Post on 13-Dec-2015
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-Measured open circuit armature voltage: 7.06Vdc-varying field rheostat decrease armature voltage.
Figure 1 Circuit diagram for self-excited shunt generator
Figure 2 Circuit diagram for synchronous motor
Figure 3 proper connection for DC self-exciting shunt generator connected to a synchronous motor
Figure 4 displayed maximum shunt current resulting in maximum armature voltage
Figure 5 running the synchronous motor connected to ammeters while generator is connected to ammeter and voltmeter
Data Analysis:After properly connecting the wires based on the figure 28-1 and 28-2, to measure the voltage at rheostat, we set the shunt current at maximum value of 400mA in order to have maximum armature voltage of 152.4V. To observe the effect of shunt field current, we decreased the shunt field current by increments of 40mA; doing so affect the voltage across the rheostat. When the field current reaches 320mA, the rheostat voltage begins to drop while other rheostat resistance and armature voltage are unaffected by the voltage drop in rheostat. Again, prolonged running synchronous motor with load (generator) produces observable heat in both motors so we had to shut it down and let it cool. ConclusionTo sum up the results, decreasing the shunt field current increases the rheostat resistance which means that shunt field current (If) is inversely proportional to rheostat resistance (RRH.) Armature voltage increases as rheostat resistance decreases means that armature voltage is also inversely proportional to rheostat resistance making armature voltage directly proportional to shunt field current. As for voltage across the rheostat (VRH), shunt field current is inversely proportional to voltage across the rheostat, VRH is also directly proportional to RRH and, VRH is directly proportional to armature voltage (Ea ). But, the conclusion on VRH only holds true when If is less than 320mA. This means that at that value of field current, the current flows in the wrong direction which reduces the residual magnetism which means that voltage build-up cannot occur.