Data

IF VRH RRH Ea

40 15.56 389 23.7280 23.99 299.875 42.3120 32.98 274.833 65160 39.5 246.875 85.2200 45.1 225.5 103240 47.5 197.92 116280 46.3 165.37 131320 42.5 132.812 140.9360 37 102.78 147.5400 30 75 152.4

-Measured open circuit armature voltage: 7.06Vdc

-varying field rheostat decrease armature voltage.

Circuit Diagram

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.

Conclusion

To 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.