Engine switching schemes for all modes. Motor control schemes

Hi all. The topic of today's article is the starting circuit of an asynchronous motor. As for me, this circuit is the simplest one that can be in electrical engineering. In this article, I have prepared two schemes for you. In the first picture there will be a circuit with a fuse to protect the control circuits, and in the second there will be no fuse. The difference between these circuits is that the fuse serves as additional element to protect the circuit from short circuit and as well as protection against spontaneous activation. For example, if you need to perform some work on the electric drive, then you disassemble the electrical circuit by turning off the machine and additionally you still need to remove the fuse and after that you can already start working.

Let's take a look at the first diagram. To enlarge the image, click on it.

Figure 1. Starting an asynchronous electric motor with a squirrel-cage rotor.

QF - any circuit breaker.

KM - electromagnetic starter or contactor. I also designated the starter coil and the starter auxiliary contact with these letters in the picture.

SB1 is the stop button

SB2 - start button

KK - any thermal relay, as well as a thermal relay contact.

FU - fuse.

KK - thermal relay, thermal relay contacts.

M - asynchronous motor.

Now we will describe the process of starting the engine.

This whole circuit can be conditionally divided into power - this is what is on the left, and into the control circuit - this is what is on the right. To start with the whole electrical circuit you need to apply voltage by turning on the QF machine. And voltage is applied to the fixed contacts of the starter and to the control circuit. Next, we press the start button SB2, during this action, voltage is applied to the starter coil and it is drawn in and voltage is also applied to the stator windings and the electric motor starts to rotate. Simultaneously with the power contacts on the starter, the KM auxiliary contacts are closed through which voltage is applied to the starter coil and the SB2 button can be released. On this, the launch process is already over, as you can see for yourself, everything is very easy and simple.

Figure 2. Starting an asynchronous motor. There is no fuse in the control circuit. To enlarge the image, click on it.

In order to stop the operation of the electric motor, just press the button SB1. By this action, we break the control circuit and the voltage supply to the starter coil stops, and the power contacts open and, as a result, the voltage on the stator windings disappears, and it stops. Stopping is as easy as starting.

That, in principle, is the whole scheme for starting an asynchronous motor. If the article helped you in some way, then share it on social media. networks, as well as subscribe to blog updates.

Sincerely, Semak Alexander!

The article considers the starting scheme of an asynchronous motor with a squirrel-cage rotor using non-reversing and reversing magnetic starters.
Squirrel-cage induction motors can be controlled using magnetic starters or contactors. When using low-power motors that do not require limitation of starting currents, the start is carried out by switching them on to the full voltage of the network. The simplest motor control circuit is shown in fig. one.

Rice. 1. Scheme of control of an asynchronous motor with a squirrel-cage rotor with a non-reversible magnetic starter
To start, the circuit breaker QF is turned on and thus the power circuit of the circuit and the control circuit are energized. When the SB1 “Start” button is pressed, the power circuit of the coil of the KM contactor is closed, as a result of which its main contacts in the power circuit are also closed, connecting the stator of the electric motor M to the mains. At the same time, the blocking contact KM is closed in the control circuit, which creates a power supply circuit for the KM coil (regardless of the position of the button contact). The motor is switched off by pressing the SB2 "Stop" button. In this case, the power supply circuit of the KM contactor is interrupted, which leads to the opening of all its contacts, the engine is disconnected from the network, after which it is necessary to turn off the QF circuit breaker.
The scheme provides the following types of protection:

From short circuits - using the QF circuit breaker and FU fuses;
from overloads of the electric motor - using thermal relays KK (opening contacts of these relays, when overloaded, open the power circuit of the KM contactor, thereby disconnecting the engine from the network);
zero protection - using the KM contactor (when the voltage drops or disappears, the KM contactor loses power, opening its contacts, and the engine is disconnected from the network).
To turn on the engine, you must again press the button SB1 "Start". If direct starting of the motor is not possible and it is necessary to limit the starting current of the asynchronous squirrel-cage motor apply undervoltage start. To do this, an active resistance or a reactor is included in the stator circuit, or a start through an autotransformer is used.

