There are several ways to start or start a three-phase electric motor, but defining which is the best or the most suitable for each type of application is not always an easy task. One of the ways to start an engine is using the direct start, thinking about it we decided to talk about the direct start, like for example what is a direct start, what is the application for direct start, and the step by step of how to start a three-phase motor using the direct starter, in addition to presenting its main characteristics. Come on, guys!
There are many ways to start a three-phase motor, be it the star-delta starter, the star-delta starter with a reversal, the autotransformer starter (compensating switch), the auto-transformer starter with a reversal, indirect starters, the indirect starter with reversion and the ones we will see , which are the direct start and direct start with the reversal.
Direct start of three-phase motors:
The direct starter for three-phase motors is relatively the simplest connection among all the starters used to drive the three-phase motors, as the motor receives power directly from the three-phase power source, and depends only on disconnecting devices to directly interfere with its operation, such as circuit breakers, thermal relays or contactors.
Although the direct start is simple and easy to perform, it has some characteristics that must be observed. The direct start directly interferes in the performance of the three-phase motor and mainly in the electrical network where the motor is installed.
The use of the direct starter is more interesting in situations where you want to obtain maximum engine performance right at the start, one of the main characteristics to be used is the starting torque, but depending on the situation, the application of the indirect starter is recommended .
Restrictions for using direct start:
There are some restrictions regarding the use of direct start on engines, which are:
- This type of start can only occur in engines with a maximum power of 7.5 CV,
- Electrical installations must be able to conduct the motor’s peak current, which happens for a short time, and withstand the rated motor current, which is the permanent current in the circuit.
- The motors must be started without load, that is, empty, only after the nominal speed has been reached should the load be applied.
Direct Match Characteristics
As we already know that the direct start directly implies the infrastructure of the supply network where this motor will be installed, we can highlight some characteristics of this type of connection, such as at the moment of starting the motor torque is nominal, its starting current is up to 8 times the rated current, it requires more robust drive devices and the maintenance cost is high.
The command circuit is responsible for containing the connections of all its components and conductors, but the command diagram has the main function of representing the logic of activation of the contacts, which will be responsible for driving the loads or components, which in this case it will be the three-phase electric motor and the traffic lights.
According to the diagram shown below, the three-phase motor will only start when two buttons are activated at the same time, as a protection measure, in addition to two signals indicating its operating states, green for the motor on and red for the motor. engine off.
Load or power diagram:
As we can see, in the power diagram we have a motor being driven through a contactor, as the load circuit is responsible for supporting the highest intensities of electric current, but which are driven according to the command circuit. The circuit below shows the three-phase motor, the contacts (NA) of the contactor, and the other protection devices, which are the fuses and the thermal relay.
Description of operation:
When pressing the S1 and S2 buttons, the electric current will pass through the buttons and reach the coil of the K1 contactor, which will be energized. This way they switch immediately, then the load (K1) and control contacts close, allowing the passage of electric current and constant energization of the coil, three-phase motor and the green signal. In addition, the normally closed contact is switched, preventing the passage of electrical energy to the red signal.