What are magnetic starters used for? Magnetic starter - purpose of the device, principle of operation and connection diagram with your own hands. Review of the best equipment manufacturers Magnetic starters remain on without load

Content:

At the dawn of electrical engineering, switching of three-phase electric motors was carried out using manual switches. They did not adequately provide electrical safety and required connection to the control panel using power lines. Further development of switching processes led to the invention of a magnetic starter, devoid of the disadvantages of a conventional switch. This device made it possible to remotely turn on the load and automatic control equipment operating processes.

The magnetic starter itself has a fairly simple structure and operating principle. It consists of two types of contacts - moving and stationary. Closing them causes the electric motor to start, and opening them switches off and stops. The contacts operate under the influence of a magnetic field.

Types of magnetic starters

The main purpose of magnetic starters is remote control of three-phase ones. They operate at alternating current voltages of 380 and 660 volts, with a frequency of 50 Hz. Basic operations include starting, stopping and reversing.

Additionally, magnetic starters in combination with thermal relays protect controlled electric motors from possible overloads with an unacceptable duration. Some starter designs include surge suppressors used in solid-state control systems.

In accordance with the connection diagram, the loads can be reversible or non-reversible. Classification by placement assumes magnetic starters of the following types:

• Open version. Installed in closed cabinets, on panels, and other places where dust, moisture and foreign objects cannot enter.
• Secure execution. Installed indoors with low dust content in the environment. Prevents water from entering the device shell.
• Dust-splash-proof design. They are installed indoors and outdoors under canopies that protect from rain and sunlight.

Additional classification of starters is carried out according to the following criteria:

• Push-button station on the device body. Irreversible starters are equipped with START and STOP buttons, and reversing devices have START FORWARD, START REVERSE and STOP buttons. On some models, an ON indicator light is mounted in the housing.
• Additional blocking and signal contacts. They are used in different combinations, as making or breaking switches. They can be built-in or equipped as a separate console. Some additional pins can be used as part of general scheme starter. For example, in reversing devices they are used to provide electrical locking.
• Coil current and voltage.
• The presence of a thermal relay in the circuit. Its main characteristic is the rated non-operation current at medium installations. Adjustment of the non-operation current is carried out within acceptable limits + 15% of face value.

Certain types of magnetic starters can be equipped with surge suppressors and other types of installation products

Magnetic starter device

The design of the magnetic starter is conventionally divided into upper and lower parts. At the top there is a movable contact system together with an arc chute. There is also a movable half of the electromagnet, which has a mechanical connection with the power contacts included in the movable contact system.

At the bottom of the device there is a coil, a return spring and the second part of the electromagnet. The main function of the return spring is to return the upper half to its original position after the power supply to the coil is stopped. Thus, the power contacts of the starter are broken.

The design of both halves of the electromagnet includes W-shaped plates, for the manufacture of which electromagnetic steel is used. The winding is a copper wire with a certain number of turns, designed to work with a certain supply voltage, value 24, 36, 110, 220 and 380 V. The supply of voltage leads to the appearance of a magnetic field in the coil. As a result, both halves tend to connect, which leads to the formation of a closed circuit. When the power is turned off, the magnetic field disappears and the upper part returns to its original position under the action of the return spring.

Operating principle

The principle of operation of a magnetic starter is already contained in its name. It works like an electromagnet when an electric current passes through the winding of the coil. After the power contacts are activated, the electric motor starts.

The general design of the device includes a main part fixed permanently and a movable armature moving along guides. In its most simplified form, the starter is a single button, the body of which is equipped with terminals for connecting power circuits and stationary contacts.

The moving part is equipped with a contact bridge that provides a double break in the power circuit to turn off the power to the load. In addition, this part is designed to provide a reliable electrical connection between the input and output wires when the circuit is put into operation. You can check the operation of the system manually. To do this, you need to press on the anchor and feel the force from the compression of the springs. It is this force that must be overcome by the magnetic field. When the armature is released, the contacts are thrown back by springs to the off position.

During operation, such manual control is not used; it is only necessary for checks. In fact, only remote switching is used under the influence electromagnetic field. The field itself arises in the coil under the influence of the electric current passing through its turns. The passage of current is significantly improved due to the laminated steel magnetic circuit, divided into two parts.

