Basic knowledge of motor windings: distance, pitch, winding coefficient

Basic knowledge of motor windings: distance, pitch, winding coefficient
Basic parameters of motor winding

1. Mechanical angle and electrical angle

When the motor winding is distributed in the iron core slot, it must be embedded and connected according to certain rules in order to output symmetrical sinusoidal AC power or generate a rotating magnetic field. In addition to being related to other parameters, when reflecting the laws of relative positions between coils and windings, we also need to use the concept of electrical efficiency. From mechanics, it is known that a circle can be divided into 360 degrees, which is commonly referred to as the mechanical angle. In electrical engineering, the angle unit used to measure electromagnetic relationships is called electrical angle. It divides each cycle of a sinusoidal alternating current into 360 degrees on the horizontal axis, which means that when a conductor passes through a pair of magnets, the corresponding electrical angle changes by 360 degrees in the electromagnetic field. Therefore, the relationship between electrical angle and mechanical angle in a motor is: electrical angle α=logarithm xPx360 °. For example, for a two motor, the logarithm p=1, and the electrical angle is equal to the mechanical angle. For a four motor, p=2, At this point, the motor has two pairs of magnets on one circumference, corresponding to an electrical angle of 2 × 360 °=720 °. and so on.

2. Distance (τ)

The distance between windings refers to the distance that each magnet occupies on the circumferential surface of the iron core. Generally refers to the slot spacing between adjacent magnetic centers of the motor iron core, and the slot spacing calculation of the inner circular air gap surface of the stator iron core; The rotor is calculated based on the slot spacing of the air gap surface on the outer circumference of the iron core. There are usually two ways to represent distance, one is by length; Another way is to express it in terms of the number of slots, which is usually more commonly used. Generally, the distance is expressed as τ=Z1/2p.

3. Pitch (y)

The number of iron core slots occupied between the two component sides of each coil in the motor winding is called pitch, also known as span. When the pitch of the coil element is equal to the distance symmetry, it is called a full distance winding, y=τ； When the pitch of the coil element is less than the distance, it is called a short distance winding, y＜τ； When the pitch of the coil elements is greater than the pitch, it is called a long-distance winding y>τ. Due to the many advantages of using shorter electromagnetic wires at the end and higher power factor, short distance windings are commonly used in double-layer stacked windings.

4. Winding coefficient

The winding coefficient refers to the product of the short distance coefficient and the distribution coefficient of the AC distributed winding, that is

Kdp1=Kd1Kp1。

5. Pitch angle (α)

The electrical angle between two adjacent slots of the motor iron core is called the slot pitch angle, usually represented by a, that is

α=total electrical angle/z1=p × 360 °/z1

6. Xiangbelt

Phase band refers to the area occupied by each phase winding in each magnetic field, usually expressed in electrical angles or slot numbers. If the windings of a three-phase motor under each pair of magnets are divided into six regions, then there will be three in each region. Due to the slot pitch angle α=360 ° P/Z, if the motor has 424 slots, the width of each phase and region is q α=Z/6P * 360P/Z=60 °. The winding wound in this distribution is called a 60 ° phase belt winding. Due to the obvious advantages of 60 ° continuous phase winding, this winding is widely used in three-phase motors.

7. Number of slots per phase (q)

The number of slots per phase refers to the number of slots occupied by each phase winding in each magnet, and the number of coils to be wound in each phase winding is determined based on it. approach

q=Z/2Pm  

Z: Number of iron core slots; 2P: Number of motors; Number of motor phases.

The calculation result, if q is an integer, is called an integer slot winding; If q is a fraction, it is called a fractional slot winding.

8. Number of conductors per slot

The number of conductors per slot of the motor winding should be an integer, and the number of conductors per slot of the double-layer winding should also be an even integer. The number of conductors per slot of the wound rotor winding is determined by its open circuit voltage, and the number of conductors per slot of the wound rotor for medium-sized motors must be equal to 2. The number of conductors per slot of the stator winding can be calculated by the following formula:

NS1=NΦ1m1a1/Z1      

NS1: number of conductors per slot of stator winding;

N Φ 1: The number of conductors per slot calculated based on the air gap magnetic density;

M1: number of stator winding phases;

A1: Number of parallel branches of stator winding;

Z1: Number of stator slots.  

9. Number of series conductors per phase

The number of series conductors per phase refers to the number of turns of the bus connected in series with each phase winding in the motor. However, the number of turns in the series bus is related to the number of parallel branches in each phase winding. For example, if the number of parallel branches in a motor is a 1-way connection, then the number of turns in all series lines of the lower coils of the motor should be added together to form the total number of turns in the phase winding bus. If there are multiple parallel branches in each phase winding of the motor, such as 2-channel connection or 3-channel connection, the number of series conductors in each phase can only be based on the number of turns of one winding connected in series. Because the number of series turns in each branch of the phase winding is the same, it is impossible to increase the number of series turns when connected in parallel to form a phase winding.

10. Number of bus cycles

The winding inside the motor is composed of coils of various sizes and shapes. Due to the fact that each coil has two component edges embedded in the iron core slot, it means that each coil needs to be embedded in two slots. In a single-layer winding, only one coil element edge is embedded in each slot, so the number of bus coils is only equal to half of the total number of slots; In a double-layer winding, two coil elements are embedded in the upper and lower layers of each slot, so the total number of coils is equal to the number of iron core slots.