Approximate value of armature winding resistance for a 5 kW DC machine is:

Explanation:

Armature Winding Resistance in DC Machines

Definition: The armature winding resistance in a DC machine refers to the resistance offered by the winding of the armature, which is the rotating part of the machine. This resistance is a crucial parameter as it affects the performance and efficiency of the DC machine. For a typical 5 kW DC machine, this resistance is usually quite low.

Calculation and Approximate Value: The armature winding resistance can be estimated based on the power rating and the design of the machine. For a 5 kW DC machine, the armature winding resistance is typically in the range of a few ohms. Given the provided options, the correct approximate value is 0.15 ohms. This low resistance is essential to minimize power losses and ensure efficient operation of the machine.

Importance of Low Armature Winding Resistance: A low armature winding resistance is critical for the following reasons:

• Minimizes I²R losses: Lower resistance reduces the power losses due to the current flowing through the armature windings.
• Improves efficiency: Lower resistance contributes to higher overall efficiency of the DC machine.
• Reduces voltage drop: Lower resistance helps in reducing the voltage drop across the armature, ensuring better performance.

Correct Option Analysis:

The correct option is:

Option 1: 0.15 ohms

This option correctly represents the approximate value of the armature winding resistance for a 5 kW DC machine. The value of 0.15 ohms aligns with the typical resistance expected for such machines, ensuring efficient operation with minimal losses.

Important Information

To further understand the analysis, let’s evaluate the other options:

Option 2: 15 ohms

This value is significantly higher than the typical resistance for a 5 kW DC machine. Such a high resistance would result in substantial power losses and inefficiency. It is not practical for the operation of a 5 kW DC machine.

Option 3: 100 ohms

A resistance of 100 ohms is far too high for the armature winding of a 5 kW DC machine. This would lead to excessive I²R losses and a considerable voltage drop, severely impacting the machine’s performance and efficiency.

Option 4: 1 kilo ohms

This option is even more unrealistic. A resistance of 1 kilo ohms in the armature winding of a 5 kW DC machine would make it virtually inoperative due to the enormous power losses and voltage drop. Such a high resistance is not feasible for practical DC machine designs.

Conclusion:

Understanding the significance of the armature winding resistance in DC machines is crucial for their design and operation. For a 5 kW DC machine, the approximate value of the armature winding resistance is around 0.15 ohms, ensuring efficient performance with minimal power losses. Higher resistance values, as given in the other options, would lead to impractical and inefficient operation, highlighting the importance of maintaining low resistance in the armature winding for optimal machine performance.