The electromagnetic starter is used for switching powerful electricity consumers, mainly in production. This article will discuss why a magnetic starter is needed, what is the principle of operation of a magnetic starter and the design of a magnetic starter. The design and principle of the starter, both for 380V and 220V circuits, are the same for a long time and have been well developed by designers.
As already mentioned, this is a switching device, in other words, a switch, this is its purpose. Starter contacts are designed for high current flowing through heating devices and powerful electric motors. These power contacts are actuated electromagnetically, so the starters can be controlled remotely using relatively low-power circuits. Therefore, a small button or limit switch can be used to connect powerful electric motors and other loads. The reversible starter ensures that asynchronous motors are turned on in any direction - clockwise or counterclockwise, at the choice of the operator or the control system.
Principle of operation
The principle of operation of a magnetic starter actually coincides with a relay. To operate the starter from pushbuttons without latching, self-locking from contacts parallel to the button is used. To turn off, a normally closed button is used, connected in series to the control circuit. When the contacts open, the starter turns off and is ready to be turned on again immediately after the contacts of the stop button are closed.
The “push-button” version of starter control is overwhelming for manual operations. In automation circuits, starters are usually kept in the on state by a continuous signal supplied from the discrete output of the controller to the intermediate relay.
There are different types of starters, among which there are reversible magnetic starters (a “headache” for novice electricians who are trying to understand how an unusual circuit works and are not used to thinking in electrical circuits). In fact, these are two starters operating strictly alternately: if one is turned on, then the other must be turned off, otherwise there will be a short circuit between the phases.
Its principle is as follows: if in one switched-on position the sequence of phases is A, B, C, then in another position there should be, for example, A, C, B, that is, two phases should swap places. This allows you to change the direction of the rotating field in asynchronous motors and run them in different directions, either clockwise or counterclockwise.
All types of magnetic starters are united by such design elements as an alternating current electromagnet, a system of moving and fixed power and auxiliary contacts. The supporting part is a body made of heat-resistant and non-flammable plastics. These plastics must be mechanically strong and not deform at elevated temperatures. Any starter is usually three-phase.
- Contact springs for smooth starting
- Moving contacts (bridges)
- Fixed contacts (plates)
- Plastic traverse
- Anchor
- Starter coil
- W-shaped part of the magnetic circuit
- Additional contacts
The classification of magnetic starters is made according to several criteria, among which the main one is usually the size of the starter. The value does not mean the dimensions or weight of the starter, but what current it can switch and how resistant it is to an arc in circuits with inductances (when the electric motor is turned off). The basis is a non-reversible magnetic starter, since the reversible ones are assembled from the latter. Magnetic starters operate under different conditions, so they are also classified according to the degree of protection: open, protected, dust-splash-proof.
The operation of a magnetic starter very often requires a thermal relay. All types of magnetic starters have structurally compatible thermal relays. They are often produced by the same manufacturer. A particularly important application of thermal relays is to protect electric motors from overheating. The thermal relay consists of two-phase bimetallic conductors (conductors with different coefficients of thermal expansion) - one for each phase.
From an electrical point of view, they are resistors with very low resistance, and thus serve as current sensors. When too much current flows through the phases (or one of them), the bimetallic strip bends and opens the magnetic contacts, that is, the contacts in the starter coil circuit. Thermal relays are connected between the starter and the load.
Modular starters are becoming more and more common. These are DIN rail mounted starters. This is a metal profile strip fixed in cabinets on a panel. The simplicity and ease of installation are exceptional. Next to the starter (contactor) you can attach thermal relays, circuit breakers, RCDs (residual current devices), microprocessor controllers and much more. Modular devices are very easy to assemble into circuits, thanks to the wire channels laid between the DIN rails. Installation is carried out with stripped wires of the required cross-section and crimped lugs. The tips are inserted into the holes of the device terminals according to the circuit diagram and clamped with screws.
Markings required for installation and repair are applied to the top side of the starters. There is a type designation, a contact diagram and in some cases manufacturers leave space for a sticker or signature of consumer data.
Great advances in power electronics over the past decades have meant that most major manufacturers now offer consumers contactless starters containing high-power semiconductor switches. They have certain advantages. They operate silently, do not spark, and have a high switching frequency.
Some models, thanks to PWM controllers, allow smooth starting of electric motors, and even network interfaces are provided for automation. Disadvantages include high price, highly qualified repair personnel and unsafe galvanic connection to the network, which can threaten repair electricians.
Conclusion
Despite the introduction of electronic switches: already outdated thyristors and triacs, powerful field-effect transistors, and promising IGBT transistors, magnetic starters retain their importance. They are the ones who reliably break circuits, without any residual currents or leaks dangerous to personnel or equipment. In fact, this is the same immortal “switch” that is guaranteed to de-energize the electrical installation. high-quality starters never jam and you need to purchase just such ones.
Switches are used to turn on lighting, and buttons and switches are used for household electrical appliances. These electrical equipment have one thing in common: they consume little power. And also - they are not turned on remotely or by automation devices. These problems are solved using magnetic starters.
Magnetic starter circuit. Device
The starter consists of two parts located in one housing: a control electromagnet and a contact system.
The control electromagnet includes a coil with a magnetic core, which includes movable and stationary parts, held open by a spring. When voltage is applied to the coil, the moving part of the magnetic circuit is attracted to the stationary part. The moving part is mechanically connected to the contact system.
The contact system includes movable and fixed groups of contacts. When voltage is applied to the starter coil, the magnetic circuit attracts the moving contacts to the stationary ones and the power circuits are closed. When the voltage is removed from the coil, under the action of a spring, the moving part of the magnetic circuit, together with the contacts, is brought to its original position.
An additional contact group is added to the power contacts of the starter, intended for use in control circuits. Its contacts are normally open (designated by numbers “13” and “14”) or normally closed (“23” and “24”).
Electrical characteristics of magnetic starters
Starter rated current- this is the current withstood by power contacts for a long time. Some models of outdated starters have different overall dimensions or “size” for different current ranges.
Rated voltage– supply voltage that the insulation between the power contacts can withstand.
Control coil voltage– operating voltage at which the starter control coil operates. Starters with coils are produced, operating from a direct or alternating current network.
