Podporina Anastasiya

Electrotechnical Faculty

Department of Electrical Systems

Speciality "Electrical systems and networks"

Investigation of the possibility to use the WACS technology of transient mode monitoring to control the electric system modes

Scientific adviser: Ivan Zabolotnuy

     Content

1. Introduction
2. Identification of the real time mode
3. Control of network capacity and safety factor
4. Control to prevent stability infringments with control of stability factor in the real time mode
5. References

     Development of the electric power systems (EPS) is accompained with complication of the technological problems in mode control. The decision of real time problems, i.e. EPS mode control in real time, causes hard complexities. Control of EPS modes is directed to provision of modes reliability and system survivability, the later being estimated by its ability to oppose the disturbances. That's why the control be both transient and emergency processes is always the actual problem.      Last years, the technology of flaxible transmission lines and technology of transient monitiring — Wide Area Measurement Systems (WAMS) are intensively implemented in EPS. WAMS realizes the technology of vector measurement of EPS mode parameters with high accurasy and with maintenance of measurement synchronization, it being one of priority development technologies of the large power supply systems of the world.

     Actuality

     The appearance and development of WAMS technology have been cauced by several factors:

• topology and structure complication of the electric power system, which lead to coplication of the occuring in them at tecnological infrigements dynamic processes;

• increase of quantity and in weight of large system failures;

• appearance and wide introduction of GPS technology, which has allowed to synchronize measurements and to recieve such important parameter for the dynamic analysis as a mutual voltage angle, which could not be determined by means of existing tion support.

     These factors define an actuality of the present work topic, where the expediency and principal realizability of such control in power supply systems are investigated by the "station — buses of infinite power".

     The work purpose: investigation of the possibility to use the WAMS technology to control the transient mode.

     Main research tasks:

• to analyse techniques of WAMS use for identification of EPS control model;

• to estimate the efficiency of determination of the self and mutual admittance matrix of generator on the basis of WAMS,

     Objecf of research: the electric power system under conditions of electromechanical transients.

     Subject of research: application of the vector representation of electric quantities in EPS transients.

     Methodology and methods of research: in the research existing numerical methods for solving the nonlinear algebraic and differential equations to calculate the steady-state and transient EPS operation modes are used. Simulation of EPS modes was carried out using, mathematical software package Mathcad.

     The scientific novelty
     Scientific novelty consists in improvement of mathematical models of synchronous generators and power plants as a whole, in development of methods of their use for determination of and mutual admittance matrixes.

     Review of researches and developments on the subject:
     WAMS represents the complex of registering devices, information transfer channels between registrators, concentrators of the data and control centers, and means of received information processing. Registrars are established in large power nodes, on intersystem communications, on power stations of secondary regulation.

     1 IDENTIFICATION OF THE SMC MATRIX IN THE REAL TIME MODE

     The control of transient parameters with the aid of WAMS allows to execute the identification of the control power supply system model in real time mode. The problem of the control model identification supposes the definition of SMC matrix, which solution can be considered by an example of the simplest scheme «the generator with self loading — buses of infinite power» (fig.2). The main measured parameters include the modules and phases of voltages at both ends of controlled power transmission, active and reactive power at the generation node.

     Definition of SMC is based on the use of known expressions where active and reactive powers depend linearly on the SMC:

where: g_1C, b_1C — mutual conductance and susceptance;
             g₁₁, b₁₁ — self conductance and susceptance. Self and mutual conductance and susceptance connected with each other by the following relationships:

     Augmenting the equations (1) with equations for derivatives:

we obtain the system of the linear equations, solution of which gives SMC matrix whikle the transitive EMF is considered to be constant.

