To start the electric motor in direct And reverse direction, a reversible control circuit is used on the magnetic starter.
At the conclusion of this article, watch a video demonstrating the detailed operation of the engine reverse starting circuit.
First, let's look at the reverse connection diagram with a 220V magnetic starter coil, and then the operation of the circuit.
Phases A, B and C of the supply voltage are supplied to the terminals of the asynchronous motor through:
— 3-pole, which protects the entire circuit and allows you to turn off the supply voltage;
— alternately through three pairs of power contacts of magnetic starters KM1 And KM2;
- thermal relay R, which serves to protect against overloads.
In order to change the direction of rotation of a three-phase electric motor, it is necessary to swap the connection of any two phases!
To do this, the motor winding circuit includes power contacts from two starters, which are connected alternately, changing the phase sequence. In our scheme, when rotating forward the sequence of phases is as follows - A, B, C. During rotation back- C, B, A. I.e. the alternation of phases A and C is reversed.
The coils of magnetic starters are connected on one side to the neutral working conductor N through a normally closed contact of a thermal relay R, on the other, through the push-button post to the phase WITH.
The push-button post consists of 3 buttons:
1) normally open button FORWARD;
2) normally open button BACK ;
3) normally closed button STOP .
To button FORWARD Normally open auxiliary contact of the starter is connected in parallel KM1, and accordingly, to the button BACK— normally open auxiliary contact of the starter KM2.
Also in the power supply circuit of the starter winding KM1 Normally closed contact of the starter is switched on KM2, and into the starter winding circuit KM2, the normally closed contact of the starter is turned on KM1. This is designed to be a lock to prevent the engine from running backwards when it is turning forwards and vice versa. Those. The engine can only be started in either direction from the stop position.
Move the three-pole lever to the on position , its contacts close, the circuit is ready for operation.
Press the button FORWARD . Magnetic starter winding power circuit KM1 closes, the coil armature retracts, closes the power contacts KM1 and auxiliary normally open contact KM1, which bypasses the button FORWARD .
Simultaneously auxiliary normally closed contact KM1 opens the magnetic starter control circuit KM2, thereby blocking the possibility of starting the engine reverse.
Three supply phases in the sequence A, B, C are supplied to the motor windings and it begins to rotate forward.
Release the button FORWARD , it returns to its original normally open state. Nowpower supply to the starter winding KM1 supplied via closed auxiliary contact KM1. The engine is running and rotating forward.
To stop the engine or start it in the other direction, you must first press the button STOP .The control circuit power is interrupted. Magnetic starter armature KM1 under the action of a spring it returns to its original state. The power contacts open, cutting off the supply voltage from the electric motor. The engine stops.
At the same time, the auxiliary contact opens KM1 in the power supply circuit of the starter winding KM1 and the auxiliary contact closes KM1 in the starter power circuit KM2.
Release the button STOP . It returns to its original, normally closed position. But since the auxiliary contact KM1 is open, power is not supplied to the KM1 starter winding, the engine remains turned off and the circuit is ready for the next start.
To start the engine in reverse direction, press the button BACK.
Power is supplied to the starter winding KM2. It is triggered by closing the power contacts KM2 in the motor power supply circuit, and an auxiliary contact KM2, which bypasses the button BACK. At the same time, another auxiliary contact KM2 breaks the starter power supply circuit KM1.
Three phases are supplied to the motor windings in the order C, B, A, and it begins to rotate in the other direction.
Release the button BACK. It returns to its original position, but power is supplied to the starter winding KM2 continues to flow through the closed auxiliary contact KM2. The motor continues to rotate in the reverse direction.
To stop, press the button again STOP. Starter winding power circuit KM2 opens. The anchor returns to its original position, opening the power contacts KM2. The engine stops. At the same time, auxiliary contacts KM2 return to their original state.
Release the button STOP, the circuit is ready for the next start.
