Distinctive features of contactors and magnetic starters. Electromagnetic contactors and magnetic starters

Why are contactors used in electrical installations and how do they differ from starters? I believe: firstly, large contactors have arc-extinguishing chambers, which means they are used to extinguish the arc; secondly, they have coils for high current (they write about them that they are designed for starting powerful motors). But the question keeps arising early, because there are small contactors without arc-extinguishing chambers and for small currents. How are they different? After all, both of them also have additional block contacts? Or have the concepts become so confused that now they call everything a contactor?

Answer 1

One specialist answered me this way: the difference is design. In a magnetic starter, the core attracts the conductive plate, and it connects two contacts with its plane. And in a contactor, when turned on, one contact hits the other.

Answer 2

If you look at some old reference books, then under the term
“magnetic starter” means a device consisting of a three-phase contactor and a thermal protection relay. There really is confusion at the moment. For example, in the Moeller catalog these devices are called starters, and in Schneider they are called contactors. I adhere to this point of view... A starter is a three-phase contactor... So, by and large, both terms are equivalent.

Answer 3

In general, in practice, for some reason everyone is called magnetic starters 0,1,2 magnitude. 3 quantities - some call it a starter, some call it a contactor. And according to theory, a really dark forest. In general, I was only recently able to find out that the abbreviation “PML” is a Licensed Magnetic Starter. No one remembers what kind of license it is, whose it is.

Answer 4

I looked in the old reference book: Contactor - a two-position switching device driven by a magnetic drive, etc. Magnetic starter - a contactor in combination with a thermal relay.

Here are definitions from a large reference encyclopedia: “Magnetic starter is an electrical device low voltage, intended for remote control(starting, stopping, changing direction) and protection of low and medium power asynchronous electric motors with a squirrel-cage rotor. There are non-reversible and reversible MPs; Special MPs are also produced for switching the windings of multi-speed electric drives. MPs consist of a contactor, a push-button station and a thermal relay. The MP contactor, as a rule, has 3 main contact systems (for inclusion in three-phase network) and from 1 to 5 block contacts"
That is, a hat with a coil and contacts is a contactor, and a magnetic starter is a set of switching devices for starting and protecting the engine - i.e., a thermal relay, a push-button post, and a contactor.

THEORY

“Electromagnetic contactor is an electrical device designed for frequent switching on and shutdowns (up to 1500 switchings per hour) of electrical power circuits of constant and alternating current. Widely used for remote control of electrical machines and devices in direct and alternating current installations at voltages up to 500-650 V and current up to 600 A.”

A contactor is a remotely controlled switching device designed for frequent switching of electrical circuits under normal (nominal) operating conditions. Depending on the type of switched current, direct and alternating current contactors are distinguished. Under certain conditions, the same contactors can switch both DC and AC loads.

Contactors are classified:

· by the type of current of the main circuit and the control circuit (including the coil) - direct, alternating, direct and alternating current;

· according to the number of main poles - from 1 to 5;

· rated current of the main circuit - from 1.5 to 4800 A;

· according to the rated voltage of the main circuit: from 27 to 2000 V direct current; from 110 to 1600 V AC with a frequency of 50, 60, 500, 1000, 2400, 8000, 10,000 Hz;

· according to the rated voltage of the switching coil: from 12 to 440 V DC, from 12 to 660 V AC with a frequency of 50 Hz, from 24 to 660 V AC with a frequency of 60 Hz;

· according to the presence of auxiliary contacts - with contacts, without contacts.

Normal operation of the devices is allowed when the voltage at the terminals of the main circuit is up to 1.1 and the control circuit is from 0.85 to 1.1 of the rated voltage of the corresponding circuits.

Contactors can operate in one, several or all of the following modes: intermittent-continuous, continuous, intermittent and short-term (GOST 18311-80). In intermittent-continuous mode, the contactor must allow operation at rated current for no more than 8 hours. The duration of the operating period for short-term operating mode is 5, 10, 15, 30 s and 10, 30, 60, 90 min.

The contactor consists of the following main components: electromagnetic or electro-pneumatic drive, main contacts with an arc extinguishing device, auxiliary contacts.

In contactors with an electromagnetic drive, the main and auxiliary contacts are connected directly to the armature of the electromagnet that controls the closing coil.