The starter control is not necessarily powered by the voltage of the power circuits; in some cases, the control circuits are independently powered. Therefore, control coils are available in a wide range of voltages.
| Alternating current | 12 | 36 | 48 | 110 | 220 | 380 |
| D.C | 12 | 36 | 48 | 110 | 220 |
Reversing magnetic starter, push-button station
The most common application of starters is motor control. Initially, the name of the device was derived from the word “start”. The circuits use additional contacts built into the case: to pick up a command from the “Start” button. By the normally closed contacts of the “Stop” button, the power supply circuit of the coil is broken and the starter disappears.
Issued reversible blocks containing two conventional starters connected electrically and mechanically. A mechanical lock prevents them from turning on at the same time. Electrical connections ensure reversal of two phases when operating different starters, as well as eliminating the possibility of supplying power to both control coils simultaneously.
For ease of installation, starters are produced in housings together with control buttons. To connect, just connect the power cable and the outgoing cable to them.
In other cases, they are used to control work push-button stations, switching the control coil circuit and connected to the starter with a control cable. For conventional starters, two buttons are used, combined in one housing - “Start” and “Stop”, for reversible ones - three: “Forward”, “Back” and “Stop”. The “Stop” button for quick shutdown in case of an accident or danger is mushroom-shaped.
Depending on the purpose, starters are made with three or four poles. But there are also devices that have one or two poles.
Manufacturers are expanding the range of manufactured devices accessories, expanding their capabilities. These include:
- additional contact blocks that allow you to connect signal lamps to the control circuit and generate commands, depending on the state of the starter, for the operation of other devices;
- time delay blocks that delay the operation or shutdown of the starter;
- sets of accessories that turn two starters into a reversible starter assembly;
- contact pads that allow you to connect cables of larger cross-section to the starter.
To protect electric motors from overloads, they are used together with starters. thermal relays. Manufacturers produce them for the corresponding device models. The thermal relay contains a contact that opens when triggered and breaks the power circuit of the starter coil. To turn it on again, the contact must be returned to its original position by pressing the button on the housing. To protect against short circuits, an automatic switch is installed in front of the starter, disconnected from the starting currents of the electric motor.
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, 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 Designed for indoor installation where the environment does not contain a significant amount of dust.
Dust-splash-proof magnetic starters Designed for both indoor and outdoor installations in places protected from sunlight and rain (under a canopy).
PML series magnetic starter
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 occurs: 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 normally closed block contacts close.
Reversing magnetic starters are two conventional starters mounted on a common base (panel) 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 even 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 the 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.
A treatise on how to connect a magnetic starter (contactor) to a push-button post.
The Internet is full of all sorts of diagrams and interpretations about how to connect a magnetic starter,
I think that for a simple person (not an electrician), who only needs to connect a magnetic starter somewhere once, these instructions are written incomprehensibly, complicatedly, with a bunch of abbreviations (which personally infuriate me) and in the end the task can become overwhelming.
In fact, connecting an electromagnetic starter (contactor) is quite simple, and in this article I will try to describe this process in as much detail as possible, humanly, without incomprehensible abbreviations and abstruse phrases.
Once again, this article is intended for ordinary people who just need to connect the damn magnetic starter.
Actually the magnetic starter itself. A little theory: this device is designed to start, stop and reverse the engine (I’m not considering a reversing starter today, I’ll write about it later). Also, the starter is very convenient in any other load control, be it lighting, heaters, other devices, in general, everything that can and should be turned on and off remotely (from a button).
It works as follows: when voltage is applied to the electromagnet coil, the core connected to pairs of contacts is drawn into the coil and the contacts close; when the voltage is removed from the coil, the contacts open.
Next is the view from the facade. It shows four pairs of contacts that close when the starter is triggered. The first three pairs of contacts are directly involved in switching the main load. The last pair of contacts, the one circled in red, is the so-called “Block Contact”, which is involved in supplying voltage to the coil at the moment when the Start button is released.
View from above. Contacts A1 and A2 are located here, these are the coil contacts to which voltage must be applied in order for everything to turn on. Contact A2 is duplicated on the contactor from below for ease of switching.
To implement the scheme, we also need a push-button station with Start and Stop buttons.
The most common model costs 70 rubles in the store.
We open it up, and the buttons, or rather their switching part, appear before our eyes.
I’ll say right away that these buttons do not differ in any way in structure, each of them has a pair of contacts, one is normally open (contacts are open) the other is normally closed (contacts are closed). Their functionality differs during operation due to different connections
So look, contacts 1 and 2 are open to each other, and contacts 3 and 4 are closed. When you press the button, contacts 1 and 2 close, contacts 3 and 4 open.
We begin the connection: first we connect the power supply wires to the main terminals of the contactor (generally the contactor is three-phase, but for the example I used only one pair of power contacts) from one of the power terminals we take a phase and pull it to the push-button station, the phase can be taken from another place.
And we bring this phase to the push-button post and connect it to terminal 4 of the Stop button.
For reference: there will ultimately be three wires between the push-button station and the starter; for switching you can use a regular VVG 3*1.5.
From terminal 3 of the Stop button, pull the wire to terminal 2 of the Start button.
Also, connect the remaining two wires to terminals 1 and 2 of the Start button,
blue after the Start button, yellow-green before.
We leave the push-button post in this state, the work with it is completed.
Let's move on to the starter.
First, we connect the neutral conductor to terminal A1 (the one for the coil).
Then, we connect the blue conductor (to avoid confusion, I marked it with black electrical tape) that came from the push-button station from terminal 1 to contact A2.
That is, the moment you press the start button, the coil will fire and the starter will close.
Next, we make sure that when the Start button is released, the starter remains on,
To do this, we connect the yellow-green wire (there is always a phase on it except for the moment when the stop button is pressed) to the terminal of the contact block.
Then, from the opposite terminal of the contact block, pull the wires to the A2 terminal duplicated at the bottom. 
That's it, the circuit is assembled and functioning.
What happens in the end and how it all works: When the start button is pressed, current flows through the blue wire to terminal A2, the coil closes and the starter is triggered. Then, when you release the Start button, the current flows past this button, through the yellow-green conductor and through the closed block contact, also to the coil, only to the duplicated contact A2, at this moment the whole system works. When we press the Stop button, we interrupt the flow of current through the contact block to the coil and the starter opens.
That's all for me, I hope I explained myself clearly and those who were not clear before understood.
Good luck to everyone in connecting magnetic starters, and I look forward to seeing you again on my website, there will be many more interesting articles written in simple language.
Starter (MES 441-14-38) - a combination of all switching devices necessary to start and stop the engine, with overload protection.
Electromagnetic starter (magnetic starter) - a starter in which the force required to close the main contacts is provided by an electromagnet.
