energy-conversion layers is the back junction layer, which is made of P-type semiconductor.

The first spacecraft to use solar panels was the US satellite Vanguard 1, launched in March 1958 with solar cells made by Hoffman Electronics. This milestone created interest in producing and launching a geostationary communications satellite, in which solar energy would provide a viable power supply. This was a crucial development which stimulated funding from several governments into research for improved solar cells. In 2007 Scientists at the U.S. Department of Energy's National Renewable Energy Laboratory (NREL) have set a world record in solar cell efficiency with a photovoltaic device that converts 40.8 percent of the light that hits it into electricity. This is the highest confirmed efficiency of any photovoltaic device to date.

Solar Energy

Solar energy is the light and heat radiated from the Sun. It influences Earth's climate and makes life possible. Since ancient times solar energy has been harnessed for human use through a range of technologies. Solar radiation along with secondary solar resources such as wind and wave power, hydroelectricity and biomass account for most of the available flow of renewable energy on Earth. Solar energy technologies can provide electrical generation by heat engine or photovoltaic means, space heating and cooling in active and passive solar buildings; potable water via distillation and disinfection, daylighting, hot water, thermal energy for cooking, and high temperature process heat for industrial purposes.
The Earth receives 174 petawatts (1015 watts) of incoming solar radiation at the upper atmosphere. Approximately 30% is reflected back to space while the rest is absorbed by clouds, oceans and land masses. The spectrum of solar light at the Earth's surface is mostly spread across the visible and near-infrared ranges with a small part in the near-ultraviolet. The absorbed solar light heats the land surface, oceans and atmosphere. The warm air containing evaporated water from the oceans rises, driving atmospheric circulation or convection. When this air reaches a high altitude, where the temperature is low, water vapor condenses into clouds, which rain onto the earth's surface, completing the water cycle.

Arc Welding Basics

Arc Welding Basics

Arc welding is a fusion process for joining metals. By applying intense heat, metal is melted at the joint between two parts, causing them to intermix - directly, or more commonly with an intermediate molten filler metal called welding rod or electrode. Upon cooling and solidification, a metallurgical bond is created. Since the joining is an intermixture of metals, the final weldment potentially has the same strength properties as the metal of the parts. This is in sharp contrast to non-fusion processes of joining (i.e. soldering, brazing etc.) in which the mechanical and physical properties of the base materials cannot be duplicated at the joint.

In arc welding, the intense heat needed to melt metal is produced by an electric arc. The arc is formed between the actual work and an electrode (stick or wire) that is manually or mechanically guided along the joint. But joining metals requires more than moving an electrode along a joint. Metals at high temperatures tend to react chemically with elements in the air - oxygen and nitrogen. When metal in the molten pool comes into contact with air, oxides and nitrides form which destroy the strength and toughness of the weld joint. Therefore, many arc-welding processes provide some means of covering the arc and the molten pool with a protective shield of gas, vapor, or slag. This is called arc shielding. This shielding prevents or minimizes contact of the molten metal with air. Shielding also may improve the weld. An example is a granular flux, which actually adds deoxidizers to the weld.

The extruded covering on the filler metal rod, provides a shielding gas at the point of contact while the slag protects the fresh weld from the air. The arc itself is a very complex phenomenon. In-depth understanding of the physics of the arc is of little value to the welder, but some knowledge of its general characteristics can be useful.

An arc is an electric current flowing between two electrodes through an ionized column of gas. A negatively charged cathode and a positively charged anode create the intense heat of the welding arc. Negative and positive ions are bounced off of each other in the plasma column at an accelerated rate. In welding, the arc not only provides the heat needed to melt the electrode and the base metal, but under certain conditions must also supply the means to transport the molten metal from the tip of the electrode to the work. Several mechanisms for metal transfer exist.

Coulomb's Law

Coulomb’s Law states as follows: The magnitude of the electrostatic force between two point electric charges is directly proportional to the product of the magnitudes of each charge and inversely proportional to the square of the distance between the charges:

where Q1 represents the quantity of charge on object 1 (in Coulombs), Q2 represents the quantity of charge on object 2 (in Coulombs), and d represents the distance of separation between the two objects (in meters). The symbol k is a proportionality constant known as the Coulomb's law constant. The value of this constant is dependent upon the medium that the charged objects are immersed in.

Coulomb's law was developed by French physicist Charles Augustin de Coulomb in the 1780s.

Coulomb

A coulomb is the amount of electric charge transported in 1 second by a steady current of 1 ampere: 1C=1A .1S
Or One coulomb is the amount of charge stored by a capacitance of one farad charged to a potential difference of one volt: 1C=1F.1V

Battery

A battery is a combination of one or more electrochemical Galvanic cells that store chemical energy that can be converted into electric potential energy, creating direct current electricity. Since the invention of the first Voltaic pile in 1800 by Alessandro Volta, the battery has become a common power source for many household and industrial applications, and is now a multi-billion dollar industry.

