To avoid pulsations and oscillations of the flux in the air gap, the number of slots per pole should be a whole number plus half. When this is not possible or advisable for other reasons, the number of slots per pole arc should an integer. Number of teeth/pole shoe = 5 and flux passes through 5 teeth. . Slot contains even number (may be 2,4,6 etc.) of coil- sides in two layers. Double-layer winding is more common above about 5kW machines Two coil –sides per slot 4-coil-sides per slot Coil- sides Coil- sides Coil - sides Overhang.

The number of slots per pole per phase determines how the winding layout is arranged. It is also disclosing information about the winding factor and its harmonics.

If the number of slots/pole/phase is an integer, the winding is called integer-slot winding.

If the number of slots/pole/phase is fractional and superior to 1, the winding is called fractional-slot winding.

If the number of slots/pole/phase is fractional and inferior to 1, the winding is called concentrated winding.

Windings with the same number of slots/pole/phase $q$ have the same winding factor. Their winding layouts consist of the same basic sequence repeated by the number of winding symmetries (or machine periodicity).
Example:
10-pole 12-slot single-layer 3-phase winding: $q=frac{12}{10cdot 3}=frac{2}{5}$, fundamental winding factor: 0.966, one winding symmetry.
20-pole 24-slot single-layer 3-phase winding: $q=frac{24}{20cdot 3}=frac{2}{5}$, fundamental winding factor: 0.966, two winding symmetries.

The number of slots/pole/phase is also an indicator about what winding factor and winding-factor harmnoics one can expect.
Example 1:
The harmonic spectrum of the winding factor of 4-pole 3-phase integer-slot windings in Fig. 1 shows that an increasing number of slots/pole/phase (from $q=1$ for the 12-slot winding to $q=5$ for the 60-slot winding) leads to a steady decrease of the fundamental winding factor. However, since the coils are distributed over several slots per pole per phase, the back-EMF gets more sinusoidal. This fact is reflected in significantly reduced winding factor harmonics of order three and higher, cf. Fig. 1.

Fig. 1 Winding factor harmonics for 4-pole 3-phase integer-slot windings with different number of slots/pole/phase.

Example 2:
For concentrated windings, the fundamental winding factor increases and decreases as a function of the number of slots/pole/phase as shown in Fig. 2. The highest fundamental winding factors are found when the number of slots is closest to the number of poles, ie. $q0007pprox 1/3$.

For A 5kw Dc Motor The Number Of Slots Per Pole Should Be

Fig. 2 Fundamental winding factor for concentrated windings as a function of the number of slots/pole/phase [1].

References:
[1] Florence Meier, Permanent-Magnet Synchronous Machines with Non-Overlapping Concentrated Windings for Low-Speed Direct-Drive Applications, Phd Thesis, Royal Institute of Technology (KTH), July 2008

Read about another glossary term

Number of armature slots in DC machine

In order to decide what number of slots (more or less) is to be used, the following merits and demerits are considered.

1. As the number of slots increases, cost of punching the slot increases, number of coils increases and hence the cost of the machine increases.

2. As the number of slots increases, slot pitch λ_s = (slot width b_s tooth width b_t) = πD/ number of slots S

decreases and hence the tooth width reduces. This makes the tooth mechanically weak, increases the flux density in the tooth and the core loss in the tooth. Therefore efficiency of the machine decreases.

If the slots are less in number, then the cost of punching & number of coils decreases, slot pitch increases, tooth becomes mechanically strong and efficiency increases, quantity of insulation in the slot increases, heat dissipation reduces, temperature increases and hence the efficiency decreases.

It is clear that not much advantage is gained by the use of either too a less or more number of slots.

As a preliminary value, the number of slots can be selected by considering the slot pitch. The slot pitch can assumed to be between (2.5 and 3.5) cm. (This range is applicable to only to medium capacity machines and it can be more or less for other capacity machines).

For A 5kw Dc Motor The Number Of Slots Per Pole Should Be Paid

Grand casino baden poker. The selection of the number of slots must also be based on the type of winding used, quality of commutation, flux pulsation etc.

When the number of slot per pole is a whole number, the number slots embraced by each pole will be the same for all positions of armature. However, the number teeth per pole will not be same.

This causes a variation in reluctance of the air gap and the flux in the air gap will pulsate. Pulsations of the flux in the air gap produce iron losses in the pole shoe and give rise to magnetic noises. On the other hand, when the slots per pole is equal to a whole number plus half the reluctance of the flux path per pole pair remains constant for all positions of the armature, and there will be no pulsations or oscillations of the flux in the air gap.

Number of teeth/pole shoe = 5 and flux passes through 5 teeth.

For A 5kw Dc Motor The Number Of Slots Per Pole Should Bet

The reluctance of the air gap is inversely proportional to the area corresponding to 5 teeth.