Thermal relay operation R and purpose of the fuse F.U. I discussed it in detail in the article, so I’m omitting the description in this article. For starters with windings designed for 380V, The connection diagram will be as follows.
Almost any electric motor can be made to rotate in one direction or the other. This is often necessary, especially when designing various mechanisms, for example, systems for closing and opening gates. Typically, the motor housing indicates the factory direction of the shaft movement, which is considered straight. Torsion in the other direction in this case will be reverse.
Simply put, reverse is a change in the direction of movement of a mechanism in the opposite direction from the selected main one. The reverse circuit can be obtained in several ways:
In the first case, by switching the gear connections connecting the drive shaft to the driven shaft, the latter is rotated in the opposite direction. All gearboxes work on this principle.
The electrical method involves a direct effect on the engine itself, where electromagnetic forces take part in changing the movement of the rotor. This method benefits from the fact that it does not require the use of complex mechanical transformations.
In order to obtain electric motor reverse, it is necessary to assemble a special electrical circuit, which is called a motor reverse circuit. It will differ for different types of electrical machines and supply voltage.
It is easier to list cases when reverse is not used. Almost all mechanics are based on transmitting torque clockwise and vice versa. This may include:
The situation that an ordinary person most often encounters in practice is the need to assemble a circuit for connecting the reverse of an asynchronous AC electric motor or a DC commutator motor.
The connection diagram of an asynchronous machine in the forward direction has a certain sequence of supplying phases A, B, C to the motor contacts. It can be modified, for example, by adding a switch that would swap any two phases. In this way you can obtain a motor reverse circuit. In practical circuits, such phases are considered to be B and A.
Optional equipment:
The scheme works as follows:
In this case, it is possible to reverse the movement of the motor shaft if there is access to the terminals of its starting and operating windings. These motors have 4 outputs: two for the starting winding connected to the capacitor, two for the working one.
If there is no information about the purpose of the windings, it can be obtained by dialing. The resistance of the starting winding will always be greater than the working winding due to the smaller cross-section of the wire with which it is wound.
In a simplified version of the motor connection diagram, 220 V is supplied to the working winding, one end of the starting winding per phase or network zero (it makes no difference). The engine will begin to rotate in a certain direction. To get a reverse circuit, you need to disconnect the end of the starting winding from the contact and connect the other end of the same winding there.
To obtain a complete working circuit diagram, you need the following equipment:
The reverse and forward circuit in this case is very similar to the connection circuit for a three-phase motor, but switching here occurs not of phases, but of the starting winding in one direction or the other.
Since a three-phase asynchronous motor will lack two phases, they need to be compensated with capacitors - starting and running, to which both windings are switched. The torsion of the shaft in one direction or another depends on where to attach the third.
The diagram below shows that winding number 3 is connected through a working capacitor to a three-position toggle switch, which is responsible for the forward/reverse engine operating modes. Its other two contacts are combined with windings 2 and 1.
When turning on the engine, you must adhere to the following algorithm of actions:
DC motors are somewhat more difficult to connect than AC electric machines. The difficulty is that the designs of such devices can be different, or rather the method of exciting the winding is different. On this basis, engines are distinguished:
Regarding the first type of devices, here the armature is not connected to the stator winding; they are each powered from its own source. This achieves the enormous power of the engines used in production.
In machine tools and fans, parallel excitation motors are used, where the source energy is the same for all windings. Electric vehicles are built on the basis of series excitation of windings. Mixed excitement is less common.
In all types of engine designs described, it is possible to start the rotor in the opposite direction from the main stroke, that is, in reverse:
When directly starting powerful three-phase electric motors using a reverse control circuit, voltage drops occur in the network. This is due to the large inrush currents flowing at this moment. To reduce the current value, use a gradual start of the motor according to the star-delta circuit.
The bottom line is that the beginning and end of each stator winding are led out into a terminal box. The circuit is controlled by three contactors. They gradually turn on the windings in a star, and then, when the engine accelerates, they bring the system to operating condition when connected in a delta.
