Fundamentals Of Electrical Engineering: Module(2)

Showing posts with label Module(2). Show all posts

Showing posts with label Module(2). Show all posts

Thursday, June 30, 2011

Module(2) June 30, 2011

solar energy photovoltaic

The photovoltaic (sometimes called �voltaic� for short) type of solar power plant converts the sun�s energy directly into electrical energy. A photovoltaic array is shown in above figure. This type of production uses various types of films or special materials that convert sunlight into direct current (DC) electrical energy systems.

Panels are then connected in series and parallel to obtain the desired output voltage and current ratings. Some systems use an energy storage device (i.e., battery) to provide electrical power during offsun- peak periods. This dc energy is converted to utility ac energy by means of a device called an inverter.

Larger-scale voltaic solar power systems are typically made of 1.5 Vdc solar cells capable of producing approximately 20 ma of electrical current each. A typical solar photovoltaic panel measuring 4 feet by 1 foot would produce approximately 50�60 watts of electrical power. Therefore, a 4 foot panel would supply power for a 60 watt lightbulb during daylight hours.

Given today�s technology and the space that is needed, direct solar voltaic systems are not practical for large-scale electric power production.

Solar plants are environmentally friendly as they produce no pollution. The main drawback to these plants is the cost of the panels and conversion equipment. Technology has produced more efficient panels at lower cost,
and direct solar systems will eventually be more cost-effective. They are currently used commercially to power small devices in remote areas. There remain several tax incentives to promote use of solar power by residential and small business consumers.

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See Also

Solar steam Power plant
a technique of steam power plant

Module(2) June 30, 2011

Wind Turbine Generators

Wind generation has increased in popularity and the technology has improved tremendously over the last decade. In the year 2006, the total installed capacity of U.S. wind generation was about 11,000 MW. Wind turbine generators are continuing to be installed worldwide. The total installed capacity worldwide is about 74,000 MW. Above figure shows typical wind generators.

Wind turbine generators tend to have a high cost per kWh produced. There is also a concern about the availability of wind on a constant basis. Most power companies do not consider wind generators to be base load units. Base load implies that units are readily available and that they are part of a 24 hour generation production schedule. They are brought online when available.

Basically, the concept of wind power is that the wind energy is converted
into electrical energy by means of modern windmills. One interesting characteristic
of wind power is the fact that power produced is proportional to the cube of the wind speed. In other words, if the wind speed is doubled, the power produced is tripled or increased by a factor of eight. Thus, what might appear to humans as modest changes in breezes severely impact wind power production.

Installation of wind power generators requires selecting sites that are relatively unrestricted to wind flow, preferably at high elevations, and within close proximity to suitable powerlines. Obviously, the site selected should have a fairly constant wind speed.
Wind power is accepted as free energy with no fuel costs. Wind power is also considered renewable energy, since wind really never goes away.

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See Also

solar energy photovoltaic
what is solar energy

Wednesday, June 29, 2011

Module(2) June 29, 2011

Combined-Cycle Power Plants (Combustion and Steam)

The combined-cycle power plant consists of two means of generation: combustion turbine and steam turbine. The combustion turbine is similar to a jet engine whose high-temperature and high-pressure exhaust spins a turbine whose shaft is connected to a generator. The hot exhaust is then coupled through a heat recovery steam generator (HRSG) that is used to heat water, thus producing steam to drive a secondary steam turbine generator.

The combustion turbine typically uses natural gas as the fuel to drive the turbine blades.
The advantage of a combined-cycle (CC) system is that in addition to the electrical energy produced by the fuel combustion engine, the exhaust from the engine also produces electrical energy. Another potential benefit of CC plants is that the end user can have steam made available to assist in other functions such as building heat and hot water and production processes that require steam (such as paper mills). Therefore, from one source of fuel (natural gas), many energy services are provided (electrical energy, steam, hot water, and building heat). Some CCs can reach efficiencies near 90%.
Above figure shows a combined-cycle power plant.

