The 220 V electromagnetic starter allows switching in alternating (and direct) current circuits. Typically, such devices are used when turning on powerful consumers - electric motors, heaters, etc. The need for it is justified in cases where it is necessary to frequently turn on and off the load.
Application of magnetic starters
Most often, electromagnetic starters are used to start, stop and reverse asynchronous electric motors. But since these devices are very unpretentious, they can be used for remote control of lighting, in compressor units, pumps, overhead cranes, electric ovens, conveyors, and air conditioners. The scope of application of magnetic starters is very wide. But recently, starters have been replaced by electromagnetic contactors. But, in fact, these two devices differ little in design and characteristics. Even the switching circuits are the same.
How does the starter work?
The electromagnetic contactor operates according to the following scheme:
- Voltage is supplied to the working coil of the electromagnetic starter.
- A magnetic field appears around this coil.
- The metal core, which is located next to the coil, is pulled inward.
- Power contacts are attached to the core.
- When the core is retracted, the power contacts close and current flows to the load.
In the simplest case, magnetic starters are controlled using just two buttons - “Start” and “Stop”. If necessary, you can reverse it - this is done by connecting two magnetic starters using a special circuit.
How does an electromagnetic starter work?
There are two main parts to this device:
- Contact block.
- Directly the starter.
The contact block is installed on top of the starter housing. It is intended to expand the functionality of the control circuit. With the help of an additional block you can:
- Reverse the movement of the electric motor.
- Power up the lamp that signals the engine is running.
- Enable additional equipment.
- But the contact attachment is not always used; in most cases, one starter is sufficient.
Contact attachment
This mechanism includes two pairs of normally open and the same number of normally closed contacts. On top of the starter there are runners and hooks, and it is to them that the attachment is attached. As a result, this system is rigidly connected to the power contacts of the starter and works simultaneously with them.
Normally closed contacts by default connect elements of a circuit, while normally open contacts break them. When the magnetic starter is turned on, when the core closes the power elements, the normally closed contacts open, and the normally open contacts close.
Magnetic starter design
In general, two parts can be distinguished - upper and lower. At the top there is a group of contacts, a moving part of the electromagnet connected to the power switches, as well as an arc-extinguishing chamber. At the bottom there is a coil and a return spring, as well as the second half of the electromagnet.
Using a spring, the upper part returns to its original position after the voltage supply to the coil stops. In this case, the power contacts open. The electromagnet is assembled from W-shaped plates made of technical transformer steel. The coil is wound with copper wire, and the number of turns depends on the voltage it is designed for.
Sectors with designations
The parameters are located on the starter; there are three sectors in total:
- The first indicates where a magnetic starter can be used, as well as general information about it. Namely: alternating current frequency, rated current value, conditional thermal current. For example, the designation AC-1 indicates that with the help of such mechanisms it is possible to switch the power circuits of heating elements, incandescent lamps, and other weakly inductive loads.
- The second sector indicates the maximum load power that can be switched with power contacts.
- The third sector usually indicates the circuit diagram of the device: it includes power and auxiliary contacts and an electromagnet coil. If there is a dotted line from the coil along all the contacts on the diagram, this means that they work synchronously.
Contact groups of starters
Power contacts are designated as follows:
- 1L1, 3L2, 5L3 are incoming, they are powered by AC or DC power.
- 2T1, 4T2, 6T3 - outgoing power contacts that connect to the load.
In fact, it doesn’t matter at all where you connect the power source and where the load. It’s just that such a scheme is generally accepted, and it must be used.
After all, if another person has to carry out repairs, he simply will not be able to immediately understand what the installer has done. The auxiliary group of contacts 13NO-14NO is designed to carry out self-recovery. In other words, this pair is used so that the start button does not have to be constantly pressed when turning on the electric motor.