More complex device. In fact, it consists of two conventional direct starters, the latter combined in one housing. The internal circuitry of the reversing device is characterized by the fact that it is impossible to run two modes at the same time - direct and reverse. This process is controlled by a blocking circuit, which can be electrical or mechanical.
It must be remembered that only qualified specialists who are authorized to work with high-voltage equipment are allowed to connect three-phase motors to a 380V network. Homemade electrical circuits can cause electrical injuries!
The direction of rotation of the motor shaft sometimes needs to be changed. This requires a reverse connection diagram. Its type depends on what kind of motor you have: direct or alternating current, 220V or 380V. And the reverse of a three-phase motor connected to a single-phase network is arranged in a completely different way.
To reversibly connect a three-phase asynchronous electric motor, we will take as a basis the circuit diagram for connecting it without reversing:
This scheme allows the shaft to rotate only in one direction - forward. To make it turn into another, you need to swap places of any two phases. But in electrics it is customary to change only A and B, despite the fact that changing A to C and B to C would lead to the same result. Schematically it will look like this:
To connect you will additionally need:
Important! In electrical engineering, a normally closed contact is a state of a push-button contact that has only two unbalanced states. The first position (normal) is working (closed), and the second is passive (open). The concept of a normally open contact is formulated in the same way. In the first position the button is passive, and in the second it is active. It is clear that such a button will be called “STOP”, while the other two are “FORWARD” and “BACK”.
The reverse connection scheme differs little from the simple one. Its main difference is the electric locking. It is necessary to prevent the motor from starting in two directions at once, which would lead to breakdown. Structurally, the interlock is a block with magnetic starter terminals that are connected in the control circuit.
To start the engine:
If you need to change direction, you must first press the “STOP” button. Then turn on another start button. An electrical lock prevents it from being activated unless the motor is switched off.
Reversing a 220V electric motor is only possible if the winding terminals are located outside the housing. The figure below shows a single-phase switching circuit, when the starting and working windings are located inside and have no outputs to the outside. If this is your option, you will not be able to change the direction of rotation of the shaft.
In any other case, to reverse a single-phase capacitor IM, it is necessary to change the direction of the working winding. For this you will need:
The circuit of a single-phase unit is almost no different from that presented for a three-phase asynchronous motor. Previously, we switched phases: A and B. Now, when changing direction, instead of a phase wire, a neutral wire will be connected on one side of the working winding, and on the other, a phase wire will be connected instead of a zero wire. And vice versa.
For a 220V power supply, it is necessary to use one or two capacitors to compensate for the missing phase: operating and starting. The direction of rotational movement depends on what the third winding is connected to.
To force the shaft to rotate in the other direction, winding No. 3 must be connected using a capacitor to a toggle switch with two positions. It should have two contacts connected to windings No. 1 and No. 2. Below is a detailed diagram.
Such a motor will play the role of a single-phase motor, since the connection was made using one phase wire. To start it, you need to move the reversing toggle switch to the desired position (“forward” or “backward”), then move the “start” toggle switch to the “on” position. At the moment of startup, you must press the button of the same name - “start”. You need to hold it for no more than three seconds. This will be enough for overclocking.
DC motors are more difficult to connect than motors powered by AC power. Because in order to connect the windings, you need to know exactly what brand your unit is. Only then can you find a suitable scheme.
But in any DC electric motor there is an armature and an excitation winding. Based on the method of their inclusion, they are divided into units:
Independently excited DC motors (shown schematically below) are used in production. Their winding has nothing to do with the armature, because it is connected to another electrical source.
Three-phase electric motors are widely used in many facilities. Due to specific operating conditions, quite often there is a need to change the direction of rotation of the shaft of a particular unit. For these purposes, the standard three-phase motor reverse circuit is best suited, used to open and close garage doors, ensure the operation of elevators, forklifts, overhead cranes and other equipment.
