POWER LOSS DUE TO THE EFFECT OF HIGH HARMONICS IN ASYNCHRONOUS ENGINES

ABSTRACT

This article describes the quality indicators of electricity, its control requirements, the limit of normal allowable values of voltage, sources of nonsinusoidal currents, formulas for determining the nonsinusoidal voltage, as well as losses due to high harmonics in asynchronous motors, an algorithm for determining the losses generated in them has been developed.

АННОТАЦИЯ

В данной статье описаны качественные показатели электроэнергии, требования к ее контролю, пределы нормальных допустимых значений напряжения, источники несинусоидальных токов, формулы определения несинусоидальности напряжения, а также потерь на высших гармониках в асинхронных двигателях, алгоритм определения образовавшиеся в них потери были развиты.

Keywords: power losses, electricity quality indicators, distribution networks, electricity loss reduction measures, additional losses, waste curve, waste calculation algorithm

Ключевые слова: потери электроэнергии, показатели качества электроэнергии, распределительные сети, мероприятия по снижению потерь электроэнергии, дополнительные потери, кривая потерь, алгоритм расчета потерь.

As a result of accelerating production processes, improving and introducing new technologies, valve converters, single-phase and three-phase electric welding equipment, high-power electric arc furnaces, and non-linear consumers with volt-ampere characteristics are increasingly used. Power transformers, magnetic amplifiers, and gas discharge lamps have such features. The feature of these devices is that they consume nonsinusoidal currents in the network when a sinusoidal voltage is applied to their terminals. Nonsinusoidal current curves can be thought of as complex harmonic oscillations consisting of a set of simple harmonic oscillations of different frequencies. The high harmonics passing through the network elements lead to a voltage drop across the resistance of the elements, which, in addition to the main sinusoidal voltage, leads to a distortion of the voltage curve, a violation of the quality of electricity in the supply network. The problem of electromagnetic compatibility arises with the minute.

Non sinusoidal voltage is characterized by the following two parameters:

1. The distortion coefficient of the voltage curve is
2. The n-th harmonic component of the voltage is the coefficient  

The distortion coefficient of the voltage curve is determined by the ratio of the fundamental value of the harmonic composition of the nosinusoidal voltage to the fundamental frequency voltage, and we can determine it as follows:

                                (1)

Where  n is the voltage value of the harmonic; n is the number of the last recorded harmonics. It is allowed to exclude harmonics with a value of not less than 0.1% in the calculation of  .

The normal allowable and maximum allowable values of the voltage sinusoidal distortion coefficient in different voltage power grids [2] are given in Table 1 as a percentage.

Table 1.

Disruption coefficient of voltage sinusoidality

The permissible values of the coefficient n - harmonic component of the voltage at the common connection points to the power grids of different nominal voltage   are given in Table 2 (in percent) [1].

Table 2.

Coefficient of n harmonic constituents of voltage

The normal values given for n = 3 and 9 belong to single-phase networks. In three-phase networks, it is taken as half of the values given in Table 3.2.

The allowable limit values of the n-th harmonic component are 1.5 times higher than those shown in Table 3.2.       

High harmonics lead to additional losses in electric motors, transformers and networks;

Capacitor batteries make it difficult to compensate for reactive power;

the service life of the insulation of electric motor devices is reduced;

the performance of automated telemechanics and communication devices deteriorates.

Temporary high current harmonics lead to additional losses in electric car exhausts. The extra waste in machine steel is usually overlooked.

The specific losses for a single harmonic are different for the area of the harmonic's forward rotation or reverse rotation. Figure 1 shows the relative losses for the average losses from the direct and inverse sequences of the phases of the high harmonic voltage vector.

Analyzing the relative waste curve, it is easy to see that the ratio has the greatest value for small-order harmonics, first, second, and third. The losses from the 13th order harmonics are insignificant and can be ignored.[1]

Figure 1. Curve of losses due to high harmonics in asynchronous motors

The total losses due to all harmonics of voltage are determined as follows:

                                                 (2)

The additional losses in an n-harmonic induction motor are determined as follows:

)                                               (3)

Where    and -'are the active resistance of the stator and the reduced active resistance of the rotor at n-harmonic frequency.

