CC BY
7UDC 621.3
Malikov A. Senior Lecturer,
Department of "Electrical Engineering, Electromechanics and Electrical Engineering",
Andijan machine-building institute Andijan, Republic of Uzbekistan Makhsudov M. T.
PhD,
Department of "Electrical Engineering, Electromechanics and Electrical Engineering",
Andijan machine-building institute Andijan, Republic of Uzbekistan Boikhanov Z. U. Student of PhD,
Department of "Electrical Engineering, Electromechanics and Electrical Engineering",
Andijan machine-building institute Andijan, Republic of Uzbekistan Маликов А. старший преподаватель, кафедра «Электротехника, электромеханика и электротехнология», Андижанский машиностроительный институт, Андижан, Республика Узбекистан Махсудов М.Т.
PhD,
кафедра «Электротехника, электромеханика и электротехнология», Андижанский машиностроительный институт, Андижан, Республика Узбекистан Боихонов З.У. докторант,
кафедра «Электротехника, электромеханика и электротехнология», Андижанский машиностроительный институт, Андижан, Республика Узбекистан E-mail: zaylobiddin 1992@gmail.com
Effect of changes in the active resistance of stator windings of an asynchronous electric motor on the output signal of a three-phase current converter Влияние изменения активного сопротивления статорных обмоток асинхронного электродвигателя на выходной сигнал трёхфазного преобразователя тока
Abstract: This article describes the effect of copper windings on the heating and temperature of the external environment when current flows in the stator windings during the operation of an asynchronous motor. There have also been laboratory experiments to detect this heat. The results show that the effect of the three-phase converter on the output signal is discussed in detail. As a result, this value is clearly expressed in the change in the active resistance of the stator windings of the induction motor. Having studied how close certain heating temperatures of the windings are to standard indicators during operation, we can evaluate the energy performance of the machine. For this purpose, we investigate the process of heating the windings of an asynchronous electric motor with a squirrel-cage rotor and the change in the active resistance of the stator windings.
Аннотация: В этой статье описывается влияние медных обмоток на нагрев и температуру внешней среды при протекании тока в обмотках статора во время работы асинхронного двигателя. Также были проведены эксперименты в лабораторных условиях для обнаружения этого тепла. Результаты показывают, что подробно рассмотрено влияние трехфазного преобразователя на выходной сигнал. В результате эта величина четко выражается в изменении активного сопротивления обмоток статора асинхронного двигателя. Изучив насколько близки определенные температуры нагрева обмоток стандартным показателям в период эксплуатации, можем оценить энергетические показатели машины. Для этой цели исследуем процесс нагрева обмоток асинхронного электродвигателя с короткозамкнутым ротором и изменение активных сопротивлений статорных обмоток.
Keywords: asynchronous motor; temperature; heating curve; active resistance; heat dissipation area; the amount of heat generated by an electric machine per unit time.
Ключевые слова: асинхронный двигатель; температура; кривая нагрева; активное сопротивление; площадь рассеивания тепла; количество тепла вырабатываемого электрической машиной в единицу времени.
I. Introduction
During operation, electric machines are always heated due to energy loss. When determining the laws of heating, it is assumed that the machine will heat up conditionally over the entire volume in the same way, heat dissipation occurs over the entire surface.
Let's write the heat balance equation for electric machines [5].
Qdt — the amount of heat released by an electric machine in elementary time;
Q — the amount of heat generated by an electric machine per unit time;
t — time;
Gcdt — the amount of heat to be absorbed and spent on heating;
G — mass of the electric machine;
c is the specific heat capacity, the amount of heat that is spent on heating 1 kG of mass per 1 OC at;
т is the difference in between the temperature of the electric machine and the ambient temperature;
Cktdt is the amount of heat dissipated from the surface of the electric machine to the medium evenly;
S — heat dissipation area;
к — коэффициент is the heat dissipation coefficient.
II. Methods
When starting an electric machine, the heating temperature will be the same as the medium, i.e. т ~ 0, since Sfo^dt ~ 0 the heat generated in electric machines is spent on increasing the temperature of its parts. Later, the amount of heat dissipated to the environmenty also increases. Thus, after some time, the electric machine will become so hot that the heat released from the machine begins to dissipate to the environment. When the temperature increase stops, thermal equilibrium is observed, that is, the heat generated from the machine begins to dissipate to the environment.
Qdt = Gcdt + SAzdt
(1)
Qdt - SAttur * dt
stable temperature of the electric machine
Ttour ~ tour ~
(2)
(3)
Typtur - temperature of steady heating of the electric machine, OC. From the (2)-th formula, we get the following:
0
T
myp
SA
From the (4)-th formula, it can be seen that the temperature of stable heating of an electric machine does not depend on the mass of the machine, but depends on the scattering area and on the scattering coefficient for the time unit of time [2].