Various types of three-phase asynchronous electric motors are widely used in industry and agriculture. They are installed in electric drives of equipment and serve as an integral part of automatic devices. Three-phase units have gained popularity due to their high reliability, simple maintenance and repair, and the ability to operate directly from the AC mains.
The specific operation of devices operating with electric motors requires a change in the direction of shaft rotation, called reverse. For such situations, special circuits have been developed, which include additional electrical devices. First of all, this is an input machine that has the appropriate parameters, contactors (2 pcs.), a thermal relay and controls in the form of three buttons combined into a common push-button station.
In order for the shaft to start rotating in the opposite direction, it is necessary to change the phase arrangement of the supplied voltage. Constant monitoring of the voltage supplied to the electric motor and contactor coils is necessary. The direct implementation of reverse in a three-phase motor is carried out by contactors (CM) No. 1 and No. 2. When contactor No. 1 is activated, the phases of the incoming voltage will be located differently than when contactor No. 2 is activated.
To control the coils of both contactors, three buttons are provided - FORWARD, BACK and STOP. They provide power to the coils depending on the phase arrangement. The order in which the contactors are turned on affects the closure of the electrical circuit in such a way that the rotation of the motor shaft in each case occurs strictly in a certain direction. The BACK button only needs to be pressed, but not held, since it itself turns out to be in the desired position under the action of self-retaining.
All three buttons are locked to prevent them from being activated at the same time. Failure to comply with this condition may result in a short circuit in the electrical circuit and equipment failure. To block the buttons, a special contact block located in the corresponding contactor is used.
Each system that provides reverse of a three-phase electric motor has specific push-button contacts combined into a common push-button post. The operation of this system is closely related to the functioning of the remaining elements of the circuit.
Everyone knows that the contactor is turned on using a control pulse received after pressing the start button. This button primarily supplies voltage to the control coil.
The on state is maintained and maintained thanks to the self-retaining principle. It consists of connecting in parallel (bypassing) an auxiliary contact to the start button, which supplies voltage to the coil. In this regard, it is no longer necessary to hold the START button pressed. Thus, the magnetic starter can turn off only after the control coil circuit is broken, so the circuit requires a button with a break contact. In this regard, control buttons combined into a push-button station are equipped with two pairs of contacts - normally open (NO) and normally closed (NC).
All buttons are made in a universal version in order to ensure instant reverse of the engine if an urgent need arises. The shutdown button, in accordance with generally accepted standards, is called STOP and is marked in red. The power button is known as the start or start button, so it is referred to variously as START, FORWARD, or REVERSE.
In some cases, a push-button post can be used in a non-reversible electric motor operation scheme, when its shaft rotates in only one direction. The start is made by the start button, and the stop will occur after a certain period of time after pressing the STOP button, when the shaft overcomes the inertia. Connecting such a circuit can be done in two ways, using control coils for 220 and 380 volts.
In all cases, before connecting the push-button post, a diagram of its installation is drawn up. First of all, the contactor is connected when there is no voltage on the input cable. For direct control, voltage can be removed from any phase that is most convenient for use. The conductor connected to the STOP button is connected together with the phase wire to the corresponding terminal of the contactor. To avoid confusion, normally open contacts are marked with numbers 1 and 2, and normally closed contacts with numbers 3 and 4.
Upon completion of installation, a jumper is installed in the button post, then a wire is connected connecting terminal 1 of the START button and the output of the contactor control coil.
Quite often, three-phase electric motors are used in domestic conditions and are connected to a single-phase network. For such cases, a reversible circuit for connecting an electric motor in a single-phase network is provided. The principle of operation of such a circuit is very simple: to perform reverse, capacitors are used, the power of which is switched between the poles of the supply voltage. The circuit is controlled by a button.
