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Module-I

Evolution of Power Systems and Present-Day Scenario

• An electric power system is a network of electrical components deployed to supply, transfer, and use electric power. An example of a power system is the electrical grid that provides power to homes and industries within an extended area.
• There are two types of electrical power such as: DC power - It is defined as the product of voltage and current and is produced by DC sources like generators, batteries, fuel cells, etc. AC power - A flow of charge that exhibits a periodic change in direction is called AC power.
• At present, India has a total Thermal capacity of 236.1 GW, and Renewable (including hydro) capacity of balance 165.9 GW. The highest peak demand in the country touched 215 GW in the current year and the same is expected to increase by 9% in the next year
• Today, with the discovery of electricity, human life has become easier by using electricity to perform many functions every day, such as lighting, heating, cooling of homes and operating various electrical appliances

Structure of Power Systems

• The power system is the complex enterprise that may be sub devided in to the following subsystems:
• Generation Substation
• Transmission Substation
• Distribution Substationb

Generating Substation

• Generating Substation in generating station the fuel (coal, water, nuclear energy, etc.) is converted into electrical energy. The electrical power is generated in the range of 11kV to 25kV, which is step-up for long distance transmission. The power plant of the generating substation is mainly classified into three types, i.e., thermal power plant, hydropower plant and nuclear power plant.

Distribution Substation

• The transmission substation carries the overhead lines which transfer the generated electrical energy from generation to the distribution substations. It only supplies the large bulk of power to bulk power substations or very big consumers.

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• Distribution Substation The component of an electrical power system connecting all the consumers in an area to the bulk power sources is called a distribution system. The bulk power stations are connected to the generating substations by transmission lines. They feed some substations which are usually situated at convenient points near the load centers. The substations distribute the power to the domestic, commercial and relatively small consumers. The consumers require large blocks of power which are usually supplied at sub-transmission or even transmission system.

Transmission Substation

Conventional sources of Electrical Energy

• Conventional energy sources such as natural gas, oil, coal, or nuclear are finite but still hold the majority of the energy market. However, renewable energy sources like wind, fuel cells, solar, biogas/biomass, tidal, geothermal, etc.
• Types of Conventional Sources of Energy:
• Coal. Coal is the most abundant conventional source of energy which could last for at least 200 years. ...
• Oil. Out of all the conventional sources of energy, oil is used abundantly all over. ...
• Petroleum and Natural Gas. ...
• Fuel Woods. ...
• Thermal Power Plant. ...
• Nuclear energy.

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Hydroelectric Power Generation

• 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.
• Constituents of Hydro-electric Plant The constituents of a hydro-electric plant are
• Hydraulic structures
• Water turbines and
• Electrical equipment.

1.Hydraulic structures in a hydro-electric power station include dam, spillways, headworks, surge tank, penstock and accessory works

1. Dam. A dam is a barrier which stores water and creates water head.
2. spillways are constructed of concrete piers on the top of the dam, used to discharge the surplus water from the storage reservoir into the river on the down- stream side of the dam.
3. Headworks. The headworks consists of the diversion structures at the head of an intake. They generally include valves for controlling the flow of water to the turbine.
4. Surge tank. Open conduits leading water to the turbine require no* protection. However, when closed conduits are used, protection becomes necessary to limit the abnormal pressure in the conduit. For this reason, closed conduits are always provided with a surge tank. A surge tank is a small reservoir or tank (open at the top) in which water level rises or falls to reduce the pressure swings in the conduit.

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2. Water turbines. Water turbines are used to convert the energy of falling water into mechanical energy. The principal types of water turbines are : (i) Impulse turbines (ii) Reaction turbines (i) Impulse turbines. Such turbines are used for high heads. (ii) Reaction turbines. Reaction turbines are used for low and medium heads.

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3.Electrical equipment. The electrical equipment of a hydro-electric power station includes alternators, transformers, circuit breakers and other switching and protective devices.

