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Department of Electrical Engineering

Faculty Member:____________________ Dated: ________________

Semester:__________________________ Section: ________________

EE-211: Electrical Network Analysis

Lab9: Balanced Three-Phase CircuitName Reg. No Report

Marks / 10

Viva Marks /

5

Total/15

Lab9: Balanced Three-Phase Circuit

Exercise Objective:

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When you have complicated this exercise you will be able to distinguish between line and

phase voltage in wye- and delta-connected AC circuits. Measured parameters in balanced

resistive loads will be used to verify the circuit calculations.

Discussion:

The windings of a three-phase AC power supply (the generation in Figure 6-1) can be

connected in either a wye configuration, or a delta configuration. These names come from

the appearance of the circuit drawings which resemble the letter Y and the Greek letter delta.

The connections for each configuration are shown in Figure 6-3, and each has definite

electrical characteristics. The voltage produced by a single winding is called the phase voltage,

EPHASE (EAN, EBN, ECN), while the voltage between any two windings is the line-to-line, or line-

voltage, ELINE (EAB, EBC, ECA).In a wye-connected system the line voltage is 3 (approximately

1.73) times greater than the phase voltage, as indicated in the following equation:

ELINE= 3 EPHASE

Note: In the EMS System the numbers 1, 2, 3 (fixed-voltage output) and 4, 5, 6 (variable-

voltage output) are used instead of the letters A, B, C for the corresponding line and phase

voltages. The neutral line is designated by N.

Figure 6-3 (a) Three-Phase Wye Configuration (b) Three-Phase Delta Configuration

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Usually, the three line wires (wires connected to points A, B, and C) and the neutral wire of a

three-phase power system are available for connection to the load, which can be set up as

either a wye-connection or a delta-connection. The two types of circuit connections are

illustrated in Figure 6-4. Circuit analysis demonstrates that the voltage between any two line

wires, or lines, in a wye-connected load is 1.73 times greater than the voltage across each

load resistor (phase voltage). Also, the line current in a delta-connected load is 1.73 times

greater than the current in each load resistor (phase current). The phase current in a delta-

connected load is therefore 1.73 times smaller than the line current.

The relationships between line and phase voltages and line and phase currents simplify the

analysis of balanced three-phase circuits. A shorthand way of writing them is,

For WYE circuits: ELINE= 3 EPHASE and ILINE = IPHASE

For DELTA circuits: ELINE = EPHASE and ILINE= 3 IPHASE

The formula for calculating active, reactive, and apparent power in balanced three-phase

circuits is the same as those used for single-phase circuits. Based on the formulas for power in

a single-phase circuit, we can state that the active power dissipated in each phase of either a

wye- or delta- connected load is:

PPHASE = EPHASE x IPHASEx cos()

Where is the angle between the phase voltage and current.

Figure 6-4 (a)Wye-Connected Load (b)Delta-Connected Load

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The total active power PT supplied to the load is therefore:

PT = 3 x EPHASE = 3 EPHASE x IPHASE x cos()

For a resistive load, cos() equals 1, therefore

PT = 3 EPHASE x IPHASE

Equipment Required:

Refer to the equipment utilization chart in appendix C to obtain the list of equipment

required for this exercise.

Procedure:

1. Install the power supply, Data Acquisition Interface and resistive load modules in theEMS workstation.

2. Make sure that the main switch of the power supply is set to the O (OFF) positionand the voltage control knob is turned fully ccw. Ensure the power supply is

connected to a three-phase wall receptacle.

3. Ensure that the DAI LOW POWER INPUT is connected to the main power supply andthe USB port cable from the computer is connected to the DAI.

4. Display the metering application. Select setup configuration file ES16-1.dai.5. Connect E1, E2 and E3 to measure the line-to-neutral and then the line-to-line fixed

voltages of the power supply shown in Figure 6-5.

CAUTION

High voltages are present in this laboratory exercise! Do not make or modify

any banana jack connections with the power on unless otherwise specified!

Note: In this manual EPHASE is used to designate the line-to-neutral voltage, and

ELINE the line-to-line voltage.

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6. Turn on the main power supply and set the 24V AC power switch to the I (ON)position.

7. Record your measurements and then turn off the power. Determine the averagevalue of the phase and line voltages.

E1-N = ___________ V E2-N = ____________ V E3-N = ___________ V

Average EPHASE

= ______________ V

E1-2 = ________ V E2-3 = ________ V E3-1 = _________ V

Average ELINE=

= _____________ V

8. Calculate the ratio of the average line to phase voltage.Figure 6-5 Measurement of Line and Phase Voltages

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9. Is the ratio approximately equal to 1.73 (3)?

10.Connect E1, E2 and E3 to measure the line-to-neutral and line-to-line variablevoltages of the power supply E4-N, E5-N, E6-N and E4-5, E5-6, E6-4.

