Three Phase Emf Generation 681w4j

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Three Phase EMF Generation

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Why 3-ø system? 3-ø power system has following advantages over the 1-ø system. 1. Power in a 1-ø system is pulsating where as that of a 3-ø system is merely constant. 2. Power to weight ratio of 3-ø alternators and other machines is high as compared to 1-ø alternator.

3. For electric power transmission and distribution of same amount of power, the requirement of conductor material is less in 3-ø system as compared to 1-ø system.

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Contd… 4. 3-phase induction motor is self-started as the magnetic flux produced by 3-phase supply is rotating in nature with constant magnitude.

5. 3-phase motors and transformers have better power factor and efficiency as compared to 1-ø motor. 6. If fault occurs in any winding of 3-phase transformer, the rest of two winding can be used in open delta to serve the 3-phase load which is not possible in 1-ø transformer. 7. A 3-phase system can be used to feed a 1-ø load, whereas viceversa is not possible.

8. DC rectified from 3-phase supply is having the ripple factor 4% and DC rectified from 1-ø supply is having the ripple factor 48.2%.

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1.Power in 1-ø Vs 3-ø system 1-ø Power is given as the product of V & I :

i.e.

Power in three phase system: 5

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2.Power to weight ratio of electrical machines To produce same amount of power, a single phase machine must be larger in size when compared to a three phase machine.

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3.Requirement of conductor material Requirement of copper for a single phase Vs three phase system is in the ratio of 2 : 0.5, which means single phase system requires 4times more copper than that of three phase system.

4.Rotatting magnetic field Rotating magnetic field is readily produced in the case of three phase alternators and induction machines whereas difficult to be produced in the case of single phase motors.

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Rotating magnetic field

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Generation of 3-ø EMF: