LECTURE NOTES ON POWER SYSTEM - I 2016 - 2017 ELECTRICAL AND ELECTRONICS ENGINEERING
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 alternatorruns 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 steamboiler 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 furnaceofsteamboiler. 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).