11.Turn on the power and adjust the voltage control to 100%. Record yourmeasurements and then turn off the power. Determine the average value of the

phase and line voltages.

E4-N = ____________ V E5-N = ____________ V E6-N = ____________ V

Average EPHASE

= _____________________ V

E4-5 = ________ V E5-6 = ________ V E6-4 = _________ V

Average ELINE =

= ______________ V

12.Calculate the ratio of the average line to phase voltage.

13.Is the ratio approximately equal to 1.73 (3)?14.Set up the three-phase, wye-connected, resistive circuit shown in Figure 6-6. Do not

connect the neutral of the resistive load to the neutral of the power supply. Connect

l1, l2, l3, E1, E2 and E3 as shown to measure the currents and voltages.

15.Set the voltmeter select switch to the 4-5 position. Turn on the power and adjustvoltage control for the line-to-line voltage ES (E4-5, E5-6 or E4-6) given in Figure 6-6.

Select setup configuration file ES16-2.dai. Measure the circuit voltages and currents

and then turn off the power.

ER1 = _____________ V ER2 = ____________ V ER3 = _____________ V

Yes No

Yes No

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IR1 = _____________ A IR2 = _____________ A IR3 = _____________ A

16.Compare the individual load voltages and load currents. Are they approximatelyequal, showing that the load is balanced?

ES

(V)

R1()

R2()

R3()

380 1100 1100 1100

17.Calculate the average phase voltage from the measurements in step 15.EPHASE

= ____________ V

18.Is the ratio of ELINE to EPHASEapproximately equal to 3?

Yes No

Figure 6-6 Three-Phase Wye-connected Resistive Load

SEE EXERCISE PROCEDURE

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19.Connect l1 as shown by the dashed line in Figure 6-6 to measure the neutral linecurrent with the power supply neutral connected to the neutral of the wye-

connected load. Select setup configuration file ES16-3.dai. Turn on the power and

record the value of IN with ES adjusted to the same value of ES as in step 15.

IN = _____________ A

20.Is the neutral current equal to zero?

21.Using the results of step 15, calculate the active power consumed in each phase ofthe circuit and the total power consumed by the load.

PR1 = ER1 x IR1= ________________ W

PR2 = ER2 x IR2= ________________ W

PR3 = ER3 x IR3= ________________ W

PT = PR1 + PR2 + PR3 = ____________ W

22.Determine the phase current using the values measured in step 15.IPHASE = ________________ A

Calculate PT using the phase voltage and current, and compare it with step 21. Are

both values approximately the same?

PT = 3 (EPHASE x IPHASE) = _________________ W

Yes No

Yes No

Yes No

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23.Turn off the power and set up the three-phase, delta-connected, resistive circuitshown in Figure 6-7. Connect l1, l2, l3, E1, E2 and E3 as shown to measure the

currents and voltages.

24.Turn on the power and adjust the voltage control for the line-to-line voltage ES (E4-5,E5-6, or E4-6) given in Figure 6-7. Select setup configuration file ES16-4.dai. Measure

the circuit voltages and currents and then turn off the power.

ER1 = _____________ V ER2 = ____________ V ER3 = _____________ V

IR1 = _____________ A IR2 = _____________ A IR3 = _____________ A

25.Compare the individual load voltages and load currents. Are they approximatelyequal, showing that the load is balanced?

ES

(V)

R1()

R2()

R3()

220 1100 1100 1100

Yes No

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26.Calculate the average phase current from the measurements in step 24.

27.Reconnect l1, l2 and l3 as shown in Figure 6-8 to measure the line currents for thedelta-connected load. Ensure that ES is set at the same value used in step 24. Select

setup configuration file ES16-5.dai. Measure and record the line currents and turn off

the power. Determine the average line current.

I1 = ______ A I2 = ______ A ` I3 = ______ A

28.Calculate the ratio of the average line current to the average phase current.

Is it approximately equal to 3?

Figure 6-7 Three-Phase Delta-connected Resistive Load

Yes No

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29.Using the results of step 24, calculate the active power consumed in each phase ofthe circuit and the total power consumed by the load.

PR1 = ER1 x IR1= ________________ W

PR2 = ER2 x IR2= ________________ W

PR3 = ER3 x IR3= ________________ W

PT = PR1 + PR2 + PR3 = ____________ W

30.Determine the phase voltage using the values measured in step 24.EPHASE = __________ V

Calculate PT using the phase voltage and current and compare it with step 29. Are both

values approximately the same?

Figure 6-8. Measuring the Line Currents in the Delta-Connected Resistive Load

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PT = 3 (EPHASE x IPHASE) = _________ W

31.Ensure that the power supply is turned off, the voltage control is fully ccw andremove all leads and cables.

Yes No