During the birth of electrical engineering, 3-phase electric motors were switched on manually using conventional switches. The switches did not create safe conditions; it was necessary to connect the control panel with power lines. As switching processes progressed further, scientists invented devices such as magnetic starters that did not have the disadvantages of a switch. This switching device provides remote connection of the load consumer and makes it possible to control the operation of the equipment.
The design of the starter is simple, as is its operating principle. The starter consists of two types of contacts: fixed and moving. When these contacts are closed, the electric motor starts, and when the contacts are disconnected, the power stops and turns off.
Varieties
Magnetic starters are designed mainly to control the operation of 3-phase electric motors at a remote level. The main operations carried out using magnetic starters are starting, shutting down or reversing.
An auxiliary function of the starter, together with a thermal relay, is to protect the electric motor from excessive loads. There are starter circuits with voltage limiters based on semiconductor elements. According to the connection diagrams, loads can be reversible or non-reversible.
According to the type of location, magnetic starters are classified:
- Open type. Placed in protected cabinets, panels, and other places inaccessible to moisture, dust and other harmful factors.
- Secure execution . Installed in rooms with a low dust content in the air, preventing access of water to the device.
- Waterproof design . They are mounted inside buildings, outside under equipped canopies from water and sun.
Auxiliary classification:
- Block with buttons on the starter body. Starters without reverse have two buttons: Start and Stop, devices with reverse are equipped with three buttons, two of them are the same as in the previous version, a Start back button has been added. Some versions of the devices include a lamp indicating switching on.
- Devices with auxiliary contacts for signals and interlocks. They are used in various combinations, as closing or disconnecting. Contacts can be built-in or mounted on a separate stand. Sometimes auxiliary contacts are used as part of the overall starter circuit. In devices with reverse, electrical interlocking is performed using additional contacts.
- The value of voltage and current of the power winding.
- Thermal relay. Its property is the nominal current at which the relay does not operate at medium settings. This current value can be adjusted within certain limits from the rated current value.
Some magnetic starters are equipped with voltage limiters and other interlocks.
Design features
The entire starter device is divided into two halves: upper and lower. In the upper half there are moving contacts along with an arc extinguishing chamber. The moving part of the magnet is also located there. It acts on power contacts.
The coil is located at the bottom along with the return spring. The property of the return spring is to return the upper half to its original state after turning off the power to the winding. This is how the power contacts are disconnected.
The device of the two halves of the electromagnet includes W-shaped plates. They are made of electromagnetic steel. The coil uses copper wire with a calculated number of turns, which are designed to operate with a supply voltage of certain values, ranging from 24 volts to 380 volts. When voltage is applied to the winding, a magnetic field is formed. The two halves try to connect, forming a closed circuit. When the voltage is turned off, the magnetic field also disappears, the upper half moves back to its original place under the action of a spring.
Operating principle
The name of the device speaks about its method of operation. It operates on the principle of an electromagnet when current passes through a coil. After the contacts are attracted, the electric motor starts.
1 - Movable contacts
2 - Movable anchor
3 - Springs
4 - Coil
5 - Stationary core
6 - Movable core
7 - Stationary contacts
The general device consists of a main part and an armature, which moves along guides. It’s easier to say that all magnetic starters are made in the form of a large button with terminals for power contacts and fixed contacts.
The moving part has a bridge with contacts, which breaks the circuit in two places to turn off the voltage. The bridge also serves for high-quality connection of wires when connecting the circuit to action. The system is checked manually. Press on the armature and feel the force of the springs, which is overcome by the electromagnet during operation. When the armature is released, the contacts return.
Such management is not required in work; it is needed for control. In reality, a remote form of connection is used by an electromagnetic field that arises in the winding from an electric current. The laminated magnetic core ensures good current conductivity.
When there is no electric current in the circuit, the magnetic field around the winding disappears, which leads to the armature moving back to its original position. When voltage is applied, the reverse process occurs. The operating engaged position of the armature affects the functioning of the device. In this position there should be a high-quality connection of contacts. At the slightest weakening of the springs, the contacts begin to burn, heat up, and the ends of the wires burn out.
Installation and connection
To ensure high-quality operation of the starters, they are installed on a flat, stationary surface, vertically. Devices with a thermal relay must be installed so that there is no temperature difference with the external environment.