In contactors with an electro-pneumatic drive, control is carried out using an electromagnetic valve that allows access compressed air to an electro-pneumatic drive.

And starters are special electromagnetic devices that are widely used in control and protection systems of electrified objects. Using the proposed mechanisms, it is possible to remotely connect, stop and disconnect electrical drives of various equipment such as industrial type, and some household items. These electromechanical units will become indispensable in cases where it is necessary to frequently start electric motors or connect electrical equipment powered by high amperage currents. Let's look at what these devices are, and what similarities and main differences there are between them.

What is a contactor?

The contactor is an electromechanical executive mechanism made in the form of a block in which high-speed contact groups are located. The contactor can function as an independent device or be used in the design of other equipment or in a control and protection system for an electrified facility. The contactor system is a switching unit that supports remote control and can be used for frequent switching of electrical circuits operating under normal operating conditions. To close / open contacts, electromagnetic drives are mainly used, which drive the actuator. Unlike a relay system, which can also close or open contacts, a contactor breaks the electrical circuit simultaneously in several places at once, while a relay does this only in one place.

What is a magnetic starter?

Magnetic starters are also switching devices, which are actually modified contactors that support switching capabilities powerful loads AC and DC. These devices are effectively used to turn on/off power electrical circuits. The proposed switching systems have a fairly wide range of applications. Their main purpose is to start, reverse current and stop a 3-phase electric asynchronous drive. In addition, these devices can be successfully used in remote control systems for various electrified objects. In addition to the main working elements, contactors can be equipped with various additional components such as thermal relays, auxiliary contact groups, automatic motor starters, etc.

What do a contactor and a starter have in common?

To understand what the differences are between these two switching systems, let’s first understand how they are similar to each other.

What a starter and a contactor have in common is that both of these devices are used to switch electrical circuits that power electrical equipment. Both contactors and starters are used to start/stop AC motors, as well as to input or output resistance stages if the starting/stopping is performed according to the rheostat principle.

Both the contactor and the starter have in their design additional pairs of contacts used for control circuits. They can be normally closed or normally open pairs of contacts.

Differences between contactors and starters

Let's look at the main differences between these two switching devices.

Dimensions.

A contactor, unlike a starter, is a rather weighty and large-sized device. For example, a 100-amp contactor, compared to the same starter, is several times heavier and has significantly larger dimensions.

Design features

If we consider the design of the contactor, then powerful power contactors with arc-extinguishing chambers immediately catch the eye. There is no protective casing as such in contactors; the contactor is mounted on special panels located in enclosed spaces.

As for the starter, its power contacts are always protected plastic case. Large cameras There is no arc extinguishing in the starters, so they are not recommended for use in powerful electrical circuits where frequent switching is required.

Security

Thanks to the use of a plastic housing in the starter, and in some cases a metal casing, these devices differ high degree protection from external factors. Therefore, such starters can be installed even outdoors, which cannot be done with contactors.

Purpose of devices

The main purpose of the starter is to start and stop 3-phase electric drives operating on alternating current. In addition, these devices can switch circuits to supply power to lighting systems, heating equipment and other electrical equipment.

As for the contactor, it is suitable for switching any DC and AC circuits.

Conclusion

Based on the above, it follows that the starter is a kind of modification of the contactor and can be used for certain purposes. Contactors, the design of which is constantly modified, can be used in almost any case to perform switching of electrical circuits. Therefore, in the modern consumer market, contactors have practically replaced starters and successfully perform their functions.

In industry, commercial and civil engineering, any tasks related to starting and stopping motors equipped with remote control are solved by contactors and starters. These devices are used where frequent starts or switching of electrical equipment with high load currents are constantly required. Let's look at what these devices are and how they differ from each other.

Definition

Contactor- this is an actuator, which is a block of high-speed switches (i.e. contact groups). He can be independent device or be part of other equipment. A contactor is a remotely controlled switching device, which is designed for frequent switching of electrical circuits under nominal (normal) operating modes. The closing or opening of contacts is usually carried out using an electromagnetic drive. Distinctive feature contactors, in comparison with electromagnetic relays, which perform approximately the same functions, is that they break the electrical circuit simultaneously in several places, and electromagnetic relays usually break the circuit only at one point.

