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Download Lesson 16: Asynchronous Generators/Induction Generators
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1/26/2016 Lesson 16: Asynchronous Generators/Induction Generators ET 332b Ac Motors, Generators and Power Systems et332bInd.ppt 1 Learning Objectives After this presentation you will be able to: Explain how an induction generator operates List application for induction generators in the use renewable resources Discuss the limitations of induction generators Compute the power developed from an induction generator using the per phase circuit model et332bInd.ppt 2 1 1/26/2016 Induction Generators Driving an induction motor faster than synchronous speed when connected to the grid results in active power generation Induction generators (asynchronous generators) designed with lower rotor R to reduce losses and machine slip. Applications: Wind Turbines, Hydraulic Turbines (small scale hydro), Gas engines fueled by natural gas or biogas cogeneration et332bInd.ppt 3 Induction Generator Starting Sequence Existing Three Phase System Breaker Electric Power Out Induction Generator Prime Mover 1.) Breaker open 2.) Increase prime mover mechanical power input until nr >ns. 3.) Close Breaker 4.) Adjust mechanical power input to match electric load. Pmech=Pe+Ploss nr >ns Generator Losses Mechanical Power In et332bInd.ppt Induction generator can not vary terminal voltage or frequency. Set by system. 4 2 1/26/2016 Induction Generator Speed Power Curves Induction Machine Speed-Power Curve Air Gap Power (kW) 100 ns 1.1ns Generator Operation 50 0 -50 Pushover Power -100 0 500 1000 1500 2000 2500 3000 3500 4000 Rotor Speed (rpm) et332bInd.ppt 5 Limitations of Induction Generations • Require existing power grid for synchronous operation. – Can not control frequency or voltage independently • Can not operate above pushover speed • Require a source of reactive power to operate – When connect to grid, system supplies reactive power to operate generator • When operating without grid connection frequency varies with power output. – Parallel capacitors supply reactive power et332bInd.ppt 6 3 1/26/2016 Induction Generator Example A three-phase, six-pole, 460 V, 60 Hz induction generator operates on a 480 V system. The generator its rated power output is 20 kW. It is driven by a turbine at a speed of 1215 rpm. The generator has the following electrical parameters: R1 =0.200 W, R2= 0.150 W, Rfe= 320 W, X1=1.20 W, X2=1.29 W, XM=42.0 W Find the active power delivered by the generator and the reactive power it requires from the system to operate. et332bInd.ppt 7 Example Solution et332bInd.ppt 8 4 1/26/2016 Example Solution et332bInd.ppt 9 Example Solution et332bInd.ppt 10 5 1/26/2016 Example Solution et332bInd.ppt 11 Isolated Operation of Induction Generators Isolated Three Phase System Isolated Induction generator requires residual flux to build voltage Electric Power Out Breaker Reactive Power from Capacitors Induction Generator Prime Mover nr >ns Generator Losses Capacitors supply reactive power to load and generator when voltage builds. Voltage falls rapidly when load is applied. When nr = ns, no power delivered Mechanical Power In et332bInd.ppt 12 6 1/26/2016 Voltage Build-up in Isolated Induction Generators jX1 R1 -jXc jXm Vin External Capacitor provides Reactive power for operation R2/s Rfe jX2 Operating point set by intersection between magnetization curve and Xc Xc0>Xc1 Voltage Vop Xc0 Xc Xc1 Current C Iop Vop Iop Iop 1 Vop 2f et332bInd.ppt 13 Voltage Build-up in Isolated Induction Generators Lab measurements determine the magnetization curve Three Phase Induction Motor Magnetization Curve 140 Stator Voltage (V) 120 100 80 60 C 40 Inductance change due to rotor motion C 2.845 10 5 F or 28.45 F 20 0 0.00 I op 1 1.18 1 Vop 2f 110 260 0.25 0.50 0.75 1.00 1.25 1.50 Stator Current (A) Lab Data et332bInd.ppt Linearized Magnetization Curve Load Line 14 7 1/26/2016 Voltage Build-up in Isolated Induction Generators Single phase motor magnetization curve Magnetization Curve-Single Phase Motor 140.00 120.00 Voltage (V) 100.00 80.00 60.00 C 40.00 C 1.27 10 4 F or 127 F 20.00 0.00 0.00 I op 1 5.74 1 Vop 2f 120 260 1.00 2.00 3.00 4.00 5.00 6.00 7.00 Current (A) Lab Measurements Linearized Data Load Line et332bInd.ppt 15 ET 332b Ac Motors, Generators and Power Systems END LESSON 16: ASYNCHRONOUS GENERATORS/INDUCTION GENERATORS et332bInd.ppt 16 8