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1.1 three phase power supply
Three phase power systems have several advantages over single phase systems: 1) They provide uniform power transmission with less vibration in three phase machines due to the constant instantaneous power. 2) They are more economical since they require less wiring to transmit the same amount of power over the same distance and power loss. 3) Large power motors prefer the steady torque produced by the rotating magnetic field generated by three phase systems.
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1.1 three phase power supply
- 1. 1.1 Three phasepower supply P. Maria Sheeba AP/ECE MZCET
- 2. IMPORTANCE OF THREEPHASE SYSTEM • Uniform power transmission and less vibration of three phase machines. – The instantaneous power in a 3φ system can be constant (not pulsating). – High power motors prefer a steady torque especially one created by a rotating magnetic field.
- 3. IMPORTANCE OF THREEPHASE SYSTEM • Three phase system is more economical than the single phase. – The amount of wire required for a three phase system is less than required for an equivalent single phase system. – Conductor: Copper, Aluminum, etc
- 4. Differences Single Phase PowerSupply 230 V, 50 Hz Not sufficient for producing large amount of power. With single-phase current, the voltage rises to a peak in one direction of flow, subsides to zero, reverses, rises to a peak in the opposite direction, subsides to zero, and so on. Single-phase current requires the use of one transformer. Three Phase Power Supply 440 V, 50 Hz Sufficient for producing large amount of power. There are three separate and distinct single-phase currents, which are combined so they can be transmitted over three or four wires and these rise to a peak in one direction, subside, reverse, and so on; however they do not peak at the same time. Three-phase current requires two or three transformers.
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- 6. 1.1.1 Introduction: • Thegenerator , motor , transformer or rectifier have only one winding is called a single phase system • If the current or voltage follows a phase difference 900 in a two windings, called two phase systems • If the phase difference is 1200 between voltages or currents in a three winding, called as Three phase systems • In poly-phase systems , there are more than three windings Advantages of three phase system: • More efficient than single phase system • Cost is less • Size is small . Compared to single phase system
- 7. Advantages of ThreePhase Circuits • The amount of conductor material is required less for transmitting same power, over the same distance , under same power loss • Three phase motors produce uniform torque , where as torque produced by single motor is pulsating • Three phase generators not produce the harmonics when they are connected in parallel • Three phase motors are self starting whereas single phase motors are not self starting
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- 9. FARADAYS LAW • Threethings must be present in order to produce electrical current: a) Magnetic field b) Conductor c) Relative motion • Conductor cuts lines of magnetic flux, a voltage is induced in the conductor • Direction and Speed are
- 10. GENERATING A SINGLEPHASE Motion is parallel to the flux. No voltage is induced. N S
- 11. x N S Motion is 45°to flux. Induced voltage is 0.707 of maximum. GENERATING A SINGLE PHASE
- 12. GENERATING A SINGLEPHASE x N S Motion is perpendicular to flux. Induced voltage is maximum.
- 13. GENERATING A SINGLEPHASE Motion is 45° to flux. x N S Induced voltage is 0.707 of maximum.
- 14. GENERATING A SINGLEPHASE N S Motion is parallel to flux. No voltage is induced.
- 15. GENERATING A SINGLEPHASE x N S Notice current in the conductor has reversed. Induced voltage is 0.707 of maximum. Motion is 45° to flux.
- 16. GENERATING A SINGLEPHASE N S x Motion is perpendicular to flux. Induced voltage is maximum.
- 17. GENERATING A SINGLEPHASE N S x Motion is 45° to flux. Induced voltage is 0.707 of maximum.
- 18. GENERATING A SINGLEPHASE Motion is parallel to flux. N S No voltage is induced. Ready to produce another cycle.
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- 20. GENERATOR WORK • Thegenerator consists of a rotating magnet (rotor) surrounded by a stationary winding (stator). • Three separate windings or coils with terminals a-a’, b-b’, and c-c’ are physically placed 120° apart around the stator.
- 21. • As therotor rotates, its magnetic field cuts the flux from the three coils and induces voltages in the coils. • The induced voltage have equal magnitude but out of phase by 120°.
- 22. GENERATION OF THREE-PHASEAC N xx S
- 23. 1.1.2 Generation ofThree Phase Voltages
- 24. BALANCED 3φ VOLTAGES •Balanced three phase voltages: – same magnitude (VM ) – 120° phase shift ( ) ( ) ( ) ( )°+=°−= °−= = 120cos240cos)( 120cos)( cos)( tVtVtv tVtv tVtv MMcn Mbn Man ωω ω ω
- 25. • Vectorially r.m.svalues of voltages induced in three windings are represented in the diagram • ER = E ∟0o v, • EY = E ∟-120o v • EB= E ∟+120o v
- 26. Three voltagesare not in phase, since there is a phase difference of The order of voltage waveform sequences in a polyphase system is called phase rotation or phase sequence. This sequence of phase shifts has a definite order. For clockwise rotation, the order is 1-2-3 (i.e) RYB (winding 1 peaks first, them winding 2, then winding 3), which is known as a positive phase sequence. MZCET 1.1.3 PHASE SEQUENCE 120
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- 28. For anti-clockwiserotation, the order is 3-2-1 (i.e) RBY (winding 3 peaks first, them winding 2, then winding 1), which is known as a negative phase sequence. If we’re using a polyphase voltage source to power resistive loads, phase rotation will make no difference at all. Whether 1-2-3 or 3-2-1, the voltage and current magnitudes will all be the same.
- 29. PHASE SEQUENCE ( ) ()°+= °−= = 120cos)( 120cos)( cos)( tVtv tVtv tVtv Mcn Mbn Man ω ω ω °+∠= °−∠= °∠= 120 120 0 Mcn Mbn Man VV VV VV POSITIVE SEQUENCE NEGATIVE SEQUENCE °−∠= °+∠= °∠= 120 120 0 Mcn Mbn Man VV VV VV
- 30. Overview of Threephase power supply Both single phase and three phase power systems refer to units using alternating current (AC) electric power. With AC power, the flow of current is constantly alternating directions. The primary difference between single phase and three phase AC power is the constancy of delivery.