HACETTEPE UNIVERSITY ELECTRICAL AND ELECTRONICS ENGINEERING ELE479 ELECTRIC MACHINERY LABORATORY II

EXPERIMENT 1 THREE-PHASE SYSTEMS - POWER MEASUREMENTS

1) THE OBJECT OF THE EXPERIMENT: To analyze a three-phase circuit: Measuring line-to-line voltages, line currents; determination of active, reactive and apparent powers for wye- or delta-connected loads.

2) PRELIMINARY a) Read Chapter 2 and Appendix A( pp. 116-130; 681-700) in Electric Machinery

Fundamentals 4th Ed., Chapman S.J. or Chapter 2 and Appendix A (pp. 57-90; pp. 628-642) in Electric Machinery 6th Ed., Fitzgerald A.E.

b) On Matlab/Simulink, carry out a simulation work for a three-phase, wye-connected source with Vph=100Vrms/phase, 50Hz source voltage, and a wye-connected load of R=30Ω per phase in series with L=140mH per phase (Fig.1); plot voltage and current for phase-A for one cycle of AC supply voltage, and verify the phase angle between voltage and current by your hand calculations; calculate the total active, reactive and apparent powers of the 3-phase system.

3) PROCEDURE

EQUIPMENT Auto-transformer(3-ph); Wattmeter; 3-ph Resistive Load; 3-ph Inductive Load; Voltmeter; Oscilloscope;

Connect the three phase wires to the resistive load by using wye connection.

Make the proper connection of wattmeter to measure the active power of one

phase.

Connect the oscilloscope probes to observe the voltage and current waveforms of

Phase-A.

Set the auto-transformer output phase voltage to 100 Vrms.

Verify the active power measured on the wattmeter by using the monitored phase

voltage and current of the same phase, and also by using the line-to-line voltage and

line current for the wye connected system.

Connect the inductive load in series with the same resistive load and repeat the

calculations above. Also find the reactive and apparent powers for this part. Verify

the phase angle between voltage and current of one phase on the oscilloscope, by

using the resistance and inductance values.

Connect the three phase wires to the inductive load only, with wye connection;

connect the oscilloscope probes to observe the voltage and current waveforms of

one phase and comment about the phase angle between voltage and current.

Repeat all the above procedures for the delta-connected load (Fig.2). Compare the

results obtained with those of the wye-connected load. Comment on the results.

Calculate the turns ratio of the autotransformer by measuring the input voltage and

output voltage rms values under no-load. Also, determine the total power dissipation

of the autotransformer from the difference between total input power and total load

power, for the resistive load condition given above.

Figure 1 - 3-Phase Wye-Wye Connected System

Figure 2 -- 3-Phase Wye-Delta Connected System