POWER GENERATION

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 AC 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 condensor 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.

Advantages of Thermal Power Plants

• Fuel used i.e coal is quite cheaper.
• Initial cost is less as compared to other generating stations.
• It requires less space as compared to hydro-electric power stations.

Disadvantages of Thermal Power Plants

• It pollutes atmosphere due to production of smoke & fumes.
• Running cost of the power plant is more than hydro electric 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 eqn:

P = gρ QH

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.

Advantages of Hydro Electric Power Station

• It requires no fuel , water is used for generation of electrical energy.
• It is neat and clean energy generation.
• Construction is simple , less maintenance is required.
• It helps in irrigation and flood control also.

Disadvantages Hydro Electric Power Station

• It involves high capital cost due to dam construction.
• Availability of water depends upon weather conditions.
• It requires high transmission cost as the plant is located in hilly areas.

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 or non conventional energy 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.
4. Wind power generation (energy available from the wind turbines)

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. downcomer 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

Overall efficiency of steam power plant is defined as the ratio of heat equivalent of electrical output to the heat of combustion of coal. The overall efficiency of a thermal power stationor plant varies from 20% to 26% and it depends upon plant capacity.

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.

points are 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 and 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 and its cost is quite cheap than petrol/diesel so generation cost is economical.
4. Maintenance is easier.
5. Thermal power plant can be installed in any location where transportation and 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 aquatic lives in the water and disturbs the ecology.
4. Overall efficiency of thermal power plant is low like less 30%.

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).

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

1. Area
2. Dam
3. Reservoir
4. Penstock
5. Storage tank
6. Turbines and generators
7. Switchgear and protection

For construction of hydro power plant first we choose the area where the water is sufficient to reserve and no crisis of water and suitable to build a 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 hold lots of water which is employed to generate power by means of turbines. 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 132 KV, 220 KV, 400 KV 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.

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 means, 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 much 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 of energy is quite less than other conventional power generation method. Amount of nuclear fuel required is also less.
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.
4. There are large deposits of nuclear fuel globally therefore such plants can ensure continued supply of electrical energy for coming thousands years.

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 is 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 specialist 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 shore.

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. The output from alternator is delivered to the bus-bars through transformer, circuit breakers and isolators.

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 factors 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 diesel plant 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 fulfill 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.

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.
5. Plant does not work satisfactorily under overload conditions for a longer period.

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 strainers, fuel transfer pump and all day fuel tank. 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 because these particles can act as an abrasive in the engine cylinder.

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 wear 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.

Engine 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 used for starting.

NOTE:-Why Supply Frequency is 50 Hz or 60 Hz?

1. Constant losses are directly proportional to frequency and its square, so they may increase system losses.
2. With higher frequencies high heat losses will occures
3. The frequency directly proportional to the rotating speed of alternator and it is not practical to construct very high speed alternators. Hence it is practically difficult to achieve high frequency electrical power during generation.

Cost of Electrical Energy

There are three kinds of expenditures involved in generating electricity. These are fixed cost, semi-fixed cost, running or operating cost.

1. Fixed Cost of Electricity: In every manufacturing unit there is some hidden expenditure which fixed. This is same for manufacturing one unit or thousand units of the items. In electric generating station like manufacturing unit, there are some hidden costs which independent of the quantity of electricity produced. These fixed expenditures are mainly due to an annual cost to run the organization, interest on capital cost and tax or rent of the land on which the organization established, salaries of high officials and interests of loans (if any) on the capital cost of the organization. Like these main costs, there are many others expenditures which do not change whether the rate of production of electrical energy units is less or more.
2. Semi-fixed Cost: There is another type costing for any manufacturing or production or any similar type of industries. These costs are not strictly fixed and also not fully dependent on the number of items manufactured or produced. These costs depend on the size of the plant. These actually depend on the assumption of a maximum number of items which can be produced from the plant at a time during peak demand period. That means the forecasted production demand of the plant determines how big will be the manufacturing or production plant. Likewise, the size of an electrical generating plant depends on the maximum demand of the connected load of the system. If the maximum demand of the load is quite higher than the average demand of the load, then the power generating plant should be constructed and well equipped to fulfill that maximum demand of the system even the peak demand lasts for less than an hour. This type of costs is referred as semi-fixed cost. It is directly proportional to the maximum demand on the power station. The annual interest and depreciation on capital investment of building and equipment, taxes, salaries of management and clerical staff, expenditure for installation etc. come under semi-fixed costs.
3. Running Cost: The concept of running cost is quite simple. It solely depends on the number of units produced or generated. In power generating plant the main running cost is the cost of fuel burnt per unit of electrical energy generation. The cost of lubricating oil, maintenance, repairs and salaries of operating staff are also accounted under running cost of the plant. Since these charges are directly proportional to the number of units generated. For generating more units of electrical energy required running expenditures are more and vies verse.

Gas Turbine Power Plant

The basic principle of all most all power generating stations except solar power generating stations is producing electricity by rotating the shaft of alternators by means of the prime mover. Major efforts are applied to arrange the motion of the prime mover in these power plants. In all cases any kind of turbine action is required to move the prime mover, in other words, we can say, the turbine is the prime mover. There is a special type of power generating station where gas turbine is used as the prime mover. This power generating plant is called a gas turbine power plant. Here the air is first compressed at desired pressure then it is brought to a combustion chamber where the compressed air is heated up by means of fuel combustion.

Then this highly compressed hot air is released from the combustion chamber through the nozzle to a turbine, called gas turbine. During expansion of pressurized and hot air, mechanical work is done to rotate the turbine. As the turbine rotates, the alternator also rotates since a common shaft is shared by both turbine and alternator in the gas turbine power plant. It is needed to be mentioned here that not only the turbine and alternator, the air compressor is also fitted on the same shaft.
This is because the mechanical power developed by the gas turbine can be shared by the air compressor for its operation along with the alternator. The mechanical energy required to compress the air must be more than the mechanical energy developed by the compressed air. But here the mechanical energy developed in the gas turbine by compressed air contributes both for compressing the air and producing the electricity. How can it be possible? The answer to this question is that the required energy developed in the system comes from the heat energy produced by combustion of fuel. Here, in the gas turbine power plant, compressed air only acts as a fluid. This type of power plant is not used for producing electrical power in commercial scale but normally used as a standby plants in a hydroelectric station for supplying auxiliary electricity during starting of the main power plant.

