Providing a protection method to support distributed generation against transient voltage instability

The analysis of transient stability in electric power systems and the penetration coefficient of scattered productions play important roles in the regulation of protective equipment, so these parameters should be considered two main factors in the electrical protection of power networks. Overcurrent relays are used as one of the simplest and most effective solutions for power system protection. The overcurrent relay has two main variables: time setting factor (TMS) and plug setting (PS). The relay operation time is a function of TMS, PS, and the current seen by the relay. This paper analyzes the transient stability of a distribution network including distributed generation to determine the protective regulation of overcurrent relays. First, the transient stability of scattered products is studied for different fault locations and their different penetration coefficients. Then, the limitations of distributed generation resources are considered in the protection coordination of overcurrent relays. Therefore, a new method is proposed to calculate the modified value of the time adjustment coefficient of the overcurrent relay. In other words, not only the protection limits but also the transient stability limits are considered in the calculation of the time adjustment factor. In fact, by applying the proposed method, not only is the coordination between overcurrent relays maintained but the instability of distributed generation sources is also prevented. The performance of the proposed protection plan is evaluated with the help of simulation in an IEEE 33-bus distribution system using ETAP software. The results show the correct performance of the proposed method for the worst error conditions. It should be noted that to carry out conservation and stability studies, the following steps are performed in order, which ultimately leads to the creation of a conservation-stability algorithm: (A) protection studies in the condition of disconnection of DG resources, (B) transient stability studies in the conditions of connection of scattered production sources, including obtaining the minimum stability time for each of the scattered production, and (C) investigating the simultaneous establishment of CTI and CCT. In this situation, two situations are possible: the simultaneous establishment of CTI and CCT, the establishment of CTI restrictions, and the non-establishment of CCT. The value of CCT for each DG is equal to the time when the speed of the DG or the power angle of its generator becomes zero. As can be seen, in the first, second, fourth, and fifth scenarios, the CCT condition of the distributed generation source is not established, and it is necessary to modify the TDS value of the main relay.