AC Contactor: What is Self-Locking?

The AC contactor works on the following principle: electricity is drawn in, the primary contact is closed and switched on, and the motor runs. The self-locking circuit of the AC contactor is described in this article. What is the contactor's self-locking feature? Let's have a look at the image first.

Contactor Self-locking Circuit Diagram

Ⅰ. Stop button

The normally closed contact should be connected to the wiring of the stop button. What is usually shut? You may think of it this way: if we don't push the stop button, it's always on; if we hit the stop button to disconnect, it's still connected; and if we release the stop button, it's still attached, so it's simple!

Ⅱ. Start button

The typically open contact should be connected to the start button. The typically open can also be referred to as the stop button. If we don't push the start button, it will constantly be disconnected. The line is connected when you press the start button. The line is severed after you release it, and the start button is disabled. Understand that the stop button is both a temporary disconnecting and a permanent connection!

Ⅲ. Fuse

You can think of it as a fuse, it's easy to understand!

Figure. 2

Principle introduction:

The circuit breaker, contactor, two buttons, a stop button, and a start button can all be seen in the diagram. We utilize the start button since it is a contactor self-locking circuit,  We utilize the stop button since it can be started and stopped. Normally, the button is closed.

Figure. 3

Wiring steps:

The blue zero line enters the contact coil A1 on circuit breaker 2p, the live line enters the red button on circuit breaker 2p, and the function shuts the circuit when the stop button is ordinarily closed. When the stop button is normally closed, two lines emerge, one of which enters the contactor's auxiliary contact. NO OPTIONS (the contactor L1—L2—-L3 contactor main contact is described here). It enters coil A2 through the normally open NO of the auxiliary contact, and the other one enters the normally open of the start button, and the function begins. The outgoing line enters the contactor's coil A2 when the start button is ordinarily open.

Run the demo:

When you press the start button SB2, the contactor coil is activated, and the main and auxiliary contacts of the contactor are closed at the same time. The mainline power supply is routed through the fuse to the contactor contacts, thermal relay, and circuit.  with the contactor's auxiliary contact closed. The contactor has been powered at this point due to the auxiliary contact's closed control circuit, 

Figure. 4

Principle analysis:

The power supply passes through the normally closed contactor KM auxiliary contact of the thermal relay because the control circuit is connected to the normally closed contacts of the thermal relay,  When we push the start button, the contactor's auxiliary contact closes the power supply to the contactor coil through the contactor's auxiliary contact. As a result, the contactor is always powered and the motor continues to run.

Figure. 5

Press the stop button no more. SB1, the control circuit is normally closed and disconnected due to the stop button, so the entire control circuit is de-energized, the contactor coil is de-energized, the main contact returns to the initial state, and the auxiliary contact returns to the initial state, and the contactor Self-locking circuit is de-energized. If you need to restart, simply press the start button, and the process will repeat itself.

The power supply incoming line and the load end outgoing line are the three major contacts on the 380V AC  contactor. The three-phase live wires L1, L2, and L3 are the entering lines, and the load end outgoing lines are T1, T2, and T3, correspondingly. The contactor's principal point of contact When the contactor is not closed, the incoming and outgoing lines correspond one by one, L 1 to T 1, L 2 to T 2, and L 3 to T 3. The primary contact is generally open when the contactor is not closed.

Ⅳ. What is always open?

The contacts are generally open if they are disconnected and not connected, and normally closed if they are linked. The terms "usually open" and "typically closed" must be clearly comprehended.

The contactor also has a generally open auxiliary contact, which is the fourth contactor contact on the right, and the top and bottom contactor contacts are also one-to-one. When the contactor is not pulled in, it is always in the ordinarily open state. The auxiliary contact's job is to control the auxiliary button. The main contact's function is to control the load end, thus it's split into two parts: the main contact and the auxiliary contact.

Figure. 6

Ⅴ. How can the contactor be operated by suction?