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See Also

Wind Turbine Generators
what is wind energy

Module(2) June 29, 2011

Combustion Turbine Generation Plants

Combustion turbine (CT) power plants burn fuel in a jet engine and use the exhaust gasses to spin a turbine generator. The air is compressed to a very high pressure. Fuel is then injected into the compressed air and ignited, producing high-pressure and high-temperature exhaust gasses. The exhaust is moved though turbine blades much the same way steam is moved through turbine blades in a steam power plant.

The exhaust gas movement through the combustion turbine results in the rotation of the generator rotor, thus
producing electricity. The exhaust from the CT remains at a very high temperature and pressure after leaving the turbine.Above figure shows a combustion turbine generator.

One of the advantages of combustion turbines is that they can actually be designed to be remotely controlled for unmanned sites. They offer fast startup times and fast installation times. In some cases, the purchase of the combustion turbine generator system can be �turnkey,� that is, the owner simply contracts for a complete installation and takes over when the plant is finished and ready to operate.

In most cases, the combustion turbine generator package is a completely self-contained unit. In fact, some of the smaller-capacity systems are actually built on trailers so that they can be moved quickly to sites requiring emergency generation.

Combustion turbines can be extremely responsive to power system
changes. They can go from no load to full load and vice versa in a matter of seconds or in a matter of minutes.

The disadvantages are limited fuel options (diesel fuel, jet fuel, or natural gas) and inefficient use of exhaust heat.

There are several environmental issues related to the use of combustion turbines. Without appropriate treatment, the exhaust emissions can be very high in undesirable gases. The high temperatures in the combustion chamber will increase the production of nitric oxide gases and their emissions.

Depending on the fuel used, there can be particulate emissions problems.
That is, particles or other materials tend to increase the opacity(smoke) of the gases. Sound levels around combustion turbine installations can be very high. Special sound reduction systems are available and used. (Note: combustion turbines are typically jet engines, very similar to those heard at airports.)

The heat rate or efficiency of a simple-cycle combustion turbine is not very good. The efficiencies are somewhere in the range of 20 to 40% maximum.

One effective way to overcome some of the cost is to incorporate a heat exchanger so the exhaust gases can be used to generate steam that will drive a secondary steam turbine. Many CTs are used as combined-cycle power plants.

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See Also

Combined-Cycle Power Plants
Combustion and Steam

Module(2) June 29, 2011

Pumped Storage Hydro Power Plants

Pumped storage hydro power production is a means of actually saving electricity for future use. Power is generated from water falling from a higher lake to a lower lake during peak load periods. The operation is reversed during off-peak conditions by pumping the water from the lower lake back to the upper lake. A power company can obtain high-value power during peak-load generation periods by paying the lower cost to pump the water back during off-peak periods. Basically, the machine at the lower level is reversible; hence, it operates as a hydro-generator unit or a motor� pump unit.

One of the problems associated with pumped storage units is the process of getting the pumping motor started. Starting the pumping motor using the system�s power line would usually put a low-voltage sag condition on the power system. The voltage sag or dip could actually cause power quality problems.

In some cases, two turbines are used in a pumped storage installation.

One of the turbines is used as a generator to start the other turbine that is used as a pump. Once the turbine is turning, the impact on the power system is much less, and the second turbine can then be started as a motor�pump.

Above figure shows a cross-sectional view a pumped storage plant. The main access tunnel was originally used to bring all of the equipment into the powerhouse: the turbine, the pumps, and the auxiliary equipment.
Note that the Tennessee Valley Authority installed a visitor center at the top of the mountain so that the installation could be viewed by the general public.

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See Also

Combustion Turbine Generation Plants
burn fuel in a jet engine

Module(2) June 29, 2011

Hydroelectric Power Plant

Hydroelectric power plants capture the energy of moving water. There are multiple ways hydro energy can be extracted. Falling water such as in a penstock, flume, or waterwheel can be used to drive a hydro turbine. Hydro energy can be extracted from water flowing at the lower section of dams, where the pressure forces water to flow. Hydroelectric power generation is efficient, cost effective, and environmentally cooperative. Hydro power production is considered to be a renewable energy source because the water cycle is continuous and constantly recharged.

Water flows much slower through a hydro turbine than does steam
through a high-pressure steam turbine. Therefore, several rotor magnetic poles are used to reduce the rotational speed requirement of the hydro turbine shaft.