Incorrect installation results in false alarms. Therefore, magnetic starters should not be installed in places with vibration and shock. Devices rated over 150 amps will vibrate and shake violently when starting up.
The thermal relay housing may become hot from other devices. This negatively affects the correct operation of the starter. Therefore, it is not recommended to place starters near hot equipment.
When connecting the wire to the contactor of the starter, its end is bent in the form of a ring. This prevents the spring washers from becoming distorted in the clamp. When connecting two wires with the same cross-section, they are placed on two opposite sides of the screw.
Before installation, the ends of the wires are tinned. In stranded wires, the ends are twisted before tinning. The ends of aluminum wires are cleaned with a file and coated with a special paste. Moving contacts and parts of the starter must not be lubricated. Before starting, magnetic starters are inspected from the outside and the serviceability of parts is checked. Moving parts should move easily by hand. The connection diagram is checked.
Maintenance
To properly care for your starter, you need to know the possible signs of device failure. Usually this is a high temperature of the case, a strong hum.
The high temperature of the device is most often associated with a short circuit of the winding between the turns. When inspecting the coil, there should be no cracks, soot, damage, or melting. In such cases, the coil needs to be replaced. Excessive heating occurs due to an increase in supply voltage above the nominal value, during overload, poor quality of contacts, and their severe wear. A strong starter hum can occur for several reasons. Most often you need to check the tightness of the anchor. Leaks may occur due to surface contamination. Another reason may be insufficient network voltage, a decrease in voltage of more than 15 percent, as well as jamming of moving elements.
To prevent such damage, constant care is required. In general, magnetic starters do not require expensive work. Dirt, moisture and dust must not be allowed inside. It is necessary to regularly monitor the tightness and quality of contacts. Compile a list of maintenance and repair work by electrician repairmen.
Service program
- External inspection for damage, chips of the body, removal of dirt. Chips and damage appear from prolonged vibration, improper installation, and defects. If the housing is damaged so much that it prevents it from being fixed to the surface, then the housing must be replaced. Particular attention is paid to checking the presence of all springs and contacts.
- Inspection of mechanical parts. The spring is tested to break the contacts. It should not be soft or too compressed. When checking the armature stroke, jamming is not allowed. Progress control is carried out by hand.
- Cleaning contacts - this activity should not be carried out if the magnetic starter is working properly. A layer with good conductivity on the contacts is very thin. Each time you clean with a file, the contacts will soon wear off. Cleaning is allowed only when carbon deposits appear. When closing the contacts there should be a tight fit, without tilting or displacement. Otherwise, adjustment is needed.
- If there are metal parts in the starter housing, then you need to check that they are not connected to the power contacts. It is also necessary to test all power contacts to ensure there are no short circuits. To do this, use a tester. The insulation resistance should not be less than 0.5 Mohm.
A magnetic starter, or electromagnetic contactor, is a switching device that switches powerful flows of direct and alternating current. Its role is to systematically turn on and off sources of electricity.
Purpose and device
Magnetic starters are built into electrical circuits for remote starting, stopping and providing protection for electrical equipment and electric motors. The operation is based on the use of the principle of electromagnetic induction.
The basis of the design is a thermal relay and a contactor combined into one device. Such a device can also operate in a three-phase network.
Such devices are gradually being replaced from the market by contactors. In terms of their design and technical characteristics, they are no different from starters, and they can only be distinguished by their name.
They differ from each other in the supply voltage of the magnetic coil. It comes in 24, 36, 42, 110, 220, 380 W AC. The devices are produced with a coil for direct current. Their use in an alternating current network is also possible, for which a rectifier is needed.
The starter design is usually divided into upper and lower parts. In the upper part there is a movable contact system combined with an arc extinguishing chamber. Also located here is the moving part of the electromagnet, mechanically connected to the power contacts. All this makes up a moving contact circuit.
At the bottom there is a coil, the second half of the electromagnet and a return spring. The return spring returns the upper half to its original state after de-energizing the coil. This is how the starter contacts break.
Contactors are:
- Normally closed. The contacts are closed and power is supplied constantly; shutdown occurs only after the starter is triggered.
- Normally open. The contacts are closed and power is supplied while the starter is running.
The second option is the most common.
Principle of operation
The principle of operation of a magnetic starter is based on the phenomenon of electromagnetic induction. If no current passes through the coil, then there is no magnetic field in it. This causes the spring to mechanically push away the moving contacts. As soon as the power to the coil is restored, magnetic fluxes appear in it, compressing the spring and attracting the armature to the stationary part of the magnetic circuit.
