Physical Characteristics And Diagnosis Technology Of Dry-Type Transformer Insulation Fault

The dry-type transformer has the characteristics of simple maintenance,low loss,oil-free and strong short-circuit resistance.It is widely used in the urban power supply system.The safety and stability of its operation directly affects the reliability of power supply.However,due to the influence of process materials,operating environment and load characteristics,the problem of insulation aging of dry-type transformer windings is still prominent,and it is prone to winding inter-turn short circuit faults,resulting in equipment burning and power supply interruption.With the continuous increase of social power consumption,the requirements for equipment insulation and its operational reliability are getting higher and higher.In order to reduce the influence of inter-turn short-circuit fault of dry-type transformer winding on distribution network,how to identify and predict winding insulation fault and put forward effective online diagnosis technology has become a hot issue in the study of dry-type transformer winding insulation state diagnosis.In practical engineering,dry-type transformers mostly use fuse protection or overcurrent protection.Although the current of the short-circuit turn increases sharply when the inter-turn short-circuit fault occurs,due to the limitation of the inherent structure of the winding,the electromagnetic parameters of the short-circuit turn of the winding cannot be actually measured,and the resulting main circuit current changes are weak,which cannot make the fuse of the drytype transformer fuse fuse or cause overcurrent protection action,resulting in serious damage to the dry-type transformer or even explosion and fire.At present,the diagnosis method of interturn short circuit fault of dry-type transformer winding is not mature.In order to ensure the safe and stable operation of distribution network,prevent equipment damage accidents and improve the early warning ability of dry-type transformer operation fault,it is necessary to further study the mechanism of inter-turn short circuit fault of low-voltage foil winding,analyze the variation characteristics of characteristic quantities before and after inter-turn short circuit fault of winding,and propose a sensitive and effective on-line monitoring method of inter-turn insulation state suitable for dry-type transformer.Firstly,this paper uses ANSYS finite element simulation software to construct the ’ fieldcircuit ’ coupling model and the ’ electromagnetic-thermal ’ multi-physics coupling model which are consistent with the actual dry-type transformer.The test platform is built in the factory,and the short-circuit,no-load and temperature rise tests of the dry-type transformer are carried out.The correctness of the model is verified by theoretical calculation and actual test.The normal rated operation and inter-turn short-circuit fault conditions are set in the external circuit model,and the physical characteristics and distribution rules of dry-type transformer foil windings under different operating conditions are simulated,which lays a foundation for the following winding insulation fault diagnosis method,and provides a theoretical basis for the implementation of measures to improve the short-circuit resistance of windings.Then,through theoretical analysis and simulation test,the difference between the per-unit value of current imbalance and the per-unit value of voltage imbalance of dry-type transformer is proposed as the characteristic quantity of inter-turn short circuit fault.By setting different contact resistances in the external circuit model of the dry-type transformer to numerically simulate the winding inter-turn deterioration process and the operation of the winding inter-turn short-circuit fault under different working conditions,it is demonstrated that the fault characteristic quantity can not only sense the winding inter-turn short-circuit fault in real time,but also overcome the inherent three-phase asymmetry and unbalanced operation.The influence of operation provides a new idea for real-time monitoring of the inter-turn insulation state of drytype transformer windings.Finally,starting from the difficulty of implementation in practical engineering,the insulation fault diagnosis technology of dry-type transformer is studied.On the basis of determining the new fault feature quantity as the basis for judging the insulation fault,a fault diagnosis method of inter-turn short circuit of dry-type transformer winding which can accurately locate the fault phase through the change rate of power loss is studied and proposed.This method can not only sensitively sense the winding insulation fault and fault phase,but also realize real-time monitoring of the winding insulation state and predict the inter-turn short circuit fault,which is helpful to improve the on-line monitoring and fault diagnosis technology of the low-voltage side winding insulation state of the dry-type transformer.