Island partitioning of smart distribution systems under emergency conditions considering frequency stability

Abstract

Island partitioning is an interesting solution for service restoration in the emergency operation of the smart distribution system. Since rapid decisionmaking is required in an emergency condition, the island partitioning without regard to the time allowed for the implementation of control actions may lead to the violation of the allowable frequency limits and the activation of frequency relays. Therefore, this paper presents a two-stage solution procedure to restore the smart distribution system in emergency condition considering the frequency stability, operational constraints, the position of switches, the load priority and controllability, the controllable and uncontrollable distributed generations, and the time delay in implementation of control actions. In the first stage, considering the frequency stability, the time interval for the implementation of control actions is determined. Then, considering this time interval, the load/generation changes and the boundaries of the partitions are determined, using the partitioning algorithm based on black widow optimization, in order to maximize the value of the restored loads/ minimize the operational cost of DGs. In the second stage, the formed partitions are adjusted to satisfy the operating constraints of the system. Applying the proposed method to the PG&E 69-bus test system, considering different scenarios, and comparing the proposed method with the previous methods show the efficiency of the proposed method.

Island partitioning of smart distribution systems in emergency situations considering voltage and frequency stability

“…The time obtained from this method is approximate and the performance of the governors is not taken into account, and it is at least 20-30% less than the real time and the time obtained from our proposed method in the paper [19]. But the purpose of having an approximate time is to know how much time is available to determine control measures, and the shorter the time, the greater the margin of safety.…”

“…In the articles cited so far, the authors have not investigated frequency stability. Therefore, in the paper [19], a two-step method for partitioning the island smart distribution grid is presented, taking into account frequency stability, controllable and uncontrollable DGs, and time delay in the implement of control measures, but voltage stability is not considered.…”

“…In reference [19], it is mentioned that there is a delay between the control measures (that is, between the border switching and the generation/load change). Also, there is a delay between the fault tripping and the implementation of control measures, which part of that is related to the time duration of decision making on control measures.…”

“…As mentioned in [19], uncontrollable DGs cannot supply loads independently, so, each partition must have at least one controllable DG. If there are m controllable DGs in each island, then that island can be split into at most m partitions.…”

“…VSM for each partition will be equal to the lowest voltage stability margin of the feeders of that partition (Eq. 19). The VSM of the all partitions will be the lowest VSM of the partitions (Eq.20).…”