Only the contactor coil will be energized, and the contactor will be drawn in if the contactor is to be pulled in. 220 volts and 380 volts are the AC  contactor coil voltage s. A 1 and A 2 are the coil voltage wiring's two connections, respectively. That is to say, the contactor with a voltage of 220 volts or 380 volts will be drawn in as long as the coils A 1 and A 2 have electricity, which should be obvious.

The coil is located in the middle of the contactor's back panel. Its purpose is to generate electromagnetic after the coil has been energized, and it has an armature in the center of the contactor's front. The ordinarily open contact of the contactor becomes a normally closed contact, and the normally closed contact becomes a normally open contact, by pushing the upper and lower contacts of the main contact and auxiliary contact of the contactor.

And we employ the contactor's self-locking main contact and auxiliary contact connections, which are ordinarily open contacts until the contactor is pulled in, at which point the contactor's contacts become normally closed contacts.  that is, above the contactor. The four contacts on top are linked to the four contacts on the bottom. The load end of the contactor will have power after the connection, and the load end will begin to run. Because no electromagnetism is generated once the coil is turned off, the armature cannot be attracted, and the coil and armature remain in the center. There is a spring that will automatically open the coil and the armature to their original positions, reverting the contactor's typically closed state to its original normally open state, disconnecting the contactor's upper and lower contacts and stopping the load. The principle must be grasped!

Now let's look at the buttons. There are two types of buttons: generally open and normally closed. The typically closed contact for the stop button must be connected, and the normally open contact for the start button must be connected. When you touch the button, the ordinarily open becomes normally closed, and the normally closed becomes normally open. When the button is released, the typically open and normally closed postures revert to their original states, which is simple to grasp!

The contactor self-locking circuit diagram, as seen above, contains numerous components such as thermal relays, fuses, indication lights, and so on. In the future, I'll go over each of these originals one by one. Today, we'll focus on self-locking wire. You might not be good if there are too many originals. As a result, we'll remove the contactor's components and solely discuss the contactor's self-locking.

The three-phase power supply is connected at the top, and the load terminal is connected at the bottom, using 380-volt contactor self-locking main connections. Coil A 1 is long-lived because it is coupled to contactor L 1. The contactor coil A 2 power supply is controlled by us. The power supply L 3 is routed through the circuit breaker or fuse to the stop button in order to regulate the contactor. The stop button must be always connected to the normally closed contact, and the power supply must then reach the normally open point of the start button.

As indicated in the diagram, the typically open point of the start button extends to the top of the contactor's auxiliary contact and is connected to contactor coil A 2. They typically open line of the start button then separates a line from the bottom of the contactor's auxiliary contact. This is a critical line. Yes, because the stop button is attached to generally closed, it is always connected if we don't touch it, therefore the auxiliary contact at the bottom is always charged. Let us discuss the principle.

Figure. 7

When we press the start button, it changes from normally open to normally closed, allowing electricity to reach coil A 2 through the auxiliary contact's top. The coils A 1 and A 2 produce a 380-volt power supply at this point, and the contactor begins to pull in. The contactor's upper and lower contacts are linked, and the motor begins to run; but, if we remove the start button, the start button will become normally open again, and the power will be shut off, rendering the contactor inoperable. it works.

When we pressed the start button, the contactor and the auxiliary contact were both pulled in, and the power supply under the auxiliary contact began to send power to the coil A 2, so the start button was released, but the auxiliary contact was still sending electricity, and the contactor formed a self-locking, and when we pressed the stop button, the power supply was cut off and the contactor was disconnected, so the power supply under the auxiliary contact began to send power to the coil A 2. The contactor self-locking principle is based on this.

When we look at the circuit diagram after knowing the physical wiring, it is simple to grasp. The contactor self-locking circuit schematic is on the right side. According to the physical wiring diagram and the self-locking circuit diagram, it is the contactor coil power supply, the position of the button, the one that is connected together is connected to normally closed, the one that is separated is to be connected to normally open, the circle M is the load motor, and it is simple to understand!