     As derivatives of active and reactive powers by mutual angle can be approximately defined by power and angle increments (in the steady–state — at irregular fluctuations of loading and rotors of generators, in transient — in processes of their appearance):

     2 CONTROL OF NETWORK CAPACITY AND SAFETY FACTOR

     The SMC matrix allows to use angular characteristics of power to determine the limits of transmitted power through controlled sections, static and dynamic stability factor for generators in real time mode.
     The estimation of dynamic stability and its factor can be executed by power criterion concerning the mutual rotors movement.
     For the elementary system «station — buses of infinite power» the kinetic energy reserved by the equivalent generator in relative movement, can be defined as follows:

where: T_i — a constant of mechanical inertia of the unit;
     P_HOM — generator rated power, MW
     s — generator rotor slip, which can be calculated approximately if to pass from differentials to increments:

     The highest possible braking energy necessary to assess the dynamic stability and its factor can be obtained by integration of the angular power characteristic, obtained by the determined values of the SMC matrix:

where: P_Г(δ) — generator electric power, MW;
     P_Т(δ) — turbine power, MW.

     In general, power of the controlled turbine can not be represented by dependence P_Т(δ). In this case, the determination of the braking energy is associated with definite difficulties because of the nonlinear nature of the time turbine power change, and in the coordinates of power and mutual angle, respectively
     Analitic solution of this problem can be obtained, if to execute a polinomial approximation of curve P_Т(δ). The degree of approximating polinomial depends on the rate of change of turbine power, which can be esrimated by experimentally taken torque-impulse response of the turbine.

     3 CONTROL TO PREVENT THE STABILITY INFRINGEMENTS WITH CONTROL OF STABILITY FACTOR IN THE REAL TIME MODE

     Being applied to problem of Pulsed Unload of Turbine (PUT) control, the identification of SMC matrix in post fault conditions allows:

• to execute an estimation of sufficiency of PUT depth for maintenance of dynamic stability of power transmission;

• to make the decision on necessity of deeper UT or disconnection of some generators if the factor of dynamic stability is not sufficient;

• to define level of restoration of turbine power on a condition of 8 %factor of static stability in the post fault mode.

     A number of works have used the simplest schemes of electric power systems in electromechanical transients. In my work, it is supposed to estimate efficiency of methods in more complex schemes, using program Power Factory.

     An important remark

     While writing the current author's abstract the master's work had not been finished yet. The final completion will be by the December, 1st of 2011, You may obtain the full work's text and all the materials from the author or his supervisor after the stated date.

1. Тундаева Д.В. Применение системы мониторинга переходных режимов для идентификации модели управления энергосистемой // Наука. Технологии. Инновации: Матералы всероссийской научной конференции молодых ученых. — Новосибирск: Изд–во НГТУ, 2007. Ч.3. С. 254–256.
2. Аюев Б.И., Куликов Ю.А. Перспективные направления использования системы мониторинга переходных процессов ЕЭС/ОЭС // Труды международной конференции «Релейная защита и авоматика энергосистем». — Чебоксары, 9–13 сентября 2007.
3. Касобов Л. С. Моделирование и учет ограничений по устойчивости для энергосистемы Таджикистана / Л. С. Касобов, науч. рук. А. Г. Фишов // Наука. Технологии. Инновации: Материалы всероссийской научной конференции молодых ученых в 7–ми частях. Новосибирск: Изд–во НГТУ, 2008. – Ч.3. С. 165–167.
4. Б.С. Стогній, О.В. Кириленко, О.Ф. Буткевич, М.Ф. Сопель. Організація моніторингу режимів енергооб’єднання України та нові можливості розв’язання задач диспетчерського керування. Журнал «Наука та інновації» №6,2009.
5. Аюев Б.И., Ерохин П.М., Куликов Ю.А. Система мониторинга переходных режимов ЕЭС/ОЭС // Технологии управления рее жимами энергосистем XXI века: Сб. докл. Всеросс. Научнопракт. конф. / Под ред. А.Г. Фишова. — Новосибирск: Изддво НГТУ, 2006. — С. 83–92 с.
6. Журавлев Д.М. Исследование и разработка применения векторного представления электрических величин в переходных режимах электроэнергетических систем. Автореферат. [Электронный ресурс]. — Режим доступа: http://www.dissercat.com/content/issledovanie-i-razrabotka-primeneniya-vektornogo-predstavleniya-elektricheskikh-velichin-v-p
7. Касобов Л.С. Оценка технической и єкономической єффективности управления режимами ЄЄС для предотвращения нарушений устойчивости. [Электронный ресурс]. — Режим доступа: http://elib.altstu.ru/elib/books/Files/pa2009_2/pdf/056kasobov.pdf