Hydro units have a number of excellent advantages. The hydro unit can be started very quickly and brought up to full load in a matter of minutes. In most cases, little or no start-up power is required. A hydro plant is almost by definition a black start unit.

Black start means that electrical power is not needed first in order to start a hydro power plant. Hydro plants have a relatively long life; 50�60 year life spans are common. Some hydroelectric power plants along the Truckee River in California have been in operation for over 100 years.Above figure shows a typical hydroelectric power plant.

The cross-section of a typical low-head hydro installation is shown in above figure. Basically, the water behind the dam is transported to the turbine by means of a penstock. The turbine causes the generator to rotate, producing electricity, which is then delivered to the load center over longdistance power lines. The water coming out of the turbine goes into the river.
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See Also

Pumped Storage Hydro Power Plants
learn how to store electric energy

Module(2) June 29, 2011

Solar steam Power plant

the last technique for steam power plants is solar power plants.
Solar power plants are environmentally friendly as they produce no pollution.
Large-scale solar reflective plants require a substantial amount of area as well as specific orientation with the sun to capture the maximum energy possible with high efficiency.

Solar energy is reflected off mirrors and concentrated on a centralized boiler system. The mirrors are parabolic-shaped and motorized to focus the sun�s energy toward the receiver tubes in the collector area of the elevated boiler. The receiver tubes contain a heat transfer fluid used in the steam�boiler� turbine system. The collector area housing the receiver tubes absorbs the focused sun energy to gain 30 to 100 times normal solar energy. The fluid in
these tubes can reach operating temperatures in excess of 400 degrees Celsius. The steam drives the turbine and then goes through a condenser for conversion back to liquid before being reheated in the boiler system.

A typicalsolar power plant is shown in above figures.

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See Also

Hydroelectric Power Plant
a technique of steam power plant

Module(2) June 29, 2011

Geothermal power plant

Geothermal power plants use hot water and/or steam located underground to produce electrical energy. The hot water and/or steam are brought to the surface where heat exchangers are used to produce clean steam in a secondary system for use with turbines. Clean steam causes no sediment growth inside pipes and other equipment, thereby minimizing maintenance.

The clean steam is converted into electrical energy much the same way as in typical fossil fueled steam plants.

Although geothermal energy is considered to be a good renewable source of reliable power, some are concerned that over the long term, the availability of this geothermal resource for power plants may be reduced over time(it may dry up, become less availabile, or lose pressure). A typical geothermal power plant is shown in Figure.

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See Also

Solar steam Power plant
a technique of steam power plant

Module(2) June 29, 2011

Pressurized Water Reactor(PWR) VS Boiling Water Reactor(BWR)-2

BOILING WATER REACTOR (BWR)

Above figure shows a boiling water reactor (BWR). Again, there is a reactor building or containment shell where the nuclear reactor and some of its complement equipment are located. The reactor housing of the BWR tends to be larger than the PWR and looks almost like an inverted lightbulb.

In a BWR, water boils inside the reactor itself, and the steam goes directly to the turbine generator to produce electricity. Similar to other steam power plants, the steam is condensed and reused. Note that the turbine building is closely coupled to the reactor building, and special constraints exist in entering the turbine building because the water can pick up radioactivity.

Note the torus at the bottom of the reactor. If there should be a reactor rupture, the water inside the reactor will flash into steam and create a very high pressure surge in the reactor building. The reactor torus is filled with cold water, which will instantly condense the steam. The torus system ensures that the pressure inside the containment dome never exceeds an acceptable level.

As with the pressurized water reactor, the reactor housing contains the fuel core and water supply flow paths. The reactor recirculation system consists of the pumps and pipes that circulate the water through the reactor. The water circulating through the reactor actually goes into the turbine itself and then condensed water goes back into the reactor. The steam separator in the reactor shell separates the water from the steam and allows the steam to pass
to the steam generator. The separated water is returned to the reactor for recirculation.

