The collector electric motor. Universal collector motor

The collector motor is a synchronous electric machine in which the current switch in the winding and the rotor position sensor are made in the form of the same device, the brush-collector assembly. This device can be of different types.

Varieties

The DC collector motor usually includes such elements as:

- Three-pole rotor on sliding bearings;

- a bipolar stator with permanent magnets;

- copper plates as brushes of the collector assembly.

This set is typical for the most low-power solutions, usually used in children's toys, where much power is not required. The structure of more powerful engines includes a few more structural elements:

- four graphite brushes in the form of a collector unit;

- a rotor with several poles on the rolling bearings;

Stator of permanent magnets with four poles.

Most often the device of the electric motor of this type is used in modern cars for realization of a drive of the fan of system of cooling and ventilation, pumps of washers, janitors and other elements. There are also more complex aggregates.

The electric motor power of several hundred watts assumes the use of a four-pole stator made of electromagnets. To connect its windings can be used in one of several ways:

- Consistently with the rotor. In this case, a large maximum torque is obtained, however, because of the large idling speed, the risk of engine damage is high.

- In parallel with the rotor. In this case, the revolutions remain stable under conditions of varying load, but the maximum torque is much less.

- Mixed excitation, when part of the winding is connected in series, and a part in parallel. In this case, the merits of the previous options are combined. This type is used for car starters.

- Independent excitation, which uses a separate power source. In this case, the characteristics corresponding to the parallel connection are obtained. This option is used quite rarely.

The collector electric motor has certain advantages: they are simply manufactured, repaired, operated, and their service life is sufficiently large. As a disadvantage, the following usually stands out: effective designs of such devices are usually high-speed and low-torque, so most drives require the installation of gears. This statement is fully justified, since an electric machine oriented at a low speed is characterized by a low efficiency, as well as related cooling problems. The latter are such that it is difficult for them to find an elegant solution.

Universal collector motor

This variant is a kind of a collector machine of a constant current, capable of operating on a constant and alternating current. The device has become widespread in some types of home appliances and hand tools due to small size, low weight, low cost and easy regulation of the revolutions. It is often found as a traction machine on the railways of the US and Europe. You can consider the device of the electric motor.

Design Features

For a better understanding of this issue, we need to consider in more detail what formed the basis of the presented device. Type of electric motor collector universal is a device of direct current, with series-connected excitation windings, optimized for operation on alternating current of the household electric power supply network. The motor rotates in one direction regardless of the polarity. This is due to the fact that the serial connection of the stator and rotor windings leads to a simultaneous change of their magnetic poles, and due to this the resultant moment is directed to one side.

What is it made of?

The alternating current collector motor assumes the use of a stator of a magnetically soft material, which is characterized by a small hysteresis. To reduce eddy current losses , this element is made from insulating plate-like plates. As a subset of AC collector machines, it is customary to isolate pulsating current aggregates, which are obtained by rectifying the current of a single-phase circuit without using pulsation smoothing.

The AC collector motor is most often characterized by this feature: in the low-speed mode, the inductive resistance of the stator windings does not allow the current to be consumed beyond certain limits, while the maximum motor torque is limited to 3-5 of the nominal value. Approximation of mechanical characteristics is achieved by using the stator winding sectioning - separate terminals are used to connect the alternating current.

A rather complicated problem involves the commutation of a powerful ac collector machine. At the moment when the section passes through the neutral, the magnetic field in the coupling with the rotor changes its direction to the opposite direction, and this causes the generation in the reactive EMF section. This happens when working on AC. In the collector machines of alternating current there is also a reactive EMF. The transformer EMF is also noted here, since the rotor is in the stator magnetic field, pulsing in time. A smooth start of the collector motor is impossible, since at this moment the amplitude of the machine will be maximum, and as we approach the synchronization speed it will decrease proportionally. As the overclocking progresses, a new increase will be noted. In order to solve the switching problem in this case, several sequential steps are proposed:

- In the design, one-turn section should be preferred, which will reduce the flow of adhesion.

