Abstract on theme "Influence of higher harmonics on capacitor battery"


Introduction.Urgency substantiation

EMC - ability of the electroreceiver (receiver) normally to function in the surrounding electromagnetic environment and not to make hindrances in this environment , inadmissible for other receivers. With regard to the problems of power supply under an electromagnetic environment defined electrical supply network to which the group of receivers is connected.

The problem EMC is in a sense analogous to the problem of environmental protection: increase capacity of electroreceivers and intensification of their work regime lead to the distortion parameters of electrical energy, which, in turn, negatively affects the modes of other network's electroreceivers. Maintenance EMC is connected with the considerable expenses causing high demands, shown to accuracy and validity of methods of estimation EMC in electrical supply networks

Maintenance of electromagnetic compatibility is one of the basic demands to electrical supply systems. Overestimate of estimations EMC leads to unnecessary increase investment, and understating - to damage from additional losses of the electric power, decrease in service life of an electric equipment, products deterioration. In this connection high demands are shown to validity and accuracy of methods for evaluating EMC both at a design stage, and in maintenance of systems of an electrical supply.

In this work EMC will be observed only from a position nonsinusoidality voltage. Nonsinusoidal regimes adversely affect the work of power equipment, systems, relay protection, automation, remote control and communication. Resulting affecting of higher harmonics economic damages are caused, mainly, by a deterioration of power parameters, reduced reliability of electrical networks and abbreviation of service life of electric equipment. And since the quantity of nonlinear capacites continuously grows, the problem of influence nonsinusoidality on an electric equipment to become every year is more and more acute.

Higher harmonics render especially strong agency on capacitors. The deformation of a curve of voltage considerably affects on the emergence and passing of ionization processes in dielectrics. In the presence of gas inclusions in isolation there occurs ionisation which essence consists in formation of volume charges and their subsequent neutralisation. Neutralisation of charges is connected with the energy dispersion which consequence is electric, mechanical and chemical affecting on surrounding dielectric. As a result, developing local defects in isolation that leads to decrease in its electric strength, increment of dielectric losses and, in the final reckoning, to service life abbreviation. Also, with nonsinusoidal voltage at the terminals of capacitor banks in their dielectric appear more active loss caused by higher harmonics. In the conditions of the industrial factories, as a rule, capacitors periodically appear in a regime close to a resonance of currents on frequency any of harmonics; due to systematic accelerations, they are easily damaged.

As can be seen from the foregoing, capacitors - one of the most sensitive to nonsinusoidality electrical equipment, therefore studying of agency on them of higher harmonics is very actual problem.

Review of existing methods for solving the problem. Alleged scientific novelty

The electromagnetic handicapes which are passing on elements of an electric network, are called as the conductive. As are in-process observed only nonsinusoid voltage the term a handicap we will refer to sinusoid distortions.

Nonsinusoid voltage EMC is the most widespread conductive handicap. n most publications, estimation of these handicapes is made for special cases of periodic distortions of a curve of voltage. However in acting networks handicapes represent random process that requires the development of common methods of analysis.

Scientific novelty of this work consists that this problem dares within the limits of the concept of dynamic modeling aftereffects the impact of a handicap on capacitor bank. Universality of such approach is caused by absence of restrictions on the type of handicap (on a model entry casual, periodic or constant processes can be submitted).

Consider also possible substitution models of capacitors.

The elementary model of capacitor is ideal capacity C. It usually apply when sinusoid distortions occur in rather small frequency range.

For example: in [4] number of considered harmonics equally 40 that matches to the maximum frequency 2000Hz. In this range such simple model is quite admissible.

In designing nomograms of handicapes with the right-angled undershooting in a sinusoid are used. In this case the ideal capacity cannot be used, as the derivative of vertical jump is equal to infinite. In this connection dynamic models of capacitors are used.

Since an exact mathematical description of such a system is difficult often use the simplified dynamic models based on the equivalent circuit design of the capacitor, matching physical essence of processes proceeding in it. According to [5-8] equivalent circuit of the capacitor looks like, presented on fig. 1.

Here: r - resistance of current carrying parts; L - equivalent inductance of the capacitor, approximately equal to the sum of inductance outs, connectors and a section internal inductance; R, C - accordingly active and capacitor resistance of dielectric.

Рисунок 1 - Figure 1 - Circuit replacement capacitor

The presented dynamic model can be used in the present work. At the same time, also it is supposed to observe more difficult models.

Aims and objectives

The aim is the creation of a dynamic model of capacitor to assess the impact nonsinusoidality voltage.

This model can be realised, for example, software environment Mathlab. In particular, with the built-in library of visual simulation of Simulink.

All process of modeling can be divided into two stages.

First is a definition of frequency characteristics and transfer function of the simulated system./p>

The second stage - modeling of system on the basis of a transfer function.

In the first stage to determine the transfer function model of the capacitor was performed realization of its equivalent circuit in accordance with the block diagram given in [2]. On fig. 2 computer equivalent circuit of the capacitor with six series chains is shown. The circuit design is typed from blocks Series RLC Branch, in the properties of which are given parameters of the elements.

Computer implementation of equivalent circuit of capacitor
Figure 2 - Computer implementation of equivalent circuit of capacitor
(animation made in the program GIF Animator, the number of frames - 6, repetitions - ∞)

By means of the program written in the environment of Mathlab, it is supposed to operate this model:

  • set entry conditions;
  • change type of graph of handicap.

Alleged practical value

The resulting dynamic model will be used to assess the adverse effects of higher harmonics in the capacitor (an increase of active power losses, reduced service life).

Conclusion

  1. Deformations of a curve of voltage have essential negative affecting on capacitors
  2. Existing methods of estimation these affecting are not universal.
  3. The universal model with possibility of the task of parameters capacitor and type of handicap aspect is required.

Here is not the final version of the abstract. Studies on this topic continues. Final alternative work is available from the author since December 2010.

Literature

  1. Введение в статическую динамику систем электроснабжения/ Шидловский А.К., Куренный Э.Г. - Киев: Наукова думка, 1984. – 273 с.
  2. Электромагнитная совместимость электроприемников промышленных предприятий/ Под ред. А.К. Шидловского. - Киев: Наукова думка, 1992. – 236 с.
  3. Электромагнитная совместимость. Несимметрия и несинусоидальность напряжения/ Кузнецов В.Г., Куренный Э.Г., Лютый А.П. – Донецк: Норд-Пресс, 2005 – 250 с.
  4. ГОСТ 13109-97. Межгосударственный стандарт. Электрическая энергия. Совместимость технических средств электромагнитная. Нормы качества электрической энергии в системах электроснабжения общего назначения. - Введ. в Украине с 01.01.2000.
  5. Комлев В.П., Малафеев С.И. Динамическая модель силового конденсатора и ее применение для расчета потерь при искажениях напряжения. - Владимир, 1982. - 12 с. - Деп. в Информэнерго 29.11.82, №1196эн - Д82.
  6. Коломытцев А.Д. Динамические показатели электромагнитной совместимости электрооборудования с системами электроснабжения промышленных предприятий по несимметрии и несинусоидальности напряжения. - Автореферат на соиск. уч. степени канд. техн. наук. - Донецк: ДПИ, 1993. - 24 с.
  7. Малафеев С.И. О динамических и энергетических характеристиках силовых конденсаторов // Оптимизация систем питания и электрооборудования электротехнологических установок: (Сб. научн. трудов). - Киев: Ин-т электродинамики АН УССР, 1989. - с. 110-116.
  8. Конденсаторы переменного тока в тиристорных преобразователях/Ермуратский В.В., Ермуратский П.В. - М.: Энергия, 1979. - 224 с.
  9. Высшие гармоники в сетях промпредприятий/Жежеленко И.В. – М.: Энергоатомиздат, 1984. – 160 с.