Stop button
Regardless of the type of electromagnetic starter used in the design, control is carried out using two buttons - “Start” and “Stop”. Reverse may be included. The stop button is different from the others in that it is red. The normally closed contacts are mechanically connected to the button. Therefore, when the devices are operating, current flows through them unhindered.
If the button is not pressed, the metal strip, under the action of a spring, closes two contacts. If you need to stop powering the device, you just need to press the button - the contacts will open. But there is no fixation; as soon as you release the button, the contacts close again.
Therefore, to control the operation of electric motors, special circuits for switching on 220V electromagnetic starters are used. Such devices can be installed on a DIN rail without any problems, so they can be used even in the smallest mounting blocks.
Start button
It is usually green or black in color and is mechanically connected to a normally open group of contacts.
As soon as you press the start button, the circuit closes and electric current flows through the contacts. The only difference from the stop button is that by default the contacts are open. The spring holds the contact group in the open position and allows the button to be returned to its initial position after starting. This is precisely the operating principle of 220V electromagnetic starters used in control circuits for large loads.
Classic connection scheme
When implementing such a scheme, the following actions are performed:
- When you press the “Start” button, the contacts are closed and voltage is supplied to the load.
- When you press the “Stop” button, the starter contacts open and the voltage supply stops.
You can connect heating elements, electric motors, and other devices as a load. A normally open 220V electromagnetic starter can be used to turn on absolutely any load.
The power part of the circuit includes:
- Contacts for connecting three phases - “A”, “B”, “C”.
- Circuit breaker. It is installed between the power source and the input of the 220V 25A electromagnetic starter. The fact is that 380V is the phase-to-phase voltage, and if you measure between zero and any of the phases, it will be equal to 220V.
- The load is a powerful consumer of electricity (motor, heating element).
The entire control circuit is connected to zero and phase “A”. The circuit consists of the following components:
- Start and stop buttons.
- Reels.
- Auxiliary contact (switched on parallel to the start button).
Operation of the classical scheme
As soon as the circuit breaker turns on, three phases appear on the upper contacts of the starter, and the entire circuit is switched to standby mode. The phase under the letter “A” passes through the circuit:
- Through closed contacts of the stop button.
- To the contact of the start button.
- To the auxiliary contact group.
In this case, the circuit is fully prepared for operation. As soon as the contacts close under the influence of the start button, voltage appears on the coil and its core is retracted. In this case, the core pulls a group of contacts along with it, closing them.
At the bottom of the magnetic starter there are power contacts, at which voltage also appears, which then goes to the electricity consumer. After releasing the start button, the power contacts will be closed due to the implementation of the “pick-up” circuit. In this case, the phase does not go through the contacts of the start button to the electromagnet, but through an auxiliary group.
Degree of protection
Devices with a degree of protection IP54 perform best. They can be used in damp and very dusty areas. You can install it in an open place without any problems. But if the installation is carried out inside a cabinet, then it is enough to use devices with a degree of protection IP20. The higher the numerical index, the more severe the conditions under which the device can be operated - this applies to any electrical device. The following factors must also be taken into account:
- The presence of a thermal relay, with the help of which the load is switched off when the maximum current consumption is exceeded. The use of such a device is especially important when controlling electric motors.
- If there is a reverse function, then the design has two coils and six contacts. Essentially, these are a pair of starters combined in one housing.
- It is imperative to take into account the wear resistance of the device, especially if the load is switched on and off very often by the starter.
Not least in the operation of any device, including a 220V electromagnetic starter, is the human factor. Unskilled workers can break the entire control chain because they do not know how to operate the equipment correctly. If the thermal protection has tripped, it cannot be switched on immediately. And you cannot restart the engine - first you need to check whether the motor is jammed or whether there is a short circuit in the power circuit.
We turn on the lighting in the house with an ordinary switch, and a small current passes through it. To turn on powerful single-phase loads at 220 Volts and 3-phase at 380 Volts, special switching electrical devices- magnetic starters. They allow you to remotely turn on and off powerful loads using buttons (you can also use a regular switch), for example, lighting an entire street or a powerful electric motor.
