Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Switched-mode power supply wikipedia , lookup
Yagi–Uda antenna wikipedia , lookup
Surge protector wikipedia , lookup
Standing wave ratio wikipedia , lookup
Opto-isolator wikipedia , lookup
Integrating ADC wikipedia , lookup
Power electronics wikipedia , lookup
Phase-contrast X-ray imaging wikipedia , lookup
ELECTRICAL TECHNOLOGY (EET 103) PN HAZIAH ABDUL HAMID SYLLABUS – PART II SYLLABUS • TOPIC 4: THREE PHASE CIRCUIT • TOPIC 5: TRANSFORMER • TOPIC 6: ELECTRICAL MACHINES TOPIC 4: THREE PHASE CIRCUIT SINGLE PHASE TWO WIRE V p SINGLE PHASE SYSTEM • A generator connected through a pair of wire to a load – Single Phase Two Wire. • Vp is the magnitude of the source voltage, and is the phase. SINLGE PHASE THREE WIRE V p V p SINGLE PHASE SYSTEM • Most common in practice: two identical sources connected to two loads by two outer wires and the neutral: Single Phase Three Wire. • Terminal voltages have same magnitude and the same phase. POLYPHASE SYSTEM • Circuit or system in which AC sources operate at the same frequency but different phases are known as polyphase. TWO PHASE SYSTEM THREE WIRE V p V p 90 POLYPHASE SYSTEM • Two Phase System: – A generator consists of two coils placed perpendicular to each other – The voltage generated by one lags the other by 90. POLYPHASE SYSTEM • Three Phase System: – 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. THREE PHASE FOUR WIRE IMPORTANCE OF THREE PHASE SYSTEM • All electric power 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. IMPORTANCE OF THREE PHASE SYSTEM • Uniform power transmission 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. IMPORTANCE OF THREE PHASE 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 THREE PHASE GENERATION FARADAYS LAW • Three things 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 important GENERATING A SINGLE PHASE S N Motion is parallel to the flux. No voltage is induced. GENERATING A SINGLE PHASE S N Motion is 45 to flux. Induced voltage is 0.707 of maximum. GENERATING A SINGLE PHASE S x N Motion is perpendicular to flux. Induced voltage is maximum. GENERATING A SINGLE PHASE S N Motion is 45 to flux. Induced voltage is 0.707 of maximum. GENERATING A SINGLE PHASE S N Motion is parallel to flux. No voltage is induced. GENERATING A SINGLE PHASE S N Notice current in the conductor has reversed. Motion is 45 to flux. Induced voltage is 0.707 of maximum. GENERATING A SINGLE PHASE S N Motion is perpendicular to flux. Induced voltage is maximum. GENERATING A SINGLE PHASE S N Motion is 45 to flux. Induced voltage is 0.707 of maximum. GENERATING A SINGLE PHASE S N Motion is parallel to flux. No voltage is induced. Ready to produce another cycle. THREE PHASE GENERATOR GENERATOR WORK • The generator 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. • As the rotor 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. GENERATION OF THREE-PHASE AC S x x N THREE-PHASE WAVEFORM Phase 1 120 Phase 2 Phase 3 120 120 240 Phase 2 lags phase 1 by 120. Phase 3 lags phase 1 by 240. Phase 2 leads phase 3 by 120. Phase 1 lags phase 3 by 120. GENERATION OF 3 VOLTAGES Phase 1 Phase 2 Phase 3 The algebraic sum of the