The boiling water reactor utilizes one cooling loop. Both water and steam exist in the reactor core (a definition of boiling). Reactor power is controlled by positioning the control rods from start-up to approximately 70% of rated power. From 70% to 100% of rated power, the reactor power is controlled by changing the flow of water through the core. As more water is pumped through the core and more steam generated, more power is produced.

In the boiling water reactor, control rods are normally inserted from
the bottom. The top of the reactor vessel is used to separate water and steam.

Advantages and Disadvantages of BWR

A major advantage of the BWR is that the overall thermal efficiency is greater than that of a pressurized water reactor because there is no separate steam generator or heat exchanger.

Controlling the reactor is a little easier than in a PWR because it is accomplished by controlling the flow of water through the core. Increasing the water flow increases the power generated. Because of the nature of the design, the reactor vessel is subjected to less radiation, and this is considered to be an advantage because some steels become brittle with exposure to excessive radiation.

The greatest disadvantage of the BWR is that the design is much more complex. It requires a larger pressure vessel than the PWR because of the amount of steam that can be released during an accident. This larger pressure vessel also increases the cost of the BWR. Finally, the design does allow a small amount of radioactive contamination to get into the turbine system.

This modest radioactivity requires that anybody working on the turbine must wear appropriate protective clothing and use the proper equipment.

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See Also

Geothermal power plant
a technique of steam power plant

Module(2) June 29, 2011

Pressurized Water Reactor(PWR) VS Boiling Water Reactor(BWR)-1

there are two different types of light-water reactor designs
used, the pressurized water reactor (PWR) and the boiling water reactor (BWR). we will discuss (PWR) this lesson and (BWR) in the next lesson .

PRESSURIZED WATER REACTOR (PWR).

The basic design of a pressurized water reactor is shown in above figure . The reactor and the primary steam generator are housed inside containment structure. The structure is designed to withstand accidental events such as small airplane crashes. The PWR steam generator separates the radioactive water that exists inside the reactor from the steam that is going to the turbine outside the shell.

In a PWR, the heat is removed from the reactor by water flowing in a closed, pressurized loop. The heat is transferred to a second water loop through a heat exchanger (or steam generator). The second loop is kept at a lower pressure, allowing the water to boil and create steam, which is used to turn the turbine generator and produce electricity. Afterward, the steam is condensed back into water and returned to the heat exchanger where it is recycled into useable steam.

The normal control of the reactor power output is by means of the control rod system. These control rods are normally inserted and controlled from the top of the reactor. Because the control rods are inserted and controlled from the top of the reactor, the design also includes special springs and release mechanisms so that if all power is lost, the control rod will be dropped into the reactor core by gravity to shut down the reactor.
Advantages and Disadvantages of PWR
A major design advantage is the fact that fuel leaks, such as ruptured fuel rods, are isolated in the core and primary loop. That is, radioactive material contained inside the fuel is not allowed to go outside of the containment shell.

The pressurized water reactor can be operated at higher temperature/pressure combinations, and this allows an increase in the efficiency of the turbine generator system.
Another advantage is that it is believed that a pressurized water reactor is more stable than other designs. This is because boiling is not allowed to take place inside the reactor vessel and, therefore, the density of the water in the reactor core is more constant. By reducing the variability of the water density, controls are somewhat simplified.

The biggest disadvantage appears to be the fact that the reactor design is more complicated. It is necessary to design for extremely high pressures and temperatures in order to ensure that boiling does not take place inside the reactor core. The use of high-pressure vessels makes the overall reactor somewhat more costly to build. Finally, under certain circumstances, the pressurized water reactor can produce power at a faster rate than the cooling water can remove heat. If this event takes place, there is a high probability of fuel rod damage.
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See Also

Boiling Water Reactor(BWR)
a technique of generating nuclear power

Module(2) June 29, 2011

Nuclear Power Plants

In nuclear power plants such as the one shown in above figure, a controlled nuclear reaction is used to make heat to produce steam needed to drive a steam turbine generator.

the Question now is What is Nuclear Energy?

