One of the significant disadvantages of powerful asynchronous electric motors is their “difficult” starting, which is accompanied by huge initial currents at this moment. As a result, a large voltage surge appears in the network. Such “failures” can negatively affect the operation of electronics or other electrical units operating on the same line.
For a smooth start, a star-delta connection circuit is used. In which, at the beginning of startup, the engine is turned on as a star, and when the motor shaft spins up to operating speed, the electronics switches it to a triangle circuit.
I will show you how to assemble a starting and control unit that will not only control starting and stopping the engine, but will also change its switching circuits when starting.
Will need
To connect we need:
- 3 starters to control the power unit;
- attachment with time delay - adjustable time relay;
- 2 attachments with normally open and closed contacts;
- "Start" and "Stop" buttons;
- 3 light bulbs for a clear view of the starter’s operation;
- single-pole circuit breaker.
Scheme
The connection is carried out according to a pre-drawn diagram.
The diagram shows the power part and control circuits. The power part includes:
- input circuit breaker;
- 3 powerful starters that control the star-delta power circuit;
- electric motor
When switched on according to the “star” circuit, the first and third starters operate; when switched on according to the “delta” circuit, the first and second starters operate. Due to the lack of possibility of connecting to a 380 V network, we will limit ourselves to a visual examination of the operation of the system without motors. Control circuits include:
- single-pole circuit breaker;
- "Start" and "Stop" buttons;
- three starter coils;
- normally closed contact;
- normally open contact;
- time relay contacts.
We are putting together a diagram to demonstrate the operation of the automatic system.
Signal lamps are connected parallel to the starter coils so that you can clearly see the operation.
System check
We turn on the circuit breaker, thereby supplying power to the entire circuit. Press the “Start” button to start the electric motor. And our first and third starters were attracted, lights 1 and 3 came on - meaning that the engine was turned on according to the “star” circuit.
After some time, the timer goes off, the first and second starters are attracted, lights 1 and 2 light up - which means the engine is connected in a delta circuit.
The time on the set-top box can be adjusted from 100 milliseconds to 40 seconds. depending on how quickly the engine revs.
We press the “Stop” button and everything stops.
When connecting the motor, it is necessary to take into account the connection of the motor phases. In this case, phase A comes to the beginning of the winding, phase B comes to the end of the winding. Phase B should come to the beginning of the second winding, phase C to the end. Phase C should come to the beginning of the third winding, and phase A to the end.
Watch the video
Be sure to watch the video, which explains in more detail and clearly the process of working and connecting the entire circuit.
