Application of DGA in the detection of collective

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DGA in the detection of collective capacitors

Abstract: overheating and discharge inside collective capacitors can cause a large number of decomposition of insulating oil, and its development can lead to serious defects such as rapid deterioration of oil insulation. Through the analysis of the results of several cases of capacitor insulating oil DGA (dissolved gas analysis), this paper believes that it is completely necessary and feasible to carry out the work of collective capacitor insulating oil DGA

key words: necessity and feasibility of integrated capacitor DGA preface

as one of the main equipment to reduce loss, save energy and improve voltage quality, integrated shunt capacitor has been more and more widely used in electricity. With the improvement of capacitor manufacturing level in China, the collective capacitor is gradually developing towards high voltage and large capacity (three-phase maximum capacity 10000 kvar, single-phase maximum capacity 6667 kvar). With the increase of the capacity and investment of single equipment, the health level of equipment is becoming more and more important. How to effectively carry out capacitor detection has become the main topic we are facing

2 abnormal examples of collective capacitor

2.1 loose internal lead connection and overheat discharge

in August 2000, the operators reported that the operating temperature of H 1 and x 3 capacitors was higher than that of similar capacitors. Later, when analyzing the oil samples of H transformer and X transformer collective capacitor oil, it was found that the dissolved gas content in H 1 and x 3 oil was very large, and the oil withstand voltage of H 1 capacitor was lower than the specified value (see Table 1)

the total hydrocarbon content in the oil of the above two groups of collective capacitors is high. It can be determined that there is capacitor oil decomposition under high energy in the two groups of collective capacitors. The decomposition product of H 1 has affected the insulation of capacitor oil, and the decomposition product has an amazing impact on the insulation. According to the operation report of H 1, the withstand voltage was 54kv at that time, and the withstand voltage value of oil decreased by 72% in two years

according to the analysis results, the material testing machine decides to hang the core of the two collective capacitors, find the fault point and filter the oil, and notify the manufacturer to the site. On August 22, 2000 and August 23, 2000, the hanging cores of H 1 and x 3 collective capacitors were inspected respectively. The on-site core hanging inspection found that there were discharge traces at the neutral point soft connection joint and casing joint of phase h 1b, the tin at the welding part of the soft connection joint had melted, and there were discharge traces at the neutral point soft connection joint and neutral point connecting piece of phase x 3a. Both of them were due to the connection screws not tightened during assembly and overheating during operation

all bolts were fastened on site and degassed with vacuum oil filter. After the two groups of capacitors were put into operation, the chromatographic tracking was carried out, and the residual gas did not increase significantly, and the operation was normal

2.2 capacitor micro water chromatography in station B

four groups of 5000kvar collective capacitors in station B were put into operation in 1998. The capacitor switching is controlled by the reactive power compensation device. Because the reactive power shortage is small and the system voltage is high, only 1 and 2 can be put into operation at ordinary times. The general survey of capacitor oil was carried out in 2001, as shown in Table 2

it can be seen from table 2 that the longer the operation time, the higher the trace moisture content, the more severe the oil pressure drop, and the higher the total hydrocarbon content. Due to the common fault: the hanging core inspection is not carried out when loading. Theoretically, this phenomenon may be related to the deterioration of insulating oil caused by long-term high-temperature overheating of connecting parts inside the capacitor, which needs to be handled

2.3 chromatographic abnormality of group 1 in station Z

six groups of 6000 kvar collective capacitors in station Z were put into operation in 1995. All six groups were put into operation at the peak load. Chromatographic survey found that 3 was abnormal. The chromatographic analysis of six groups of capacitors is shown in Table 3

it can be seen from the horizontal comparison of six groups of capacitors in Table 3 that there are obvious abnormalities in 3

3 necessity and feasibility of adding DGA in the operation of collective capacitor

3.1 necessity

DL/T preventive test code for power equipment stipulates that the routine test items in the operation of collective capacitor include phase to phase and pole to shell insulation resistance, capacitance value, insulation oil breakdown voltage and oil leakage inspection, phase to phase and pole to shell AC withstand voltage test (after necessary and hanging core inspection), etc, It mainly focuses on the detection of insulation index and capacitor output characteristics. The discharge caused by the high local field strength caused by the lax overall assembly process and the overheating caused by the loosening of the connecting parts cannot be detected. On the one hand, these defects may cause serious ablation of the connection parts, on the other hand, they may lead to rapid deterioration of oil insulation. According to the inspection cycle of 5 years (DL/T596-1996 code for preventive test of power equipment, 1-5 years, many units reduce the power outage time, which is generally set as 5 years). These defects are likely to have developed into major accidents before the next inspection

3.2 feasibility

DGA is very successful in transformer fault detection. It is a detection method with high sensitivity in transformer insulation detection. Although the composition of capacitor insulating oil is different from that of transformer oil, the basic composition is still Cho compound, and some products of cracking under high energy should be the same. From the above analysis results, the characteristic gas of transformer oil has strong applicability to capacitor oil. Therefore, from the perspective of test equipment, there should be no problem. The existing chromatographic analyzer can be used for gas analysis in capacitor oil. Now the key is to establish the judgment standard. Although there are many kinds of capacitor oil, dodecyl benzene oil is mainly used between the shell of collective capacitor and the shell of internal unit capacitor, which creates a more convenient environment for the establishment of standards. I hope my introduction can help you make your machine work! For more information about FRP tensile testing machine, please pay attention to the premise of this site. Therefore, it is entirely possible to conduct a small-scale research to establish the judgment standard of this oil

4 Conclusion

4.1 internal overheating and discharge of collective capacitor can lead to a large amount of decomposition of insulating oil, damage of connecting parts and rapid deterioration of insulating oil. Therefore, it is necessary to carry out DGA project. The current chromatographic analyzer can be applied to capacitor DGA

4.2 it is suggested that the research and manufacturing units of collective capacitor should carry out the research on the cracking composition of dodecyl benzene oil under different energy as soon as possible


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