The modern development of batteries started with the Voltaic pile, invented by the Italian physicist Alessandro Volta in 1800. A battery is a device that converts chemical energy directly to electrical energy. It consists of one or more voltaic cells. Each voltaic cell consists of two half cells connected in series by a conductive electrolyte. One half-cell is the negative electrode (the anode) and the other is the positive electrode (the cathode). In the redox reaction that powers the battery, reduction occurs in the cathode, while oxidation occurs in the anode. The electrodes do not touch each other but are electrically connected by the electrolyte, which can be either solid or liquid. In many cells, the materials are enclosed in a container, and a separator, which is porous to the electrolyte, which prevents the electrodes from coming into contact.

Arc Welding

Arc welding is a process which uses the concentrated heat of an electric arc to join metal by fusion of the parent metal and the addition of metal to joint usually provided by a consumable electrode. Either direct or alternating current may be used for the arc, depending upon the material to be welded and the electrode used.

Arc welding uses a welding power supply to create an electric arc between an electrode and the base material to melt the metals at the welding point. They can use either direct (DC) or alternating (AC) current, and consumable or non-consumable electrodes. The welding region is sometimes protected by some type of inert or semi-inert gas, known as shielding gas, and/or an evaporating filler material. The process of arc welding is widely used because of its low capital and running costs.

Electric Arc: Voltaic Arc

An electric arc is a continuous electric discharge of high current between two carbon points as electrodes, forming a luminous arc of intense brilliancy and heat by the passage of a powerful voltaic current. The phenomenon is exploited in the carbon-arc lamp, once widely used in film projectors. In the electric-arc furnace an arc struck between very large carbon electrodes and the metal charge provides the heating. In arc welding an electric arc provides the heat to fuse the metal. The discharges in low-pressure gases, as in neon and sodium lights, can also be broadly considered as electric arcs.

Also known as voltaic arc, the various shapes of electric arc are emergent properties of nonlinear patterns of current and electric field and it results in a very high temperature, capable of melting or vaporizing most materials. Industrially, electric arcs are used for welding, plasma cutting, for electrical discharge machining, as an arc lamp in movie theater projectors, and followspots in stage lighting.

Sound

Sound is vibration transmitted through solid, liquid, or gaseous matter; particularly, sound means those vibrations composed of frequencies capable of being detected by ears. The mechanical vibrations that can be interpreted as sound are able to travel through all forms of matter, gases, liquids, and solids, as longitudinal or transverse (solid) waves. The matter that supports the sound is called the medium. Sound cannot travel through vacuum. Matter in the medium is periodically displaced by a sound wave, and thus oscillates. The energy carried by the sound wave converts back and forth between the potential energy of the extra compression or lateral displacement strain of the matter and the kinetic energy of the oscillations of the medium.

The speed of sound depends on the medium through which the waves are passing, and is often quoted as a fundamental property of the material. Those physical properties and the speed of sound change with ambient conditions. For example, the speed of sound in gases depends on temperature. In 20°C (68°F) air at sea level, the speed of sound is approximately 343 m/s (767.3 mph). In fresh water, also at 20°C, the speed of sound is approximately 1482 m/s (3,315.1 mph).

Acoustics

Acoustics is the science that deals with the production, transmission, and reception of sound through gaseous, liquid, and solid medium. A scientist who works in the field of acoustics is an acoustician. The application of acoustics in technology is called acoustical engineering. There is often much overlap and interaction between the interests of acousticians and acoustical engineers. The science of acoustics spreads across so many facets of our society - music, medicine, architecture, industrial production, warfare and more.

The word "acoustic" is derived from the ancient Greek word ακουστός, meaning able to be heard (Woodhouse, 1910, 392). The Latin synonym is "sonic". After acousticians had extended their studies to frequencies above and below the audible range, it became conventional to identify these frequency ranges as "ultrasonic" and "infrasonic" respectively, while letting the word "acoustic" refer to the entire frequency range without limit.

Capacitor

A capacitor is an electrical device that can store energy in an electric circuit. A capacitor functions much like a battery, but charges and discharges much more efficiently. A basic capacitor is made up of two plates separated by a dielectric. The process of storing energy in the capacitor is known as "charging", and involves electric charges of equal magnitude, but opposite polarity, building up on each plate. A capacitor's ability to store charge is measured by its capacitance, in units of farads.

Capacitors are often used in electric and electronic circuits as energy-storage devices. They can also be used to differentiate between high-frequency and low-frequency signals. This property makes them useful in electronic filters. Practical capacitors have series resistance, internal leakage of charge, series inductance and other non-ideal properties not found in a theoretical, ideal, capacitor.

Capacitors are occasionally referred to as condensers. This term is considered archaic in English, but most other languages use a cognate of condenser to refer to a capacitor. A wide variety of capacitors have been invented, including small electrolytic capacitors used in electronic circuits, basic parallel-plate capacitors, mechanical variable capacitors, and the early Leyden jars, among numerous other types of capacitors.

Electromagnetic Induction

Electromagnetic induction is the production of an electromotive force (emf) either by motion of a conductor through a magnetic field so as to cut across the magnetic flux or changing magnetic field about the conductor. The process by which an emf is induced in one circuit by a change of current in a neighboring circuit is called mutual induction.

That effect was first observed in 1831 by English physicist Michael Faraday (1791–1867) and shortly thereafter by American physicist Joseph Henry (1797–1878). Electromagnetic induction is an incredibly useful phenomenon with a wide variety of applications. Induction is used in power generation and power transmission.