Advantages of Gas Turbine Power Plant

1. There is no need of boiler as in the case of a steam power generating plant. As the boiler is not used the auxiliaries associated with the boiler are also absent in the gas turbine power plant hence the design is much simpler than the steam power plant.
2. For the same reasons as mentioned above, the size of the gas turbine power plant is much smaller than that of a same capacity steam power plant.
3. The manufacturing, engineering, installation and commissioning costs are much lower. The running cost is also less than that of same rated steam power plant.
4. As the design and construction are simpler than a same capacity steam power plant, the maintenance cost also smaller in the gas turbine power plant.
5. Gas turbine itself is much simpler in design and construction than a steam turbine.
6. This power plant can be started much quickly even in cold condition.
7. In steam power plant the boiler is kept operative even at off-load condition because restarting a boiler is much expensive and time-consuming process. But in the case of a gas turbine power plant entire plant can be kept inoperative at offload condition. Hence, this system is free from standby losses.

Disadvantages of Gas Turbine Power Plant

1. For running the gas turbine system, compressed air is required. When the plant runs, the compressor runs and supplies the required compressed air. But when the plant just starts its operation, there is no compressed air previously available but this required compressed air cannot be produced before the compressor is run. The drawback of the system can be overcome by running the compressor by some external means before actual starting the plant.
2. In this system, a major part of the mechanical power developed by the gas turbine is utilized to run the compressor which causes the low output of the system.
3. A major portion of the heat energy of fuel combustion is lost to exhaust air. The exhaust heat cannot be reutilized efficiently like as in the case of a steam power plant.
4. The internal temperature of the combustion chamber is very high. This highly tempted part of the system reduces the overall life span of a gas turbine power plant compared to other forms of a power plant.

Solar Electricity

When sunlight strikes on photo-voltaic solar cells, solar electricity is produced. That is why this is also referred to as Photo Voltaic Solar, or PV Solar.

Principles of Solar Electricity

Generation of electricity by using solar energy depends on the photo voltic effect(The effect due to which light energy is converted to electric energy in certain semiconductor materials is known as photovoltaic effect). In photo voltaic effect, p n junction produces electric potential when it is exposed to sunlight. For that purpose, we make n type semiconductor layer of the junction very thin. It is less than 1 µm thick. The top layer is n layer. We generally refer it as emitter of the cell.

The bottom layer is p type semiconductor layer and it is much thicker than top n layer. It may be more than 100 µm thick. We call this bottom layer as base of the cell. The depletion region is created at the junction of these two layers due to immobile ions.

When sunlight strikes on the cell, it easily reaches up to p n junction. The p n junction absorbs the photons of sunlight ray and consequently, produces electrons holes pairs in the junction. Actually, the energy associated with photon excites the valence electrons of the semiconductors atoms and hence the electrons jump to the conduction band from valence band leaving a hole behind each.

The free electrons, find themselves in the depletion region will easily pass to the top n layer because of attraction force positive ions in the depletion region. In the same way the holes find themselves in the depletion region will easily pass to the bottom p layer because of attraction force of negative ions in the depletion region. This phenomenon creates a charge difference between the layers and resulting to a tiny potential difference between them.

The unit of such combination of n type and p type semiconductor materials for producing electric potential difference in sunlight is called solar cell. Silicon is normally used as the semiconductor material for producing such solar cell.

Conductive metal strips attached to the cells take the solar cell or photo voltic cell is not capable of producing desired electricity instead it produces very tiny amount of electricity. Hence for extracting the desired level of electricity required numbers of such cells are connected together in both parallel and series to form a solar module or photo voltaic module. Actually, only sunlight is not the factor. The main factor is light or beam of photons to produce electricity in the solar cell. Hence a solar cell can also work in cloudy weather as well as in moonlight but then electricity production rate becomes law as it depends upon the intensity of incident light ray.

Application of Solar Electricity

Solar electric power generation system is useful for producing moderate amount of power. The system works as long as there is a good intensity of natural sunlight. The place where solar modules are installed should be free from obstacles such as trees and buildings otherwise there will be the shade on the solar panel which affects the performance of the system. It is a general view that solar electricity is an impractical alternative of the conventional source of electricity and should be used when there is no traditional alternative of the conventional source of electricity available. But this is not the actual case. Often it seems that solar electricity is more money saving alternative than other traditional alternatives of conventional electricity.

There are mainly four types of solar power stations.

1. Stand Alone or Off Grid type Solar Power Plant
2. Grid Tie type Solar Power Plant
3. Grid Tie with Power Backup or Grid Interactive type Solar Power Plant
4. Grid Fallback type Solar Power Plant.

Let us discuss a brief introduction of each type of solar power plant.

Stand Alone or Off Grid Solar Power Station

This is most commonly used photo-voltaic installation used to provide localized electricity in absence of conventional source of electric power at certain location. As the name prefers this system does not keep any direct or indirect connection with any grid type network.

In standalone system the solar modules produce electric energy which is utilized to charge a storage battery and this battery delivers electricity to the connected load. Standalone systems are normally small system with less than 1 kilo watt generation capacity.

Grid Tie Solar Power Station

In some countries facility is available of selling power to the local or national grid. This is gaining popularity in Europe and the United States. This system facilitates both electric utility companies as well as the consumers. Here consumers can generate electricity by their own plant and can sell the surplus to the electricity utility company through grid connected to their plant. As the consumers sell the power they can earn money as return of their investment for installation of captive power plant on the other hand electric utility companies can reduce their capital investment on their own plant for power generation. In a grid-tie solar system, consumers consume electricity produced by solar captive power plant during sunny day time and also export surplus energy to grid but at night while solar plant does not produce energy, they import electric energy from grid for consumption. The main disadvantage of this system is that if there is a power cut in the grid, the solar modules should be disconnected from the grid. This system is not always very profitable especially where overall maximum demand of the system does not occur at the peak sunny period of the day. In hot climate where the power demand for air conditioning machines becomes maximum during peak sunny period of the day, this grid tie solar power generation system works most efficiently.