Rice. 2 Scheme of control of an asynchronous motor with a squirrel-cage rotor with a reversible magnetic starter
On fig. 2 shows the control circuit of an asynchronous motor with a squirrel-cage rotor with a reversible magnetic starter. The circuit allows direct starting of an asynchronous squirrel-cage motor, as well as changing the direction of rotation of the motor, i.e. produce a reverse. The engine is started by turning on the QF circuit breaker and pressing the SB1 button, as a result of which the KM1 contactor receives power, closes its power contacts and the motor stator is connected to the network. To reverse the engine, press the SB3 button. This will turn off the KM1 contactor, after which the SB2 button is pressed and the KM2 contactor is turned on.
Thus, the motor is connected to the network with a change in the phase sequence, which leads to a change in the direction of its rotation. The circuit uses blocking from possible erroneous simultaneous activation of contactors KM2 and KM1 using break contacts KM2, KM1. The engine is disconnected from the network by the SB2 button and the QF circuit breaker. The circuit provides for all types of motor protection, considered in the control circuit of an asynchronous motor with a non-reversible magnetic starter.

MINISTRY OF EDUCATION OF UKRAINE

SEVASTOPOL HIGHER VOCATIONAL SCHOOL № 3

Graduation Written

EXAMINATION PAPER

"Installation of the electric motor control circuit"

Group 7/8 student:

Levitsky Pavel Vladimirovich

By profession:

ship electrician.

Supervisor:

E.I. Korshunova

Sevastopol.

1. Introduction. The role of electrical engineering in the development of shipbuilding

2 Main body

2.1 Motor control circuit

2.2 The main elements of the scheme and their purpose.

2.3 The principle of operation of the electrical circuit of the fan

2.4 Wiring technology

3. Materials used for mounting the circuit

4. Tools

5. Safety

Literature

1. Introduction. The role of electrical engineering in the development of shipbuilding

Electrical engineering in shipbuilding is of great importance. This branch of science and technology associated with the production, conversion and use of electrical energy.

Shipbuilding uses electrical and magnetic phenomena. Many kilometers of electrical wiring arteries are laid on ships, numerous electric drives of ship mechanisms are mounted, modern automatic devices, navigation and radio equipment are installed and adjusted.

The reliability and durability of the launched vessel depends on the reliability of electrical devices.

In 1832, Faraday discovered the law of electromagnetic induction and thus laid the foundation for electrical engineering. The year of birth of the ship's electric drive can rightfully be considered 1838, when the Russian scientist B.S. Yakobi created the world's first rowing electrical installation. The electric motor he made direct current was installed on a small boat and tested on the Neva. The engine was powered by a galvanic battery. A very weak energy base in the first half of the 19th century hampered the development of the electric drive, and electricity was used on ships only for lighting.

The first serious work on the formation of a ship's electric drive on Russian courts were undertaken in the second half of the 19th century. So in 1886 on the cruisers "Admiral Nakhimov", "Admiral Kornilov", "Lieutenant Ilyin" electric fans were used, and in 1892 on the armored cruiser "Twelve Apostles" for the first time in world practice, an electric steering gear was installed. The use of electric motors to drive lifting devices began in 1897 with the installation of an electric winch on the Europa transport ship. In subsequent years, electrification of steering and anchor devices was carried out on the cruisers "Gromoboy", "Pallada" and others.

A real revolution in the development of ship power engineering was the work of the Russian inventor of the three-phase current M.O. Dolivo-Dobrovolsky. Created by him synchronous generators, three-phase transformer and asynchronous motors have transformed the ship power plant. Since 1908, alternating current began to be introduced on ships, which gave great technical and economic advantages. On the cruiser "Bayan" and the minelayer "Amur" were installed sump pumps driven by asynchronous motors. Built according to the project of Academician A.N. Krylov, battleships of the Sevastopol type had a three-phase current ship power plant.

Russia and Ukraine have created a huge number of ships equipped with complex systems automation with a high degree of electrification of ship mechanisms and systems. The power of generating units of ship power plants has increased significantly.

Electrical engineering is very important on ships. To ensure normal working conditions and habitability, electric lighting is necessary. Heating appliances are designed to generate heat necessary for cooking, increase the temperature of the surrounding air, liquids, individual elements prone to freezing, as well as meeting the domestic needs of passengers and crew. The safety of cargo navigation, the life of people and the safety of cargo depend on many electrical devices, for example, a steering gear, fire and drainage pumps, a radio station, navigation devices, an emergency lighting network, etc. The electrification of mechanisms serving anchor, mooring, cargo and rescue devices makes it possible to automate these labor-intensive processes.