Since the starter operates only under the influence of electromagnetic induction, the contacts open during power outages and when the network voltage drops by more than 60% of the nominal value. When the voltage is restored again, the contactor does not turn on on its own. To activate it, you will need to press the “Start” button.
If it is necessary to change the direction of rotation of an asynchronous motor, reversing devices are used. Reverse occurs thanks to 2 contactors, activated in turn. When the contactors are turned on simultaneously, a short circuit occurs. To eliminate such situations, the design includes a special lock.
Varieties and types
Starters manufactured according to Russian standards are divided into 7 groups depending on the rated load. The zero group can withstand a load of 6.3 A, the seventh group - 160 A.
This must be remembered when choosing magnetic starters.
The classification of foreign analogues may differ from that accepted in Russia.
It is necessary to be guided by the type of execution:
- Open. Suitable for installation in closed cabinets or places isolated from dust.
- Closed. Installed separately, in dust-free rooms.
- Dust-splashproof. Can be installed anywhere, including outdoors. The main condition is the installation of a canopy that protects from sunlight and rain.
By type, the electromagnetic starter can be selected according to the following parameters:
- Standard versions in which voltage is supplied to the starter with further attraction of the core and activation of the contacts. In this case, depending on whether the starter is normally closed or normally open, the electrical equipment is turned on or off.
- Reversible modifications. This device is a reverse with electromagnets. This design eliminates the possibility of turning on 2 devices at the same time.
The marking of the magnetic starter encodes its technical characteristics. The designation is located on the body and may contain the following meanings:
- Device series.
- Rated current, the designation of which is written in a range of values.
- The presence and design of a thermal relay. There are 7 degrees.
- Degree of protection and control buttons. There are 6 positions in total.
- Availability of additional contacts and their types.
- Compliance of fastenings with standard mounting frames.
- Climate compliance.
- Accommodation options
- Wear resistance.
There are several options for installing magnetic contactors in control systems, starting with the simplest control of electric motors and ending with installation with holding the contact button, or reverse.
Connection diagram for 220 V
Any electrical connection diagram contains 2 circuits, including for a single-phase network. The first is the power one, through which power is supplied. The second is a signal one. It helps control the operation of the device.
The connected contactor, thermal relay and control buttons form a single device, which is marked as a magnetic starter in the diagram. It ensures the proper functioning and safety of electric motors under various operating conditions.
Contacts for connecting the device's power are located in the upper part of the case. They are designated A1 and A2. So, for a 220 V coil, 220 V voltage is supplied. The order in which “zero” and “phase” are connected does not matter.
On the bottom of the case there are several contacts marked L1, L2, L3. The power supply for the load is connected to them. Whether it is constant or variable does not matter, the main thing is the limitation of 220 V. The voltage is removed from contacts T1, T2, T3.
Connection diagram for 380 V
The standard circuit is used in cases where it is necessary to start the engine. Control is carried out using the “Start” and “Stop” buttons. Instead of a motor, any load can be connected through magnetic starters.
In the case of power supply from a three-phase network, the power section includes:
- Three-pole circuit breaker.
- Three pairs of power contacts.
- Three-phase asynchronous electric motor.
The control circuit is powered from the first phase. It also includes the “Start” and “Stop” buttons, a coil and an auxiliary contact connected in parallel to the “Start” button.
When you press the “Start” button, the first phase hits the coil. After this, the starter is triggered and all contacts are closed. The voltage passes to the lower power contacts and is supplied to the electric motor through them.
The circuit may differ depending on the nominal voltage of the coil and the voltage of the supply network used.
Connection via push-button post
The circuit connecting magnetic starters through a push-button post requires the use of an analog adapter. Contact blocks come with 3 or 4 outputs. When connecting, it is necessary to determine the direction of the cathode. Then the contacts are connected through the switch. To do this, use a two-channel trigger.
If you connect a device with automatic switches, then an electronic regulator is used for them. The blocks may be located on the controller. The most common devices are those with broadband connectors.
Before we begin the practical connection of the starter, let us recall a useful theory: the contactor of the magnetic starter is turned on by a control pulse emanating from pressing the start button, which supplies voltage to the control coil. Keeping the contactor in the on state occurs according to the self-retaining principle - when an additional contact is connected in parallel with the start button, thereby supplying voltage to the coil, as a result of which there is no need to hold the start button pressed.
