BASICS OF ELECTRICAL ENGINEERING GENERATING STATIONS BASICS OF ELECTRICAL ENGINEERING 1

INTRODUCTION Electrical Energy Hence, bulk electric power is required. Considered as the supplier of all other forms of energy. Easily converted into other forms of energy. Cheaper than other forms. Economical to use this for domestic, commercial, industrial and agricultural purposes. Hence, bulk electric power is required.

GENERATING STATIONS Employs a Prime-mover coupled to an alternator. Prime-mover converts energy from some other form into mechanical energy. Alternator converts mechanical energy into electrical energy. Electrical energy is transmitted and distributed with the help of conductors to various consumers. Classification of generating stations Hydro-electric power stations Thermal power stations Nuclear power stations

HYDRO-ELECTRIC POWER STATION Utilize the potential energy of water at a high level for the generation of electrical energy. Cannot be located every where. Requirement Ample quantity of water at sufficient head. Suitable site must be available Amount of power developed depends on Quantity of water available Rate at which its available Head – created by constructing a dam across a river/lake. Utilized to drive the water turbines coupled to alternators and therefore, the generation of electrical power.

SCHEMATIC ARRANGEMENT

SCHEMATIC ARRANGEMENT Reservoir Two types Natural reservoir : lake in high altitude. Artificial reservoir : formed by constructing a dam across a river. It stores water during rainy season. It helps to maintain a steady water head for the turbine to operate. The water level of the reservoir is called head race. Penstock It is a conduit that takes the water from the reservoir to the power house. Steel pipes: For carrying water at medium and high pressure. RCC pipes: for low pressure. A pressure tunnel is taken off from the reservoir to the valve house if there is an obstruction.

Valve house It contains main sluice valves for controlling water flow to the power station and isolating valves for cutting off water supply in case of penstock bursts (automatic). Surge tank It is a small additional storage facility provided just before the valve house. Provided for better regulation of water pressure in the system. Power house It houses turbine and the generator. Turbine: Hydraulic to mechanical energy. Generator: Mechanical to Electrical energy. The used water from the turbine is released through the tail race.

ADVANTAGES No fuel is required. Hence operating costs are low. Highly reliable and cheap in operation and maintenance. Very neat and clean plant – no smoke or ash is produced. Robust and have got longer life. Highly skilled engineers are required for construction, but, few experienced persons are required later on. The dam and reservoir serve the purpose of irrigation and flood control.

DISADVANTAGES It requires large area. Construction cost is high, requires long time for erection. Long transmission lines are required – since plants are located in hilly areas. Uncertainty about availability of water – depends on weather condition.

THERMAL POWER PLANT

THERMAL POWER PLANT Types Steam Power Plant : Coal, oil or gas Gas Power Plant : Oil or gas Diesel Power Plant : Diesel oil Steam Power Plant Heat of combustion of fuels is utilized by boilers to raise the steam at high pressure and temperature. Steam produced is used in driving the steam turbines coupled to generators and thus in generating electrical energy. Steam generated is also used for industrial purposes such as in paper mills, textile mills, sugar mills and refineries, chemical works, breweries, plastic manufacture, food manufacture . The steam coming out of the turbine is condensed to water and recycled.

LAYOUT OF THERMAL POWER PLANT

SCHEMATIC ARRANGEMENT FUEL AND ASH CIRCUIT Fuel from storage is fed to the boiler through fuel handling device for burning. Ash – due to combustion of coal collects at the back of the boiler and is removed to ash storage through ash handling equipment. AIR AND FUEL GAS CIRCUIT Air required for combustion is drawn from atmosphere by a forced draught fan. This air is pre-heated in the air pre- heater by heat of flue gases and sent to the boiler. Flue-gases coming out of the boiler will have high temperature and is first passed to the super heater then to the economiser and then to air pre-heater and finally exhausted to the atmosphere through chimney.

SUPERHEATER It is a heat exchanger that increases the steam pressure and also eliminates the last traces of moisture in the steam by using the high temperature flue gases from the boiler . ECONOMISER The water to the boiler is heated to a temperature by using the heat from the flue gases. BOILER Part that generates steam at high pressure. Fuel and air in the correct proportion is sent in for combustion. Water is converted to steam inside the boiler.

STEAM AND CONDENSATE CIRCUIT The steam produced in the boiler is sent to the turbine through the super heater. The steam coming out of the turbine is condensed to water using condenser and cooling tower arrangement. The boiler feed pump sends this water to the boiler through the economiser. COOLING WATER CIRCUIT Cooling water – supplied from a natural source of supply – river, sea or cooling towers – circulated through the condenser for condensing the steam and finally discharged to the suitable position near the source of supply. Circulation of cooling water – helps – maintaining a low pressure in the condenser.

TURBINE AND ALTERNATOR Steam turbines are designed to run at high speed. Alternator for steam power plants shall be suited for high speed operation.

ADVANTAGES Fuel used is cheaper. Less space is required in comparison with that of hydro-electric plants. Cheaper in initial cost in comparison with other types of power plants of same capacity. Cheaper in production cost in comparison with that of diesel power plant. Can be installed in any place.

DISADVANTAGES High maintenance and operating costs. Pollution of atmosphere due to fumes and residues from pulverized fuels. Requirement of water in huge quantity. Handling of coal and disposal of ash is quite difficult. Requires long time for erection and put into action.

NUCLEAR POWER PLANT

NUCLEAR POWER PLANTS Nuclear energy is converted into electrical energy. Main atomic fuels – Uranium and Thorium. The energy is generated as a result of nuclear fission reaction in a reactor. In reactor heat energy released from reactor is utilized in raising steam at high temperature and pressure – which drives the steam turbine and converts steam energy into mechanical energy and then alternator converts it into electrical energy.

SCHEMATIC ARRANGEMENT 25

SCHEMATIC ARRANGEMENT Nuclear power plant consists of Nuclear reactor – for heat generation Heat exchanger – for converting water into steam Steam turbine Alternator Condenser Reactor and cooling circuit have to heavily shielded to eliminate radiation hazards. Nuclear reactor Heat energy produced is produced in breaking of atoms of Uranium by fission process.

SCHEMATIC ARRANGEMENT Nuclear reactor Heat energy is produced in breaking of atoms of Uranium by fission process. Moderators: to slow down the neutrons produced during nuclear reaction. Control rods: absorbs neutrons and reduces the rate of reaction. Heat exchanger Steam is generated using the heat transferred from the reactor. Heat transfer is done by the coolant circulated through the reactor and the heat exchanger.

SCHEMATIC ARRANGEMENT Steam produced in the heat exchanger is utilized to drive the turbine. Turbine – drives the alternator – which converts mechanical energy into electrical energy. Output from alternator – delivered to the bus bars through transformer, circuit breakers and isolators.

ADVANTAGES The amount of fuel required is quite small, therefore, there is no problem of transportation, storage etc. These plants need less area as compared to any other type. These plants can be located near the load centers, therefore, primary distribution cost is reduced. These plants are most economical in large quantity. There are large deposits of nuclear fuels available all over the world. Such plants can ensure continued supply of electrical energy for thousands of years. Less polluting compared to thermal power plant. Availability of power is independent of weather conditions.

DISADVANTAGES The initial capital cost is very high as compared to other types of power plants. The erection and commissioning of the plant requires greater technical knowledge. The fission by products are generally radio-active and may cause a dangerous amount of radio-active pollution. The fuel used is expensive. The disposal of radio-active wastes is difficult.