In apartments Starters are not used, but they are often used in production, in garages in the country for starting, protecting and reversing asynchronous electric motors. It’s clear from the name that its main purpose is to start electric motors. And in addition, together with a thermal relay, the magnetic starter protects the motor from erroneous starts and damage in emergency situations: overloads, winding insulation failure, loss of one phase, etc.
Starters are often installed for turning on and off not only engines, but also other high-kilowatt loads - street lighting, heaters, etc.
After a power outage it will turn itself off and turn on only after pressing the “Start” button again. But if you use the simplest control scheme for your home using a conventional switch, then in the on position the starter will always operate. It works on the principle of a relay, only unlike it, it controls powerful loads up to 63 Kilowatts; for larger loads, a contactor is used. To automate control, for example, street lighting, you can connect control timers, motion or lighting sensors to the coil contacts.
Design and principle of operation of a magnetic starter
The basis is the electromagnetic system, consisting of a coil, a stationary part of the core and a movable armature, which is attached to an insulating cross-beam with movable contacts. Wires from the electrical network are connected to the fixed contacts using bolted connections on one side, and to the load on the other.
To protect against erroneous switching on are installed on the sides or on top above the main block contacts, which, for example, in a reversible circuit with two starters, when one starter is turned on, block the second one from turning on. If two turn on at once, an interphase short circuit will occur, because changing the direction of rotation of an asynchronous motor is achieved by swapping 2 phases. That is, on the connection side of the electric motor, jumpers are made between the starters with alternating 2 phases on one of them. Also, one pair of contact blocks is required to keep the starter in the on state after releasing the “Start” button. We will look at the connection diagram in detail in the next article.
Principle of operation The starter is quite simple. To turn it on, you need to apply operating voltage to the coil. When turned on, it consumes very little current through the control circuit; their power ranges from 10 to 80 watts, depending on the size.
When turned on, the coil magnetizes the core and the armature is drawn in, which closes the main and auxiliary contacts. The circuit closes and electric current begins to flow through the connected load.
To turn it off, you need to de-energize the coil., and the return spring returns the armature to its place - the block and the main contacts open.
A thermal relay is installed between the starter and the 3-phase asynchronous motor, which protects it from overload currents in emergency situations.
Attention, The thermal relay does not protect against short circuits, so it is necessary to install the required size of circuit breaker in front of the starter.
The operating principle of a thermal relay is simple- it is selected for a certain operating current of the engine; when its limit is exceeded, the bimetallic contacts heat up and open, which open the control circuit and turn off the starter. The connection diagram will be discussed in the next article.
Technical characteristics of magnetic starters.
The main technical characteristics can be found out from the symbol, most often consisting of three letters and four numbers. For example, PML-X X X X:
- First two the letters indicate magnetic starter.
- Third letter indicates the series or type of starter. There are PML, PME, PMU, PMA...
- The first number after the letters indicates the size of the starter in terms of rated current:
- The second digit indicates the presence of thermal protection and the characteristics of the electric motor.
- The third number indicates the presence of buttons and the degree of protection.
IP54 - splash- and dust-proof housing, IP40 - only dust-proof housing.
- The fourth digit is the number of auxiliary circuit contacts.
A magnetic starter is a switching device for electrical circuits with high currents. In everyday life, magnetic starters are used in country houses, for remote connection of street lighting or home craftsman's machines powered by electric motors.
The design of a magnetic starter and its operation are tritely simple: a spring, a choke and a moving armature. When current appears in the choke, the armature closes the contacts of the starter and power is supplied to the installation. We interrupt the current through the inductor, the armature opens the contacts of the starter, and the power to the installation is turned off. By installation we mean a receiver of electrical energy that is switched by a magnetic starter (electric motor, street lighting).
Connecting a magnetic starter - connection diagram
There are two fundamentally different schemes for connecting a magnetic starter:
- simple non-reverse circuit (start and stop);
- reverse circuit for connecting the electric motor (start, forward, reverse).
