Direct and indirect motor starting

Used in all sectors of industrial activities, three-phase electric motors have various applications in industrial machinery and equipment. However, to start the motor, there is a large energy demand to bring the machine out of rest. This causes a large peak current at the moment of forward output, which can trigger protection circuits. Therefore, to avoid these large currents when starting the motor, there is the indirect output.

Therefore, the objective of this article is to show what is the direct and indirect starting of three-phase motors, what are their applications and advantages.

What is the direct match?

Direct starting of an electric motor consists of starting the alternating current motor directly on the electrical network, connecting all the coils at the same time. Therefore, when the motor is started, the nominal voltage is applied directly to the stator on its bearings. The main benefit is the cost savings with other components that would be intermediaries between the motor and the electrical network, since it does not require the purchase of other devices, as well as the cost of energy and maintenance.

direct output

In this way, when starting directly, the motor windings are connected during activation directly to the source of alternating current, by means of a switch or contactor. Therefore, the entire procedure is carried out safely using electrical controls.

Direct starting is simple to implement, requiring few components and a three-phase motor. Therefore, one of the biggest benefits is related to its economy. Its cost is not high compared to the results that the machine will obtain and the implantation can take several years.

The disadvantage of this type of starting is the need to oversize the protection devices to withstand the initial peak current, so that they do not activate. The initial peak current also leads to faster motor wear.

Who can perform this procedure?

To start the motor directly, it is necessary to have knowledge of three-phase electrical networks and understand the operation of a three-phase motor. Therefore, the professional who has mastered electrical controls can start engines.

Only through this knowledge can direct motor starting be carried out safely. Therefore, if you need to start the engine, look for qualified professionals and ask for references from reliable people, since possible damage to the engine could replace the entire machine or even irreparable damage to its structure. 

Indirect start, star-delta connection

THE indirect output It is another method of starting motors, whose objective is to reduce the initial peak of electrical current. The indirect starting operation consists of connecting the motor to pass a lower current at first, until it leaves the inertial state. Then, there must be a change in the connection of the coils with the electrical commands so that the total current passes through the motor and can develop the nominal rotation, and, consequently, avoid the peak of the electrical current.

One of the best known forms of indirect output is the star-delta starter, whose name is due to its type of connection (star and delta) in relation to three-phase motors.

What are three-phase indirect motor starters?

Therefore, indirect starts on three-phase motors are starts that use electrical control methods to reduce the starting current and cause the motor to start in stages. This prevents high starting currents from interfering with the operation of motor protection circuits.

The 4 ways to perform an indirect match

To decrease the level of the electric current of a three-phase electric motor, four main ways can be used to realize an indirect output. 

Three-phase motor: indirect or direct starts

When questioning the reason why indirect starts of three-phase motors are applied, it is necessary to begin by explaining that, with respect to direct starting in this type of motor, one of its main damages lies in the high value of the electric current at the moment of the ignition (boot), that forces it to overcome inertia to leave the rest state and that generates the need for robust cables and components in its installation.

This factor is presented as unfavorable because, in addition to the high implementation cost, there is, of course, a very significant, and even excessive, cost! – on the daily consumption of electrical energy used by the motor.

The solution is to invest in indirect starts of three-phase motors to achieve this reduction with the guarantee of safety and efficiency, and, of course, preserving the integrity of the motor!

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