In the motors under consideration, the excitation winding is made with a small number of turns, but is designed for high currents. All the features of these motors are related to the fact that the field winding is turned on (see Fig. 5.2, V) in series with the armature winding, as a result of which the excitation current is equal to the armature current and the generated flux Ф is proportional to the armature current:

Where A=/(/ i) - nonlinear coefficient (Fig. 5.12).

Nonlinearity A is related to the shape of the motor magnetization curve and the demagnetizing effect of the armature reaction. These factors appear when /i > /yang (/yang is the rated armature current). At lower currents A can be considered a constant value, and when /i > 2/i n the motor is saturated and the flux depends little on the armature current.

Rice. 5.12.

The basic equations of a sequential excitation motor, in contrast to the equations of independent excitation motors, are nonlinear, which is associated, first of all, with the product of variables:

When the current in the armature circuit changes, the magnetic flux F changes, inducing eddy currents in the massive parts of the machine's magnetic circuit. The influence of eddy currents can be taken into account in the motor model in the form of an equivalent short-circuit loop described by the equation

and the equation for the armature circuit is:

where w B, w B t - the number of turns of the field winding and the equivalent number of turns of eddy currents.

In steady state

From (5.22) and (5.26) we obtain expressions for the mechanical and electromechanical characteristics of a series-excited DC motor:

To a first approximation, the mechanical characteristics of a sequential excitation motor, without taking into account the saturation of the magnetic circuit, can be represented as a hyperbola that does not intersect the ordinate axis. If you put L I ts = /? i + /? в = 0, then the characteristic will not intersect the abscissa axis. This characteristic is called perfect. The real natural characteristic of the engine crosses the x-axis and due to saturation of the magnetic circuit at torques greater M n straightens (Fig. 5.13).

Rice. 5.13.

A characteristic feature of the characteristics of a series excitation motor is the absence of an ideal idle point. As the load decreases, the speed increases, which can lead to uncontrolled acceleration of the engine. It is impossible to leave such an engine without load.

An important advantage of series-excited motors is their high overload capacity at low speeds. With a current overload of 2-2.5 times, the motor develops a torque of 3.0...3.5 Mn. This circumstance has determined the widespread use of sequential excitation motors as a drive for electric vehicles, for which maximum torques are required when starting off.

Changing the direction of rotation of series-excited motors cannot be achieved by changing the polarity of the armature circuit supply. In series-excited motors, when reversing, it is necessary to change the direction of the current in one part of the armature circuit: either in the armature winding or in the field winding (Fig. 5.14).

Rice. 5.14.

Artificial mechanical characteristics for speed and torque control can be obtained in three ways:

• introducing additional resistance into the motor armature circuit;
• changing the voltage supplying the motor;
• bypassing the armature winding with additional resistance. When additional resistance is introduced into the armature circuit, the rigidity of the mechanical characteristics decreases and the starting torque decreases. This method is used when starting series-excited motors receiving power from sources with unregulated voltage (from contact wires, etc.) In this case (Fig. 5.15), the required starting torque value is achieved by sequentially short-circuiting the sections of the starting resistor using contactors K1-KZ.

Rice. 5.15. Rheostatic mechanical characteristics of a sequential excitation motor: /? 1to - Riao- resistance of the stages of the additional resistor in the armature circuit

The most economical way to regulate the speed of a series-excited motor is to change the supply voltage. The mechanical characteristics of the engine shift down parallel to the natural characteristic (Fig. 5.16). In form, these characteristics are similar to rheostatic mechanical characteristics (see Fig. 5.15), however, there is a fundamental difference - when regulated by changing the voltage, there are no losses in additional resistors and the regulation is smooth.

Rice. 5.1

Series-excited motors, when used as a drive for mobile units, in many cases are powered from a contact network or other power sources with a constant voltage supplied to the motor; in this case, regulation is carried out using a pulse-width voltage regulator (see § 3.4). Such a diagram is shown in Fig. 5.17.

Rice. 5.17.