In a simple (non-reverse) connection diagram, the following elements “participate”:
- Magnetic starter;
- Asynchronous electric motor with squirrel-cage rotor;
- Start and stop buttons;
- Thermal relay (optional, but desirable to protect the motor from current overloads).
Let's supplement this diagram with two working diagrams:
Where to use the starter in everyday life
In a private house, through the starter you need to connect all the electric motors available on the territory, street lighting and powerful household appliances, for example, heating elements. Motors, because it’s supposed to be so, and street lighting, because the starter will provide remote, safe connection of street lighting from anywhere in the house. You can place the starter in the switchboard room, and the control buttons (on, off) where convenient.
Connecting a magnetic starter - example
I won’t talk about the internal design of the starter, the arc-extinguishing chambers and the insulating cross-arm; that’s in the video at the bottom of the article. I will show you the practical connection of an electric motor through a magnetic starter.
For work we will prepare:
- Actuator;
- Thermal relay;
- Electrical cable. We calculate based on the power of the electric motor;
- Push-button point with two buttons in one housing;
- Electric motor installed on site.
Starter, push-button point, motor Electrical installation work for installing a magnetic starter
- From the three-phase (1 in the yellow diagram above), which we place before the starter, we connect the power cable to the starter;
- From the starter output we lay a cable to the push-button point;
- We lay the cable from the button to the electric motor.
Note: In this article we will limit ourselves to connecting an asynchronous motor without reversing. That is, only start and stop.
To connect a magnetic starter according to the above diagram, you need to find and understand the purpose of the contacts on the starter and buttons. Therefore, let’s look at the push-button point first, and then look at the starter.
Buttons (push-button point) for starter operation
For a simple, non-reversible connection of the starter, we need a push-button point with two buttons. As an example, I took an old series in an ebonite case.
The buttons are designed to close and open an electrical circuit. For this purpose, the button structure has closed and open contacts. It is correct to say that open contacts are normally open, and closed contacts are normally closed.
For proper connection, it is important to identify open and closed contacts. They are usually designated by numbers 1-2 and 3-4 respectively.
We understand that when you press a button, open contacts are closed, and open contacts are closed. Now let's look at the starter terminals.
Starter terminals required for connection
We place the starter in front of us and look at it with the naked eye, that is, we do not disassemble it.
- Starter input terminals. Input terminals for connecting phase wires: 1L1, 2L2, 3L3;
- Additional input terminal: 13NO (21NC);
- Output terminals. Phase wire output terminals: 4T1, 5T2, 6T3.
- Additional (auxiliary) output terminal: 14NO (22 NC);
In the off state, contact pairs: 1L1-4T1; 2L2-5T2; 3L3-6T3 are open. Visually we see that the traverse (the orange plate in the middle of the device) is in the upper position.
- On the starter we see contact A2, this is the output of one contact of the starter choke. There are starters (older models) with terminals A1 and A2 for outputting two contacts of the starter choke.
Starter coil terminal A2 
Starter coil terminals A1 and A2 There are no more contacts on the case.
Connecting a starter with a push-button point
- We connect the incoming phase to terminal 1L1 of the starter;
- We connect the motor to terminals 4T1 and working zero, without a starter;
- From terminal 1L1 we connect the wire going to pin 1 of the “Start” button with a cable;
- From contact 2 of the “Start” button we run a loop to contact 3 of the “Stop” button;
- From terminal 4 of the “Stop” button we run a cable to contact A2 of the magnetic starter coil (it’s on the body). If there is a coil contact A1 on the body, connect zero to it;
- From the auxiliary contacts of the starter NO13 and NO14 we throw wires to terminals 1-2 of the “Start” button;
- Before the starter, on the power supply side, you need to install a circuit breaker on the phase conductors;
- A thermal relay must be installed parallel to the switch, up to terminals 1L1-3L3. It will protect the starter from overload;
- The connection is complete. Turn it on.
