Selected data compilation of windings for multi-winding, multi-speed motors
Multi-speed motors typically have only one set of windings. Speed regulation is achieved by changing the winding connections and altering the number of poles. Motors that use two sets of windings to change speed are relatively rare. This article provides data for two motor windings.
I. The first unit
Nameplate:
Core dimensions:
Outer diameter 240mm , inner diameter 145mm , length 277mm, number of slots 36
Winding data:
II. Second unit
Nameplate:
Core dimensions:
Outer diameter 187mm , inner diameter 123mm , length 165mm, number of slots 36
Winding data:
Basic knowledge of motor windings
1. Mechanical and Electrical Angles
In mechanics, we know that a circle can be divided into 360°, which is what we commonly refer to as a mechanical angle. In electrical engineering, the unit for measuring electromagnetic relationships is called an electrical angle. It is calculated by dividing each cycle of a sinusoidal alternating current into 360° on the horizontal axis , meaning that when a conductor passes through a pair of magnetic poles, it changes electromagnetically by 360° electrical angle.
Therefore, the relationship between electrical angles and mechanical angles in a motor is as follows:
Electrical angle α = number of pole pairs x P x 360°
For example, for a two-pole motor, the number of pole pairs p=1 , and the electrical angle equals the mechanical angle. For a four-pole motor, p=2 , and the motor has two pairs of magnetic poles per circumference, corresponding to an electrical angle of 2 × 360° = 720°. And so on.
2. Polar moment (τ)
The pole pitch of a winding refers to the distance of each magnetic pole occupying the circumference of the iron core. There are usually two methods of representing pole pitch: one is by length, and the other is by the number of slots. It is more common to use the number of slots. Generally, the pole pitch is expressed as:
τ=Z1/2p
3. Pitch (y)
The number of iron core slots occupied between the two elements of each coil in a motor winding is called the pitch, also known as the span.
When the coil element pitch is equal to the pole pitch, it is called a full-pitch winding, y=τ
When the coil element pitch is less than the pole pitch, it is called a short-pitch winding , y < τ.
When the coil element pitch is greater than the pole pitch, it is called a long-pitch winding (y>τ).
Because short-pitch windings have many advantages, such as shorter end lengths, less electromagnetic wire consumption, and higher power factor, they are used without exception in the most widely used double-layer lap windings.
4. Winding coefficient
The winding factor refers to the product of the short-pitch factor and the distribution factor of the AC distributed winding, i.e.
Kdp1=Kd1Kp1
5. Slot pitch angle (α)
The electrical angle between two adjacent slots of a motor core is called the slot pitch angle, usually denoted by α.
α = total electrical angle / z1 = p × 360° / z1
6. Phase band
A phase zone refers to the area occupied by each phase winding at each magnetic pole, usually expressed in electrical angles or slot count. If the windings of a three-phase motor under each pair of magnetic poles are divided into six zones, then there are three zones per pole. Since the slot pitch angle α = 360°P/Z, if the motor has 4 poles and 24 slots, then the width of each zone per phase is...
qα = Z/6P*360P/Z = 60°
A winding arranged in this manner is called a 60° phase-band winding. Due to the significant advantages of 60° continuous phase-band windings, this type of winding is used in the vast majority of three-phase motors.
7. Number of slots per pole per phase (q)
The number of slots per pole per phase refers to the number of slots occupied by each phase winding in each magnetic pole. The number of coils to be wound in each pole per phase winding is determined based on this.
q=Z/2Pm
Z: Number of core slots; 2P: Number of motor poles; m: Number of motor phases.
If the calculated result q is an integer, it 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 in the motor windings should be an integer, and for double-layer windings, the number of conductors per slot should be an even integer. The number of conductors per slot in the wound rotor windings is determined by its open-circuit voltage; for medium-sized motors, the number of conductors per slot in the wound rotor must be equal to 2. The number of conductors per slot in the stator windings can be calculated using the following formula:
NS1=NΦ1m1a1/Z1
NS1: Number of conductors per slot in the stator winding;
NΦ1: Number of conductors per slot calculated based on air gap magnetic flux density;
m1: Number of phases in the stator winding;
a1: Number of parallel branches in the stator winding;
Z1: Number of stator slots.