Grid tie solar systems are of two types one with single macro central inverter and other with multiple micro inverters. In the former type of solar system, the solar panels as well as grid supply are connected to a common central inverter called grid tie inverter as shown below. The inverter here converts the DC of the solar panel to grid level AC and then feeds to the grid as well as the consumer’s distribution panel depending upon the instant demand of the systems. Here grid-tie inverter also monitors the power being supplied from the grid. If it finds any power cut in the grid, it actuates switching system of the solar system to disconnect it from the grid to ensure no solar electricity can be fed back to the grid during power cut. There is on energy meter connected in the main grid supply line to record the energy export to the grid and energy import from the grid.

As we already told there is another type of grid-tie system where multiple micro-inverters are used. Here one micro inverter is connected for each individual solar module. The basic block diagram of this system is very similar to previous one except the micro inverters are connected together to produce desired high AC voltage. In previous case the low direct voltage of solar panels is first converted to alternating voltage then it is transformed to high alternating voltage by transformation action in the inverter itself but in this case the individual alternating output voltage of micro inverters are added together to produce high alternating voltage.

Grid Tie with Power Backup Solar Power Generation

It is also called grid interactive system. This is a combination of a grid-tie solar power generation unit and storage battery bank. As we said, the main drawback of grid tie system is that when there is any power cut in the grid the solar module is disconnected from the system. For avoiding discontinuity of supply during power cut period one battery bank of sufficient capacity can be connected with the system as power backup.

Grid Fallback Solar Power Generation

Grid fallback is most reliable and stable system mainly used for electrifying smaller households. Here solar modules charge a battery bank which in turn supplies distribution boards through an inverter. When the batteries are discharged to a pre-specified level, the system automatically switches back to the grid power supply. The solar modules then recharge the batteries and after the batteries are being charged up to a pre-specified level again the system switches back to solar power. We do not sell electricity back to the electricity utility companies through this system. All the power that we produce is utilized for ourselves only.
Although we do not have any direct earning benefit from this system but the system has its own big advantages. This system is most popular where there is no facility of selling power to the grid.
Grid fallback system has all advantages of grid interactive system except power selling, but it adds benefit of using own power whenever it is required irrespective of position and condition of sun in the sky.

Solar Panels

The main part of a solar electric system is the solar panel. There are various types of solar panel available in the market. Solar panels are also known as photovoltaic solar panels. 

Batteries

In grid-tie solar generation system, the solar modules are directly connected to inverter not with load. The power collected from solar panel not in constant rate rather it varies with intensity of sunlight. This is the reason why solar modules or panels do not feed any electrical equipment directly instead they feed an inverter whose output is synchronized with external grid supply. Inverter takes care of the voltage level and frequency of the output power from the solar system it always maintains it with that of grid power level. As we get power from both solar panels and external grid power supply system, the voltage level and quality of power remain constant. As the stand-alone or grid fallback system is not connected with grid any variation of power level in the system can directly affects the performance of the electrical equipment fed from it. So there must be some means to maintain the voltage level and power supply rate of the system. A battery bank connected parallel to this system takes care of that. Here the battery is charged by solar electricity and this battery then feeds a load directly or through an inverter. In this way variation of power quality due to variation of sunlight intensity can be avoided in solar power system instead an uninterrupted uniform power supply is maintained. Normally Deep cycle lead acid batteries are used for this purpose. These batteries are typically designed to make capable of several charging and discharging during service. The battery sets available in the market are generally of either 6 volt or 12 volts. Hence number of such batteries can be connected in both series as well as parallel to get higher voltage and current rating of the battery system.

Controller

This is not desirable to overcharge and under discharge a lead acid battery. Both overcharging and under discharging can badly damage the battery system. To avoid these both situations a controller is required to attach with the system to maintain flow of current to and fro the batteries.

Inverter

It is obvious that the electricity produced in a solar panel is DC. Electricity we get from the grid supply is AC. So for running common equipment from grid as well as solar system, it is required to install an inverter to convert DC of solar system to AC of same level as grid supply. In off grid system the inverter is directly connected across the battery terminals so that DC coming from the batteries is first converted to AC then fed to the equipment. In grid tie system the solar panel is directly connected to inverter and this inverter then feeds the grid with same voltage and frequency power.

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MUST HAVE TO KNOW THINGS IN ELECTRICAL ENGINEERING

Fleming's right-hand rule (for generators) shows the direction of induced current when a conductor attached to a circuit moves in a magnetic field. It can be used to determine the direction of current in a generator's windings.

Fleming's left-hand rule

Whenever a current carrying conductor is placed in a magnetic field, the conductor experiences a force which is perpendicular to both the magnetic field and the direction of current.

According to Fleming's left hand rule, if the thumb, fore-finger and middle finger of the left hand are stretched to be perpendicular to each other as shown in the illustration at left, and if the fore finger represents the direction of magnetic field, the middle finger represents the direction of current, then the thumb represents the direction of force. Fleming's left hand rule is applicable for motors.

NOTE: Fleming's left hand rule is for motors and Fleming's RIGHT hand rule hand rule is for generators.

Conductance

It is defined as a special property of a conductor which determines how easily an current can flow through it.

Equation or Formula of Electrical Conductance

Let us take a piece of conductor of length l and cross sectional area A. If length of the conductor is increased, the electrons have to drift more paths. Hence more chance of inter atomic collision. That means current gets much harder path to travel, means electrical conductance of the conductor is reduced.
Thus conductance is inversely proportional to length of the conductor.If cross sectional area of conductor is increased then current gets more drift electrons. Hence, conductance of the conductor is increased.From equation (1) and (2),Where, σ = constant of proportional known as conductivity or specific conductance.

Definition of Electrical Conductivity

Conductivity is a material of per unit volume.
Electrical conductivity is a basic property of material. Due to this property one material can conduct electricity. Some materials are good conductor of electricity that means current can pass through them very easily; again some materials do not allow current to flow through them. The material through which current passes easily, called good conductor of electricity in other words, the electrical conductivity of these materials is high. On the other hand the materials do not allow the current to flow through them are called electrical insulators. There are some materials whose electrical conductivity is not as high as conductor and also not as poor as insulator, they have an intermediate conductivity and these type of materials are known as semiconductors.