How does a magnetic starter trigger and work?
When the circuit breaker is turned on, the phase current is supplied to the starter contacts L and to terminal 1 of the start button.
To start the engine, press the “Start” button. The normally open contacts of the “Start” button close, current is supplied to the starter coil, which closes the contact groups of the L-T starters.
Release the “Start” button. If there were no additional contacts in the starter, the engine would stop. But the additional starter contacts NO13 and NO14 are closed and remain closed when the “Start” button is released. This prevents the starter coil power supply from opening. We see that the traverse on the body is recessed, and we hear a characteristic click.
When you press the “Stop” button, the coil circuit simply opens, and it is released - the starter cross-arm rises, and we hear a characteristic click.
Important! Additional contacts of the starter play an important role in connecting the starter. It remains to be recalled that additional contacts, which pick up the functions of the “Start” button, are located on the starter to the left of the input and output working contacts and are marked NO13 and NO14.
This topic needs to be considered from magnetic starters from representatives of the Soviet era. Prominent representatives are PML and the like. Starters are used to switch powerful loads using a control signal with a low current. The control signal is supplied to the coil, which creates a magnetic field. This, in turn, creates a force on the magnetic core, which is mechanically connected to movable power contacts and block contacts.
The magnetic starter can be divided into two parts: upper and lower. In the lower part there is a coil and a stationary part of the magnetic circuit, the coil terminals.
The general view of the old starter is shown above. Closer to the viewer there are power contacts, they are numbered from 1 to 6. Next we see block contacts, they are needed to implement additional functions of the circuit and self-recovery.
Interesting:
The starter contacts are closed only when voltage is applied to the coil. Control panels for such devices are usually equipped with non-latching buttons, which means that the starter will only be turned on when you hold the button down.
If this is good for some schemes, for example, for a hoist, winch and other lifting mechanisms, then for engines operating in long-term operation this is in no way suitable; imagine a control scheme for a pump that must operate without stopping.
You can, of course, use latching buttons and toggle switches, but it is more clear to use the “Start” and “Stop” buttons on the remote control, so a self-retaining circuit through block contacts is used.
Why did I start the article about modern switching devices by considering a classic example? It's simple - they are still found in huge numbers at enterprises, industrial facilities, etc. In addition, they have a very large margin of safety, both in terms of resource and in terms of operation in overloaded modes.
The structure of modern models of magnetic starters
Let's look not at a particular case, but at modern devices in general. Individual points may differ and depend on the specific model or manufacturer, so I will try to cover as wide a range of information as possible.
Let's start with the general appearance of a modern starter.
On the front part in front of us there are 4 pairs of contacts. Three of them, marked type 1L1 and 2T1, are power contacts for connecting the load to a three-phase power supply. Contacts marked “L” are used to connect the power source, and “T” are used to connect the consumer.
In general, you can connect the network both from the top side (L) and from the bottom (T). But following the markings and connections described in the first method will make the circuit more visual and simplify its maintenance for other electricians who will work with it besides you. It is customary to start the power supply from the top side.
The pair of contacts 13NO-14NO are self-retaining contacts, or block contacts. Their purpose is described above.
Interesting:
The main difference between modern contactors is the marking of the terminals; you need to remember that the terminals marked “L” and “T” are used to connect power lines - power and load. Contacts marked NO and NC are used to implement self-recovery and other functions of the circuits. In this case, NC are normally closed (closed), and NO are normally open (open).
The normal state of contacts is a state in which there is no external influence on the button or starter, i.e. when the button is NOT pressed, and in the case of the starter there is no voltage on the coil and it is turned off.
Such starters also consist of an upper and a lower part; for variety, let’s consider the upper part using the example of another starter.
As you can see, all the components are the same as on the old domestic copies. However, pay attention to the yellow detail - the insulating traverse; on the previous copy it was made in brown. Firstly, by its position you can judge the state of the starter. If it is retracted, the starter is turned on, and if it is level or slightly protrudes above the cover, it is turned off.
