Do you know what a direct starter is? What are the types of keys and their main applications? Do you know how to install and how to apply a key for direct starting of electric motors? What is the power diagram and function control of a switch and start? If for some of these questions you have questions or want to understand more about these switching and protection devices, you are in the right place. Come with me to learn more about the subject together.
Direct Start Key
Direct start switches are solutions for driving single-phase and three-phase electric motors, they allow users to switch on / off maneuvers providing protection to the circuit and motor.
These switches are mounted in thermoplastic boxes or in metal boxes, the main manufacturers of compact direct starter drives are Weg, Siemens, Steck and SEW. These switches are manufactured in a very compact form for easy installation in machines, equipment and industrial electrical installations.
The starters have a high degree of protection, normally manufactured with a degree of protection between IP 55 and IP 66, they are in accordance with the NBR 5410 standard for industrial electrical installations and NR10 that deals with safety in electrical installations.
The types of starter keys covered in this article are direct starter drives, ready to be used, so they are easy to install and use. Its operation takes place through electrical devices that, according to the switch model, may have circuit breakers, fuses, power contactors and thermo-magnetic protection relays. This entire circuit is electrically interconnected and has a basic control circuit for activation and protection.
Observe the electrical power and control diagram for a starter switch:
Limitation of direct start keys
We must point out that these switches perform a direct start , mainly in three-phase motors, we can highlight that when a motor generates current peaks, it can reach 13X IN, that is, the starting current of a motor, when activated by a direct starter it can reach 13X more than the working current.
This effect of the current is called the peak inrush current, this phenomenon occurs due to the effort of the rotor, because at the moment of starting it requires a lot of induced energy, in turn the stator also absorbs the same energy demand from the grid, this occurs until the rotor is able to break the starting inertia. This network energy is consumed in an induced current in the rotor that seeks to reach the synchronous speed of the rotating magnetic field.
The sudden oscillations of current generated at the start of the motors can generate surges in the supply network, often causing a voltage drop, damaging other equipment and physical installations such as electrical cables and circuit components. Due to these factors, energy concessionaires limit consumers powered by the secondary network (supply in secondary voltage), to direct starts of maximum power 7.5 KW or 10 CV in three-phase system, in single-phase systems the maximum power allowed is 3.5 KW or 5 CV. There is no such requirement for consumers in the primary voltage since they have their own substations (ND51-CEMIG).
Due to these limitations we use as maximum working power of these 10CV switches, this is valid for consumers in a secondary network, in the case of consumers in a primary network, it is not common to use starters in engines larger than 30 CV, since direct starts generate the same peak current effect on your electrical installations.
Most common starter applications
We can see that the power of the direct starter switches is limited to engines with less power, as we concluded earlier engines up to 10CV, normally the application of these switches is limited to engines that do not have a high starting torque, they also do not require high torque of the engines . For this type of feature, we use the keys mainly in industries, residential and rural areas to drive small engines, irrigation and pumping systems, machinery and equipment, fans and exhaust fans, swimming pools and small motor vibrators.
Starting key types
The main types of activation using starters are described below:
- Three-phase and single-phase direct start
This type of start switch consists of a simple direct start that has a thermal relay to protect the circuit.
- Three-phase direct start with fuse
This type of three-phase starter has three NH fuses and a thermal relay to protect the circuit and motor
- Direct start-up of three-phase and single-phase motor pumps
This type of start switch consists of a simple direct start that has a thermal relay to protect the circuit, its difference is that it was specifically designed for use in motor pumps, having a level control within its control circuit.
- Three-phase direct start with manual switching for 2 motors
This type of starter consists of a simple direct start for three-phase motors, it has a thermal relay to protect the circuit, but two motors can be started individually.
- Three-phase direct start with protection against phase failure
This type of three-phase starter has a thermal relay for protection of the circuit and also has a relay for phase loss detection that monitors the network, protecting the circuit and preventing motor burns due to lack of phase.
- Three-phase reversing start
This type of three-phase starter has two contactors, they are activated individually, to perform the inversion of the phases and thus make it possible to start counterclockwise and clockwise.
- Direct start with motor-breaker
This type of three-phase starter has a motor circuit breaker for protection against overloads and short circuits, doing an excellent job in protecting the circuit and motor.
To learn more about the concepts of a direct start we recommend the video below that will show the assembly of a direct start step by step and the basic concepts of this drive:
We can conclude that the applications through direct starters are wide, but limited by the effects of the starting current, characteristic of this type of drive, in this way the power of the motor to be driven is limited to small motors of maximum power at 10CV (consumers secondary network).