- The active resistance of the section needs to be increased, for which the most promising elements are the resistors in the collector plates, where there is good cooling.

- The collector should be actively ground with brushes of maximum hardness with the greatest resistance.

- The reactive EMF can be compensated by using additional poles with series windings, and the parallel windings are suitable for compensation of the transformer EMF. Since the value of the latter parameter is a function of the angular velocity of the rotor and the magnetizing current, similar windings require the use of subordinate control systems, which do not yet exist.

- The frequency of the supply circuits should be as low as possible. The most popular options are 16 and 25 Hz.

- The reversal of the RCA is performed by switching the polarity of the stator or rotor windings.

Advantages and disadvantages

For comparison, the following conditions are used: the devices are connected to a household electric network with a voltage of 220 volts and a frequency of 50 Hz, while the engine power is the same. The difference in the mechanical characteristics of the devices may be a disadvantage or advantage, depending on which requirements are imposed on the drive.

So, the collector electric motor of alternating current: advantages in comparison with the direct current unit:

- The connection to the network is made directly, without the need for additional components. In the case of the DC unit rectification is required.

- Starting current is much less, which is very important for devices used in everyday life.

- With a control circuit, its device is much simpler - rheostat and thyristor. If the electronic component comes out of line, then the collector motor, the price of which depends on the capacity and is from 1400 rubles and more, will remain operational, but will immediately turn on at full capacity.

There are some disadvantages:

- Due to the losses for stator reversal and inductance, the overall efficiency is markedly reduced.

- The maximum torque is also reduced.

Electric motors single-phase collector have certain advantages in comparison with asynchronous:

- compactness;

- Absence of binding to the network frequency and speed;

- significant starting torque;

- Proportional reduction and increase in revolutions in the automatic mode, as well as an increase in torque with increasing load, while the supply voltage remains unchanged;

- The speed control can be smooth over a fairly wide range by changing the supply voltage.

Disadvantages in comparison with an asynchronous motor

- when the load changes, the revolutions will be unstable;

- brush-collector unit makes the device not too reliable (the need to use the maximum hard brushes significantly reduces the resource);

- commutation of an alternating current causes strong sparking on the collector, thus radio interference is formed;

- high noise level during operation;

- The collector is characterized by a large number of parts, which makes the engine quite massive.

The modern collector electric motor is characterized by a resource comparable with the possibilities of mechanical transmissions and working bodies.

Other comparisons

When comparing the collector and asynchronous motors of the same power, regardless of the nominal frequency of the latter, a different characteristic is obtained. This will be described in more detail below. The universal collector motor realizes a "soft" characteristic. In this case, the moment is directly proportional to the load on the shaft, while the revolutions are inversely proportional to it. The nominal torque is usually less than a maximum of 3-5 times. Restriction of idle speed is characterized exclusively by losses in the engine, and with the inclusion of a powerful unit without load, it can collapse.

The characteristic of the asynchronous motor is "fan", that is, the unit maintains a speed of rotation close to the nominal, increasing the moment as sharply as possible with a slight decrease in speed. If we are talking about a significant change in this indicator, then the engine torque not only does not increase, but falls to zero, which leads to a complete stop. The idling speed slightly exceeds the rated ones, while remaining constant. The characteristic of a single-phase asynchronous motor is an additional set of problems associated with starting, since it does not develop a starting torque under normal conditions. The magnetic field of a single-phase stator, pulsating in time, splits into two fields with opposite phases, so that starting without any possible tricks becomes impossible:

- capacity, creating an artificial phase;

- split groove;

- active resistance, which forms an artificial phase.

Theoretically, the field rotating in antiphase reduces the maximum efficiency of a single-phase asynchronous aggregate to 50-60% due to losses in a supersaturated magnetic system and windings loaded with counter current currents. It turns out that on one shaft there are two electric cars, while one works in the driving mode, and the second - in the mode of opposition. It turns out that the electric motors Single-phase collectors do not know competitors in the respective networks. Than they deserve such a high popularity.

