How is it? Physics of the question.
Until recently, the start-up of units with an electric drive was carried out by connecting the electric motor to the network by pushing it to the full voltage of the network. This method is the simplest and cheapest. To start the drive, you do not need anything other than a switching device (switch, contactor, starter). But is direct launch so harmless? It is known from Newtonian mechanics that it takes a little more effort to bring a body out of a state of rest than to maintain its subsequent movement. In other words, it is harder to move the cabinet from its place than to roll it on the hardwood floor! So it is in electrodynamics: when starting an electric drive, a significant starting current appears in the network. The value of this current exceeds the rated current of the unit several times, and depends on the design of the electric motor and the conditions for starting the unit. In turn, launch conditions can be light, medium and severe. It's not worth talking about light, medium, and the difficult conditions for starting up units with an electric drive require appropriate measures to be taken against disruption of the electrical network. Many companies are trying to solve this issue, one of them is here: instart-info.ru
A hard start characterizes the operation of mechanisms such as:
- high pressure feed pumps;
- blowing fans and smoke exhausters;
- various types of mills and crushers.
The excess of the starting current of these mechanisms over the rated one reaches 7 - 8 times, i.e., if there is a 500 kW electric motor with a rated current of 1000 A, then its starting current can reach 8000 A. This is already comparable to the short-circuit current (KZ). The turnaround time of such units can reach several tens of seconds. When a current of this magnitude flows in the network, a voltage drop occurs, and the more significant, the lower the power of the network. A decrease in voltage for such a long time leads to equipment malfunctions, up to the disconnection of consumers and power sources. Starting currents are especially dangerous for the electric motor itself:
- overheating of iron, windings and insulation;
- violation of the fastening of the winding in the grooves and in the frontal parts;
- increased loads on the shafts and bearings of the unit.
All these factors lead to premature engine failure.
What to do?
The most effective way to reduce the harmful effect of overcurrents on electrical equipment is the use of starting devices - frequency converters (FC) or soft starters (SCP). Both devices exclude direct starting from full mains voltage and all its negative consequences.
The inverter is a frequency generator that allows a continuously variable voltage to be applied to the drive�
