Novel distributed feed line automatic protection method applied to FTU

Abstract

The invention discloses a novel distributed feed line automatic protection method applied to an FTU. The method includes the steps: accurately determining a fault moment through the zero sequence current of a feed line; calculating transient fault components of a phase current and the zero sequence current; performing four-layer wavelet decomposition for the transient fault components of the phase current and then obtaining a fault phase; performing four-layer wavelet decomposition for the transient fault components of zero sequence current, and determining whether grounding protection is started according to the ratio of energy of free vibration components of the transient fault components of zero sequence current; determining the ration of the transient capacitive current total energy of the fault phase to the average transient capacitive current total energy of non-fault phases, and determining whether the grounding protection is started; and determining whether fault phase grounding protection is started according to a cross correlation coefficient of an autocorrelation estimation sequence of the fault phase and the two non-fault phases. A morphological gradient technology is adopted to process the zero sequence current, extract current abrupt change information and accurately capture the moment when a fault occurs. Through the method, people can directly and accurately identify whether a feed line malfunctions on three-phase current information collected by an FTU.

Description

technical field [0001] The invention relates to the field of relay protection of electric power systems, in particular to a new method for automatic protection of distributed feeders applied to FTU. It is suitable for single-phase grounding protection of neutral point non-effective grounding system. Background technique [0002] Most distribution networks with a voltage level of 66kV and below in my country adopt the non-effective neutral point grounding method, and this system is often called a small current grounding system. In this mode, when a single-phase grounding fault occurs in the power grid, the fault current is small (especially the grounding system through the arc suppressing coil), although the regulations allow continuous operation for 1 to 2 hours, the voltage of the non-grounded phase after the fault becomes the line voltage, which is harmful to the system. Insulation brings hidden dangers and threats. It is necessary to cut off the faulty line as soon as po...

AI Technical Summary

Problems solved by technology

[0004] The existing single-phase grounding protection devices for small current systems are still mainly based on line selection devices for steady-state power frequency signals. According to the statistical results of authoritative departments, the overall line selection accuracy of line selection devices in actual operation is less than 70%. Misselection, The probability of rejection is very high, and the line selection of steady-state power frequency signals is affected by the following aspects: (1) the influence of the compensation current of the arc suppression coil; (2) the influence of the transition resistance; (3) the influence of the unbalanced current of the current transformer (4) The influence of ground fault location

[0005] Because a single-phase grounding will produce a transient fault component that is several to ten times larger than the steady-state component, the small current grounding protection method based on the transient signal will have a good fault identification ability, but the transient signal appears for a short time, Fast attenuation, accompanied by high-frequency interference, relatively difficult to detect, need to use appropriate modern signal processing methods for analysis and processing

Now the processing of fault transient signals generally adopts wavelet analysis method, which is easily affected by impulse noise

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