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Unit 7: Type of Generator I READING AND COMPREHENSION TYPES OF GENERATORS 10 Steam Units: Steam-electric (thermal) generating units are typically the large base load plants Steam produced in a boiler turns a turbine to drive an electric generator (Figure 3a) Fossil fuels (coal, petroleum and petroleum products, natural gas or other gaseous fuels) and other combustible fuels, such as biomass and waste products, are burned in a boiler to produce the steam Nuclear plants use nuclear fission as the heat source to make steam Geothermal or solar thermal energy also produce steam The thermal efficiency of fossil-fueled steam-electric plants is about 33 to 35 percent The waste heat is emitted from the plant either directly into the atmosphere, through a cooling tower, or sent to a lake for cooling A water pump brings the residual water from the condenser back to the boiler Figure 3a Schematic of generic thermal generator 15 Gas Units: Gas turbines and combustion engines use the hot gas from burning fossil fuels, rather than steam, to turn a turbine that drives the generator These plants can be brought up quickly, and so are used as peaking plants The number of gas turbines is growing as technological advances in gas turbine design and declining gas prices have made the gas turbine competitive with the large steam-electric plants However, thermal efficiency is slightly less than that of the large steam-electric plants (Figure 3b) The gas wastes are disposed of through an exhaust stack 47 Figure 3b Schematic of gas turbine 20 Combined-Cycle Units: Combined cycle plants first use gas turbines to generate power and then use the waste heat in a steam-electric generator to produce more electricity Thus, combined-cycle plants make more efficient use of the heat energy in fossil fuels New technology is improving the thermal efficiency of combined-cycle plants, with some reports of 50 to 60 percent thermal efficiency (Figure 3c) Figure 3c Schematic of combined cycle 25 30 35 Cogenerating Units: Cogenerators, also known as combined heat and power generators, are facilities that utilize heat for electricity generation and for another form of useful thermal energy (steam or hot water), for manufacturing processes or central heating There are two types of cogeneration systems: bottom-cycling and top-cycling In a bottom-cycling configuration, a manufacturing process uses high temperature steam first and a waste-heat recovery boiler recaptures the unused energy and uses it to drive a steam turbine generator to produce electricity In one of two top-cycling configurations, a boiler produces steam to drive a turbine-generator to produce electricity, and steam leaving the turbine is used in thermal applications such as space heating or food preparation In another top-cycling configuration, a combustion turbine or diesel engine burns fuel to spin a shaft connected to a generator to produce electricity, and the waste heat from the burning fuel is recaptured in a waste-heat recovery boiler for use in direct heating or producing steam for thermal applications (Figure 3d) 48 Figure 3d Cogeneration Schematic Other Units: The kinetic energy in moving water and wind is used to turn turbines at hydroelectric plants and wind facilities to produce electricity Other types of energy conversion include photovoltaic (solar) panels that convert light energy 40 directly to electrical energy, and fuel cells that convert chemical energy directly to electrical energy Task Rephrasing Rewrite the following sentences, replacing the words in italics with expressions from the passage which have similar meanings: Steam produced in a boiler spins a turbine to drive an electric generator Fossil fuels (coal, petroleum and petroleum products, natural gas or other gaseous fuels) and other flammable fuels, such as biomass and waste products, are burned in a boiler to produce the steam The waste heat is discharged from the plant either directly into the atmosphere, through a cooling tower, or sent to a lake for cooling The gas wastes are disposed of through an chimney The number of gas turbines is growing as technological progress in gas turbine design and declining gas prices have made the gas turbine competitive with the large steam-electric plants Task Contextual reference What the pronouns in italics in these sentences refer to? Gas turbines and combustion engines use the hot gas from burning fossil fuels, rather than steam, to turn a turbine that drives the generator (line 12) (a) Gas turbines and combustion engines (b) The hot gas (c) Steam (d) A turbine 49 However, thermal efficiency is slightly less than that of the large steam-electric plants (line 16) (a) Gas turbine design (b) The gas turbine (c) The large steam-electric plants (d) Thermal efficiency In a bottom-cycling configuration, a manufacturing process uses high temperature steam first and a waste-heat recovery boiler