Lecture Notes on Power Station Engineering

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VEER SURENDRA SAI UNIVERSITY OF TECHNOLOGY BURLA, ODISHA, INDIA DEPARTMENT OF ELECTRICAL ENGINEERING Lecture Notes on Power Station Engineering Subject Code: BEE1504 5th Semester B.Tech. (Electrical Engineering) Lecture Notes Power Station Engineering Syllabus MODULE-I (10 HOURS) Introduction to different sources of energy and general discussion on their application to generation. Hydrology: Catchments area of a reservoir and estimation of amount of water collected due to annual rainfall, flow curve and flow duration curve of a river and estimation of amount stored in a reservoir formed by a dam across the river, elementary idea about Earthen and Concrete dam, Turbines: Operational principle of Kaplan, Francis and Pelton wheel, specific speed, work done and efficiency. Hydro plant: - head gate, penstock, surge tank, scroll case, draft tube and tail race, classification of plants, turbines different heads, plant capacity as a base load and peak load station, power plant auxiliaries. MODULE-II (10 HOURS) Thermal Power: Overall plant components in Block diagrams indicating the air circuit, coal and ash circuit, water and steam circuit, cooling water circuit; various types of steam turbines, ash and coal handling system, water tube boiler, fire tube boiler, super heater, economizer, air preheater, dust collection, draft fans and chimney; condensers, feed water heaters, evaporate and makeup water, bleeding of steam; cooling water system; Governors, plant layout and station auxiliaries. MODULE-III (10 HOURS) Nuclear Power: Introduction to fission & fusion, reactor construction, controlled chain reaction, operational control of reactors, Brief study of various types of reactors (Boiling water, pressurized water, sodium graphite, breeder) layout of nuclear power plant. Electrical System: Different types of alternators, methods of cooling Excitation system: - Shaft mounted D.C. Generator, elements of static and brush less excitation, field flashing. MODULE-IV (10 HOURS) AVR: - magnetic amplifier and thyristor converter type/DVR. Main transformer, unit transformer and station reserve transformer, commissioning tests of alternators and transformers. Choice of size and number of generating units: Review of the terms maximum demand, load factor, diversity factor, plant capacity and use factor, load & load duration curve and their effect on the generating capacity. Reserve units (hot, cold and spinning- reserve), Effect of power-factor on the generating capacity and economy, Different types of power tariffs, Brief idea about national grid and its operational problems. Department of Electrical Engineering, Veer Surendra Sai University of Technology Burla Page 3 Lecture Notes Power Station Engineering Module-1 Introduction Loads Concept of MW, MWh, Units, Million Units (MU) Structure of Power System Power Generation Concept of Frequency Prime movers and Generators Salient Pole and Cylindrical type Alternators Sources of Energy  How can we keep providing humankind with energy-derived advantages without damaging the environment, affecting societal stability or threatening the wellbeing of future generation?  Sustainable energy can be thought of as a living harmony between the equitable availability of energy sources to all people and the preservation of earth for future generations.  Electricity is an intermediate energy product that is made from primary energy sources. Power is the rate of energy exchange between two systems.  The various sources of energy in the Indian context are as follows. As is obvious, the major source of generation is coal based thermal power plant. Thermal, nuclear and hydro powers are known as conventional energy sources which is the subject matter of this course. Department of Electrical Engineering, Veer Surendra Sai University of Technology Burla Page 12 Lecture Notes Power Station Engineering Installed Capacity in India Table 1: Installed Capacity as on 30-11-2014 Source Subtype Capacity (MW) Remarks Thermal Coal 153571 Gas 22971 Diesel 1199 Total 177742 Nuclear 4780 Hydro 40798 RES Wind 21136 Solar 2632 Biopower 4119 Department of Electrical Engineering, Veer Surendra Sai University of Technology Burla Page 13 Lecture Notes Power Station Engineering Hydro Power Potential P = gρQH Where P = Power available in water 2 g = 9.81 m/s 3 Q = flow or discharge (m /s) H = Height of fall of water or head (m) -3 P = 9.811000QH10 kW = 9.81 QH kW P= 9.81 QHη kW where η = efficiency of the turbine-generator assembly  Rain falling on earth’s surface has potential energy relative to oceans.  This energy is converted to shaft work when the water falls through a vertical distance.  