Ground protection method for small-current ground system

Abstract

The invention discloses a ground protection method for a small-current ground system, which comprises a data acquisition step, a data processing step and a data analysis step, wherein the data acquisition step comprises: calculating ground null sequence admittance Y0kd of an outgoing line by a single-phase grounding test or circuit parameters and acquiring a null sequence voltage U0 and a null sequence current I0 of protection access in real time; the data processing step comprises: calculating the null sequence admittance Y0k of the outgoing line, calculating the null sequence compensation admittance Y'0k of the outgoing line, calculating a null sequence compensation admittance angle phik of the outgoing line, and storing the sequence of the null sequence compensation admittance angles phik of N cycles; and the data analysis step comprises: judging the amplitude value of the null sequence compensation admittance Y'0k, if the amplitude of the null sequence compensation admittance Y'0kis more than a start threshold value, determining the null sequence compensation admittance angle phik, if phik is more than 100 DEG and less than or equal to 280 DEG, determining that the line is a faulty line, if phik is more than 80 DEG and less than or equal to 100 DEG, executing step (4), inspecting the sequence of the null sequence compensation admittance angles phik of N cycles, if phik ofmore than 170 DEG and less than or equal to 280 DEG appeared once, determining that the line is a faulty line, and returning to the judgment of the step.

Description

technical field [0001] The invention relates to a grounding protection method for a small current grounding system. Background technique [0002] my country's medium and low-voltage power grid generally adopts the neutral point non-grounding method, small resistance grounding method or arc suppression coil grounding method. When a ground fault occurs in the system, the characteristic quantities such as the magnitude and direction of the zero-sequence current of the grounding line are affected by the system operation mode. The impact is large, which brings difficulties to the judgment of grounding protection and seriously affects the reliability of power supply. [0003] Therefore, when a ground fault occurs in a small current grounding system, how to quickly and accurately select the fault line has great practical significance. [0004] Traditional grounding protection methods include the following: [0005] 1. Zero sequence voltage (current) method [0006] Principle: Whe...

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Problems solved by technology

[0007] Disadvantages: When a ground fault occurs in a small current grounding system, the non-fault line also has zero-sequence voltage and zero-sequence current; The zero-sequence current of the fault line is still small

[0010] Disadvantages: This method is only suitable for high-voltage long lines with ungrounded neutral points. For arc-suppression coil-grounded systems, due to the compensation of arc-suppression coils, the zero-sequence current of the fault line no longer lags behind the zero-sequence voltage by 90°. The angle of lag varies between 90° and 270° depending on the degree of harmonicity; for small resistance grounding systems and low-voltage short lines, the angle of zero-sequence current and zero-sequence voltage of fault lines varies between 90° and 180°

[0013] Disadvantages: This method is only suitable for high-voltage lines that pass through the arc suppression coil series and parallel resistance (the insulation resistance is very large, and the capacitance to ground plays a leading role)

For the neutral point ungrounded system, there is no zero-sequence active current in the fault line and the non-fault line; and the non-fault line of the low-voltage short line also has active current, this method cannot achieve selectivity

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