In this article you will learn what magnetic starters are, consider their connection schemes, and most importantly, care for the devices. Today, electric motors with a short-circuited rotor are widely used in industry (their share is approximately 95-96%). They work in a duet with magnetic starters. In addition, starters expand the capabilities of the electric drive. But first things first, you need to answer the question of what purpose they are intended for.
Destination starters
The wiring diagram for a single-phase magnetic starter allows switching of any consumer. Of course, if his food is also produced from one phase. And to be more precise, the MP allows you to remotely control an electric drive or other device. For example, a non-reversible starter is only capable of turning the consumer on or off from the AC mains.
But reverse MPs can not only do the above. They are able to change the connection of the phases to the electric motor. And this means that the rotor will begin to rotate in the opposite direction. MP control is carried out using the buttons:
- "Start";
- "Stop";
- "Reverse" (if necessary).
Moreover, these buttons have a supply voltage of no more than 24 volts. All control is carried out using low voltage. And to power the coil of the electromagnet is no longer required.
Types of magnetic starters
The magnetic starter, the connection diagram of which is given in the article, can be made in three versions. It all depends on the conditions under which it is operated. So, the open version of the starters is designed for installation in electrical panels. Mounting is done on a DIN rail. It goes without saying that the electrical panel must be protected from the ingress of foreign objects, such as dust or liquid.
The second type of enclosure is protected. Although it is intended for indoor installation, not shields, it is still unacceptable to get a large amount of dust on it, and even more so liquid. If it is necessary to install magnetic starters, the connection diagrams of which are given in the article, in conditions of high humidity, then it is more reasonable to use dust and water tight. True, they have a limitation - installation on the street is allowed, but only on condition that sunlight and rain do not fall on it.
Magnetic starter design
Any 220V magnetic starter, the connection diagram of which is shown, consists of one main part - a magnetic system. This is a coil wound around a metal core, and a movable anchor. All this is in a plastic case. But this is the basis, there are still many little things, for example a traverse, sliding along the guide axes. There is an anchor on it. In addition, interlocking and main contacts are connected to it. They are equipped with springs that help to open when the power of the electromagnet is turned off.
How does the starter work
The work of MP is based on elementary physics. When applying voltage to the winding, a magnetic field arises around the core. As a result of this, the movable anchor begins to be attracted to the core. This is how any magnetic starter works, the connection scheme can only differ (depending on the presence of a reverse). Incidentally, the reverse movement can be carried out using two ordinary MP. Starter contacts are normally open by default.
When the anchor moves to the core, they close. But there is another design in which, by default, the contact group is normally open. In this case, the picture is the opposite. Therefore, when voltage is applied to the coil, the circuit closes and the electric drive starts to work. But when the coil power is turned off, the electromagnet stops working. Return springs come into play, which force the contact group to move to its original position.
Starter circuit
To begin with, it is worth considering what a magnetic starter looks like, a reverse circuit if used. In fact, these are two identical devices combined in one housing. With the same success, as mentioned earlier, you can use simple MPs, if you know the switching scheme. The starters have a lock, which is carried out by means of normally closed contacts. The fact is that it is unacceptable that they both turn on at the same time. Otherwise, a phase closure occurs.
There is also a mechanical protection installed in the starter housing. But it can not be used if an electrical degree of protection is provided. The peculiarity of the reverse is that it is necessary to completely disconnect the drive from power. To do this, first disconnect the electric motor from the network. After this, it is necessary that the rotor completely stops rotation. And only after that it is allowed to turn on the engine in the opposite direction. Please note that the power of the starter should be twice as large as that of the motor, if counter-activation or braking is applied.
Thermal relay
Now consider a typical 380V magnetic starter. The connection scheme does not do without additional protection. And such is the thermal relay installed on the starter housing. The main task of a thermal relay is to prevent thermal overloads of the motor. They, of course, will be present, but insignificant, overheating of the electric motor becomes impossible. A bimetallic plate acts as a thermal overload meter . Protection, however, is similar to the design of a circuit breaker.
A thermal relay mounted on magnetic starters allows for minor adjustments. The so-called setting is the setting of the maximum value of the current consumed by the electric motor. Typically, this setting is made with a screwdriver. The engine has a groove under it, as well as graduation. The procedure is simple, just set the arrow on the plastic disk opposite the corresponding label with the value of the maximum current consumption. Please note that thermal relays are not capable of short circuit protection. Use circuit breakers for this purpose.
How starters are mounted
It is worth noting that the connection scheme of the PML magnetic starter allows the possibility of their installation inside the electrical panels. But there are requirements for all starter designs. To ensure high reliability of operation, it is necessary that the installation is carried out only on a perfectly flat and hard surface. Moreover, it should be vertically located. To put it simply, then on the wall of the electrical panel. If there is a thermal relay in the design, then it is necessary that the temperature difference between the MP and the electric motor is minimal.
In order to exclude false triggering of the starter or its protection, it is unacceptable to mount the device in places that are subject to shock, jolting, vibration, shock. Including installation on the same panel with electric starters, for which the current is more than 150 Amperes, is prohibited. When such devices turn on and off, a sharp blow occurs. The connection of wires must also be carried out correctly. In order to improve contact and so that there is no warping of the spring washers of the clamps, it is necessary to bend the wires in the form of a circle or the letter "P".
Starting starter
Always try to comply with electrical safety precautions, never work without turning off the power. If you have little experience, then you should always have a diagram at hand. A photo of connecting a magnetic starter is given in this article, you can familiarize yourself. What must be done before starting the starter? The most important thing is to conduct a visual inspection for cracks, distortions, phase closures. Remember to disconnect the entire drive circuit from power. Try to press the beam with your hands, it should move freely along the guides. Check carefully in the system all the magnetic starters, wiring diagrams of power conductors.
Pay attention to the connection of the starter solenoid coil. Also check that it is within the acceptable range. If 24 V is needed, then feed so much. Check all control wires if they are connected correctly to the Start, Stop, and Reverse buttons (if necessary). Is there a grease solution on the contacts? If not, apply it, otherwise the lock may not work in a timely manner. After that, you can turn on the circuit and start the drive. Please note that the coil of the electric magnet may be humming slightly in this condition.
How to care for starters
That's all, completely magnetic starters, connection schemes are considered, it remains to mention about caring for them. During operation, it is necessary to constantly monitor the status of the magnetic starter. The main care work is to prevent the formation of a layer of dust, and especially dirt, on the surface of the starter or thermal relay. From time to time, contacts must be tightened to connect to the network and to the drive. Dust must be removed with a rag or compressed air (only not wet). It is forbidden to clean the contacts, as this affects the resource of the device. Replace if necessary. Service life depends on many factors, but the most important is the mode of operation. If the starter is constantly in motion, commutes, then it will not last long. Its resource is measured in the number of on and off cycles, and not in hours or years.