This shaft work is used to drive water turbines to generate electricity. Department of Electrical Engineering, Veer Surendra Sai University of Technology Burla Page 14 Lecture Notes Power Station Engineering Hydrology • First requirement – Q (discharge) • Hydrology deals with occurrence and distribution of water over and under earth’s surface. – Surface Water Hydrology – Ground Water Hydrology • Watershed, catchment area or drainage area: length of the river, size and shape of the area it affects, tributaries, lakes, reservoirs etc. • Investigation of run-off for past few years is required for power potential studies of a HPP. Objectives of Hydrology • To obtain data regarding the stream flow of water that would be available, • To predict the yearly possible flow • To calculate the mean annual rainfall in the area under consideration from a record of the annual rainfall for a number of years, say 25 to 30 • To note the frequency of dry years • To find maximum rainfall and flood frequency Various terms related to Hydrology • Rainfall is also known as precipitation and can be measured by rain gauges. • Some part of precipitation is lost due to evaporation, interception and transpiration. • Transpiration: Plants absorbing moisture and giving it off to the atmosphere • Stream flow = precipitation – losses • Stream flow = surface flow + percolation to ground • Surface flow is also known as run-off. • Hydrograph: 3 – shows the variation of stream flow in m /s with time for a particular river site. The time may be hour, week, month or a year. – The area under hydrograph gives the total volume of flow Department of Electrical Engineering, Veer Surendra Sai University of Technology Burla Page 15 Lecture Notes Power Station Engineering • Flow duration curve: – shows the percentage of time during the period when the flow was equal to greater than the given flow. – The area under FDC gives the total quantity of run-off during a period • Mass curve – indicates the total volume of run-off in cubic meters up to a certain time. – the slope of the curve at any point shows the rate of flow at that time – Used for estimating the capacity of storage reservoir • Storage: – to ensure water availability during deficient flow and thus increasing the firm capacity – Storage also results in more energy production • Pondage: – Storing water in small ponds near the power plant as the storage reservoir is away from plant – To meet the power demand fluctuations over a short period of time e.g. 24 hours • Primary Power: power that will be available 90 % of the time • Secondary Power: power that will be available 75 % of the time • Dump Power: power that will be available 50 % of the time. • Maximum flow estimation: gives estimation of floods and helps in design of dam and spillway. Department of Electrical Engineering, Veer Surendra Sai University of Technology Burla Page 16 Lecture Notes Power Station Engineering Site Selection for Hydropower Plants • Availability of Water: Run-off data for many years available • Water Storage: for water availability throughout the year • Head of Water: most economic head, possibility of constructing a dam to get required head • Geological Investigations: strong foundation, earthquake frequency is less • Water Pollution: excessive corrosion and damage to metallic structures • Sedimentation: capacity reduces due to gradual deposition of silt • Social and Environmental Effects: submergence of areas, effect on biodiversity (e.g. western ghat), cultural and historic aspects • Access to Site: for transportation of construction material and heavy machinery new railway lines or roads may be needed • Multipurpose: power generation, irrigation, flood control, navigation, recreation; because initial cost of power plant is high because of civil engineering construction work Department of Electrical Engineering, Veer Surendra Sai University of Technology Burla Page 17 Lecture Notes Power Station Engineering Types of Dams Figure 1: Earth and Rockfill Dam Figure 2: Arc Dam Department of Electrical Engineering, Veer Surendra Sai University of Technology Burla Page 18 Lecture Notes Power Station Engineering Figure 3: Arc Gravity Dam Department of Electrical Engineering, Veer Surendra Sai University of Technology Burla Page 19 Lecture Notes Power Station Engineering Classification of Hydropower Plants According to water flow regulation: 1. Runoff river plants without pondage 2. Runoff river plants with pondage 3. Hydroelectric plants with storage reservoir According to Load: 1. Base load plants 2. Peak load plants 3. Pumped storage plants According to head: 1. High head plants (100m) 2. Medium head plants (30-100 m) 3. Low head plants (30 m) Department of Electrical Engineering, Veer Surendra Sai University of Technology Burla Page 20 Lecture Notes Power Station Engineering Components of a HPP Figure 4: Schmatic of a Hydropower Plant The various components of HPP are as follows: 1. Catchment area 2. Reservoir 3. Dam 