At high frequencies in the stator and rotor coils, the surface effect is sharp and the resistance increases, so:

                                       (4)

For high-voltage asynchronous motors, 'can be calculated as:  

The calculation formula for determining the total losses from high harmonics can be given as follows:

            (5)

where is the multiplication of the starting current; -- nominal copper losses of the stator; - is the coefficient that takes into account the increase in losses in the stator copper due to the n-th temporal harmonic. The graph of the dependence   is shown in Figure 1. The ordinate axis shows the average values of   for the cases that form the systems of the nth harmonics in the forward and reverse order. When constructing a curve, the average value of the multiplication of the starting current is

Figure 2. Algorithm for calculating losses due to high harmonics in asynchronous motors

Nominal losses in the stator copper of large electric motors account for an average of 20% of the total losses in the  motor. With this in mind, Figure 1 shows the second ordinate showing the additional power dissipation from the higher harmonics relative to the total rated engine losses . The use of these curves is very convenient for detecting losses in asynchronous motors due to their high harmonics.

Studies [2] have shown that overheating of asynchronous electric motors in enterprises, even in high-harmonic networks, has not been observed at (, both at rated load and at low load. The following is an algorithm for calculating active power losses due to high harmonics in asynchronous motors [5].

Using the above algorithm, the sequence of calculation of active power losses due to the effect of high harmonics in asynchronous motors is given. We'll need the sizes we need to enter first. They are ,  , n , , where --n is the harmonic voltage,is the voltage at the first harmonic,  is the frequency of the starting current of the motor, n is the number of last recorded harmonics,   n is the harmonic. nominal value The active power losses generated by entering them into the program are calculated by the following formula.

=                              (6)

The results of the calculation are summarized in the form .

Figure 3. Software about calculating losses due to high harmonics in asynchronous motors

Based on this algorithm, software was developed in C++ builder 6. This software quickly and conveniently calculates the additional power dissipation caused by high harmonics in asynchronous motors based on the above algorithm and displays the results in a generalized way. To do this, we use the following parameters: the nominal losses of the stator in the copper coil , the frequency of the starting current , the sum of the coefficients of non sinusoidality , the introduction of voltage harmonics sequence number n and The result is generated on the screen by pressing the calculation button. In this case, we can perform computational work in a short time and high, and any user can use this program.

Methods of reducing the level of harmonics. Improving the curve shape of the mains current. One way to reduce nosinusoidality in power grids is to improve the curve of the mains current with valve converters. This can be achieved by compensating for high harmonics, adding currents of 3rd, 9th, 15th and higher order harmonics to the transformer windings, or by providing special laws governing the converters.

In the first case, the magnetic moment of the high harmonics is generated in the third winding (T) of the transformer (Figure 1). Due to this magnetic driving force, the magnetic flux is opposite to the main current of the transformer. As a result of this combination of currents, the high harmonics of the magnetic flux are compensated. The F filter is the limit for the first harmonic. The K amplifier is designed to amplify high harmonic currents.

Figure 4. Rectifier transformer circuit to compensate for high harmonic magnetic flux

When performing this circuit, the flow of canonical and abnormal harmonics and the mains currents of the converter can be suppressed. This circuit can be less expensive in some cases (for instance for power lines) when using converters and resonant filters.

The disadvantages of this scheme are its complexity, the need to use three-phase transformers and low speed. The circuit may be suitable for high-power converters operating in "quiet" mode.

The positive effect of improving the harmonic composition of the mains current can be achieved by controlling the switch valves in accordance with special laws [4]. Such adjustment systems should improve the nosinusoidality coefficient by measuring the high harmonics of the current and influencing the turning angles of the thyristor, or ensuring that the individual harmonics are suppressed. Currently, the implementation of such adjustment laws is based on microprocessor technology.