In the absence electric current, the magnetic field around the coil also disappears. This results in the armature being thrown upward due to the energy of the springs. When the current begins to flow through the winding again, magnetic forces arise, causing the armature to move downward.

The lower position of the armature affects the operation of the entire device. In this position, the contacts should be securely connected to each other. If loosened, the contacts may burn, excessive heating and subsequent burnout of the wires.

Installation and connection of an electromagnetic starter

To ensure further reliable operation of magnetic starters, it is recommended to install these devices on a flat surface, firmly fixed in a vertical position. Installation of starters must be carried out under conditions of a minimum difference in ambient temperatures.

Incorrect installation may result in false alarms. Therefore, avoid places subject to vibration, strong shocks and shocks. For example, electromagnetic devices with current ratings greater than 150 A produce noticeable shock and shock when turned on.

Thermal relays may be subject to additional heating from other heat sources. This has a negative impact on the entire operation of these devices. Therefore, they should not be placed near thermal equipment or in those parts of the cabinets that are most susceptible to heating.

When one conductor is connected to the contact terminal of the starter, its end is bent into a ring or U-shape. This connection method prevents distortion of the spring washers installed in the clamp. If two conductors with approximately the same cross-section are connected to the clamp at once, their ends should have a straight shape and be located on both sides of the clamping screw.

Before connecting copper wires, their ends must be tinned. In stranded wires, the ends are pre-twisted before tinning. The ends of the aluminum wires are cleaned with a fine file and then covered with technical petroleum jelly or a special paste. Lubrication of contacts and moving parts of the device is not allowed.

Before starting, it is necessary to inspect the magnetic starter from the outside and check the serviceability of all its parts. All moving elements must move freely by hand. Check all electrical connections with the diagram.

Magnetic starter care

In order to properly care for a magnetic starter, you need to be well aware of the possible malfunctions of this device. As a rule, this is an increased temperature of the parts and a strong hum of the device.

The increased temperature is primarily associated with interturn short circuits of the coil. In such cases, it needs to be replaced. In addition, excessive heating can occur due to an increase in network voltage above the rated voltage, as well as during overloads, weak contact connections and unacceptable contact wear.

Excessive device humming can occur for a variety of reasons. Among them, first of all, it is worth noting the loose fit of the armature to the core, as a result of contamination of the surfaces or their damage. Another serious reason is jamming of moving parts, as well as a decrease in network voltage by more than 15% of the nominal value.

In order to avoid such malfunctions, timely maintenance is required. In general, a magnetic starter does not require any expensive measures. First of all, you need to prevent dirt, dust and moisture from getting inside the device. It is necessary to regularly check the condition of the contacts and the tightness of the clamps. There is a certain list of activities for maintenance and repairs performed by electrical specialists.

Magnetic starters are intended mainly for remote control of three-phase asynchronous electric motors with a squirrel-cage rotor, namely:

• for starting by direct connection to the network and stopping (turning off) the electric motor (irreversible starters),

• for starting, stopping and reversing the electric motor (reversing starters).
  

Besides this, starters with thermal relay They also protect controlled electric motors from overloads of unacceptable duration.

Open magnetic starters designed for installation on panels, in closed cabinets and other places protected from dust and foreign objects.

Protected magnetic starters are intended for installation indoors, in which environment does not contain significant amounts of dust.

Dust-splash-proof magnetic starters Designed for both indoor and outdoor installations in places protected from sunlight and rain (under a canopy).

Magnetic starter PML series

Magnetic starter device

Magnetic starters have magnetic system, consisting of an armature and a core and enclosed in a plastic case. Placed on the core retractor coil. A traverse slides along the guides of the upper part of the starter, on which the armature of the magnetic system and bridges of main and blocking contacts with springs.

The operating principle of the starter is simple: when voltage is applied to the coil, the armature is attracted to the core, normally open contacts close, normally closed contacts open. When the starter is turned off, the opposite picture: under the action of return springs, the moving parts return to their original position, while the main contacts and normally open block contacts open, and the normally closed block contacts close.

