Electric Power Generation

Electric Power Generation

Before Michael Faraday had discovered his famous law of electromagnetic induction, battery were the only source of electric power. After that, DC generator was developed, but it could produce only a few hundred volts of electric power and naturally this low voltage power could not transmitted efficiently to a large distance. In the latter half of eighteen centuries, AC electric power generation, transmission and distribution came into the picture. In an AC system, it became possible to step up voltage of electric power to desire level for efficient transmission to a long distance. After that 3-phase induction motor was developed which was much simpler in construction. Generation, transmission and distribution of AC power were much easier than DC power; hence very fast AC power system became the most popular means of electric power.

Electric Power Generation

The AC power is generated in 3 phase system as 3-phase AC electric power generation is most economical. 3 phase AC generator is commonly known as the alternator. An alternator has balanced three phase winding on its stator and an electromagnetic field is rotated inside the stator. Due to this system, rotating magnetic field cuts the stator winding’s conductor and as a result, electricity is induced in the stator windings. From terminals of the stator three phase power is obtained. In an alternator, rotating electromagnet is energized by the DC source. The rotor is driven by some external means with the help of thermal, hydel, wind or other forms of energy. For example, in thermal power plant, the rotor of the alternator is rotated by means of a turbine shaft and the turbine is driven by means of high temperature and pressure steam. The steam is produced in a boiler by burning coal in the furnace.As the stator winding is perfectly balanced, the three phase power produced in an alternator is also balanced that means phase difference between two consecutive phases is 120 degrees (electrical).

Frequency, Voltage and Interconnected System

If p is the number of poles and N is the RPM of an alternator, frequency of the generated voltage will be Np/120. In India the frequency of generated power or simply power frequency is 50 Hz. In USA it is 60 Hz. In modern power plants there are generally more than one number of alternators run in parallel. Not only in a single plant, may alternators, of other plants also be interconnected to run parallel. This arrangement improves flexibility and efficiency of the power system. When the power stations of different locations are interconnected by means of transmission lines, the total network is referred as a grid. In other word grid is a system by which alternators of all power plants connected to that grid run in parallel. If any of the alternators becomes out of service, still power can be fed by other alternators without affecting availability of the system. As many numbers of alternators are connected and run in parallel, the frequency and voltage of the system becomes much stable irrespective of degree of loading present in the system. The main drawback of the grid system is, when an alternator is connected to the grid, its frequency, voltage and phase sequence must match with that of the grid, and the process of matching the said parameters of alternator with the grid is not a simple task and the process is called synchronizing.

Conventional Source of Electric Power Generation

There are mainly three conventional source of electric power generation, and they are thermal hydel, and nuclear energy.

Thermal Power Generation

In thermal power plant coal or diesel is burnt to produce sufficient heat. This heat energy is utilized to produce high temperature and high pressure steam in the boiler. This steam is then passed through the turbine blades and the turbine shaft rotates due to this steam pressure. The rotor of an alternator is mechanically coupled with the turbine shaft and hence it also rotates. This rotation produces electric power.

Hydel Power Generation

Here the water head is used to rotate the rotor shaft of an alternator. Water head can be naturally available or it can be created. In hilly region water head can be naturally available in the hill top natural lakes. In plain land, it can be created by constructing dams across suitable rivers. In comparing to a thermal power plant, hydel plants are more echo-friendly as they are free from fuel combustion. Also the running cost of hydel plant is much cheaper than that of thermal plants as there is no need of fuel to be burnt. Although running cost of a hydel power plant is quite low, but initial constructional cost of this plant is quite high as compared to thermal power plant. As because, there is huge involvement of money in construction of dams and other necessary civil buildings. Water turbine generally runs at a low speed, hence number of poles in the generator is higher to achieve fixed 50 Hz power frequency. The number of pole in a hydel alternator may be up to 20 or more.

Nuclear Power Generation

It is estimated that, the coal reserve of our country will be exhausted within next 40 years if the coal is continued to be consumed in present rate. The solution of this situation is a nuclear power plant as thought. In a nuclear power station, Uranium 235 is subjected to nuclear fission. In fission process, U 235 is bombarded by a beam of neutrons. The collision of neutrons with the nucleus of U 235 creates huge heat energy along with other neutrons. These newly created neutrons are called fission neutrons which again hit by other U 235 nuclear and create mare heat energy and other fission neutrons. During fission process the nucleus of U 235 is divided into two parts. The fission process is commutative in nature. That is why, a nuclear reaction is a chain reaction and hence it should be allowed to be occurred in a controlled manner. The moderates and control rods are used to control this chain reaction. Moderates are used to reduce the velocity of neutrons and control rods are used to absorb neutrons for maintaining, required number of neutrons for the process. Moderates are made of heavy water or pure carbon and control rods are made of cadmium or boron steel. The speed of the nuclear reaction can be controlled by inserting control rods up to a desire deep into the reaction chamber. By pushing down and pulling up the control rods, the output of the nuclear generating plant is controlled. Although this process is not manual, it is controlled by the automatic feedback control system. The heat generated during fission is taken out from the reactor by means of coolant consisting of liquid sodium or some gaseous fluids. The coolant is circulated between heat exchanger and the reactor. It takes heat from the reactor and gives the heat to the water in the heat exchanger. Thus the water in the heat exchanger is converted to high pressure and high temperature steam. This steam then drives a turbine and exhausts into a condenser where it is condensed into water and cooled down for re- feeding to the heater changes again via a feed water pump. The main advantage of nuclear power plant is its minimum fuel consumption. It has been observed that for running a 1000 MW thermal power plant, nearly 6 X106 kg of coal to be burnt every day, whereas in a nuclear power plant only 2.5 kg of Uranium to be consumed daily for getting same output. But the initial investment of nuclear power plant is quite high. It produces electricity without causing any air pollution, but, it has always a chance of radiation hazard because of leakage in reactor chamber. Another major disadvantage of this plant is its disposals, as because its disposals are not free from radioactivity.

