Differences Between Electrical Degree And Mechanical Degree

Many people get confused about the electrical degree and mechanical degree. Well, to get clear and give an idea about this we have provided the following post.

We consider an alternator with two poles once and four poles once to clear the understand about electrical degree and mechanical degree. An alternator consists of conductors on stator and poles on the rotor. But for the understanding purpose, we consider conductors are rotating and poles are stationary. Because of relative motion between the conductors and poles emf is induced inside the conductor.

Two pole alternator:

Consider a two-pole alternator with a conductor as shown in following the figure.

Position 1: At this point velocity vector V is parallel to magnetic flux lines of poles(indicated by dotted line). So at this position conductors do not cut the flux lines, there will not be the change in flux so emf induced inside the conductor is zero.

Position 2: Now conductor rotates to position 2.Velocity vector V is the perpendicular to magnetic flux lines of poles. So at this position maximum amount of flux is cut by conductors, there will be the maximum amount of change in flux so emf induced is maximum at this point.

Position 3: Now conductor rotates to position 3. At this point velocity vector V is the parallel to magnetic flux lines of poles. So at this position conductors do not cut the flux lines, there will not be the change in flux so emf induced inside the conductor is zero.

Position 4: Now conductor rotates to position 4.Velocity vector V is the perpendicular to magnetic flux lines of poles. So at this position maximum amount of flux is cut by conductors, there will be the maximum amount of change in flux so emf induced is maximum at this point.

So for one complete rotation of the conductor i.e, 360 degrees there will be two maximum positions of emf this is indicated in the following figure.

Induced emf inside the alternator is sinusoidal in nature. Two maximum peaks are 360 degrees. The conductor rotation angle is the mechanical degree and emf wave cycle degree for one complete rotation of conductor gives an electrical degree.

Here mechanical degree is equal to the electrical degree which is 360 degrees. Since for one complete rotation of conductor one complete emf cycle is produced.

Four pole alternator:

Consider a four pole alternator with a conductor as shown in following the figure.

Position 1: t this point velocity vector V is parallel to magnetic flux lines of poles(indicated by dotted line). So at this position conductors do not cut the flux lines, there will not be the change in flux so emf induced inside the conductor is zero.

Position 2: Now conductor rotates to position 2.Velocity vector V is the perpendicular to magnetic flux lines of poles. So at this position maximum amount of flux is cut by conductors, there will be the maximum amount of change in flux so emf induced is maximum at this point.

Position 3: Now conductor rotates to position 3. At this point velocity vector V is the parallel to magnetic flux lines of poles. So at this position conductors do not cut the flux lines, there will not be the change in flux so emf induced inside the conductor is zero.

Position 4: Now conductor rotates to position 4.Velocity vector V is the perpendicular to magnetic flux lines of poles. So at this position maximum amount of flux is cut by conductors, there will be the maximum amount of change in flux so emf induced is maximum at this point.

Position 5: Now conductor rotates to position 5. At this point velocity vector V is the parallel to magnetic flux lines of poles. So at this position conductors do not cut the flux lines, there will not be the change in flux so emf induced inside the conductor is zero.

Position 6: Now conductor rotates to position 6.Velocity vector V is perpendicular to magnetic flux lines of poles. So at this position maximum amount of flux is cut by conductors, there will be the maximum amount of change in flux so emf induced is maximum at this point.

Position 7: Now conductor rotates to position 7. At this point velocity vector V is the parallel to magnetic flux lines of poles. So at this position conductors do not cut the flux lines, there will not be the change in flux so emf induced inside the conductor is zero.

Position 8: Now conductor rotates to the position 8.Velocity vector V is perpendicular to magnetic flux lines of poles. So at this position maximum amount of flux is cut by conductors, there will be the maximum amount of change in flux so emf induced is maximum at this point.

So for one complete rotation of the conductor i.e, 360 degrees there will be four maximum positions of emf this is indicated in the following figure.

Induced emf inside the alternator is sinusoidal in nature. Four maximum peaks are 720 degrees. The conductor rotation angle is mechanical degree and emf wave cycle degree for one complete rotation of conductor gives an electrical degree.

Here mechanical degree is 360 degrees and an electrical degree is 720 degrees.  Since for one complete rotation of the conductor, two complete emf cycles are produced.

This says that an electrical degree depends on number poles inside the alternator. Now we can obtain the relation between a mechanical degree and an electrical degree as

360° mechanical = 360° ✕ P/2 electrical

P = number of poles

1° mechanical = (P/2)° electrical.

In this post, we have discussed difference between the mechanical degree and electrical degree.