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Three phase ac circuit
The document discusses the three-phase AC circuit, emphasizing its efficiency and reliability in power generation and distribution. It outlines the characteristics of balanced three-phase systems, including voltage and current relationships, along with different connection types (wye and delta). Additionally, it explains the importance of phase voltages and line voltages, as well as the concept of phase and line currents in three-phase systems.
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Three phase ac circuit
- 1. Vishvakarma Government Engineering College, Chandkheda Name–Darshil Vekaria(150170106061) Branch–Civil Engineering Subject- EEE Topic –Three Phase AC. Circuit
- 2. Three PhaseSystem: ◦ A generator consists of three coils placed 120 apart. ◦ The voltage generated are equal in magnitude but, out of phase by 120. Three phase is the most economical polyphase system. Circuit or system in which AC sources operate at the same frequency but different phases are known as polyphase.
- 3. All electricpower is generated and distributed in three phase. ◦ One phase, two phase, or more than three phase input can be taken from three phase system rather than generated independently. ◦ Melting purposes need 48 phases supply.
- 4. Uniform powertransmission and less vibration of three phase machines. ◦ The instantaneous power in a 3 system can be constant (not pulsating). ◦ High power motors prefer a steady torque especially one created by a rotating magnetic field. Three phase system is more economical than a single phase.
- 5. THREE-PHASE WAVEFORM Phase 2lags phase 1 by 120. Phase 2 leads phase 3 by 120. Phase 3 lags phase 1 by 240. Phase 1 leads phase 3 by 240. Phase 1 Phase 2 Phase 3 120 120 120 240 120 120 120 240
- 6. Balanced threephase voltages: 1) same magnitude 2) 120 phase shift 120cos240cos)( 120cos)( cos)( tVtVtv tVtv tVtv MMcn Mbn Man BALANCED 3 CURRENTS •Balanced three phase currents: 1) same magnitude 2) 120 phase shift 240cos)( 120cos)( cos)( tIti tIti tIti Mc Mb Ma
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- 8. Balanced PhaseVoltage: all phase voltages are equal in magnitude and are out of phase with each other by 120. Balanced Load: the phase impedances are equal in magnitude and in phase.
- 9. Phase voltageis measured between the neutral and any line: line to neutral voltage Line voltage is measured between any two of the three lines: line to line voltage. PHASE CURRENTS and LINE CURRENTS• Line current (IL) is the current in each line of the source or load. • Phase current (I) is the current in each phase of the source or load.
- 10. SOURCE LOAD CONNECTION WyeWye Y-Y Wye Delta Y- Delta Delta - Delta Wye -Y
- 11. Common connectionof source: WYE ◦ Delta connected sources: the circulating current may result in the delta mesh if the three phase voltages are slightly unbalanced. Common connection of load: DELTA ◦ Wye connected load: neutral line may not be accessible, load can not be added or removed easily.
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- 15. Phase voltageis measured between the neutral and any line: line to neutral voltage n a b c Vab Vbc Vca Vbn Vcn Van Ia Ib Ic Van Vbn Vcn
- 16. Line voltageis measured between any two of the three lines: line to line voltage. n a b c Vab Vbc Vca Vbn Vcn Van Ia Ib Ic Vab Vbc Vca
- 17. 30VVL Magnitude- VL LEAD their corresponding V by 30 LV 3 V •POWER –The instantaneous power is constant. )cos(3 cos 2 3 )()()()( rmsrms MM cba IV IV tptptptp
- 18. Phase voltagesare equal to the voltages across the load impedances.
- 19. BCCAc ABBCb CAABa III III III 120II 120II 30I3I ac ab ABa RELATIONSHIP BETWEEN Iand IL IIL 3 30IIL 1. Magnitude 1. Phase - IL LAG their corresponding I by 30
- 20. The linecurrents are obtained from the phase currents by applying KCL at nodes A,B, and C.
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