A magnetic starter (MP) is the most common electrical device for starting electric motors. Its main advantages: remote control of starts, simplicity of circuits, protection against undervoltage and overload, acceptable weight and size parameters, which can be called external properties, since they to a certain extent affect the quality of the entire system.
The external properties of MPs are constantly being improved (for example, in Russia a MP circuit with protection against network phase failure was recently patented). Large manufacturers representing these products in Russia: OJSC Kashinsky Electrical Equipment Plant, OJSC Uralelectrokontaktor, OJSC Novosibirsk Low-Voltage Equipment Plant, OJSC Cheboksary Electrical Equipment Plant (Russia), EKFelectrotechnica (Russia), SchneiderElectric (France), GeneralElectric (USA), Moeller (Germany), ABB (Germany), Siemens (Germany), Legrand (France), ChintGroupCo (China), etc.
Magnetic starters are selected depending on environmental conditions and control circuit according to:
Rated voltage;
Rated current;
The current of the heating element of the thermal relay;
Retractor coil voltage.
Ump ≥ Un mouth; (1.1)
Imp ≥ In mouth, (1.2)
where Ump, Imp are the rated values of voltage (V) and current (A) of the magnetic starter, respectively;
Un mouth, In mouth - respectively, the rated values of voltage (V) and current (A) of the electrical installation.
Thermal relays are checked for compliance of their rated current 1tr n, the rated current of the heating element Ine, the upper Iset max and the lower Iset min limits for adjusting the set current and the set current setting Iset p with the rated motor current In dv:
Itr n ≥ Ine ≥ In dv; (1.3)
Iset max ≥ In dv ≥ Iset min; (1.4)
Iset r = In dv. (1.5)
For electric motors with a low load factor and operating current Iр dv, in order to increase the reliability of protection, use the following ratio:
The rated phase current of the electric motor Iн dv or according to the conventions adopted in electrical machines - I1 nom f is determined by the formula:
where P2 nom is the rated power of the electric motor, kW;
U1л - rated line voltage, V;
m - efficiency factor, p.u.;
cos f - power factor, p.u.
The most general and widespread requirement that a consumer makes when choosing an MP is the value of the switched current, and according to this parameter, the MPs from the above manufacturers can be divided into several groups:
1) MP with currents (we are talking about maximum current values) up to 100 A, and this includes MP series PML for currents of 10-80 A, series PMU for currents 9-95 A;
2) MP with currents up to 400 A, representatives of which are MP series PMA for currents 40-160 A, series PM12 for currents 10-250 A (Russia) and foreign magnetic starters ChintGroupCo series NC1 and NC3 for currents 9-370 A;
3) MP with currents up to 1000 A, representatives of which are MP from the Moeller DIL series for currents of 20-855 A;
4) MP with currents above 1000 A, which include MP GE Power Controls series CL and CK for currents of 25-1250 A and MP CHEAZ-Benedikt for currents of 10-1200 A.
Among other things, for switching currents from 100 A to 1000 A, Russian manufacturers offer contactors of the KT-6000, MK6 series and vacuum contactors of the KV1 and KT12 series for general industrial use. Table 1.1 presents the indicators of the first group of MPs, as the most widespread.
For the MPs shown in Figure 1.1, belonging to groups 1, 2, 3 and 4, the corresponding indicators are presented in Table 1.
Rice. 1.1.
Analysis of the characteristics (see Table 1.1) shows that all MPs have almost identical parameters (the differences are insignificant). In this case, as a rule, when choosing a MP, they are guided by two fundamental indicators: operating mode and load power. However, with strict restrictions on size, preference should be given to MP No. 7 and No. 5, the dimensions of which are almost one and a half times smaller than the others, all other parameters being equal.
In terms of power consumed by the coils when turned on, the most economical is MP No. 6, with savings ranging from 13 to 30%. In terms of overall service life, preference should be given to MPs No. 1, 2, 3, 6. In terms of estimated cost, MPs No. 1 and No. 2 are the leaders, since the cost of the remaining MPs is significantly higher.
It should be noted that in practice, especially when using MP in automated control systems, preference is given to imported devices, because their auxiliary contacts provide the so-called “dry contact” used in microprocessor technology devices.
In addition, the undoubted advantages of imported MP include:
MP version with DC coils (the exception is OJSC VNIIR, which supplies PM12 starters with DC coils);
MP nomenclature | |||||||
Engine power, kW | |||||||
Power consumed by coils when turned on, VA | |||||||
Power consumed by coils when holding, VA | |||||||
Mechanical wear resistance, starting frequency per hour | |||||||
Total resource, million cycles | |||||||
Electrical wear resistance, switching frequency per hour | |||||||
Response time: short circuit, ms | |||||||
Response time: opening, ms | |||||||
Minimum incl. ability: voltage V/current A | |||||||
Dimensions, HxWxC mm | |||||||
Weight, kg |
A very wide range of not only standard accessories for MP (auxiliary contact blocks, thermal relays, surge suppressors), but also all kinds of devices that greatly simplify the installation and maintenance of devices.
Considering the fact that the uninterrupted operation of an electric motor largely depends on the reliability of the motor, such an important indicator of reliability as the technical availability factor deserves special consideration. This indicator takes into account not only the failure rate, but also the time required to restore the operation of the MP, characterizing the likelihood that the device will work at the right moment and the system will perform the required tasks. For most MPs listed in Table 1.1, manufacturers do not indicate such indicators as mean time between failures or failure rate in the technical characteristics of the product. However, the accumulated statistical data on the operation of the above series of MPs allows us to obtain the following averaged data on the availability factor: for Russian-made MPs No. 1, 3, 7 (Table 1.1) the availability coefficient is 0.9905, for Ukrainian-made MPs No. 2 - 0.9812 , and for imported MPs No. 4, 5, 6 - 0.9383. Thus, at facilities of increased importance, where high reliability is required, it is more advisable to use MP No. 1,3,7.
Taking into account the extremely wide distribution of MPs, reducing the power consumed by them is of great importance. In an electromagnetic starter, power is consumed in an electromagnet and a thermal relay. Losses in an electromagnet are approximately 60%, in thermal relays - 40%. In order to reduce losses in the electromagnet, cold-rolled steel E-310 is used. MP series PML and PM12 have a switching capacity of up to 20 * 106 operations and a switching frequency of up to 1200 per hour (Table 1.1). The choice of MP is carried out according to the rated network voltage, the rated supply voltage of the coils and the rated switching current of the electrical receiver.
It is allowed to select the MP according to the “starter size”: 1 value - 10 A, 4.5 kW; 2nd value - 25 A, 11 kW, 3rd value - 40 A, 18 kW; 4th value - 63 A, 30 kW; 5th value - 100 A, 45 kW; 6th value - 160 A, 75 kW; 7th size - 250 A, 110 kW.
This term characterizes the permissible MP current through power contacts at a voltage of 380 Volts and in the AC-3 starter operating mode.
Categories of MP application: AC-1 - active or low inductive MP load; AC-3 - direct start mode of a squirrel-cage motor, shutdown of a rotating motor; AC-4 - starting an electric motor with a squirrel-cage rotor, turning off stationary or slowly rotating engines, countercurrent braking.
All necessary parameters are indicated on the MP housings. This allows you to check the compliance of the mounted MP for a specific circuit during installation. For imported MPs, the main parameter is not the “starter size”, but the power for which the MP is designed under various conditions. More often than not, this turns out to be more convenient when choosing the desired MP.
The design of many MPs provides for the possibility of quick hinged installation on them: additional normally closed or normally open contacts; ON or OFF delay relay with delay time up to 160 s; thermal relays.
Electromagnetic starters of the PML series are designed for remote starting by direct connection to the network, stopping and reversing three-phase asynchronous electric motors with a squirrel-cage rotor at voltages up to 660V AC with a frequency of 50 Hz, and when equipped with three-pole thermal relays of the RTL series - to protect controlled electric motors from overloads of unacceptable duration and from currents arising when one of the phases breaks. MPs can be equipped with surge suppressors such as surge arresters. With this configuration, the MPs are suitable for operation in control systems using microprocessor technology when the switching coil is bypassed with an interference suppression device or with thyristor control. Rated alternating voltage of switching coils: 24, 36, 40, 48, 110, 127, 220, 230, 240, 380, 400, 415, 500, 660V frequency 50 Hz and 110, 220, 380, 400, 415, 440V frequency 60 Hz MP type PML for currents of 10...63 A have a linear magnetic system of the Sh-shaped type. The contact system is located in front of the magnetic one. The moving part of the electromagnet is integral with the traverse, which contains movable contacts and their springs. Thermal relays of the RTL series are connected directly to the starter housings.
Structure of marking of MP type PML.
PML-X1 X2 X3 X4 X5 X6 X7 X8:
PML - series of electromagnetic starters;
X1 - starter value based on rated current;
1 - 10 (16) A; 2-25 A; 3 - 40 A; 4 - 63 (80) A; 5 - 125 A; 6 - 160 A; 7 - 250 A.
X2 - MP version according to purpose and the presence of a thermal relay:
1- irreversible MP without thermal relay;
2- irreversible MP with thermal relay;
5 - reversible MP without a thermal relay with mechanical interlocking for the degree of protection IP00, IP20 and with electrical and mechanical interlocking for the degree of protection IP40, IP54;
6 - reversible MP with a thermal relay with electrical and mechanical interlocking;
7 - MP with a star-delta circuit, degree of protection IP54 (MP for a three-phase asynchronous motor, in the starting position of which the stator windings are connected by a star, and in the operating position by a delta).
X3 - MP version according to the degree of protection and the presence of control buttons and a warning lamp:
0 - IP00; 1 - IP54 without buttons; 2 - IP54 with “Start” and “Stop” buttons;
3 - IP54 with “Start”, “Stop” buttons and a signal lamp (manufactured only for voltages 127, 220 and 380 V, 50 Hz);
4 - IP40 without buttons; 5 - IP40 with “Start” and “Stop” buttons; 6 - IP20.
X4 - number and type of auxiliary circuit contacts:
0 - 1z (for current 10 and 25 A), 1z + 1p (for current 40 and 63 A), alternating
1 - 1p (for current 10 and 25 A), alternating current;
2 - 1z (for current 10, 25, 40 and 63 A), alternating current;
5 - 1z (for 10 and 25 A), direct current;
6 - 1р (for current 10 and 25 A), direct current).
X5 - earthquake-resistant version MP (C);
X6 - MP version with mounting on standard rails P2-1 and
X7 - climatic version (O) and placement category (2, 4); X8 - version for electrical wear resistance (A, B, C). MP series PML (Fig. 1.2) consist of a fixed part (Fig. 1.2, item 2), fixed in the base, and a moving part (Fig. 1.2, item 3) with contacts for switching the power circuit. The operation of the MP is controlled using an electromagnetic coil
control (Fig. 1.2, item 4), located on the middle rod of the fixed part of the W-shaped magnetic circuit.
Under the influence of the electromagnetic field of the retractor coil (Fig. 1.2, item 4), which occurs when current flows through it, the two parts of the magnetic circuit are closed (Fig. 1.2, item 3, 4) overcoming the resistance of the return spring (Fig. 1.2, item 9), as well as springs of movable contacts. In this case, the contacts close and the device is switched.
Rice. 1.2.
1 - base made of heat-resistant plastic; 2 - fixed part of the magnetic circuit; 3 - moving part of the magnetic circuit; 4 - electromagnetic control coil; 5 - contact clamps; 6 - metal platform (for starters with a rating of over 25 A); 7 - traverse with moving contacts; 8 - fastening screw; 9 - return spring; 10 - aluminum rings; 11 - fixed contact; 12 - clip with a notch for fixing the conductor
On the MP you can install a 2-pin or 4-pin attachment with a different set of normally open and closed contacts. Contact attachments (CP) are mechanically connected to the MP from the side of the input terminals (top) and fixed above the MP cross-arm. The fastening method provides a rigid and reliable connection between the gearbox and the MP.
The PKL series contact attachment (Fig. 1.3) is designed to increase the number of auxiliary contacts in electric drive control circuits up to 440 V DC and up to 660 V AC
low current with a frequency of 50 and 60 Hz. CPs are installed on MP series PML-1000....PML-4000 and on intermediate relays of the RPL series. Structure of the symbol of the KP series PKL PKL-X1 X2 X3 X4 4 X5:
PKL - symbol of the series;
X1 - number of closing contacts (0; 1; 2; 4);
X2 - number of normally open contacts (0; 1; 2; 4);
X3 - version of the attachment according to the degree of protection;
Rice. 1.3
X4 - climatic version O, OM according to GOST 15150-69;
X5 - version for switching wear resistance in normal switching mode:
A - 3-106 cycles; B - 1.6-106 cycles.
