DG islanding operation detection methods in combination of harmonics protection schemes

Usages of Renewable Energy resources is increasing in different sections of energy consumption in the world. An unfortunate forecast for use of fossil-fuel sources has provide huge amount of uncertainty and concerns about the future of energy consumption and future resources for feeding the systems and hence it has been resulted in increase in use of replacement sources of energy most importantly the renewable sector including wind and solar systems. These sources are important due to not only non-dependence of them on fossil sources, but also due to significant reduction they can achieve in generation of CO₂ and other greenhouse gases. These sources can be used in two different techniques. They can only provide necessary energy for a group of known loads, or they can distribute their energy generation toward network for use of all loads possible. This second wayout generate some advantages and disadvantages. It can enhance the voltage profiles and reduce power losses on systems, but it can also mislead the protection equipments and provide dangers of electrifying since they are generation sources connected directly to the distribution power systems. Also, if the main networks eject from the grid (based on the operation of circuit breakers or black out, etc.) these sources can keep generating electricity in an "Islanding" mode which is not suitable if it happens unintentionally. In this paper, several methods are explained to provide techniques to recognize and detect these incidents and to prevent them by using circuit breakers and other protective equipments. Since both reliability and security of DGs implementations is important for sources, it is needed to cut the electricity generation when it is needed and not to cut it when it is not necessary to keep feeding the loads as maximum period as possible and this fact leads us to provide secure methods to make sure that unacceptable conditions are certainly reached. Due to this statement, combination of- ordinary methods is a more secure method for recognizing the islanding operation mode and make sure that these criteria is reached. Based on IEEE1547 Standard, islanding operation must be detected and disconnected in a maximum of 2 seconds period and this should be observed on all detection and protection methods of Anti-Islanding state for DGs.