Starter (magnetic)- this is a modified contactor that has additional equipment (usually a thermal relay, fuses, additional contact group or automatic starter electric motor).

Comparison

There are three types of contactors: alternating current, direct current, and sometimes direct-alternating current.

DC devices are used to turn on and off power receivers in electrical circuits direct current; in reuse devices automatic switching on, in drives of high-voltage switches. This equipment(single-pole and double-pole devices) is designed to work with voltages from 22 to 440 V and currents up to 630 A.

DC contactor MK 2-20B-U3 63A

AC devices are used to turn on starting resistors, heating devices, to control a three-phase asynchronous electric motor with a squirrel-cage rotor, to start three-phase transformers, braking electromagnets, etc. AC devices are designed for switching AC electrical circuits.

Magnetic starters are usually used for remote control of asynchronous three-phase electric motors with a squirrel-cage rotor. An electromagnetic starter is a combined electromechanical control and distribution device designed to start and accelerate to the rated speed of the engine, as well as to ensure its uninterrupted operation, protecting connected circuits and the electric motor from operating overloads and power outages. Magnetic starters equipped with surge suppressors are used in control systems using microprocessor technology. Starters work with alternating voltage from 24 to 660 Volts and a frequency of 50-60 Hertz or s constant voltage from 34 to 440 V.

Magnetic starter PME-213

Conclusions website

1. The contactor can be a stand-alone device or part of other equipment.
2. A contactor is a device in which movable contacts are located on a rotating shaft. During rotation, the moving contacts close with the stationary contacts, resulting in the start of the electric motor. In a magnetic starter, the moving contacts produce reciprocating movements.
3. A contactor is a high-speed contact group designed for repeated switching over a certain period of time and controlled by an external source.
4. The starter is an independent mechanism equipped additional equipment: thermal relays, automatic engine starting or an additional group of contacts, as well as fuses.
5. In addition to simple on/off, a magnetic starter switches the directions of rotation of the electric motor rotor, changing the phase sequence; for this it is equipped with additional contactors.
6. Contactors, compared to starters, can switch huge currents.

The main purpose of contactors and magnetic starters is to control electric motors and close power circuits with high currents. The operating principle of the devices is identical. The difference is that a magnetic starter is the same contactor or two, assembled into a device with protective functions, the possibility of blocking, alarm circuits.

Contactor device

A contactor is an electromagnetic device that allows you to switch power electrical circuits through a control current of small values, which powers the solenoid coil of the device.

The operation of a contactor is based on the phenomenon of attraction of the electromagnet armature to the core during the flow of current. An articulated linkage system is attached to the anchor. Electrical contacts are separated from the lever by insulation. The moving contacts are pressed against the stationary ones, closing the operating current circuit. The device is turned on as long as the coil is energized.

Depending on the type of current, contactors are divided into:

• alternating current;
• direct current.

Depending on the number of poles, the devices are:

• unipolar;
• bipolar;
• three- and four-pole.

All devices consist of a magnetic system and a set of contacts: working and auxiliary.

Magnetic system

The components of the magnetic system are:

1. Electromagnet coil;
2. The core on which the coil is mounted;
3. Anchor, movable reinforcement made of iron plates.

When the coil is energized, the current flowing through it creates a magnetic flux, which is closed in a circle through the core, armature, air gap and fittings. It causes attraction of the armature to the core. As soon as the current stops, the springs return the armature to its original position. At the first moment after switching on the contactor, a relatively large current flows through the coil, and then its value decreases when the armature comes into full contact with the core.

Important! For reliable operation contactor, it is important to ensure correct adjustment and assembly of the magnetic system. Loose fasteners of elements influence the formation of vibrations.

In small contactors (up to 15 A), the tight connection between the armature and the core can sometimes cause the armature to "stick" due to residual magnetism. To prevent this, some devices have a thin insert made of copper or brass. In larger contactors, the phenomenon of magnetic “sticking” is rare due to the powerful springs.

Contact system

1. Fixed contacts are mounted on a rigid base embedded in the insulation;
2. The moving contacts are attached to mobile bases, equipped with strong springs and connected to the electromagnet armature through a hinged arm.

Important! Good adhesion of contact surfaces is one of the main conditions efficient work devices.

Copper contacts oxidize very quickly, and a large transition resistance appears in the oxide layer, increasing the heating of the parts. Excessive temperature, in turn, causes increased oxidation and “carbon deposits” of contacts that will require cleaning.

For reliable operation important have correct positioning contacts and the corresponding initial and final pressure forces. This is achieved by adjustment. With use, the springs may weaken, so it is necessary to periodically check the correct position of the contacts.

When the device turns off under load, sparks and even an electric arc occur at the working contacts. To protect adjacent phases from short circuit deionization chambers made of fire-resistant insulating material are used. Usually this is an accessory of powerful devices.

In addition to the main contacts, the devices contain auxiliary contacts, which are characterized by less cross section, since a small control current flows through them. However, it is also important to monitor the condition of these elements due to their importance in the operation of the system.

Many people think that the amount of switched current and, accordingly, large dimensions are what distinguishes a contactor from a magnetic starter. However, it is not. Modern contactors can be of modest size, designed for low currents.

Magnetic switch

A magnetic starter is a contactor or two (reversible) most commonly used to start and stop induction motors.

The device is often equipped with a thermal relay that protects the circuit from overloads and additional contacts that are initially in a closed or open state. These distinguishing features characterize a magnetic starter, although the contactor is the basis of its design.

The thermal relay is connected to the power contacts of the device. His internal organization consists of bimetallic plates that heat up when exposed to current. Their temperature bending causes the relay contacts in the coil control circuit to open. A de-energized coil breaks the power circuit of the electric motor.

Unlike a contactor, a magnetic starter can reverse an electric motor, that is, start it in the forward and reverse directions. To do this, an apparatus is assembled from two contactors and a station with control buttons.

Important! The circuit must include interlocks to prevent simultaneous closure of both groups of power contacts.

Classification of devices

Mainly contactors and magnetic starters, according to Russian standards, are divided depending on the switched load currents. The devices are grouped into 7 classes, arranged in ascending order: from 6.3 A to 160 A.

Devices are produced that differ in design:

1. Open type. Installation of such devices is possible only in dust- and moisture-proof places, for example, in special cabinets;

1. Closed type. They can be installed in industrial premises outside of cabinets, but the penetration of moisture and heavy dust must be excluded;
2. Protected type. These are devices with a practically sealed housing. Allowed for installation in outdoor conditions. It is only necessary to avoid exposure to direct sunlight and rain.

There are differences between three-phase devices in the supply current of the electromagnet coil. For some starters, the coil is switched to a phase voltage of 220 V, for others - to a linear voltage of 380 V.

Operation of contactors and magnetic starters

In order for the devices to serve for a long time and without failure, it is necessary to carry out the following activities regularly under operating conditions:

1. Visual inspection. It reveals obvious damage and deformation of the casing. By removing the cover, you can inspect the condition internal parts. In working condition, check whether there are any vibrations and extraneous noise. If the contactor hums during operation, check the tightness of the armature and the reliability of the mechanical connections;
2. Controlling the progress of the anchor. By manually pressing, you can check the smoothness of its movement, the absence of interference, and the clarity of the spring;
3. Checking and cleaning contacts. If there is no “carbon deposits” on the contacts, then cleaning is not necessary due to the possibility of destruction of the thin coating. The contacts must be aligned and all poles must be in contact with as much of the surface as possible at the same time. Otherwise, adjustment is made;
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5.1 General information

Contactor– a device for switching power electrical circuits. They are widely used in remote control systems for electric drives and automation. Categories of application of contactors are characterized by the parameters of the circuits they switch, depending on the nature of the load.

a) AC contactors: AC-1, AC-2, AC-3, AC-4, AC-11, AC-22.

b) DC contactors: DS-1, DS-2, DS-3, DS-4, DS-5, DS-11, DS-12.

The rated current of the contactor I nom is the current that can be passed through the closed main contacts for 8 hours without switching, and the temperature rise of the contactor parts should not be more than permissible.

The rated voltage U H is the highest voltage of the switched circuit for which the contactor is designed to operate.

Mechanical wear resistance is determined by the number of on/off cycles of the contactor without repairing or replacing its components and parts. It amounts to 10÷20 million operations.

Switching wear resistance is determined by the number of cycles of the VO circuit with current, after which contact replacement is required. It amounts to 2÷3 million operations.