Intermediate relays (RP) of the RPL series (Fig. 1.4) are intended for use as components in stationary installations, mainly in control circuits for electric drives at voltages up to 440 V DC and up to 660 V AC with a frequency of 50 and 60 Hz. The relays are suitable for operation in control systems using microprocessor technology when the retractor coil is bypassed with an arrester limiter or with thyristor control. If necessary, one of the PKL or PVL attachments can be installed on the RP. RP version M also allows the installation of one or two side PCB attachments. Rated contact current -16 A.
Structure of the symbol RP series RPL RPL-X1 X2 X3 X4 X5 4 X6:
RPL - symbol of the series;
X1 - relay version according to the type of control circuit current:
1 - with AC control;
X2 - number of closing contacts;
X3 - number of normally open contacts;
X4 - version of the attachment according to the degree of protection:
M - version with degree of protection IP20;
The absence of a letter means a set-top box with a degree of protection IP00;
Rice. 1.4.
X5 - climatic version O, OM according to GOST 15150-69;
X6 - Design for switching wear resistance in normal switching mode: A - 3⋅10 6 cycles; B - 1.6⋅10 6 cycles.
The PPL-04 memory attachment turns the RPL series RP into a bistable one. It consists of an electromagnet and a latch, which allows you to keep the relay contact system in the on position after de-energizing the relay winding. When voltage is applied to the winding of the memory device, the latch is released, and the RP returns to the state corresponding to the initial state of the single-stable RP.
Pneumatic time delay attachments of the PVL series (Fig. 1.5) or simply “attachment” are designed to create a time delay when turning on or off the MP. Attachments can only be installed on RP relays of the RPL series and on MP series PML-1000...PML-4000.
The attachment is installed on top of the MP, sliding along the guides until it stops, while the latch of the attachment with its protrusions extends beyond the protrusions on the MP body. The mounting method ensures a rigid and reliable connection between the attachment and the MP.
Rice. 1.5.
PVL series attachments are available: with a range of time delays from 0.1 to 15 s, from 0.1 to 30 s, from 10 to 100 s and from 10 to 180 s; with degrees of protection IP00 and IP20, in two wear resistance versions: A - 3⋅10 6 cycles; B - 1.6⋅10 6 cycles.
To increase the number of auxiliary contacts of the MP control circuit (with the PVL series attachment installed), a side-mounted attachment of the PKB series is used. The main characteristics of the PVL series consoles are given in Table 1.2.
RTL series relays (hereinafter referred to as “relays”) are designed to protect three-phase asynchronous motors with a squirrel-cage rotor from overload currents of unacceptable duration, including those arising from current asymmetry in the phases and from the loss of one of the phases.
Relays can be attached directly to the PML series MP or mounted individually on a rail or screwed to a panel. Individual installation of relays is carried out using terminal blocks of the KRL type (up to 100A). For currents up to 93 A, relays RTL-1000, 2000, 2000D are used.
Overall and installation dimensions of relays of the RTL-1000 and RTL-2000 types are shown in Figure 1.6.
Structure of the symbol for RTL series relays.
RTL-X1 XXX2 X3 X4 X5 X6 4:
RTL - letter designation of the relay series;
X1 is a figure indicating the rated current of the relay:
1 - version for currents up to 25A; 2 - version for currents up to 93A;
ХХХ2 - numbers indicating the range of setting currents (see Table 1.3);
X3 - relay version with reduced overall dimensions:
D - letter designating the design of the RTL-2000 relay for installation with magnetic starters PML-4160DM, PML-4560DM;
K - letter designating the version of the RTL-2000 relay for installation with PML-3000D magnetic starters;
M - letter designating the design of the relay with the degree of protection of the contact terminals IP20 in accordance with GOST 14255-69;
X4 - relay return method: 1 - manual return; 2 - self-return;
X5 - trip class: B - trip class 10, absence of letter - trip class 10A;
X6 - climatic version O, OM according to GOST 15150-69;
It is allowed to operate the relay when integrated into the MP shell or a complete device for the UHL3 version.
The main characteristics of the RTL series relays are given in Table 1.3.
Rice. 1.6. a) RTL-1000 and c) RTL-2000 - for connection to a contactor; b) RTL-1000 and d) RTL-2000 - for individual installation with terminal block type KRL-1 and 2, respectively
By analogy with the relays of the RTL series, the electrothermal relays of the RTL-M and RTL-M2 series (Fig. 1.7) are intended, first of all, for overload protection of asynchronous electric motors with a squirrel-cage rotor and are used in conjunction with PML and PML-N contactors as part of the MP. The relays are manufactured in two sizes, used with the corresponding group of contactors. The body is made of heat-resistant injection molded plastic and consists of a base and a cover. The design of the relay is “bulk” and pre-prepared functional units are placed in the base during assembly: thermobimetallic plate heaters with rigid leads welded to them for connection to the contactor and output terminals, a reset rail, a control mechanism with bridge contacts of “secondary” switching circuits.
Starter rated current, A | Limits of regulation of non-operation current, A | Rated voltage, V | Power consumed by one pole, W | Electric motor power, kW at voltage, V 50 Hz, 60 Hz |
|||||||
RTL2061DM04 | |||||||||||
RTL2063DM04 | |||||||||||
Rice. 1.7.
The design of the relay includes a mechanism for accelerating response during sudden overloads, which makes it possible to practically eliminate the failure of the protected electric motor in the event of a sudden jamming of the rotor or destruction of the bearings. All relay versions have control over the operating current, which makes it possible to accurately set the setting for a specific consumer (electric drive, process unit, etc.).
The RTL-M series covers the current range of 0.1-80 A and has 20 designs; it is somewhat simpler in design than the RTL-M2, since it does not have a “Manual Automatic” switch (Fig. 1.8) to return to its original state after operation.
Rice. 1.8. : a) – RTL 1001-M–RTL 2063-M; b) – RTL 1001- M2 – RTL 2065- M2
The RTL-M2 series covers the current range of 0.1-93 A and has 21 versions.
Advantages of relays RTL-M and RTL-M2:
The relays are fixed using a special protrusion and rigid power connection terminals directly to the MP;
The series are made in two sizes: size 1 is coupled with MP of the PML series for a current of up to 25 A, size 2 is for MP with a current of 40-95 A;
The presence of two groups of free contacts: 95-96 - for opening, 97-98 - for closing;
Two modes of returning the relay mechanism to its original state after cooling of thermobimetallic heaters: manual “Reset” button, automatic;
The presence of an acceleration mechanism of 40% response at high overload currents or phase imbalance with thermal compensation elements;
Possibility of sealing the relay after adjustment to the operating parameters of the protected equipment.