Reversing magnetic starters are two conventional starters mounted on common ground(panels) and having electrical connections that provide electrical interlock through normally closed blocking contacts of both starters, which prevents one magnetic starter from turning on when the other is turned on.

See the most common circuits for connecting a non-reversible and reversible magnetic starter here:. These circuits provide zero protection using a normally open contact of the starter, which prevents the starter from spontaneously turning on when voltage suddenly appears.

Reversing starters can also have mechanical locking, which is located under the base (panel) of the starter and also serves to prevent the simultaneous activation of two magnetic starters. With electrical blocking through the normally closed contacts of the starter itself (which is provided by its internal connections), reversing starters operate reliably without mechanical blocking.

Reversing magnetic starter

Motor reverse using a reversing starter, it is carried out through a preliminary stop, i.e. according to the scheme: turning off the rotating engine - complete stop - turning on reverse rotation. In this case, the starter can control an electric motor of the appropriate power.

In the case of using reversing or braking of the electric motor by back-switching, its power should be selected below 1.5 - 2 times the maximum switching power of the starter, which is determined by the state of the contacts, i.e. their wear resistance when operating in the applied mode. In this mode, the starter must operate without mechanical interlock. In this case, electrical interlocking through the normally closed contacts of the magnetic starter is required.

Magnetic starters of protected and dust-splash-proof versions have a shell. Starter shell The dust-splash-proof design has special rubber seals to prevent dust and water splashes from entering the starter. The inlet holes into the shell are closed with special samples using seals.

Thermal relays

A number of magnetic starters are equipped with thermal relays, which provide thermal protection of the electric motor against overloads of unacceptable duration. Adjustment relay setting current- smooth and is produced by the setpoint regulator by turning it with a screwdriver. Look here about. If it is impossible to implement thermal protection in intermittent operating mode, magnetic starters without a thermal relay should be used. Thermal relays do not protect against short circuits

Thermal relays

Scheme of direct start and protection of an asynchronous motor with a squirrel-cage rotor (a), (b) – starting characteristic of the motor (1) and protective characteristic of the thermal relay (2)

Installation of magnetic starters

For reliable operation, magnetic starters must be installed on a flat, rigidly reinforced vertical surface. Starters with thermal relays are recommended to be installed at the lowest difference in air temperature between the starter and the electric motor.

To prevent false alarms, it is not recommended to install starters with thermal relays in places subject to shocks, sharp shocks and strong shaking (for example, on a common panel with electromagnetic devices with rated currents of more than 150 A), since when turned on they create large shocks and shocks .

To reduce the influence on the operation of the thermal relay of additional heating from extraneous heat sources and to comply with the requirement that the air temperature surrounding the starter is not allowed to exceed 40 °C, it is recommended not to place thermal devices (etc.) next to magnetic starters and not to install them with a thermal relay in the upper, most heated parts of the cabinets.

When connecting one conductor to the contact clamp of a magnetic starter, its end must be bent into a ring- or U-shape (to prevent distortion of the spring washers of this clamp). When connecting two conductors of approximately equal cross-section to a clamp, their ends should be straight and located on both sides of the clamping screw.

The connecting ends of copper conductors must be tinned. The ends of stranded conductors must be twisted before tinning. When connecting aluminum wires, their ends must be cleaned with a fine file under a layer of CIATIM lubricant or technical petroleum jelly and additionally coated with quartz vaseline or zinc-vaseline paste after stripping. The contacts and moving parts of the magnetic starter must not be lubricated.

Before starting the magnetic starter it is necessary to carry out an external inspection and make sure that all its parts are in good working order, as well as that all moving parts can move freely (by hand), check the rated voltage of the starter coil with the voltage supplied to the coil, make sure that all electrical connections are made according to the diagram.

When using starters in reverse modes, by pressing the movable crossbar by hand until the main contacts touch (start to close), check for the presence of a solution of normally closed contacts, which is necessary for reliable operation of the electrical interlock.

When the magnetic starter is turned on, a small electromagnet hum, characteristic of laminated magnetic systems.

Caring for magnetic starters during operation

Maintenance of starters should consist, first of all, of protection of the starter and thermal relay from dust, dirt and moisture. Make sure that the terminal screws are tightly tightened. It is also necessary to check the status of the contacts.