recaptures the unused energy and uses it to drive a steam turbine generator to produce electricity (line 28) (a) High temperature steam (b) A waste-heat recovery boiler (c) The unused energy (d) A manufacturing process Other types of energy conversion include photovoltaic (solar) panels that convert light energy directly to electrical energy, and fuel cells that convert chemical energy directly to electrical energy (line 39, 40) (a) Other types of energy conversion; fuel cells (b) Photovoltaic panels; fuel cells (c) Energy conversion; electrical energy (d) Photovoltaic panels; light energy Task Checking facts and ideas Decide if these statements are true or false Quote from the passage to support your decisions Combined cycle plants first use gas turbines to generate power and then use the waste heat in a steam-electric generator to produce more electricity Coal, petroleum and petroleum products, natural gas are combustible fuels Biomass and waste products are combustible fuels The thermal efficiency of fossil-fueled steam-electric plants is not over 50 percent Cogenerators only utilize heat for electricity generation In a top-cycling configuration, the waste heat from the burning fuel is recaptured in a waste-heat recovery boiler for producing electricity The moving water provides kinetic energy for generating electricity Combined-cycle units could be reached 50 to 60 percent thermal efficiency The waste heat is emitted from the plant directly into the atmosphere 10 Gas turbines mainly use the steam from burning fossil fuels to drive generators 50 II USE OF LANGUAGE Task Describing function To describe the function of X (an apparatus, a device, equipment and so on), we answer the question What does X do? EXAMPLE What does a switch do? It changes the condition of a circuit We can emphasize function by using this pattern: The function of X is to sth The function of a switch is to change the condition of a circuit Now identify the following components and explain the function of each component with the help of this list A boiler A nuclear plant A gas turbine An electric generator A cooling tower A water pump A condenser An exhaust stack Photovoltaic panels 10 Fuel cells (a) (b) (c) (d) (e) (f) (g) (h) (i) (j) converts chemical energy directly to electrical energy turns a turbine to drive an electric generator converts light energy directly to electrical energy uses nuclear fission to make steam disposes the gas wastes generates steam brings the residual water from the condenser back to the boiler emits the heat wastes from the plant directly into the atmosphere extracts energy from a flow of combustion gas converts mechanical energy into electrical energy 51 Task Describing position and connection When describing the position of a component or how it is connected in a circuit, phrases of this pattern are used: Be + participle + preposition Attached to Applied to Connected across Connected between Connected to Located within Mounted on Mounted under Wired to Wound round EXAMPLES Battery Bulb The bulbs are connected across the battery Helicopter Microwave Radar antenna Microwave radar antenna is mounted under helicopter 10 GHz Radar antenna van 52 10 GHz Radar antenna (1)…… van during non-contact experiment at Skagit River When a number of solar cells (2)…… each other and mounted in a support frame, it is referred to as a module wires steel core Wires (3)……… a steel core Air preheater (4)… the boiler Turbine (5)… the generator Pulverizer (6)… stoker and boiler Turbine and generator (7)… powerhouse 53 III INFORMATION TRANSFER Task Reading generator rating plates The capacity of a synchronous generator is equal to the product of the voltage per phase, the current per phase, and the number of phases It is normally stated in megavolt-amperes (MVA) for large generators or kilovolt-amperes (kVA) for small generators Both the voltage and the current are the effective, or rms, values (equal to the peak value divided by ) The voltage rating of the generator is normally stated as the operating voltage between two of its three terminals—i.e., the phase-to-phase voltage For a winding connected in delta, this is equal to the phase-winding voltage For a winding connected in wye, it is equal to times the phase-winding voltage The capacity rating of the machine differs from its shaft power because of two factors —namely, the power factor and the efficiency The power factor is the ratio of the real power delivered to the electrical load divided by the total voltage–current product for all phases The efficiency is the ratio of the electrical power output to the mechanical power input The difference between the two power values is the power loss consisting of losses in the magnetic iron due to the changing flux, losses in the resistance of the stator and rotor conductors, and losses from the winding and bearing friction In large synchronous generators, these losses are generally less than percent of the capacity