The mechanical characteristics of the electric motor provide it with a certain scope of use. Small turns limited by the frequency of the alternating current network make asynchronous aggregates of similar capacity larger in weight and size in comparison with universal collector ones. However, when the inverter is connected to a power circuit with a high frequency, it is possible to achieve commensurable dimensions and weight. The stiffness of the mechanical characteristics of the electric motor remains, to which the losses for current conversion are added, as well as the frequency increase, and the magnetic and inductive losses increase.

Analogs without a collector node

The AC collector motor has an analog which is closest to it in terms of its mechanical characteristic, a valve, where the brush and collector assembly was replaced by an inverter equipped with a rotor position sensor. The following system is used as an electronic analog of this unit: rectifier, synchronous motor with rotor angular position sensor, combined with inverter. However, the presence of permanent magnets in the rotor leads to a reduction in the maximum torque while maintaining the dimensions.

Operating principle

The device of the collector motor demonstrates how the device converts electrical energy into a mechanical one and in the opposite direction. This indicates its ability to use as a generator. It is worthwhile to consider in more detail the collector electric motor, the circuit of which will demonstrate its capabilities.

The laws of physics clearly indicate that when a current flows through a conductor in a magnetic field, a certain force is exerted on it. In this case, the rule of the right hand, which directly affects the power of the electric motor, works. The collector electric motor works on this basic principle.

Physics teaches us that the basis for creating the right things are small rules. This served as the basis for creating a frame rotating in a magnetic field, which made it possible to create a collector electric motor. The diagram shows that a pair of conductors is placed in the magnetic field, the current of which is directed in opposite directions, and hence the forces too. Their sum and gives the necessary torque. The device of the electric motor is much more complicated, since it contains a whole complex of necessary elements, in particular, a collector providing the same current direction above the poles. The unevenness of the stroke was eliminated by placing several more coils at the anchor, while the permanent magnets were replaced by coils, which made it possible to avoid the need to use a direct current. This made it possible to give a single direction to the torque.

Repair of electric motors by one's own hands

Like any other device, this unit may fail for any reason. If the electric motor, the photo of which you can see in our review, can not dial the required number of revolutions, or when it is started, the shaft does not rotate, it is required to check whether its fuses have burned, there are no breaks in the armature electrical circuit, whether the device itself is overloaded. Very often overload results in the consumption of an abnormal current. To eliminate this malfunction, you need to carefully inspect the mechanical transmission and brake, and then eliminate the causes of overloads.

The device of the electric motor is such that at start-up it consumes a certain current. If it is larger than the nominal value, it is required to check the consistency of the connection of the parallel and series windings with respect to each other, and also with respect to the rheostat. When repairing electric motors by oneself, most often specific mistakes are made. In particular, the shunt winding can be connected in series with the electrical resistor of the rheostat, or connected to one pole of the electric network.

The consistency check of the field wiring is made by connecting one end of the shunt winding with the anchor end, and the second one with an electrical conductor coming from the arc of the rheostat. Usually the cross-section of this electrical conductor is slightly smaller than the others, so it can be detected without a megaohmmeter. After the power switch is turned on and the rheostat slider is shifted to the middle position, power is applied to the free ends. By means of a control lamp, all conductive ends are sequentially checked. When touching one of them, the lamp should light up, but with the other - no. So the whole electric motor is tested. The price of the work will depend on the type of failure of the unit.

If the device operates at a speed that is less than the rated speed, then the main reasons for this are usually: low mains voltage, device overload, large exciting current. If an invalid character is noted, it is required to check the excitation electric circuit, eliminate all detected defects, after which it is possible to establish the normal value of the excitation current. In some cases, it may be necessary to rewind the motors.

When the reason for the inoperability of the unit is the wrong coupling of the parallel and sequential excitation winding, it is required to restore the correct connection order. If it is not possible to eliminate such a problem in a simple way, it may be necessary to rewind the motors. It is also necessary to check the value of the voltage in the electrical network, as with increasing its nominal value, the device revolutions may increase.