The contacts of modern magnetic starters do not require special care. The wear life of the contacts depends on the conditions and operating mode of the starter. Stripping contacts of starters is not recommended, since removal of contact material during stripping leads to a decrease in the service life of the contacts. Only in some cases of severe melting of the contacts when the emergency mode of the electric motor is turned off is it possible to clean them with a small needle file.

If, after long-term operation of the magnetic starter, a buzzing sound of a rattling nature appears, it is necessary to clean the working surfaces of the electromagnet from dirt with a clean rag, check for the presence of an air gap, and also check for jamming of the moving parts and cracks on the short-circuited turns located on the core.

When disassembling and subsequent reassembling a magnetic starter, the relative position of the armature and core that was before disassembly should be maintained, since their worn-in surfaces help eliminate humming. When disassembling magnetic starters, it is necessary to wipe dust from the internal and external surfaces of the plastic parts of the starter with a clean and dry rag.

In the title of this electrical device For electrical installations of 0.4 kV, two fundamental steps are taken at once:

1. actuation as an electromagnet from the passage of electric current through the coil winding;

2. starting the electric motor using power contacts.

Structurally, any magnetic starter consists of a permanently fixed part and a movable armature moving along skids. It is highlighted in blue in the picture.

How does the electromagnetic system work?

In a very simplified way, the starter can be represented as one button, on the body of which there are terminals with connected power circuits and stationary contacts. A contact bridge is mounted on the moving part. Its purpose:

1. ensuring a double break in the power circuit to turn off the power to the electric motor;

2. reliable electrical connection of incoming and outgoing wires when the circuit is put into operation.

When you manually press on the anchor, you can clearly feel the compression force of the built-in springs, which must be overcome by magnetic forces. When the armature is released, these springs throw the contacts to the off position.

This method of manual control of the starter is not used during operation of the circuit; it is used during checks. During operation, the starters are controlled only remotely due to the action of electromagnetic fields.

For this purpose, a coil winding with turns wound on it is placed inside the housing. It is connected to a voltage source. When current is passed through the turns around the coil, a magnetic flux is created. To improve its passage, a laminated steel magnetic circuit was created, cut into two parts:

the lower half permanently fixed in the device body;

movable, part of the anchor.

In the de-energized state, there is no magnetic field winding around the coil; the armature is thrown upward by the energy of the springs from the stationary part. Under the influence of magnetic forces arising after the passage of electric current through the winding, the armature moves downward.

Attracted to the stationary part of the magnetic circuit, its movable half creates a single structure with minimal magnetic resistance. Its value during operation is influenced by:

violations of adjustment adjustments;

corrosion of steel parts of the magnetic circuit and its fastening;

surface wear;

technical condition of springs, their fatigue;

defects in the short-circuited turn of the magnetic circuit.

The movement of the anchor inside the housing is limited by two boundary values. In the lower pulled position, a reliable clamp of the contact system must be created. Its weakening leads to burning of the contacts, an increase in the value of the transient electrical resistance, excessive heating and subsequent burning of the wires.

An increase in the magnetic resistance of the magnetic circuit for any reason is manifested by an increase in noise due to the appearance of vibrations, which lead to a weakening of the clamping of the contact system and, ultimately, to failures in the operation of the magnetic starter.

How does the power contact system work?

Structurally, power contacts are designed for reliable and long-term operation. For this they:

made of technical silver alloys applied by special methods to copper jumpers;

created with a margin of safety;

manufactured in a form that provides maximum electrical contact when switched on and can withstand the electric arc that occurs when the load breaks.

Three-phase circuits use magnetic starters with three power and several additional contacts that repeat the position of the armature and are used in motor control circuits. All of them are drawn on the diagrams in a position corresponding to the absence of current in the coil and the uncompressed state of the springs.

When the starter is triggered, the control contacts close (called “closing”) or, conversely, open the circuit. In a pulled position, they create a platform in the form of a point. To do this, the stationary part is made as a plane or a sphere (in critical units), and the movable part as a sphere.

