Study On Fault Characteristics And Protection Methods Of The Current Distribution Network With PV

With the third energy revolution,renewable energy has attracted wide attention because of its environmental advantages and the characteristics of sustainable development.Solar energy has the characteristics of no geographical constraints,large reserves and no pollution and the full utilization of solar energy in China is conducive to the energy transition.The photovoltaic power is usually connected to the distribution network near the load,assisting the traditional centralized power plant to supply the power to the users and this has changed the topology of distribution network and made the size and direction of the short-circuit current is uncertain.These bring the severe challenge to the traditional protections which can no longer meet the requirements,therefore the research on relay protection scheme which is reliable and security for PV access is urgent.Based on the practical engineering mathematical model of photovoltaic cell,a battery simulation model is built in PSCAD.Not only the influence of battery temperature and intensity of illumination on output power,open circuit voltage and short circuit current is simulated,but also the principle of maximum power point tracking is briefly introduced and the three common maximum power point tracking methods are simulated and analyzed.In PSCAD,combined with the requirement of PV grid connection,a PV mathematical model with low voltage ride through control is established.A simulation model of 10 kV voltage level distribution network with PV is built,and the output characteristics of PV under short circuit fault are simulated and analyzed.Combined with three typical cases,that is,two phase short circuit fault occurred in upstream feeder section of PV,two phase short circuit fault occurred in feeder section between PV and three phase short circuit fault occurred in downstream feeder section of PV,the short circuit current computational formula of distribution network containing PV under different output states is given.The fault characteristics of distribution network containing PV are analyzed theoretically,and verified by simulation.The influence of the access of the PV on the traditional three section current protection and the improved instantaneous current quick break protection is analyzed.This paper proposes an adaptive voltage protection scheme which measures negative sequence voltage,positive sequence and negative sequence current in where protection relay is located to accomplish setting of first segment and second segment protection.By comparing the setting value with positive sequence voltage amplitude measured in where protection relay is located to accomplish protection,the protection scheme can deal with interphase short circuit fault and two-phase earth short circuit fault and can realize the protection of whole line length.In addition,this paper proposes a fault location method based on feeder terminal unit for distribution network with PV which can protect four kinds of short circuit fault accurately and fast and accomplish the instantaneous protection of whole feeder section.