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THREE PHASE CIRCUITSA.B.C.PREPARATION1.Three Phase Voltages and Systems2.The Determination of Phase Sequence3.Blondel's Theorem and Its Consequences4.ReferencesEXPERIMENT1.Equipment List2.Three Phase Power Supply3.Balanced Three Phase Resistive Loads4.Unbalanced Three Phase Resistive Loads5.The Three Phase TransformerREPORT1.Three Phase Power Supply2.Balanced Three Phase Loads3.Unbalanced Three Phase Loads4.The Three Phase TransformerThree Phase Circuits - 1

1.Three Phase Voltages and SystemsThree Phase Circuits - 2

Three Phase Circuits - 3

Three Phase Circuits - 4

Three Phase Circuits - 5

2.The Determination of Phase SequenceThree Phase Circuits - 6

Three Phase Circuits - 7

3Blondel’s Theorem and Its ConsequencesThree Phase Circuits - 8

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4Chapman, Stephen J., 2002. Electric Machinery and Power SystemFundamentals. McGraw HillThree Phase Circuits - 10

B.EXPERIMENT - THREE PHASE CIRCUITS1.Equipment Lista. The standard instrument rack found at each station.b. Various current shunts and probes.c. One single-phase wattmeter.d. One three-phase transformer.e. One Phase Sequence Indicator (PSI).f. One rheostat module with two 50-Ω rheostats rated at 4.5 Amp each.g. Various power cords.2.Three Phase Power Supplya. A schematic of the Phase Sequence Indicator (PSI) is provided on the next page.Plug this device into the Three Phase (3φ) wall power source using the 3-PhaseCord Set and determine the phase sequence (ABC or CBA) using the PSI. Besure the switch is in the NORMAL position. Also, observe the Phase A andPhase B waveforms on the oscilloscope using two 10X Probes or the A/100 andB/100 test points with coaxial cables. Determine their phase relationship and thephase angle between them using the scope. Copy this display. Now repeat theabove step for Phase A and Phase C and record the display. Next reverse thephase sequence by flipping the switch to REVERSE and observe the lamppattern. Be sure and return the switch to the NORMAL position for the rest of theexperiment. Finally, observe the voltage waveform for the Star Point (STAR) onthe Phase Sequence Indicator on the scope and copy this display.b. Being fully aware of the potential for an electric shock, and therefore careful toshut off the 3-phase breaker each time the DMM connections are moved,accurately measure the rms values for the three line-to-line voltages and thethree line-to-neutral voltages at your station using three DMMs.c. The "green" neutral wire on the 3-phase supply provides a return to ground. It iswell and thoroughly grounded and will remain at Mother Earth potential as longas there is no IR voltage drop, i.e, as long as the neutral return current is zero.This is the case for perfectly balanced three phase voltage sources and perfectlyThree Phase Circuits - 11

Input Phase CBACAThree Phase Circuits - 12Input Phase ABCReverseACNormalBB