Power contacts are more responsible and must withstand increased loads. They are made to create a contact line consisting of many points. For this purpose, the stationary part is made of a plane or a cylinder, and the movable part is made only of a cylinder.

Magnetic starters produced by domestic manufacturers are classified according to their ability to work with loads of different powers into 7 groups and are designated by increasing values ​​from zero with a switching current up to 6.3 amperes inclusive and up to the sixth (160 A).

Starters produced by foreign manufacturers are classified according to other criteria.

Electricians servicing magnetic starters and supervising their operation are required to monitor the quality of contact pads and their cleanliness. The current opinion is that “In modern starters, the contacts are made reliably and do not need to be inspected” not quite correct.

The cleanliness of contacts depends on many factors, including:

load mode;

switching frequency;

environmental conditions.

They all appear differently on each specific device. Therefore, they must be periodically monitored and, at the first sign of contamination, washed with alcohol. When it is not available for such work, they use an ordinary school eraser, which, while cleaning the metal, leaves its crumbs, which have dielectric properties, on the outer surface.

They are removed by wiping the surfaces with thin dried wooden sticks from non-resinous tree varieties. Best suited for these purposes:

When wiping contacts, hardwood additionally polishes the surfaces being treated.

Minor burnout of contact surfaces can be removed with homemade “blues”. This is what electricians call flat pieces of strong metal plates (usually made from broken hacksaw blades for metal), the surface of which is lightly treated with the finest sandpaper.

Such a tool allows you to remove a very thin layer of burnt metal and bring the contacts into working condition, maintaining their original shape. You cannot use fine sandpaper or needle files for such purposes. You can quickly break the formed contact line. “Sandpaper” also clogs the surface being treated with abrasive crumbs.

Schemes for connecting electric motors with magnetic starters

Easiest controls

This motor connection can be made using the picture below.

Three-phase power ≈380 through power contacts K1-s is supplied to the electric motor, the temperature of the windings of which is controlled by a thermal relay kt. The control system is powered from any phase and zero. It is quite acceptable to replace the working zero with a ground loop.

In order to increase electrical safety, a separation or step-down transformer TP1 is used. Its secondary winding cannot be grounded.

The simplest fuse FU protects the control circuit from possible short circuits. When the operator presses the “Start” button, a circuit is created in the control circuit for current to flow through the winding of the starter K1, which simultaneously closes its power contacts K1-c. The amount of time the worker presses the button is how long the engine runs. For human convenience, such buttons are mounted with a trigger mechanism.

A running electric motor can be turned off when the button is pressed:

removing power from the power distribution board;

by pressing the “Stop” button;

operation of the thermal relay kt when the engine overheats;

fuse blown.

Such schemes are used where, according to technology, it is necessary to keep your hands constantly on the equipment and not be distracted from the production process. An example would be working with the press.

Scheme with holding the button by the starter contact

Adding to the considered circuit just one closing contact of the K1-y starter allows you to set the “Start” button to be blocked by this addition and eliminates the need to constantly press it. Otherwise, the scheme completely repeats the previous algorithm.

Reverse circuit

Many machine tool drives require changing the direction of rotation of the motor rotor during operation. This is done by changing the alternating phases of the power circuit - switching the connection points of any two windings with the engine turned off. In the picture below, the windings of phases “B” and “C” are swapped. Phase "A" does not change.

The circuit already includes two magnetic starters No. 1 and No. 2. The motor can only rotate from one of them, clockwise or in the opposite direction. To do this, a break contact for controlling the counter-rotation starter is introduced into the control chain of each winding K1 and K2. It blocks the simultaneous connection of both starters.

To change the direction of rotation of the engine, the operator must:

press the “Stop” button. The gap it creates opens the control circuit and interrupts the flow of current through the operating starter. In this case, the springs release the armature, and the power contacts turn off the power supply from the electric motor;

wait for the rotor to stop rotating and press the “Start” button of the next starter. The current will flow through its coil, the button will be held by the closing contact, and the winding circuit of the reverse rotation starter will be broken by the breaking contact.

Design features of various models

If previously magnetic starters were equipped with power contacts and one or two of their position repeaters for closing or opening, then modern models are equipped with additional structural elements, due to which they have a greater number of capabilities.

