Lab_10

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Seyed Nikan Hossein Attar A01230368 ELEX 2105: Circuit Analysis 2 Page 1 of 9 The original document was provided by Mark Lane and Norm Cousins Lab 10: 3-Phase systems, Wye-loads Objective • Verify the voltage magnitude and phase relationships for a 4-wire, 3-phase supply. • Verify the voltage, current and power relationships for balanced and unbalanced wye loads. Introduction The lab is supplied by a 208/120 V, 4-wire system. For safety reasons we do not use these voltages. The 3- phase “box” on the bench: a) ‘Plugs in’ to the 208 V lab system. b) Contains 3 transformers. c) Steps the lab voltages down to 28/16 V. d) Isolates the output voltages from ground. Identify the output terminals on the 3-phase box: Green ground (earth) – connects to the metal chassis and to the 208/120 V system ground through the grounding pin of the power plug. Red Line A – from the low voltage side of the transformer bank. Black Line B – from the low voltage side of the transformer bank. Blue Line C – from the low voltage side of the transformer bank. White Neutral – from the low voltage side of the transformer bank. This terminal is ISOLATED from the 208 V lab system.

Seyed Nikan Hossein Attar A01230368 ELEX 2105: Circuit Analysis 2 Page 2 of 9 The original document was provided by Mark Lane and Norm Cousins Preparation 1. Draw a diagram for a 3-phase, 4-wire , balanced resistive load Y-Y system. Use capital letters for the generator side and small letters for the load side to label the nodes. Put a 1 ohm current sampling resister on line A and a 10 ohm sampling resistor to measure the current in the neutral line. Use 4 channels of the scope to measure the phase voltages on the generator side as well the current in line A (the voltage drop across the 1 ohm sampling resistor). 2. Redraw the diagram for a 3-wire system similar to the previous one. The load wye-point is now disconnected — name this node ‘y’.

Seyed Nikan Hossein Attar A01230368 ELEX 2105: Circuit Analysis 2 Page 3 of 9 The original document was provided by Mark Lane and Norm Cousins 3. Prepare the following table for the supply voltage. VAN VBN VCN VAB VCA θVAN - θVBN θVAN - θVCN θVBN - θVCN θVAB - θVCA θVAB - θVBC 16 16 16 16 28.4 27.3 120 -120 120

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Seyed Nikan Hossein Attar A01230368 ELEX 2105: Circuit Analysis 2 Page 4 of 9 The original document was provided by Mark Lane and Norm Cousins 4. Prepare the following table for the measurements Balanced 4-wire Balanced 3-wire Unbalanced 4-wire Unbalanced 3-wire Van/ay 16 15.8 15.7 17.4 Vbn/by 16 16.3 15.9 10.5 Vcn/cy 16 16.1 15.8 21.2 Ia 0.02875 0.02821 0.02804 0.03107 Ib 0.02875 0.02875 0.1325 0.0875 Ic 0.02857 0.02875 0.07182 0.09636 Vab 28.4 28.2 28.1 27.5 IAa 0.02875 0.02821 0.02804 0.03107 In 0 n/a 0.0769 n/a θVab - θIa 30 28.7 30 10.3 Vyn N/A 0.151 N/A 6.14 Pt (1st method) 1.38289 1.37729 3.68164 3.5023 Pt (2nd method) 1.22475 1.20879 Pre-lab requirements: • Two schematics showing all the probes. • One table for the measured values at the source side • One table to record the measurements of the load side. • No prediction or calculation is needed.

Seyed Nikan Hossein Attar A01230368 ELEX 2105: Circuit Analysis 2 Page 5 of 9 The original document was provided by Mark Lane and Norm Cousins Procedure Part A: 3-Phase Supply Voltages 5. Measure the magnitudes of V AN , V BN , V CN , V AB , V BC and V CA . Verify that the magnitudes are correct. 6. View the following waveform pairs on the scope and measure their relative phase angles: • V AN and V BN ; • V AN and V CN; • V BN and V CN . While viewing V AN and V BN on the scope, use the scope’s MATH feature to also display V AB . Note that math functions are between Channels 1&2 and between 3&4, but only those two pairs. Measure the relative phase angles between V AB and the other two waveforms. 7. Based on your measurements, draw a phasor diagram that includes V AN , V BN , V CN , and V AB . The phasor diagram requires arrowheads, directions and magnitudes, and is to be drawn to scale. Part B: Balanced, 4-Wire, Resistive Wye Load 8. Connect the resistive loads provided in the lab to form the largest possible wye load, then make the following 9 measurements: • the phase voltages at the load (V an , V bn , V cn ); • the 3 phase currents at the load • line current, I Aa ; • line voltage, V ab ; • neutral current, I n .

Seyed Nikan Hossein Attar A01230368 ELEX 2105: Circuit Analysis 2 Page 6 of 9 The original document was provided by Mark Lane and Norm Cousins Measure the phase displacement between V AB and I Aa (use a 1 ohm current sampling resistor). Based on your measurements, determine the total power in 2 different ways: i. Calculate the power for each phase of the load, then sum the results; ii. Calculate P = √3 * V Line * I Line * cos θ , [where θ = (  V ab –  I a – 30  )]. Part C: Balanced, 3-Wire, Resistive Wye Load 9. With the (same) largest possible wye load, remove the neutral connection to the load. The load wye-point is now disconnected — name this node ‘y’. Measure: • the phase voltages at the load (V ay , V by , V cy ); • the 3 phase currents at the load • line voltage, V ab ; • line current, I Aa ; • the phase displacement between V ab and I Aa ; • the voltage difference between the load wye-point and the neutral, V yN .

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Seyed Nikan Hossein Attar A01230368 ELEX 2105: Circuit Analysis 2 Page 7 of 9 The original document was provided by Mark Lane and Norm Cousins Based on your measurements, determine the total power in 2 different ways (as before). Compare with the results obtained for the 4-wire load. Part D: Unbalanced, 3-Wire, Resistive Wye Load 10. Change the load to make it unbalanced: • keep the phase A load unchanged; • make the phase B load as small as possible; • make the phase C load bigger than phase B but smaller than phase A. The load wye-point remains disconnected. Repeat each and every measurement which you had made in the previous step.

Seyed Nikan Hossein Attar A01230368 ELEX 2105: Circuit Analysis 2 Page 8 of 9 The original document was provided by Mark Lane and Norm Cousins Based on your measurements, determine the total power (there is only 1 correct way to do this). Part E: Unbalanced, 4-Wire, Resistive Wye Load 11. Keep the same (unbalanced) load, but restore the neutral connection to the wye-point. Repeat each and every measurement which you had made for the balanced, 4-wire load. Based on your measurements, determine the total power in 2 different ways. Compare the 2 results. Which method gives the correct result?