Unit of Conductance

As we mentioned earlier conductance is reciprocal of resistance of resistance. That is,Unit of resistance is ohm and that is why unit of conductance is generally written as mho - the reverse spelling of ohm. A modern electrical engineering, mho is named by Siemens.

Unit of Conductivity

The equation of conductivity, we have already deducted as,Hence, unit of conductivity is,Here, S is Siemens.

Resistance

Electrical resistance may be defined as the basic property of any substance due to which it opposes the flow of current through it.

If one volt across a conductor produces one ampere of current through it, then the resistance of the conductor is said to be one ohm (Ω).

 The resistance of any substance depends on the following factors,

1. The resistance of a substance depends on its length.
2. The resistance of a substance depends on its cross sectional area.
3. The resistance of a substance depends on the nature of material of the substance.
4. The resistance of a substance depends on the temperature of the substance.

Resistance of the conductor increases with increasing length of the conductor. This relation is also linear. Electrical resistance R of a conductor or wire isWhere, L is the length of the conductor.

Second Law of Resistivity

The current through any conductor depends on the numbers of electrons pass through a cross-section of conductor per unit time. So, if cross section of any conductor is larger then more electrons can cross the cross section. Passing of more electrons through a cross-section per unit time causes more current through the conductor. For fixed voltage, more current means less Electrical resistance and this relation is linear. So it can be concluded like that, resistance of any conductor is inversely proportional to its cross-sectional area.Electrical resistance R of a conductor or wire isWhere, A is the cross-sectional area of the conductor.
Combining these two laws we get,
Electrical resistance R of a conductor or wire isWhere, ρ (rho) is the proportionality constant and known as resistivity or specific resistance of the material of the conductor or wire. Now if we put, l = 1 and a = 1 in the equation,We get, R = ρ. That means resistance of a material of unit length having unit cross - sectional area is equal to its resistivity or specific resistance.
Resistivity of a material can be alliteratively defined as the electrical resistance between opposite faces of a unit cube of that material.

The unit of resistivity is Ω-m in MKS system and Ω-cm in CGS system.

Electric Conductor

A conductor of electricity is a material or substance which allows to flow of electric current when subjected to a potential difference. This electric current is continue to flow till the potential difference exists. For a given potential difference, the density of electric current in conductor represents how efficient a conductor is. Based on the resistivity the conductors can be classified into two categories i.e. low resistivity/high conductivity materials and high resistivity/low conductivity materials.

In equilibrium condition the conductor exhibits the following properties –

1. Resistance
2. Inductance
3. The electric filed inside the conductor is zero
4. The charge density inside the conductor is zero
5. Free charge exists only on the surface of the conductor
6. At the conductor surface, the electric field is normal to the surface.

Resistance of Electric Conductor

Conductors of electricity generally possessed very low resistance for flow of electricity. Ideally the resistance of a perfect conductor is zero. However, practically the resistivity of conductors varies from low to high. The conductor having low resistivity/high conductivity are used as conductor for winding of electrical machines, for transmission line, for electrical contact, earth wire etc. The conducting materials having high resistivity/low conductivity are used for making filaments incandecent lamp and heating elements for electric heaters, Ovens, furnaces.

Inductance of Electric Conductor

When a conductor is used on AC supply a magnetic flux is produced. Which is consists of two parts. Internal flux and external flux. The value of internal flux is very low as compare to external flux. Due to this flux linkage to conductor itself an inductance is come into picture. This inductance results in extra voltage drop in conductor. Moreover, this inductance is also effect the current distribution over the cross-section area of conductor. Due to which, current prefers to flow through outer part of cross-sectional area. This effect is called Skin effect. This current distribution over cross-sectional area is also effected by the flux linkage to conductor due to current following through nearby conductor. This is called Proximity effect These both effects Skin effect and Proximity effect exist only for AC supply. These effects do not exist for DC supply, as the flux produced by DC supply remains constant over the time.

The Electric Field Inside the Conductor is Zero

The electrical field inside a perfect conductor is zero. If the electric field exists inside the conductor, it will extract a force on electron and accelerate them. But in equilibrium condition the net force on electron is zero. Hence, electric filed does not exists inside the conductor. Means the electric field must be external to the conductor. This property of conductor make it suitable to be used for electrostatic shielding for electrical equipment.

The Charge Density Inside the Conductor is Zero

This electric charge does not exists inside the conductor. The mutual electrostatic repulsion force, between like charges i.e. electrons, demands that the electrons must be as far as possible. This electrostatic repulsion force pushes the electrons to the surface on conductor. Due to which there is no electric charge exists inside the conductor results in zero charge density inside the conductor.

Free Charge Exists Only on the Surface of the Conductor

As discussed above, the charge particle does not exist inside the conductor. Due to electrostatic repulsion force, the electrons move to outer surface of the conductor. Due to which there is no electric charge exists inside the conductor. Hence, free electric charge exits only on the surface of the conductor.

The Conductor Surface, The Electric Field is Normal to The Surface

If we go through the boundary condition of dielectric to conductor, the electric field is normal to the surface of conductor and tangent part of electric field to surface is zero. Means, the electric field intensity is normal to the surface of conductor and the tangential part of electric field intensity is zero.

Magnetic Field

The space around a magnet within which the influence of the magnet can be predicted, is called magnetic field.

We can visualize or map a magnetic field with a small free to rotate magnetic needle. If we place the said magnetic needle in front of the North Pole of a bar magnet, the north end of the needle will face outwards from the North Pole of the bar magnet. If we push the magnetic needle towards the direction of the north end of the needle, the alignment of the needle will change further towards the South Pole of the magnetic bar. If the needle further proceeds along the alignment of north head of the needle, again the alignment of the needle is further changed towards the magnetic South Pole of the bar.

In this way if we move the magnetic needle and follow the alignment of needle head at each position of the needle, we will find that the needle will ultimately comes to the south pole of the magnetic bar following a typical curvature path.This path of travelling a magnetic needle following the alignment of needle itself, from North to South Pole of a bar magnet is referred as magnetic lines of force. There are possibilities of number of such magnetic paths in a magnetic field as shown below.