instantaneous voltages of the three phases equals zero. Phase 1 is ready to go positive. Phase 2 is going more negative. Phase 3 is going less positive. S x x N THREE PHASE QUANTITIES BALANCED 3 VOLTAGES • Balanced three phase voltages: – same magnitude (VM ) – 120 phase shift v an (t ) VM cos t vbn (t ) VM cos t 120 vcn (t ) VM cos t 240 VM cos t 120 BALANCED 3 CURRENTS • Balanced three phase currents: – same magnitude (IM ) – 120 phase shift ia (t ) I M cos t ib (t ) I M cos t 120 ic (t ) I M cos t 240 PHASE SEQUENCE van (t ) VM cos t vbn (t ) VM cost 120 vcn (t ) VM cost 120 Van VM 0 Van VM 0 Vbn VM 120 Vbn VM 120 Vcn VM 120 Vcn VM 120 POSITIVE SEQUENCE NEGATIVE SEQUENCE PHASE SEQUENCE EXAMPLE • Determine the phase sequence of the set voltages: van 200 cost 10 vbn 200 cost 230 vcn 200 cost 110 Ans: Negative Sequence BALANCED VOLTAGE AND LOAD • Balanced Phase Voltage: 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. THREE PHASE CIRCUIT • POWER – The instantaneous power is constant p(t ) pa (t ) pb (t ) pc (t ) VM I M 3 cos 2 3Vrms I rms cos( ) THREE PHASE CIRCUIT • Three Phase Power, S T S A S B S C 3 S THREE PHASE QUANTITIES QUANTITY SYMBOL Phase current I Line current IL Phase voltage V Line voltage VL PHASE VOLTAGES and LINE VOLTAGES • Phase voltage is 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. THREE PHASE CONNECTION SOURCE-LOAD CONNECTION SOURCE LOAD CONNECTION Wye Wye Y-Y Wye Delta Y- Delta Delta - Delta Wye -Y SOURCE-LOAD CONNECTION • Common connection of 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. WYE CONNECTION WYE CONNECTED GENERATOR Ia a Van Vab n Vbn Ib Vca b Vcn Vbc Ic c WYE CONNECTED LOAD a a Y Z ZY b OR b Load ZY c n c n ZY ZY ZY Load BALANCED Y-Y CONNECTION PHASE CURRENTS AND LINE CURRENTS • In Y-Y system: IL Iφ PHASE VOLTAGES, V • Phase voltage is measured between the neutral and any line: line to neutral voltage Ia a VVanan n VVbnbn Vab Ib Vca b VVcn cn Vbc Ic c PHASE VOLTAGES, V Van VM 0 volt Vbn VM 120 volt Vcn VM 120 volt LINE VOLTAGES, VL Ia • Line voltage is measured between any two of the three lines: line to line voltage. a Van Vab ab n Vbn Ib b Vcn V V bc bc Ic c VVcaca LINE VOLTAGES, VL Vab Van Vbn Vbc Vbn Vcn Vca Vca Van Vab 3VM 30 Vbc 3VM 90 Vca 3VM 150 Van VM 0 volt Vbn VM 120 volt Vcn VM 120 volt LINE VOLTAGE (VL) PHASE VOLTAGE (V) Vab 3 VM 30 volt Vbc 3 VM 90 volt Vca 3 VM 150 volt PHASE DIAGRAM OF VL AND V Vca Vcn Vab 30° 120° Vbn Vbc -Vbn Van PROPERTIES OF PHASE VOLTAGE • All phase voltages have the same magnitude, V Van Vbn Vcn • Out of phase with each other by 120 PROPERTIES OF LINE VOLTAGE • All line voltages have the same magnitude, VL Vab Vbc Vca • Out of phase with each other by 120 RELATIONSHIP BETWEEN V and VL 1. Magnitude VL 3 V 2. Phase - VL LEAD their corresponding V by 30 VL V 30 EXAMPLE • Calculate the line currents Single Phase Equivalent Circuit • Phase ‘a’ equivalent circuit 5-j2 10 j8 Van Ia ZY 1100 Ia 6.81 21.8 16.15521.8 I b I a 120 6.81 141.8A I c I a 240 6.81 261.8 6.8198.2A DELTA CONNECTION DELTA CONNECTED SOURCES DELTA CONNECTED LOAD OR BALANCED - CONNECTION PHASE VOLTAGE AND LINE VOLTAGE • In - system, line voltages equal to phase voltages: VL Vφ PHASE