| At present,epoxy-cast dry-type power transformers are widely used in power systems,especially because of its excellent fire resistance,corrosion resistance,environmental performance,in more and more urban distribution network can see its shadow.With the increase in the operating life of the dry-type transformers,the level of its partial discharge increase,accompanied by the emergence of insulation damage and even cause the failure of the entire transformer.Many scholars have studied the partial discharge characteristics of epoxy resin dry-type transformers,analyzed the mechanism of partial discharge and insulation damage,but the research on epoxy resin dry-type transformers in actual operation is still quite few,Provide guidance on actual running dry transformers.Therefore,it is of great theoretical and practical significance to study the partial discharge characteristics of dry-type power transformers which are actually running in power system and provide guidance for the operation of dry-type transformers and to further improve the manufacturing process.The main research is to use 10kV and 35kV epoxy cast dry type transformers as the research object,which uses epoxy resin as the insulating material.Based on the structure of epoxy resin dry-type transformers,the simplified model of dry-type transformers is built,the electric field distribution of dry-type transformers is calculated,and the possible partial discharge positions of the dry-type transformers are analyzed.The Followed by the pulse current method,to build epoxy resin dry-type transformer partial test system.And set the circuit parameters to correct the test system of measurement accuracy,and according to the field test environment to take shielding,filtering and other anti-jamming measures make the measurement system more accurate measurement.Based on the test system to measure the partial discharge of epoxy resin dry-type transformers,the characteristics and types of external and external discharge of epoxy-type dry-type transformer windings are studied,and further used to analyze the causes of partial discharge phenomena and on this basis improve the manufacturing process.Finally,the change of partial discharge of epoxy resin dry-type transformers at different temperatures is analyzed,and the test standards are provided for reference.By simulating the electric field at the end of the dry-type transformer,it is found that the electric field intensity Emax decreases with the increase of the distance M between the high-pressure side and the low-voltage side,and decreases with the increase of the distance parameter H between the coil-iron yoke,And the electric field distribution is best when the distance between M is 40mm,H is 80mm,the inter-turn insulation dimension is S>0.7mm,and the interlayer insulation dimension is more than 0.7mm.On the basis of the test system constructed in this paper,the dry-type transformer partial discharge characteristic test was carried out to obtain the spectrum of bubble discharge,air gap discharge,surface discharge and tip corona discharge inside insulation,and their differences were analyzed,The bubble discharge is positive and negative half-week symmetry,air gap discharge observed obvious discharge traces,surface discharge,in the positive half-cycle discharge times,the amplitude is large.The tip corona discharge is symmetrical in the-90 degree area.The temperature of the dry-type transformer will also have an impact on the partial discharge,its specific performance for the partial discharge of the starting voltage and extinguished voltage will drop with the temperature rise,in a fixed voltage discharge is a partial discharge The temperature changes in a proportional relationship and the temperature rise led to increased discharge capacity.Finally,according to the cause of the partial discharge and easy to damage the site,from the structural design,casting technology and other aspects of the dry-type transformer manufacturing process to make constructive comments. |
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