New distance protection principle without resistance measurement as a robust line protection in the presence of high load flows

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Protection systems are indispensable for electrical power grids restraining grid faults like short-circuits or conductor failures. Distance protection is a very frequently applied protection relay world wide. This relay measures the distance between the relay and the fault location with respect to the line impedance per unit which consists of the complex value of line resistance and line reactance. In this way the distance relay ensures a fast, selective and reliable fault clearing and prevents the grid from major damages as well as supply interruptions.High fluctuating load flows take place in the presence of power infeeds of renewable energy sources and increasing energy trading. Using the distance protection principle these can lead to unwanted supply interruptions and wide-area grid failures. World-wide blackout scenarios in the past prove this phenomena. The reason for that lies in the relative small measured resistance during high load flows which encroaches into the protection impedance zone and pretends a grid fault to the relay. Additionally the adjustment of the resistive protection zone reach cannot be represented analytically in a sufficient way.In this research project a new approach of the distance protection principle is conducted. This dispenses with the resistance measurement completely. The fault detection will be realized separately based on physical grid figures. The distance determination will be done exclusively by the reactance measurement which is fully sufficient under physical points of view. The benefits are the inherent safety against high load flows, the high flexibility of adaption of the fault detection regarding changing grid or short-circuit conditions and the avoidance of the resistive zone reach, which is up to now the most frequently source of errors during protection setting calculation. The new approach will be implemented on a relay prototype and subjected to lab tests with real time grid simulation facilities.