The proper switching time consists of the time of increase in the flux in the electric magnet to the starting flux value and the time of movement of the armature. Most of this time is spent building up the flow.

The actual shutdown time is the time from the moment the electric magnet is de-energized until the contacts open. It is determined by the time the flow decays from the steady value to the release flow.

The contactor has the following main components: a contact system, an arc extinguishing device, an electric magnet and a system of auxiliary contacts.

5.2 DC contactors

Designed for switching DC circuits and driven by a DC electric magnet.

Contactors of the KPV - 600 series, KTPV - 600 type, KP 7, KP 207, KMV - 521, KMG16, KMG19, MK5, MK6, DC series MK and others are produced.

Rated voltages: main circuit – 220, 440 V; retractor coil - 24, 48, 60, 110, 220, 440 V.

Contact system. Linear rolling contacts are used, and in the MK series, bridge type. To prevent vibration of the contacts, the contact spring creates a preliminary pressure of approximately 50% of the final pressure.

Contactors of the KPV series have two versions of the contact system: with normally open and closed contacts.

In DC contactors, arc extinguishing devices with electromagnetic blowing and a current coil are most widely used.

Electromagnet. Valve-type electric magnets are common. In order to increase mechanical wear resistance, rotation of the armature on a prism is used.

When the electric magnet is turned on, the forces of the return and contact springs are overcome. The traction characteristic of the electric magnet should at all points be higher than the characteristic of these springs with a minimum permissible voltage on the coil 0.85U H and its heated state.

The most difficult moment when turning on is overcoming the force at the moment of contact with the main contacts, since the electric magnet must develop significant force with a large working gap.

For DC contactors, the return coefficient KV = U OTP / U SR is small (0.2÷0.3), which does not allow the contactor to be used to protect the motor from voltage drop.

The highest voltage on the coil should not exceed 1.1U H, since at higher voltages the wear of the contacts increases due to increased armature impacts, and the temperature of the coil may exceed the permissible value.

In order to reduce the MMF of the coil, and therefore the power it consumes, the working stroke of the armature is selected small - 8-10 mm. For reliable arc extinguishing at low currents, a contact gap of 17-20 mm is required. In this regard, the distance of the point of contact of the movable contact from the axis of rotation of the movable system is taken to be 1.5-2 times greater than the distance from the axis of the pole to the axis of rotation.

5.3 AC contactors.

Available for currents from 10 to 1000A with the number of main contacts from one to five (Fig. 31)

Due to more favorable arc extinguishing conditions, the gap between the main contacts is smaller than in DC contactors.

The moving contact, unlike DC contactors, is flat without rolling.

Figure 31. AC contactor solenoid design.

For ease of use, the movable and fixed contacts are made easily replaceable.

Bridge type is common in AC contactors. contact system with two circuit breaks per pole, which ensures rapid extinguishing of the arc in the absence of flexible connections. Ceramic metal is used as the material for the main contacts, and silver or bimetal (copper coated with a thin silver plate) is used for auxiliary contacts.

The arc extinguishing system consists of a series coil, core, pole plates and ceramic chamber. Arc suppression grids are widely used in AC contactors.

Electromagnet. Electric magnets are widely used

with W and P-shaped magnetic cores. To absorb the impact of the anchor on the fixed core, the latter is attached to the base using springs.

In order to eliminate vibration of the armature in the on position, short-circuited turns are installed on the poles of the magnetic system, which are most effective with a small working gap. To ensure a tight fit of the poles, their surface must be ground.

Due to the change in the inductance of the coil, the current when the armature is attracted is significantly less than when it is released. Inductive reactance magnet coils , if we take into account that , then .

.

15 times.

The electric magnets of AC contactors can also be powered by DC power.

Due to the great starting current It is unacceptable to supply voltage to the coil if the armature is held in the released state for some reason.

The relatively high return coefficient Kv=0.6÷0.7 allows the use of AC contactors to protect motors from a decrease in mains voltage.

The actuation and release of an alternating current magnet occurs much faster than that of a direct current magnet. The actual response time of the contactors is 0.03÷0.05 s, and the release time is 0.02 s.

When the coil is powered from a DC network, a special coil with a boost resistor is used, which is shunted by the opening auxiliary contact of the contactor (Fig. 33).

