Method of eliminating ferromagnetic resonances

Abstract

The invention discloses a method of eliminating ferromagnetic resonances. A sine fitting algorithm is utilized to identify ferromagnetic resonances and one-phase grounding faults, according to the method, zero sequence voltage sampling data are subjected to fitting, whether zero sequence voltages are in fundamental frequency quantity can be judged according to the amplitude of a fitting function, wave distortion characteristics of the zero sequence voltages in the fundamental resonances are utilized to construct a wave distortion degree function, and degrees of wave distortion are calculated to distinguish the fundamental resonances and the one-phase grounding. The method has the advantages of being simple in principle, small in calculation amount, and high in sensitivity, the fundamental resonances and the one-phase grounding are accurately distinguished, and moreover ferromagnetic resonance faults are eliminated.

Description

Technical field [0001] The invention relates to the electromagnetic field, and in particular to a method for eliminating ferromagnetic resonance. Background technique [0002] PT (voltage transformer) ferromagnetic resonance overvoltage is the most common type of internal overvoltage in ungrounded neutral systems and causes the most accidents. In order to limit the PT ferromagnetic resonance overvoltage, those skilled in the art have proposed various solutions. [0003] (1) PT open triangle connects to damping resistor. Its shortcomings are as follows: When selecting a resistance, if the resistance is too large, it will not have the effect of eliminating the agreement. If the resistance is too small, when the system is single-phase grounded and runs continuously for 1 to 2 hours, the PT is required to be large enough Heat capacity, therefore, incandescent lamps are generally selected as damping resistors, taking advantage of their low cold resistance and high cold resistance. Ho...

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Problems solved by technology

The device has limitations in application: ①It can only ensure that the PT does not saturate, and it is invalid for other PTs in the system, so each PT must be installed with a nonlinear resistance resonance eliminator to achieve the effect of resonance elimination; ②When the system When a single-phase ground fault occurs, the zero-sequence voltage measured by PT has errors, so it is not suitable to use this device in occasions that require high measurement accuracy of zero-sequence voltage (such as fault distance measuring devices)

③When the system is in normal operation, the voltage at both ends of the open triangle of the voltage transformer rises. If the volt-ampere characteristics of the three-phase electromagnetic voltage transformer itself differ too much, the open triangle voltage will increase a lot, which will affect the signal action of the system insulation monitoring device.

This method also has its own problems: ① Just like installing a non-linear resistance resonance eliminator, it can only ensure that the PT does not saturate, and cannot suppress the ferromagnetic resonance of the entire system; There may be a phenomenon that the circulating current is too large and the primary winding and the remaining winding are overheated; ③In this wiring mode, the zero-sequence PT becomes the only metal channel from the ground to the ground of the neutral point ungrounded power grid, and in actual operation, it often occurs due to the charging current of the capacitor Too large, the accident of zero sequence PT burning

[0006] (4) There is no technical solution for identifying ferromagnetic resonance and single-phase grounding faults using the sinusoidal fitting algorithm

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