9. Number of conductors in series per phase
The number of series conductors per phase refers to the number of series bus turns in each phase winding of the motor. However, this number of series bus turns is related to the number of parallel branches in each phase winding. For example, if the motor has only one parallel branch connection, then the number of series wire turns of all the coils under each pole of the motor should be added together to obtain the number of bus turns of the phase winding.
If each phase winding of a motor has multiple parallel branches, i.e., the motor is connected in a 2-way or 3-way configuration, the number of series conductors in each phase can only be determined by the number of turns of the series conductors in one of the windings. This is because the number of turns of the series conductors in each branch of the phase winding is the same, and the number of turns of the series conductors cannot be increased after they are connected in parallel to form a phase winding.
10. Total number of coils
The windings inside a motor are composed of coils of various sizes and shapes. Since each coil has two elements embedded in the iron core slots, each coil must be embedded in two slots. In a single-layer winding, because only one coil element is embedded in each slot, the total number of coils is only half the total number of slots; in a double-layer winding, because two coil elements are embedded in each slot (both upper and lower layers), its total number of coils is equal to the number of iron core slots.
DC motor windings
I. Characteristics of DC motor windings: (as shown in the figure)
1. First pitch: y1, the distance spanned by the two element sides of each element on the armature surface, expressed in terms of the number of slots.
Example: If the upper element is in slot 1 and the lower element is in slot 5, then y1 = 5 - 1 = 4. To maximize the induced electromotive force in the winding, y1 should be close to the pole pitch. (Pole pitch is the distance between two adjacent main poles, expressed in slot number.)
2. Second pitch: y2, in two elements connected in series by the same commutator segment, is the distance between the bottom edge of the first element and the top edge of the second element, expressed by the number of slots. y2 is negative for lap windings and positive for wave windings.
3. Composite pitch: y, the distance between corresponding sides of two elements connected in series. y = y1 + y2.
4. Commutator pitch: yk, the distance between two commutator segments connected to the two ends of the same component, expressed as the number of commutator segments. y=yk.
II. Basic types of windings:
1. Single-lap winding:
The two output terminals of a component are connected to two adjacent commutator segments; adjacent components are connected in series, with the start end of the subsequent component connected to the end end of the preceding component and connected to the same commutator segment. The end end of the last component is connected to the start end of the first component, forming a closed loop. The terminals of two components connected in series are tightly overlapped. Examples illustrating the connection characteristics and branch composition are provided below:
Example 1: Given a pole pair number p=2, slot number Z=16, element number S=K=16, y1=4, and yk=1, draw the development diagram of a single-layer winding.
(I) Pitch Calculation
Single stack: y1=yk=1, integer distance: y1=16/4=4, y2=y-y1=1-4=-3.
(II) Winding Connection Table
(vi) Number of parallel branches of the winding:
The number of parallel branches in a single-lap winding is equal to the number of poles in the motor. The number of parallel branch pairs is equal to the number of pole pairs, i.e., a = p.
Number of brushes = Number of branches = Number of poles
2. Single-wave winding:
The two commutator segments connected to the two ends of each component are far apart, yk>y1, and the components form a wavy shape after being connected in series. Y1 should be close to the pole pitch, and yk satisfies the following formula:
After completing one revolution, the steering wheel moves forward (+, right turn) or backward (-, left turn) one steering wheel segment compared to its starting position.
Example 2: Draw the development diagram of a left-hand short-pitch single-wave winding, where 2p=4, Z=S=K=15.
(vi) Number of parallel winding branches:
The number of parallel branches in a single-wave winding is always equal to 2, regardless of the number of main poles.
Besides the two basic types, single-lap and single-wave, motor windings also come in other types, such as: compound lap, compound wave, hybrid winding, and concentric winding. The difference between various windings lies in the number of parallel branches.