Atoms are the building blocks from which all matter is formed. Everything is made up of atoms. Atoms are made up of a nucleus(with protons and neutrons) and orbiting electrons. The number of atomic particles (sum of neutrons, protons, and electrons) determines the atomic weight of the atom and type of element in the periodic table. Nuclear energy is contained within the center of atoms (nucleus) where the atom�s protons and neutrons exist. Nature holds the particles within the atom�s nucleus together by a very strong force. If a nucleus of a large element (such as uranium 235) is split apart into multiple nuclei of different element compositions, generous amounts of energy are released in the process.

The heat emitted during this process (nuclear reaction) is used to produce steam energy to drive a turbine generator. This is the foundation of a nuclear power plant.

There are basically two methods used to produce nuclear energy in order to produce heat to make steam.

The first process is called fission. Fission is the splitting of large nuclei atoms such as uranium inside a nuclear reactor to release energy in the form of heat to be used to produce steam to drive steam turbine electrical power generators.

The second process is called Fusion.
Fusion is the combining of small nuclei atoms into larger ones, resulting in an accompanying release of energy. However, fusion reactors are not yet used to produce electrical power because it is difficult to overcome the natural mutual repulsion force of the positively charged protons in the nuclei of the atoms being combined.

In the fission process, certain heavy elements, such as uranium, are split when a neutron strikes them. When they split, they release energy in the form of kinetic energy (heat) and radiation. Radiation is subatomic particles or high-energy light waves emitted by unstable nuclei.

The process not only produces energy and radiation, it also provides additional neutrons that can be used to fission other uranium nuclei and, in essence, start a chain reaction.

The controlled release of this nuclear energy using commercial grade fuels is the basis of electric power generation. The uncontrolled release of this nuclear energy using more highly enriched fuels is the basis for atomic bombs.

The reactor is contained inside an obvious containment shell. It is made up of extremely heavy concrete and dense steel in order to minimize the possibility of a reactor breach due to an accidental.

Nuclear power plants also have an emergency backup scheme of injecting boron into the reactor coolant. Boron is an element that absorbs neutrons very readily. By absorbing neutrons, the neutrons are not available to continue the nuclear reaction, and the reactor shuts down.

The most widely used design for nuclear reactors consists of a heavy
steel pressure vessel surrounding the reactor core. The reactor core contains the uranium fuel. The fuel is formed into cylindrical ceramic pellets about one-half inch in diameter, which are sealed in long metal tubes called fuel tubes.
The tubes are arranged in groups to make a fuel assembly. A group of fuel assemblies forms the reactor core.

Controlling the heat production in nuclear reactors is accomplished by using materials that absorb neutrons. These control materials or elements are placed among the fuel assemblies. When the control elements, or control rods as they are often called, are pulled out of the core, more neutrons are available and the chain reaction increases, producing more heat.

When the control rods are inserted into the core, more neutrons are absorbed, and the chain reaction slows down or stops, producing no heat. The control rod drive system controls the actual output power of the electric power plant.

Most commercial nuclear reactors use ordinary water to remove the heat created by the fission process. These are called light water reactors. The water also serves to slow down or moderate the neutrons in the fission process. In this type of reactor, control mechanisms are used such that the chain reaction will not occur without the water to serve as a moderator.

In the United States, there are two different types of light-water reactor designs used, the pressurized water reactor (PWR) and the boiling water reactor (BWR).

we will discuss two types in details in next lessons.

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See Also

Pressurized Water Reactor(PWR)
a technique of generating nuclear power

Module(2) June 29, 2011

Fossil Fuel Power Plants

Coal power plant

Steam turbine power plants can use coal, oil, natural gas, or just about any combustible material as the fuel resource. However, each fuel type requires a unique set of accessory equipment to inject fuel into the boiler, control the burning process, vent and exhaust gases, capture unwanted byproducts, and so on.

Some fossil fuel power plants can switch fuels. For example, it is common for an oil plant to convert to natural gas when gas is less expensive than oil. Most of the time, it is not practical to convert a coal burning power plant to oil or gas unless it has been designed for conversion. The processes are usually different enough so that switching will not be cost effective. Coal is burned in two different ways in coal fired plants. First, in traditional coal fired plants, the coal is placed on metal conveyor belts inside the boiler chamber.

