Points Of Distribution Network Research Articles

A Two-Stage Multi-Scenario Optimization Method for Placement and Sizing of Soft Open Points in Distribution Networks

The Soft Open Point (SOP) is an emerging power electronic device for active power flow control, reactive power compensation and post-fault service restoration in power distribution networks. In this paper, a novel two-stage multi-scenario optimization method for SOP placement and sizing is proposed to minimize power losses and active power curtailment of distributed generation (DG) in distribution systems. In Stage 1, the Loss Sensitivity Index (LSI) and Voltage Deviation Index (VDI) are used to identify candidate locations of SOPs, and a new method to estimate the LSI is proposed. In Stage 2, a mathematical optimization model is developed using AC power flow to optimally size each voltage source converter (VSC) of a SOP; the power factor constraint at the substation/grid interconnection is incorporated in this model to ensure security of the upstream grid. The proposed method is validated by a modified IEEE 33-node test system and a large 404-node unbalanced distribution system operated by Saskatoon Light and Power in Saskatoon, Canada.

Multiple Sources Restoration for Soft Open Points in Distribution Networks With a Two-Stage Accelerated Algorithm

Soft open points (SOPs) connected to distribution networks are instrumental in improving operational performance during outage periods, such as power supply reliability and power quality, and they have not been sufficiently studied. To fully harness the potential benefits of SOPs, a multiple-source distribution service restoration (DSR) strategy considering SOPs is proposed in this paper. The power outputs of distributed energy resources (DERs) and SOP flexibility are exploited to enhance the load restoration level and mitigate voltage deviations over a time horizon. Additionally, to cope with uncertainties, the chance-constrained method is adopted by the proposed strategy to allow intermittent renewable resources to participate in DSR. DSR is formulated as a mixed-integer linear programming (MILP) problem with many integer variables, making it very challenging to solve. To reduce the computational complexity, a two-stage accelerated algorithm (TSAA) is proposed. This allows us to solve a relaxed MILP problem in the first stage to decide the radial topology. An accelerated MILP problem is solved in the second stage to determine the load status as well as the outputs of the DERs and SOPs. Case studies on an IEEE 33-bus distribution network illustrate the effectiveness of the proposed DSR strategy and the feasibility of TSAA in reducing the computation time.

Resilience-Oriented Co-Deployment of Remote- Controlled Switches and Soft Open Points in Distribution Networks

Soft open points (SOPs) can perform load transferring and voltage support, helping to expand the range of service restoration in distribution networks (DNs) under fault scenarios. In addition, in the field of DN restoration, SOPs are usually controlled in coordination with switch actions (e.g., the network reconfiguration). However, in the planning level, the coordinated deployment of SOPs and remote-controlled switches (RCSs) has never been studied in the literature. To this end, for the first time, this paper proposes a co-deployment framework for SOPs and RCSs incorporating active management of flexible resources for resilience improvement in DNs, in which the coupled multiple recovery stages are also modeled and included. The objective is to minimize the investment cost of SOPs and RCSs, along with the cost caused by de-energized loads, with the consideration of exhaustive DN operation constraints over proactive islanding, degradation, isolation and restoration stages. Furthermore, resilience-cost tradeoff is analyzed to help DN managers determine equipment investment plans. The formulated model is further transformed into a mixed-integer second-order cone programming model that can be thus efficiently solved. Simulation results on modified IEEE 34-node and IEEE 123-node test systems verify the effectiveness of the proposed model.

A Robust Mixed-Integer Convex Model for Optimal Scheduling of Integrated Energy Storage—Soft Open Point Devices

Soft open points (SOPs) are power electronic devices which can replace conventional normally open points in distribution networks. SOPs enable full control of active power flow between the interconnected feeders and can inject reactive power at each node to which they are connected. SOPs integrated with energy storage (ES) have been recently proposed to realize both spatial and temporal flexibility in active distribution networks. The flexibility provided by integrated ES-SOP devices will allow network operators to run their networks closer to their limits, but only if there is appropriate management of the uncertainty arising from demand and renewable generation. The only existing model of an ES-SOP uses nonconvex nonlinear equations, neglects uncertainty, and represents converter losses in an oversimplistic manner. This paper presents a robust mixed-integer convex model for the optimal scheduling of integrated ES-SOPs to ensure a zero probability of constraint violation. Losses of the subsystems comprising the ES-SOP are modeled using a proposed binary-polynomial model, enabling efficient scheduling of the energization state of subsystems to reduce no-load losses. The ES-SOP is considered in this paper to be owned by the network operator to: 1) manage power flow constraints, 2) minimize cost of losses, and 3) maximize arbitrage profit.

Voltage Unbalance Compensation in Distribution Feeders Using Soft Open Points

Soft open points (SOPs) are power electronic devices that may replace conventional normally-open points in distribution networks. They can be used for active power flow control, reactive power compensation, fault isolation, and service restoration through network reconfiguration with enhanced operation flexibility and grid resiliency. Due to unbalanced loading conditions, the voltage unbalance issue, as a common problem in distribution networks, has negative impacts on distribution network operation. In this paper, a control strategy of voltage unbalance compensation for feeders using SOPs is proposed. With the power flow control, three-phase current is regulated simultaneously to mitigate the unbalanced voltage between neighboring feeders where SOPs are installed. Feeder voltage unbalance and current unbalance among three phases are compensated with the injection of negative-sequence and zero-sequence current from SOPs. Especially in response to power outages, three-phase voltage of isolated loads is regulated to be balanced by the control of SOPs connected to the feeders under faults, even if the loads are unbalanced. A MATLAB/Simulink model of the IEEE 13-bus test feeder with an SOP across feeder ends is implemented, and experimental tests on a hardware-in-the-loop platform are implemented to validate the effectiveness of the proposed control strategy.

