Electric leakage protection method and system for mining variable-frequency driving system

Abstract

The invention belongs to the technical field of mining variable-frequency driving, and discloses an electric leakage protection method and system for a mining variable-frequency driving system. The method comprises the following steps: S1 carrying out the four-path synchronous sampling of a three-phase output voltage and a ground leakage current of a frequency converter; S2 performing common-modetransformation on the measured three-phase voltage to obtain a common-mode voltage value; S3 performing Fourier transform on the common-mode voltage and the common-mode current to obtain a harmonic voltage and a harmonic current, and setting the frequency upper limit of the Fourier transform as the switching frequency of the frequency converter; S4 rejecting all harmonic signals of which the voltage amplitude is smaller than a voltage threshold or the current amplitude is smaller than a current threshold; and then successively calculating the phase difference between each harmonic voltage andach eharmonic current with the same frequency in the remaining harmonic waves, if the phase difference is within + / -10 degrees, judging that the resistive circuit occupies the main component, and outputting an electric leakage protection signal. According to the invention, the graded leakage protection function is realized, and the safety and reliability of the mining variable-frequency driving system are improved.

Description

technical field [0001] The invention belongs to the field of variable frequency drive systems for mines, and in particular relates to a leakage protection method and system for variable frequency drive systems for mines. Background technique [0002] With the promotion and use of frequency conversion drive systems in coal mines, especially on airborne equipment, coal shearers, continuous miners, shuttle cars, and bolters mostly use frequency conversion traction systems. Due to the traditional leakage protection system, there must be a grounding resistance. , resulting in only one set of leakage protection at the rear end of the entire transformer. If there are multiple sets, they will inevitably affect each other and cannot work normally. That is, at the back end of the transformer, all electrical equipment share a set of leakage protection, and the insulation status of other electrical equipment is completely dependent on it, which loses the meaning of hierarchical protecti...

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Problems solved by technology

[0002] With the promotion and use of frequency conversion drive systems in coal mines, especially on airborne equipment, coal shearers, continuous miners, shuttle cars, and bolters mostly use frequency conversion traction systems. Due to the traditional leakage protection system, there must be a grounding resistance. , resulting in only one set of leakage protection at the back end of the entire transformer. If there are multiple sets, they will inevitably affect each other and cannot work normally.

That is, at the back end of the transformer, all electrical equipment share a set of leakage protection, and the insulation status of other electrical equipment is completely dependent on it, which loses the meaning of hierarchical protection. If the insulation to the ground is low, it is difficult to accurately locate point of failure

For the AC power supply system, the current conventional detection principle in coal mines is zero-sequence voltage current and additional DC method. For standard power frequency electrical equipment, its performance can be fully satisfied, but for variable frequency drive devices, due to the existence of high frequency leakage current, Its zero-sequence voltage and current detection method does not work properly

The additional DC detection method can be barely used, but for the high-power four-quadrant variable frequency drive device, which often malfunctions, it can only be barely used by reducing the sensitivity.

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