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Synchronous Motor.pptx
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- 2. CONTENT TORQUE & TORQUE ANGLE BLONDEL DIAGRAM EFFECT OF CHANGEIN EXCIATION. EFFECT OF CHANGE IN LOAD. CONCULSION Presentation Title Presentation title 2
- 3. TORQUE IN A SYNCHRONOUS MOTOR Torquecauses an a object to acquire angular acceleration. Torque is a measure of the force the can cause an object to rotate about an axis. Torque is a vector quantity. The direction of the torque vector depend on the direction of the force on the axis. Presentation title 3
- 4. TORQUE IN A SYNCHRONOUSMOTOR Presentation title 4 This Photo by Unknown Author is licensed under CC BY-SA The mechanical power developed (Pm) by any synchronous motor can be expressed as − Pm=2πNSτg60Watts Also, the mechanical power developed (Pm) is, Pm=VIaCos(δ−φ), Where, NS is the synchronous speed in RPM. τgis the gross-torque in N-m.
- 5. TORQUE IN A SYNCHRONOUSMOTOR Presentation title 5 This Photo by Unknown Author is licensed under CC BY-SA Therefore, the gross torque of the synchronous motor is given by, τg=602π*PmNS = 9.55×PmNSN−m And the shaft torque is given by, τsh=9.55×PoNSN−m
- 6. Types of Torquein a Synchronous Motor Presentation title 6 Starting Torque Running Torque Pull-in Torque Pull-out Torque
- 7. Torque angle ofa synchronous motor. Presentation title 7 • A synchronous motor is meant to rotate at synchronous speed i.e, speed of the rotating field. • If the motor is loaded, the rotor lags behind the synchronous speed. Thus the rotor goes out of sync with the rotating resultant field. • Angle between rotor and the rotating resultant field is called Torque angle. • With the help of torque angle, the stability of the motor can be analyzed. Similarly, when the motor is suddenly unloaded the rotor slips ahead of the rotating field. • At any instant, separation between rotor and rotating field is calculated by an angle called Torque Angle.
- 8. Blondel diagram insynchronous motor. Presentation title 8 The Blondel diagram of a synchronous motor is an extension of a simple phasor diagram of a synchronous motor. For a synchronous motor, the power input to the motor per phase is given by, Pin = Vph Iph cos The gross mechanical power developed per phase will be equal to the difference between Pin per phase and the per phase copper losses of the winding. Copper loss per phase = (Iaph)2 Ra Pm = Vph Iph cos? – (Iaph)2 Ra
- 9. Presentation title 9 Formathematical convenience let Vph = V and Iaph = I, Pm = VI cos – I2 Ra I2 Ra – VI cos + Pm = 0 fd
- 10. Thus if excitationis varied while the power is kept constant, then working point B while move along the circle of constant power. Let O’B = Radius of circle = r OO’ = Distant d Applying cosine rule to triangle OBO’, 10
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- 12. 12 One of themost important characteristics of a synchronous motor is that, by changing the field excitation of the motor, its power factor can be made both lagging and leading. The change in the power factor of the synchronous motor with the change in excitation can be explained with the help of its phasor diagram. Pi= Vef/Xs Sinδ = 3VIaCosφ Since V and XS are constant for a given synchronous motor, thus for constant power output, EfSinδ=Constant IaCosφ=Constant Effect of Changing Field Excitation on Synchronous Motor at Constant Load
- 13. 13 •If the synchronousmotor is under-excited, it has a lagging power factor. •If the synchronous motor is normally-excited, it has unity power factor. •If the synchronous motor is over-excited, it has a leading power factor.
- 14. Presentation title 14 Effectof Load Change on a Synchronous Motor In induction motors and DC motors, when the mechanical load attached to the shaft of the motor is increased, the speed of the motor decreases. The decrease in the speed reduces the back EMF so that additional current is drawn from the source to carry the increased load at a reduced speed. But, this action cannot take place in a synchronous motor, since it runs at a constant speed (i.e., synchronous speed) at all loads.
- 15. Presentation title 15 Fora synchronous motor, the armature current per phase is given by, Ia=V−Ef/Zs=Er/Zs When the load on a synchronous motor is increased, then •The motor continues to run at synchronous speed • The torque angle (δ) increases •The magnitude of the excitation voltage (Ef) remains constant •The armature current (Ia) drawn from the supply increases.
- 16. Presentation title 16 Whenthe load on a synchronous motor is decreased, then •The motor continues to run at synchronous speed. •The torque angle (Ia) decreases. •The magnitude of the excitation voltage (Ef) remains constant. •The armature current (Ia) drawn from the supply decreases.
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