Thermal overload relays of the RTL series. The Telemecanique trademark of Schneider Electric is designed to protect AC circuits and electric motors from overload, phase asymmetry, delayed start-up and rotor jamming and can be installed directly under the MP series PMU (Fig. 1.9).
Rice. 1.9.
Relays of type: RTL1U cover the current range of 0.1-25 A and have 14 versions; RTL2U covers the current range of 23-40 A and has 3 versions; RTL3U covers the current range 17-104 A and has 7 designs and RTL4U covers the current range 51-630 A and has 10 designs.
The average response time depending on the multiplicity of the setting current for the RTL.U series relay is shown in Figure 1.10.
Advantages of RTL.U series relays:
The relays have built-in protection against open or phase loss, rotor jamming in the form of a mechanical “rocker arm” system;
The relays have two modes: manual (relay charging by pressing a button) and automatic (spontaneous charging of the relay after the bimetallic plates have cooled);
The relay has a “Testing” function (simulation of the operation of a thermal relay without overload);
Current settings are set by turning the dial. The disc is closed with a transparent cover that can be sealed;
Relays RTL1U-RTL3U have movable contact terminals, which makes it easy to connect them to different standard sizes of MP type PMU09-95 without the use of additional tools;
The RTL4U relay is mounted separately from the contactor. The electrical connection is made using wires.
Rice. 1.10. : 1 - symmetrical three-phase mode from a cold state; 2 - symmetrical two-phase mode from a cold state; 3 - symmetrical three-phase mode after a long flow of current equal to the set current (hot state); 4 - three phases from the hot state (maximum setting); 5 - three phases from hot (minimum setting)
To change the settings of the RTL.U series relays, you need to open the transparent cover (Fig. 1.11, item 1) above the settings adjustment dial. Set the setting current in amperes by rotating the disk (Fig. 1.11, item 1).
To change the re-cocking mode, you must first open the transparent cover and turn the blue “RESET” switch (Fig. 1.11, item 4):
Turn left (Fig. 1.12, a) - manual re-cocking;
Turn to the right (Fig. 1.12, b) - automatic re-cocking.
The RESET switch remains in the automatic position.
re-cocking until forced return to the manual re-cocking position. When the lid is closed, the switch is locked. Manual re-cocking is carried out by pressing the blue “RESET” button.
Rice. 1.11.
Rice. 1.12.
The “Stop” function is activated by pressing the red “STOP” button (Fig. 1.11, item 5). Pressing the “STOP” button (Fig. 1.13, a):
Changes the state of a normally open (NO) contact;
Does not change the state of a normally closed (NC) contact. The STOP button can be locked with a U-shaped bracket
(Fig. 1.13, b). When the lid is closed, the device is locked.
Rice. 1.13.
Rice. 1.14.
The “Testing” function is activated by pressing the red “TEST” button with a screwdriver (Fig. 1.11, item 6). Pressing the “TEST” button (Fig. 1.14, a) simulates the operation of a relay during an overload and:
Changes the position of NO and NC contacts;
Changes the position (Fig. 1.14, b) of the relay activation indicator (Fig. 1.11, item 7).
Thermal overload relays type LRD and LR97 series D of the Telemecanique trademark are designed to protect AC circuits and electric motors (with a rated current of 0.1-150 A) from overload, phase asymmetry, delayed start-up and rotor jamming and can be installed directly under the MP type LC1 : LC - designation of the main module of the Tesys series contactor, 1 - irreversible contactor.
Class 10A relays type: LRD-01-35 (catalog no.) cover the current range 0.1-38 A and have 16 versions; LRD-3322-3365 cover the current range of 17-104 A and have 8 versions; LRD-4365-4369 cover the current range of 80-140 A and have 3 versions.
The installation kit (Fig. 1.15, a, item 1) is designed for direct connection of the NC contact of the LRD relay (Fig. 1.15, a, item 2) to the LC1 type MP (Fig. 1.15, a, item 3).
The terminal block (Fig. 1.15, b, item 1) is designed for mounting the LRD relay (Fig. 1.15, b, item 2) on a 35 mm rail or screw connection to the mounting plate (Fig. 1.15, b, item 3) with a seat size of 110 mm. The design of the relay allows the installation of a device for remote shutdown or electrical return (Fig. 1.15, b, item 4), as well as a device for remote activation or electrical return (Fig. 1.15, b, item 5). In addition, you can install a lock on the front panel of the relay (Fig. 1.15, b, item 6) of the “Stop” button.
Using flexible conductors LAD-7305 (Fig. 1.15, c, item 1) for LRD type relays (Fig. 1.15, c, item 2) and LA7-D305 (Fig. 1.15, c, item 3) for relays LRD-3 (Fig. 1.15, c, position 4) you can remotely control the “Return” function.
The adapter device for the door locking mechanism (Fig. 1.15, d, item 1) allows for remote control of relays such as LRD (Fig. 1.15, d, item 2) and LRD-3 (Fig. 1.15, d, item 3) using a handle with a spring return for the “Stop” button (Fig. 1.15, d, item 4) and / or for the “Return” button (Fig. 1.15, d, item 5).
Rice. 1.15.
The average response time depending on the multiplicity of the set current for a three-pole thermal overload relay of the D series, type LRD, is shown in Figure 1.16.
Rice. 1.16.
1 - symmetrical load, 3 phases, from a cold state;
2 - symmetrical load, 2 phases, from a cold state;
3 - symmetrical load, 3 phases, with long-term flow of the set current (from a hot state)
The electronic overcurrent relay LR97 D (Fig. 1.17) is designed to provide the most complete protection for electric motors and complements the range of existing LRD type relays.
The use of these electronic relays is recommended to provide protection for electric motors operating in mechanisms with increased load torque, as well as devices with high inertia or a high probability of jamming in steady state operation:
Conveyors, crushers and mixers;
Fans, pumps and compressors;
Centrifuges and dryers;
Presses, lifts, processing machines (sawing, planing, broaching, belt grinding).
An electronic relay can be used to provide protection for electric motors during slow starts or frequent starts.
Relay LR97 D has two protective functions with preset parameters: 0.5 s when the rotor of electric motors is blocked and 3 s when a phase is lost.