Disabling the magnetic starter in this case is possible only if the control coil circuit is broken, which makes it obvious that it is necessary to use a button with a break contact. Therefore, the starter control buttons, which are called push-button posts, have two pairs of contacts - normally open (open, normally closed, NO, NO) and normally closed (closed, normally closed, NC, NC)
This universalization of all the buttons of the push-button station was made in order to anticipate possible schemes for providing instant engine reverse. It is generally accepted to call the shutdown button the word: “ Stop"and mark it in red. The switching button is often called the start button, start button, or is designated by the word “ Start», « Forward», « Back».
If the coil is designed to operate from 220 V, then the control circuit switches the neutral. If the operating voltage of the electromagnetic coil is 380 V, then a current flows in the control circuit, “removed” from the other supply terminal of the starter.
Connection diagram for a 220 V magnetic starter
Here, the current is supplied to the magnetic coil KM 1 through a thermal relay and terminals connected in a chain of buttons SB2 for turning on - “start” and SB1 for stopping - “stop”. When we press “start”, electric current flows to the coil. At the same time, the starter core attracts the armature, resulting in the closure of the moving power contacts, after which voltage is supplied to the load. When the “start” is released, the circuit does not open, since the KM1 block contact with closed magnetic contacts is connected parallel to this button. Thanks to this, phase voltage L3 is supplied to the coil. When you press “stop,” the power is turned off, the moving contacts return to their original position, which leads to de-energization of the load. The same processes occur when the thermal relay P operates - a break in the zero N supplying the coil is ensured.
Connection diagram for a 380 V magnetic starter
Connecting to 380 V is practically no different from the first option, the only difference is in the supply voltage of the magnetic coil. In this case, power is provided using two phases L2 and L3, whereas in the first case - L3 and zero.
The diagram shows that the starter coil (5) is powered from phases L1 and L2 at a voltage of 380 V. Phase L1 is connected directly to it, and phase L2 is connected through button 2 “stop”, button 6 “start” and button 4 of the thermal relay, connected in series to each other. The principle of operation of such a circuit is as follows: After pressing the “start” button 6, through the switched on button 4 of the thermal relay, the voltage of phase L2 reaches the coil of the magnetic starter 5. The core is retracted, closing the contact group 7 to a certain load (electric motor M), and current is supplied, voltage 380 V. If the “start” is turned off, the circuit is not interrupted, the current passes through contact 3 - a movable block that closes when the core is retracted.
In the event of an accident, thermal relay 1 must be activated, its contact 4 is broken, the coil is turned off and the return springs bring the core to its original position. The contact group opens, relieving the voltage from the emergency area.
Connecting a magnetic starter via a push-button post
This circuit includes additional start and stop buttons. Both “Stop” buttons are connected in the control circuit in series, and the “Start” buttons are connected in parallel. This connection allows switching with buttons from any position.
Here's another option. The circuit consists of a two-button post “Start” and “Stop” with two pairs of contacts, normally closed and open. Magnetic starter with a control coil for 220 V. The power supply for the buttons is taken from the terminal of the power contacts of the starter, number 1. The voltage approaches the “Stop” button, number 2. It passes through a normally closed contact, along the jumper to the “Start” button, number 3.
We press the “Start” button, the normally open contact number 4 closes. The voltage reaches the target, number 5, the coil is triggered, the core is retracted under the influence of the electromagnet and sets in motion the power and auxiliary contacts highlighted in dotted lines.
The auxiliary block contact 6 bypasses the contact of the “start” button 4, so that when the “Start” button is released, the starter does not turn off. The starter is turned off by pressing the “Stop” button, number 7, the voltage is removed from the control coil and the starter is turned off under the influence of the return springs.
Connecting the motor via starters
Irreversible magnetic starter
If it is not necessary to change the direction of rotation of the engine, then the control circuit uses two non-fixed spring-loaded buttons: one in the normal position is open - “Start”, the other is closed - “Stop”. As a rule, they are manufactured in a single dielectric housing, and one of them is red. Such buttons usually have two pairs of contact groups - one normally open, the other closed. Their type is determined during installation work visually or using a measuring device.