Non Conventional Source of Electrical Power Generation

Although the main sources of electric power generation are thermal, hydel, and nuclear power plants, but still there are many other non conventional sources of power available. These non conventional sources, like wind power, solar power, MHD generation, fuel cell, etc. are becoming the promising alternative sources for electric power generation.

Power Plants and Types of Power Plant

What is Power Plant?

A power plant or a power generating station, is basically an industrial location that is utilized for the generation and distribution of electric power in mass scale, usually in the order of several 1000 Watts. These are generally located at the sub-urban regions or several kilometers away from the cities or the load centers, because of its requisites like huge land and water demand, along with several operating constraints like the waste disposal etc. For this reason, a power generating station has to not only take care of efficient generation but also the fact that the power is transmitted efficiently over the entire distance. And that’s why, the transformer switch yard to regulate transmission voltage also becomes an integral part of the power plant. At the center of it, however, nearly all power generating stations has an A.C. generator or an alternator, which is basically a rotating machine that is equipped to convert energy from the mechanical domain (rotating turbine) into electrical domain by creating relative motion between a magnetic field and the conductors. The energy source harnessed to turn the generator shaft varies widely, and is chiefly dependent on the type of fuel used.

Types of Power Station

A power plant can be of several types depending mainly on the type of fuel used. Since for the purpose of bulk power generation, only thermal, nuclear and hydro power comes handy, therefore a power generating station can be broadly classified in the 3 above mentioned types. Let us have a look in these types of power stations in details.

Thermal Power Station

A thermal power station or a coal fired thermal power plant is by far, the most conventional method of generating electric power with reasonably high efficiency. It uses coal as the primary fuel to boil the water available to superheated steam for driving the steam turbine. The steam turbine is then mechanically coupled to an alternator rotor, the rotation of which results in the generation of electric power. Generally in India, bituminous coal or brown coal are used as fuel of boiler which has volatile content ranging from 8 to 33 % and ash content 5 to 16 %. To enhance the thermal efficiency of the plant, the coal is used in the boiler in its pulverized form. In coal fired thermal power plant, steam is obtained in very high pressure inside the steam boiler by burning the pulverized coal. This steam is then super heated in the super heater to extreme high temperature. This super heated steam is then allowed to enter into the turbine, as the turbine blades are rotated by the pressure of the steam. The turbine is mechanically coupled with alternator in a way that its rotor will rotate with the rotation of turbine blades. After entering into the turbine, the steam pressure suddenly falls leading to corresponding increase in the steam volume. After having imparted energy into the turbine rotors, the steam is made to pass out of the turbine blades into the steam condenser of turbine. In the condenser, cold water at ambient temperature is circulated with the help of pump which leads to the condensation of the low pressure wet steam. Then this condensed water is further supplied to low pressure water heater where the low pressure steam increases the temperature of this feed water, it is again heated in high pressure. This outlines the basic working methodology of a thermal power plant.

Nuclear Power Station

The nuclear power generating stations are similar to the thermal stations in more ways than one. How ever, the exception here is that, radioactive elements like Uranium and thorium are used as the primary fuel in place of coal. Also in a Nuclear station the furnace and the boiler are replaced by the nuclear reactor and the heat exchanger tubes.For the process of nuclear power generation, the radioactive fuels are made to undergo fission reaction within the nuclear reactors. The fission reaction, propagates like a controlled chain reaction and is accompanied by unprecedented amount of energy produced, which is manifested in the form of heat. This heat is then transferred to the water present in the heat exchanger tubes. As a result, super heated steam at very high temperature is produced.
Once the process of steam formation is accomplished, the remaining process is exactly similar to a thermal power plant, as this steam will further drive the turbine blades to generate electricity.

Hydro-Electric Power Station

In Hydro-electric plants the energy of the falling water is utilized to drive the turbine which in turn runs the generator to produce electricity. Rain falling upon the earth’s surface has potential energy relative to the oceans towards which it flows. This energy is converted to shaft work where the water falls through an appreciable vertical distance. The hydraulic power is therefore a naturally available renewable energy given by the equation:P =gρQH
Where g = acceleration due to gravity = 9.81 m/sec ²
ρ = density of water = 1000 kg/m ³
H = height of fall of water.
This power is utilized for rotating the alternator shaft, to convert it to equivalent electrical energy.
An important point to be noted is that, the hydro-electric plants are of much lower capacity compared to their thermal or nuclear counterpart. For this reason hydro plants are generally used in scheduling with thermal stations, to serve the load during peak hours. They in a way assist the thermal or the nuclear plant to deliver power efficiently during periods of peak hours.

Types of Power Generation

As mentioned above, depending on the type of fuel used, the power generating stations as well as the types of power generation are classified. Therefore the 3 major classifications for power production in reasonably large scale are :- 1) Thermal power generation.
2) Nuclear power generation.
3) Hydro-electric power generation.
Apart from these major types of power generations, we can resort to small scale generation techniques as well, to serve the discrete demands. These are often referred to as the alternative methods of power generation and can be classified as :-
1) Solar power generation. (making use of the available solar energy)
2) Geo-thermal power generation. (Energy available in the Earth’s crust)
3) Tidal power generation.
These alternative sources of generation has been given due importance in the last few decades owing to the depleting amount of the natural fuels available to us. In the centuries to come, a stage might be reached when several countries across the globe would run out of their entire reserve for fossil fuels. The only way forward would then lie in the mercy of these alternative sources of energy which might play an instrumental role in shaping the energy supplies of the future. For this reason these might rightfully be referred as the energy of the future.

