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Basic Power Plant Operation 2014 NA PGS Technical Leadership Training 1 Objectives • Explain how a turbine works • Discuss the principles of operation for Steam Turbine and Gas Turbines • Describe the operation of a Combined Cycle Power Plant • Discuss how Generators make electricity • Discuss factors that affect maintenance cycles Conservation of Energy • The law of conservation of energy states that energy can be neither created nor destroyed. However, energy can change forms, and energy can flow from one place to another. • The flow of heat is a form of energy transfer. • Work is a process of transferring energy to or from a system. What Makes a Turbine Spin? Why are Turbines Shaped This Way? Gas Turbine Gas Turbine History • 1791: first patent for a gas turbine resembling present day units was issued • Manufacture of a gas turbine that could efficiently provide useful power was not attainable until high temperature materials became available • 1949: GE placed its first gas turbine into commercial operation Brayton Cycle • The Brayton cycle is the thermodynamic cycle that describes the workings of a constant pressure heat engine. • There are 3 processes: – Compression – Combustion – Expansion Gas Turbine Plant Layout Thermal Efficiency • Ratio of work extracted from hot gas to the heat that is added. • How much of the available energy did the turbine use? Naming Convention • Frame Size (3,5,6,7,9) denotes the size railcar that the machine will ship on. • Number designation is the number of shafts the machine has (i.e. MS5001 has one shaft) • Letter designations indicate horsepower (due to increased firing temp), increasing from A. • Incremental design changes are indicated by additional letters (6FA, 6FB) Steam Turbine Steam Turbine History • 1882: Thomas Edison put the central station power system into operation, using a steam-piston engine as the prime mover -> fairly efficient • 1896: Charles Curtis designed a more efficient system to drive a generator and offered his invention to GE in Schenectady > steam turbine • 1901: GE offered its first turbine for sale Rankine Cycle • The Rankine cycle is the thermodynamic cycle of a heat engine that converts heat into mechanical work. • There are 4 processes: – Wpump : energy added by the feedpump – Qin : heat transferred into the system – Wturbine : energy extracted by the turbine – Qout : heat transferred out by the condenser Basic Steam Plant Layout High Temp Low Pressure High Temp High Pressure Low Temp High Pressure Low Temp Low Pressure Thermal Efficiency • Ratio of work extracted from steam to the heat that is added. • How much of the available energy did the turbine use? Naming Convention • Letter Designator (A,B,C,D) determined by basic characteristics: – Full or half speed – Tandem or cross-compounded – Number of low pressure flowpaths – Reheat or non-reheat • Variation within basic characteristics results in a new code (1,2,3) – Position of valves – Position of crossovers – Types of nozzles – HP-IP in separate or same shell • Suffix is included if further differentiation is needed (A,D,E,H,R,X) D11H D – Full speed, reheat, double-flow condensing turbine 11 – Off-shell valves, single shell high pressure section with diaphragm first stage H – Special low pressure section designed for high back pressure applications Combined Cycle Power Plant General Description • Uses the Gas Turbine Brayton Cycle in combination with the Steam Turbine Rankine Cycle • GE Trade name is STAG (STeam and Gas). Most common configuration is S207FA. • Used to increase overall plant efficiency. AC Generator Electricity Basics • Voltage: a measure of how strongly the electrons are being pushed through a conductor • Current: a measure of the rate of electron flow through a conductor Voltage Induction • Three things are necessary to induce a voltage: – Magnetic Field – Current Carrying Conductor – Relative Motion Between the Two Generator Excitation • Generator Excitation System either: – Takes part of generator AC output and rectifies it to DC to supply the generator field windings, or – Takes power from the Grid and rectifies it to DC to supply the generator field windings • Applying a voltage to the generator rotor turns it into a large electro-magnet Stator Cooling • Electricity flowing through a generator creates a great deal of heat, which must be removed. • Three methods: – Air Cooling – Hydrogen Gas Cooling – Liquid Cooling Hydrogen Seals Maintenance Considerations