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20
Shayumova Zamira Mustafayevna, the basic doctoral student, Scientific and Technical Center, Uzbekistan, Tashkent
E-mail: [email protected]
APPLICATIONS OF A CONTROLLED ELECTRIC DRIVE WITH REACTIVE POWER COMPENSATION
Abstract: The article gives the possibility of using a regulated electric drive with reactive power compensation. At the same time, the advantage of using frequency converters is analyzed, which allows saving energy, which is actual for today.Methods for improving the shape of the input current or for compensating the reactive power are given. These theoretical concepts are justified by a description of the graph of the dependence of the efficiency of an induction motor 4AI160S4 on the load.
Keywords: frequency converters, power, harmonics, motor, compensation, regulation, frequency.
In power supply networks with an electric load, they input transformer is heated. Saving energy will decrease.
have transients that can change the supply voltage. Due to the increase in the capacity of the induction motor used in the wires and the increase in the price of electricity, the problem of reactive power compensation is the main reason for the operation of power supply systems. As the control and increase of accuracy and achievement of power indicators, AC electric drives with frequency, frequency-current and vector control are competitive in accuracy, speed and control ranges with respect to DC electric drives.
Every year, the installed power of frequency converters (inverters) in enterprises is increasing, because in addition to automation of production processes, they save energy, which is very important for today. The frequency control method provides:
• smooth control of engine speed in a wide range on both sides of the nominal;
• rigid artificial characteristics;
• constant overload capacity.
If the installed power of the drive is no more than 10% of the power of the transformer input, then there are no special issues. If the total installed power of the frequency converters will be more than 20-30%, then there will necessarily arise questions related to the operation of frequency converters. Compensation for reactive power will become difficult due to overheating of the capacitors of the compensating plants [1]. It is possible to alter the compensating units by installing in series with the capacitors the suppressing chokes, but as a result, the
Frequency converters with a direct current link, namely such frequency converters in the overwhelming majority used in a frequency-controlled electric drive, consume a current from the network, the shape of which is far from being sinusoidal. As a result, in the input network there are odd and not multiple three higher harmonics - these are 5, 7, 11, 13, 17, etc.It is the higher harmonics that create problems for us [2].
Recently, to improve the shape of the input current or compensation of reactive power, active filters are used that are connected in parallel to the mains. The functionality of active filters is much more passive. For example, in the active filter, you can program one or more harmonics to be suppressed, you can work in compensation mode. Active filters are simply necessary for those enterprises in which all methods of suppressing the higher harmonics do not give the expected result. The share of the electric drive accounts for about 70% of all generated electricity. Therefore, the efficiency of using this electricity is of great technical and economic importance. Power to the electric drives comes from the industrial AC network frequency of 50 Hz. Electric drives consume active power from the network.
Active power is expended on useful work and covering losses in the entire electromechanical system of the working machine. Analyzing the efficiency of the use of electrical energy, it is necessary to distinguish between the energy efficiency of the process itself, which is carried out by a working machine with an electric drive,
Section 11. Technical science
and the efficiency of the actual drive, characterized by its efficiency, which is the ratio of the output power P.np of this device to the input power Pue, (or energy) to the spent P sash:
' " " (1)
where nemntmnn
eng itran tconv
n =
P...
P
inp
spent
AP
where AP is the loss in this device, AP =
Puse (1 -n)
n
Since the power part of the electric drive consists of an electric motor, a transmission and a converter device, the efficiency of the electric drive:
n n engn tranH conv
- Efficiency of the engine, transmission and conversion devices, respectively.The efficiency of the converter device, made on the basis of power semiconductor devices, is quite large.The losses in the converter are mainly determined by the direct voltage drop in the semiconductor device. On average, we can assume that U = 2 V, for bridge circuits U = 4.0 V.
Figure 1. Dependence of the efficiency of an induction motor 4AI160S4 on the load
Thus, the nominal losses for 440 V converters are 1%, and for converters with a voltage of 220V - 2%. Taking into account losses in the reactive elements of semiconductor converters, their efficiency can be taken equal to 0.95 ... 0.98.Losses in mechanical transmission devices (reducer, transmission, etc.) are determined mainly by frictional forces [3]. These losses, and consequently, the efficiency of mechanical transmission depend on the type of bearings used, the class of gears, lubrication systems, etc. The efficiency of a mechanical transmission depends essentially on the moment being transmitted. Under the efficiency of a working machine (PM) is understood the product of the efficiency of an electric drive at the efficiency of a working machine.
In the alternating current network, from which power is supplied to the electric drive, the reactive power circulates, as a result of which the network is supplied with a reactive current that does not generate work. The reactive power is estimated by cos^, where the angle p is the phase of the shift of the first harmonic of the cur-
rent with respect to the first harmonic of the voltage. In asynchronous short-circuited motors, the nominal cosp = 0.7 ... 0.8. The underload of the induction motor leads to a further decrease in cosp. In drives according to the TP-D system, cosp = cos a, which is determined by the delay set by the pulse-phase control system, the opening of the thyristors. Therefore, in the TA -D drives at high speed, cosp in the AC power supply will be high (0.8 ... 0.9), as the speed decreases, when the angle a increases, cosp will decrease [4]. When the TP-D drive is turned on, "reactive power" throws occur.
In modern systems of a regulated electric drive, uncontrolled rectifiers tend to use the regulation of the voltage applied to the motor windings by pulse-width methods.In this case, the cos^ in the mains will be at least 0.95. In terms of reactive power compensation for many electricity consumers, it is effective to use high-power synchronous motors for unregulated electric drives, which, when overexcited, can generate reactive power to compensate for it in the power system of the enterprise.
References:
1. Rozanov Yu. K. "Fundamentals of power electronics." - M. Energoatomizdat,- 1992.
2. Zhezhelenko I. V. "Higher harmonics in power supply systems of industrial enterprises". - M. Energoatomizdat -1984.
3. Control methods used in frequency converters for controlling AC motors. (Electronic resource) URL: http://dataural.ru/stati.
4. Leznov B. S. Energy saving and adjustable drive in pumping and blowingplants.-M.: Energoatomizdat, - 2006.360 p.