Independent regulation of the excitation flux of a series-excited motor is possible if the armature winding is shunted with a resistance (Fig. 5.18a). In this case, the excitation current is = i + / w, i.e. contains a constant component that does not depend on the engine load. In this case, the engine acquires the properties of a mixed-excitation engine. Mechanical characteristics (Fig. 5.18.6) acquire greater rigidity and intersect the ordinate axis, which makes it possible to obtain a stable reduced speed at low loads on the motor shaft. A significant drawback of the circuit is the large energy losses in the shunt resistance.

Rice. 5.18.

DC motors with series excitation are characterized by two braking modes: dynamic braking And opposition.

Dynamic braking mode is possible in two cases. In the first, the armature winding is closed to resistance, and the excitation winding is powered from the network or other source through an additional resistance. The characteristics of the motor in this case are similar to the characteristics of an independent excitation motor in dynamic braking mode (see Fig. 5.9).

In the second case, the diagram of which is shown in Fig. 5.19, when the KM contacts are disconnected and the HF contacts are closed, the engine operates as a self-excited generator. When switching from the motor mode to the braking mode, it is necessary to maintain the direction of the current in the excitation winding in order to avoid demagnetization of the machine, since in this case the machine goes into self-excitation mode. The mechanical characteristics of this mode are presented in Fig. 5.20. There is a limiting speed cf, below which self-excitation of the machine does not occur.

Fig.5.19.

Rice. 5.20.

In the counter-connection mode, additional resistance is included in the armature circuit. In Fig. Figure 5.21 shows the mechanical characteristics of the engine for two back-up options. Characteristic 1 is obtained if, when the engine is running in the “forward” direction B (point With) change the direction of the current in the excitation winding and introduce additional resistance into the armature circuit. The engine goes into reverse mode (point A) with braking torque M brake

Fig.5.21.

If the drive operates in load lowering mode, when the task of the drive is to slow down the lifting mechanism when operating in the “backward” direction H, then the engine is turned on in the “forward” direction B, but with a large additional resistance in the armature circuit. The drive operation corresponds to the point b on mechanical characteristic 2. Operation in counter-switching mode is associated with large energy losses.

The dynamic characteristics of a series-excited DC motor are described by a system of equations arising from (5.22), (5.23), (5.25) upon transition to the operator form of notation:

In the block diagram (Fig. 5.22) the coefficient A= D/i) reflects the saturation curve of the machine (see Fig. 5.12). We neglect the influence of eddy currents.

Rice. 5.22.

It is quite difficult to determine the transfer functions of a sequential excitation motor analytically, therefore the analysis of transient processes is carried out by computer modeling based on the diagram shown in Fig. 5.22.

Mixed-excitation DC motors have two field windings: independent And consistent. As a result, their static and dynamic characteristics combine the characteristic properties of the two types of DC motors discussed earlier. To which type does one or another mixed excitation motor belong more depends on the ratio of the magnetizing forces created by each of the windings: v/ p.v = v / p.v i> where v' p.v is the number of turns of the winding of independent and sequential excitation .

Initial equations of a mixed excitation motor:

where in, R B ,w b - current, resistance and number of turns of the independent excitation winding; Lm- mutual inductance of the excitation windings.

Steady state equations:

From where the equation of the electromechanical characteristic can be written as:

In most cases, the series field winding is performed at 30...40% MD C, then the ideal no-load speed exceeds the rated speed of the motor by approximately 1.5 times.

Electric motors driven by direct current are used much less frequently compared to motors powered by alternating current. In domestic conditions, DC electric motors are used in children's toys, powered by conventional DC batteries. In production, DC electric motors drive various units and equipment. They are powered by powerful batteries.

Design and principle of operation

DC motors are similar in design to AC synchronous motors, with the difference being the type of current. Simple motor demonstration models used a single magnet and a frame with current passing through it. Such a device was considered as a simple example. Modern engines are highly sophisticated devices capable of developing great power.

The main winding of the motor is the armature, which is supplied with power through the commutator and brush mechanism. It rotates in a magnetic field formed by the poles of the stator (motor housing). The armature is made of several windings laid in its grooves and secured there with a special epoxy compound.