For example, complete products from leading manufacturers allow you to perform various functions for controlling three-phase electric motors, including reversing by integrating additional equipment into the starter. The consumer only has to connect the electric motor and power wires to the purchased module, and the circuit itself is already installed and configured for certain loads.

A promising technical solution is considered to be a scheme that allows:

spin the motor rotor to the rated speed by connecting its windings in a star configuration;

switch on under load when switching to delta.

The housings of magnetic starters can be open or protected from the penetration of dust and/or moisture by a special shell with seals.

Selected modern models of low power.

Powerful magnetic starters can have an arc extinguishing system installed, which occurs when the current is switched off by power contacts.

Today, switching starting electromagnetic devices are used in various electrical equipment. They are an intermediate link between power units and electrical equipment control systems, controlling the switching on and off of electrical circuits. Read below to learn how magnetic starters are designed, what types of devices exist, and what their purpose is.

Magnetic starter: device and principle of operation, equipment

A magnetic electric starter is a low-voltage device for monitoring and distributing current energy. The design of the device is quite simple: the device consists of two parts - upper and lower, combined into a plastic case.

At the top of the starter there is:

• Block of moving contacts;
• Arcing grid;
• The moving part of the electromagnet.

The contact power block, in this case, is closely connected with the moving part of the electromagnet. The arc extinguishing grid in the device acts as a device that serves to prevent and eliminate electric arc fires. A traverse with a magnetic system armature and bridges of power and additional contacts with springs slides along the runners at the top of the device.

The lower part of the electromagnetic device has in its design:

• Retractor coil;
• Return spring;
• Part of an electromagnet.

The retractor coil has a cylindrical shape and a winding made of copper conductor. The number of turns of the coil depends on the calculated supply voltage. The magnet in the device consists of W-shaped, steel, electromagnetic plates. The armature and the core make up the magnetic circuit.

The principle of operation of the device is quite simple: it is based on the effect of a magnetic field on various moving parts of the starter.

So, current is supplied to a coil located on the core. After the current supply is stopped, the magnetic field disappears, the return spring sends the upper part of the device to its original place. At the same time, the contacts that were open are closed, and the closed ones are opened.

Power contact system: magnetic starter device

Modern magnetic starters can be equipped with additional protection and control devices. Most often, starters are equipped with thermal emergency shutdown relays and low-current contact starting control groups. Reproduction of contacts when modifying a magnetic starter is carried out through a contact block. Therefore, the contact system of the starter is called an attachment.

The contact power system of a three-phase magnetic starter consists of three power (main) contacts and one auxiliary.

Power contacts are used to switch powerful loads. Therefore, they are made from copper jumpers coated with technical silver. The additional contact in the block acts as a blocking contact: when using a standard connection diagram, it locks the starter in working condition.

Depending on the type of influence on the electrical circuit, power contacts are divided into:

• Normally closed;
• Normally open.

The contacts are activated when current enters the starter coil. During this, the core pulls the contacts along with it, which makes the normally closed contacts open and the normally open contacts closed.

Auxiliary contacts for time delay starters

To increase the number of power contacts of the electromagnetic device, additional attachments are used. At the same time, the contacts in such attachments are selected taking into account the maximum current of the main ones. So, for starters of the first and second values, the current of the additional contacts must be equal to the current of the main ones or be less than the maximum value. Separately, additional contacts (attachments) with a delay are identified. The main task of such set-top boxes is to maintain a certain time when turning the device on and off.

Pneumatic attachments are used in control circuits for electric drives:

• Under tension DC power 440 V and frequency 50 Hz;
• Under tension AC power 660 V and frequency 60 Hz.

If a pneumatic PVL attachment is already installed, in order to increase the number of auxiliary contacts of the electrical control circuit, use a contact side attachment of the PKB series. The attachment is mounted using special latches on its body.

What types of magnetic starters are there?

Magnetic electric starters are distinguished by their ability to work with loads of different powers. Domestic starters are divided into 7 groups and can switch power in the range from 7.5 to 45 kW.

In addition, according to their design and operating principle, starters are divided into:

• Reversible (for example, PML 1502, 3100);
• Irreversible (for example, starter PME 211, PAE 311 or “frog”).