We can map a magnetic field by using iron filings. Here, we keep a bar magnet below a horizontally placed card board. Now we will sprayed fine iron flings on the card. We will find that, the iron filings set themselves in the form of curve chains between north and south pole of the bar magnet. This curve chains of iron filings indicate the lines of force of the magnetic field of the bar magnet.The lines of force is the line on which if we place a magnetic north pole it will experience the magnetic force in the direction along the tangent drawn on curve (lines of force) on that point. We can also define the line of force as a curve, along which a free to move unit north pole travels from north pole to south pole of a magnet due to influence of magnetic field.

FLUX

Flux can be used in various concepts, such as

Magnetic Flux

It means the number magnetic field lines passing through a closed surface. Its SI unit is – Weber and in CGS is – Maxwell. It is denoted as Φ_m.

If we place an imaginary isolated unit north pole in a magnetic field it will experience a repulsive force from north pole and an attractive force from south pole of the magnet which has created the field. Due to these both forces, acting on the isolated unit north pole, the north pole will move along a particular path in the field if the pole is free to do so. If we place the same isolated unit north pole at different distance from the magnet in the field, it may follow a different path of travelling.

We call these paths of travelling of the unit north pole in the field, as lines of force. As we can place this imaginary isolated unit north pole at infinite number of points in the field, there may be infinite numbers of lines of force in the field. But visualize a magnetic field with infinite number of lines of force is useless for any scientific calculation. So we have to develop some unique concept, so that we can represent a magnetic field according to its entire strength. We take the unit of magnetic flux as weber. If a field has &hi; weber flux, it means the field has total φ number of lines of force. Like isolated north pole, the concept of lines of force in a magnetic field is also imaginary. It does not has any physical existence. This is only used for different magnetic calculation and for explaining different magnetic properties.

Properties of Magnetic Flux

1. Magnetic flux of a filed is considered as the total number of magnetic lines of force in the field. These are also called magnetic flux lines.
2. Each magnetic flux line is closed loop.
3. Each magnetic flux line starts from north pole of a magnet and comes to the south pole through the field and continues from south pole to north pole in the body of the magnet.
4. No two flux lines cross each other.
5. Two similar lines of force travel side by side but repeal each other.
6. The lines of force are stretched like elastic cord.

Magnetic Flux Density

The number of magnetic lines of force passing through a unit area surface perpendicular to the magnetic field is called magnetic flux density. If total φ Weber flux perpendicularly through a surface of area A m², Magnetic flux density of the field would be,We generally represent magnetic flux density by capital letter B.

Electric Charge

Every matter in this universe is made of atoms. The atoms are electrically neutral. This is because, each atom has equal number of protons and electrons. Protons have positive charge. In an atom, protons sit in the central nucleus along with electrically neutral neutrons. The protons are strongly bounded in the nucleus. So, protons cannot be detached from the nucleus by any normal process. Each electron revolves round the nucleus in definite orbit in the atom. Electrons have negative charge. The quantity of electric charge of an electron is exactly equal to that of a proton but in opposite in nature. The electrons are negative and protons are positive. So, a piece of matter normally electrically neutral, since it is made of electrically neutral atoms.

The electrons are also bounded in the atoms but not all. Few of the electrons which are farthest from the nucleus may be detached by any means. If some of these detachable electrons of neutral atoms of a body, are removed, there will be a deficit of electrons in the body. After, removal of some of the detachable electrons from the neutral body, the total number of protons in the body becomes more than total number of electrons in the body. As a result the body will become positively charged.
Not only a body can give away electrons, it may also absorb some extra electrons, supplied from outside. In that case, the body becomes negatively charged.
So, deficit or excess of electrons in a body of matter is called electric charge.
Charge of an electron is very small and it is equal to . So, total  number of electrons have electric charge of 1 Coulomb. So, if a body deficits  number of excess electrons, the body will be of 1 coulomb negative electric charge. number of electrons, the body will be of 1 coulomb positive electric charge. On the other hand, if a body has  number of excess electrons, the body will be of 1 coulomb negative electric charge.

Charged body is an example of static electricity. This is because, the electric charge is confined in the body itself. Here, the charge is not in motion.
But when the electric charge is in motion, it causes electric current. Electric charge has the potential of doing work. That means it has potential to either attract opposite nature of charge or repulse same nature of charge. A charge is the result of separating electrons and protons.

Statement of Coulomb’s Law

First Law

Like charge particles repel each other and unlike charge particles attract each other.

Second Law

The force of attraction or repulsion between two electrically charged particles is directly proportional to the magnitude of their charges and inversely proportional to the square of the distance between them.

Formulas of Coulomb’s Law

According to the Coulomb’s second law,Where,

1. ‘F’ is the repulsion or attraction force between two charged bodies.
2. ‘Q₁’ and ‘Q₂’ are the electrical charged of the bodies.
3. ‘d’ is distance between the two charged particles.
4. ‘k’ is a constant that depends on the medium in which charged bodies are presented. In S.I. system, as well as M.K.S.A. system k=1/4πε. Hence, the above equation becomes.
The value of ε₀ = 8.854 × 10^-12 C²/Nm².Hence, Coulomb’s law can be written for medium as,Then, in air or vacuum ε_r = 1. Hence, Coulomb’s law can be written for air medium as,The value of εr would change depends on the medium. The expression for relative permittivity ε_r is as follows;

Principle of Coulomb’s Law

Suppose if we have two charged bodies one is positively charged and one is negatively charged, then they will attract each other if they are kept at a certain distance from each other. Now if we increase the charge of one body keeping other unchanged, the attraction force is obviously increased. Similarly if we increase the charge of second body keeping first one unchanged, the attraction force between them is again increased. Hence, force between the charge bodies is proportional to the charge of either bodies or both.Now, by keeping their charge fixed at Q₁ and Q₂ if you bring them nearer to each other the force between them increases and if you take them away from each other the force acting between them decreases. If the distance between the two charge bodies is d, it can be proved that the force acting on them is inversely proportional to d².This development of force is not same for all mediums. As we discussed in the above formulas, εr would change for various medium. So, depends on the medium, creation of force can be varied.

