SYNCHRONOUS MACHINES LABORATORYSTARTING, OPERATING AND SHUTDOWN PROCEDURESMarch 12, 2009Demonstration Step 1 - DC Motor Driving AC GeneratorDC Motor Start–up ProcedureDC Motor Shutdown ProcedureDemonstration Step 2 - AC Machine Equivalent Reactance (X)1. Short secondary of current transformer to protect current meter from startup surge. Turn on the AC supply, and raise the voltage to 175V (line-to-line). With zero field current, the AC machine will be a poor induction motor. With the DC machine providing virtually no load, the AC machine will rotate, but its speed may be far below synchronous speed. Un-short the current transformer3. Take readings per Step 2 of the laboratory procedure (i.e. phase voltage, line current, phase power)Demonstration Step 3 - AC Motor Driving DC Generator with Resistive LoadAC Motor Start–up ProcedureShutdown ProcedureSynchronous MachinesA. PreparationB. DemonstrationC. ReportSynchronous Machines - 1Synchronous Machines - 2A.Synchronous Machines - 3[F][G][H]Synchronous Machines - 4[I][J][K]Synchronous Machines - 5Synchronous Machines - 6B. DEMONSTRATION In this exercise we will take data sufficient to plot several Vee-curves for a synchronous motor. We will also take data that will allow inference of the machine reactance and the approximate relation of machine induced voltage to field current. From this latter information, you are to calculate and plot theoretical Vee-curves for the synchronous motor and compare them with the experimental ones.1. For Ifield = 0.0 (0.5) 3.5 A in the synchronous machine, rotate it with a DC motor and measure the open circuit output voltage (E) of the synchronous machine at its synchronous speed (1200 rpm). You may also wish to vary the excitation of the DC machine to see its effect on rotor speed. Be sure to conclude with a measurement of open circuit voltage with Ifield slowly lowered to 0.0 A.2. With Ifield = 0.0 Amp and the field poles demagnetized, apply 175 V (line-line, 3-phase, 60 Hz), to the AC machine and measure and record line current, phase voltage, and phase power. This allows calculation of the machine’s equivalent reactance.3. Connect the DC machine as a separately excited DC generator driving a load of 6 ohms. Set the field current of the AC machine initially to 0.5A. Start the AC machine by bringing the supply voltage up to 208 V (line-line). Quickly increase the field current so that it runs as a synchronous motor and adjust the field current to approximately 1.5 Amps. Next, insert a DC generator field current (close switch) and vary the field current as needed to change the DC generator voltage and load power and, therefore, the AC machine load to obtain a phase power PA = 200 W. Be sure the phase voltage VA is 120V. Now vary the AC machine field current Ifield 0.0 (0.5) 3.5A to obtain a curve of IA versus Ifield for PA = 200 W. Adjust the DC machine field current as required to maintain PA = 200 W. Repeat for PA = 450 W and 700 W. Note that at each power setting, VA should be reset to 120 V at an Ifield setting yielding near minimum IA. For each PA and Ifield setting, record input power PA, line current IA, and phase voltage VA, and field currentIfield. This data allows plotting experimental Vee-curves (IA versus Ifield at constant PA) for the motor. Also, near each minimum value of IA, record DC generator voltage VDC and load current IDC. This data allows calculation of the efficiency of this AC to DC power converter system.Synchronous Machines - 7C. REPORT SPECIAL INSTRUCTION: For each step below, include tabular presentations of the raw experimental data and the reduced or calculated data as required. 1. Using the data obtained in B.1, make a plot of the E values versus Ifield and obtain a smooth best fit curve for these data points. Comment on these results. (Note that E = EA.)2. Using the data obtained in B.2, calculate X. Show your calculation in detail. Discuss the effectof any uncertainty in a on the calculated value of X.3. (a) Using the data obtained in B.3, plot on the same chart the experimental Vee-curves showing armature current (I) versus field current (If) for each of the input power settings. (Notethat I = IA = IX and If = Ifield.) (b) Examine each of these Vee-curves and their corresponding data and determine for each power P the minimum value of armature current (I) and the corresponding field current (Ifm) for each Vee-curve. Make a table showing P, I, and Ifm. (Note that P = PA = PX and V = VA.)(c) Determine the experimental afm = E/V for each value of Ifm using the measured phase voltage (V) and E from the E versus Ifield best fit curve obtained in Step 1 above.(d) Calculate normalized phase power (p) for each P using Equation [F], i.e., p = P/[V2/X]. Make a table showing afm, V, P, and p. (e) Plot the experimental afm values as a function of normalized phase power (p) to the synchronous motor for each of the power settings. (f) Finally, calculate the theoretical amin data points computed using Equation [K] and plot on the chart from Part (e) above. Comment cogently on the comparison of afm and amin.4. (a) For each value of normalized power p, calculate and plot on the same chart the theoretical Vee-curves for this motor showing i versus a. To do this, first choose a value for Ifield, second, obtain E from the curve fit obtained in Step 1 above, third, calculate a as E/V, and fourth, calculate i from the Equation [H] relating i to a and p. Repeat this set of calculations for a sequence of Ifield values for each value of normalized power p. Finally, plot the calculated theoretical data and connect these theoretical (i, a) data points with a smooth curve. (b) For each value of normalized power p, create experimental Vee-curve data (i versus ). Note that i is given by the first definition in Equation [G].Synchronous Machines - 8(c) Finally, overlay the experimental (i, a) points on the corresponding theoretical graphs, but do not connect these points, so that the theory and experiment can be compared.(d) Comment on the correspondence of the experimental (i, a) points to the theoretical Vee- curves. Give possible reasons for the differences between the two.5 (a) Assuming the three phase synchronous machine presents a balanced load to the three phase power supply, calculate the total three phase power drawn by the synchronous machine for each power setting P when operating at unity power factor
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