2.-main contact;

3.- arc extinguishing chamber;

4.-current arc extinguishing coil;

5.- insulation board.

The contactor has auxiliary 2 C and 2 P contacts located to the left of the main contact.

Figure 33. Design of single-pole direct current contactors, for a current of 2500 A, voltage up to 1000 V KP 7U3 - without tripping springs, KP 207U3 - with tripping springs.

AC contactors are produced following types: KT6000/00, KT6000/20, KTP6000/00, KTP6000/2, KT64, KTP64, KT65, KTP65, KT series (KT7000B, KTP7000B, KT6500, KTP6500, KT7039), KT7000, KNT, MK series, G15, KMG16, KMG19, KMG17-19, KMG17D19, KMG18-19, KMG18D19, KT6600, KT6000B, KT6000A, KTP6000B, KT7100U, KT7200U and others.

Rated voltage: main circuit - 380, 660, 1140 V, retractor coil -24, 36, 42, 110, 127, 220, 230, 240, 380, 400, 415, 500, 660 V.

Gersikone contactors series KMG15, types KMG16, KMG19,
KMG17-19, KMG17D19, KMG18-19, KMG18D19.

KMG – magnetically controlled sealed contactor. The main element of contactors is the gersikon - power reed switch.

Number of poles – 1, 2, 3

Rated currents – 6.3; 10 A

Rated voltage – alternating 380 V, direct 75 V.

Rated voltage of switching coils:

On direct current – ​​12, 24, 48, 60, 10, 20 V;

On alternating – 110, 127, 220 V.

MK series contactors. Designed to work in power circuits of direct current - 220, 440 V and alternating current - 380, 500, 660 V.

Rated current: main circuit 40, 63, 100, 160 A; auxiliary contacts 10A.

Contactors with an arcless switching unit are designed for operation in intermittent and short-term operating modes.

The contactors have a monoblock design. Basic assembly units: magnetic system, contact systems of the main and auxiliary circuits. Arcless switching contactors have a semiconductor block.

The magnetic system of all contactors, with the exception of MK1-10, MK2-10, is two-coil; the coils are connected in parallel or in series depending on the voltage of the control circuit.

The main circuit contact systems are structurally designed in the form of one-, two- and three-element blocks, bridge type.

KT6600 series contactors AC 660V with AC control 36-600V, 66 series. Rated current 63, 100, 160 A.

Number of main contacts 2, 3, 4, 5.

Monobloc contactor design with rotary system. The contactor consists of el. magnet, contact-arc system and auxiliary contact block.

The armature of the electric magnet is penetrating; a screen is installed on the upper pole of the core.

The main contacts (movable) are finger type, contact parameters are adjustable. Electrical magnetic arc extinction is used. Arc chutes are separate for each pole. To limit arc emission, spring flame arresters are installed in the chambers, and to speed up extinguishing, a potential horn of a moving contact is installed.

The main contacts are made with contact pads made of a metal-ceramic composition based on silver. Auxiliary contacts are based on silver. Auxiliary contacts are bridge type with a silver contact part.

Contactors of the KT6000/00, KTP6000/00, KT6000/20 series.

KT – control of alternating current, KTP – direct current. In=16 A.

Highest frequency inclusions per hour are 600, and for KT6000/20-60 per hour.

After switching on the KT6000/20 contactors, the voltage is removed, and the moving contactor system is held in the on position by a latching mechanism.

The contactor is switched off using an electric switch. the magnet of the latching mechanism when it is turned on to voltage. After disconnecting the voltage contactors with electric magnet coils, the latches are automatically removed.

Contacts are made of silver.

Contactors of the KT6000/2, KT6000/3 series.

2 – with closing contacts and a latch;

3 – with make and break contacts and a latch.

Rated current of NO contacts – 130, 250, 630, 1000 A. NO contacts – 1, 2, 3. Permissible switching frequency 60 per hour.

Magnetic, contact-arc system, auxiliary circuit contacts are installed along the rack and shaft of the contactor.

The latching mechanism of the contactors is installed above the magnetic system. Contactors have el. a magnetic arc extinguishing device consisting of an arc extinguishing coil, a magnetic core, a fixed contact horn and an arc extinguishing chamber with a narrow slot.