Thermal Power Generation Plant or Thermal Power Station

Thermal power generation plant or thermal power station is the most conventional source of electric power. Thermal power plant is also referred as coal thermal power plant and steam turbine power plant. Before going into detail of this topic, we will try to understand the line diagram of electric power generation plant.

Theory of Thermal Power Station

The theory of thermal power station or working of thermal power station is very simple. A power generation plant mainly consists of alternator runs with help of steam turbine. The steam is obtained from high pressure boilers. Generally in India, bituminous coal, brown coal and peat are used as fuel of boiler. The bituminous coal is used as boiler fuel has volatile matter from 8 to 33 % and ash content 5 to 16 %. To increase the thermal efficiency, the coal is used in the boiler in powder form.In coal thermal power plant, the steam is produced in high pressure in the steam boiler due to burning of fuel (pulverized coal) in boiler furnaces. This steam is further supper heated in a super heater. This supper heated steam then enters into the turbine and rotates the turbine blades. The turbine is mechanically so coupled with alternator that its rotor will rotate with the rotation of turbine blades. After entering in turbine the steam pressure suddenly falls and corresponding volume of the steam increases. After imparting energy to the turbine rotor the steam passes out of the turbine blades into the condenser. In the condenser the cold water is circulated with the help of pump which condenses the low pressure wet steam. This condensed water is further supplied to low pressure water heater where the low pressure steam increases the temperature of this feed water, it is again heated in high pressure. For better understanding we furnish every step of function of a thermal power station as follows,
1) First the pulverized coal is burnt into the furnace of steam boiler.
2) High pressure steam is produced in the boiler.
3) This steam is then passed through the super heater, where it further heated up.
4) This supper heated steam is then entered into a turbine at high speed.
5) In turbine this steam force rotates the turbine blades that means here in the turbine the stored potential energy of the high pressured steam is converted into mechanical energy.

Line Diagram of Power Plant

6) After rotating the turbine blades, the steam has lost its high pressure, passes out of turbine blades and enters into a condenser.
7) In the condenser the cold water is circulated with help of pump which condenses the low pressure wet steam.
8) This condensed water is then further supplied to low pressure water heater where the low pressure steam increases the temperature of this feed water, it is then again heated in a high pressure heater where the high pressure of steam is used for heating.

9) The turbine in thermal power station acts as a prime mover of the alternator.

Overview of Thermal Power Plant

A typical Thermal Power Station Operates on a Cycle which is shown below.

The working fluid is water and steam. This is called feed water and steam cycle. The ideal Thermodynamic Cycle to which the operation of a Thermal Power Station closely resembles is the RANKINE CYCLE. In steam boiler the water is heated up by burning the fuel in air in the furnace & the function of the boiler is to give dry super heated steam at required temperature. The steam so produced is used in driving the steam Turbines. This turbine is coupled to synchronous generator (usually three phase synchronous alternator), which generates electrical energy. The exhaust steam from the turbine is allowed to condense into water in steam condenser of turbine, which creates suction at very low pressure and allows the expansion of the steam in the turbine to a very low pressure. The principle advantages of condensing operation are the increased amount of energy extracted per kg of steam and thereby increasing efficiency and the condensate which is fed into the boiler again reduces the amount of fresh feed water.The condensate along with some fresh make up feed water is again fed into the boiler by pump (called the boiler feed pump). In condenser the steam is condensed by cooling water. Cooling water recycles through cooling tower. This constitutes cooling water circuit. The ambient air is allowed to enter in the boiler after dust filtration. Also the flue gas comes out of the boiler and exhausted into atmosphere through stacks. These constitute air and flue gas circuit. The flow of air and also the static pressure inside the steam boiler (called draught) is maintained by two fans called Forced Draught (FD) fan and Induced Draught(ID) fan.
The total scheme of a typical thermal power station along with different circuits is illustrated below.

Inside the boiler there are various heat exchangers, viz.’ Economiser’, ‘Evaporator’ (not shown in the fig above, it is basically the water tubes, i.e. down comer riser circuit), ‘Super Heater’ (sometimes ‘Reheater’, ‘air preheater’ are also present).
In Economiser the feed water is heated to considerable amount by the remaining heat of flue gas.

The Boiler Drum actually maintains a head for natural circulation of two phase mixture (steam + water) through the water tubes.
There is also Super Heater which also takes heat from flue gas and raises the temperature of steam as per requirement.

Efficiency of Thermal Power Station or Plant

The overall efficiency of a thermal power station or plant varies from 20% to 26% and it depends upon plant capacity.

Installed plant capacity	Average overall thermal efficiency
upto 1MW	4%
1MW to 10MW	12%
10MW to 50MW	16%
50MW to 100MW	24%
above 100MW	27%

Thermal Power Plant Location

A thermal power station or thermal power plant has ultimate target to make business profit. Hence for optimizing the profit, the location of the station is much important factor. Power generation plant location plays an optimizing part in the economy of the station.
The most economical , location of power plant can be determined by graphical method as described below, The most economical and ideal power plant location is the center of gravity of the load because for such a power generation plant the length of the power transmission network will be minimum, thus the capital cost to the system is reduced. Let’s explain the graphical method, say, X and Y be two reference axes. Let’s Q₁(x₁, y₁), Q₂(x₂, y₂), Q₃(x₃, y₃), Q₄(x₄, y₄),……………………………………….and Q_n(x_n, y_n) are n numbers of load centers. From the above graph we get, the coordinates of the center of gravity of the load, Q(x, y) where,

Obviously the location of thermal power station is best at the center of gravity of the load, but many times it is not possible to establish a thermal power plant at the CG of the load. Since normally CG point of the load may be at the heart of the city. so other many points to be considered to decide the best optimized location of the power plant.
1) The electric power generation plant must be constructed at such a place where the cost of land is quite reasonable.
2) The land should be such that the acquisition of private property must be minimum.
3) A large quantity of cooling water is required for the condensers etc of thermal power generation plant, hence the plant should preferably situated beside big source of natural water source such as big river.
4) Availability of huge amount of fuel at reasonable cost is one of the major criterion for choosing plant location.
5) The plant should be established on plane land.
6)The soil should be such that it should provide good and firm foundation of plant and buildings.
7) The thermal power plant location should not be very nearer to dense locality as there are smoke, noise steam, water vapors etc.
8) There must be ample scope of development of future demand.
9) Place for ash handling plant for thermal power station should also be available very near by.
10) Very tall chimney of power station should not obstruct the traffics of air ships.