2.Main part

2.1 Motor control circuit

The functional diagram of the control of an asynchronous motor with a squirrel-cage rotor is shown in Figure 1.

Fig. 1. Functional diagram of asynchronous motor control.

Three-phase alternating current is supplied to the circuit breaker, which is used to connect a three-phase asynchronous motor. In addition to the contact system, the circuit breaker has combined releases (thermal and electromagnetic), which ensures automatic shutdown in case of prolonged overload and short circuit. From the circuit breaker, power is supplied to the magnetic starter. Magnetic starter - a device for remote control of the engine. It starts, stops and protects the motor from overheating and severe voltage drop. The main part of the magnetic starter is a three-pole electromagnetic contactor. From the magnetic starter, control is transferred to a three-phase asynchronous AC motor. The asynchronous motor is simple in design and easy to maintain. It consists of two main parts - the stator - the fixed part and the rotor - the rotating part. The stator has grooves in which a three-phase stator winding connected to the AC mains is placed. This winding is designed to create a rotating circular magnetic field. The rotation of the circular magnetic field is provided by a phase shift relative to each other of each of the three three-phase current systems by an angle equal to 120 degrees.

The stator windings for connection to the mains voltage 220V are connected by a triangle (Fig. 8). Depending on the type of rotor winding, machines can be with a phase and squirrel-cage rotor. Despite the fact that the motor with a phase rotor has the best starting and regulating properties, the motor with a squirrel-cage rotor is simpler and more reliable in operation, and also cheaper. I chose a squirrel-cage motor because most motors in the industry today are squirrel-cage motors. The winding of the rotor is carried out as a squirrel wheel, hot aluminum is poured into the grooves of the rotor under pressure. The rotor winding conductors are connected to form a three-phase system. The motor drives the fan. Fans used on ships are distinguished depending on the pressure they create. The fan mounted in the circuit is a low pressure fan. Usually fans are not regulated or reversed, so their drive has the simplest control scheme, which is reduced to start, stop and protection.

principled circuit diagram of non-reversible control of a three-phase asynchronous electric motor with a squirrel-cage rotor by means of an automatic switch and a magnetic starter with a two-pole thermal relay is shown in Figure 2.

From the power board, power is supplied to the circuit breaker with thermal and electromagnetic overcurrent releases. The magnetic starter circuit is drawn up in compliance with the recommended conventional graphic designations for the elements of automatic motor control circuits. Here, all elements of the same apparatus are designated by the same letters.

Fig. 2. Scheme of control of an asynchronous motor with a squirrel-cage rotor winding.

So, the main closing contacts of a linear three-pole contactor located in the power circuit, its coil and auxiliary closing contacts located in the control circuit are marked with the letters KL. The heating elements of the thermal relay included in the power circuit, and the remaining break contacts with manual reset of the same relay to their original position, which are in the control circuit, are marked with the letters RT. When the three-pole switch is turned on, after pressing the start button CNP, the coil of the linear three-pole contactor KL is turned on and its main closing contacts KL connect the stator winding of the three-phase asynchronous motor AD to the supply network, as a result of which the rotor starts to rotate. At the same time, the auxiliary closing contacts of the KL are closed, shunting the start button of the KnP, which allows it to be released. Pressing the stop button KNS disconnects the power supply circuit of the CL coil, as a result of which the contactor armature drops out, the main make contacts of the CL open and the motor stator winding is disconnected from the mains.

2.2 The main elements of the circuit and their purpose

To control asynchronous electric motors, relay-contactor devices are used that implement typical starting, reverse, braking, and stopping circuits of the electric drive.
On the basis of typical relay-contactor control schemes, control schemes for electric drives of production mechanisms are developed. Starting of asynchronous motors with a small power squirrel-cage rotor is usually carried out using magnetic starters. In this case, the magnetic starter consists of an AC contactor, two electrothermal relays built into it.
The simplest control scheme for an asynchronous electric motor with a squirrel-cage rotor. The circuit uses the power supply of power circuits and control circuits from a source of the same voltage (Fig. 4.9). To improve the reliability of the operation of relay contactor devices, mostly designed for low voltage, and to improve the safety of operation, circuits with power supply of control circuits from a low voltage source are used.
If the switch S1 is turned on, then to start the electric motor, you must press the button S2 ("start"). In this case, the coil of the contactor K1M will receive power, the main contacts K1 (1-3) M in the power circuit will close and the motor stator will be connected to the network. The electric motor will start to rotate. At the same time, the make auxiliary contact K1A closes in the control circuit, bypassing the button S2 (“start”), after which this button does not need to be kept pressed, since the coil circuit of the KlM contactor remains closed. Button S2 is self-returning and returns to its original open state due to the action of the spring.