The coal is burned while on the belt as the belt slowly traverses the bottom of the boiler. Ash falls through the chain conveyor belt and is collected below where it is sometimes sold as a useful by-product for other industries.

In pulverized coal power plants, the coal is crushed into a fine powder and injected into the furnace where it is burned similar to a gas.
Pulverized coal is mixed with air and ignited in the furnace. Combustion by-products include solid residue (ash) that is collected at the bottom of the furnace and gases that include fine ash, NO2, CO, and SO2, which are emitted into the atmosphere through the stack. Depending on local environmental regulations, scrubber and baghouse equipment may be required and installed to collect most of these by-products before they reach the atmosphere.

Scrubbers are used to collect the undesirable gases to improve the quality of the stack output emissions. Baghouses are commonly used to help collect fly ash.
Above figure shows the layout of a typical steam power plant. Notice the steam line used to transfer superheated steam from the boiler to the turbine and then through the condenser where it is returned to a water state and recycled.
Notice the steam turbine connected to the generator. The turbine speed is controlled by the amount of steam applied in order to control frequency.

When load picks up on the electrical system, the turbine shaft speed
slows down and more steam is then placed on the turbine blades to maintain frequency. Notice how coal is delivered to the boiler and burned.

Exhaust is vented through the stack. Scrubbers and bags remove the by-products before they enter the atmosphere. Water from a nearby reservoir is pumped to the condenser where it is used to convert steam back into water and recycled.

Note that the ramp in front lifts the coal to the pulverizer where it is crushed before being injected into the boiler and burned. Plant operators must be careful to not allow the spontaneous combustion of coal while it is stored in the yard.
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See Also

Nuclear Power Plants
What is Nuclear Energy?

Module(2) June 29, 2011

Steam Turbines

Steam turbine and electric generator

High-pressure and high-temperature steam is created in a boiler, furnace, or heat exchanger and moved through a steam turbine generator (STG) that converts the steam�s energy into rotational energy that turns the generator shaft. The steam turbine�s rotating shaft is directly coupled to the generator rotor. The STG shaft speed is tightly controlled for it is directly related to the frequency of the electrical power being produced.

High-temperature, high-pressure steam is used to turn steam turbines
that ultimately turn the generator rotors. Temperatures on the order of 1,000�F and pressures on the order of 2,000 pounds per square inch (psi) are commonly used in large steam power plants. Steam at this pressure and temperature is called superheated steam, sometimes referred to as dry steam.

The steam�s pressure and temperature drop significantly after it is applied across the first stage turbine blades. Turbine blades make up the fan-shaped rotor to which steam is directed, thus turning the shaft.

The superheated steam is reduced in pressure and temperature after it passes through the turbine. The reduced steam can be routed through a second stage set of turbine blades where additional steam energy is transferred to the turbine shaft. This second stage equipment is significantly larger than the first stage to allow for additional expansion and energy transformation. In some power plants, the steam following the first stage is redirected back to the boiler where it is reheated and then sent back to the second turbine stage for a more efficient energy transformation.

Once the energy of the steam has been transferred to the turbine shaft, the low-temperature and low-pressure steam has basically exhausted its energy and must be fully condensed back to water before it can be recycled. The condensing process of steam back to water is accomplished by a condenser and cooling tower(s). Once the used steam is condensed back to warm water, the boiler feed pump (BFP) pumps the warm water back to the boiler where it is recycled. This is a closed-loop processes. Some water has to be
added in the process due to small leaks and evaporation.

The condenser takes cold water from nearby lakes, ponds, rivers,
oceans, deep wells, cooling towers, and other water sources and pumps it through pipes in the condenser. The used steam passes through the relatively cold water pipes and causes dripping to occur. The droplets are collected at the base of the condenser (the well) and pumped back to the boiler by the BFP.

The overall steam generation plant efficiency in converting fuel heat energy into mechanical rotation energy and then into electrical energy ranges from 25 to 35%. Although it is a relatively low-efficiency system, steam turbine generation is very reliable and is commonly used as base load generation units in large electric power systems. Most of the inefficiency in steam turbine generation plants comes from the loss of heat into the atmosphere in the boiler process.the question now is how can i make this steam??
I may use Fossil fuels (coal, gas, oil),Nuclear energy, Geothermal,or Solar-heated steam.we will Explain all of this systems in the next lessons.