Advantages & Disadvantages of Thermal Power Station

Advantages: 1) Economical for low initial cost other than any generating plant.2) Land required less than hydro power plant.
3) Since coal is main fuel & its cost is quite cheap than petrol/diesel so generation cost is economical.
4) There are easier maintenance.
5) Thermal power plant can be installed in any location where transportation & bulk of water are available.
Disadvantages: 1) The running cost for a thermal power station is comparatively high due to fuel,maintenance etc.
2) Large amount of smoke causes air pollution.The thermal power station is responsible for Global warming.
3) The heated water that comes from thermal power plant has an adverse effect on the lives in the water and disturbs the ecology.
4) Overall efficiency of thermal power plant is low like less 30%.

Hydro Power Plant | Construction Working and History of Hydro power plant

Power system mainly contains three parts namely generation, transmission and distribution. Generation means how to generate electricity from the available source and there are various methods to generate electricity but in this article we only focused on generation of electricity by the means of hydro or water (hydro power plant). As we know that the power plant is defined as the place where power is generated from a given source, so here the source is hydro that’s why we called it hydro power plant. In hydro power plant we use gravitational force of fluid water to run the turbine which is coupled with electric generator to produce electricity. This power plant plays an important role to protect our fossil fuel which is limited, because the generated electricity in hydro power station is the use of water which is renewable source of energy and available in lots of amount without any cost. The big advantage of hydro power is the water which the main stuff to produce electricity in hydro power plant is free, it not contain any type of pollution and after generated electricity the price of electricity is average not too much high.

Construction and Working of Hydro Power Plant

Fundamental parts of hydro power plant are a) Area b) Dam c) Reservoir d) Penstock e) Storage tank f) Turbines and generators g) Switchgear and protection For construction of hydro power plant first we choose the area where the water is sufficient to reserve and no any crisis of water and suitable to build a dam, then we construct the dam. The main function of dam is to stop the flow of water and reserve the water in reservoir. Mainly dam is situated at a good height to increase the force of water. Reservoir stocks up lots of water which is employed to generate power by means of turbines. After that Penstock, the pipe which is connected between dam and turbine blades and most important purpose of the penstock is to enlarge the kinetic energy of water that’s why this pipe is made up of extremely well-built material which carry on the pressure of water. To control the pressure of water means increase or decrease water pressure whenever required, we use a valve. Storage tank comes in picture when the some reason the pressure of water in reservoir is decreases then we use storage tank it is directly connected to penstock and use only in emergency condition. After that we employ turbine and generator. Turbine is the main stuff, when water comes through the penstock with high kinetic energy and falls on turbine blades, turbine rotates at high speed. As we know that the turbine is an engine that transfers energy of fluid into mechanical energy which is coupled with generator and generator converts mechanical energy into electrical energy which we utilize at the end. In hydro power plant we also add switchgears and protections which control and protect the whole process inside the plant. The control equipments consists control circuits, control devices, warning, instrumentation etc and connect to main control board. After generating electricity at low voltage, we use step up transformer to enlarge the level of voltage (generally 132KV, 220KV, 400KV and above) as per our requirement. After that we transmit the electric power to the load center, and then we step down the voltage for industrial and large consumer and then again we step down the voltage to distribute electricity at domestic level which we used at home. This is the whole process of generating electricity by the means of hydro (hydro power plant) and then transmitting and distributing electricity.

History of Hydro Power Plant

First hydro power is used by the Greekins to spin water wheels for crushing wheat into flour before more than 2000 years ago. In the 1700's, hydropower was generally used for pumping irrigation (non-natural use of water on the way to the land) water. We start to generate electricity from hydro power in 1882 when United States (U S) establishes a first hydro power station which generate 12.5 kilowatts (KW) of power. The rapid growth of hydro power comes in 1900’s when hydraulic reaction turbine comes in picture as a result in 1900’s hydro power plants fulfill the requirement of 40% of total United States' electricity. In between 1905-1911 largest hydro power station (Roosevelt Dam) is built by the united state and its generated capacity is increased from 4500kW to 36,000kW.In 1914 S.J. Zowski developed the high specific speed reaction (Francis) turbine runner for low head applications. 1922 the first time a hydroelectric plant was built specifically for crest power. In 1933 Hoover Dam, Arizona generated electricity first time. In 1940 over 1500 hydro power plants generate about one third of the United States' electrical energy.If we compare the countries on the basis of generated electricity by the means of hydro power, Canada on the top after that United State then Brazil then Russia then China then Norway and at 7th number India is present. India fulfills the 3.5% power to the total world power through hydro power plants. In India scope of hydro power is very good, first hydro power station, capacity of 130kW establishes in Asia at mounts of Darjeeling in 1898 and after that in 1902 Shimsh (Shivanasamudra) is established and both located in India. Now a day in India the leading hydro power plant is located of river Naptha Jhakri hydro project of 1500MW in Himachal Pradesh. In India main boost come in the field of hydro power in august 1998 when the Government of India publicized a plan on ‘Hydro Power Development’ after that in November 2008 once again Indian government announced this plan and as a result India become leading country list to produce hydro power. This a general idea about hydro power plant.