The make and break contacts are made with metal-ceramic overlays based on silver.

Contactors of the KT6000A, KT6000B, KTP6000B, KT7000B series.

Rated current – ​​100, 160, 250, 400, 630 A.

Number of poles: 2, 3, 4, 5.

A – increased switching capacity – 500 thousand cycles

B – modernized.

Switching frequency per hour from 30 to 1200.

Contactors are made with a rotary type magnetic system.

The main contacts are finger type.

Contactors of types KT7100U, KT7200U. In=63, 125 A.

U - unified, for integration into magnetic starters.

Monoblock type structures with a rotating moving system.

The main movable contacts are finger type, contact parameters are adjustable. Electrical magnetic arc extinction is used. Contact pads made of metal-ceramic composition of silver. Auxiliary contacts of bridge type made of silver.

Contactors types KP7, KP207. In = 2500 A, Un = 600 V.

Single pole. The contactor consists of a magnetic system with two switching coils, a contact system and an arc extinguishing device (Fig. 33). The contact system has two pairs of parallel-connected main contacts and one pair of arc extinguishing contacts. The arcing coil is connected in series with the arcing contacts, and the main contacts, in the closed state, bypass the arcing contacts. Main contacts with silver plates.

Vacuum contactors KT12R series.

R - mining. In = 250, 400 A; Un=600, 1140 V.

Switching frequency per hour, VO cycles up to 1200. Designed for switching on and off IM with K3 rotor, transformers, etc.

Three vacuum arc extinguishing chambers.

Full armature travel 9 mm.

Semiconductor arc extinguishing device the MK contactor is shown in Fig. 35, A

Figure 35. Schemes of semiconductor attachments for contactors.

The main contacts of the main battery are shunted by thyristors VS1 and VS2, which are controlled through diodes VD2 and VD3. Let the direction of the current during a given half-cycle correspond to that shown in Fig., then the voltage applied between the GC bridge and the upper fixed main contact opens VS1 through VD2, through which the circuit current begins to flow. After the current passes through zero, the thyristor closes and the shutdown process ends.

If the current has reverse polarity, then diode VD3 and thyristor VS2 work.

To protect the control transitions of thyristors from overvoltages, diodes VD1 and VD4 are used.

The RC circuit reduces the overvoltage on the thyristors.

I-terminals for the front connection of conductors, II for the rear

1 - fixed contact,

2-moving contact

3-arc extinguisher horn

4- lever connected to the anchor

5-adjustment screw

6- moving contact spring

7-adjusting nut

9,10 - flexible connection

11 block

12-rail

16-arc chamber

17- steel plate (flame extinguishers)

Figure 34. Design of the AC contactor KT 64-3U3 for a current of 100 A, voltage 380 V. (Modification KT 6000)

In Fig. 35, b shows the semiconductor device of contactors KT64, KTP64, KT65, KTP65 (Fig. 34) for one phase. In parallel with the main battery, thyristors VS1 and VS2 are switched on in back-to-back parallel mode. Control is carried out from current transformers TT, mounted on the main contact bus. When the contactor is on, current flows only through the contacts, because The voltage drop across them is less than the threshold voltage of the thyristors.

When the contactor is turned off, the current passes into the circuit of thyristors, which are in the on state under the influence of control from the CT. In this case, an arc does not form, since the drop on the thyristors does not exceed 4÷5 V, which is less than on an arc.

When the sign of the sinusoidal current changes, the control pulses are removed, and when the sinusoidal current passes through zero for the first time, the thyristors are closed.

Conventional arc chutes are also available if the device fails.

5.4 Magnetic starters.

They are the main type of control equipment for low-voltage (up to 660 V) IMs with a K3 rotor. To protect them from reboots of unacceptable duration and “phase loss,” electric thermal relays are installed in the starter.

When turning on the blood pressure Ip=(5÷6)In. With such a current, even slight vibration of the contacts quickly disables them. In order to reduce the vibration time, the contacts and moving parts of the starters are made as light as possible, their speed is reduced, and the contact pressure is increased.

When the engine is turned off, the recovering voltage at the contacts is equal to the difference between the mains voltage and the motor emf. As a result, a voltage of (15-20)% Un appears on the contacts, i.e. shutdown occurs under lighter conditions.