The control circuit wire is connected to the first terminal of the closed contacts of the Stop button. Two wires are connected to the second terminal of this button: one goes to any of the closest open contacts of the “Start” button, the second is connected to the control contact on the magnetic starter, which is open when the coil is disconnected. This open contact is connected by a short wire to the controlled terminal of the coil.
The second wire from the “Start” button is connected directly to the terminal of the retractor coil. Thus, two wires must be connected to the controlled “pull-in” terminal - “direct” and “blocking”.
At the same time, the control contact closes and, thanks to the closed Stop button, the control action on the retractor coil is fixed. When the Start button is released, the magnetic starter remains closed. Opening the contacts of the “Stop” button causes the electromagnetic coil to be disconnected from the phase or neutral and the electric motor is turned off.
Reversing magnetic starter
To reverse the motor, two magnetic starters and three control buttons are required. Magnetic starters are installed next to each other. For greater clarity, let’s conditionally mark their supply terminals as 1-3-5, and those to which the motor is connected as 2-4-6.
For a reversible control circuit, the starters are connected as follows: terminals 1, 3 and 5 with the corresponding numbers of the adjacent starter. And the “output” contacts are crosswise: 2 from 6, 4 from 4, 6 from 2. The wire feeding the electric motor is connected to three terminals 2, 4, 6 of any starter.
With a cross connection scheme, simultaneous operation of both starters will result in a short circuit. Therefore, the conductor of the “blocking” circuit of each starter must first pass through the closed control contact of the adjacent one, and then through the open one of its own. Then turning on the second starter will cause the first one to turn off and vice versa.
Not two, but three wires are connected to the second terminal of the closed “Stop” button: two “blocking” and one supplying the “Start” button, connected in parallel to each other. With this connection scheme, the “Stop” button turns off any of the connected starters and stops the electric motor.
- Before assembling the circuit, you need to free the working area from the current and check that there is no voltage with a tester.
- Set the core voltage designation which is mentioned on it and not on the starter. It can be 220 or 380 volts. If it is 220 V, phase and zero go to the coil. Voltage marked 380 means different phases. This is an important aspect, because if connected incorrectly, the core may burn out or will not fully start the necessary contactors.
- Starter button (red) You need to take one red “Stop” button with closed contacts and one black or green button with the inscription “Start” with invariably open contacts.
- Please note that power contactors only force or stop the phases, and the zeros that come and go, conductors with grounding are always combined at the terminal block, bypassing the starter. To connect a 220 Volt core to the addition, 0 is taken from the terminal block into the design of the starter organization.
To supply power to motors or any other devices, contactors or magnetic starters are used. Devices designed to be powered on and off frequently. The connection diagram for a magnetic starter for a single-phase and three-phase network will be discussed further.
Contactors and starters - what's the difference?
Both contactors and starters are designed to close/open contacts in electrical circuits, usually power ones. Both devices are assembled on the basis of an electromagnet and can operate in DC and AC circuits of different powers - from 10 V to 440 V DC and up to 600 V AC. Have:
- a certain number of working (power) contacts through which voltage is supplied to the connected load;
- a number of auxiliary contacts - for organizing signal circuits.
So what's the difference? What is the difference between contactors and starters? First of all, they differ in the degree of protection. Contactors have powerful arc extinguishing chambers. This leads to two other differences: due to the presence of arc arresters, contactors are large in size and weight, and are also used in circuits with high currents. For low currents - up to 10 A - only starters are produced. By the way, they are not produced for high currents.
There is one more design feature: the starters are produced in a plastic case, with only the contact pads exposed outside. Contactors, in most cases, do not have a housing, therefore they must be installed in protective housings or boxes that will protect against accidental contact with live parts, as well as from rain and dust.
In addition, there is some difference in purpose. The starters are designed to start asynchronous three-phase motors. Therefore, they have three pairs of power contacts - for connecting three phases, and one auxiliary one, through which power continues to flow to operate the engine after the “start” button is released. But since a similar operating algorithm is suitable for many devices, a wide variety of devices are connected through them - lighting circuits, various devices and instruments.
Apparently because the “filling” and functions of both devices are almost the same, in many price lists the starters are called “small contactors”.
Design and principle of operation
To better understand the connection diagrams of a magnetic starter, you need to understand its structure and operating principle.
The base of the starter is a magnetic circuit and an inductor. The magnetic core consists of two parts - movable and stationary. They are made in the form of the letters “Ш” with their “legs” facing each other.