Step-down Transformer

A step-down transformer is a transformer that has more turns wound around on the primary coil than on the secondary coil and therefore the voltage induced in the secondary coil is smaller than the primary coil voltage. So if there are 2,000 turnings on the primary coil and 200 turnings on the secondary coil, then the voltage induced in the secondary coil is ten times smaller than the primary coil voltage. In other words, the voltage output in a step-down transformer is smaller than the voltage input.

Step-up Transformer

A step-up transformer is a transformer which has more turns of wire wound around its secondary winding than on the primary, thus increasing the input voltages applied to the primary coil. When voltage is applied to a primary coil or input, it magnetizes the iron core, inducing a voltage in the other secondary coil. Using a step up transformer to increase the voltage does not give you something for nothing. As the voltage goes up, the current goes down by the same proportion. The power equation shows that the overall power remains the same: Power=Voltage x Current.

Transformer

A transformer is a device that transfers an alternating current from one electric circuit to another by means of electromagnetic induction, transforming voltage from one level to another, usually from a higher voltage to a lower voltage. A changing current in the first circuit, the primary, creates a changing magnetic field. This changing magnetic field induces a changing voltage in the second circuit, the secondary. This effect is called mutual induction.

A transformer is made up of two or more coils of insulated wire wound around a core made of iron. The number of times the wires are wrapped around the core ("turns") is very important and determines how the transformer changes the voltage.

If a load is connected to the secondary circuit, electric charge will flow in the secondary winding of the transformer and transfer energy from the primary circuit to the load connected in the secondary circuit. The secondary induced voltage VS, of an ideal transformer, is scaled from the primary VP by a factor equal to the ratio of the number of turns of wire in their respective windings: Vs/Vp=Ns/Np.

Electrical transformers can be wound to have either a single-phase or a three-phase configuration. Transformers come in a range of sizes from a thumbnail-sized coupling transformer hidden inside a stage microphone to huge units weighing hundreds of tons used to interconnect portions of national power grids. All operate with the same basic principles, although the range of designs is wide.

The transformer principle was demonstrated in 1831 by Michael Faraday, although he used it only to demonstrate the principle of electromagnetic induction and did not foresee its practical uses. The first widely used transformer was the induction coil, invented by Irish clergyman Nicholas Callan in 1836. He was one of the first to understand the principle that the more turns a transformer winding has, the larger electromotive force it produces.

Heat Recovery Steam Generator

A heat recovery steam generator is a heat exchanger which recovers heat from a hot gas stream. It produces steam that can be used to drive a steam turbine. A common application for a heat recovery steam generator is in a combined-cycle power station, where hot exhaust from a gas turbine is fed to a heat recovery steam generator to generate steam which in turn drives a steam turbine. This combination produces electricity more efficiently than either the gas turbine or steam turbine alone.

Another application for a heat recovery steam generator is in diesel engine combined cycle power plants, where hot exhaust from a diesel engine is fed to a heat recovery steam generator to generate steam which in turn drives a steam turbine. The HRSG is also an important component in cogeneration plants. Cogeneration plants typically have a higher overall efficiency in comparison to a combined cycle plant. This is due to the loss of energy associated with the steam turbine.

A heat recovery steam generator consists of three major components. They are the Evaporator, Superheater, and Economizer. The different components are put together to meet the operating requirements of the unit.

Steam Turbine

A steam turbine is a turbine which is driven by the pressure of steam discharged at high velocity against the turbine blades. As a mechanical device, a steam turbine extracts thermal energy from pressurized steam, and converts it into useful mechanical work. It has almost completely replaced the reciprocating piston steam engine, invented by Thomas Newcomen and greatly improved by James Watt primarily, because of its greater thermal efficiency and higher power-to-weight ratio. Because the turbine generates rotary motion, it is particularly suited to be used to drive an electrical generator - about 80% of all electric generation in the world is by use of steam turbines.

The steam turbine is a form of heat engine that derives much of its improvement in thermodynamic efficiency through the use of multiple stages in the expansion of the steam, as opposed to the one stage in the Watt engine, which results in a closer approach to the ideal reversible process. In a steam turbine, the steam is expanded, generating work, in a number of stages. These stages are characterized by how the energy is extracted from them and are known as impulse or reaction turbines. Most modern steam turbines are a combination of the reaction and impulse design. Typically, higher pressure sections are impulse type and lower pressure stages are reaction type.

Large steam turbines are used by power stations to drive electric generators to produce most of the world's electricity. Most of these centralized stations are of two types: fossil fuel power plants and nuclear power plants. The turbines used for electric power generation are most often directly coupled to their generators. As the generators must rotate at constant synchronous speeds according to the frequency of the electric power system, the most common speeds are 3000 r/min for 50 Hz systems, and 3600 r/min for 60 Hz systems. In installations with high steam output, as may be found in nuclear power stations, the generator sets may be arranged to operate at half these speeds, but with four-pole generators.

Turbine

A turbine is a rotary engine that extracts energy from a fluid flow. Claude Burdin (1788-1873) coined the term from the Latin turbo, which means vortex, during an 1828 engineering competition. Benoit Fourneyron (1802-1867), a student of Claude Burdin, built the first practical water turbine. The simplest turbines have one moving part, a rotor assembly, which is a shaft with blades attached. Moving fluid acts on the blades, or the blades react to the flow, so that they rotate and impart energy to the rotor. Early turbine examples are windmills and water wheels.

