Study On Special Problems Of Relay Protection Of The Contact Transmission Line In Wind And Photovoltaic Power Farm System

Based on an actual wind-solar complementary field parameter in Inner Mongolia,this paper establishes a more detailed equivalent model containing multiple types of new energy generating units,and studies the fault characteristics and the contact transmission line protection performance of each unit.New energy can be divided into double-fed(Double-Fed Induction Generator,DFIG)and inverter(Permanent Magnet Synchronous Generator,PMSG,Photovoltaic Power Generation systems,PVG).By analyzing the power generation principle of each generator set,each unit is modeled separately,and the Low Voltage Ride Through(LVRT)capability of the doubly-fed wind generator is realized by a Crowbar circuit,and the control strategy of the Crowbar circuit is optimized.The Crowbar circuit is switched periodically to reduce the frequency offset of the fault current.During the fault period,the grid is provided with reactive power.The LVRT capability of the direct-drive wind generator is achieved with a DC unloading circuit,and the safety of the protection converter is ensured during the fault.The RTDS(Real Time Digital Simulator)platform was used to verify the steady-state characteristics and transient characteristics of each single unit,which showed the rationality of the model.The equivalence method of wind-solar complementary electric field affects its transient characteristics,and then affects the fault current characteristics of the contact transmission line.By analyzing and comparing the characteristics of different equivalent methods,a wake effect Jensen model considering the obstructed area was established,and nine generator were applied to wind-solar field using variable-scale reduction orders.And it is verified by simulation.The results show that it is can meet the research of relay protection of the contact transmission line.Fault characteristics are the basis for the study of relay protection problems.Different control strategies have different fault characteristics.Firstly,the fault current transient characteristics of doubly-fed power supply and inverter power supply are theoretically analyzed.It is concluded that the double-fed power supply current contains a pre-rotational frequency component that is slightly related to the Crowbar control,resulting in the frequency offset of fault current when the fault occurs.;inverter power supply theoretically does not cause a frequency offset in the fault current,but the phase angle of its fault current is related to its control strategy.Then from the theoretical and simulation point of view,the Crowbar control strategy of the DFIG constructed in this paper can effectively reduce the degree of fault current frequency offset,and reduce the impact of the deviation of the Fourier algorithm based on the power frequency on the relay protection.Finally,the short-circuit characteristics of various faults in connection under different operating conditions are simulated and analyzed,and it is concluded that the frequency offset of the fault current is significantly reduced when the control strategy is applied to the contact transmission line protection installation.The main display characteristic is the weak power supply characteristics,which has a great influence on the phase selection element.Taking the protection provided by the CSC103 B protection device as an example,the impact of large-scale new energy access on current differential protection,distance protection,phase selection elements and reclosing is analyzed.A new method of closed-loop experiment was proposed to test the performance of the protection device.The results show that the phase-differential current differential protection can operate reliably,but the sensitivity decreases.The distance protection has the ability to withstand a certain transition resistance,and the phase selection element with a low voltage phase selection can accurately select phases.Put forward reasonable configuration suggestions for the protection and reclosing of the multi-transmission line of the field.Finally,the work of the project is summarized and prospected.