Nuclear Power Station or Nuclear Power Plant

 Electrical power can be generated by means of nuclear power. In nuclear power station, electrical power is generated by nuclear reaction. Here, heavy radioactive elements such as Uranium (U²³⁵) or Thorium (Th²³²) are subjected to nuclear fission. This fission is done in a special apparatus called as reactor. Before going to details of nuclear power station, let’s try to understand what is fission? In fission process, the nuclei of heavy radioactive atoms are broken into two nearly equal parts. During this breaking of nuclei, huge quantity of energy is released. This release of energy is due to mass defect. That mean, the total mass of initial product would be reduced during fission. This loss of mass during fission is converted into heat energy as per famous equation E = mc², established by Albert Einstein. The basic principle of nuclear power station is same as steam power station. Only difference is that, instead of using heat generated due to coal combustion, here in nuclear power plant, heat generated due to nuclear fission is used to produce steam from water in the boiler. This steam is used to drive a steam turbine. This turbine is the prime mover of the alternator. This alternator generates electrical energy. Although, the availability of nuclear fuel is not plenty but very less amount of nuclear fuel can generate huge amount of electrical energy. This is the unique feature of a nuclear power plant. One kg of uranium is equivalent to 4500 metric tons of high grade coal. That means complete fission of 1 kg uranium can produce as much heat as can be produced by complete combustion of 4500 metric tons high grade coal. This is why, although nuclear fuel is much costlier, but nuclear fuel cost per unit electrical energy is still lower than that cost of energy generated by means of other fuel like coal and diesel. To meet up conventional fuel crisis in present era, nuclear power station can be the most suitable alternatives.

Advantages of Nuclear Power Station

1. As we said, the fuel consumption in this power station is quite low and hence, cost for generating single unit is quite less than other conventional power generation method.
2. A nuclear power station occupies much smaller space compared to other conventional power station of same capacity.
3. This station does not require plenty of water, hence it is not essential to construct plant near natural source of water. This also does not required huge quantity of fuel; hence it is also not essential to construct the plant near coal mine, or the place where good transport facilities are available. Because of this, the nuclear power station can be established very near to the load centre.

Disadvantages of Nuclear Power Plant

1. The fuel is not easily available and it is very costly.
2. Initial cost for constructing nuclear power station is quite high.
3. Erection and commissioning of this plant is much complicated and sophisticated than other conventional power station.
4. The fission by products are radioactive in nature, and it may cause high radioactive pollution.
5. The maintenance cost is higher and the man power required to run a nuclear power plant is quite higher since speciality trained people are required.
6. Sudden fluctuation of load cannot be met up efficiently by nuclear plant.
7. As the by products of nuclear reaction is high radioactive, it is very big problem for disposal of this by products. It can only be disposed deep inside ground or in a sea away from sea share.

Different Components of Nuclear Power Station

A nuclear power station has mainly four components.

1. Nuclear reactor,
2. Heat exchanger,
3. Steam turbine,
4. Alternator.

Let’s discuss these components one by one:

Nuclear Reactor

In nuclear reactor, Uranium 235 is subjected to nuclear fission. It controls the chain reaction that starts when the fission is done. The chain reaction must be controlled otherwise rate of energy release will be fast, there may be a high chance of explosion. In nuclear fission, the nuclei of nuclear fuel, such as U²³⁵ are bombarded by slow flow of neutrons. Due to this bombarding, the nuclei of Uranium is broken, which causes release of huge heat energy and during breaking of nuclei, number of neutrons are also emitted.These emitted neutrons are called fission neutrons. These fission neutrons cause further fission. Further fission creates more fission neutrons which again accelerate the speed of fission. This is cumulative process. If the process is not controlled, in very short time the rate of fission becomes so high, it will release so huge amount of energy, there may be dangerous explosion. This cumulative reaction is called chain reaction. This chain reaction can only be controlled by removing fission neutrons from nuclear reactor. The speed of the fission can be controlled by changing the rate of removing fission neutrons from reactors.
A nuclear reactor is a cylindrical shaped stunt pressure vessel. The fuel rods are made of nuclear fuel i.e. Uranium moderates, which is generally made of graphite cover the fuel rods. The moderates slow down the neutrons before collision with uranium nuclei. The controls rods are made of cadmium because cadmium is a strong absorber of neutrons.
The control rods are inserted in the fission chamber. These cadmium controls rods can be pushed down and pull up as per requirement. When these rods are pushed down enough, most of the fission neutrons are absorbed by these rods, hence the chain reaction stops. Again, while the controls rods are pulled up, the availability of fission neutrons becomes more which increases the rates of chain reaction. Hence, it is clear that by adjusting the position of the control rods, the rate of nuclear reaction can be controlled and consequently the generation of electrical power can be controlled as per load demand. In actual practice, the pushing and pulling of control rods are controlled by automatic feedback system as per requirement of the load. It is not controlled manually. The heat released during nuclear reaction, are carried to the heat exchanger by means of coolant consist of sodium metal.

Heat Exchanger

In heat exchanger, the heat carried by sodium metal, is dissipated in water and water is converted to high pressure steam here. After releasing heat in water the sodium metal coolant comes back to the reactor by means of coolant circulating pump.

Steam Turbine

In nuclear power plant, the steam turbine plays the same role as coal power plant. The steam drives the turbine in same way. After doing its job, the exhaust steam comes into steam condenser where it is condensed to provide space to the steam behind it.

Alternator

An alternator, coupled with turbine, rotates and generates electrical power, for utilization.