The lower part is fixed to the body and is stationary, the upper part is spring-loaded and can move freely. A coil is installed in the slot in the lower part of the magnetic circuit. Depending on how the coil is wound, the rating of the contactor changes. There are coils for 12 V, 24 V, 110 V, 220 V and 380 V. On the top of the magnetic circuit there are two groups of contacts - movable and fixed.
In the absence of power, the springs press out the upper part of the magnetic circuit, the contacts are in their original state. When voltage appears (press the start button, for example), the coil generates an electromagnetic field that attracts the upper part of the core. In this case, the contacts change their position (picture on the right).
When the voltage drops, the electromagnetic field also disappears, the springs push the moving part of the magnetic circuit up, and the contacts return to their original state. This is the operating principle of an electromagnetic starter: when voltage is applied, the contacts close, and when voltage is lost, they open. Any voltage can be applied to the contacts and connected to them - either constant or alternating. It is important that its parameters are not greater than those declared by the manufacturer.
There is one more nuance: the starter contacts can be of two types: normally closed and normally open. Their operating principle is clear from the names. Normally closed contacts are switched off when triggered, while normally open contacts are closed. The second type is used to supply power; it is the most common.
Connection diagrams for a magnetic starter with a 220 V coil
Before we move on to the diagrams, let’s figure out what and how these devices can be connected. Most often, two buttons are required - “start” and “stop”. They can be made in separate housings, or they can be a single housing. This is the so-called push-button post.
Everything is clear with individual buttons - they have two contacts. One receives power, the other leaves it. There are two groups of contacts in the post - two for each button: two for start, two for stop, each group on its own side. There is also usually a ground terminal. Nothing complicated either.
Connecting a starter with a 220 V coil to the network
Actually, there are many options for connecting contactors; we will describe a few. The diagram for connecting a magnetic starter to a single-phase network is simpler, so let's start with it - it will be easier to understand further.
Power, in this case 220 V, is supplied to the coil terminals, which are designated A1 and A2. Both of these contacts are located at the top of the case (see photo).
If you connect a cord with a plug to these contacts (as in the photo), the device will be in operation after the plug is inserted into the socket. In this case, any voltage can be applied to the power contacts L1, L2, L3, and it can be removed when the starter is triggered from contacts T1, T2 and T3, respectively. For example, a constant voltage from a battery can be supplied to the inputs L1 and L2, which will power some device that will need to be connected to the outputs T1 and T2.
When connecting single-phase power to the coil, it does not matter which output is supplied with zero and which with phase. You can switch the wires. Even most often, the phase is supplied to A2, since for convenience this contact is located on the bottom side of the housing. And in some cases it is more convenient to use it and connect the “zero” to A1.
But, as you understand, this scheme for connecting a magnetic starter is not particularly convenient - you can also supply conductors directly from the power source by building in a regular switch. But there are much more interesting options. For example, you can supply power to the coil through a time relay or light sensor, and connect a power line to the contacts. In this case, the phase is connected to contact L1, and zero can be taken by connecting to the corresponding coil output connector (in the photo above it is A2).
Diagram with start and stop buttons
Magnetic starters are most often installed to turn on an electric motor. It is more convenient to work in this mode if there are “start” and “stop” buttons. They are connected in series to the phase supply circuit to the output of the magnetic coil. In this case, the diagram looks like the figure below. note that
But with this method of switching on, the starter will operate only as long as the “start” button is held down, and this is not what is required for long-term operation of the engine. Therefore, a so-called self-catching circuit is added to the circuit. It is implemented using auxiliary contacts on the starter NO 13 and NO 14, which are connected in parallel with the start button.
In this case, after the START button returns to its original state, power continues to flow through these closed contacts, since the magnet has already been attracted. And power is supplied until the circuit is broken by pressing the “stop” key or by triggering a thermal relay, if there is one in the circuit.
Power for the motor or any other load (phase from 220 V) is supplied to any of the contacts marked with the letter L, and is removed from the contact marked T located underneath it.
It is shown in detail in what order it is better to connect the wires in the following video. The whole difference is that not two separate buttons are used, but a push-button post or push-button station. Instead of a voltmeter, you can connect a motor, pump, lighting, or any device that operates on a 220 V network.
