| Distribution transformer is an important electrical equipment widely used in power system,which is related to the safe and stable operation and power supply reliability of distribution network.Statistics show that the damage of distribution transformers is mostly caused by winding short-circuit faults.Due to the influence of factors such as insufficient short-circuit resistance and long-term overload of transformer windings,the winding inter-turn insulation is deteriorated,resulting in inter-turn and inter-strand short-circuit faults.It has occurred from time to time,causing great economic losses and hidden dangers that cannot be ignored.The research on transformer winding short-circuit faults has also become a technical hotspot of common concern at home and abroad.When a slight inter-turn and inter-strand short-circuit fault occurs in the winding of the distribution transformer,the over-current protection action cannot be caused.When the fault further develops,the electrothermal effect will accelerate the deterioration of the winding insulation,resulting in the winding burning and deformation,and the insulation of the distribution transformer suffers irreversible damage.In recent years,although the inter-turn short-circuit fault detection technology of transformer windings has developed rapidly,the effective and affordable distribution transformer winding short-circuit detection methods and devices are still missing.It is urgent to propose a convenient and reliable online detection method for distribution transformer winding short-circuit.Therefore,it is of great significance to study the characteristics of transformer winding short-circuit fault and propose an on-line detection method for winding short-circuit fault of distribution transformer according to the change of characteristic quantity,which is of great significance to reduce the probability of equipment accident and improve the reliability of power supply.Firstly,this paper takes a distribution transformer with a model of S13-M-200 / 10 as the research object.By building an experimental platform in the factory,no-load and short-circuit tests are carried out to obtain the actual test values of no-load current,no-load loss,short-circuit impedance and load loss.Based on the ’ field-circuit ’ coupling principle,the finite element software ANSYS Maxwell is used to establish a distribution transformer simulation model that is consistent with the actual transformer size and the low-voltage winding is two flat copper wires.By comparing the simulation value,actual test value and rated value of the high and low voltage side voltage,current and performance parameters of the transformer.Verify the rationality of the simulation model.Secondly,on the basis of the above model,the inter-turn short-circuit and inter-strand short-circuit faults of the windings at different positions at a certain time are set in the external circuit to show the changes of the parameters of the transformer before and after the fault.The variation characteristics and distribution rules of the parameters such as short-circuit loop current,main loop current,active loss,equivalent resistance,spatial magnetic field and short-circuit electromagnetic force after different faults in the distribution transformer winding are analyzed.The change mechanism of the characteristic state quantity after the short-circuit of the distribution transformer winding is revealed.At the same time,the state quantity with the most obvious change rate and easy detection is studied,which provides a theoretical basis for the short-circuit detection of the distribution transformer winding.Finally,combined with the characteristics of short-circuit fault of distribution transformer winding,taking active loss and equivalent resistance as the main electrical state variables of on-line detection,an on-line detection method for short-circuit fault of transformer winding that can identify the fault phase is proposed to perceive the insulation state of transformer winding in real time.At the same time,with the help of family defects and operation inspection records,referring to relevant regulations and technical standards,a distribution transformer operation state evaluation model based on multi-state quantities is established.The operation state of the distribution transformer is judged by calculating the deduction value of each characteristic quantity,which provides a theoretical reference for the operation and maintenance of the distribution transformer and the detection of the winding state. |
