Basic knowledge of motor windings: pole pitch, pitch, winding coefficient
1. Mechanical angle and electrical angle
When the motor windings are distributed in the core slots, they must be embedded and connected according to a certain rule to output symmetrical sinusoidal alternating current or generate a rotating magnetic field. In addition to being related to some other parameters, we also need to use the concept of electrical cost to reflect the law of relative positions between each coil and winding. From mechanics, we know that a circle can be divided into 360°, and this 360° is what we usually call a mechanical angle. In electrical engineering, the angle unit for measuring electromagnetic relations is called electrical angle, which divides each cycle of sinusoidal alternating current into 360° on the horizontal axis, that is, when the conductor space passes through a pair of magnetic poles, the electromagnetic angle changes by 360°. Therefore, the relationship between electrical angle and mechanical angle in the motor is: electrical angle α = pole pair number xP x360°. For example, for a two-pole motor, the number of pole pairs p=1, and the electrical angle is equal to the mechanical angle. For a four-pole motor, p=2, and there are two pairs of poles in one circumference of the motor, and the corresponding electrical angle is 2×360°＝720°. And so on.
2. Pole pitch (τ)
The pole pitch of the winding refers to the distance between each pole on the circumferential surface of the core. It usually refers to the slot spacing between the centers of two adjacent poles of the motor core. The stator core is calculated by the slot spacing of the inner circle air gap surface; the rotor is calculated by the slot spacing of the outer circle air gap surface of the core. Usually, there are two ways to express the pole pitch, one is to express it in length; the other is to express it in the number of slots. It is customary to express it in the number of slots. Generally, the pole pitch is τ=Z1/2p.
3. Pitch (y)
The number of core slots occupied by each coil element side of the motor winding is called the pitch, also known as the span. When the pitch of the coil element is equal to the pole pitch, it is a full-pitch winding, y=τ; when the pitch of the coil element is less than the pole pitch, it is called a short-pitch winding, y＜τ; and when the pitch of the coil element is greater than the pole pitch, it is called a long-pitch winding y＞τ. Since short-pitch windings have many advantages such as shorter ends, less electromagnetic wire material, and higher power factor, short-pitch windings are used without exception in the most commonly used double-layer windings.