rating These losses must be removed from the generator by a cooling system to maintain the temperature within the limit imposed by the insulation of the windings SYNCHRONOUS GENERATOR DATA Unit Number: Total number of units with listed specifications on site: _ Manufacturer: Type: Date of manufacture: _ Serial Number (each): Phases: Single Three R.P.M.: Frequency (Hz): _ Rated Output (for one unit): _Kilowatt _Kilovolt-Ampere Rated Power Factor (%): Rated Voltage (Volts): _Rated Amperes: Field Volts: Field Amps: Motoring power (kW): Synchronous Reactance (Xd): % on KVA base Transient Reactance (X’d): % on KVA base Subtransient Reactance (X’d); % on KVA base Negative Sequence Reactance (Xs): _% on KVA base Zero Sequence Reactance (Xo): % on KVA base Neutral Grounding Resistor (if applicable): _ I 22 t or K (heating time constant): _ Additional information: 54 IV GUIDED WRITING Task Sentence building Join the following groups of sentences to make the longer sentences Use the words printed in italics at the beginning of each group You may omit words and make whatever changes you think are necessary in the word order and punctuation of the sentences while In any generator, the whole assembly carrying the coils is called the armature, or rotor The stationary parts constitute the stator but There are advantages and disadvantages to all types of generators Consumer generators most often run on either gasoline, diesel, or propane that A direct-current (DC) generator is a rotating machine A rotating machine supplies an electrical output with unidirectional voltage and current if An induction machine can operate as a generator The induction machine is connected to an electric supply network operating at a substantially constant voltage and frequency when Generators offer a level of safety and security A power supply is unstable because These three factors energy, environment, and economy are interdependent Advances in one must be compatible with the others 55 V READING AND SUMMARIZING Study this passage carefully and answer the questions which follow: STRUCTURE AND PRINCIPLE OF ENGINES We have used thermal engines widely since they invented in the 17th century There are many kinds of the engine, and they are used in our life In this session, the structure, the principle and the characteristics of the thermal engines and the power source are presented • 1769: J Watt invented a reciprocating steam engine with a condenser • 1816: R Stirling invented a hot air engine (Stirling engine) which utilizes a reheat energy • 1839: J Ericsson developed several hot air engines (Ericsson engine) in these days • 1876: N Otto developed a spark ignition engine (gasoline engine) • 1883: C Laval developed a steam turbine • 1892: R Diesel invented the principle of a compression ignition engine (Diesel engine) • 1930: F Whittle invented a gas turbine for an airplane • 1944: A practical rocket engine is developed in Germany • 1952: F Bacon invented a fundamental fuel cell Reciprocating Steam Engine The reciprocating steam engine is the first engine which was reached practical use This engine obtains a mechanical power using static pressure of the steam After the Industrial Revolution, it had been used as the power sources for industries and transportations while a long time But it is replaced by internal combustion engines, and not used nowadays Generally, the steam engine consists of a boiler, a heater, a piston, a cylinder, condenser and a water pump as shown in a right figure An intake and an exhaust valve are located on the top of the cylinder 56 Stirling Engine The Stirling engine consists of two pistons as shown in a right figure It is a closed cycle external combustion engine which uses the working gas repeatedly without any valve A memorable characteristic of this engine is that a regenerator is adopted in order to obtain a high efficiency In those days invented the engine, this had been called 'Hot air engine' together with an Ericsson engine described bellow After many developments, the Stirling engines in the present come to get a high power and a high efficiency by using high pressure helium or hydrogen as the working gas But this engine has not reached practical use yet, because it has several problems such as a heavy weight and a high production cost Ericsson Engine J Ericsson developed several engines by reforming the Stirling engine (called the hot air engine in these days) One of them is called the Ericsson engine nowadays It is an opened cycle external combustion engine with two valves at a supply cylinder and power cylinder as shown in a right figure Also, most of the engines invented by J Erickson were used the regenerator Gasoline Engine Nowadays, the gasoline engine (spark ignition engine) is used widely as the power source of automobiles As the principle of this engine, a mixture gas of the fuel and the air is compressed in the cylinder at the first And the gas explodes by use of an ignition