Study On Rotor Ground Protection For Large Generating Units

With the continuous development of the power system,more and more large generating units are put into operation.The grounding fault of rotor winding is one of the most common fault forms of the generator.If the rotor grounding fault can not be alerted or processed in time,the short circuit of the winding will lead to the serious consequences of the vibration of the unit and the burning of the rotor and so on,which seriously threatens the operation safety of the large generator.Therefore,it is of great importance to deeply study the one-point ground protection of rotor and improve the stability and reliability of protection,so as to ensure the safe and stable operation of large generating units.Firstly,the traditional principle of one-point ground protection for generator rotor and its disadvantages in practical application are analyzed.It is proposed to optimize the circuit structure by introducing additional auxiliary power,so that the switching sampling circuit can connect the positive or negative terminals of the rotor winding separately.The calculation method of the new principle ground resistance is studied and the sensitivity of the scheme is analyzed,and it can meet the actual operational needs.The new method can also effectively solve the problem that the generator cannot detect the ground fault when the rotor voltage is zero during starting or stopping,and it can be well applied to brushless excitation unit.Traditional superimposed dc voltage type grounding protection cannot directly measure the ground resistance and ground position.A protection scheme based on DC50 V injection produced by the protection device is proposed.The ground resistance and fault location are calculated by measuring the open and close current and changing the internal resistance of the injection circuit periodically by electronic switch.A channel design scheme for two-stage second-order low-pass filtering hardware is proposed.By deducing and simulating the effect of the excitation winding of large generator set on the measurement precision of ground capacitance,a new method of variable switching period and additional sampling value is proposed.In view of the existing rotor grounding protection cannot be achieved two sets of put into operation at the same time,based on ac/dc injection double set of configuration scheme,using 50 v and 220 v dc power frequency ac injection at the same time,run by the original double coordination mechanism effectively eliminate the mutual influence between the two sets of protection.The test results and test run of the prototype based on the paper scheme show that the scheme can meet the requirements of one-point grounding and dual operation in the real sense.