Power System / Week No. 1 Chapter 1 & 2: Introduction and

Power System / Week No. 1 Chapter 1 & 2: Introduction and Generating Stations

Energy is the basic necessity for the economic development of a country.

• The availability of huge amount of energy in the current times has resulted in a shorter working day, higher agricultural and industrial production, a healthier and more balanced diet and better transportation facilities.

• There is a close relationship between the energy used per person and his standard of living.

• Energy exists in different forms in nature but the most important form is the electrical energy.

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1.1 Importance of Electrical Energy

Energy may be needed as heat, as light, as motive power etc.

In fact, the development of a country is measured in terms of per capita consumption of electrical energy.

Electrical energy is superior to all other forms of energy due to the following reasons:

• (i) Convenient form. It can be easily converted into other forms of energy.

• (ii) Easy control. The electrically operated machines have simple and convenient starting, control and operation.


• (iii) Greater flexibility. It can be easily transported from one place to another with the help of conductors.

• (iv) Cheapness. Electrical energy is much cheaper than other forms of energy.

• (v) Cleanliness. Electrical energy is not associated with smoke, fumes or poisonous gases. Therefore, its use ensures cleanliness and healthy conditions.

• (vi) High transmission efficiency. The electrical energy can be transmitted conveniently and efficiently from the centers of generation to the consumers with the help of overhead conductors known as transmission lines.


1.2 Generation of Electrical Energy

The conversion of energy available in different forms in nature into electrical energy is known as generation of electrical energy.

Energy is available in various forms from different natural sources such as pressure head of water, chemical energy of fuels, nuclear energy of radioactive substances etc.

All these forms of energy can be

converted into electrical energy

by the use of suitable arrangements.

The arrangement essentially employs

(see Fig. 1.1) an alternator coupled to

a prime mover.


The prime mover is driven by the energy obtained from various sources such as burning of fuel, pressure of water, force of wind etc.

1. 3 Sources of Energy

Electrical energy is produced from sources of energy available in various forms in nature. These sources of energy are :

(i) The Sun (ii) The Wind (iii) Water (iv) Fuels (v) Nuclear energy.

Out of these sources, the energy due to Sun and wind has not been utilized on large scale due to a number of limitations.

At present, the other three sources viz., water, fuels and nuclear energy are primarily used for the generation of electrical energy.

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(i) The Sun. The Sun is the primary source of energy.

• The heat energy radiated by the Sun can be focused over a small area by means of reflectors.

• This heat can be used to raise steam and electrical energy can be produced with the help of turbine-alternator combination.

(ii) The Wind. This method can be used where wind flows for a considerable length of time.

• The wind energy is used to run the wind mill which drives a small generator.

(iii) Water. When water is stored at a suitable place, it possesses potential energy because of the head created.

• This water energy can be converted into mechanical energy with the help of water turbines.

• The water turbine drives the alternator which converts mechanical energy into electrical energy.


(iv) Fuels. The main sources of energy are fuels such as, solid fuel as coal, liquid fuel as oil and gas fuel as natural gas.

• The heat energy of these fuels is converted into mechanical energy by suitable prime movers such as steam engines, steam turbines.

• The prime mover drives the alternator which converts mechanical energy into electrical energy.

(v) Nuclear energy. Just before the end of Second World War, it was discovered that large amount of heat energy is liberated by the fission of uranium and other fissionable materials.

• It is estimated that heat produced by 1 kg of nuclear fuel is equal to that produced by 4500 tones of coal.

• The heat produced due to nuclear fission can be utilized to raise steam with suitable arrangements.

• The steam can run the steam turbine which in turn can drive the alternator to produce electrical energy.


1.4 Schematic Arrangement of Power System

Electric power systems consist of :

• Power generation Station

• Transmission and distribution circuits

• Substations

• Transformers,

• Voltage control equipment

• Protection equipment, together with equipment that facilitates monitoring, communication, and information processing to enable decision and control.

The process to plan and build such facilities takes many years.

A schematic arrangement of a power system is shown in the following Fig. 1.2.

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Principle of Power System/ Dr. Ramzi A. Abdul-Halem

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A schematic arrangement of Power System

Fig. 1.2 A schematic arrangement of Power System


A distribution system connects all the loads in a particular area to the transmission lines. Individual power systems are organized in the form of electrically connected areas or regional grids. Each area of regional grid operates technically and economically independently; but these are finally interconnected to form a national grid (which may even form an international grid). The subtransmission system is also sometimes designated to indicate the portion of the overall system that interconnects the EHV and HV transmission system to the distribution system. We distinguish between these various portions of the power system by voltage levels as follows: · Generation: 1kV-30 kV · EHV Transmission: 500kV-765kV · HV Transmission: 230kV-345kV · Subtransmission system: 69kV-169kV · Distribution system: 120V-35kV


1.5 Generating Stations

1.5.1 Generating Stations Bulk electric power is produced by special plants known as generating stations or power plants.