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See Also

Fossil Fuel Power Plants
coal, oil, or natural gas

Monday, June 27, 2011

Module(2) June 27, 2011

Generator prime mover

Power generation plants produce the electrical energy that is ultimately delivered to consumers through transmission lines, substations, and distribution lines. Generation plants or power plants consist of three-phase generator(s), the prime mover, energy source, control room, and substation. The generator portion has been discussed already in the previous lessons. The prime movers and their associated energy sources are the focus of this lesson.

The mechanical means of turning the generator�s rotor is called the
prime mover. The prime mover�s energy sources include the conversion process of raw fuel, such as coal, to the end product(steam)that will turn the turbine. The bulk of electrical energy produced in today�s interconnected power systems is normally produced through a conversion process from coal, oil, natural gas, nuclear, and hydro. To a lesser degree, electrical power is produced from wind, solar, geothermal, and biomass
energy resources.

The more common types of energy resources used to generate electricity and their associated prime movers that are discussed in this Module include:

Steam turbines

Fossil fuels (coal, gas, oil)
Nuclear
Geothermal
Solar-heated steam

Hydro turbines

Dams and rivers
Pump storage

Combustion turbines

Diesel
Natural gas
Combined cycle

Wind turbines
Solar direct (photovoltaic)
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See Also

Steam Turbines power plants
nuclear or steam or Geothermal

Module(2) June 27, 2011

Generator connections

There are two ways to connect three windings that have a total of six leads(the ends of the winding wires) symmetrically. The two symmetrical connection configurations of a three phase generator (or motor) are called delta and wye(some people say Star).
Above Figure shows these two connection types. Generators usually have their stator windings connected internally in either a delta or wye configuration.

The generator nameplate(like the ID of any equipment.it contain all data about the machine) specifies which winding configuration is usedon the stator Delta or Wye

Delta
Delta configurations have all three windings connected in series, as shown inabove figure. The phase leads are connected to the three common points where windings are joined.
Wye
The wye configuration connects one lead from each winding to form a common point called the neutral. The other three phase leads are brought out of the generator separately for external system connections. The neutral is often
grounded to the station ground grid for voltage reference and stability.
Grounding the neutral is discussed later in this course.
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See Also

Generator prime mover
nuclear or steam or hydrulic

Module(2) June 27, 2011

Generator speed

when we speak about the generator speed we have to speak about two important factors.first factor is Rotor poles
Rotor Poles
Increasing the number of magnetic poles on the rotor enables rotor speeds to be slower and still maintain the same electrical output frequency. Generators that require slower rotor speeds to operate properly use multiple-pole rotors.

For example, hydropower plants use generators with multiple-pole rotors because the prime mover (i.e., water) is very dense and harder to control than light-weight steam.
The relationship between the number of poles on the rotor and the speed of the shaft is determined using the following mathematical formula:

Rotor speed (RPM) = 7200/ Number of poles

Above figure shows the concept of multiple poles in a generator rotor. Since these poles are derived from electromagnets, having multiple windings on a rotor can provide multiple poles.

Second Factor is the output frequency.the following relationship determines the relation between the frequency and speed
Frequency = (no. of poles * Rotor speed)/120 (HZ)

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See Also

Generator connections
wye or delta

Module(2) June 27, 2011

three phase power generator

When three coils are placed in the presence of a changing magnetic field, three voltages are produced. When the coils are spaced 120 degrees apart in a 360 degree circle, three phase AC voltage is produced. As shown in above Figure, three phase generation can be viewed as three separate single-phase generators, each of which are displaced by 120 degrees. Large and small generators that are connected to the power system have three basic components: stator, rotor, and exciter. We will now discuss these three basic components.

The Stator
A three-phase AC generator has three single-phase windings. These three windings are mounted on the stationary part of the generator, called the stator. The windings are physically spaced so that the changing magnetic field present on each winding is 120� out of phase with the other windings. A simplified drawing of a three-phase generator is shown in above Figure.

