Study On Corrosion Prediction Method For Grounding Down Conductor Of Converter Station

The scattered current of the grounding device of the converter station flows into the soil through the grounding conductor,which will cause electrochemical corrosion to the grounding conductor.The scattered current of the DC field contains the DC component in addition to the AC component.Therefore,the grounding conductor is subjected to DC electrochemical corrosion in addition to natural corrosion and AC electrochemical corrosion.Since the grounding down conductor is closer to the surface,the soil has a higher oxygen content and the leakage current density flowing through the grounding down conductor is the largest,so the corrosion of the grounding down conductor is usually more serious than the grounding grid conductor.In addition,since the converter station is mainly composed of three fields: DC field,AC field,and AC filter field,the leakage current components and amplitudes of the main equipment in different fields may be different,and the electrochemical corrosion effects may also be different.Therefore,it is necessary to carry out research on the corrosion prediction method of the grounding down conductor of the converter station,and to clarify the area and equipment type that need to be paid attention to in the converter station.At the same time,the traditional three-index corrosion prediction method for grounding grid conductors only considers the corrosion effects of AC current and soil influence.Therefore,this method is not applicable to the corrosion prediction of the grounding down conductor of the DC field.Based on the above research background,this paper studies the corrosion prediction method of the grounding down conductor of the converter station.The corrosion prediction methods of the grounding down conductor of different fields are proposed by simulation test and field measurement.The main research contents and results are as follows:(1)A method for measuring the scattered current in different regions of the DC field of the converter station is proposed.The analysis of the scattered current of the converter station is carried out.It is found that the scattered current is equal to the difference between the leakage current of the positive and negative mirror points in the high-voltage pole region of the DC field.For the neutral field of the DC field,the scattered current is approximately equal to the leakage current.Based on the principle of discrete Fourier transform and least squares,the extraction procedure of AC and DC components of scattered current is written.(2)The corrosion characteristics of the grounding conductor under AC and DC are summarized.The corrosion characteristics test of the grounding conductor under AC and DC is carried out.It is found that the influence of DC current on the conductor is much greater than the AC current of the same amplitude,and the influence of the mixed current on the conductor is approximately equal to the sum of the effects of the individual component alone;For the corrosion test of the grounding conductor considering the circulation condition,it is found that the DC circulation will slightly accelerate the corrosion rate of the grounding conductor,and the corrosion of the conductor has a concentrated effect,mainly concentrated in the outer region of the corner.(3)The corrosion prediction method for the grounding down conductor of the converter station is proposed.The concept of equivalent corrosion cross-sectional area ratio is proposed and the corresponding physical model is constructed.The corresponding formula for calculating the equivalent corrosion cross-sectional area is proposed for different fields of the converter station.The accuracy of the corrosion prediction method was verified by excavation inspection of a ±500kV converter station grounding down conductor.