CURRENTS, I • Line voltages are equal to the voltages across the load impedances. PHASE CURRENTS, I • The phase currents are obtained: VBC VCA VAB I AB , I BC , I CA ZΔ ZΔ ZΔ LINE CURRENTS, IL • The line currents are obtained from the phase currents by applying KCL at nodes A,B, and C. LINE CURRENTS, IL I a I AB I CA I b I BC I AB I c I CA I BC I a 3 I AB 30 I b I a 120 I c I a 120 PHASE CURRENTS (I) I AB I BC I CA VAB ZΔ VBC ZΔ VCA ZΔ LINE CURRENTS (IL) I a 3 I AB 30 I b I a 120 I c I a 120 PHASE DIAGRAM OF IL AND I PROPERTIES OF PHASE CURRENT • All phase currents have the same magnitude, Iφ I AB I BC ICA Vφ ZΔ • Out of phase with each other by 120 PROPERTIES OF LINE CURRENT • All line currents have the same magnitude, I L Ia I b Ic • Out of phase with each other by 120 RELATIONSHIP BETWEEN I and IL 1. Magnitude IL 3 IF 2. Phase - VL LAG their corresponding V by 30 IL IF 30 EXAMPLE A balanced delta connected load having an impedance 20-j15 is connected to a delta connected, positive sequence generator having Vab = 3300 V. Calculate the phase currents of the load and the line currents. Given Quantities ZΔ 20 j15 25 36.87 Vab 3300 Phase Currents VAB 3300 I AB 13.236.87A ZΔ 25 38.87 I BC I AB 120 13.2 - 83.13A I CA I AB 120 13.2156.87A Line Currents I a I AB 3 30 13.236.87 3 30 A 22.866.87 I b I a 120 22.86 - 113.13A I c I a 120 22.86126.87A BALANCED DELTA-WYE SYSTEM EXAMPLE A balanced positive sequence Yconnected source with Van=10010 V is connected to a -connected balanced load (8+j4) per phase. Calculate the phase and line currents. Given Quantities • Balanced WYE source –Van= 10010 V • Balanced DELTA load –Z= 8+j4 Phase Currents VAB I AB ZΔ VAB= voltage across Z = Vab= source line voltage VAB 3 Van 30 VAB 173.240 V 173.240 I AB 19.3613.43 8 j4 Phase Currents I AB 19.3613.43 I BC I AB13.43 120 I BC 19.36 106.57 A I CA 19.3613.43 120 I CA 19.36133.43 A Line Currents I a 3 I AB 30 3 (19.36) 13.43 30 I a 33.53 16.57 A I b I a 120 33.53 136.57 A I c I a 120 33.53 103.43 A DELTA TO WYE CONVERSION Z Z 3 THREE PHASE POWER MEASUREMENT FOUR WIRE SYSTEM • Each phase measured separately: IA Phase A A VAN Phase B PA W V IB A VBN Phase C PB W V IC A VCN Neutral (N) PC W V THREE PHASE THREE WIRE SYSTEM The three phase power is the sum of the two wattmeters reading PT PAB PCB IA PAB A VAB = VA - VB Phase A W V Phase B VCB = VC - VB IC A V W Phase C PCB EXAMPLE Determine the total power (P), reactive power (Q), and complex power (S) at the source and at the load Single Phase Equivalent Circuit • Phase ‘a’ equivalent circuit 5-j2 10 j8 Known Quantities • V =Van = 1100 V • ZY = 10+j8 • Zline =5-j2 Line/Phase Currents Van Ia Zline Z Y 1100 Ia 6.81 21.8 16.15521.8 Source & Load Power φ φ Ssource 3V I (2087 j834.6)VA Ps 2087 W, Qs 834.6 Var 2 SLoad 3 I φ Z (1392 j1113)VA PL 1392 W, Q L 1113 Var EXAMPLE A three phase motor can be regarded as a balanced Y-load. A three phase motor draws 5.6 kW when the line voltage is 220 V and the line current is 18.2 A. Determine the power factor of the motor Known Quantities • PLoad =5600 W • VL = 220 V • IL = 18.2 A Power factor • Power factor = cos |S| Q S 3Vφ I φ 3 VL I L 6935.13 VA P P S cos θ P 5600 cos θ 0.8 S 6935.13