4. Spillways 5. Conduits 6. Surge tanks 7. Draft tubes 8. Power house 9. Switchyard for power evacuation Dam  Develops a reservoir to store water  Builds up head for power generation Spillway  To safeguard the dam when water level in the reservoir rises Department of Electrical Engineering, Veer Surendra Sai University of Technology Burla Page 21 Lecture Notes Power Station Engineering Intake  Contains trash racks to filter out debris which may damage the turbine Forebay  Enlarged body of water just above the intake Figure 5: Forebay Conduits  Headrace is a channel which lead the water to the turbine  Tailrace is a channel which carries water from the turbine  A canal is an open waterway excavated in natural ground following its contour.  A flume is an open channel erected on a surface above ground.  A tunnel is a closed channel excavated through an obstruction.  A pipeline is a closed conduit supported on the ground.  Penstocks are closed conduits for supplying water “under pressure” from head pond to the turbines. Department of Electrical Engineering, Veer Surendra Sai University of Technology Burla Page 22 Lecture Notes Power Station Engineering Figure 6: Forebay with Penstock Figure 7: Penstocks Surge Tank  A surge tank is a small reservoir in which the water level rises or falls to reduce the pressure swings so that they are not transmitted to the penstock.  Water Hammer o Load on the turbine is suddenly reduced Department of Electrical Engineering, Veer Surendra Sai University of Technology Burla Page 23 Lecture Notes Power Station Engineering o Governor closes turbine gates o Sudden increase of pressure in the penstock  Negative Pressure o Load on the generator is suddenly increased o Governor opens the turbine gates o Tends to cause a vacuum in the penstock  When the gates are closed, water level rises in the surge tank and when the gates are suddenly opened, surge tank provides the initial water supply. Figure 8: Surge Tank Draft Tubes The function of the draft tube is to  To reduce the velocity head losses of the water  To allow the turbine to be set above the tailrace to facilitate inspection and maintenance Department of Electrical Engineering, Veer Surendra Sai University of Technology Burla Page 24 Lecture Notes Power Station Engineering Figure 9: Elbow Type Draft Tube Figure 10: Straight conical type draft tubes Scroll Casing: Takes the water from penstock to turbine blades Department of Electrical Engineering, Veer Surendra Sai University of Technology Burla Page 25 Lecture Notes Power Station Engineering Figure 11: Scroll Casing Tailrace:  A tailrace is required to discharge the water leaving the turbine into the river.  The design of the tail race should be such that water has a free exit. Figure 12: Tail race Department of Electrical Engineering, Veer Surendra Sai University of Technology Burla Page 26 Lecture Notes Power Station Engineering Power House 1. Hydraulic turbines 2. Electric generators 3. Governors 4. Gate valves 5. Relief valves 6. Water circulation pumps 7. Air ducts 8. Switch board and instruments 9. Storage batteries 10. Cranes Switchyard 1. Step up transformers 2. Instrument transformers 3. Transmission lines Figure 13: A switchyard under construction Department of Electrical Engineering, Veer Surendra Sai University of Technology Burla Page 27 Lecture Notes Power Station Engineering Hydraulic Turbines Types of Hydraulic Turbines 1. According to the head and quantity of water available a. Low head (2-15m) b. Medium head (16-70m) c. High head (71-500m) d. Very high head (500m) 2. According to the name of the originator a. Francis b. Kaplan c. Pelton 3. According to the nature of working of water on blades Table 2: Impulse and Reaction Turbines Impulse Reaction Available head of water converted into kinetic Flow of water takes place in a closed conduit energy in a nozzle system The free jet strikes a bucket which revolves Part of P.E. is converted into K.E. and part into around a shaft pressure energy Turbines are above ground Water flows in a closed conduit system and turbines are submerged in water After energy production, water falls freely Water falls through a draft tube through the passage into tail race 4. According to the direction of flow of water a. Radial b. Axial c. Tangential (Deriaz) 5. According to the axis of the turbine shaft: vertical, horizontal Comparison of Turbines Table 3: Comparison of Turbines Turbine Head (m) Specific Speed (metric) Kaplan 30 to 70 300 to 1000 Francis 40 to 400 60 to 300 Pelton 400 m 10 to 50 Department of Electrical Engineering, Veer Surendra Sai University of Technology Burla Page 28 Lecture Notes Power Station Engineering Figure 14: Kaplan Turbine Figure 15: Kaplan Turbine Department of Electrical Engineering, Veer Surendra Sai University of Technology Burla Page 29

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