Turbines develop torque by reacting to the fluid's pressure or weight. The pressure of the fluid changes as it passes through the turbine rotor blades. A pressure casement is needed to contain the working fluid as it acts on the turbine stage(s) or the turbine must be fully immersed in the fluid flow (wind turbines). The casing contains and directs the working fluid and, for water turbines, maintains the suction imparted by the draft tube.

Turbine engines produce thrust by increasing the velocity of the air flowing through the engine. A turbine engine consists of an air inlet, compressor, combustion chambers, turbine section, and exhaust. The turbine engine has the following advantages over a reciprocating engine: less vibration, increased aircraft performance, reliability, and ease of operation. Turbine engines are classified according to the type of compressors they use. The compressor types fall into three categories—centrifugal flow, axial flow, and centrifugal-axial flow. Compression of inlet air is achieved in a centrifugal flow engine by accelerating air outward perpendicular to the longitudinal axis of the machine. The axial-flow engine compresses air by a series of rotating and stationary airfoils moving the air parallel to the longitudinal axis. The centrifugalaxial flow design uses both kinds of compressors to achieve the desired compression. The path the air takes through the engine and how power is produced determines the type of engine. There are four types of aircraft turbine engines—turbojet, turboprop, turbofan, and turboshaft.

Gas, steam, and water turbines have a casing around the blades that contains and controls the working fluid. Credit for invention of the modern steam turbine is given to British Engineer Sir Charles Parsons (1854 - 1931). A device similar to a turbine but operating in reverse is a compressor or pump. The axial compressor in many gas turbine engines is a common example.

Francis turbines and most steam turbines use this concept. For compressible working fluids, multiple turbine stages may be used to harness the expanding gas efficiently. Newton's third law describes the transfer of energy for reaction turbines. The primary numerical classification of a turbine is its specific speed. This number describes the speed of the turbine at its maximum efficiency with respect to the power and flow rate. The specific speed is derived to be independent of turbine size. Given the fluid flow conditions and the desired shaft output speed, the specific speed can be calculated and an appropriate turbine design selected.

How a Turbine Works

LM6000 Gas Turbine

The General Electric LM6000 gas turbine is a stationary gas turbine which is derived from the family CF6 jet engines. The aircraft version of the engine is called CF6-80C2 turbofan engine that is used to drive several types of commercial aircraft like the Boeing 740-400.

The LM6000 gas turbine was developed in 1992 by General Electrics, who was one of the first developers of the aeroderivative; a gas turbine designed first as a flight engine, then redesigned for industrial use. The following have been changed to convert the CF6-80C2 to the LM6000:

• Front fan removed and inlet guide vanes added.


• Low pressure compressor from the CF6-50/ LM used.


• Front and rear frames adapted.


• Output shafts added to the front of the low pressure compressor.


• Bearing 7R added.


• Balancing disk added to the low pressure turbine.


• Hydraulic control system for the variable geometry added.

The LM6000 gas turbine is a dual-rotor, concentric drive shaft gas turbine, capable of driving a load from the front and rear of the low-pressure rotor. The main components consist of a variable inlet guide vanes assembly, a 5-stage low-pressure compressor, a 14-stage variable-geometry high-pressure compressor, an annular combustor, a 2-stage high-pressure turbine, a 5-stage low-pressure turbine, an accessory gear box assembly, and accessories.

The low-pressure rotor consists of the low-pressure compressor and the low-pressure turbine that drives it. Attachment flanges are provided on both the front and the rear of the the low-pressure rotor for connection to the packager-supplied power shaft and load. The high-pressure rotor is made up of the 14-stage high-pressure compressor and the 2-stage high-pressure turbine that drives it. The high and low-pressure turbines drive the high and low-pressure compressors through concentric drive shafts.

Air enters the gas turbine at the variable inlet guide vanes and passes into the low-pressure compressor. The low-pressure compressor compresses the air by a ratio of aproximately 2.4:1. Air leaving the low-pressure compressor is directed into the high-pressure compressor. Variable bypass valves are arranged in the flow passage between the two compressors to regulate the airflow entering the high-pressure compressor at idle and at low power. To further control the airflow, the high-pressure compressor is equipped with variable stator vanes.

High-pressure compressor compresses the air to a ratio of 12:1, resulting in a total compression ratio of 30:1, relative to ambient. From the high-pressure compressor the air is directed into the signal annular combustor section, where it mixes with the fuel from the 30 fuel nozzles. An igniter initially ignites the fuel-air mixture and, once combustion is self-sustaining, the igniter is turned off. The hot gas that results from the combustion is directed into high-pressure turbine that drives the high-pressure compressor. This gas further expands through the low-pressure turbine, which drives the low-pressure compressor and the output load.

The Brayton Cycle

Four processes occur in gas turbine engines. These processes were first discribed by George Brayton and called the Brayton Cycle, which occur in all internal combustion engines. The Brayton steps are as follows:

1.Compression occurs between the intake and the outlet of the compressor. During this process, pressure and temperature of the air increases.