The LR97 D relay can be used to provide mechanical protection for industrial installations. To implement this function, the minimum value is set on the O-TIME disk (Fig. 1.17, item 7), which ensures shutdown within 0.3 s.
Rice. 1.17. : 1 – RESET button; 2 – TEST/STOP button; 3 – readiness/operation status indicator; 4 – relay activation indicator; 5 – setting the LOAD current; 6 – setting the start time D-TIME; 7 – setting the O-TIME response delay; 8 – manual/automatic re-cocking setting; 9 – mode setting: 1-phase / 3-phase
The monitoring and protection functions provided by the LR97 D relay are most suitable for the following applications:
Monitoring the operation of electric motors that have a significant starting time, with a high probability of a difficult start: electric motors with increased load torque and significant inertia;
Monitoring the operation of electric motors in steady state mode, detection function for increased load torque: (electric motors with a high probability of “sticking” or blocking of moving parts, electric motors with increasing torque);
Monitoring mechanical failures and damage;
Fast overload detection compared to thermal protection devices based on I2t function;
Protection of electric motors for special applications: (long starts; frequent starts: from 30 to 50 per hour); electric motors with a variable load when operating in steady state, when the thermal overload relay cannot be used due to its characteristics (inertia of “thermal memory”).
Relay LR97 D has two setting time ranges:
D-TIME (Fig. 1.17, item 6): start time;
O-TIME: non-operation time (maximum permissible deviation time when operating in steady state).
The D-TIME function is only used when starting the motor. At the moment of starting, the overload detection function is not activated, which allows you to start the electric motor without tripping the protection relay, even under significant overloads. During steady state operation, when the current exceeds the set value due to overload or phase failure, the relay will operate after the time entered using the O-TIME dial.
The red LED indicator (Fig. 1.17, item 3) signals that a shutdown has occurred.
To configure the relay, just follow 5 simple steps:
Set all three tuning dials (LOAD, D-TIME and O-TIME) to maximum values;
Set the D-TIME dial to the time value corresponding to the motor start time;
When the electric motor switches to constant load mode, set the current value by turning the LOAD dial (Fig. 1.17, item 5) counterclockwise until the red LED indicator starts flashing;
Slowly turn the LOAD dial clockwise until the LED stops flashing;
Set the threshold relay response time using the dial
For quick diagnosis of conditions, two LED indicators (green and red) are provided, showing the relay status and operating modes (Table 1.4).
The electrical circuit for switching on the LR97 D relay connected to the KM1 contactor when controlling an electric motor is shown in Figure 1.18.
Rice. 1.18.
Table 1.4
Diagrams of relay operation for three operating modes of the electric motor: start-up, mechanical jamming of the rotor and overload are shown in Figure 1.19. At the moment of starting, the overload detection function is not activated, and the starting time set on the D-TIME dial is longer than the time at which the motor starting current is greater than the set current (Fig. 1.19). As a result, the protection relay does not operate. If the rotor jams during operation of the electric motor, then after a time of 0.5 seconds has elapsed from the moment the current in the stator windings of the motor reaches a value equal to three times the set current, the relay is activated (Fig. 1.19).
Rice. 1.19. Diagram of operation of the LR97 D relay during startup and mechanical jamming of the rotor, short-term and long-term overload
In the event of a variable load, in which the current in the stator windings of the electric motor during its change does not exceed three times the set current, and the duration of the current change itself is less than the time of non-operation of the O-TIME relay (Fig. 1.19), the relay operating mode remains unchanged (the protection does not operate ). If the operating time of the variable load is greater than or equal to the non-operation time of the O-TIME relay (Fig. 1.19), the protection relay is activated.
Returning the relay to its original state is carried out in three ways: 1- manually, using the “Return” button (Fig. 1.17); 2 - automatic, implemented using the re-cocking button (Fig. 17) after a fixed time equal to 120 s, with the exception
cases when the protection is triggered due to the rotor starting (the time setting on the D-TIME dial is incorrectly selected), the rotor is jammed and in the event of a phase failure; 3 - electrical, ensured by a short-term power outage for at least 0.1 s.
Diagrams of relay operation for the case of: phase loss during startup, phase loss in steady state operation of the electric motor and overload are shown in Figure 1.20. From the diagrams above it can be seen that if a phase is lost or broken, the protection relay is activated after a time of 3 s (preset parameter). In the event of an overload, the relay operation diagrams coincide with those shown for the corresponding modes in Fig. 1.19.
Rice. 1.20. Diagram of operation of the LR97 D relay during phase loss during startup and steady operation of the electric motor, short-term and long-term overload
The relay operation diagram for the case of protecting the electric motor from mechanical overloads (shocks) on the rotor side is shown in Figure 1.21. As noted above, to implement the relay’s protective function against mechanical shocks, it is necessary to select a setting on the O-TIME dial that corresponds to the minimum value, which will ensure shutdown within 0.3 s (Fig. 1.21).
Rice. 1.21. Diagram of operation of the LR97 D relay under mechanical overloads on the rotor side of the electric motor
The essence of the connection diagram for any MP comes down to controlling the power of its coil. It is known that the activation and shutdown of the MP (retraction and return of power contacts) occurs by closing and opening the coil power circuit.
The connection diagram for a magnetic starter with a control coil for a voltage of 220 V is shown in Figure 1.22.
Rice. 1.22.
Power is supplied to the coil of the magnetic starter KM1 through the contacts of the “Start” button - SB2, “Stop” SB1 and thermal relay P, connected in series to its circuit. When the “Start” button is pressed, its contacts close and power is supplied to the coil further through the closed contacts of the button "Stop". The MP core attracts the armature, closing the power movable contacts, and voltage is applied to the load.
When the “Start” button is released, the coil circuit is not broken, since block contact KM1 with closed contacts is connected in parallel with SB2 (the armature of the magnetic starter is retracted) - phase voltage L3 will flow to the coil through them.
By pressing the “Stop” button, the power supply circuit of the coil is broken, the group of moving contacts returns to its original state and the load is thus de-energized. The same thing happens when there is a current overload of the electric motor; additional thermal energy is released on the heating elements of the thermal relay P, which triggers the opening contact of the thermal relay, interrupting, in this case, zero N, which powers the coil KM1 of the magnetic starter.
The connection diagram for a magnetic starter with a 380 V coil is shown in Figure 1.23.
The differences between these two MP connection schemes are only in the supply voltage of the coil. In the first case, when connecting an MP with a coil operating voltage of 220 V, zero and phase L3 were used to power it, in the second - two supply phases L2 and L3.