The stator may consist of field windings or permanent magnets. In low-power motors, permanent magnets are used, and in high-power motors, the stator is equipped with field windings. The stator is closed at the ends with covers with built-in bearings that serve to rotate the armature shaft. A cooling fan is attached to one end of this shaft, which creates air pressure and circulates it through the inside of the engine during operation.

The operating principle of such an engine is based on Ampere's law. When you place a wire frame in a magnetic field, it will rotate. The current passing through it creates a magnetic field around itself that interacts with the external magnetic field, which leads to rotation of the frame. In modern motor design, the role of the frame is played by an armature with windings. Current is supplied to them, as a result a current is created around the armature, which causes it to rotate.

To alternately supply current to the armature windings, special brushes made of an alloy of graphite and copper are used.

The leads of the armature windings are combined into one unit, called a collector, made in the form of a ring of lamellas attached to the armature shaft. As the shaft rotates, the brushes alternately supply power to the armature windings through the commutator lamellas. As a result, the motor shaft rotates at a uniform speed. The more windings the armature has, the more uniformly the engine will operate.

The brush assembly is the most vulnerable mechanism in the engine design. During operation, copper-graphite brushes rub against the commutator, repeating its shape, and are pressed against it with constant force. During operation, the brushes wear out, and conductive dust, which is a product of this wear, settles on the engine parts. This dust must be removed periodically. Dust removal is usually performed with air under high pressure.

Brushes require periodic movement in the grooves and blowing with air, since accumulated dust can cause them to get stuck in the guide grooves. This will cause the brushes to hang above the commutator and cause the engine to malfunction. Brushes periodically require replacement due to wear. The commutator wear also occurs where the commutator contacts the brushes. Therefore, when worn, the armature is removed and the commutator is turned on a lathe. After grooving the commutator, the insulation located between the lamellas of the commutator is ground down to a small depth so that it does not destroy the brushes, since its strength significantly exceeds the strength of the brushes.

Kinds

DC electric motors are divided according to the nature of excitation:

Independent excitation

With this type of excitation, the winding is connected to an external power source. In this case, the motor parameters are similar to a permanent magnet motor. The rotation speed is adjusted by the resistance of the armature windings. The speed is controlled by a special control rheostat connected to the excitation winding circuit. If the resistance decreases significantly or the circuit breaks, the armature current increases to dangerous values.

Electric motors with independent excitation must not be started without load or with a small load, as its speed will increase sharply and the motor will fail.

Parallel excitation

The field and rotor windings are connected in parallel to one current source. With this scheme, the field winding current is significantly lower than the rotor current. The parameters of the motors become too rigid; they can be used to drive fans and machine tools.

Engine speed control is provided by a rheostat in a series circuit with the field windings or in the rotor circuit.

Sequential excitation

In this case, the exciting winding is connected in series with the armature, as a result of which the same current passes through these windings. The rotation speed of such a motor depends on its load. The engine must not be started at idle speed without load. However, such an engine has decent starting parameters, so a similar circuit is used in heavy electric vehicles.

Mixed excitement

This scheme involves the use of two field windings located in pairs on each pole of the motor. These windings can be connected in two ways: with the summation of the fluxes, or with their subtraction. As a result, the electric motor can have the same characteristics as motors with parallel or series excitation.

To make the motor rotate in the other direction, the polarity is changed on one of the windings. To control the speed of rotation of the motor and its start, stepwise switching of different resistors is used.

Features of operation

DC electric motors are environmentally friendly and reliable. Their main difference from AC motors is the ability to adjust rotation speed over a wide range.

Such DC motors can also be used as a generator. By changing the direction of the current in the field winding or in the armature, you can change the direction of rotation of the motor. The engine shaft speed is adjusted using a variable resistor. In motors with a series excitation circuit, this resistance is located in the armature circuit and allows the rotation speed to be reduced by 2-3 times.