2.Combustion occurs in the combustion chamber where fuel and air are mixed to explosive proportion and ignited. The addition of heat causes a sharp increase in volume.

3.Expansion occurs as hot gas accelerates from the combustion chamber. The gases at constant pressure and increased volume enter the turbine and expand through it.

4.Exhaust occurs at the engine exhaust stack with a large drop in volume and at a constant pressure.

Gas Turbine Basic Principles

Air compressed inside a balloon exerts force upon the confine of the balloon. The air has mass and the mass of the air is proportional to its density, and density is proportional to temperature and pressure. Air molecules are driven farther apart as temperature increases. The air mass confined inside the balloon accelerate from the balloon, creating a force when it is released. This force increases as mass and acceleration increase as stated in Newton’s Second Law (F=MA).

The force created by the acceleration of the air mass inside the balloon results in an equal and opposite force that causes the balloon to be propelled in the opposite direction, as stated in the Newton’s Third Law; “every action produces an equal and opposite reaction.

Replacing the air inside the balloon sustains the force and allows a load to be driven by the flow of the air mass accelerating across and driving a turbine. Replacing the balloon with a turbine, fuel is injected between the compressor and the turbine to further accelerate the air mass, thus, multiplying the force used to drive the load.

Combined Cycle Power Plant

The Combined Cycle power plant is a combination of a fuel-fired turbine with a Heat Recovery Steam Generator (HRSG) and a steam powered turbine. These plants are very large, typically rated in the hundreds of mega-watts. A combined cycle power plant employs more than one thermodynamic cycle. Heat engines are only able to use a portion of the energy their fuel generates (usually less than 50%). The remaining heat from combustion is generally wasted. Combining two or more "cycles" such as the Brayton cycle and Rankine cycle results in improved overall efficiency.

In a combined cycle power plant, or combined cycle gas turbine plant, a gas turbine generator generates electricity and the waste heat is used to make steam to generate additional electricity via a steam turbine; this last step enhances the efficiency of electricity generation. Most new gas power plants in North America and Europe are of this type. In a thermal power plant, high-temperature heat input to the power plant, usually from burning of fuel, is converted to electricity as one of the outputs and low-temperature heat as another output. As a rule, in order to achieve high efficiency, the temperature difference between the input and output heat levels should be as high as possible. This is achieved by combining the Rankine (steam) and Brayton (gas) thermodynamic cycles.

Combined cycle plants are usually powered by natural gas, although fuel oil, synthesis gas or other fuels can be used. The supplementary fuel may be natural gas, fuel oil, or coal. Next generation nuclear power plants are also on the drawing board which will take advantage of the higher temperature range made available by the Brayton top cycle, as well as the increase in thermal efficiency offered by a Rankine bottoming cycle.

Electric Motor: AC Motors

An electric motor uses electrical energy to produce mechanical energy. Electric motors are found in household appliances such as fans, refrigerators, washing machines, pool pumps, floor vacuums, and industrial machines such as lathes and grinders. According to the kind of electrical current a motor works on, there are two types of motors; DC motors, and AC motors.

A DC motor is designed to run on DC electric power. Two examples of pure DC designs are Michael Faraday's homopolar motor, and the ball bearing motor, which is a novelty. By far the most common DC motor types are the brushed and brushless types, which use internal and external commutation respectively to create an oscillating AC current from the DC source -- so they are not purely DC machines in a strict sense.

An AC motor is an electric motor that is driven by an alternating current. There are two types of ac motors; asynchronous and synchronous electric motors. The induction ac motor is a common form of asynchronous motor and is basically an ac transformer with a rotating secondary. The primary winding is in the stator and is connected to the power source and the shorted secondary (rotor) carries the induced secondary current. Torque is produced by the action of the rotor (secondary) currents on the air-gap flux. The synchronous motor differs greatly in design and operational characteristics, and is considered a separate class of ac motor.

Induction ac motors (asynchronous) are the simplest and most rugged electric motor and consists of two basic electrical assemblies: the wound stator and the rotor assembly. The induction ac motor derives its name from currents flowing in the secondary member (rotor) that are induced by alternating currents flowing in the primary member (stator). The combined electromagnetic effects of the stator and rotor currents produce the force to create rotation.

A synchronous electric motor is an AC motor distinguished by a rotor spinning with coils passing magnets at the same rate as the alternating current and resulting magnetic field which drives it. Another way of saying this is that it has zero slip under usual operating conditions. Contrast this with an induction motor, which must slip in order to produce torque.

In 1882, Nikola Tesla invented the rotating magnetic field, and pioneered the use of a rotary field of force to operate machines. He exploited the principle to design a unique two-phase induction motor in 1883. In 1885, Galileo Ferraris independently researched the concept. In 1888, Ferraris published his research in a paper to the Royal Academy of Sciences in Turin.

Introduction of Tesla's motor from 1888 onwards made possible the efficient generation and long distance distribution of electrical energy using the alternating current transmission system, also of Tesla's invention (1888). Before the invention of the rotating magnetic field, motors operated by continually passing a conductor through a stationary magnetic field (as in homopolar motors).Tesla had suggested that the commutators from a machine could be removed and the device could operate on a rotary field of force.