Reversing starters have two magnets in their design, thanks to which they are able to spin and move in any direction depending on the operator’s command. Moreover, regardless of how the starter is designed, it may or may not have overload protection.

Depending on the installation location, magnetic starters are of closed and open type.

Separately, dust-proof electromagnetic contactors are distinguished. The first types of starters are installed in standard places that are not characterized by large accumulations of dust or mechanical influences from foreign objects (for example, electrical cabinets). Dust-proof starters are not affected by sunlight and precipitation, and can be installed under canopies on the street. To identify the type of starter, a standardized decoding has been invented that allows you to determine the meaning of each letter and number in the designation on the electrical device.

Main functions and purpose of a magnetic starter

What is a magnetic starter used for? The main purpose of the starting electromagnetic device is to turn the engine on and off. A study of arc suppression in AC contactors indicates that, most often, starters are used to control asynchronous three-phase electric motors. This is explained by the simplicity of the starter design. In addition, when included in the circuit, starters not only turn the electric motor on and off, but also monitor its operation.

Thus, a magnetic starter performs the following functions:

• Provides engine starting and engine acceleration;
• Controls the continuity of work in accordance with a given time period;
• Protects the motor from overloads;
• Changes the direction of rotation of the motor;
• Responsible for countercurrent braking;
• Provides engine shutdown.

At the same time, the starter provides zero protection for the electric drive. So, in the event of an unplanned power outage, the engine ignition switch (controller) may be in a non-zero position. Zero protection prevents the motor from spontaneously turning on when power is restored: the motor starts up only after the operator’s command.

Why do you need a magnetic starter: scope of application

In addition to controlling a three-phase asynchronous motor, a magnetic starter can be used to control the operation of powerful electricity consumers (for example, a pump, an air conditioner). In everyday life, magnetic starters are most often used to turn on a heating system (for example, heating elements).

In addition, starters are used in circuits:

• Remote control of lighting devices;
• Control of thermal furnaces;
• Compressor control.

Thus, the scope of application of starters is extremely wide. This is due to the simplicity of their design and the ease of incorporating devices into the circuit. In addition, finding a starter at an affordable price is not difficult: buying used electrical devices is especially popular today.

Magnetic starter device (video)

Almost no modern electrical equipment can do without a device for turning on and off the electrical circuit - a magnetic starter. A modern magnetic electric starter is a modified two-position electromagnetic electrical contactor. Knowing how a magnetic starter works and what types of devices are distinguished, you can include a contactor in any circuit. And the above recommendations for installing additional contacts will help you improve your device!

A magnetic starter (hereinafter referred to as PM) is a switching device, which is one of the elements of magnetic contactors, switching high loads of various sizes, and is also used in electrical circuits with regular switching on and off of current.

The main task of the PM is to start, pause and reverse three-phase asynchronous mechanisms. Very often, these types of devices are used in closed electrical circuits for remote control. Examples:

1. compressor devices;
2. heating stoves;
3. air conditioners;
4. conveyor belts for various purposes.

We can safely state that the scope of application of a magnetic contactor is very wide.

Operating principle, magnetic starter design

The essence is quite simple and clear:

1. The contactor winding is supplied with power voltage.
2. The winding itself excites a magnetized field, which draws a metal core with working electrical contacts attached to it into the internal space.
3. Closing of contacts, after which a current arises in a closed electrical circuit. The device is controlled by controllers: “forward”, “backward”, “start”, “stop”.

Operational controllers work on the principle of a limit switch, thereby ensuring proper control of the mechanism.

PM has two main parts:

1. Contact block (CB). It often works according to schemes where it is necessary to use auxiliary contacts, examples: reverse of an electric motor, connections using an additional equipment starter, operating alarm. Contact block (addition with contact outputs) – necessary to expand the number of electrical contacts.
2. Magnetic starter (MP).

The contact block has a built-in set of electrical contacts. This system complex allows you to connect the structure with the starter itself and form one solid module.

How to connect the contact block correctly?

This block is installed on the top of the contactor, where there are special connectors with hooks.

The working circuit has two pairs of closed contacts, as well as two pairs of open connectors.

