Ilya Vatolin Abstract CAD electric part power station

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ABSTRACT

Subject: "CAD electric part power station "

author: Ilya Vatolin

THE ALGORITHM OF THE CALCULATION A SHORT-CIRCUIT CURRENTS IN SCHEME BY VOLTAGE UNTIL 1 KV

               The problem putted thus as was the possible connect the fragments of the schemes by voltage more 1 kV and less 1 kV. As well as execute of calculations in the multinode scheme of the free configuration.
     The program must provide the possibility of the calculation of symmetrical and asymmetrical of the short circuits for a minimum and maximum condition of working schemes. As the method of analysis in algorithm of the program is accepted the method of the approximate calculation of the short-circuit currents in the concrete units. The resistances of the elements of scheme were present to the mohm. The calculation of the single-phase of the short-circuit currents is provided in accordance with Schedrin rules with use of the method of the symmetrical components.
     The calculation of the periodic constituent of the short-circuit currents of the i-source is executed by means of the method of the node voltages. The potentials in the nodes determine at moment of the short-circuit. And further on expression (1.1) is calculation of the periodic constituent a short-circuit currents of the i-source:

formula

Inoi- the periodic constituent of the short-circuit currents of the i-source for t=0; Eфi - the electromotive force of the i-source (phase value)
Uyфi- the voltage in the node, to which is connected source (phase value); Zi- the internal resistance of the i-source.

The particularity of the algorithm consists in that except inductive resistances are taken into account and active resistances that allows to define constants of the decay time of individual constituents of the short-circuit currents. The aperiodic constituent defined in that case, as amount of the currents of branches, because she is a calculation on separate for each connect of equivalent constants of the decay time of the individual constituents current, such of the method on GOST 27514-87 [1] and GOST 28249-93 [2].

где m – the number of the independent branches of the scheme; Inoi - the periodic constituent of the short-circuit currents of the i-source for t=0; Tai- the constant of the decay of the aperiodic constituent a short-circuit current of the i-source.
The constant of time of the fading aperiodic constituent of the short-circuit current for separate sources define as relation conditional to real constituent resistance of scheme relatively of the examined source:

formula

It is known that of the calculation of the symmetrical of short-circuit is done for one phase provided that resistances of all three phases of the elements alike
The surge of the short-circuit current from i-sources is defined as:

formula

    The active elements of the analytical model- an electric system, generators and electric motors, synchronous compensators are presented a voltages and internal resistances, all other passive elements - only resistances.
    For the calculation asymmetrical of the short-circuit current is provided the automatic shaping the equivalent circuit of positive phase-sequence, negative phase-sequence and zero phase-sequence.
    The calculation is made of the node potential method (the base of the decision of the combined equations there is the square-root method) that allows to find the potentials in all point of the analytical model and enables the determination of the infeed current the place of the short-circuit from each of the sources of voltages.
    In program is provided possibility of the calculation of the heat pulse of the short-circuit current. For this must be beforehand given the interrupting time of the circuit breaker main and reserve protection. The calculation of the integral of the Joule is executed with provision for action of the periodic constituent current of the short circuit.
    For determination of the resistances of elements of the scheme are used as source catalogue data, and the calculation is executed on formula expressed in structured scheme on fig. 1.1

The structured scheme of the block of the creation of elements of the equivalent circuits of positive phase-sequence and zero phase-sequence sequences.

Figure 1.1 - The structured scheme of the block of the creation of elements of the equivalent circuits of positive phase-sequence and zero phase-sequence sequences.

     Literature:
     1. ГОСТ 27514-87 короткие замыкания в электроустановках. Методы расчета в электроустановках переменного тока с напряжением свыше 1 кВ. - 40 с.
     2. Ульянов С. А. Электромагнитные переходные процессы в электрических системах. - М.: Энергия , 1970 - 517 с.
     3. Баков Ю.В. Применение электрической чести электростанций с применением ЭВМ: Учеб. пособие для вузов - М.: Энергоатомиздат, 1991 - 272с
     4. Околович М. Н. Проектирование электрических станций: Учебник для вузов. - М.: Энергоиздат, 1982. - 400 с., ил.
     5. IEC60909-0 (2001): Calculation of short-circuit currents.
     6. IEC60909-1 (2002): Factors for the calculation of short-circuit currents according to IEC 60909-0.
     7. IEC 60909-2 (2002): Electrical equipment - Data for shot-circuit currents calculation in accordance with IEC 909 (1988).
     8. IEC 60909-4 (2002): Examples for the calculation of short-circuit currents.
     9. http://www/mpei.ru Официальный сайт "МЭИ" (ТУ).

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