Brush Electric Generator

The Brush Generator is an electric generator which converts rotational shaft horsepower into electrical energy. Rated output is 50 MW under ideal conditions, when driven by an LM6000 gas turbine producing approximately 55,000 shp. The generator is installed in an isolated pressurized enclosure to prevent explosive gas leakage from the engine into the generator compartment, where possible ignition could occur. It also provides enclosed filtered air cooling.

The unit is bolted to the gas turbine-generator package skid, such that the rotor is axially aligned with the engine drive shaft. The stator core is built into a fabricated steel frame and consists of a low-loss silicon, steel-segmented stampings insulated by a layer of varnish on both sides. The stampings are divided into short sections radial ventilating ducts extending from the center through to the outer ends. The stator windings are arranged in patterns to minimize circulating currents.

The rotor is machined from a single alloy-steel forging of tested metallurgical properties. Longitudinal slots are machined radially in the body in which the rotor windings are installed. The windings are secured against centrifugal force by steel wedges fitted into the dovetail opening machined in the rotor slots. The coils are insulated from the slot walls by molded slot liners. Molded ring insulation is provided at the coil ends to separate and support the coils under thermal and rotational stresses. A centering ring held into place shrink fit restricts axial movement.

The exciter assembly consists of a permanent magnet alternator (PMA), an exciter stator and rotor, and a rotating diode rectifier. These components are installed at the non-drive end of the generator shaft.

The permanent magnet stator consists of a single-phase winding in a laminated core. Twelve permanent magnets rotate on the rotor inside the stator to produce aproximately 125 VAC at 50 Hz. The PMA output voltage is rectified and regulated by the modular automatic voltage regulator.

Electric Generator

Using electromagnetic induction, an electrical generator is a device that converts mechanical energy into electrical energy. The source of mechanical energy may be a steam turbine or gas engine, water falling through a turbine, an internal combustion engine, a wind turbine, a hand crank, compressed air or any other source of mechanical energy.

The generator is based on the principle of electromagnetic induction discovered in 1831 by Michael Faraday, a British scientist. Faraday discovered that if an electric conductor, like a copper wire, is moved through a magnetic field, electric current will flow (be induced) in the conductor. So the mechanical energy of the moving wire is converted into the electric energy of the current that flows in the wire.

The Dynamo was the first electrical generator capable of delivering power for industry. The dynamo uses electromagnetic principles to convert mechanical rotation into a pulsing direct current through the use of a commutator. The first dynamo was built by Hippolyte Pixii in 1832. Through a series of accidental discoveries, the dynamo became the source of many later inventions, including the DC electric motor and the AC alternator. A dynamo machine consists of a stationary structure, which provides a constant magnetic field, and a set of rotating windings which turn within that field. On small machines the constant magnetic field may be provided by one or more permanent magnets; larger machines have the constant magnetic field provided by one or more electromagnets, which are usually called field coils.

An alternating current genarator is a device that converts mechanical energy into alternating current electrical energy. An alternating current (AC) generator is also called alternator, but usually the word refers to small rotating machines driven by automotive and other internal combustion engines. Most alternators use a rotating magnetic field but linear alternators are occasionally used. In the UK, large alternators in power stations, which are driven by steam turbines, are called turbo-alternators.

Alternating current generators; one driven by gas turbine, the other by steam turbine, at a powerplant.

A direct current generator

Three-Phase Electricity

Three-phase electricity is a method of alternating current electric power transmission. It is the most common method used by electric power distribution grids worldwide to distribute power. It is also used to power large motors and other large loads. A three-phase system is generally more economical than others because it uses less conductor material to transmit electric power than equivalent single-phase or two-phase systems at the same voltage.

Phase is a term used to describe alternating current. Phase explains the timing of the electron movements. Three-phase electricity is common worldwide because it is a cheaper and easier way to transmit electricity. But most homes only use single-phase electricity. Phase is a term used to describe one feature of alternating current. If wires are in phase it means that timing of the electron movement, back and forth, is the same. The electrons are in step or in time or in phase. Much of its efficiency is because there is always voltage in at least one wire. The idea of three phase power was discovered by Nikola Tesla (1856 -1943), a Serbian-born American engineer.

Three-phase power removes the need for a neutral or 'return path'. This is because joining the three phases together results in no overall current flow. Three-phase power is an arrangement that fits in very nicely with generator design. The 120° phase separation allows close to the optimum spacing and size of the copper conductors around the stator bore. The 3-phase generator is the cheapest form to make. Multiple phase generators are made for specific purposes, usually military, but they are expensive.

Ampere

The ampere is a unit of electric current, or amount of electric charge per unit time. The ampere is an SI base unit, and is named after André-Marie Ampère, one of the main discoverers of electromagnetism. One ampere is defined to be the constant current which will produce an attractive force of 2×10–7 newton per meter of length between two straight, parallel conductors of infinite length and negligible circular cross section placed one meter apart in a vacuum. The definition is based on Ampere's force law. The ampere is a base unit, along with the metre, kelvin, second, mole, candela and the kilogram: it is defined without reference to the quantity of electric charge.The SI unit of charge, the coulomb, "is the quantity of electricity carried in 1 second by a current of 1 ampere."