This option is suitable for mechanisms with long downtime, since the rheostat gets very hot during operation. An increase in speed is created by including a rheostat in the exciting winding circuit.

For motors with a parallel excitation circuit, rheostats are also used in the armature circuit to reduce the speed by half. If you connect a resistance to the excitation winding circuit, this will allow you to increase the speed up to 4 times.

The use of a rheostat is associated with the release of heat. Therefore, in modern engine designs, rheostats are replaced by electronic elements that control speed without excessive heating.

The efficiency of a DC motor is affected by its power. Weak DC motors are inefficient and have an efficiency of about 40%, while 1 MW electric motors can have an efficiency of up to 96%.

Advantages of DC motors

• Small overall dimensions.
• Easy controls.
• Simple design.
• Possibility of use as current generators.
• Fast starting, especially typical for motors with a sequential excitation circuit.
• Possibility of smooth adjustment of shaft rotation speed.

Flaws

• For connection and operation, you must purchase a special DC power supply.
• High price.
• The presence of consumables in the form of copper-graphite wear-out brushes and a wear-out commutator, which significantly reduces the service life and requires periodic maintenance.

Scope of use

DC motors have become widely popular in electric vehicles. Such engines are usually included in the following designs:

• Electric vehicles.
• Electric locomotives.
• Trams.
• Electric train.
• Trolleybuses.
• Lifting and transport mechanisms.
• Children's toys.
• Industrial equipment with the need to control rotation speed over a wide range.

DC motors are not used as often as AC motors. Below are their advantages and disadvantages.

In everyday life, DC motors are used in children's toys, since they are powered by batteries. They are used in transport: in the subway, trams and trolleybuses, and cars. In industrial enterprises, DC electric motors are used to drive units that use batteries for uninterrupted power supply.

DC Motor Design and Maintenance

The main winding of a DC motor is anchor, connected to the power source via brush apparatus. The armature rotates in the magnetic field created by stator poles (field windings). The end parts of the stator are covered with shields with bearings in which the motor armature shaft rotates. On one side, mounted on the same shaft fan cooling, driving a flow of air through the internal cavities of the engine during operation.

The brush apparatus is a vulnerable element in the engine design. The brushes are ground to the commutator in order to repeat its shape as accurately as possible, and are pressed against it with constant force. During operation, the brushes wear out, conductive dust from them settles on the stationary parts, and must be removed periodically. The brushes themselves must sometimes be moved in the grooves, otherwise they get stuck in them under the influence of the same dust and “hang” above the commutator. The characteristics of the motor also depend on the position of the brushes in space in the plane of rotation of the armature.

Over time, brushes wear out and need to be replaced. The commutator at the points of contact with the brushes also wears out. Periodically, the armature is dismantled and the commutator is turned on a lathe. After grinding, the insulation between the commutator lamellas is cut to a certain depth, since it is stronger than the commutator material and will destroy the brushes during further processing.

DC motor connection circuits

The presence of field windings is a distinctive feature of DC machines. The electrical and mechanical properties of the electric motor depend on the way they are connected to the network.

Independent excitation

The excitation winding is connected to an independent source. The characteristics of the motor are the same as those of a permanent magnet motor. The rotation speed is controlled by the resistance in the armature circuit. It is also regulated by a rheostat (adjusting resistance) in the excitation winding circuit, but if its value decreases excessively or if it breaks, the armature current increases to dangerous values. Motors with independent excitation cannot be started at idle speed or with a low load on the shaft. The rotation speed will increase sharply and the motor will be damaged.

The remaining circuits are called self-excited circuits.

Parallel excitation

The rotor and excitation windings are connected in parallel to one power source. With this connection, the current through the excitation winding is several times less than through the rotor. The characteristics of electric motors are rigid, allowing them to be used to drive machines and fans.

Regulation of the rotation speed is ensured by the inclusion of rheostats in the rotor circuit or in series with the excitation winding.

Sequential excitation

The field winding is connected in series with the armature winding, and the same current flows through them. The speed of such an engine depends on its load; it cannot be turned on at idle. But it has good starting characteristics, so a series excitation circuit is used in electrified vehicles.

