lect24 - Lecture 24 - EE743 3-Phase Induction Machines...

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Lecture 24 - EE743 Lecture 24 - EE743 3-Phase Induction Machines Torque Speed characteristics Professor: Ali Keyhani Professor: Ali Keyhani
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2 Importance of T-speed characteristics Torque speed characteristic of a motor is important from the point of view of its applications to specific situations. To calculate the torque produced by the machine, first, we compute the motor power. The motor power, or the mechanical power supplied to the load is The electrical power inputted to the machine can be calculated from the eq. circuit given below losses in em P P P - =
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3 Importance of T-speed characteristics
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4 Machine Torque Power dissipated is Motor power P em is Motor torque can be calculated from { } + = = s R R I I V P ' 2 1 2 1 * 1 1 1 3 ~ ~ Re 3 ext rotor R R R X a X R a R + = = = 2 2 2 ' 2 2 2 ' 2 ( 29 ( 29 ' 2 1 2 1 2 2 1 2 1 3 3 R R I R a R I P + = + = ( 29 2 1 ' 2 ' 2 1 ' 2 1 2 1 1 3 3 I R s s R R s R R I P em - = + - + = m em em T P ϖ = 2 1 ' 2 1 3 I R s s T m em - =
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5 Machine Torque Since T m can be written as Substituting for I 1 in equation (3), we will have ( 29 s sync m - = 1 ϖ 2 1 ' 2 3 I s R T sync em = ( 29 2 ' 2 1 2 ' 2 1 2 1 2 1 X X s R R V I + + + = ( 29 2 ' 2 1 2 ' 2 1 2 1 ' 2 3 X X s R R V s R T sync em + + + =
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6 Power calculations Figure 2 shows the plot of equation (3) for the values of slip from zero to unity. In Fig.1 . This corresponds to the normal range of the speed of an induction motor from starting ( ϖ m =0, s=1) to the synchronous speed ( ϖ m = ϖ sync , s=0) ( 29 ext R R a R + = 2 2 ' 2
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7 s max and T
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lect24 - Lecture 24 - EE743 3-Phase Induction Machines...

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