In addition, you can force it to turn on if there are problems with the coil's power circuit. You just need to press the traverse with a screwdriver or something else. Be careful not to get electrocuted; such switching of powerful loads, especially motors, can be dangerous. It is not recommended to do this if you do not have the proper qualifications.
What else do you need to know about starters?
When connecting the starter, carefully check what voltage the coil is designed for. The fact is that coils are mainly found for voltages of 220 and 380 volts, this is indicated by the corresponding designation on its body.
The coil contacts are marked A1 and A2. One of the coil contacts can be duplicated on the opposite side of the starter for ease of connection and circuit assembly. This is reflected in the picture below, note on this side only one of the ends of the coil - A2.
Starter specifications information is as follows.
The starter cannot switch the same current for different types of load. The case may have a sticker or inscriptions with characteristics.
AC-3 and AC-1 are categories of application, they say that it can switch an inductive load, such as an electric motor, with a current of up to 9 A, and in the case of using an active load (heating elements and incandescent lamps) up to 25 A. The sticker can consist of several sectors with similar information or useful data, such as this.
A diagram showing the location of the contacts may be printed on the front panel or side.
The contact diagram looks like this. It shows the names of the terminals and their position in the normal state (disconnected coil).
Block of additional contacts for a magnetic starter, what is it and how to use it?
The traverse has one more additional function - connection with an additional contact block. Pay attention to its appearance and shape; there are hooks on its protruding part.
The contact block is an additional module that is mounted on top of the starter.
Typically there are 2 or 4 pairs of contacts in the contact block. 2 pairs are made in a normally open form, and 2 pairs are made in a closed form. These contacts can be used both for switching low power loads and for implementing additional functions.
Additional features and equipment
It is worth noting that in addition to the block with contacts, additional equipment is also connected to the starters.
Thermal protection, additional block contacts, voltage limiters, reversible blocking, start delay timer. In the picture you see additional equipment for the starter manufactured by ABB.
Each manufacturer may produce other sets of additional devices. Engineers of large companies have provided solutions for a number of production problems that are implemented using starters. Previously, this had to be done using separate modules, and this increased both the number of wires located in the panel to connect operational circuits and units, and the total space occupied.
I have already said that the magnetic starter is usually connected through non-latching buttons. Such buttons are installed in a button post. One of the common options is a PKE type post, shown in the photo below.
If you need to implement engine rotation in both directions, use a post with three buttons:
“Stop” is usually red.
"Forward";
Inside the case, you will find terminals on the back of the buttons, each with a pair of normally closed ones and a pair of normally open ones, located on opposite sides.
Take a look at the diagram; to connect a starter via a push-button station, the phase wire is connected through a normally closed pair of contacts of the “stop” button to a normally open pair of the “start” button. From the second terminal of the “start” button, the wire goes to the coil.
One end of the coil is connected to zero (if it is 220 V) or to another phase (if the coil is 380 V). And the second to the wire from the start button. In this case, a normally open pair of block contacts from the starter is connected parallel to the start button (the same self-retaining device).
To do this, one of the contacts is connected by a jumper to the output of the coil, which is connected to the “start” button, so as not to lay an extra cable to the button station, and the second output of the block contact is connected to the terminal of the “start” button that is connected to the phase wire, from "Stop" buttons.
Contacts “13NO-14NO” - normally open pairs of block contacts, in English. these are the ones that NO.
Only three wires are laid to the push-button post:
Phase to “STOP”;
To the "START" button;
From the block contacts to the phase on “START” for self-retaining.
conclusions
Modern starters, although they differ in appearance and certain functionality, however, perform the same tasks as before. Starters of different types can be interchanged; you only need to provide the current for which a specific model is designed.
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 size - 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 right 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 moving 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 movable 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 |
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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 supplies 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.