Calculation method of direct-current components of short circuit current of power supply system

Abstract

The invention relates to a calculation method of direct-current components of short circuit current of a power supply system. A key problem of calculation of direct current components of short circuit current is researched; a frequency domain equivalent theory of the direct-current component calculation is provided; based on the principle, the method for calculating direct current of the short circuit current and attenuation features by use of a transfer impedance is provided. In the method, effects on short circuit current and direct current component calculation imposed by frequency are considered, and features of mathematical models of a complex electric power system network are combined, so the calculation results are quire precise, and the method is simple to operate, and usable for routine calculation of engineering.

Description

technical field [0001] The invention relates to a method for calculating power fault quantity, in particular to a method for calculating the DC component of short-circuit current in a power system. Background technique [0002] With the rapid development of the economy, the electricity load of the whole society continues to rise, and the installed capacity of the power system is expanding year by year; The short-circuit current level will increase further. In order to reduce transmission loss, the reactance-resistance ratio in the transmission network composed of power transformers and transmission lines is also increasing, resulting in slower and slower attenuation of the DC component in the short-circuit current of the system, and the series reactance used to limit the short-circuit current makes the problem more serious. serious. Although our country only considers the periodic component in the routine check of the breaking capacity of the circuit breaker, and does not ...

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Problems solved by technology

The limit frequency method is only valid when the time constants of each branch are not much different; the two-branch method can only deal with two branches at a time and the time constant of one of the branches must be fixed in advance, which is widely used in multi-power mesh networks. Inconvenient; and the essence of both is to perform equivalent transformation on the power network described by the power frequency impedance, so it is difficult to determine whether the equivalent impedance under the power frequency is used to participate in the calculation and the DC component attenuation without frequency characteristics is appropriate

The equivalent frequency method needs to select the corresponding equivalent frequency f according to the table lookup at different times of concern c , to calculate the equivalent impedance Z c , but this method needs to calculate the equivalent frequency at different times after the short circuit, and find the equivalent impedance at the corresponding equivalent frequency, which greatly increases the calculation workload

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