To disconnect the electric motor from the network, the button S3 (“stop”) is pressed. The coil of the contactor K1M is de-energized and the closing contacts K1(1-3)M disconnect the stator windings from the mains. At the same time, auxiliary contact K1A opens. The circuit returns to its original, normal state. The rotation of the electric motor stops.
The scheme provides protection of the motor and control circuit against short circuits by fuses F 1(1-3), protection against motor overload by two electrothermal relays F2(1-2). The spring drive of the contacts of the magnetic starter K 1 (1-3) M, K1A for opening implements the so-called zero protection, which, in the event of a power failure or a significant decrease in voltage, disconnects the motor from the mains. After the normal voltage is restored, the engine will not start spontaneously.
More precise protection against undervoltage or loss of voltage can be performed using an undervoltage relay, the coil of which is connected to two phases of the power circuit, and its normally open contact is connected in series with the contactor coil. In these schemes, instead of installing circuit breakers with fuses at the input, air automata are used.
Scheme of control of an asynchronous electric motor with a squirrel-cage rotor using a magnetic starter and an air circuit breaker. The F1 circuit breaker eliminates the possibility of a single phase break from protection operation during a single-phase short circuit, as happens when fuses are installed (Fig. 4.10). There is no need to replace the elements in the fuses when their fuse burns out.

Hello, dear visitors and guests of the site.

Today Dranitsyn Kirill Eduardovich, a student of SBEI SPO "KPK" in Chernushka, Perm Territory, sent his work to the competition "".

So, I beg your attention.

Equipment:

1. general purpose.

2. (to start, stop the engine).

3. Thermal relay TRN (for squirrel-cage rotor against overloads).

4. Start/stop button.

Work tool:

• flat screwdriver
• side cutters
• solid
• round nose pliers
• pliers
• three-phase plug

Scheme of irreversible start of an asynchronous motor with a squirrel-cage rotor

Before starting work, I would like to explain ordinary concepts for understanding the circuit:

• normally closed contact in the start / stop button under the numbers (3-4)
• normally open contact in the start/stop button under the numbers (1-2)

Algorithm (execution order) for assembling the circuit of non-reversible start-up of an asynchronous motor (IM)

1. Power circuit:

1.1. We take the extreme 2 wires (phase A and C) coming from the engine

1.2. We connect these wires to the upper contacts of the thermal relay

1.3. We connect the third wire from the engine to the magnetic starter, connecting it to pin 3 (phase B)

1.4. We connect the lower contacts of the thermal relay with a magnetic starter

1.5. We connect one lower contact of the thermal relay with contact 1 on the magnetic starter

1.6. We connect the other lower contact of the thermal relay to pin 5 on the magnetic starter

2. Control circuit:

2.1. Contact 6 on the magnetic starter is connected by a wire to the normally closed contact of the "Stop" button

Normally closed contacts on the "Stop" button under the numbers 3 and 4.

2.2. We make a jumper from the normally closed contact of the "Stop" button to the normally open contact of the "Start" button

2.3. We block the normally open contact: we connect contact 2 of the "Start" button with the auxiliary contact of the magnetic starter 13

2.4. We connect the normally open contact 1 of the "Start" button with the auxiliary contact of the magnetic starter 14

2.5. With a jumper we connect the block contact of the magnetic starter 13 with the magnetic starter coil (contact - A2)

2.6. From the magnetic starter coil (contact A1), we supply power to normally closed contacts

2.8. We connect the power cord to the contacts of the magnetic starter - 2, 4, 6

2.9. Before starting, check the circuit again!

2.10. We start the engine.

P.S. If you have questions about starting diagram of an asynchronous motor with a squirrel-cage rotor, then ask them in the comments to this article.