What Does an Armature Winder Do?

The armature winding is composed of a certain number of armature coils connected according to a certain rule. It is the circuit part of the DC motor and also the part that induces electromotive force and generates electromagnetic torque for electromechanical energy conversion. The coil is wound with insulated round or rectangular cross-section wires and is embedded in the armature core slot in two layers. The upper and lower layers and the coil and the armature core must be properly insulated and compressed with slot wedges. The ends of the armature windings of large motors are usually fastened to the winding support.

Chinese name: Armature winding

Foreign name: armature winding

Armature winding

The coil group of the motor's armature is wound and connected according to a certain rule. It is one of the main components of the electromechanical energy conversion in the motor. The coils that make up the armature winding are either single-turn or multi-turn. Each turn can also be wound by several parallel wires. Shown when a coil is placed in a slot.

Armature winding design requirements: The armature winding's composition should be able to generate sufficient induced electromotive force and allow a certain armature current to generate the required electromagnetic torque and electromagnetic power. In addition, non-ferrous metals and insulation must be saved. Material, simple structure and reliable operation. ^[1]

The armature winding is divided into two categories: DC armature winding and AC armature winding. They are used for DC motors and AC motors, respectively.

Common terms for armature winding

Element (coil): The winding coil is called a winding element and is divided into single and multiple turns. An element is composed of two element edges and terminal wires. The edge of the element is placed in the slot. It can cut the magnetic field lines to generate the induced electromotive force. It is called "effective side". The terminal line is placed outside the slot and does not cut the magnetic line. One component edge of each component is placed on the upper level of one slot, and the other component edge is placed on the lower level of the other slot.

Element head and end: Each element leads to two wires connected to the commutator, one of which is called the head end and the other is called the end. The two end points of each element are respectively connected to different commutation pieces, and each commutation piece is connected to two different coil ends.

Real slot: The slot actually opened on the motor armature is called a real slot. The number of real slots is represented by Q.

Virtual slots: Unit slots (the number of component edges in each layer is equal to the number of virtual slots), and each virtual slot has a component edge on the upper and lower layers. The number of virtual slots is represented by Q. It is assumed that there are virtual slots in each layer of the slot. If the number of real slots is Q and the number of virtual slots is Q, then Q = Q.

Polar axis: the centerline of the magnetic pole.

Geometric neutral line: refers to the mechanical boundary between the N and S poles of the main magnetic pole.

Physical neutral line: The boundary where the magnetic field of the N and S poles is zero is called the physical neutral line. ^[2]

Armature winding DC armature winding

Double-layer windings are usually used. The active part of the coil contains left and right active edges. The effective edge placed in the groove near the slot is called the upper edge, and the effective edge near the bottom of the groove is called the lower edge. The upper and lower layers in the same slot are separated by insulating paper. The distance in the circumferential direction of the upper and lower effective edges of the same coil is the span of the coil, which is usually expressed in multiples of the slot pitch (distance between two adjacent slots). The span is approximately equal to one pole distance (the distance between two adjacent magnetic poles, which is also usually expressed in multiples of the slot distance).

Check for armature winding open circuit There are three types of DC armature windings: stacked winding, wave winding and frog winding. The two outgoing ends of each coil are connected to the two commutator segments of the commutator. The distance between the two on the circumferential surface of the commutator is called the commutator pitch, which is represented by Ys. Different forms of winding have different commutator pitches.

Armature winding

It means that two elements connected in series always have the terminating part of the latter element superimposed on the terminating part of the previous element, and the entire winding advances in a folded manner.

There are single-windings and multi-windings. Single-stacked windings connect adjacent coils under the same magnetic pole in series to form a parallel branch, so there is a parallel branch corresponding to a magnetic pole. The basic feature of single-stack winding is that the number of parallel branches is equal to the number of magnetic poles. The branches are connected in parallel by brushes.

The commutator pitch of single-stack winding coils is Ys = 1. Ys> 1 is called cascade winding. The more commonly used is the cascade winding of Ys = 2, also known as the double cascade winding. Double-stacked windings have two parallel branches under one magnetic pole. For example, when a four-pole DC motor uses double-stack windings, there are 8 parallel branches. The branches are also connected in parallel by brushes. The number of brush sets is equal to the number of poles of the motor. Half of them are positive brushes and the other half are negative brushes. The number of parallel branches of the stacked winding is large, which is equal to the number of poles or an integral multiple of the number of poles, so it is also called a parallel winding.

Armature winding

Refers to connecting the corresponding elements in a magnetic field of the same polarity separated by a pair of poles in series, like a wave-like progression.

