STUDY OF BASIC ELEMENTS OF VARIOUS POWER PLANTS

1 of 3 PRACTICAL – 1 STUDY OF BASIC ELEMENTS OF VARIOUS POWER PLANTS

Aims: - (1) To know different types of power plants. (2) To know energy conversions in various power plants (3) To know about basic elements of various power plants. Introduction:Basically power plant is an energy transformation unit. In general the meanings of the words ‘power plant’ & ‘power station’ are same. But logically there is a big difference. This difference can be easily understood by their definitions. (a) Power Plant:- Power plant is an arrangement of various apparatus in which continuously electrical/mechanical power is gained in bulk as output by utilization of given form of  energy as input and distributed to various consumers. (b) Power Station: - Power station is complex unit where numbers of power plants (units) are usually located to generate mechanical and/or electrical power in bulk, continuously and from where it is transmitted to various consumers. So, the object in design and operation of power plant (station) is to generate electrical power safely, efficiently and economically. (A) TYPES OF POWER PLANTS:Power plants are classified in many ways. Some of the ways are listed below. 1. Accordin According g to to type of Ener Energy gy Source: Source: a) Therma Thermall Power Power Plant Plant c) Nuclea Nuclearr Power Power Plant Plant I. Stea Steam m Powe Powerr Plan Plantt d) Solar Solar Power Power Plant Plant II. Diesel Diesel Power Power Plant Plant e) Wind Wind Energy Energy Power Power Plant Plant III. Gas Turbin Turbinee Power Power Plant Plant f) Tidal Tidal Power Power Plant Plant b) Hydel Hydel Power Power Plant Plant g) Geothermal Geothermal Power Plant 2. Accord According ing to Load: Load: a) Ba Base Load Power Plant b) Peak Load Power Plant 3. Accordin According g to Types Types of Utilizati Utilization: on: a) Stand Stand by Power Power Plant Plant d) Nurser Nursery y Power Power Plant Plant b) Emerge Emergency ncy Power Power Plant Plant e) Pump Storage Storage Power Plant c) Total Total Energy Energy (cogen (cogenera eratio tion) n) f) Mobile Mobile Power Power Plant Plant Power Plant 4. Accordin According g to Capacity Capacity and Ownership: Ownership: a) Central Power Plant b) Captive Power Plant 5. Accordin According g to Location Location:: a) Pe Peat Head Power Plant b) Load center Power Plant (B) ENERGY CONVERSION IN VARIOUS POWER PLANTS: Power Power plant plant is and energy energy transf transform ormati ation on (conve (conversi rsion) on) unit. unit. One type type of energy energy is converted into another type (mainly electrical energy) in power plants. Here energy conversion steps of various power plants are given as under. (C) BASIC ELEMENTS OF VATIOUS POWER PLANTS:I. Basic Elements Elements of Steam Steam (Ther (Thermal) mal) Power Power Plant Plant:: a) Steam Steam Generat Generator  or  b) Steam Steam Turbin Turbinee c) Cond Conden ense ser  r  d) Feed Feed Pump Pump e) Altern Alternato atorr (Generat (Generator) or)

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Basic Elements of Diesel Engine Power Plant: a) Diesel Engine b) Alternator (Generator) III. Basic Elements of Gas Turbine Power Plant: a) Compressor  b) Combustion Chamber  c) Gas Turbine d) Alternator (Generator) IV. Basic Elements of Nuclear Power Plant (BWR) a) Atomic Reactor  b) Steam Turbine c) Condenser  d) Feed Pump e) Alternator (Generator) Here, we will see some of the basic elements of steam (thermal) power plant in detail. (a) Steam Generator:A thermal power plant using steam as a working substance works basically on the Rankine Cycle. Steam of desired quality and quantity is generated in the boiler  (steam generator). The steam generator is a complex combination of economizer, evaporator, superheater, reheater and air preheater. In addition, it has various auxiliaries like furnaces, stokers, pulverizing systems, burners, fans, stacks and ash handling equipments. Modern power plant steam generators are essentially of two basic types. 1. Sub critical Steam Generator  2. Supercritical Steam Generator  Sub critical steam generator operates below 225 bars, usually about 130 bars to 180 bars. Supercritical steam generators operates above 225 bars La Mount, Benson, Loeffler, Schmidt-Hartmann, Velox, Stirlling, BHEL are some of the high pressure steam generator (boilers) used in modern steam (thermal) power plants. (b) Steam Turbine:A steam turbine is a prime mover which continuously converts the energy of  high pressure, high temperature steam supplied by a steam generator, into shaft work. While the low temperature steam exhausted to a condenser. This energy conversion essentially occurs in two steps. 1) The high pressure, high temperature steam first expands in nozzles and comes out at a high velocity. 2) The high velocity jets of steam coming out of nozzle, impinge on the blades mounted on a wheel, get deflected by an angle and suffer a loss of momentum, which is absorbed by the rotating wheel in producing torque. There are mainly two types of turbines: - (1) Impulse turbine and (2) Reaction turbine. In impulse turbine, all pressure drop of steam occur in the nozzles and there is no pressure drop as steam flows through the passage between two blades, where as in reaction turbine pressure drop occurs both in the nozzles or the fixed row of blades, as well as in the moving row of blades. (c) Condenser:-

The exhaust steam from turbine is condensed at constant pressure in a condenser, to recover the high quality of feed water for reuse in the cycle. There are two objects of using a condenser in a steam plant. 1. To reduce the turbine exhaust pressure so as to increase the specific output of  the turbine. 2. To recover high quality feed water in the form of condensate and feed it back  to the steam generator without any further treatment. There are two broad classes of condenser, 1. Direct Contact Type Condenser: - Where the condensate and cooling water directly mix and comes out as a single stream. 2. Surface Condenser: - Which are indirect heat exchangers, where the two fluids do not come in the direct contact and the heat released by the condensation of steam is transferred through the walls of the tubes into the cooling water continuously circulating inside them. Generally surface condensers are used in power plants because it reduces the back pressure considerably (higher vacuum) and pure condensate is obtained. (d) Feed Pump:Feed pumps are used to supply feed water to the steam generator at required rate and pressure. For small capacity, low pressure steam generator generally reciprocating pumps are utilized as feed pump and for high capacity, high pressure steam generators generally multistage centrifugal pumps are utilized as feed pumps. (e) Alternator (Generator):The alternator (electric generator) is the most important part of the power  plant as all other units in the power plant are installed for the purpose of driving alternator. The principle of electromagnetic induction is used for the generation of  electric power with the help of generator. All modern typed of alternating current generators (alternators) essentially of a fixed stator and revolving rotor. The stator  core carries three phase winding in which alternating emf is induced when the shaft of  the rotor is revolved with the help of the prime mover. The rotor is carrying field magnet and coils which provide the magnetic flux of the machine. The field is excited by a direct current brought into the field circuit by means of two rotor slip-rings and set of brushes riding on them. The magnitude of the induced voltage in the single phase of the stator  winding depends upon the strength of the magnetic field, the speed of rotation and number of stator coils in series. ------------------------------------------xxxxxxxxxxxxxxxxxxxxxx----------------------------