It may seem to a person new to electrical engineering that electrical appliances and equipment to control their work are incredibly complex. In fact, this is not entirely true, and the basis of almost all powerful systems is an electromagnetic contactor or starter. Only completely electronic devices are dispensed with without such solutions. Knowing how the connection diagram of the magnetic starter is performed, it is possible not only to repair it yourself, but also to carry out simple installation.
The main element of ballasts (ballasts)
Magnetic starter is an electromechanical device designed for direct switching of circuits with voltage up to 1 kV. It contains several contact pairs, through which the switching of lines and the distribution of electrical energy are carried out.
Sometimes, the design of the starter includes a thermal relay that implements the protection function of the connected equipment. Depending on the version, open and closed contactors are distinguished. A striking example of the former is the famous “frogs” or “frogs”, in which to access the internal elements it is enough to remove the fixing pin (PAE class). The second is almost all the rest (PML, PMA) installed inside the dustproof enclosures.
Remembering Electrical Engineering
Before we look at how to connect a magnetic starter, it is worth recalling a physics course in high school. As you know, when an electric current passes through a conductor, a special type of matter arises around it - a magnetic field, which has an attractive effect on most metals.
If you take a thin conductor and wind it on a metal core, then due to the magnetization of the latter, the resulting field is significantly enhanced. It is this principle that underlies the operation of the starter.
Design
Structurally, the magnetic starter is a product, the “heart” of which is a coil consisting of a magnetic circuit (U- or W-shaped base made of sheet electrical steel with high internal resistance) and a thin varnished wire wound on it. The second part is physically a continuation of the first, but is separated from it, being mobile. Before applying current to the coil, there is a space between the ends of both parts, which is provided by a throwing spring. As soon as a magnetic field arises, the magnetic circuit is assembled together, providing circular magnetic flux and contact pairs. The circuit of the magnetic starter is as follows: a system of contacts is fixed on the movable attracted part, which, depending on the installation method, when the coil is activated, touch (normally open) or discard (normally closed) from the fixed, providing circuit switching. Contact groups are divided into two types: main (power circuit) and auxiliary (alarm, blocking). So simple.
We study the location
Most contactors allow switching of three pairs of power contact groups and up to a dozen additional ones. The connection diagram of the magnetic starter is described on numerous resources, but it is not clear to everyone.
Anyone who is familiar with such equipment, and so will do everything right, while others "remain at their own." Today we will try to explain in simple terms what the wiring diagram for a magnetic starter looks like.
We pick up the contactor and carefully examine it. All bolted connections are somehow marked. Unfortunately, there is no single standard, or rather, each has its own, although most often manufacturers adhere to the following notation:
1. Connections 1, 3, 5 on the one hand, and on the other, directly opposite them - 2, 4, 6. These are the conclusions of the movable and fixed contacts in the power contact groups. The larger the rated current, the larger the dimensions of the bolts and pads.
2. Near or on the side of the unit there are several more contacts, designated 31, 32, etc. Also opposite each other. They serve for signal and blocking circuits.
3. At the very bottom, on opposite sides of the contactor housings, two contacts are placed - A1 and A2. These are the findings of the coil.
This is the basis. Sometimes, in some models, a special block of additional pairs of contacts can be mounted on top, driven by a rod on the moving part of the magnetic circuit.
Device check
The connection diagram of the magnetic starter can be checked with an indicator. Actually, even at the installation stage, these devices simplify the work.
Contact indicator can be purchased at any electrical store. It is also possible to use the vertebrae from a battery, a light bulb and two wires, but only when checking de-energized circuits. So, we charge the indicator so that when the two probes touch, the lamp lights up or there is an audible signal to verify the presence of a conductive track. We put one probe on the clamp 1, and the other - alternately on 2, 3, 5, 4, 6. This is necessary to check the absence of “clamps”, which, if any, will necessarily lead to interphase closure. If everything is fine, then you need to use a screwdriver to press on the movable part of the rod (PML, PMA) or use your hands to squeeze the two parts of the starter (toad), that is, simulate the operation. When checking in this position, the circuit should only be on lines 1-2, 3-4 and 5-6.
If the auxiliary contacts are hidden and cannot be seen, then you need to ring them to determine the normal state. Suppose that when pressed, the pairs 31-32 and 41-42 show the circuit, but 51-52 and 61-62 ring when the parts of the magnetic circuit are not closed. The first two are called normally open, that is, they do not conduct current without applying voltage to the coil.
And the latter are called normally closed, forming a circuit precisely with the disconnected position of the starter.
And finally, with the help of dialing or indicator you need to check the coil for integrity. To do this, one probe should touch A1, and the other - A2. The signal light should be on.
All of the above should be performed without connected wires, and even more so without supplying power to the circuit. The magnetic starter circuit can be checked without fulfilling this condition, but only by specialists who, for obvious reasons, are unlikely to read about connecting an electromagnetic contactor.
Roll up your sleeves
The wiring diagram for connecting the magnetic starter depends on the equipment that is fed through it. Therefore, as an example, we consider the classic case when you need to turn on a three-phase AC motor with squirrel-cage rotor.
We take a three-core cable of suitable cross section and connect one side of it to the motor terminals. The veins on the other hand are cleaned and fixed with bolted joints on contacts 2, 4, 6 of the starter. If, due to the nature of the installation, it is more convenient to use 1, 3, 5, then this is allowed. Next, to the terminals 1, 3, 5 we bring three wires from the power automaton. That is, after pressing the
switch button , the
voltage of 380 V will be present on the three bolts of the contactor
. From any of the lower jaws of the machine there is a wire to the normally closed “Stop” button and the normally open start button, from which the line then leads to the output of coil A1.
The connection diagram of the magnetic starter depends on the voltage for which the coil is designed. If
220 V is indicated on it
, then terminal A2 must be connected to the ground with a wire. In the case of 380 V, instead of ground, the line must be extended to one of the two lower jaws of the machine. When checking the indicator (in the on state) between the above sponge and the contact on the stop button of the device should be displayed 380 V.
How does this scheme work?
The above implementation is the simplest, without locks, hooks and alarms, but it is fully operational. Even the stop button in this case is optional. After turning on the machine and pressing the "Start" button, voltage will be applied to the coil of the contactor, it will magnetically attract the moving part of the magnetic circuit, and the contacts on the rod will work by passing voltage to the motor through 1-2, 3-4, 5-6. If you release the button, the coil will “fall off” and the circuit will be sorted.
Improvement
No less interesting is the magnetic reversing starter. Physically, this device is two contactors of the same type, which, thanks to a special triggering algorithm, are capable of changing the alternation of phases supplied to the motor.
As a result, the direction of rotation changes. The reversing magnetic starter can be implemented independently, by using two devices (KM1, KM2) and making changes to the classical circuit. There are also ready-made factory solutions, which are not only more compact, but also contain mechanical protection from "overflown".
Unplanned mode
The correct connection scheme for a reversing magnetic starter necessarily involves the use of interlocks. It is necessary so that an inquisitive person does not introduce an element of unpredictability into the chain, while simultaneously pressing the “Forward” and “Back” buttons. The reversible magnetic starter is connected as follows:
- We connect one contactor in the same way as a non-reversing one.
- Bridges are placed between terminals 1, 3, 5 of both devices.
- Outgoing lines are bridged as 2-6, 4-4 and 6-2.
- The wire from the control button to the coil KM1 must go through a normally closed contact KM2. And vice versa. This is how zero protection is realized - an electric lock from simultaneously pressing two power buttons. In the case of mechanical protection, such a connection can be omitted, although it will not be superfluous.