Site Selection of Nuclear Power Station

1. Availability of water : Although very large quantity of water is not regulated as hydro-electric power plant, but still sufficient supply of neutral water is obvious for cooling purposes in nuclear power station. That is why it is always preferable to locate this plant near a river or sea side.
2. Disposal of Water : The by products or wastes of nuclear power station are radioactive and may cause severe health hazards. Because of this, special care to be taken during disposal of wastes of nuclear power plant. The wastes must be buried in sufficient deep from earth level or these must be disposed off in sea quite away from the sea share. Hence, during selecting the location of nuclear plant, these factor must be taken into consideration.
3. Distance from Populated Area : As there is always a probability of radioactivity, it is always preferable to locate a nuclear station sufficiently away from populated area.
4. Transportation Facilities : During commissioning period, heavy equipments to be erected, which to be transported from manufacturer site. So good railways and road ways availabilities are required. For availability of skilled manpower good public transport should also be present at the site.

Diesel Power Station

For generating electrical power, it is essential to rotate the rotor of an alternator by means of a prime mover. The prime mover can be driven by different methods. Using diesel engine as prime mover is one of the popular methods of generating power. When prime mover of the alternators is diesel engine, the power station is called diesel power station.
The mechanical power required for driving alternator comes from combustion of diesel. As the diesel costs high, this type of power station is not suitable for producing power in large scale in our country. But for small scale production of electric power, and where, there is no other easily available alternatives of producing electric power, diesel power station are used. Steam power stations and hydro power plants are mainly used to produce maximum portion of the electrical load demands. But for steam power station, sufficient supply of coal and water are required. For hydro power station, plenty source of water and big dams are required. But where all these facilities are not available, such as no easy way of coal transportation and no scope of constructing dam, there it is established.
Diesel power plants are also popularly used as standby supply of different industries, commercial complexes, hospitals, etc. During power cut, these diesel power generators are run to fulfil required demand.

Advantages of Diesel Power Station

1. This is simple in design point of view.
2. Required very small space.
3. It can also be designed for portable use.
4. It has quick starting facility, the small diesel generator set can be started within few seconds.
5. It can also be stopped as when required stopping small size diesel power station, even easier than it’s starting
6. As these machines can easily be started and stopped as when required, there may not be any standby loss in the system.
7. Cooling is easy and required smaller quantity of water in this type power station.
8. Initial cost is less than other types of power station.
9. Thermal efficiency of diesel is quite higher than of coal.
10. Small involvement is less than steam power station.

Disadvantages of Diesel Power Station

1. As we have already mentioned, the cost of diesel is very high compared to coal. This is the main reason for which a diesel power plant is not getting popularity over other means of generating power. In other words the running cost of this plant is higher compared to steam and hydro power plants.
2. The plant generally used to produce small power requirement.
3. Cost of lubricants is high.
4. Maintenance is quite complex and costs high.

Different Components of Diesel Power Station

In addition to diesel generator set or DG set there are many other auxiliaries attached to at diesel power station. Let’s discuss one by one.

Fuel Supply System

In fuel supply system there are one storage tank, where oil in stored. Strainer : This oil then pump to dry tank, by means of transfer pump. During transferring from main tank to smaller dry tank, the oil passes through strainer to remove solid impurities. From dry tank to main tank, there is another pipe connection. This is over flow pipe. This pipe connection is used to return the oil from dry tank to main tank in the event of over flowing. From dry tank the oil is injected in the diesel engine by means of fuel injection pump.

Air Intake System

This system supplies necessary air to the engine for fuel combustion. It consists of a pipe for supplying of fresh air to the engine. Filters are provided to remove dust particles from air.

Exhaust System

The exhaust gas is removed from engine, to the atmosphere by means of an exhaust system. A silencer is normally used in this system to reduce noise level of the engine.

Cooling System

The heat produced due to internal combustion, drives the engine. But some parts of this heat raise the temperature of different parts of the engine. High temperature may cause permanent damage to the machine. Hence, it is essential to maintain the overall temperature of the engine to a tolerable level. Cooling system of diesel power station does exactly so. The cooling system requires a water source, water source, water pump and cooling towers. The pump circulates water through cylinder and head jacket. The water takes away heat from the engine and it becomes hot. The hot water is cooled by cooling towers and is re-circulated for cooling.

Lubricating System

This system minimises the water of rubbing surface of the engine. Here lubricating oil is stored in main lubricating oil tank. This lubricating oil is drawn from the tank by means of oil pump. Then the oil is passed through the oil filter for removing impurities. From the filtering point, this clean lubricating oil is delivered to the different points of the machine where lubrication is required the oil cooler is provided in the system to keep the temperature of the lubricating oil as low as possible.

Starting System

For starting a diesel engine, initial rotation of the engine shaft is required. Until the firing start and the unit runs with its own power. For small DG set, the initial rotation of the shaft is provided by handles but for large diesel power station. Compressed air is made for starting.

Cogeneration | Combined Heat and Power

Cogeneration is also called as combined heat and power or combine heat and power. As it name indicates cogeneration works on concept of producing two different form of energy by using one single source of fuel. Out of these two forms one must be heat or thermal energy and other one is either electrical or mechanical energy.

Cogeneration is the most optimum, reliable, clean and efficient way of utilizing fuel. The fuel used may be natural gas, oil, diesel , propane, wood, bassage, coal etc. It works on very simple principle i.e the fuel is used to generate electricity and this electricity produces heat and this heat is used to boil water to produce steam , for space heating and even in cooling buildings. In conventional power plant , the fuel is burnt in a boiler , which in turn produces high pressure steam. This high pressure steam is used to drive a tribune, which is in turn is connected to an alternator and hence drive an alternator to produce electric energy.The exhaust steam is then sent to the condenser, where it gets cool down and gets converted to water and hence return back to boiler for producing more electrical energy. The efficiency of this conventional power plant is 35% only. In cogeneration plant the low pressure steam coming from turbine is not condense to form water, instead of it its used for heating or cooling in building and factories, as this low pressure steam from turbine has high thermal energy. The cogeneration plant has high efficiency of around 80 - 90 %. In India, the potential of power generation from cogeneration plant is more than 20,000 MW. The first commercial cogeneration plant was built and designed by Thomas Edison in New York in year 1882. As shown in above diagram, in traditional power plant, when we gave fuel as input we get electrical energy and losses as output but in case of cogeneration with fuel as input, the output is electrical energy, heat or thermal energy and losses. In convential power plant , with 100% energy input ,only 45% of energy is used and rest 55% is wasted but with cogeneration , the total energy used is 80% and energy wasted is only 20% . It means with cogeneration the fuel utiliuzation is more efficient and optimized and hence more economical.

