A two-step protection algorithm for smart distribution systems with DGs

Increasing penetration of distributed generators (DGs) is gradually changing distribution networks from a radial structure into a multi-source one. In addition, some distribution systems are in slightly meshed structures for the interest of smart grids. The traditional protection philosophy is being challenged because the coordination among protection devices is affected by the bi-directional power flow and the intermittent nature of DGs. This paper proposes a communication-based protection algorithm considering the impact of bi-directional power flow in distribution networks with DGs. The proposed algorithm detects and isolates fault sections by a 2-step search procedure. In step 1, an injected power calculation, in conjunction with a tabu search algorithm, is used to narrow down the fault-section search region by using the voltage measurements. Step 2 precisely detects the fault section by comparing current phase angle changes. A typical distribution network in Beijing, China and the IEEE 30-node system are used to illustrate and validate the proposed method.