The dependence of the heating temperature of an electric machine on time t is determined from the following equation:
t = TyCT(l - e~r) (5)
e is the base of the natural logarithm;
T is the heating constant;
t = /(t)-Figure 1 shows a graph based on (4) the heating curve formula.
Figure 1 — Heating curve
According to Figure 1, it takes a long time to reach a stable heating temperature of an electric machine.
The segment of the tangent drawn by the curve of the heating line of the graph at the beginning is quantitatively equal to the heating constant t [6].
According to GOSTU 183-74 for gas condition(surrounding area) media at a temperature of 40°C. Therefore, the temperature rise of parts of an electric machine is determined by the following expression:
T t our — 0t our ~ 4 0 (6)
here is the stable heating temperature of parts of an electric machine.
Determination of the physical stable temperature of the electric machine is made by the method of resistance difference, that is, the measured active resistance rj of the winding resistance of the electric machine before starting and the measured resistance r2 during the achievement of stable heating. This amount of time depends on the operating mode of the electric machine.
Stable heating temperature of the winding
0iyp tour — ^ ^ 01 (7)
0 1 — winding temperature before starting the electric machine, OC;
k is the temperature coefficient, for copper and aluminum k = 0.004 OOc-1.
Having studied how close certain heating temperatures of windings are to standard indicators during operation, we can evaluate the energy performance of the machine. For this purpose, we study the process of heating the windings of an asynchronous electric motor with a closed-loop rotor and the change in the active resistances of the stator windings [7, 10].
III. Results
The investigated three-phase electric motor with a closed-loop rotor with a power of 750 W, stator windings are connected to the network by a star (Fig. 2).
In the initial state, that is, before switching on to the network (temperature in the stator part t = 33.2OC), the results of measuring resistances are given below:
1) U1 — U2 yes 10.14 Q;
2) V1 — V2 yes 10.18 Q;
3) W1 — W2 yes 10.19 Q.
After starting the electric motor, heating begins, the temperature rises, and as a result, the resistance of the stator windings also increases, which are calculated using the expression below
R2 = Ri [1+ X(t2° - tj0)] (8)
After starting the electric motor, we can monitor the temperature using the sensor placed on the stator part. With an increase in the duration of operation of the electric motor, an increase in temperature is observed. That is, after starting the electric motor
— after 3 minutes of operation, the sensor reading is 37.5 °C;
— after 23 minutes of operation, the sensor reading is 55.1 °C;
— after 37 minutes of operation, the sensor reading was 62.8 °C.
After the last temperature measurement, the electric motor is disconnected from the grid and the active resistances of the stator winding are measured, we have the following results:
1) U1 — U2 yes 11.40 Q;
2) V1 — V2 yes 11.45 Q;
3) W1 — W2 yes 11.43 Q.
The results obtained show that in the operating state of an asynchronous motor, there is a change in the resistance of the stator windings, the magnitude of the change depends on the duration of operation and on the strength of the current flowing through the stator windings.
To study the effect of changes in the resistance of stator windings on signals in the form of output voltages of measuring elements located on the stator slots, we consider the operation of a three-phase asynchronous motor with three measuring elements located on the stator slots (Fig. 2).
Figure 2 — Three-phase asynchronous electric motor with three measuring windings
After starting the asynchronous electric motor, we calculate the negative voltage at the outputs of three element current-to-voltage converters located on the stator slots (u1-u2, v1-v2, w1-w2) for constant loads. After starting the electric motor, three minutes after starting at the voltage outputs of the current converter:
1) u1 — u2 yes 3,665 V;
2) v1 — v2 yes 3,631 V;
3) w1 — w2 yes 3,721 V,
— identified after completing 23 minut of work
1) u1 — u2 yes 3,658 V;
2) v1 — v2 yes 3,619 V;
3) W1 — w2 yes 3.71 V,
— identified after completing 31 minut of work
1) u1 — u2 yes 3,656 V;
2) v1 — v2 yes 3,616 V;
3) W1 — W2 yes 3,714 V.
IV. Conclusion
As the obtained results show, changes in the resistance of the stator windings at the outputs of the three-phase current converter (7) to voltage will lead to a corresponding change in the signals in the form of voltages (8).
here uj is the voltage of the stator windings at the terminals, Ij is the current passing through the stator windings, Pj, Xj is the active and reactive resistances^ of the stator windings, wj is the number of turns of the stator windings, wism is the number of turns of the measuring winding.
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