In operation, the starter has to disconnect the engine from the network immediately after starting. In these cases, it turns off a current equal to 6In and a recovery voltage equal to Un of the network.

According to current standards, after turning on and off the stalled motor 50 times, the starter must be suitable for further operation.

Taking into account the operating conditions of the starter. They use a bridge contact system with a double circuit break, and this allows arc-free switching without the use of arc extinguishing devices. The current-carrying bars from the clamps to the fixed contacts are made in such a way that the electric dynamic forces blow the arc off the contacts.

The magnetic system includes a U or Sh - shaped forward-moving electric magnet (Fig. 32). Contact pressure is created by a spring resting against the traverse.

1- fixed contacts;

2-moving contacts;

3-pin bridge;

4- pressure spring;

5- detail of connection of contact bridges;

6- traverse;

7- electromagnet armature;

8- return spring;

9- electromagnet coil;

10-building.

Figure 32. Typical design of a linear magnetic starter.

Return starter to initial position occurs due to a spring located inside the electric magnet.

To eliminate armature vibration, K3 turns are used.

High ratio The return of alternating current electric magnets allows you to protect the engine from a decrease in network voltage (the electric magnet releases at U = (0.6÷0.7) Un).

For reversible drives, two starters are used, interlocked electrically or mechanically.

Magnetic starters of the PML, PMA, PM12 series and PMA-0000, PMU types are produced.

The technical data of starters indicates their rated current and rated motor power at various voltages, as well as the category of application.

In PMA series starters for currents from 40 to 160A and voltage 380-660 V, the electric magnet can be of either alternating or direct current.

The starters are equipped with electric thermal relays of the TRP (single-phase), TRN (two-phase), RTT and RTL (three-phase) types. TRP and RTL relays have a combined heating system. The relay is returned to its original position after activation by a button.

Starters can be equipped with overvoltage limiters of the arrester type (Fig. 37), which should limit switching overvoltages on the control coils. Can be built into the arc chute additional consoles: contact type PCL or PVL pneumatic attachments, “Start” or “Stop” buttons and a signal lamp.

a) on R-C element base b) on a varistor c) on a diode

element base element base

Figure 37. Electrical circuit diagrams for the connection of surge suppressors.

Electrical thermal relays are connected directly to the starter housings.

In seismic-resistant starters, zener diodes are switched in series and in parallel with the switching coil.

PML series starters. They can be made with three-pole RTL relays and be equipped with surge arresters. Starter size according to In 1-10A, 2-25A, 3-40A,
4-63A. May have additional attachments: PKL, PVL, “Start”, “Stop” buttons, signal lamps.

Contactors of starters have a linear magnetic system of the Ш-shaped type.

Starters type PMA-0000. They can be equipped with three-pole relays RTT5-06, surge arresters on R-C or varistor element base, control buttons and a signal lamp. Starter size: 0 - to 6.3A.

The starters have a W-shaped magnetic system.

PMA series starters. Designed to control three-phase IMs with a K3 rotor with a power from 18.5 to 75 kW. In the presence of relays RTT-2P, RTT-3P or posistor protection devices AZP or UVTZ-1M protect motors from overloads of unacceptable duration.

Electrical thermal relays with temperature compensation and manual reset have a non-operation current control range (0.85-1.15)In.

Starters can be equipped with: arrester, “Start”, “Stop” buttons, signal lamp.

Starter sizes: 3-40A; 4-63A; D-80A; 5-100A; 6-160A. Rated voltages of AC switching coils: 24-660 V; DC: 24-440 V.

Starter contactors of the 3rd magnitude have a linear W-shaped magnetic system.

Starter contactors of 4.5 and 6th magnitude have a forward-running magnetic system of the U-shaped type. In them, the vertical movement of the armature with the help of an L-shaped lever is converted into the horizontal movement of a traverse bearing movable main contacts.

PM12 series starters. They can be equipped with: arrester, RTT-5 relay, “Start”, “Stop” buttons, signal lamp.

Designation rated current: 004-4A; 016-16A; 025-25A; 040-40A;
063-63A.

Contactors of starters have a linear W-shaped magnetic system.

5.5 Thyristor starter.

One of the circuit options is shown in Fig. 36.