Mixed excitement

With this scheme, two excitation windings are used, located in pairs on each of the poles of the electric motor. They can be connected so that their flows are either added or subtracted. As a result, the motor can have characteristics similar to a series or parallel excitation circuit.

To change the direction of rotation change the polarity of one of the excitation windings. To control the start of the electric motor and its rotation speed, stepwise switching of resistances is used.

Creating a magnetic flux to generate a torque. The inductor must include either permanent magnets or field winding. The inductor can be part of both the rotor and the stator. In the engine shown in Fig. 1, the excitation system consists of two permanent magnets and is part of the stator.

Types of commutator motors

According to the design of the stator, a commutator motor can be either.

Diagram of a permanent magnet brushed motor

The brushed direct current motor (DCM) with permanent magnets is the most common among the DCMCs. This motor includes permanent magnets that create a magnetic field in the stator. Commutator DC motors with permanent magnets (CMDC PM) are usually used in tasks that do not require high power. PM DC motors are cheaper to produce than commutator motors with field windings. In this case, the torque of the PM DC is limited by the field of the permanent magnets of the stator. Permanent magnet DCDC reacts very quickly to voltage changes. Thanks to the constant stator field, it is easy to control the motor speed. The disadvantage of a permanent magnet DC motor is that over time the magnets lose their magnetic properties, resulting in a reduced stator field and reduced motor performance.

Advantages:
• best price/quality ratio
• high torque at low speeds
• fast response to voltage changes

Flaws:
• permanent magnets lose their magnetic properties over time and under the influence of high temperatures

Commutator motor with field windings

According to the connection diagram of the stator winding, commutator electric motors with field windings are divided into motors:

Independent excitation circuit

Parallel excitation circuit

Series excitation circuit

Mixed excitation circuit

Engines independent And parallel excitation

In independently excited electric motors, the field winding is not electrically connected to the winding (figure above). Usually the excitation voltage U OB differs from the voltage in the armature circuit U. If the voltages are equal, then the excitation winding is connected in parallel with the armature winding. The use of independent or parallel excitation in an electric motor drive is determined by the electric drive circuit. The properties (characteristics) of these engines are the same.

In parallel-excitation motors, the field winding (inductor) and armature currents are independent of each other, and the total motor current is equal to the sum of the field winding current and the armature current. During normal operation, with increasing voltage supply increases the total motor current, which leads to an increase in the stator and rotor fields. As the total motor current increases, the speed also increases and the torque decreases. When the engine is loaded The armature current increases, resulting in an increase in the armature field. As the armature current increases, the inductor current (excitation winding) decreases, resulting in a decrease in the inductor field, which leads to a decrease in motor speed and an increase in torque.

Advantages:
• almost constant torque at low speeds
• good adjusting properties
• no loss of magnetism over time (since there are no permanent magnets)

Flaws:
• more expensive than KDPT PM
• the motor goes out of control if the inductor current drops to zero

A brushed parallel-excitation motor has decreasing torque at high speeds and high, but more constant torque at low speeds. The current in the inductor and armature windings does not depend on each other, thus, the total current of the electric motor is equal to the sum of the inductor and armature currents. As a result, this type of motor has excellent speed control performance. The shunt-wound brushed DC motor is typically used in applications that require power greater than 3 kW, particularly in automotive and industrial applications. Compared to, a parallel excitation motor does not lose its magnetic properties over time and is more reliable. The disadvantages of a parallel excitation motor are higher cost and the possibility of the motor going out of control if the inductor current drops to zero, which in turn can lead to motor failure.

In series-excited electric motors, the excitation winding is connected in series with the armature winding, and the excitation current is equal to the armature current (I in = I a), which gives the motors special properties. At small loads, when the armature current is less than the rated current (I a < I nom) and the magnetic system of the motor is not saturated (F ~ I a), the electromagnetic torque is proportional to the square of the current in the armature winding:

• where M – , N∙m,
• c M is a constant coefficient determined by the design parameters of the engine,
• Ф – main magnetic flux, Wb,
• I a – armature current, A.