The Rotor
The rotor is the center component that when turned moves the magnetic field. A rotor could have a permanent magnet or an electromagnet and still function as a generator. Large power plant generators use electromagnets so that the magnetic field can be varied. Varying the magnetic field strength of the rotor enables generation control systems to adjust the output voltage according
to load demand and system losses. A drawing of an electromagnet
is shown in above Figure.
The operation of electromagnets is described by Len�s law before.

Electromagnets
Applying a DC voltage (battery) to a coil of wire produces a magnetic field. The coil�s magnetic field will have a north and a south pole as shown in above Figure. Increasing the voltage or the number of turns in the winding increases the magnetic field. Conversely, decreasing the voltage or number of turns in the winding decreases the magnetic field. Slip rings are electrical
contacts that are used to connect the stationary battery to the rotating rotor,as shown in above Figure.

The Exciter
The voltage source for the rotor, which eventually creates the rotor�s magnetic field, is called the exciter, and the coil on the rotor is called the field.
Most generators use slip rings to complete the circuit between the stationary exciter voltage source and the rotating coil on the rotor where the electromagnet produces the north and south poles.
Note: Adding load to a generator�s stator windings reduces rotor speed because of the repelling forces between the stator�s magnetic field, and the rotor�s magnetic field since both windings have electrical current flowing through them. Conversely, removing load from a generator increases rotor speed. Therefore, the mechanical energy of the prime mover that is responsible for spinning the rotor must be adjusted to maintain rotor speed or frequency under varying load conditions. Do you feel confused confused about this lesson? Leave your question now in a comment.

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Generator speed
factors related to generator speed

Module(2) June 27, 2011

single phase electric generator

We will now study how a generator works.you now know the faraday's law. Keep in mind that virtually all generators in service today have coils of wire mounted on stationary housings, called stators, where voltage is produced due to the magnetic field provided on the spinning rotor. The rotor is sometimes called the
field because it is responsible for the magnetic field portion of the generator. The rotor�s strong magnetic field passes the stator windings (coils), thus producing or generating an alternating voltage (AC) that is based on Faraday�s Law.The amplitude of the generator�s output voltage can be changed by changing the strength of rotor�s magnetic field. Thus, the generator�s output voltage can be lowered by reducing the rotor�s magnetic field strength.

Placing a coil of wire (conductor) in the presence of a moving magnetic field produces a voltage, as discovered by Faraday. This principle is graphically presented in above Figure .While reviewing the drawing, note that changing the rotor�s speed changes the frequency of the sine wave. Also recognize the fact that increasing the number of turns (loops) of conductor or wire in the coil increases the resulting output voltage.

Do you feel confused confused about this lesson? Leave your question now in a comment.

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three phase power generator
theory of operation and main components

Module(2) June 27, 2011

Physical laws you have to know

Before we start Module(2) we need to know two important Physical laws.If you understand this two laws,you will understand how voltage is Generated in Powr stations.you also will know how Electricity is produced and consumed.

Faraday�s Law
AC voltage is generated in electric power systems by a very fundamental physical law called Faraday�s Law. Faraday�s Law represents the phenomena behind how electric motors turn and how electric generators produce electricity.

Faraday�s Law is the foundation for electric power systems.
Faraday�s Law states,

�A voltage is produced on any conductor in a changing magnetic field.� It may be difficult to grasp the full meaning of that statement at first. It is, however, easier to understand the meaning and significance of this statement through graphs, pictures, and animations.
In essence, this statement is saying that if one takes a coil of wire and puts it next to a moving or rotating magnet, a measurable voltage will be produced in that coil. this is shown on the above figure.

Ampere�s and Lenz�s Law
The second basic physical law that explains how electric power systems work is the fact that current flowing in a wire produces a magnetic field.
Ampere�s and Lenz�s law states that �a current flowing in a wire produces a magnetic field around the wire� .This law describes the relationship between the production of magnetic fields and electric current flowing in a wire. In essence, when a current flows through a wire, a magnetic field surrounds the wire.the above figure shows this law. Do you feel confused confused about this lesson? Leave your question now in a comment.

See Also

single phase electric generator
theory of operation and main components

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