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EXPERIMENT NO. 6
DETERMINATION OF PHASE AND LINE QUANTITIES IN THREE
PHASE STAR AND DELTA CONNECTED LOADS
AIM: To determine phase and line quantities in three phase star and delta connected
loads.
APPARATUS REQUIRED:
Sl. NO. NAME OF EQUIPMENT RANGE^ QUANTITY
1 Fuse board with TPST 15A/250V 1 No. 2 3 ϕ Auto-transformer 0 - 400V 1 No.
3 A.C Voltmeter 0 - 400V 2 No.
4 A.C Ammeter 0 - 10A 2 No.
- Lamp Load 1 No.
THEORY:
Line Voltage: Potential difference between any two phases is the line voltage of three phase
supply.
For a balanced system, VRY=VYB=VBR=VL=line voltage
Phase Voltage: Potential difference between two ends of any one phase is phase voltage of three
phase supply. In star connection, it is the voltage between any one phase(R-phase or Y-phase or
B-phase) and the neutral (VRN, VYN, VBN).
Line Current: Current flowing in the supply line (IR, IY, IB) are line currents,
For a balanced system, IR=IY=IB=IL=Line currents
Phase Current: Current flowing in each of the phases of the load or supply (IRR’, IYY’, IBB’) are
line currents.
Star Connection: Similar ends of three impedances Zrr’, Zyy’ and Zbb’ are connected together form
common point r’y’b’ called neutral as shown in Figure 6.1.
Fig 6. 1
IR, IY, IB are called supply line currents(line currents) Irr’(Irn), Iyy’(Iyn), Ibb’(Ibn) are called phase
currents.
Delta Connection: Two dissimilar ends of three impedances Zrr’, Zyy’ and Zbb’ are connected in
series to form delta connection as shown in Figure 6.2.
Fig.6.
Note: rr’:R – phase; yy’:Y-phase; bb’: B-phase; N: neutral
Similar end like r’, y’ and b’ of Resistive load are connected together to form common junction
(node or point) called neutral point, N(r’y’b’). open ends like r,y,b of Resistive load are connected
to the supply.
A) STAR CONNECTION:-
CIRCUIT DIAGRAM
Fig 6. Fig.6.
PROCEDURE:
- Make the connections as per the circuit diagram shown in Fig.6.3.
- With the auto-transformer in minimum position, switch ON the supply.
- Vary the auto-transformer such that voltmeter VL = 150V.
- Note down the corresponding readings of ammeters and voltmeters.
PROCEDURE:
- Make the connections as per the circuit diagram shown in Fig.6.4.
- With the auto-transformer in minimum position, switch ON the supply.
- Vary the auto-transformer such that voltmeter VL = 150V.
- Note down the corresponding readings of ammeters and voltmeters.
- For delta connection, verify 3
L PH
I
(^) I and VL=VPH.
- Repeat the same procedure for different voltages of VL=200V, VL=250V.
- Bring back the auto-transformer to minimum position, switch OFF the supply. Remove all
connections.
TABULAR COLUMN
SL. NO VL (V) VPH (V) IPH (A) IL (A) (^) IPH=IL/ √ 3
CALCULATION:
VL = VPh= ………………..volts 3
I I
L (^) PH = …………….. Amp
RESULT:
VIVA QUESTIONS
What is the difference between star and delta?
What are the types of 3 phase connections?
Explain line and phase voltage.
What is the relation between line and phase parameters in star connections?
What is the relation between line and phase parameters in delta connections?
What are the Advantages of 3 phase system?
Define phase, line & neutral?
Define phase current and line current?
Define balanced and unbalanced load?
