Analysis And Diagnosis For The Insulation Fault Of Power Transformer

The power transformer is both the core device of transformer substation and one of the most important and crux devices in interconnected power systems under secure operation according to the energy strategy of "nationwide interconnection, sending power from west to east and mutual supply between south and north", of which the operation condition would influence the secure operation of the power system. It has been proved that most of power transformer faults are caused by insulation accidents. Insulating oil and insulated paper are major insulated materials. They will age easily to cause accident under external stress. The oil issue can be tackled by replacing or filtering. Solid insulation may influence the long-term operation of power transformer. Thus, it is necessary to investigate the fault diagnosis technology of power transformer and ensure that the transformer is working under normal condition. This article subjects to study the insulation faults of power transformer. It has developed research and investigation in three aspects of sulfur corrosion in high-voltage transformer insulating oil, furfural content determination in oil and dissolved gas analysis and neural network application in fault diagnosis.1. An organism called Benzyl disulfide (DBDS) has been detected in most of the sulfur corrosion transformer accident abroad. But sulfur corrosion failures of transformer insulating oil have been rarely reported at home. By simulating the existence of DBDS, we could find the influence of it thus to analyze the causes and responses of sulfur corrosion of transformer insulating oil in details. The results show that in some extent the insulation property would lower and the volume resistivity and dielectric losses decrease in the samples adding DBDS. The SEM shows copper samples adding DBDS have depositions at their surface which have similar distribution of the atomic structure of copper sulfide. It is believed these depositions are copper sulfide. An additional increase would cause in the tanδwhen the copper sulfide trigger charge accumulation in the contaminated clearance. Therefore, it is very likely that the increasing heat would cause the growth of conductivity of insulated paper. The dielectric strength becomes weaker and weaker so that it cannot support the voltage at the edge of the oil tape and lead to electrical breakdown between adjacent conductors. The copper sample in simulation experiment is in static corrosion while the actual operation of oil in the transformers and reactors is in circulation state. The sulfur corrosion in transformer raised by copper sulfide deposit is more complex. Experiment shows that oil with DBDS is influenced significantly by temperature. At the high-temperature parts of the copper windings, the metal passivator will consume quickly and lose its original protective effect. The consequence is that the sulfur corrosion cannot fundamentally be issued even if adding copper passivator into the oil. 2. The concentration of furfural is an important indicator in transformer oil. The aging circumstance of insulation materials of oil-type transformers can be judged rapidly by testing the content of the furfural. High performance liquid chromatography was used to test the furfural content in oil while the optimal condition was acquired through experiments. The methanol was used as the extraction of furfural in the oil, the detection wavelength is 271nm, the mobile phase volume ratio is 1:1 and the testing flow is 0.8mL/min. The content of furfural in power transformers of different operated years and different voltage ratings have been tested. The measurement results show that the longer operated years, the higher furfural content. In addition, various forms of oil processing like oil complement, oil spills, oil change would lead to portions of loss of furfural, which may have certain impact on reflecting solid insulation circumstance accurately. Thus, it is of necessity to test the oil-paper insulation equipment's furfural content in oil regularly.3. The Dissolved Gas Analysis (DGA) is an effective method to diagnose the faults of power transformer. This technology has been widely used in diagnosing the type of internal potential insulation faults in power transformer and predicting the faults' development level. The mechanism of gas formation in the power transformer oil has been analyzed, the insulating faults have been judged by using the characteristic gas method and the improved three-ratio method and the connection of the diagnosis type and the content of gas in the oil has been explored. The monitoring data of a transformer owned by EHV Power Transmission Company of Hunan Province tended to be abnormal. The DGA technology was used to track and analyze it and they finally found the potential faults of the transformer. The accuracy of power transformer fault diagnosis method based on dissolved gases characteristic quantity has been confirmed by hanging-type examination results. A new transformer fault diagnosis network model has been established with particle swarm algorithm and back propagation neural network. Compared with the traditional three ratio method, this network method based on diagnostic method has achieved a better fault identification and classification and at the same time, the diagnostic accuracy has improved significantly. In short, this method is expected to have a bright application prospect.