Integration Protection Strategy Of Microgrid Considering The Operating Characteristicsof Microgrid And The Distribution Network

Microgrid is a kind of new power grid, organized distributed generation includingwind turbines, photovoltaic cells, solar cells and energy storage unit into distributionnetwork. Microgrid has two operating modes, it can be incorporated into the main grid andalso be run without the main grid, which greatly improved the load side of power supplyreliability of microgrid. The parallel operation of distributed generation in microgrid willchange the volume, direction and distribution, and that will disturb the traditional relayprotection method in distribution network. In order to hold the advantages of improvingthe reliability of loading power supply in distribution network system and solve the theproblem in traditional protection method, this paper presents a new microgrid protectionand self-healing system, which choose the fault component method as protection principle,supported by communication network, to include a number of distributed power load andplace the object into the region to protect and realize the limited selectivity.The traditional single-supply-and-spoke distribution network will be changed into amulti-source network after using microgrid in the distribution network system. In annormal operation system, the load distribution will keep changing with puting distributedgeneration into or out; and when system failure the short-circuit current size, orientationand distribution also changing. Thus, the cooperative relation in conventional relayprotection methods can no longer set up, and protection of the selectivity and sensitivitywill be greatly impacted. According to analysis, the major impact of relay protection ingrid-connected operation of microgrid for the distribution network are discribed infollowing aspects: The first, leading to lower sensitivity of the line relay protection inserious cases may even refuse to move; second, resulting in malfunction of the relayprotection in the line; the third, leading to error protection action when the adjacentsection of the line without time limit current quick break protection and the selectivelossing; fourth, the existence of distributed power led unsuccessful reclosing. Althoughdomestic and foreign scholars have provided a variety of protection methods to deal withmicrogrid access to the distribution network, but most programs just to improve a certainaspects of the traditional relay protection method, so in practical applications it is still alarge limitation, and it can not truly meet the protection requirements when microgridaccess to the distribution network.Microgrid can max out the advantages of distributed generation, microgrid run intothe distribution network is the future development trend of the city grid. The system in thispaper, using the negative sequence component as a protection criterion, effectively avoidthe multi-source micro-network topology; the area as the protection objects, both to protect the most load supply reliability, and also save costs with the economic value inpractical application. The program will place the distribution network systems after themicrogrid accessing, including distributed power and the load is divided into severalregions, deploy voltage transformer and current transformer configuration at the outlet ofeach protected areas, collecte each region the amount of negative sequence mutation ofvoltage according to the amount of electrical current, then use to calculate the regionnegative sequence impedance value as a criterion of this protection method. In theprotection area, it uses wireless sensor communication network within the region to graspthe overall electrical quantities, through the design of the protection coordinationalgorithms with overall coordination, positioning the fault location accurately andefficiently, fault removal of the region and back into the main network operation, toachieve microgrid self-healing capabilities.This paper proposed a new method of microgrid protection algorithms, includingalgorithms that respond to high impedance ground fault and unbalanced load switching, toavoid the unbalanced load switching and high impedance grounding the correctness of theprotection. This protection method to verify the correctness and reliability by usingPSCAD/EMTDC simulation software to build a model of a typical microgrid structure,and take simulation experiment in each type of fault, the verification results show thereliable operation of this program in many kinds of fault conditions.