There are single wave winding and complex wave winding. The characteristic of the single-wave winding is that all the coils under the same polarity are connected in series according to a certain rule to form a parallel branch. Therefore, the entire armature winding has only two parallel branches. In the commutator pitch formula of the wave winding coil, P is the number of pairs of magnetic poles; k is the number of commutation pieces; a is a positive integer such that Ys is equal to an integer, which is equal to the number of parallel branch pairs of the wave winding. The single wave winding a = 1, and a = 2 complex wave winding is called double wave winding. It can be regarded as a complex wave winding composed of two single wave windings in parallel, so there are 4 parallel branches; a> The two can be deduced by analogy, but they are rarely used.

Armature winding diagram

From the principle of parallel circuit connection, wave winding only requires two sets of brushes, that is, a set of positive brushes and a set of negative brushes. However, in general, the number of brush sets of wave windings in a DC motor is still equal to the number of poles. This is to reduce the current load on the contact surfaces of the brushes and the commutator blades, thereby reducing the length of the commutator. In addition, the commutation of the coil current is also beneficial.

DC armature windings often cause uneven distribution of current in the parallel branches for some reason, which increases copper consumption and overheats the armature windings; sometimes it also causes harmful sparks under the brushes, which adversely affects the operation of the motor. Directly connecting the theoretical equipotential point inside the armature winding with a wire can improve the operating conditions of the motor. The connection conductors specially provided for this purpose are called equalizing lines.

Armature winding

A type of DC armature winding that is a mixture of appropriately matched stacked and wave windings. The coils of the stacked winding and the wave winding are connected to the same commutator and work in parallel. It is named because its coil combination looks like a frog. Because this kind of winding has a voltage equalizing line function between the wave winding coil and the stacked winding coil, there is no need to additionally connect a voltage equalizing line. DC motors using frog windings have good operating performance, so their applications are becoming increasingly widespread.

The armature winding is the core part of the DC motor. When the armature rotates in a magnetic field, an electromotive force is induced in the armature winding. When current flows in the armature winding, armature magnetomotive force is generated, which interacts with the air gap magnetic field and generates electromagnetic torque. Electromotive force interacts with current to absorb or emit electromagnetic power. The electromagnetic torque interacts with the rotor speed to absorb or release mechanical power. The two exist at the same time, which constitutes the mutual conversion of electromagnetic energy and mechanical energy, and completes the basic functions of DC motors. Therefore, the armature winding plays an important role in DC motors.

Armature winding other categories

According to different connection methods, the armature winding can be divided into: (1) single-stack winding , (2) single-wave winding ; (3) multi-layer winding ; (4) complex-wave winding ; (5) hybrid winding, etc. The main difference is that when viewed from the outside of the brush, the armature windings are connected into different numbers of parallel branches to meet the requirements of different rated voltages and currents, of which single-stacked winding and single-wave winding are two basic types. Due to space limitations, this book mainly introduces single stack and single wave windings.

Armature winding characteristics

Although there are different types of armature windings, they have the same characteristics in structure: they are all formed by winding elements (components for short) with the same structural shape connected according to certain rules. The winding element is also called a coil. The total number of elements of a motor is represented by s. Each element has two effective edges that are placed in the slot and can cut the magnetic flux induced electromotive force. The part outside the slot does not cut the magnetic flux and does not induce electromotive force, which is called the end. The element can be divided into single-turn element and multi-turn element. The former has only one conductor on its side, and the latter has multiple conductors wound in series. The number of element turns is N. It means that each component has two lead wires, one for the head end and one for the tail end, and they are connected to different commutators.

The various components of the winding are connected to each other through commutator pieces. In this way, both the first end of the component and the tail end of the other component must be connected on the same commutator piece, so that the number of components of the entire armature winding S and the number of commutation pieces X are equal, that is, S = K.

The winding element is embedded in the slot of the armature core. As shown in Figure 7-8 (a) of Chapter 7, one element edge is placed on the upper layer of the slot, called the upper layer edge, and the other side is embedded in The lower layer of the other slot is called the lower edge. Effective edges of different components are placed on the upper and lower layers of the same slot, and one component has only two edges. In this way, the number of slots Q of the armature should be equal to the number of components J.

In order to correctly embed the winding in the slot and connect it with the commutator, the pitch of various winding elements on the armature and commutator should be understood first. The so-called pitch refers to the distance between the edges of two related elements, which is usually expressed by the number of slots or the number of commutation pieces.

First pitch

2. Second pitch J2

y2 is the distance between the lower edge of the component and the upper edge of the component to which it is connected, in virtual slots.

3 Composite pitch y and commutator pitch yt

y is the distance between the corresponding sides of two elements in series, measured in virtual slots. The relationship between y and y1, y2 is

y = y1 ten y2

yK is the distance between the head and tail of a component on the commutator, expressed by the number of commutation pieces. The size of yK should make the direction of the electromotive force of the cascaded components-so as not to reverse each other. Figure 9-2 (a) is a single-stack winding with yx = 1. Figure 9-2 (b) is a single-wave winding with a large yx. But they are all connected in series with the components of the induced electromotive force in the same direction.