Connecting a 380 V asynchronous motor via a starter with a 220 V coil
This circuit differs only in that three phases are connected to contacts L1, L2, L3 and three phases also go to the load. One of the phases is energized to the starter coil - contacts A1 or A2. In the figure this is phase B, but most often it is phase C as it is less loaded. The second contact is connected to the neutral wire. A jumper is also installed to maintain power supply to the coil after the START button is released.
As you can see, the scheme has remained virtually unchanged. Only it added a thermal relay that will protect the engine from overheating. The assembly procedure is in the next video. Only the assembly of the contact group differs - all three phases are connected.
Reversible circuit for connecting an electric motor through starters
In some cases, it is necessary to ensure that the motor rotates in both directions. For example, for the operation of a winch, in some other cases. A change in the direction of rotation occurs due to phase reversal - when connecting one of the starters, two phases must be swapped (for example, phases B and C). The circuit consists of two identical starters and a button block, which includes a common “Stop” button and two “Back” and “Forward” buttons.
To increase safety, a thermal relay has been added, through which two phases pass, the third is supplied directly, since protection in two is more than enough.
Starters can be with a 380 V or 220 V coil (indicated in the specifications on the cover). If it is 220 V, one of the phases (any) is supplied to the coil contacts, and “zero” from the panel is supplied to the second. If the coil is 380 V, any two phases are supplied to it.
Also note that the wire from the power button (right or left) is not fed directly to the coil, but through the permanently closed contacts of another starter. Contacts KM1 and KM2 are shown next to the starter coil. This creates an electrical interlock that prevents two contactors from being supplied with power at the same time.
Since not all starters have normally closed contacts, you can take them by installing an additional block with contacts, which is also called a contact attachment. This attachment snaps into special holders; its contact groups work together with the groups of the main body.
The following video shows a diagram of connecting a magnetic starter with reverse on an old stand using old equipment, but the general procedure is clear.
Consider their connection diagrams, and most importantly, care for the devices. Today, electric motors with short-circuit rotors are widely used in industry (their share is approximately 95-96%). They work in tandem with magnetic starters. In addition, starters expand the capabilities of the electric drive. But first things first, you first need to answer the question of what purposes they are intended for.
Purpose of starters
The connection diagram of a single-phase magnetic starter allows switching of any consumer. Of course, if its power is also supplied from one phase. To be more precise, the MP allows remote control of an electric drive or other device. For example, an irreversible starter is only capable of turning on or disconnecting a consumer from the network
But reverse MPs can do not only the above. They are able to change the connection of phases to the electric motor. This means that the rotor will begin to rotate in the opposite direction. The MP is controlled using the buttons:
- "Start";
- "Stop";
- "Reverse" (if necessary).
Moreover, these buttons have a supply voltage of no more than 24 Volts. All control is carried out using low voltage. And no more is required to power the electromagnet coil.
Types of magnetic starters
The magnetic starter, the connection diagram of which is given in the article, can be made in three versions. It all depends on the conditions under which it is used. Thus, the open version of the starters is intended for installation in a DIN rail. It goes without saying that the electrical panel must be protected from the entry of foreign objects, such as dust or liquid.
The second type of case is protected. Although it is intended for installation indoors, and not in panels, it is still unacceptable for it to get exposed to large amounts of dust, much less liquid. If it is necessary to install magnetic starters, the connection diagrams of which are given in the article, in conditions of high humidity, then it is wiser to use dust- and moisture-proof ones. True, they have a limitation - installation on the street is allowed, but only on the condition that it is not exposed to sunlight or rain.
Design of magnetic starters
Any connection diagram for which is given consists of one main part - the magnetic system. This is a coil wound around a metal core and a movable armature. All this is housed in a plastic case. But this is the basics; there are still many little things, for example a traverse that slides along the guide axes. There is an anchor on it. In addition, blocking and main contacts are connected to it. They are equipped with springs that help open when the power to the electromagnet is turned off.
How does a starter work?
The operation of MP is based on elementary physics. When you apply voltage to a winding, a magnetic field is created around the core. As a result of this, the movable armature begins to be attracted to the core. This is how any magnetic starter works, the connection diagram may differ (depending on the presence of reverse). By the way, this can also be done using two conventional MPs. The starter contacts are normally open by default.
