External Characteristic of a DC Generator

The external characteristic of a DC generator shows the relationship between the terminal voltage of the generator and the armature current, while keeping the excitation (field current) constant. This characteristic is important as it provides information about the performance of the generator under different load conditions.

Plotting Terminal Voltage vs Armature Current at Constant Excitation

When plotting the external characteristic of a DC generator, the terminal voltage is plotted on the y-axis and the armature current is plotted on the x-axis. The excitation (field current) is kept constant throughout the plot.

Explanation of Option A

Option A states that the external characteristic is plotted between the terminal voltage and armature current at constant excitation. This is the correct answer because the external characteristic is indeed plotted in this manner.

Reason for Choosing Terminal Voltage vs Armature Current

The terminal voltage of a DC generator is the voltage available at the output terminals of the generator, which is the voltage supplied to the external load. This voltage is affected by the armature current, which is the current flowing through the armature winding of the generator.

By plotting the terminal voltage against the armature current, we can observe how the terminal voltage changes as the load current increases or decreases. This allows us to analyze the generator's ability to maintain a stable voltage output under varying load conditions.

Constant Excitation

In the external characteristic plot, the excitation (field current) is kept constant. This means that the magnetic field strength in the generator remains unchanged throughout the plot. By keeping the excitation constant, we can focus on the effect of the armature current on the terminal voltage.

Importance of External Characteristic

The external characteristic plot helps in determining the performance of the DC generator. It provides information about the voltage regulation capability of the generator, which is its ability to maintain a constant terminal voltage under varying load conditions.

The slope of the external characteristic curve indicates the voltage regulation of the generator. A steep slope indicates good voltage regulation, meaning that the terminal voltage remains relatively constant even with changes in load current. On the other hand, a shallow slope indicates poor voltage regulation, where the terminal voltage drops significantly as the load current increases.

Conclusion

In conclusion, the external characteristic of a DC generator is plotted between the terminal voltage and armature current at constant excitation. This plot helps in analyzing the generator's voltage regulation capability and understanding its performance under different load conditions.