Limitation of Coulomb’s Law

1. Coulomb’s law is valid, if the average number of solvent molecules between the two interesting charge particles should be large.
2. Coulomb’s law is valid, if the point charges are at rest.
3. It is difficult to apply the Coulomb’s law when the charges are in arbitrary shape. Hence, we cannot determine the value of distance ‘d’ between the charges when they are in arbitrary shape.

Electric Field Strength or Electric Field Intensity

The force acting on a unit positive charge inside an electric field is termed as electric field strength.

Electric field strength or electric field intensity is the synonym of electric field. Electric field strength can be determined by Coulomb's law.According to this law, the force ‘F’ between two point charges having charge Q₁ and Q₂Coulomb and placed at a distance d meter from each other is given by,Here, ε_o is the permittivity of vacuum = 8.854 × 10^-12 F/m and ε_r is the relative permittivity of the surrounding medium.

Now, let us put Q₂ = + 1 Coulomb and let us denote force F by E in the equation (1), and by doing these we get,This equation shows the force acting the a unit positive charge placed at a distance d from charge Q₁.As per definition this is nothing but of electric field strength of charge Q₁ at a distance d from that charge.
Now, we got the expression of electric field strength or intensity. Now, by combining this expression with equation (1), we get,The above expression shows that, if we place a charge at any point in an electric field, the product of the electric field strength at that point and the charge of the body gives the force acting on the body at that point in the field. The above expression can also be rewritten as,Depending on this expression, the electric field strength can be expressed in Newton/Coulomb. The electric field strength has direction and hence it is vector quantity.
Intensity means the magnitude or amount. Now field intensity similarly means the magnitude of the strength of the field. Finally electric field intensity or strength can be written as,So far we have discussed about the electric field intensity at a point due to the influence of a single charge, but there may be a case where, the point is under the filed of more than one charged bodies. In that case, we first have to calculate, the electric field strength at that point for individual charges and the we have to vectorially add up all the field strengths to get resultant field strength at that point.

Electric Potential

Electric potential at a point in an electric field is defined as the amount of work to be done to bring a unit positive electric charge from infinity to that point.

If two electrically charged bodies are connected by a conductor, the electrons starts flowing from lower potential body to higher potential body, that means current starts flowing from higher potential body to lower potential body depending upon the POTENTIAL DIFFERENCE of the bodies and resistance of the connecting conductor.

So, electric potential of a body is its charged condition which determines whether it will take from or give up electric charge to other body. Electric potential is graded as electrical level, and difference of two such levels, causes current to flow between them. This level must be measured from a reference zero level. The earth potential is taken as zero level. Electric potential above the earth potential is taken as positive potential and the electric potential below the earth potential is negative.

The unit of electric potential is volt. To bring a unit charge from one point to another, if one joule work is done, then the potential difference between the points is said to be one volt. So, we can say,

Capacitor and Capacitance

Capacitor is a passive element that stores electric charge statistically and temporarily as an static electric field. It is composed of two parallel conducting plates separated by non-conducting region that is called dielectric, such as vacuum, ceramic, air, aluminum, etc.
The capacitance formula of the capacitor is represented by,C is the capacitance that is proportional to the area of the two conducting plates (A) and proportional with the permittivity ε of the dielectric medium. The capacitance decreases with the distance between plates (d). We get the greatest capacitance with a large area of plates separated by a small distance and located in a high permittivity material. The standard unit of capacitance is Farad, most commonly it can be found in micro-farads, pico-farads and nano-farads.

General uses of Capacitors

1. Smoothing, especially in power supply applications which required converting the signal from AC to DC.
2. Storing Energy.
3. Signal decoupling and coupling as a capacitor coupling that blocks DC current and allow AC current to pass in circuits.
4. Tuning, as in radio systems by connecting them to LC oscillator and for tuning to the desired frequency.
5. Timing, due to the fixed charging and discharging time of capacitors.
6. For electrical power factor correction and many more applications.

Charging a Capacitor

Capacitors are mainly categorized on the basis of dielectric used in them. During choosing a specific type of capacitors for a specific application, there are numbers of factors that get considered. The value of capacitance is one of the vital factors to be considered. Not only this, many other factors like, operating voltage, allowable tolerance stability, leakage resistance, size and prices are also very important factors to be considered during choosing specific type of capacitors.

We know that capacitance of a capacitor is given by,Hence, it is cleared that, by varying ε, A or d we can easily change the value of C. If we require higher value of capacitance (C) we have to increase the cross-sectional area of dielectric or we have to reduce the distance of separation or we have to use DIELECTRIC MATERIAL with stronger permittivity.

If we go only for the increasing area of cross-section, the rise of the capacitor may become quite large; which may not be practically acceptable. Again if we reduce only the distance of separation, the thickness of dielectric becomes very thin. But the dielectric cannot be made too thin in case its dielectric strength in exceeded.

Types of Capacitors

The various types of capacitors have been developed to overcome these problems in a number of ways.

Paper Capacitor

It is one of the simple forms of capacitors. Here, a waxed paper is sandwiched between two aluminium foils.
Process of making this capacitor is quite simple. Take place of aluminium foil. Cover this foil with a waxed paper. Now, cover this waxed paper with another aluminium foil. Then roll up this whole thing as a cylinder. Put two metal caps at both ends of roll. This whole assembly is then encapsulated in a case. By rolling up, we make quite a large cross-sectional area of capacitor assembled in a reasonably smaller space.

Air Capacitor

There are two sets of parallel plates. One set of plates is fixed and another set of plates is movable. When the knob connected with the capacitor is rotated, the movable set of plates rotates and overlapping area as between fixed and movable plates vary. This causes variation in effective cross-sectional areas of the capacitor. Consequently, the capacitance varies when one rotates the knob attached to the air capacitor. This type of capacitor is generally used to tune the bandwidth of a radio receiver.

Plastic Capacitor

When various plastic materials are used as dielectric material, the capacitors are said to be plastic capacitors. The plastic material may be of polyester, polystyrene, polycarbonate or poly propylene. Each of these materials has slightly different electrical characteristics, which can be used to advantage, depending upon the proposed application.