Conversely, an ampere is one coulomb of charge going past a given point in the duration of one second; that is, in general, charge Q is determined by steady current I flowing per unit time t as: Q=It

Voltage

Voltage, or electrical tension, is the difference of electrical potential between two points of an electrical circuit expressed in volts. It is the measurement of the potential for an electric field to cause an electric current in an electrical conductor. Voltage should actually be called potential difference. It is the electron-driving force in electricity, called electromotive force (emf) and the potential difference is responsible for the pushing and pulling of electrons or electric current through a circuit. In other words, electrical potential difference can be thought of as the ability to move electrical charge through a resistance.

In The Search For Dark Matter

The Exotic Particles Would Explain a Lot About the Universe, and That Promise Has Scientists Going Underground.

You might think an astrophysicist would spend much of his time with his head in the stars. Instead, Sean Paling often squeezes into a cage with a bunch of burly miners and travels for six minutes in darkness to the bottom of Britain's deepest working mine.

At a lab here, 3,300 feet underground, Dr. Paling is searching for one of the most elusive objects in the universe: a wimp, or weakly interacting massive particle. Wimps are leading candidates for dark matter, which is believed to account for up to 95% of the mass of the universe. Something that big would be easy to spot except for the fact that dark matter is invisible. That doesn't stop the elusive mass from making its presence felt by the immense gravitational tug it exerts on stars, galaxies and other cosmic bodies.

"For 20 years, the miners have been asking if I've found it yet, and for 20 years I've been saying no," says Dr. Paling, an astro-particle physicist at England's Sheffield University, who has been searching for wimps at Boulby since 1989. "You can understand their confusion."

Unraveling the secret of dark matter is one of the grandest prizes of astrophysics because it is the key to understanding the shape, size and even the fate of the universe. Knowing how much dark matter there is will tell us whether the universe will keep expanding, or expand to a point and then collapse, or get bigger and bigger and then stop. More parochially, it can help us predict how Earth's neighborhood, the Milky Way galaxy, formed and how it might evolve.

But it is a difficult quest. Wimps rarely interact with normal matter such as atoms; indeed, billions of wimps may be darting right through the Earth every second without hitting anything. Detectors must be installed deep underground because on the surface, the profusion of other cosmic rays would crowd out a wimp's signal, which is feeble, because wimps move relatively slowly.

Wimp hunts have been going on for years in the U.K., Italy, Spain and France, as well as at a disused iron mine in Minnesota. The race intensified in April, when scientists working beneath Italy's Gran Sasso mountain announced that they had found signals of dark matter streaming in from space, though the results are in dispute.

The newest competitor on the scene is the European Organization for Nuclear Research, or CERN, the group that runs Europe's new Large Hadron Collider outside Geneva. CERN scientists hope to find evidence of dark matter in a different way, by smashing together subatomic particles at high speed and seeing if any wimps emerge.

Which group will get there first? "It depends on who nature is kind to," says Tom Le Compte, a particle physicist at CERN and Argonne National Laboratory in Argonne, Ill.

The U.K. project is unusual because it is based in a working mine, a tough environment for an experiment that relies on minute measurements and ultra-clean, ultra-sensitive equipment. The 35-year-old potash mine, near England's northeast coast, has more than 620 miles of dark and dusty tunnels, including some that delve under the North Sea.

"Unlike the miners," says Dr. Paling, "we are ever so delicate."

Dr. Paling and his colleagues first set up an extremely basic wimp detector at the mine. In 2003, a £2 million ($3.1 million) investment got them a full-scale lab with far more sensitive machines. It is run by Sheffield University, Rutherford Appleton Laboratory and other British and international groups.
One recent morning, Dr. Paling donned miner's gear -- overalls, boots, helmet, lamp and respirator -- and took the ride down the shaft. As he and his colleagues walked to the lab, a grimy, salt-encrusted vehicle went rattling by, carrying a group of miners to an underground excavation area 30 minutes away.

Dr. Paling pointed upward and said: "You can't feel it, but only one-millionth of the cosmic rays hit you here, compared to on the surface. We expect some are wimps."

The dark-matter lab is a long, narrow structure, suspended by cables inside a cavern. There are places in the mine where the temperature reaches 111 degrees Fahrenheit. "It's because you're closer to hell," jokes David Pybus, a spokesman for Cleveland Potash Ltd., which operates the mine.

That day, in a tunnel far from the lab, a loud, remote-controlled excavator made a racket as it gnawed through the walls of a tunnel, spewing salt everywhere. To keep out such contaminants, the lab is protected by a series of doorways and air blowers. Also vital to the operation is a local "cleaning lady" with a mop and bucket.

Most wimp detectors contain a target material, typically a liquid or a solid that is particularly sensitive; one of the detectors at Boulby uses carbon disulfide gas. The hope is that a wimp of cosmic origin will fly through the surrounding rock and, if the scientists get really lucky, strike a particle of the target material. By studying the collision, a computer can tell whether the particle is a wimp or something else.

That is the challenge. Although the walls of the mine give off only very low amounts of radiation, the detector picks up the signals of alpha, gamma and other forms of radiation emitted by materials in the lab, including the detector itself. Dr. Paling and his colleagues struggle to keep these background effects to a minimum.