Rice. 1.23.
A reversible diagram for connecting an electric motor to the supply network using an MP is shown in Figure 1.24. Connecting a three-phase electric motor using a reversible circuit is required in cases where, during its operation, it is necessary to quickly change the direction of rotation of the shaft. Unlike the usual connection diagram, this diagram contains two magnetic starters, two “Start” buttons and one “Stop” button.
Changing the direction of rotation of the electric motor shaft occurs by changing the phasing (phase connection order) in its power supply and is set by pressing the “Start1” or “Start2” button.
The power contacts of magnetic starters KM1 and KM2 are connected in such a way that when one of them is triggered, the phase order in the power supply will be different from the phasing when the other is triggered.
The circuit works as follows: by pressing the “Start1” (SB1) button, the power circuit of the KM1 coil is closed, the power contacts KM1 are drawn in and closed (shown in dotted lines in the diagram) and power with the phase sequence L1, L2, L3 is supplied to the electric motor terminals. To avoid erroneous activation of the “Start2” button, a normally closed block contact of the second magnetic starter KM2 is connected in series with the KM1 coil circuit.
Rice. 1.24.
The engine is stopped by pressing the “Stop” button (SB3) - its contacts “break” the supply phase of the L3 coil. Interrupting the power supply to the KM1 coil leads to the return of the movable power contacts of this MP to their original position, thus the electric motor is turned off.
By pressing the “Start2” (SB2) button, the power circuit of the KM2 coil is closed by analogy, the power contacts of KM2 are drawn in and closed (highlighted in blue in the diagram) and power is now supplied
already with the order of phases L3, L2, L1, it is supplied to the motor terminals. Thus, the motor shaft will now rotate in the opposite direction.
Blocking of the KM1 magnetic starter, in case of erroneous activation of the “Start1” button, is also carried out here by sequentially connecting a normally closed block contact of another MP into the coil power circuit. In this case, a normally closed block contact KM1 is connected in series to the KM2 circuit.
The electrical circuit diagram of a non-reversible MP with a relay, with control buttons and signal lamps built into the shell, is shown in Figure 1.25.
By supplying the switching device from the distribution board (circuit breaker, switch) with voltage to the terminals of the three-pole circuit breaker QF (the red signal lamp HL1 lights up), the circuit is prepared for operation.
Rice. 1.25.
After the circuit breaker is turned on (the green signal lamp HL2 is lit), voltage is supplied to its terminals and to the main closing contacts of the KM magnetic starter. The coil of the KM magnetic starter is connected to the network through the contacts of the thermal relay and the “Start” (SB2) and “Stop” (SB1) control buttons. When you press the “Start” button, voltage is supplied to the coil of the KM magnetic starter through the closed contacts of the “Stop” button and the closed contacts of the KK thermal relay. An electric current passes through the KM coil, creates a magnetic field that attracts the armature to the core, and thereby closes the main and auxiliary contacts of the KM magnetic starter, shunting the closing contacts of the “Start” button, which can then be released. Voltage is supplied to the windings of the electric motor M, and it starts, as indicated by the HL3 lamp.
To turn off the electric motor, press the “Stop” button. The coil loses power, after which the armature, under the action of return springs, moves away from the core and the contacts open.
When there is a current overload of the electric motor, additional thermal energy is released on the heating elements of the KK thermal relay, which leads to the activation of the breaking contact of the KK thermal relay, and the circuit of the KM coil is opened.
The electrical circuit diagram of a reversible MP with a relay, with control buttons and signal lamps built into the shell, is shown in Figure 1.26.
Rice. 1.26. Electrical circuit diagram of a reversible MP with a relay, with control buttons and signal lamps built into the shell
When the “Forward” button (SB2) is pressed, a voltage of 380 V is supplied to the coil of the magnetic starter KM1 through the closed contacts of the “Stop” button (SB1) and the closed contacts of the thermal relay KK. The electric control current passes through the KM1 coil, creates a magnetic field that attracts the armature to the core, and thereby closes the main and auxiliary contacts of the KM1 magnetic starter, shunting the closing contacts of the “Forward” button. Voltage is supplied to the windings of the electric motor M, and it starts, as indicated by the HL3 lamp. To turn off the electric motor, press the “Stop” button.
Changing the direction of rotation of the electric motor rotor is carried out by pressing the “Back” button SB3). In this case, the electric control current passes through the KM2 coil, closing the main and auxiliary contacts of the KM2 magnetic starter, shunting the closing contacts of the SB3 button. Voltage is supplied to the windings of the electric motor M (the HL4 lamp is lit), but at the same time the direction of rotation of the magnetic field changes (the voltage of phase “A” is supplied to terminal “3”, and the voltage of phase “C” is supplied to terminal “1” of the electric motor), then there is a change in the order of phase alternation.
To avoid erroneous activation of the “Back” button, a normally closed block contact of the second magnetic starter KM2 is connected in series to the KM1 coil circuit.
The presence of a mechanical interlock in the design of the reversible MP prevents the occurrence of a short circuit between phases when the main closing contacts of the magnetic starters KM1 and KM2 are simultaneously closed. Due to this, the appearance of voltage on the coil of the second contactor does not trigger it. In addition, after turning on the KM1 magnetic starter, the KM1 opening contact breaks the coil circuit of the KM2 magnetic starter, and when the SB3 button is pressed, no emergency modes will occur. There is a similar electrical blocking in the circuit of the KM1 coil (break contact KM2).
It should be noted that electrical blocking can be performed by using the break contacts of the “Forward” and “Back” buttons, which are switched on instead of the break contacts KM1 and KM2, for example, in the absence of break contacts in the MP design. Then, when you press the SB2 button, the power supply circuit of the KM2 coil is broken and when you press the SB3 button, the KM2 coil will remain de-energized.
The high return coefficient of the electromagnets of AC contactors makes it possible to protect against a decrease in the mains voltage (the electromagnet releases at U = (0.6-0.7)^other). When the mains voltage is restored to the nominal value, the MP does not turn on spontaneously, because the closing block contacts KM1 and KM2 and the closing contacts of the “Forward” and “Back” buttons are open.
The circuit provides for grounding - the motor housing is connected to the neutral N. In the event of a breakdown of the insulation of the electric motor or the supply cable to the housing, a short circuit mode will occur in the circuit (a short circuit current will flow through the “phase - housing - zero” circuit), which will lead to operation electromagnetic release of the QF circuit breaker. The circuit breaker will de-energize the circuit.