This type of capacitors is constructional, more or less same as paper capacitor. That means, a thin sheet one of the earlier mentioned plastic dielectrics, is kept between two aluminium foils. That means, here the flexible thin plastic sheet is used as dielectric instead of waxed paper. Here, the plastic sheet covered by aluminium foil from two sides, is first rolled up, then fitted with metal end caps, and then the whole assembly is encapsulated in a case.

Plastic Film Capacitor

Plastic capacitor can be made also in form of film capacitor. Here, thin strips or films of plastic are kept inside metallic strips. Each metallic strip is connected to side metallic contact layer alternatively; as shown in the figure below. That means, if one metallic strip is connected to left side contact layer, then the very next is connected to right side contact layer. And there are plastic films in between these metallic strips. The terminals of this type of capacitors are also connected to side contact layer and whole assembly is covered with insulated non metallic cover.

Silvered Mica Capacitor

A silvered mica capacitor is very accurate and reliable capacitor. This type of capacitors has very low tolerance. But on the other hand, cost of this capacitor is quite higher compared to other available capacitors in the market. But this high cost capacitor can easily be compensated by its high quality and performance. A small ceramic disc or cylinder is coated by silver compound. Here, electrical terminal is affixed on the silver coating and the whole assembly is encapsulated in a casing.

Ceramic Capacitor

Construction of ceramic capacitor is quite simple. Here, one thin ceramic disc is placed between two metal discs and terminals are soldered to the metal discs.Whole assembly is coated with insulated protection coating.

Mixed Dielectric Capacitor

The way of constructing this capacitor is same as paper capacitor. Here, instead of moving waxed paper as dielectric, paper impregnated with polyester is used as dielectric between two conductive aluminium foils.

Electrolyte Capacitor

Very large value of capacitance can be achieved by this type of capacitor. But working voltage level of this electrolyte capacitor is low and it also suffers from high leakage current. The main disadvantage of this capacitor is that, due to the use of electrolyte, the capacitor is polarized. The polarities are marked against the terminals with + and – sign and the capacitor must be connected to the circuit in proper polarity.

A few micro meter thick aluminium oxide or tantalum oxide film is used as dielectric of electrolyte capacitor. As this dielectric is so thin, the capacitance of this type of capacitor is very high. This is because; the capacitance is inversely proportional to thickness of the dielectric. Thin dielectric obviously increases the capacitance value but at the same time, it reduces working voltage of the device. Tantalum type capacitors are usually much smaller in size than the aluminium type capacitors of same capacitance value. That is why, for very high value of capacitance, aluminium type electrolyte capacitors do not get used generally. In that case, tantalum type electrolyte capacitors get used.

Aluminium electrolyte capacitor is formed by a paper impregnated with an electrolyte and two sheets of aluminium. These two sheets of aluminium are separated by the paper impregnated with electrolyte. The whole assembly is then rolled up in a cylindrical form, just like a simple paper capacitor. This roll is then placed inside a hermetically sealed aluminium canister. The oxide layer is formed by passing a charging current through the device, and it is the polarity of this charging process that determines the resulting terminal polarity that must be subsequently observed. If the opposite polarity is applied to the capacitor, the oxide layer is destroyed.

Energy Stored in Capacitor

While CAPACITOR is connected across a BATTERY, charges come from the battery and get stored in the capacitor plates. But this process of energy storing is step by step only.
At the very beginning, capacitor does not have any charge or potential. i.e. V = 0 volts and q = 0 C.Now at the time of switching, full battery voltage will fall across the capacitor. A positive charge (q) will come to the positive plate of the capacitor, but there is no work done for this first charge (q) to come to the positive plate of the capacitor from the battery. It is because of the capacitor does not have own voltage across its plates, rather the initial voltage is due to the battery.

First charge grows little amount of voltage across the capacitor plates, and then second positive charge will come to the positive plate of the capacitor, but gets repealed by the first charge. As the battery voltage is more than the capacitor voltage then this second charge will be stored in the positive plate. At that condition a little amount of work is to be done to store second charge in the capacitor. Again for the third charge, same phenomenon will appear. Gradually charges will come to be stored in the capacitor against pre-stored charges and their little amount of work done grows up.It can’t be said that the capacitor voltage is fixed. It is because of the capacitor voltage is not fixed from the very beginning. It will be at its maximum limit when potency of capacitor will be equal to that of the battery.
As storage of charges increases, the voltage of the capacitor increases and also energy of the capacitor increases. 
So at that point of discussion the energy equation for the capacitor can’t be written as energy (E) = V.q
As the voltage increases the electric field (E) inside the capacitor dielectric increases gradually but in opposite direction i.e. from positive plate to negative plate.Here dx is the distance between two plates of the capacitor.Charge will flow from battery to the capacitor plate until the capacitor gains as same potency as the battery.
So, we have to calculate the energy of the capacitor from the very begging to the last moment of charge getting full.

Suppose, a small charge q is stored in the positive plate of the capacitor with respect to the battery voltage V and a small work done is dW.
Then considering the total charging time, we can write that,Now we go for the energy loss during the charging time of a capacitor by a battery.
As the battery is in the fixed voltage the energy loss by the battery always follows the equation, W = V.q, this equation is not applicable for the capacitor as it does not have the fixed voltage from the very beginning of charging by the battery.
Now, the charge collected by the capacitor from the battery isNow charge lost by the battery isThis half energy from total amount of energy goes to the capacitor and rest half of energy automatically gets lost from the battery and it should be kept in mind always.

Construction of Plate Capacitor

Capacitor is constructed by using two conducting surfaces or plates and an insulating material (i.e. Dielectric like mica, paper, air etc) between these two surfaces.

Working of Capacitor

As a capacitor is passive component, it does not generate energy. But it is able to store energy from an energy source like a battery or another charged capacitor. When a battery(DC Source) is connected across a capacitor, one surface, named plate I gets positive end of the battery and another surface, named plate II gets negative end of the battery. When battery is connected, the full voltage of that battery is applied across that capacitor. At that situation, plate I is in positive potency with respect to the plate II.

