Research On Development Characteristics And Detection Methods Of Interturn Short Circuit Fault In Distribution Transformer

Distribution transformer is the core equipment in distribution network.It has the characteristics of large quantity,wide distribution and scattered installation position.Its stable operation directly affects the power supply quality of the majority of users.Due to the low cost of a single device,power grid enterprises pay far less attention to the operation and maintenance of distribution transformers than the main network equipment.Field operation experience shows that inter-turn short-circuit fault is one of the most common faults in distribution transformers,and its severity is usually high.Current research on interturn short circuit of transformer is mainly aimed at the fault characteristics of permanent short circuit of turns at different positions.Once permanent interturn short circuit occurs,it will quickly lead to protection trip,equipment damage and even ignition and fire accident,which is difficult to realize the early warning and effective control of fault.Based on the operating conditions of distribution transformers,this paper focuses on the development process of winding interturn short circuit fault in the early stage,and studies the development and evolution characteristics of winding current-carrying,magnetic leakage,electrodynamic loss,heating,vibration and other characteristic variables.Firstly,ANSYS finite element simulation software is used to establish the fault model of 10kV distribution transformer with different degrees of interturn short circuit.The change of current,magnetic leakage field and electric force of turns before and after interturn short circuit and under different short circuit impedances is obtained by simulation calculation.It is found that with the development of interturn short circuit,the winding outgoing current changes little,while the current of short circuit turns,magnetic leakage field near short circuit turns and the electric force of short circuit turns increases significantly and can reach tens of times of normal operation.Secondly,multi-physical field coupling simulation is used to build the"electromagnetic structure" field coupling model,and the electromagnetic parameters are substituted into the temperature field harmonious response analysis module for finite element calculation.The characteristics of active power loss,heating and vibration before and after interturn short circuit and under different short circuit impedances are simulated and analyzed.The results show that with the development of short circuit between turns,the winding temperature increases sharply and the amplitude increases to 20 times of the normal operation.Active power loss,temperature and vibration parameters are taken as the key points in the detection of interturn insulation defects of distribution transformers.Finally,a test platform for the development process of interturn short circuit of 10kV distribution transformer was established in the laboratory,and the coil model of interturn short circuit fault was designed and made.The changes of temperature,active power loss and vibration parameters in the development process of interturn short circuit fault were verified by experiments.At the same time,combined with the test results,the field case and the stress calculation of the test fault model,it is found that the temperature parameters and vibration parameters under the fault model are the main factors of insulation failure and fault deterioration in the fault process.Long-term failure stress will make the coil ablative melting,friction extrusion deformation,resulting in permanent inter-turn short circuit and fault further expansion,and even insulation breakdown.