When the armature moves towards the core, they close. But there is another design in which the contact group is normally open by default. In this case, the picture is the opposite. Consequently, when voltage is applied to the coil, the circuit is closed and the electric drive begins to operate. But when the power to the coil is turned off, the electromagnet stops working. Return springs come into action, forcing the contact group to move to its original position.
Starter connection diagram
To begin with, it’s worth considering what a magnetic starter looks like, and the “reverse” connection diagram if used. Essentially, these are two identical devices combined in one housing. With the same success, as was said earlier, you can use simple MPs if you know the switching diagram. The starters have an interlock, which is carried out through normally closed contacts. The point is that it is unacceptable for both of them to turn on at the same time. Otherwise, a phase short circuit will occur.
There is also mechanical protection installed in the starter housing. But it can not be used if an electrical degree of protection is provided. The peculiarity of the reverse is that it is necessary to completely disconnect the electric drive from the power supply. To do this, first disconnect the electric motor from the network. After this, it is necessary for the rotor to completely stop rotating. And only after this is it possible to turn the engine in the opposite direction. Please note that the starter power must be twice that of the motor if back-switching or braking is used.
Thermal relay
Now let's look at a typical 380V magnetic starter. Its connection diagram cannot be done without additional protection. And this is a thermal relay installed on the starter housing. The main task of a thermal relay is to prevent thermal overload of the motor. They, of course, will be present, but they will be insignificant; overheating of the electric motor becomes impossible. The protection acts as a thermal overload meter, however, it is similar to the design of a circuit breaker.
The thermal relay installed on magnetic starters allows for minor adjustments. The so-called setpoint is the setting of the maximum value of current consumed by the electric motor. Typically, this adjustment is made using a screwdriver. The engine has a groove for it, as well as graduation. The procedure is simple, you just need to place the arrow on the plastic disk opposite the corresponding mark with the value of the maximum current consumption. Please note that thermal relays are not capable of short circuit protection. Use circuit breakers for this purpose.
How starters are mounted
It is worth noting that the magnetic connection diagram allows for the possibility of their installation inside electrical panels. But there are requirements for all starter designs. To ensure high operational reliability, it is necessary that installation is carried out only on a perfectly flat and rigid surface. Moreover, it must be vertically located. To put it simply, on the wall of the electrical panel. If there is a thermal relay in the design, then it is necessary that the temperature difference between the MP and the electric motor be minimal.
To avoid false triggering of the starter or to protect it, it is unacceptable to install the device in places that are subject to shock, shaking, vibration, and jolts. In particular, installation on the same panel with electric starters with a current of over 150 Amperes is prohibited. When such devices are turned on and off, a sharp shock occurs. The wire connections also need to be done correctly. In order to improve contact and to prevent distortion of the spring washers of the clamps, it is necessary to bend the wires in the shape of a circle or the letter “P”.
Turning on the starter
Always try to follow electrical safety precautions and never work without turning off the power. If you have little experience, then you should always have a diagram at hand. A photo of connecting a magnetic starter is given in this article, you can read it. What needs to be done before starting the starter? The most important thing is to conduct a visual inspection for cracks, distortions, and phase short circuits. Remember that the entire drive circuit must be disconnected from power. Try to press the traverse with your hands; it should move freely along the guides. Check carefully all magnetic starters and power conductor connection diagrams in the system.
Pay attention to the connection of the starter solenoid coil. Also check that it is within the acceptable value. If 24 V is needed, then supply that much. Check all control wires to see if they are correctly connected to the Start, Stop, Reverse buttons (if necessary). Is there a lubricant solution on the contacts? If not, apply it, otherwise the lock may not work in a timely manner. After this, you can turn on the circuit and start the drive. Please note that the electric magnet coil may hum slightly in this condition.
How to care for starters
That's all, magnetic starters and connection diagrams have been completely reviewed; all that remains is to mention their care. During operation, it is necessary to constantly monitor the condition of the magnetic starter. The main maintenance work is to prevent the formation of a layer of dust, and even more so dirt, on the surface of the starter or thermal relay. From time to time, the contacts for connection to the network and to the drive must be tightened. Dust must be removed either with a rag or compressed air (not wet). It is prohibited to clean the contacts, as this will affect the service life of the device. Replacement is carried out if necessary. The service life depends on many factors, but the most important is the operating mode. If the starter is constantly in motion, making switching, then it will not last long. Its resource is measured in the number of on and off cycles, and not in hours or years.