Need for Cogeneration

a) Cogeneration helps to improve the efficiency of the plant. b) Cogeneration reduce air emissions of particulate matter, nitrous oxides, sulphur dioxide, mercury and carbon dioxide which would otherwise leads to greenhouse effect. c) It reduces cost of production and improve productivity. d) Cogeneration system helps to save water consumption and water costs. e) Cogeneration system is more economical as compared to conventional power plant

Types of Cogeneration Power Plants

In a typical Combined heat and power plant system there is a steam or gas turbine which take steam and drives an alternator. A waste heat exchanger is also installed in cogeneration plant, which recovers the excess heat or exhaust gas from the electric generator to in turn generate steam or hot water. There are basically two types of cogeneration power plants, such as- • Topping cycle power plant • Bottoming cycle power plant Topping cycle power plant- In this type of Combine Heat and Power plant electricity is generated first and then waste or exhaust steam is used to heating water or building . There are basically four types of topping cycles. a) Combined-cycle topping CHP plant - In this type of plant the fuel is firstly burnt in a steam boiler . The steam so produced in a boiler is used to drive turbine and hence synchronous generator which in turn produces electrical energy . The exhaust from this turbine can be either used to provide usable heat, or can be send to a heat recovery system to generate steam, which maybe further used to drive a secondary steam turbine.b) Steam-turbine topping CHP Plant- In this the fuel is burned to produce steam, which generates power. The exhaust steam is then used as low-pressure process steam to heat water for various purposes.
c) Water- turbine topping CHP Plant- In this type of CHP plant a jacket of cooling water is run through a heat recovery system to generate steam or hot water for space heating. d) Gas turbine topping CHP plant- In This topping plant a natural gas fired turbine is used to drives a synchronous generator to produce electricity. The exhaust gas is sent to a heat recovery boiler where it is used to convert water into steam, or to make usable heat for heating purposes.
Bottoming cycle power plant - As its name indicate bottoming cycle is exactly opposite of topping cycle. In this type of CHP plant the excess heat from a manufacturing process is used to generate steam, and this steam is used for generating electrical energy. In this type of cycle no extra fuel is required to produce electricity, as fuel is already burnt in production process.

Configuration of Cogeneration Plant

• Gas turbine Combine heat power plants which uses the waste heat in the flue gas emerging out of gas turbines.
 • Steam turbine Combine heat power plants that use the heating system as the jet steam condenser for the steam turbine.
• Molten-carbonate fuel cells have a hot exhaust, very suitable for heating.
• Combined cycle power plants adapted for Combine Heat and Power.

Magneto Hydro Dynamic Power Generation

The MHD generation or, also known as magneto hydrodynamic power generation is a direct energy conversion system which converts the heat energy directly into electrical energy, without any intermediate mechanical energy conversion, as opposed to the case in all other power generating plants. Therefore, in this process, substantial fuel economy can be achieved due to the elimination of the link process of producing mechanical energy and then again converting it to electrical energy .

History of MHD Generation

The concept of MHD power generation was introduced for the very first time by Michael Faraday in the year 1832 in his Bakerian lecture to the Royal Society. He in fact carried out an experiment at the Waterloo Bridge in Great Britain for measuring the current, from the flow of the river Thames in earth's magnetic field. This experiment in a way outlined the basic concept behind MHD generation over the years then, several research work had been conducted on this topic, and later in August 13, 1940 this concept of magneto hydro dynamic power generation, was imbibed as the most widely accepted process for the conversion of heat energy directly into electrical energy without a mechanical sub-link.

Principle of MHD Generation

The principal of MHD power generation is very simple and is based on Faraday’s law of electromagnetic induction, which states that when a conductor and a magnetic field moves relative to each other, then voltage is induced in the conductor, which results in flow of current across the terminals. As the name implies,the magneto hydro dynamics generator shown in the figure below, is concerned with the flow of a conducting fluid in the presence of magnetic and electric fields. In conventional generator or alternator, the conductor consists of copper windings or stripswhile in an MHD generator the hot ionized gas or conducting fluid replaces the solid conductor. A pressurized, electrically conducting fluid flows through a transverse magnetic field in a channel or duct. Pair of electrodes are located on the channel walls at right angle to the magnetic field and connected through an external circuit to deliver power to a load connected to it. Electrodes in the MHD generator perform the same function as brushes in a conventional DC generator. The MHD generator develops DC power and the conversion to AC is done using an inverter.

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The power generated per unit length by MHD generator is approximately given by,

Where u is the fluid velocity, B is the magnetic flux density, σ is the electrical conductivity of conducting fluid and P is the density of fluid.

It is evident from the equation above, that for the higher power density of an MHD generator there must be a strong magnetic field of 4-5 tesla and high flow velocity of conducting fluid besides adequate conductivity.

MHD Cycles and Working Fluids

The MHD cycles can be of two types, namely 1) Open cycle MHD. 2) Closed Cycle MHD. The detailed account of the types of MHD cycles and the working fluids used, is given below.

