Study On Characteristics And Detection Methods Of Turn-to-turn Short Circuit Fault Of Hydro-generator Rotor Winding

In hydro-generator,turn-to-turn short-circuit of excitation windings is more likely to occur than other faults.After the turn-to-turn short-circuit fault occurs in the generator,the excitation current increases,the reactive power output decreases,and the electromagnetic force of the generator rotor is unbalanced,which increases the vibration amplitude of the generator set.At present,there is a lack of effective online monitoring method for the turn-to-turn short-circuit fault of hydro-generator,and a slight turn-to-turn short-circuit fault cannot be detected in time,which leads to further deterioration of the fault and threatens the safe and stable operation of the generator set.Therefore,it is necessary to put forward a new method of fault detection in order to improve the efficiency of monitoring and diagnosis of turn-to-turn short circuit fault of hydro-generator rotor.In this paper,main work is as follows:(1)By comparing the magnetic field of a hydro-generator under normal and fault conditions,the variation of excitation magnetic potential in the case of a short-circuit fault between turns of the rotor windings of the generator is analyzed.Based on the principle of magneto-dynamic force balance,the variation law of the main magnetic field of the hydro-generator before and after a short-circuit fault between turns of the rotor windings is deduced.The 550 MW hydro-generator is the object of the study,set up the two-dimensional operation model of the generator's normal and the rotor winding circuit,and then,through the air drive,the air gap magnetic flux density,the voltage current verified the model's correctness.At the same time,calculating the magnitude and direction of the power of the generator to balance the power of the generator at the point of the malfunction.(2)Based on the power of the hydro-wheel generator,the stator core is generally used in the form of an empty cold,and the center of the iron core is divided into a series of segments,between the segment and the segment,and the heat emanates from the center of the core,and the way that the power of the iron core is released,and the way that the 550 MW hydro-generator is set up to install the U-type detection coil.By using the hydro-generator simulation model established in this paper,set the simulation model for different degrees of short circuit at no-load and rated load operating condition,the magnetic flux expression through the detection coil is deduced according to the movement rule of the main magnetic field of the generator,and the induction electromotive force of the coil is further obtained,and the waveform characteristic of the electromotive force induced electromotive force according to the respective short circuit degree can be determined,and the fault magnetic pole position can be located.(3)Based on hydro-generator stator core with fully insulated metal wear heart screw structure,operation process of generator through a heart screw induction voltage can reflect the change of main magnetic field the characteristic,proposed using wear heart screw instead of sensor detection of generator rotor winding inter-turn short circuit fault.By using the hydro-generator simulation model established in this paper,the inter-turn short-circuit degree is set up to obtain the variation law of the cross-core screw induced voltage.According to the characteristics of the induced voltage waveform,the inter-turn short-circuit degree of the rotor windings of the hydro-generator can be determined and the position of the fault magnetic pole can be located.