Increase the number of phases of the converter. One of the most common measures to reduce the high harmonics produced by valve converters is to increase the number of these phases.

The most common method is to improve the harmonic composition of the valve-converter network current using complex multi-bridge converter circuits that provide 12, 18, 24, and more phase rectifiers. For example, a 12-phase rectifier circuit can compensate for 5, 7, 17, 19, and other high harmonics. It should be noted that the effect of reducing the level of high harmonics in multi-phase circuits is reflected in the uniform loading of the converters and the symmetry of the phase control systems of the valves.

Reducing harmonics through supply chain methods. This is achieved through the rational construction of the power supply system, which ensures the allowable level of voltage harmonics in the consumer tires.

The most common methods are the use of high voltage transformers; supply nonlinear loads from separate transformers or connect them to separate windings of three-phase transformers; parallel connection to nonlinear loads of synchronous and asynchronous motors.

Reference:

1. Литвак В.В., Маркман Г.З., Харлов Н.Н. Энергосбережение и каче­ство электрической энергии в энергосистемах: Учебное пособие (издание 2-е). - Томск: Изд-во ТПУ, 2004. - 162 с.
2. ГОСТ 13109-97. Нормы качества электрической энергии в системах электроснабжения общего назначения. - М.: Изд-во стандартов, 1998. - 31 с.
3. Лукутин Б.В. Энергоэффективность преобразования и транспорти­ровки электроэнергии. - Томск: Изд. «Курсив», 2000. - 130 с.
4. Жежеленко И.В. Высшие гармоники в системах электроснабжения пром предприятий. - 2-е изд., перераб. и доп. - М.: Энергоатомиздат, 1984. - 160 с.
5. I.Kholiddinov, A.Abdullaev, M.Abdurakhmonova  Algorithm for determining the nosinusoidality coefficient of electrical quality index for welding equipment.// Universum: технические науки 5(98) Май 2022, Часть 12
6. Abdullayev A. A. et al. Asinxron dvigatellarda yuqori garmonikalar tasiridan kelib chiqqan isroflar //Involta Scientific Journal. – 2022. – Т. 1. – №. 6. – С. 278-285.
7. Xolidinov I. X., Qodirov A. A., Kamoliddinov S. Kuchlanish o ‘zgarishini reaktiv quvvatni avtomatik kompensatsiyalash qurilmasida rostlash //Academic research in educational sciences. – 2022. – Т. 3. – №. 3. – С. 973-981.
8. Zuhriddin H. et al. Reactive power compensation in power grids //Universum: технические науки. – 2021. – №. 11-6 (92). – С. 87-90.
9. Эргашев К. Р. У., Абдуллаев А. А. У. Импульсный источник питания для светодиодных осветителей //Universum: технические науки. – 2020. – №. 12-5 (81). – С. 14-16.
10. Kh E. A. et al. Increasing efficiency of turbo generators in heat electric centers // European science. – 2019. – №. 6. – С. 48.
11. Эралиев Х. А. У. и др. Восстановление разреженного состояния в сравнении с обобщенной оценкой максимального правдоподобия энергосистемы // Проблемы современной науки и образования. 2019. – №. 12-2 (145).– С. 80-84.
12. Bozorovich N. M. et al. Obtaining and researching of thermoelectric semiconductor materials for high-efficienting thermoelectric generators with an increased efficiency coefficienT //Проблемы современной науки и образования. – 2019. – №. 12-2 (145). – С. 69-73.
13. Эргашев К. Р. У., Абдуллаев А. А. У. Переходные процессы на источниках питания светодиодов и методы их устранения //Universum: технические науки. – 2020. – №. 12-5 (81). – С. 44-47.
14. Хамидов А.М., Абдуллаев А.А., Эргашев К. Р Разработка цифровой модели энергосистемы для проведения испытаний устройств автоматика ликвидации асинхронного режима (АЛАР). – 2021. – №. 11-5 (92). – С. 81-85.