Since the supply voltage is 220 V, the motor windings will be connected as a star, and three terminals will be connected to the terminal block. On the control button, a jumper is installed between the terminals, after which the capacitor output is connected to one of them. The second terminal of the capacitor is connected to the winding of the electric motor, which is not connected to the network.
The switch is then connected to the motor, then the supply voltage is applied. The finished system needs to be turned on and the reverse operation checked.
IMPORTANT! Before connecting the electric motor, you must ensure that it is correct in accordance with its specifications.
(hereinafter referred to as the starter) is a switching device designed to start and stop the engine. The starter is controlled through an electric coil, which acts as an electromagnet; when voltage is applied to the coil, it acts with an electromagnetic field on the movable contacts of the starter, which close and turn on the electrical circuit, and vice versa, when the voltage is removed from the starter coil, the electromagnetic field disappears and the starter contacts are under the action of the spring returns to its original position, breaking the circuit.
The magnetic starter has power contacts designed for switching circuits under load and block contacts which are used in control circuits.
Contacts are divided into normally open- contacts that are in their normal position, i.e. before applying voltage to the coil of the magnetic starter or before mechanical impact on them, are in an open state and normally closed- which in their normal position are in a closed state.
The new magnetic starters have three power contacts and one normally open block contact. If it is necessary to have a larger number of block contacts (for example, during assembly), an attachment with additional block contacts (contact block) is additionally installed on the magnetic starter on top, which, as a rule, has four additional block contacts (for example, two normally closed and two normally open).
Buttons for controlling an electric motor are included in push-button stations; push-button stations can be one-button, two-button, three-button, etc.
Each button of the push-button post has two contacts - one of them is normally open, and the second is normally closed, i.e. Each of the buttons can be used both as a “Start” button and as a “Stop” button.
This diagram is the simplest diagram for connecting an electric motor; it does not have a control circuit, and the electric motor is turned on and off by an automatic switch.
The main advantages of this scheme are its low cost and ease of assembly, but the disadvantages of this scheme include the fact that circuit breakers are not intended for frequent switching of circuits; this, in combination with inrush currents, leads to a significant reduction in the service life of the machine; in addition, this scheme does not include Possibility of additional motor protection.
This scheme is also often called simple motor starting circuit, in it, unlike the previous one, in addition to the power circuit, a control circuit also appears.
When you press the SB-2 button (the “START” button), voltage is applied to the coil of the magnetic starter KM-1, while the starter closes its power contacts KM-1 starting the electric motor, and also closes its block contact KM-1.1 when the button is released SB-2 its contact opens again, but the coil of the magnetic starter is not de-energized, because its power will now be provided through the KM-1.1 block contact (i.e. the KM-1.1 block contact bypasses the SB-2 button). Pressing the SB-1 button (the “STOP” button) leads to a break in the control circuit, de-energizing the magnetic starter coil, which leads to the opening of the magnetic starter contacts and, as a result, to stopping the electric motor.
To change the direction of rotation of a three-phase electric motor, you need to swap any two phases supplying it:
If it is necessary to frequently change the direction of rotation of the electric motor, the following is used:
This circuit uses two magnetic starters (KM-1, KM-2) and a three-button post; the magnetic switches used in this circuit, in addition to a normally open block contact, must also have a normally closed contact.
When you press the SB-2 button (START 1 button), voltage is applied to the coil of the magnetic starter KM-1, while the starter closes its power contacts KM-1 starting the electric motor, and also closes its block contact KM-1.1 which bypasses the button SB-2 and opens its block contact KM-1.2 which protects the electric motor from turning on in the opposite direction (when the SB-3 button is pressed) until it stops first, because An attempt to start the electric motor in the opposite direction without first disconnecting the KM-1 starter will result in a short circuit. To start the electric motor in the opposite direction, you need to press the “STOP” button (SB-1), and then the “START 2” button (SB-3), which will power the coil of the KM-2 magnetic starter and start the electric motor in the opposite direction.
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