Normally open contact (NO) – when not working, it is always in the open position (pair 1-2). Therefore, for current to pass through it, it must be closed.

Normal closed contact (NC) – its non-working position is the closure of the connectors (pair 3-4). In this situation, when the contact opens, there will be no current through the magnetic starter.

PM is a structure consisting of two basic fragments:

1. top;
2. lower

The upper part is a moving contact system, an arc-extinguishing chamber and a moving element of an electric magnet, connected to the connectors by the moving area of ​​the mechanism.

The lower part consists of a winding, a return spring and a second fragment of the magnet body.

The role of the spring is to return the initial position of the upper region of the device, thus, in the absence of contact of the magnetic connector, there is no current in the winding.

Types of MP

There are a wide variety of starters. This section will tell you about magnetic starters for mines and mines.

Mine - used to start mechanisms with reverse, maintaining a safe distance. Also, the main objectives of such a device are:

1. short circuit neutralization;
2. overload of the three-phase motor mechanism;
3. motor jamming.

Mine contactors often use three-phase alternating current networks with an industrial frequency (50 Hz) and a voltage of 380 – 650 V. The neutral of electrical converters is created insulated for safe operation in coal mines, as well as to avoid exposure to fragments of coal dust and hazardous gases.

Main features:

1. a reversible magnetic starter starts the electric motor;
2. use of vacuum PM;
3. quite a wide range of used powers.

The starter itself is a collection of electrical devices designed and connected in an explosion-proof housing. The protective shell has several blocks, which are separated from each other by corrosion-resistant partitions.

The upper half of the body is equipped with an observation window with an LED instrument panel. When working in mines, the process can be simplified by connecting a photo relay, which in turn optimizes the operation of magnetic devices in low light conditions.

Mine starting mechanisms are necessary when working with a three-phase alternating current network, with a voltage of about 800 - 1000 V. The transformer neutral, similar to a mine starter, is isolated from the effects of various types of hazardous gases and dust. Mining apparatuses have a set of mechanisms installed in a shell, which is protected from moisture and contains the main elements:

1. cable entry devices;
2. lid with instant opening;
3. explosion-proof enclosure;
4. interlocking disconnector.

The housing on the disconnector side is closed with a lid with a window, allowing observation of the disconnection mechanism. On the side of the cover, there is an element that blocks the opening of the cover if the disconnector is turned on.

A distinctive feature of devices of this type is the manufacture of an electrical system in the form of 3 blocks:

1. protection;
2. management;
3. contactor

Connection diagram

One of the basic elements of a magnetic contactor is a button.

The buttons carry out “Start”, “Back”, “Forward”, “Stop”

The above elements provide remote control of the starter.

The "Stop" button activates a break contact, which allows voltage to flow to the control circuit.

The “Start” button is needed so that the contact closes and current will flow through it.

The diagram shown in Fig. 7, shows the standard starting of the engine motor.

How to connect a magnetic starter? Proper attention must be given to the above scheme.

This circuit is divided into two parts:

• Power - power comes from an alternating voltage source (380 V) and is divided into three main phases:

The power block contains switch QF1, several power terminals: 1L1-2T1, 3L2-4L2, 5L3-6T3 and motor “M”.

• Control circuit – receives a signal from phase “A”. In the same chain there are:
  • stop signal – SB1;
  • “start” signal – SB2;
  • contactor windings KM1;
  • additional element 13NO-14NO.

The 13NO-14NO connection circuit is carried out in parallel with SB2.

By launching QF1, phases “A”, “B”, “C” fall on contacts 1L1, 3L2, 5L3 and move to the standby position. The arrival of phase “A” to contact “3” is carried out through the “Stop” button. The 13NO element continues to remain in the standby position on these two contacts. Electric circuit ready. Required condition work with electric motors – electrical diagrams with a thermal relay that has the property of protecting the device from current overloads.

Modern contactor starters, auto-switches can be placed in one panel on one DIN rail. The automated control system (ACS), which is responsible for the interaction of all elements of magnetic installations, technological processes and controllers, is based on the use of magnetic starters.

The information provided in this article will allow you to easily design this kind of circuit and use it for the required purpose.

Video about connecting a magnetic starter