Determination of optimal breakpoint set of overcurrent relays using modified depth-first search and mixed-integer linear programming

In the process of determination of breakpoints for overcurrent relays (OCR), different sets with equal number of OCRs can be selected as minimum breakpoint set (MBPS). Therefore, determination of the most appropriate MBPS is an issue which must be considered. This paper proposes a prioritization between different MBPSs based on the sum of operating times of OCRs. In this case, a set which results the minimum sum of operating times is selected as the appropriate MBPS. For this purpose, the proposed method combines two problems: Determination of MBPS and coordination of OCRs, and is expressed in mixed-integer linear programming (MILP) form. Also, a modified depth-first search (DFS) algorithm is applied to determine the OCRs contained loops of studied networks. It is shown that the proposed method has the capability to be combined with previous defined expert rules in this field in order to consider the network conditions in the process of determination of optimal breakpoint set (OBPS). The proposed method has been implemented on various size networks, and the results show the effectiveness of proposed method in determining breakpoint set with the least number in first priority and minimum operating times of relays in second priority.</p

New Load Shedding Method for Dealing with Critical Conditions of Smart Network Caused by Fault-Induced Delayed Voltage Recovery

The phenomenon of Fault-Induced Delayed Voltage Recovery (FIDVR) appears in networks with high penetration of induction motor loads because the increase in requested reactive powers of motor loads after clearing the fault prevents the rapid return of the bus voltage to the pre-fault level. Load shedding is one of the effective ways to deal with the FIDVR phenomenon, which causes the amount of demand to approach the production of reactive power. In this paper, a wide-area load-shedding method is presented, which performs based on network conditions and loads. Since the introduced indicators for determining the locations and amounts of loads to be shed are based on the values of bus voltages, loads currents, and network impedance matrix; therefore, the proposed method can effectively shed the loads and deal effectively with FIDVR. The voltage estimation process is an important tool to predict the voltages at future moments and is defined based on the modified Gauss-Seidel load flow and the three-order model of the induction motor. This tool enables the proposed method to understand the effect of applying load shedding on voltage recovery and prevents the application of unnecessary ones

Adaptive distance protection for zone-1 optimal reach to mitigate the impact of network state changes using setting groups

Distance relays are a crucial component of transmission network protection, and factors such as remote infeed make it challenging to ensure both security and dependability of the protection system. To address this challenge, this paper proposes an adaptive protection based on precalculated settings using the setting group (SG) capability of existing numerical distance relays. This scheme optimizes the zone-1 coverage of the relay in the R-X plane to include faults on the designated line as much as possible (dependability) while excluding faults outside the intended line (security). The paper considers the effects of different topologies (N-0, N-1, and specific N-2 topologies) and pre-fault line loads on the apparent impedance measured by the relay. Given these different topologies and line-loading scenarios, the total number of Network States (NSTs) can become significantly larger than the available number of SGs, making it impractical to assign a distinct SG to each NST directly. This necessitates mechanisms to group similar NSTs and assign an SG to each NST group. To overcome this challenge, a hybrid Particle Swarm Optimization-Binary Integer Linear Programming (PSO-BILP) algorithm is proposed. This algorithm simultaneously determines the optimum relay’s settings for each SG and identifies the proper SG to activate in each NST. The PSO component optimizes the relay’s settings, while the BILP component assigns the optimal SG for each NST. The effectiveness of this method is demonstrated through implementation and testing on the IEEE 39-bus network, showcasing significant improvements in the protection system’s performance

Optimal coordination of directional overcurrent relays considering non-standard curves and multiple network topologies using tlbo-lp

In this article, Directional Over-current Relay (DOCR) Coordination was performed considering various network topologies and the non-standard curve for the overcurrent relay. In practice, usually the network topology changes by switching lines and the overcurrent relay coordination might be removed. The purpose of this article is to maintain relay coordination while the network topology is changed and to get the best setting and reduce the operating time of relays. For coordinating and setting overcurrent relays, a hybrid TLBO method was used which combined Teaching-Learning Based Optimization (TLBO) and LP. Four variables were used to set overcurrent relays and the algorithm obtained specific settings for each relay. The proposed algorithm was also compared with the conventional methods. The results show that the TLBO-LP method and using non-standard curve will improve the operating time of overcurrent relay, increase coordination between them and maintain the DOCR coordination by changing the network topology and switching line