مجله کیفیت و بهره وری صنعت برق ایران
سال یازدهم شماره 3 (پیاپی 28، پاییز 1401)

The changes in configurations of distribution networks due to the outages of any upstream substations or distributed generations (DGs) is one of the essential challenges in the design of distribution systems. The changes in topologies of the network affect the protective schemes and might lead to coordination constraint violations in different operation modes and configurations. It is inevitable to appear some coordination constraint violation if only the base grid-connected operation mode and configuration is considered in the optimal protection settings. The adaptive protective schemes have several advantages compared to those using only one setting group, and their speed would be more desired. Although different research works have been done in the literature in adaptive protective schemes, there is a research gap about considering the limited number of setting groups for directional overcurrent relays (DOCRs), besides other aspects of active distribution networks and adaptive schemes. This research tries to fill such a research gap by proposing a new optimized adaptive protection system, considering various network configurations, by the limited number of setting groups. Since the proposed optimal settings for DOCRs are applied to a limited number of setting groups, it would be practical. Optimizing the standard relay characteristics in the proposed method is another contribution. Test results of applying the introduced method on the distribution portion of the IEEE 30-bus test system highlight the advantages of this study. Simulation results infer that 54.27% improvement in operating time of the protection system is achievable through applying the proposed method compared to available adaptive ones because of optimizing the relay characteristics.

The distribution network is always exposed to many blackouts due to its size. Reducing downtime, reducing undistributed energy, increasing reliability and thus customer satisfaction are important goals of a distribution company. The performance of power systems is affected by many factors such as various errors, network maneuvers and unwanted equipment out of service. Protective switches can reduce subscribers' downtime and redistributed energy and associated costs by isolating a faulty network point. On the other hand, due to the high costs of purchasing, installing, and maintaining protective equipment such as reclosers and sectionalizers, distribution companies seek to minimize these costs. Therefore, determining the minimum number of reclosers and sectionalising awitches necessary for reliable protection of the network and their optimal installation location is one of the basic needs of distribution network operators. The main purpose of this study is to determine the number and optimal location of recloser and sectionalising awitches protection equipment in the distribution network using an improved genetic algorithm. The proposed method is tested on one of the distribution feeders in Bojnourd city called Nader and its results are compared with other evolutionary methods such as genetics, frog mutation and particle swarm optimization.

Nowadays, the need has increased to manage distributed energy resources due to advances in the renewable energies industry, the distance between energy resources and local loads, growth in the number of electric vehicles, and high power transmission costs. In this regard, important challenges, such as power exchange management between distributed energy resources and electric vehicle batteries, have been raised for optimal use of the power generated from these resources. Since home consumers are supposed to have wind turbines or photovoltaics installed to the supply part of their power consumption, the impact of wind and solar radiation uncertainties on their output power should be considered. Considering these challenges and in an attempt to flatten the difference curve between the generated power of resources and consumption power of local loads, this paper proposes an efficient method based on mean-field theory to control the charge and discharge of electric vehicle batteries. On the other hand, with the increase in the number of electric vehicles and distributed energy resources, the control of charging and discharging of too many batteries requires heavy and time-consuming calculations. This paper proposes an innovative method by introducing some coefficients for online estimation of the charge and discharge of batteries, which leads to a reduction in the volume of calculations. To this end, a compromise has been made between the performance, the volume of calculation reduction, and the necessity of these calculations. Simulation results illustrate the quality and efficiency of the charge and discharge estimation of batteries based on the proposed method.

Distributed Generation (DG) has a various effect on distribution networks such as reducing the losses, improving the voltage profile, reliability and etc. Also these units can affect other levels of power system like as reducing transmission lines congestion and post ponding generation expansion programs, these units change the HLI reliability indices, these indices describe the risk of load shading due to outages in the generation system. Forming a capacity outage probability table (COPT) is the classic way to calculate these reliability indices. Due to the fact that the number of installed DGs in a power system is much greater than the number of conventional units, COPT will have numerous rows, hence the burden of the calculating process of it will be huge. Fortunately, as the high possibility to categorize the installed DGs in the group with the same capacity and different force outage rates (FORs), this paper purposes an analytical method to reduce COPT states and accelerate its calculating process.

Resilience characteristics in power systems refer to the system's ability to withstand against severe disturbances with a low probability of occurrence. As extreme dust storms in the south and southwest in recent years have caused heavy damage to the IRAN's electricity industry, in this paper, a bi-level planning model is proposed to simultaneous hardening of distribution lines and substations against this phenomenon. In the first and second levels of the proposed model, the investment costs of distribution system hardening and total expected operating costs are minimized subject to financial and operational constraints, respectively. The planning results in different case studies have shown that the simultaneous hardening planning of substations and distribution lines can, in addition to reducing operating costs in the emergency conditions, play a significant role in reducing investment costs. The proposed model is implemented on a large-scale power distribution system in Khuzestan province, and the simulation results confirm the efficiency of the proposed scheme at different budget levels.

Due to the expansion and development of the distribution networks and the use of distributed generators (DGs), the level of short-circuit current has increased significantly. Increasing the short circuit current level provides several challenges for network equipment. In this paper, the effects of using the inter-line fault current limiter (IFCL) to reduce the short-circuit current and improve the stability of DGs installed in the 230/63/20 kV AMIRABAD substation as a case study are investigated. It includes several output feeders for connecting loads and four DGs to a common coupling point 20 kV bus. In this substation, the connection of DGs to supply the power required by consumers, has increased the short-circuit current to a greater amount than the nominal capacity of the equipment. Also the occurrence of short-circuit in one of the feeders has led to voltage sag in the common bus and the instability of the generators. This has caused the exit of generators and sensitive loads connected to parallel feeders and finally reduce the reliability. IFCL consists of several rectifier bridge circuits and a common limiting resistor. It inserts the common limiting resistor in fault path for limiting the fault current level and consequently the voltage drop in the case of short circuit of the feeders. To prove the efficiency of the proposed structure for solving the problems of the studied network, the substation components in PSCAD / EMTDC software are simulated. The simulation results show that the proposed IFCL effectively reduces the fault current and voltage drop, as well as improves the stability of DGs.