A generating station essentially employs a prime mover coupled to an alternator for the production of electric power.

The prime mover (e.g., steam turbine, water turbine etc.) converts energy from some other form into mechanical energy.

The alternator converts mechanical energy of the prime mover into electrical energy.

The electrical energy produced by the generating station is transmitted and distributed with the help of conductors to various consumers.


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Depending upon the form of energy converted into electrical energy, the generating stations are classified as under : • (i) Steam power stations • (ii) Hydroelectric power stations • (iii) Diesel power stations • (iv) Nuclear power stations

1.5.1.1 Steam Power Station (Thermal Station) A generating station which converts heat energy of coal combustion into electrical energy is known as a steam power station. A steam power station basically works on the Rankine cycle. Steam is produced in the boiler by utilizing the heat of coal combustion. The steam is then expanded in the prime mover (i.e., steam turbine) and is condensed in a condenser to be fed into the boiler again. The schematic arrangement of steam power station is shown in Fig. 1.3


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The steam turbine drives the alternator which converts mechanical energy of the turbine into electrical energy. This type of power station is suitable where coal and water are available in abundance and a large amount of electric power is to be generated.

1.5.1.2 Hydro-electric Power Station A generating station which utilizes the potential energy of water at a high level for the generation of electrical energy is known as a hydro-electric power station. Hydro-electric power stations are generally located in mountainous areas where dams can be built conveniently and large water reservoirs can be obtained. In a hydro-electric power station, water head is created by constructing a dam across a river or lake. From the dam, water is directed to a water turbine.


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The water turbine captures the energy in the falling water and changes the hydraulic energy (i.e., product of head and flow of water) into mechanical energy at the turbine shaft.

The turbine drives the alternator which converts mechanical energy into electrical energy.

Hydro-electric power stations are becoming very popular because the reserves of fuels (i.e., coal and oil) are lessening day by day.

Schematic Arrangement of Hydro-electric Power Station is shown in Fig. 1.4.


Fig. 1. 4 Schematic Arrangement of Hydro-electric Power Station


Dam


1.5.1.3 Diesel Power Station A generating station in which diesel engine is used as the prime mover for the generation of electrical energy is known as diesel power station.

In a diesel power station, diesel engine is used as the prime mover.

The diesel burns inside the engine and the products of this combustion act as the “working fluid” to produce mechanical energy.

The diesel engine drives the alternator which converts mechanical energy into electrical energy.

As the generation cost is considerable due to high price of diesel, therefore, such power stations are only used to produce small power.

Although steam power stations and hydro-electric plants are always used to generate bulk power at cheaper cost, yet diesel power stations are finding favor at places where demand of power is less, sufficient quantity of coal and water is not available and the transportation facilities are inadequate.


These plants are also used as standby sets for continuity of supply to important points such as hospitals, radio stations, cinema houses and telephone exchanges.

Schematic Arrangement of Diesel Power Station is shown in Fig. 1.5.


1.5.1.4 Nuclear Power Station

A generating station in which nuclear energy is converted into electrical energy is known as a nuclear power station.

In nuclear power station, heavy elements such as Uranium (U235) or Thorium (Th232) are subjected to nuclear fission in a special apparatus known as a reactor.

The heat energy thus released is utilized in raising steam at high temperature and pressure.

The steam runs the steam turbine which converts steam energy into mechanical energy.

The turbine drives the alternator which converts mechanical energy into electrical energy.


The most important feature of a nuclear power station is that huge amount of electrical energy can be produced from a relatively small amount of nuclear fuel as compared to other conventional types of power stations.

It has been found that complete fission of 1 kg of Uranium (U235) can

produce as much energy as can be produced by the burning of 4,500 tons of high grade coal.

Schematic arrangement of Nuclear Power Station is shown in Fig. 1.6.


Fig. 1.6 Schematic arrangement of Nuclear Power Station


Nuclear Power Station


1.5.1.5 Gas Turbine Power Plant A generating station which employs gas turbine as the prime mover for the generation of electrical energy is known as a gas turbine power plant. In a gas turbine power plant, air is used as the working fluid. The air is compressed by the compressor and is led to the combustion chamber where heat is added to air, thus raising its temperature. Heat is added to the compressed air either by burning fuel in the chamber or by the use of air heaters. The hot and high pressure air from the combustion chamber is then passed to the gas turbine where it expands and does the mechanical work. The gas turbine drives the alternator which converts mechanical energy into electrical energy. Gas turbine power plants are being used as standby plants for hydro-electric stations, as a starting plant for driving auxiliaries in power plants etc. 7/31/2012 Principle of Power System/ Dr. Ramzi A. Abdul-Halem 24

Schematic Arrangement of Gas Turbine Power Plant is shown in Fig. 1.7


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Power System / Week No. 1 Chapter 1 & 2: Introduction and