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Lesson 16: Asynchronous Generators/Induction Generators

ET 332b Ac Motors, Generators and Power Systems

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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

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Induction Generators Driving an 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 fueled by or biogas

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Induction Generator Starting Sequence

Existing Three Phase System 1.) Breaker open 2.) Increase prime mover mechanical power input

until nr >ns. Electric Breaker 3.) Close Breaker Power Out 4.) Adjust mechanical power input to match electric Induction Prime load. Generator Mover Pmech=Pe+Ploss

nr >ns

Generator Losses Induction generator can

Mechanical not vary terminal voltage Power In or frequency. Set by system. et332bInd.ppt 4

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Induction Generator Speed Power Curves Induction Machine Speed-Power Curve 100 ns 1.1ns

) Generator W

k Operation (

50 r e w o P 0 p a G

r i A -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

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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.

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Example Solution

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Example Solution

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Example Solution

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Example Solution

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Isolated Operation of Induction Generators

Isolated Three Phase System Isolated Induction generator requires residual flux to build voltage

Electric Power Breaker Out Capacitors supply reactive Reactive Power from power to load and Capacitors generator when voltage builds. Induction Prime Generator Mover Voltage falls rapidly when nr >ns load is applied.

Generator When nr = ns, no Losses power delivered

Mechanical Power In

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Voltage Build-up in Isolated Induction Generators

jX1

R1 R2/s External Capacitor provides -jXc jXm Vin Rfe Reactive power for operation jX2

Operating point set by intersection

Xc0>Xc1 between magnetization curve and Xc Vop

e Xc0 V g op a t l Xc1 o X 

V c Iop

Iop  1  I Current op C    Vop  2f 

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Voltage Build-up in Isolated Induction Generators

Lab measurements determine the magnetization curve

Three Phase Induction Motor Magnetization Curve

140

120

100

80

60 Voltage (V)

Iop  1  1.18  1  40 C        V  2f  110  260  Inductance op 5 change 20 C  2.84510 F or 28.45 F due to rotor 0 motion 0.00 0.25 0.50 0.75 1.00 1.25 1.50 Stator Current (A)

Lab Data Linearized Magnetization Curve Load Line

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Voltage Build-up in Isolated Induction Generators

Single phase motor magnetization curve

Magnetization Curve-Single Phase Motor

140.00

120.00

100.00

80.00

60.00

Voltage Voltage (V) I  1  5.74  1  C  op      40.00 Vop  2f  120  260  20.00 C 1.27104 F or 127 F

0.00 0.00 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

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