Current from the battery tries to flow through this capacitor from its positive plate (plate I) to negative plate (plate II) but cannot flow at max value due to separation of these plates with an insulating material. Rather a very small current will flow through this insulating material (dielectric) from Positive to Negative plate depending upon the value of strength of this dielectric.
An electric field will form inside the capacitor dielectric from positive to negative plate. As time goes on, positive plate (plate I) will accumulate positive charge from the battery and negative plate (plate II) will accumulate negative charge from negative end of the battery. After a certain time, the capacitor holds maximum amount of charge as per its capacitance with respect to this voltage. This time span is called charging time of this capacitor.Now, after removing this battery from this capacitor, these two plates will hold positive and negative charges with respect to a certain voltage level for long time. Thus this capacitor acts as energy source.If two ends (plate I and plate II) get shorted through a load, a current will flow through this load from plate I to plate II up to all charges get vanished from both plates. This time span is known as discharging time of the capacitor.

How does a Capacitor Respond in DC?

Suppose a capacitor is connected across a battery through a switch. When switch is ON, i.e. t = 0⁺, a certain value of current will flow through this capacitor. After a certain time (i.e. charging time) capacitor never allow current to flow through it further. It is because of maximum number of charges are accumulated on both surfaces and capacitor acts as a battery which has positive end connected to the positive end of the battery and negative end connected to the negative end of the battery with same potency. Due to zero potential difference between battery and capacitor, no current will flow through it. So, it can be said that, initially a capacitor is short circuited and finally open circuited when it gets connected across a battery.

How does a Capacitor Respond in AC?

Suppose a capacitor is connected across an AC source. Consider, at a certain moment of positive half of this alternating voltage, plate I gets positive polarity and plate II negative polarity. Just at that moment plate I accumulates positive charges and plate II accumulates negative charges. But at the negative half of this applied AC voltage, plate I gets negative charges and plate II positive charges. And so on. There is no flow of electron between these two plates as they change their polarity with the change of source polarity. The capacitor plates get charged and discharged alternatively by the AC.

Types of Capacitor

The types of capacitor are as follows:

Polarized Capacitor

Polarized Capacitors are broadly Classified into following catagories.
Electrolytic Capacitor
Aluminum Electrolytic Capacitor

1. Non Solid
2. Hybrid Polymer
3. Solid Polymer

Tantalum Electrolytic Capacitor

1. Non Solid
2. Solid MnO₂
3. Solid Polymer

Niobium Electrolytic Capacitor

1. Solid MnO₂
2. Solid Polymer

Super Capacitor Double Layer

1. Class I
2. Class II
3. Class III
4. Class IV

Pseudo Capacitor

1. Class I
2. Class II
3. Class III
4. Class IV

Non Polarized Capacitor

1. Metal Insulated Semiconductor Capacitor
2. Ceramic Capacitor
• Class I
• Class II
3. Film Capacitor
• Metalized (Paper as Dielectric)
• Film/Foil (PP Film, PET Film, PEN Film, PPS Film, PTFE Film)

RMS or Root Mean Square Value of AC Signal

Why rms values are used in AC system?
What does an average and rms value mean?
Why all the ratings of AC systems are in rms not in average value? 
What is the difference between rms and average value? 
These are the questions which come in our minds every time when we are dealing with AC circuits.Suppose, we have a simple DC circuits (figure - 1) and we want to replicate it in an AC circuit. We got every thing same, except supply voltage which is now to be an AC supply voltage. Now, the question is what should be the value of AC supply voltage so that our circuit works exactly same as that of DC.Let us put same value of AC supply voltage (AC V_peak = 10 volt) which is in our DC circuits. By doing that we can see (figure 3) for a half cycle how the AC voltage signal is not covering up the whole area (blue area) of constant DC voltage, which means our AC signal can not supply the same amount of power as our DC supply.

Which means we must increase the AC voltage to cover the same area and see if it is supplying the same amount of power or not.We found that (figure 4) by increasing the peak voltage V_peak up to (π/2) times of DC supply voltage we can actually cover the whole area of DC in AC. When the AC voltage signal completely represents the DC voltage signal then that value of DC signal is called the "average value" of AC signal.Now our AC voltage should supply the same amount of power. But when we switched-on the supply surprisingly, we found that AC voltage is supplying more power than the DC. Because an average value of AC supplies same amount of charges but not the same amount of power. So, to get same amount of power from our AC supply we must decrease our AC supply voltage.We found that by decreasing the peak voltage V_peak up to √2 times DC voltage we get same amount of power flowing in both the circuits. When the AC voltage signal supply same amount of power as in DC then that value of DC voltage is called root mean square or rms value of AC.
We are always concerned about how much power is flowing through our circuits irrespective of how much electrons are needed to supply that power and that is the reason why we always use the rms value of AC supply instead of average value everywhere in AC system.

Conclusion
Average value of an AC current represent the equal amount of charges in DC current.RMS value of an AC current represent the equal amount of power in DC current

AC current takes less amount of charges to supply the same amount of DC power.

Active and Passive Elements

Active elements of an electrical circuit are those elements which can continuously give as well as take energy to and from the circuit, respectively.eg Voltage source and Current source.

Passive elements of an electric circuit are those elements which cannot deliver or absorb energy continuously. As per this definition, resistance, inductance and capacitance are taken as basic passive elements of an electric circuit.

Resistor:
Resistor is taken as passive element since it can dissipate energy as heat as long as current flows through it but in any situation a resistor cannot deliver energy to the circuit. Resistance is the property of any substance by which it can resist the flow of current through it. An electrical conductor has very low resistance, whereas an insulator has very high electrical resistance. The unit of resistance is ohm, which can be represented by the symbol Ω.
Inductor:
An inductor is also considered as passive element of circuit, because it can store energy in it as magnetic field, and can deliver it to the circuit, but not in continuous basis. The energy absorbing and delivering capacity of an inductor are limited and transient in nature. That is why, an inductor is taken as passive element of a circuit.
Capacitor:
For same reason, a capacitor is considered as passive element, because it can store energy in it as electric field and deliver it to the circuit, but not in continuous basis. The energy dealing capacity of a capacitor is limited and transient too.