plug, and generates the output power As good characteristics of the engine, it can be realized a smaller and light weight engine, and has a possibility of the high engine speed and high power Also, the maintenance of the engine is very simple 57 Steam Turbine The steam turbine has rotating blades instead of the piston and the cylinder of the reciprocating steam engine This engine is used as the power source in the thermal and nuclear power plants The steam turbine utilizes dynamic pressure of the steam, and converts a thermal energy to a mechanical energy, though the reciprocating steam engine utilizes the static pressure of the steam The both engines use the energy that is obtained at the expansion of the steam Diesel Engine The Diesel engine (compression ignition engine) is the internal combustion engine as well as the gasoline engine, and used widely as the power source of the ship and the automobile As the principle of this engine, the air is entered in the cylinder, and it is compressed adiabatically to a high temperature at the first When the mists of the fuel are jetted into the high temperature cylinder, it combusts automatically, and the engine obtains the output power It can get the higher efficiency than that of the gasoline engine for a high compression ratio Also this engine has economical advantage because it can use inexpensive light oil and heavy oil as the fuel However it may have the problems such as large vibrations and noises, and increase of the engine weight for the high pressure in the cylinder Gas Turbine As the principle of the gas turbine, a working gas (air) is compressed by a compressor and heated by combustion energy of the fuel at the first The working gas becomes the high temperature and high pressure The engine converts the energy of working gas into the rotating energy of the blades, making use of the interaction between the gas and the blades a As shown in the below figure, there are two types of the gas turbine One is the open cycle type (internal type), and another is the closed cycle type (external type) Basic components of both types are the air compressor, a combustor and the turbine 58 The gas turbine can handle a larger gas flow than that of the reciprocating internal combustion engines, because it utilizes a continued combustion Then the gas turbine is suitable as the high power engine The gas turbine for airplanes (called a jet engine) makes use of this advantage Rocket Engine The rocket engine obtains a combustion gas of high temperature and high pressure from the fuel and an oxidizer in combustor The combustion gas becomes high speed with an adiabatic expansion through a nozzle, and is jetted to the rear the engine It is obtained a propulsive force by a reaction of the high speed gas a of The jet engine and the rocket engine obtains the propulsive force in the same way by using the reaction of the working gas However, it is difference from the jet engine that the rocket engine has the total gas including the oxidizer itself Then it can get the propulsive force even if there is no air, so it is used as the propulsive power source in the space Fuel Cell Above thermal engines change the energy of the fuel to the mechanical power by way of thermal energy On the other hand, the fuel cell changes the chemical energy of the fuel to the electric energy directly The fuel cell consists of the anode and the cathode which are separated by an electrolyte layer When the fuel is supplied to the anode, and the oxidizer is supplied to the cathode, it generates the electric energy 59 How the steam turbine converts a thermal energy to a mechanical energy? What is called 'Hot air engine' ? Can jet engine get the propulsive force even in case of without air? Why? Where does the rocket engine obtains a combustion gas of high temperature and high pressure ? Why can the gas turbine handle a larger gas flow than that of the reciprocating internal combustion engines? 60 [...]... good characteristics of the engine, it can be realized a smaller and light weight engine, and has a possibility of the high engine speed and high power Also, the maintenance of the engine is very simple 57 Steam Turbine The steam turbine has rotating blades instead of the piston and the cylinder of the reciprocating steam engine This engine is used as the power source in the thermal and nuclear power plants ... the boiler Turbine (5)… the generator Pulverizer (6)… stoker and boiler Turbine and generator (7) … powerhouse 53 III INFORMATION TRANSFER Task Reading generator rating plates The capacity of... STRUCTURE AND PRINCIPLE OF ENGINES We have used thermal engines widely since they invented in the 17th century There are many kinds of the engine, and they are used in our life In this session, the... principle and the characteristics of the thermal engines and the power source are presented • 176 9: J Watt invented a reciprocating steam engine with a condenser • 1816: R Stirling invented a