Open Cycle MHD System

In open cycle MHD system, atmospheric air at very high temperature and pressure is passed through the strong magnetic field. Coal is first processed and burnet in the combustor at a high temperature of about 2700°C and pressure about 12 atp with pre-heated air from the plasma. Then a seeding material such as potassium carbonate is injected to the plasma to increase the electrical conductivity. The resulting mixture having an electrical conductivity of about 10 siemens/m is expanded through a nozzle, so as to have a high velocity and then passed through the magnetic field of MHD generator. During the expansion of the gas at high temperature, the positive and negative ions move to the electrodes and thus constitute an electric current. The gas is then made to exhaust through the generator. Since the same air cannot be reused again hence it forms an open cycle and thus is named as open cycle MHD.

Closed Cycle MHD System

As the name suggests the working fluid in a closed cycle MHD is circulated in a closed loop. Hence, in this case inert gas or liquid metal is used as the working fluid to transfer the heat. The liquid metal has typically the advantage of high electrical conductivity, hence the heat provided by the combustion material need not be too high. Contrary to the open loop system there is no inlet and outlet for the atmospheric air. Hence the process is simplified to a great extent, as the same fluid is circulated time and again for effective heat transfer.

Advantages of MHD Generation

The advantages of MHD generation over the other conventional methods of generation is given below.1) Here only working fluid is circulated, and there are no moving mechanical parts. This reduces the mechanical losses to nil and makes the operation more dependable.
2) The temperature of working fluid is maintained the walls of MHD.
3) It has the ability to reach full power level almost directly.
4) The price of MHD generators is much lower than conventional generators.
5) MHD has very high efficiency, which is higher than most of the other conventional or non-conventional method of generation.

Thermoelectric Power Generators or Seebeck Power Generation 

The term theroelectric is combination of two words thermo and electric and as its name indicates thermal means heat energy and electric means electrical energy. Thermoelectric power generators are the devices which used to convert temperature difference between two junctions into electrical energy. A working of thermoelectric generator is based on Seebeck effect. According to which, a loop of two dissimilar metal develops an emf when the two junctions are kept at different temperature. That is why it is also referred as Seebeck Power Generation. A thermo-electrical generator basically consists of heat source, which is kept at high temperature and a heat sink, which is maintained at a temperature less than the heat source. The temperature difference between heat source and heat sink causes direct current to flow through the load. In this type of energy conversion there is no intermediate energy conversion like in case of most of the conversion so, it is also called direct power conversion. The power generated due to Seebeck power generation is single phase DC and given by I²R_L or VI where R_L is the load resistance.
The output voltage and output power are increased either by increasing the temperature difference between the hot and cold ends or by connecting several thermoelectric power generators in series. The current will continue to flow as long as heat is supplied to the hot junction and removed from the cold junction. This current produced by thermoelectric or Seebeck power generation is DC in nature and can be converted into ac by using invertors and its voltage level can be further step up by using transformers. The energy conversion through thermoelectric or Seebeck power generation is reversible process i.e the direction of energy flow can be reversed. If we remove load and supply DC power across the terminals where load was connected, the heat can be easily drawn from the thermoelectric power generator.

Performance Analysis of Thermoelectric Power Generator

Consider a thermoelectric power generator having heat source at one end and heat sink at other end. The heat source is kept at high temperature as compare to heat sink. Let the temperature difference between two junctions is ΔT. The sides of generating device are insulated so, the heat flows along the length only. The applied heat to the hot junction causes the electrons in the n type block and the holes in the p type block to flow away from the heat junction and thereby producing a electrical potential difference. The circuit is completed by connecting a load resistance, R_L. The current will start flowing through this load resistance, R_L.

The voltage of this generator is given by V = α ΔT where α is Seebeck coefficient and ΔT is the temperature difference between hot and cold junction. Let R is the internal resistance of the thermoelectric power generator then the current flowing through the external resistance R_L is given by,

Substitute the value of voltage in above equation we get current,

We know that power flow to external load is given by, P_L = I²R_L Substitute the value of I,

This power will be maximum when R = R_L So, maximum power is given by,

In Seebeck Power Generation the term (α² / R) is called figure of merit. For power to be maximum ΔT and (α² / R) should have large value or we can say internal resistance should be low and this can be done by decreasing the length and increasing the diameter. ΔT can be increased by increasing the temperature difference between heat source and heat sink.

Efficiency of Thermoelectric Power Generator

The efficiency of thermoelectric power generator is defined as the ratio of power developed, P_L across load resistance, R_L to the heat flow, Q from the source,

Materials Suitable for Thermoelectric Power Generators

The most commonly used material for this generator is lead telluride. Lead telluride is a compound made of lead and tellurium having small amount of bismuth or sodium. Other compounds used for making thermoelectric power generators are bismuth telluride, bismuth sulphide, germanium telluride, zinc antimonite, tin telluride and indium arsenide etc.

Application of Thermoelectric Generators

• For increasing the fuel efficiency of cars, thermoelectric generators are used. These generator use heat produced when the vehicle is running.
• Seebeck Power Generation is used to supply power to spacecrafts.
• These generators are used to supply power to remote stations like weather stations, relay stations etc.

Limitations of Thermoelectric Power Generators

• High output resistance required - As explained earlier for getting high output voltage and power several thermoelectric generators are connected in series, which in turn increases the total output resistance. Therefore for transferring high power efficiently large resistances are needed. This problem can be overcome by connecting more thermoelectric elements in parallel rather in series because it causes decrease in effective resistance.
• Thermoelectric power generators generate less electric power for the same heat flow i.e they have low efficiency as compared to other mechanical generators. For the same energy input, the Seebeck Power Generation produces less output as compare to other energy converters.
• Low thermal characteristics - The heat dissipation of any device depends upon its thermal conductivity. Any good thermoelectric power generator has low thermal conductivity and hence poor heat dissipation. So, these generators are efficient only when small power is required.
• Thermoelectric generators are costly as compare to other generators.