In the construction of a DC generator, if a coil covers a span of 180 electrical degrees, then it is called a/an _______coil..

Explanation:

DC Generator Coil Span and Full Pitch Coil

Definition: In the construction of a Direct Current (DC) generator, the term "coil span" refers to the distance between the two sides of a coil in terms of electrical degrees. When a coil in a DC generator covers a span of 180 electrical degrees, it is referred to as a full pitch coil. This means that the coil spans exactly half of the armature's circumference, ensuring that it picks up the maximum possible induced electromotive force (EMF).

Working Principle: The working principle of a DC generator is based on Faraday's law of electromagnetic induction, which states that an electromotive force (EMF) is induced in a conductor when it experiences a change in magnetic flux. In a full pitch coil, the two sides of the coil are positioned at points of maximum magnetic flux change, typically 180 electrical degrees apart. This positioning ensures that the coil experiences the maximum rate of change of magnetic flux, thereby inducing the maximum possible EMF.

Advantages of Full Pitch Coil:

• Maximum Induced EMF: A full pitch coil captures the maximum possible induced EMF because it spans the entire pole pitch, where the magnetic flux change is greatest.
• Symmetrical Construction: Full pitch coils lead to a more symmetrical and balanced construction of the armature winding, which contributes to the smooth operation of the generator.

Disadvantages:

• Increased End Winding Length: Full pitch coils have longer end windings, which can increase the resistance and the copper losses in the armature winding.
• Space Constraints: The longer end windings can also lead to space constraints within the armature slots, making the construction more complex and potentially less efficient in terms of space utilization.

Applications: Full pitch coils are commonly used in DC generators and motors where maximum EMF induction is desired. They are suitable for applications requiring high efficiency and performance, such as in power generation and electric propulsion systems.

Correct Option Analysis:

The correct option is:

Option 1: Full pitch

This option correctly describes a coil in a DC generator that covers a span of 180 electrical degrees. Such a coil is known as a full pitch coil, and it is designed to capture the maximum induced EMF by spanning the entire pole pitch.

Additional Information

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

Option 2: Back pitch

Back pitch refers to the distance, in terms of armature slots, between the two sides of a coil on the back of the armature core. It is not specifically related to the electrical degree span of the coil but rather to the physical positioning of the coil sides in the armature slots. Hence, this option does not correctly describe a coil span of 180 electrical degrees.

Option 3: Average pitch

Average pitch is the average distance between the two sides of a coil in terms of armature slots. It is used to describe the overall winding distribution in the armature but does not specifically relate to a coil span of 180 electrical degrees. Therefore, this option is incorrect in the context of the question.

Option 4: Front pitch

Front pitch is the distance, in terms of armature slots, between the two sides of a coil on the front of the armature core. Similar to back pitch, it refers to the physical positioning of the coil sides and is not related to the electrical degree span of the coil. Thus, this option is not correct for a coil spanning 180 electrical degrees.

Conclusion:

Understanding the concepts of coil span and pitch in DC generators is crucial for correctly identifying the types of coils used in their construction. A full pitch coil, as explained, spans 180 electrical degrees and is designed to capture the maximum induced EMF. This characteristic makes it suitable for applications requiring high efficiency and performance. By evaluating the other options, it becomes clear that terms like back pitch, average pitch, and front pitch refer to different aspects of the coil's physical positioning within the armature slots and do not describe a coil span of 180 electrical degrees.