Adaptive Research On Relay Protection Of Distribution System With Distributed Wind Power

With the emergence of energy crisis and social environmental issues, it is nowbecoming the consensus and inevitable trend of development of every country to developrenewable energy and build a sustainable energy system in recent years. And wind energy isthe most beneficial for commercial develepment of all renewable energies. Nowadays,more and more wind power becomes a distributed generator, which has been connected todistribution networks or load centers. These distributed generators can effectively solve theshortages that power grid can not track load changes flexibly and local faults are easy tospread. It can aslo reduce power loss of transmission lines. Not only can it cooperate withpower grid, but aslo improve the grid peak-valley properties, which can raise reliablity ofpower supply. However, the original grid structure of a distribution network will changewhen this distributed wind power is connected to the network which will become a powergrid with several generators. The relay protection may malfunction, resulting in hazards. Onthe other hand, wind power must have low-voltage ride through capability and can’t be cutoff arbitrarily during a grid fault. Therefore, it is very important to study adaptive researchon relay protection ofdistribution system with distributed windpower generators.The paper first discusses the basic concept of distribution network of our coutry’s,including voltage level calssification and its main utility. A detailed decription of thedistribution network’s main structure has been given. On the basis of its main structures, therelay protection of distribution network is divided into two classes, one is overcurrentprotection and the other is a relay protection using sectionalizers to isolate short-circuitfault.We analysis the characteristics of short-circuit current of doubly-fed inductiongenerator(DFIG) during a short-circuit fault on the basis of low-voltage ride throughfeatures in detail. The short-circuit current is very different when terminal voltage of DFIGsags to different depth. And the short-circuit current expressions are derived in differentvoltage depth, which are verified in PSCAD/EMTDC.Adaptive research on relay protection of distribution network with distributed DFIGs accessed from different locations is analysed based on an actual distribution network. Itmay cause negative impact to relay protection, as failure or uncorrect to operate. Therefore,the relay protection needs to be configured again. However, a DFIG is difficult to beindicated an impedance potential source, and simulation methods become unusefulnessbecause of the increased penetration of wind turbines. Hence, a new method for accuratecalculation of short-circuit current of each branch and voltage of each node is proposed inthis paper, and it is verified accurate and valid with a example of Tianjin10kV distributionsystem.On the basis of the new method for short-circuit current calculation in chapter4, a relayprotection configuration method is proposed which makes relay cofiguration and setting ofdistribution network with DFIGs come true. And this method is aslo verified effective.