CHAPTER 8 INTRODUCTION TO THREE PHASE CIRCUIT DMT

CHAPTER 8: INTRODUCTION TO THREE PHASE CIRCUIT DMT 122 CIRCUIT THEORY 2 SEMESTER 2 2018/2019 1

SINGLE PHASE SYSTEM Two wire type Three wire type 2

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. § Use at normal household 3

2 -PHASE SYSTEM § A generator consists of two coils placed perpendicular to each other § The voltage generated by one lags the other by 90. 4

3 -PHASE SYSTEM § A generator consists of three coils placed 120 apart. § Consist of 3 sources § The voltage generated are equal in magnitude but, out of phase by 120. 5

IMPORTANCE OF 3 - PHASE SYSTEM § All electric power is generated and distributed in three phase. § Uniform power transmission (instantaneous power is constant) and less vibration of three phase machines. § Three phase system is more economical than the single phase. 6

BALANCED 3 -PHASE VOLTAGES § Produced with a 3 -phase ac generator. § Generator consist of rotating magnet (rotor) & stationary winding (stator) § 3 separate windings (coils) with terminal a-a’, b-b’ and cc’ placed 120° apart around the stator § When rotor rotates, magnetic field induced a voltage with same magnitude but of phase 120°. Balanced 3 -phase voltages : equal in magnitude & out of phase by 120° 7

BALANCED 3 VOLTAGES § Balanced three phase voltages: § same magnitude (VM ) § 120 phase shift +ve sequence -ve sequence 8

BALANCED 3 CURRENTS § Balanced three phase currents: § same magnitude (IM ) § 120 phase shift 9

POSITIVE PHASE SEQUENCE § POSITIVE SEQUENCE (abc)10

NEGATIVE PHASE SEQUENCE § NEGATIVE SEQUENCE (acb) 11

DETERMINE THE SEQUENCE USING PHASOR DIAGRAM 12

EXAMPLE 1 § EXAMPLE 2 13

3 -PHASE QUANTITIES QUANTITY SYMBOL Phase current I Phase voltage V Line current IL Line voltage VL 14

PHASE VOLTAGES and PHASE CURRENTS § Phase voltage (V ) : measured between the neutral and any line voltage. § Phase current (I ) : the current in each phase of the source or load. 15

PROPERTIES OF PHASE VOLTAGE § 16

PROPERTIES OF PHASE CURRENT § All phase currents have the same magnitude, § Out of phase with each other by 120 17

LINE VOLTAGES and LINE CURRENTS § Line voltage (VL) : measured between any two of the three lines. § Line current (IL) : the current in each line of the source or load. 18

PROPERTIES OF LINE VOLTAGE § 19

PROPERTIES OF LINE CURRENT § All line currents have the same magnitude, § Out of phase with each other by 120 20

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 magnitude and in phase. are equal in 21

SOURCE-LOAD CONNECTION SOURCE LOAD Wye (Y) Delta (∆) CONNECTION 22

SOURCE LOAD Delta (∆) Wye (Y) CONNECTION 23

BALANCED Y-Y CONNECTION § 24

BALANCED Y-Y CONNECTION § Total impedance per phase, ZY 25

BALANCED Y-Y CONNECTION § 26

BALANCED Y-Y CONNECTION § 27

BALANCED Y-Y CONNECTION § 28

EXAMPLE 3 § Calculate : (assume negative sequence) i. The line voltages ii. The line currents 29

EXAMPLE 4 Calculate : (assume positive sequence) i. The line voltages ii. The line currents 30

BALANCED ∆ - ∆ CONNECTION § 31

BALANCED ∆ - ∆ CONNECTION § 32

BALANCED ∆ - ∆ CONNECTION § 33

BALANCED ∆ - ∆ CONNECTION § 34

EXAMPLE 5 A balanced delta connected load having an impedance 20 -j 15 is connected to a delta connected, positive sequence generator having Vab = 330 0 V. Calculate : i. the phase currents ii. the line currents. 35

EXAMPLE 6 § 36