Who wants to strain, spend their money and time to re-equip devices and mechanisms that work fine anyway? As practice shows - to many. Although not everyone in life encounters industrial equipment equipped with powerful electric motors, it is constantly encountered, if not so voracious and powerful, electric motors in everyday life. Well, probably everyone used the elevator.
- 1 Electric motors and loads - a problem?
2 What is a smooth start for?
- 2.1 Video: Smooth start, adjustment and protection of the collector. engine
3 Variants of systems of soft start electric motors
- 3.1 System "star-triangle"
- 3.2 Video: Connection of a three-phase asynchronous electric motor by a star or a triangle
- 3.3 Electronic soft starter system
- 3.4 Single phase starting circuit
- 3.5 Two Phase Starting Circuit
- 3.6 Three phase starting circuit
- 4 Soft start do it yourself
Electric motors and loads - a problem?
The fact is that virtually any electric motors, at the time of starting or stopping the rotor, experience enormous loads. The more powerful the engine and the equipment they set in motion, the greater the cost of starting it.
Probably the most significant load on the engine at the time of start-up is a repeated, albeit short-lived, excess of the rated operating current of the unit. After a few seconds of work, when the electric motor comes to its regular speed, the current consumed by it, too, will return to normal levels. To provide the necessary power supply have to increase the power of electrical equipment and conductive lines, which leads to their appreciation.
When you start a powerful electric motor, due to its large consumption, there is a "drawdown" voltage power, which can lead to failures or failure of equipment powered with it from one lines. In addition, the service life of the power supply equipment is reduced.
In the event of emergency situations that caused the engine to burn out or severe overheating, properties of transformer steel may change so that after repair the engine will lose up to thirty percent of power. Under such circumstances, it is no longer suitable for further operation and requires replacement, which is also not cheap.
What is a smooth start for?
It would seem that everything is correct, and the equipment is designed for it. That's just always there is a "but." In our case there are several:
- at the time of starting the electric motor, the supply current can exceed the rated four and a half to five times, which leads to significant heating of the windings, and this is not very good;
- the start of a direct-start motor leads to jerks, which primarily affect the density of the same windings, increasing the friction of conductors during operation, accelerates the destruction of their isolation and, over time, can lead to inter-turn closure;
- The above jerks and vibrations are transmitted to the entire unit being driven. This is completely unhealthy, because may damage its moving parts.: gear systems, drive belts, conveyor belts or just imagine yourself riding in a twitching elevator. In the case of pumps and fans, this is the risk of deformation and destruction of turbines and blades;
- Do not forget about the products that may be on the production line. They may fall, fall apart or break due to such a jerk;
- well, and probably the last of the points that deserve attention is the cost of operating such equipment. It is not only about expensive repairs associated with frequent critical loads, but also about the tangible amount of electricity that is not effectively consumed.
It would seem that all the above-mentioned operational difficulties are inherent only in powerful and cumbersome industrial equipment, however, this is not so. All this can be a headache for any average man in the street. First of all it concerns the electric tool.
The specificity of the use of such units as jigsaws, drills, grinders and the like, suggest multiple start-up and shutdown cycles for a relatively short period of time. This mode of operation, to the same extent, affects their longevity and energy consumption, like their industrial counterparts. With all this we should not forget that the system of smooth start can not regulate the working speed of the motor or reverse their direction. It is also impossible to increase the starting torque or reduce the current lower than that required to start the rotation of the rotor of the electric motor.
Video: Smooth start, adjustment and protection of the collector. engine
Variants of systems of soft start electric motors
One of the most widely used launch systems for industrial asynchronous motors. Its main advantage is simplicity. The engine starts when switching the windings of the system "star", after which, when recruiting regular speed, automatically switches to switching "triangle". This start option allows you to achieve a current of almost a third belowthan with the direct start of the electric motor.
However, this method is not suitable for mechanisms with a small inertia of rotation. These include, for example, fans and small pumps, due to the small size and weight of their turbines. At the time of the transition from the configuration of the "star" to the "triangle", they dramatically reduce the speed or even stop. As a result, after switching, the motor essentially starts up again. That is, in the end, you won’t achieve not only the saving of engine resource, but also, most likely, you will receive an over-expenditure of electricity.
Video: Connection of a three-phase asynchronous electric motor by a star or a triangle
Electronic soft starter system
Smooth engine start can be made using triacs included in the control circuit. There are three schemes of such inclusion: single-phase, two-phase and three-phase. Each of them is distinguished by its functionality and final cost, respectively.
Using such schemes, usually it is possible to reduce the starting current up to two or three nominal. In addition, it is possible to reduce the significant heat inherent in the above-mentioned star-delta system, which contributes to an increase in the service life of electric motors. Due to the fact that the engine start control occurs due to voltage reduction, the acceleration of the rotor is carried out smoothly, and not abruptly, like other schemes.
In general, several key tasks are assigned to the soft start systems:
- the main one is the reduction of the starting current to three to four nominal;
- reduction of the motor supply voltage, in the presence of adequate power and wiring;
- improvement of starting and braking parameters;
- emergency protection of the network against overcurrent.
Single phase starting circuit
This scheme is designed to start electric motors with a power of no more than eleven kilowatts. This option is used in the event that you want to soften the blow at start-up, and braking, smooth start and lowering of the starting current do not matter. First of all, because of the impossibility of organizing the latter, in such a scheme. But due to cheaper production of semiconductors, including triacs, they are discontinued and are rarely found;
Two Phase Starting Circuit
This scheme is designed to regulate and start engines up to two hundred fifty watts. Such soft start systems sometimes complete bypass contactor to reduce the cost of the device, however, this does not solve the problems of asymmetry of the supply phases, which can lead to overheating;
Three phase starting circuit
This scheme is the most reliable and universal system of smooth start of electric motors. The maximum power of the motors controlled by such a device is limited exclusively by the maximum temperature and electrical endurance of the applied triacs. Him universality allows to realize the mass of functions, such as: dynamic brake, reverse lift, or balancing of the magnetic field and current limiting.
An important element of the latter, from the mentioned schemes, is a bypass contactor, which was mentioned earlier. is he allows you to ensure the correct thermal mode of the motor soft start system, after the engine starts working at regular speed, preventing its overheating.
Existing to date soft starters of electric motors, in addition to the above properties, are designed to work together with various controllers and automation systems. Have the ability to turn on the command of the operator or the global control system. Under such circumstances, at the moment of switching on the loads, the appearance of interference may occur that could lead to failures in the operation of automation, and therefore, it is worthwhile to attend to the protection systems. The use of soft start circuits can significantly reduce their impact.
Soft start do it yourself
Most of the above systems are practically not applicable in domestic conditions. First of all, for the reason that at home we rarely use three-phase asynchronous motors. But single-phase collector motors - more than enough.
There are many schemes of the device of smooth start of engines. The choice of a particular depends entirely on you, but in principle, having certain knowledge of radio engineering, skillful hands and desire, it’s quite you can assemble a decent homemade starterwhich will extend the life of your power tools and home appliances for many years.