Advantages Of A Hydroelectric Power Plant

• No fuel is required as potential energy is stored water is used for electricity generation
• Neat and clean source of energy
• Very small running charges - as water is available free of cost
• Comparatively less maintenance is required and has longer life
• Serves other purposes too, such as irrigation

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Disadvantages

• Very high capital cost due to construction of dam
• High cost of transmission – as hydro plants are located in hilly areas which are quite away from the consumers

Thermal Power Generation

• A thermal power station is a type of power station in which heat energy is converted to electrical energy. In a steam-generating cycle heat is used to boil water in a large pressure vessel to produce high-pressure steam, which drives a steam turbine connected to an electrical generator. The low-pressure exhaust from the turbine enters a steam condenser where it is cooled to produce hot condensate which is recycled to the heating process to generate more high pressure steam. This is known as a Rankine cycle.

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• The design of thermal power stations depends on the intended energy source: fossil fuel, nuclear and geothermal power, solar energy, biofuels, and waste incineration are all used. Certain thermal power stations are also designed to produce heat for industrial purposes; for district heating; or desalination of water, in addition to generating electrical power.

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• Fuels such as natural gas or oil can also be burnt directly in gas turbines (internal combustion). These plants can be of the open cycle or the more efficient combined cycle type.

Advantages of thermal power plant are:

• Thermal power station has less initial cost as compared to hydro-electric generating station.
• It requires less space as compared to the hydro-electric power station.
• The fuel cost is less as compared to gas.
• Hung amount of power can be generated by TPS.
• The cost of generation is less as compared to diesel power station.

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Disadvantages of thermal power plant are:

• The running cost of thermal power station is more as compared to hydro power station.
• It pollutes the atmosphere due to production of large amount of smoke and fumes.
• Maintenance cost is more.
• Skilled persons are required for erecting and maintaining the power station.
• Land requirement is more for storage of coal and ash.

Nuclear Power Generation

• A nuclear power plant is a thermal power station in which the heat source is a nuclear reactor. As is typical of thermal power stations, heat is used to generate steam that drives a steam turbine connected to a generator that produces electricity.
• Nuclear power plants are a type of power plant that use the process of nuclear fission in order to generate electricity. They do this by using nuclear reactors in combination with the Rankine cycle, where the heat generated by the reactor converts water into steam, which spins a turbine and a generator.

Components and Operation

• Nuclear Reactor

The reactor is a key component of a power plant, as it contains the fuel and its nuclear chain reaction, along with all of the nuclear waste products. The reactor is the heat source for the power plant, just like the boiler is for a coal plant. Uranium is the dominant nuclear fuel used in nuclear reactors, and its fission reactions are what produce the heat within a reactor. This heat is then transferred to the reactor's coolant, which provides heat to other parts of the nuclear power plant.

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• Steam Generation

The production of steam is common among all nuclear power plants, but the way this is done varies immensely.

The most common power plants in the world use pressurized water reactors, which use two loops of circling water to produce steam. The first loop carries extremely hot liquid water to a heat exchanger, where water at a lower pressure is circulated. It then heats up and boils to steam, and can then be sent to the turbine section.Boiling water reactors, the second most common reactor in power generation, heat the water in the core directly to steam

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• Turbine and Generator

Once steam has been produced, it travels at high pressures and speeds through one or more turbines. These get up to extremely high speeds, causing the steam to lose energy, therefore, condensing back to a cooler liquid water. The rotation of the turbines is used to spin an electric generator, which produces electricity that is sent out the the electrical grid.

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• Cooling Towers

They work to reject waste heat to the atmosphere by the transfer of heat from hot water (from the turbine section) to the cooler outside air. Hot water cools in contact with the air and a small portion, around 2%, evaporates and raises up through the top. Moreover, these plants do not release any carbon dioxide—the primary greenhouse gas that contributes to climate change

Advantages of nuclear energy

• One of the most low-carbon energy sources.
• It also has one of the smallest carbon footprints.
• It's one of the answers to the energy gap.
• It's essential to our response to climate change and greenhouse gas emissions.
• Reliable and cost-effective

Disadvantages of nuclear power plant

• Disposal and storage of nuclear waste.
• Uranium decomposes into harmful sub atomic masses.
• Accidental leakage of radiation and large-scale accidents can be catastrophic..
• Installation cost is very high as compared to the other power station.