In case of four pole, lap wound machine if the air gap under each pole is the same, then what will be the result?

Explanation:

Four Pole Lap Wound Machine with Equal Air Gap Under Each Pole

Definition: A lap wound machine refers to the type of winding configuration in electrical machines where each coil's end is connected to the adjacent commutator segment, resulting in multiple parallel paths. In a four-pole machine, there are four magnetic poles, and the air gap under each pole is typically kept uniform to ensure consistent magnetic flux distribution.

Working Principle: In a lap wound machine, the armature winding is divided into as many parallel paths as the number of poles in the machine. For a four-pole machine, there will be four parallel paths. When the air gap under each pole is uniform, the magnetic flux density across the armature is more evenly distributed. This affects the current and voltage in the winding paths.

Analysis of the Correct Option:

Correct Option: Option 3: Current in each path will not be the same

In a lap wound machine with a uniform air gap under each pole, the magnetic flux distribution should ideally be symmetrical. However, in practical scenarios, even with an equal air gap, other factors such as slight manufacturing imperfections, uneven saturation of the magnetic core, or minor misalignments can cause variations in the flux linkage across different parts of the armature. Since the current in each path of a lap wound machine depends on the induced electromotive force (EMF) in the respective coils, these variations in flux linkage lead to unequal induced EMFs in the parallel paths. Consequently, the currents in the parallel paths will also differ slightly.

For example, if one path experiences a slightly higher flux density due to unavoidable non-uniformities, the induced EMF in that path will be higher, leading to a higher current in that path compared to the others. This imbalance in current distribution can cause uneven heating and may affect the machine's overall efficiency and performance. Therefore, even with an equal air gap under each pole, the current in each path of a four-pole lap wound machine will not be the same.

Important Information:

To further understand the implications of this condition, let us evaluate the other options:

Option 1: There will be reduced eddy currents

This option is incorrect. Eddy currents are induced circulating currents in the core material of the machine caused by changing magnetic fields. The uniformity of the air gap under each pole does not directly influence the eddy currents. Instead, eddy currents depend on factors such as the rate of change of magnetic flux, core material properties, and lamination thickness. Therefore, maintaining an equal air gap under each pole will not necessarily reduce eddy currents.

Option 2: There will be reduced hysteresis loss

This option is also incorrect. Hysteresis loss occurs in the magnetic core material due to the repeated magnetization and demagnetization cycles as the machine operates. Hysteresis loss depends on the properties of the core material, such as its hysteresis loop area, and the frequency of operation. While a uniform air gap can help ensure consistent magnetic flux distribution, it does not directly reduce hysteresis loss, which is determined by the material and operating conditions rather than the air gap uniformity.

Option 4: It will result in higher terminal voltage

This option is incorrect. The terminal voltage of a machine depends on the total induced EMF in the armature windings and the voltage drop across the internal resistances and brushes. While a uniform air gap can contribute to a more consistent flux distribution, it does not inherently result in a higher terminal voltage. The terminal voltage is primarily influenced by the machine design, operating speed, and load conditions.

Option 5: Not provided in the question

Since there is no information or specific context provided for Option 5, it is not considered relevant to the analysis. The correct answer remains Option 3.

Conclusion:

In a four-pole lap wound machine, even if the air gap under each pole is uniform, the practical imperfections and variations in flux linkage can lead to unequal induced EMFs in the parallel paths. This results in unequal currents in the paths, making Option 3 the correct answer. Understanding this phenomenon is crucial for the design and analysis of electrical machines to ensure their efficient and reliable operation. The other options are either unrelated to the air gap uniformity or are not directly impacted by it, as explained above.