A Kind of Scheme for Microgrid Protection

Abstract

Microgrid protection is one of the crucial technologies of microgrid. In this paper, a new microgrid protection scheme was proposed, which is suitable for microgrid working in both grid-connected and island modes. We proposed a solution for the challenging problem in AC microgrid, as the limitation for fault current level, the effect on the protection by the change of power direction and the complexity of microgrid network structure .This paper also analyzed theory and practical application of the protection scheme proposed, and the validity and good performance of the protection scheme was validated. Introduction Microgrid is a small medium voltage and low voltage power network which is composed by many distributed power supplies and regional loads [1]. It can operate when connecting to the large grid and also can run in planned island mode. The microgrid should have perfect protection and control function [2, 3, 4], in order to improve the power supply reliability of the load and utilization rate of the distributed power supply. For the moment, many countries have demonstration project of microgrid, microgrid protection is in research stage, and there is no unified standard. The function of microgrid protection is limited, for example, it is not suitable for the complex structure of microgrid, and it is not sensitive to high impedance ground fault protection. In this paper we use current phase comparison differential protection as feeder main protection, the protection scheme is more applicable to microgrid from the protection principle, and it also has higher sensitivity. In this paper, a backup protection scheme for microgrid was also proposed, which is composed of low voltage and directional elements. General Method of Microgrid Protection The literature [5] is an important document for microgrid protection. A protection scheme using digital relays with a communication network was proposed for the protection of the microgrid system, It used instantaneous current differential protection as feeder main protection, the two sampling absolute value of the differential current exceed the setting value ,the protection device act outlet tripping. Some papers take adaptive protection in microgrid such as literature [6], a centralized controller was required to store several sets of protection setting values. The microgrid would change to corresponding protection setting value in different running states. The protection need special communication network which covering the main part of the microgrid, we consider that this kind of protection is only applicable to microgrid which with small scale and simple structure, it will cause setting calculation difficulty in large scale microgrid, and this kind of protection belongs to the centralized protection, relatively easy to appear the entire microgrid operation accident. The literature [7] proposed to detect the fault and fault types by the conversion of the three-phase voltage of the microgrid to abc-dq changed. Some papers proposed the protection scheme based on negative sequence current component, it can be used in simple microgrid, but the setting calculation will be quite complicated in microgrid with complex structure. We also consider the method of using fault current component to form the protection, in order to reduce the influence of load current of differential protection. 6th International Conference on Electronic, Mechanical, Information and Management (EMIM 2016) © 2016. The authors Published by Atlantis Press 1384 Protection Scheme of Microgrid We Proposed Main Protection of Microgrid. As microgrid in Fig. 1, the preliminary simulation calculation is carried out in the literature [3], for example we proposed the Protection scheme and use it in this typical microgrid.