One of the current Boulby detectors is called Drift II, for directional recoil identification from tracks. It is specially designed to tap into something called the wimp wind. As the earth rotates on its axis and also zooms around the sun, there are times when a stream of wimps would be expected to come straight at you -- in your face, as it were -- and other times when the wind would be at your back. If scientists can detect such a modulation, it would be extra evidence for wimps, since such a directionally changing signal can't be mimicked by background sources.

On a computer screen, Dr. Paling watched as the detector registered a series of particle collisions. The first he dismissed as an alpha particle, based on the length of its track. Another turned out to be a gamma particle. No wimps today. Dr. Paling doesn't usually study each collision in real time, but inspects a record compiled by the computer.

If scientists armed with sufficiently sensitive detectors fully explore the range of possible wimp interactions with matter and still don't find the elusive particles, it would mean that wimps may not exist -- and some basic observations about the universe would have to be re-examined.

"A little doubt starts to occur in your mind now and again," Dr. Paling says. "Then you look at a galaxy that's rotating 10 times faster than is possible given the missing mass, and you know the wimps are out there."

Magnetic Field

Magnetic fields are produced by electric currents and by magnets at all points in the space around it. It can be either macroscopic currents in wires, or microscopic currents associated with electrons in atomic orbits. The magnetic field B is defined in terms of force on moving charge in the Lorentz force law. The interaction of magnetic field with charge leads to many practical applications. Magnetic field sources are essentially dipolar in nature, having a north and south magnetic pole. The SI unit for magnetic field is the Tesla, which can be seen from the magnetic part of the Lorentz force law Fmagnetic = qvB to be composed of (Newton x second)/(Coulomb x meter). A smaller magnetic field unit is the Gauss (1 Tesla = 10,000 Gauss).

When a conductor is exposed to a magnetic field an electrical current is produced. By constantly reversing its polarity, the electrical current fluctuates back and forth in the opposite direction. This fast and constant reversal of the electrical current direction is called alternating current (AC).

Permanent magnets are objects that produce their own persistent magnetic fields. All permanent magnets have both a north and a south pole. Like poles repel and opposite poles attract. The magnetism in a permanent magnet arises from properties of the atoms, in particular the electrons, that compose it. Each atom acts like a little individual magnet. If these magnets line up, they combine to create a macroscopic magnetic effect. For more details about what happens both microscopically and macroscopically, see the article ferromagnetism.

Alternating Current (AC)

Alternating current is an electric current that repeatedly reverses its flow of electrons back and forth 60 times per second, or 60 Hertz, as opposed to direct current, whose direction remains constantly in one way. So, in other words, alternating current, or AC, means that the electrical current is alternating directions in a repetitive pattern. The usual waveform of an alternating current (AC) power circuit is a sine wave, as this results in the most efficient transmission of energy. However in certain applications different waveforms are used, such as triangular or square waves.

Used generically, AC refers to the form in which electricity is delivered to businesses and residences. The electrical current in your house is alternating current. This comes from power plants that are operated by the electric company. Those big wires you see stretching across the countryside are carrying AC current from the power plants to the loads, which are in our homes and businesses.

Alternating current is generated when a conductor is exposed to a magnetic field that constantly changes its polarity. At a power plant, an electrical generator rotor rotate a coil of wire connected to magnets to create an artificial magnetic field that constantly reverses polarity, inducing an alternating current on the generator stator coils of wire. This rotating magnetic field was invented by Nicolas Tesla, an American inventor born in Croatia.

Direct Current: DC Electricity

Direct current is the continuous, one-way flow of electrons through a conductor such as a copper wire. This constant movement of electrons in one way is similar to the flow of water through a pipe. A DC (direct current) circuit is necessary for the current of electron to flow. This circuit consists of a source of electrical energy, such as a battery or solar cells, and a metal wire running from the positive end of the source to the negative terminal.

Direct current is used in nearly all electronic systems as their power supply and also to charge batteries, which are the primary sources of DC. Some railway propulsion use direct current, too, specially in urban areas. High voltage direct current is used to interconnect alternating current power grids.

Direct current is commonly found in many low-voltage applications, specially where these are powered by batteries, which can produce only DC, or solar power systems, since solar cells can produce only DC. Most automotive applications use DC, although the alternator is an AC device which uses a rectifier to produce DC. Most electronic circuits require a DC power supply. Applications using fuel cells, mixing hydrogen and oxygen together with a catalyst to produce electricity and water as byproducts, also produce only DC.

Resistance: Ohm's Law

Resistance is the opposition offered by a substance to the passage through it of a steady electric current. We can say that conductive materials such as aluminum offer the least resistance to the flow electrons (electrical current), whereas the insulating materials offer strong resistance. In physics the electrical unit of resistance is called Ohm (Ω).

The resistance of a wire is directly proportional to its length, and inversely proportional to its width. That is to say that the longer the wire is, the more resistance it will offer; and the wider it is, the less resistance it will offer. So, Ω=length/width.

Ohm's law: the Ohm's law states that the strength of an electric current through a conductor between two points is directly proportional to the potential difference (the voltage) across the two points, and inversely proportional to the resistance between them. The equation that describes this relationship is:

I= V/Ω, whereas I is the current in ampere, V the potential difference in volts, and Ω the resistance. The law was named after the German physicist Georg Ohm, who described measurements of applied voltage and current through simple electrical circuits containing various lengths of wire.