Armature winding AC armature winding

AC armature windings can be divided into two types: coiled and caged.

AC armature winding

There are the following classifications of coiled windings.

Armature windings are classified by number of phases

There are single-phase windings and three-phase windings. If it is three-phase, it is required that the three-phase windings are symmetrically distributed in the spatial position of the magnetic field, that is, the electrical angles of each phase differ by 120 °.

The three-phase winding can be connected into a star (Y) or a triangle (), as shown in Figure 4. If 6 line ends such as D1 D6 are drawn out, they can be connected into Y or shape as required. For example, in order to reduce the starting current, the asynchronous motor is connected into a Y shape when starting, and a delta shape when running.

There is also a star-delta hybrid connection. This hybrid connection can be in series or parallel. The star-delta hybrid connection can be used to obtain a twelve-phase current system from a three-phase power supply.

In the parallel hybrid connection, circulating current is easily generated between the star winding part and the delta winding part, so in practice, the serial hybrid connection is mostly used.

Armature windings are classified by phase band

According to the electrical angle (phase band) of each phase winding continuously occupying space on the circumference, there are windings such as 120 ° phase band, 60 ° phase band, and 30 ° phase band. Generally, three-phase AC motors use 60 ° phase band windings. Under the same number of series conductors, the induced electromotive force of the 60 ° phase band winding is about 15% larger than that of the 120 ° phase band winding. Although the 30 ° phase band winding can further improve the winding utilization rate, it is only used in some occasions with special requirements, such as in high-efficiency motors, because the windings are complicated to manufacture and the induced electromotive force is not much improved.

Armature windings are classified by the number of layers of coil sides in the slot

There are single-layer winding, double-layer winding and single-double-layer winding.

Single-layer windings are mostly used for low-power motors. Compared with the double-layer winding, the number of coils is halved, so the workload of winding and embedding is less. The double-layer winding can choose the winding span to improve the electromotive force and magnetomotive force waveform, or to weaken a specific harmful harmonic. All coils have the same geometric dimensions, which is easy to manufacture, and the end structure is neat, which is conducive to heat dissipation and high mechanical strength. Therefore, except for small motors, double-layer windings have been widely used in all capacity ranges. The single-double-layer winding is a variant of the double-layer short-distance winding. Its performance is the same as that of the corresponding double-layer short-distance winding, but the end wiring is short. One of the disadvantages is the different geometries of the coils.

q Armature windings are classified by the number of slots per phase per phase q

There are two types: integer and fractional slots. Integer slot windings are the most widely used.

Fractional slot windings are mainly used to weaken the extremely harmful tooth harmonics in synchronous motors, improve the electromotive force waveform and reduce surface losses. Used a lot in low-speed multi-pole hydro-generators. Compared with integer slot windings, the magnetic flux potential of fractional slot windings has more harmonics, which must be prevented from causing vibration and noise.

Armature winding other

In addition, the single-layer winding can be divided into three types according to the connection method of the coil end: concentric type, chain type and cross type.

Cage winding is the most widely used type of AC armature winding in asynchronous motors. Its structure is very different from the stator winding. There is a conductor bar in each slot of the rotor core of the asynchronous motor. There are two end rings outside the notches on the two ends of the iron core to connect the two ends of all conductor bars respectively to form a short circuit. If the core of the magnetic circuit part is removed and only the conductive circuit part is considered, the shape of this winding is like a cage (see three-phase asynchronous motor), hence the name. Each conductor of a cage winding is one phase. It can be combined with a rotating magnetic field of any number of poles to induce a current in it. The induced electromotive force in the cage winding is small, so insulation is generally not required.

Evolution of armature winding

Armature winding toroidal armature winding

advantage

The winding is not limited by the number of poles, that is, the same winding can be used by motors with different pole numbers.

Disadvantage

The inner conductor of the hollow core cannot cut the magnetic pole flux (no magnetic flux can be cut) to generate an electric potential, that is, only one semiconductor generates the electromotive force, which wastes material and increases the armature resistance. Manual winding is required, which is time-consuming to manufacture, and the insulation treatment is not easy to make self-inductive Increased mutual inductance causes poor commutation.

Armature winding drum armature winding

advantage

The conductor utilization rate is higher than that of toroidal windings. Formed windings can be used. Easy winding and easy insulation and mutual inductance are smaller than toroidal windings. Therefore, commutation is better than toroidal windings.

Disadvantage

It cannot be applied to motors with different numbers of poles, and the direction of electromotive force or electromagnetic force may be reversed and partially offset. ^[2]