(Khujand, Khujand Polytechnic institute TTU named after academician M.S. Osimi)
SIMULATION OF SOFT START OF SYNCHRONOUS ELECTRIC DRIVES
The main negative factors affecting the starting modes of synchronous electric drives of pumping units of irrigation water supply systems were identified, computer simulation of direct and soft start of synchronous electric drive was made, the simulation results are shown in graphs and a brief conclusion was made on the study.
Key words: pumping units, synchronous electric motor, starting currents, motor heating, modeling, soft start.
In this work, the object of the study was adopted high-voltage pumping units of the irrigation pumping station of the first lift. Disturbing effects on the facility were adopted modes of starting the units and the hot climate of the area. Taking into account all factors, the studies were carried out at the ANS-1 irrigation pump station, which is located in the Asht district of the Sogd region of the Republic of Tajikistan. Four pumping units of the 1200V-6.3/100-A series with a capacity of 8 MW each are installed in ANS-1 [1, 2, 3]. The electric drive is salient-pole synchronous electric motors (SM) with a vertical design with regulation of the performance of pumping units by turning on or off the units. This method is ineffective and dangerous, in view of the fact that each shutdown and inclusion are carried out with dynamic electromagnetic transients. In addition, hydraulic shocks, in turn, during start-ups damage and wear out the mechanical parts of equipment and joints of pipelines . Each start-up of a high-voltage SM passes through multiple jumps in the currents and moments of the motor, with voltage deviation, heating of the motor and losses, which reduce the technical life of the units and the entire equipment [4, 7, 8]. At the same time, if we add the still hot climate to the negative impacts, then the transitional regimes of pumping units can be very critical. Therefore, eliminating or minimizing the negative factors affecting the electric pumping units at startup is a very urgent issue that needs to be investigated and optimized.
With the development of power electronics, various types of semiconductor converters with different functions and capabilities, such as current inverters and voltage regulators, serving only for the soft start of high-voltage AC motors became available. The elimination of negative factors during start-up can be achieved with the use of soft starters (device for soft starts), since they are cheaper than the inverter by almost two to three times, and are good for alternating soft start of several electric motors [3, 4]. For this purpose, in this work, we simulated a transient process with direct and soft start of SM. The main program for modeling was adopted by the MATLAB/Simulink package with which we obtained the transient start-up graphs of the high-voltage SM shown in figures 1 and 2.
As the simulation results (see in Fig. 2) show, using the soft starter provides fairly favorable conditions for transient processes, namely, it limits the inrush current and jumps in the amplitudes of the oscillations of the electromagnetic moments of SM. In addition, modern soft starters provide the following advantages :
- significantly reduces dynamic loads on bearings of the electric motor;
- improving the operating conditions of electrical equipment;
- significantly reduces current, power losses and voltage deviations in the network when starting the electric motor;
- an increase in the number of permissible starts and the launch of electric motors from sources of limited power;
- improving the reliability and service life of equipment.
As a result of the study of transients of the electric drive of pumping units of the ANS-1 irrigation pump station, it was shown that to optimize starting conditions, it is sufficient to use a soft starter, which are cheaper and can be used to turn on several electric motors in turn. The results of computer simulation showed that the negative effects of currents and moments can be reduced with the help of soft starters.
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