As the load increases, the magnetic system of the motor becomes saturated and the proportionality between the current I a and the magnetic flux F is violated. With significant saturation, the magnetic flux Ф practically does not increase with increasing Ia. The graph of the dependence M=f(I a) in the initial part (when the magnetic system is not saturated) has the shape of a parabola, then upon saturation it deviates from the parabola and in the area of ​​​​heavy loads turns into a straight line.

Important: It is unacceptable to connect series-excited motors to the network in idle mode (without load on the shaft) or with a load less than 25% of the rated load, since at low loads the armature rotation frequency increases sharply, reaching values ​​at which mechanical destruction of the motor is possible, therefore in drives With sequential excitation motors, it is unacceptable to use a belt drive, if it breaks, the engine goes into idle mode. The exception is series excitation motors with a power of up to 100-200 W, which can operate in idle mode, since their power of mechanical and magnetic losses at high rotation speeds is commensurate with the rated power of the motor.

The ability of series excitation motors to develop a large electromagnetic torque provides them with good starting properties.

The series-excited brushed motor has high torque at low speeds and develops high speeds when there is no load. This electric motor is ideal for devices that need to develop high torque (cranes and winches), since the current of both the stator and rotor increases under load. Unlike parallel excitation motors, a series excitation motor does not have an accurate speed control characteristic, and in the event of a short circuit in the excitation winding, it may become uncontrollable.

A mixed excitation motor has two field windings, one of them is connected in parallel to the armature winding, and the second in series. The ratio between the magnetizing forces of the windings may be different, but usually one of the windings creates a greater magnetizing force and this winding is called the main winding, the second winding is called the auxiliary winding. The field windings can be switched on in a coordinated and counter-current manner, and accordingly the magnetic flux is created by the sum or difference of the magnetizing forces of the windings. If the windings are connected accordingly, then the speed characteristics of such a motor are located between the speed characteristics of parallel and series excitation motors. Counter-connection of windings is used when it is necessary to obtain a constant rotation speed or an increase in rotation speed with increasing load. Thus, the performance characteristics of a mixed excitation motor approach those of a parallel or series excitation motor, depending on which of the excitation windings plays the main role

Electric motors are machines that can convert electrical energy into mechanical energy. Depending on the type of current consumed, they are divided into AC and DC motors. This article will focus on the latter, which are abbreviated as DBT. DC motors surround us every day. They are equipped with battery-powered power tools, electric vehicles, some industrial machines and much more.

Design and principle of operation

The structure of a DFC is similar to an AC synchronous electric motor; the difference between them is only in the type of current consumed. The motor consists of a stationary part - a stator or inductor, a moving part - an armature and a brush-collector assembly. The inductor can be made in the form of a permanent magnet if the motor is low-power, but more often it is equipped with an excitation winding having two or more poles. The armature consists of a set of conductors (windings) fixed in grooves. The simplest model of a DFC used only one magnet and a frame through which current passed. This design can only be considered as a simplified example, while the modern design is an improved version that has a more complex structure and develops the necessary power.

The operating principle of a DPT is based on Ampere's law: if a charged wire frame is placed in a magnetic field, it will begin to rotate. The current passing through it forms its own magnetic field around itself, which, upon contact with an external magnetic field, will begin to rotate the frame. In the case of one frame, the rotation will continue until it takes a neutral position parallel to the external magnetic field. To set the system in motion, you need to add another frame. In modern DPTs, the frames are replaced by an armature with a set of conductors. Current is applied to the conductors, charging them, resulting in a magnetic field around the armature, which begins to interact with the magnetic field of the field winding. As a result of this interaction, the anchor rotates at a certain angle. Next, the current flows to the next conductors, etc.
To alternately charge the armature conductors, special brushes made of graphite or a copper-graphite alloy are used. They play the role of contacts that close the electrical circuit to the terminals of a pair of conductors. All terminals are isolated from each other and combined into a collector unit - a ring of several lamellas located on the axis of the armature shaft. During engine operation, the contact brushes alternately close the lamellas, which allows the engine to rotate evenly. The more conductors the armature has, the more uniformly the DPT will operate.

DC motors are divided into:
— electric motors with independent excitation;
— electric motors with self-excitation (parallel, series or mixed).
The DCT circuit with independent excitation provides for connecting the excitation winding and the armature to different power sources, so that they are not electrically connected to each other.
Parallel excitation is realized by parallel connection of the inductor and armature windings to one power source. These two types of engines have tough performance characteristics. Their rotational speed of the working shaft does not depend on the load, and it can be adjusted. Such motors have found application in machines with variable loads, where it is important to regulate the shaft rotation speed
With series excitation, the armature and field winding are connected in series, so the value of the electric current is the same. Such motors are “softer” in operation, have a larger speed control range, but require a constant load on the shaft, otherwise the rotation speed may reach a critical point. They have a high starting torque, which makes starting easier, but the shaft rotation speed depends on the load. They are used in electric vehicles: in cranes, electric trains and city trams.
The mixed type, in which one excitation winding is connected to the armature in parallel, and the second in series, is rare.

Brief history of creation

M. Faraday became a pioneer in the history of the creation of electric motors. He was unable to create a full-fledged working model, but it was he who made the discovery that made this possible. In 1821, he conducted an experiment using a charged wire placed in mercury in a bath containing a magnet. When interacting with a magnetic field, the metal conductor began to rotate, converting the energy of the electric current into mechanical work. Scientists of that time worked to create a machine whose operation would be based on this effect. They wanted to get an engine that worked on the piston principle, that is, so that the working shaft moved reciprocatingly.
In 1834, the first direct current electric motor was created, which was developed and created by the Russian scientist B. S. Jacobi. It was he who proposed replacing the reciprocating motion of the shaft with its rotation. In his model, two electromagnets interacted with each other, rotating a shaft. In 1839, he successfully tested a boat equipped with a DPT. The further history of this power unit is essentially an improvement of the Jacobi engine.

Features of DBT

Like other types of electric motors, DPT is reliable and environmentally friendly. Unlike AC motors, it can be adjusted in a wide range of shaft speed and frequency, and it is easy to start.
A DC motor can be used both as a motor and as a generator. It is also possible to change the direction of shaft rotation by changing the direction of the current in the armature (for all types) or in the field winding (for motors with sequential excitation).
Rotation speed control is achieved by connecting a variable resistance to the circuit. With sequential excitation, it is located in the armature circuit and makes it possible to reduce speed in ratios of 2:1 and 3:1. This option is suitable for equipment that has long periods of inactivity, because the rheostat heats up significantly during operation. An increase in speed is ensured by connecting a rheostat to the excitation winding circuit.
For shunt-wound motors, rheostats are also used in the armature circuit to reduce the speed within 50% of the nominal values. Setting the resistance in the excitation winding circuit allows you to increase the speed up to 4 times.
The use of rheostats is always associated with significant heat losses, so in modern engine models they are replaced with electronic circuits that allow speed control without significant energy losses.
The efficiency of a DC motor depends on its power. Low-power models are low-efficiency, with an efficiency of around 40%, while 1000 kW motors can have an efficiency of up to 96%.

Advantages and disadvantages of DBT

The main advantages of DC motors include:
— simplicity of design;
— ease of operation;
— the ability to regulate the shaft rotation speed;
— easy starting (especially for engines with sequential excitation);
— possibility of use as generators;
- compact dimensions.
Flaws:
- have a “weak link” - graphite brushes that wear out quickly, which limits their service life;
- high cost;
— when connecting to the network, they require current rectifiers.

Scope of application

DC motors are widely used in transport. They are installed in trams, electric trains, electric locomotives, steam locomotives, motor ships, dump trucks, cranes, etc. In addition, they are used in tools, computers, toys and moving mechanisms. They can often be found on production machines, where it is necessary to regulate the speed of the working shaft over a wide range.