A Reliability-Based Method to Quantify the Capacity Value of Soft Open Points in Distribution Networks

Soft open points (SOPs) are power electronic devices which provide interconnection between two feeders in place of normally open points in electricity distribution networks. SOPs can continuously control active power flow between feeders and inject reactive power controllably at both nodes, which can be used to provide substantial capacity support to the system. This paper provides a reliability-based method to quantify the capacity value (the additional load which can be accommodated without reducing reliability) of SOPs using the Effective Load Carrying Capability method within a Monte Carlo Simulation (MCS). Optimization of post-fault active/reactive power injections by SOPs to minimize energy not supplied is formulated (directly in matrix form) as a second-order cone programming problem. This results in very low computational times which enables embedding of the optimization problem within the MCS. The proposed methodology is applied to a modified real-world distribution network considering three different SOP sizes (5 SOPs totalling 2.5, 5, 10 MVA) across three redundancy levels (N-1, N-0.75, N-0.5), and on an unbalanced network with distributed generation. Results demonstrate capacity values ranging from 2.4–12.84 MVA. When operating under a relaxed redundancy level, the capacity value of a given SOP capacity can more than double relative to N-1.

Overvoltage Analysis during Earth Fault for Different Treatment of Neutral Point in Distribution Network

Abstract The paper consists of three parts. In the introduction and the first part of this paper are given basic theoretical considerations on possible ways for treatment of the neutral point in distribution grids with special reference to the method of neutral grounding of distribution transformers through a low ohmic resistor and a compensation coil. The second part gives the use analysis of a low ohmic resistor and a compensation coil as the future choice of neutral point grounding on the particular distribution grid powered by a substation TS 35/10 kV. In the third part of the paper, the results were obtained using an adequate dynamic distribution model, using the EMTP-ATP software package. Also, in this part, calculations are made for neutral grounding through a low ohmic resistor, a compensation coil, as well as in the case of isolated grids, and a comparison of the obtained values of the overvoltage coefficients.

Affection of multiple feeding water supply network on the concentration of trihalomethane. (Dept.C)

The previous researches studied the concentration of (THMs) in water networks having only one feeding source. This research illustration the effect of multiple feeding source for water supply network on the concentration of (THMs). This research focuses on the evaluation and assessment of THMs contamination in Fayoum Water Supply Network. To investigate the influence of multiple feeding source for a distribution water network on the THMs contaminant, an intensive 5-months sampling programmed was undertaken. pH, Free Chlorine, Bromine, Temperature, Travel Time, TOC and THMs were all measured. Results showed that the concentration of THMs in all the selected points in the distribution network were less than the maximum acceptable concentration for THMS, and the chloroform is the predominant THMS compound (it represents an average of 50% of total THMS ). It was noticed that an average chlorine consumption of 0.1 mg/L leads to the increase of THMs concentration by 2.0 to 2.5 μg/L. An increase in temperature by 5°C leads to the increase of THMs concentration by 27% to 32%. The higher the initial THMs formation after post-chlorination, the lower the relative increase in THMs in the distribution system. The mixing between two feeding sources is better for the distribution network not only for flexibility in operation, but also for the properties of the water and the concentration of THMs at point of mixing between conventional treatment plant & small plant is less than the concentration of THMS at point in distribution network for small plant only.

Model and observation of dispatchable region for flexible distribution network

Soft open points (SOPs), defined as the power electronic devices installed to replace normally open points in distribution network, can improve the flexibility of power control and thus further enhance the reliability and economy of power grids. Flexible distribution network (FDN) is a system-level concept to describe the distribution network equipped with multiple SOPs. Region method is to describe the secure range of the system operating in a geometric view. This paper adopts the region method to observe FDN for the first time. Firstly, the model of dispatchable region of FDN is proposed. The constraints of region space are formulated, considering SOPs, power flow, thermal capacity and voltage profile. Secondly, a simulation-based observation approach is also proposed to obtain the region projections on 2D and 3D sub-space. To illustrate the approach clearly, 2 small cases are given preceding a 7-feeders IEEE RBTS case. The region projections of case grids are observed and their topological characteristics are compared with those of traditional distribution network (TDN). The results indicate that FDN has advantages over traditional distribution network in operation security. For example, the region projections of FDN on 2-dimensional sub-space are about 2–4 times larger than those of TDN with the same network topology. The dispatchable region can be further developed into a useful tool for the secure and high-efficient operation of FDN in the future.

Novel Distributed Active and Reactive Power Management Approach for Renewable Energy Resource and Loads in Distribution Network

This paper proposes active and reactive power management based on distributed optimization method that is employed to minimize loss, voltage variation of buses, load shedding and variation of power generation. In this approach, energy efficiency is improved and voltage profile is kept in an acceptable range under different operating conditions of renewable energy resources and loads. Three various power control methods such as (1) active power control (APC), (2) reactive power control (RPC) and (3) simultaneous APC with RPC are implemented by proposed active and reactive power management unit (ARMU). Measurement units collect essential information and send them to ARMU in each bus. ARMU determines the active and reactive power set points of dispatchable DGs and loads and reactive set points of non-dispatchable DGs in each bus. Also ARMU updates set point in less than one second and all controllable units contribute to voltage and power control which is proper for online optimization. Simulation results show the superior performance of this control method to regulate dynamic active and reactive power set points in distribution network.

Grid Side Unbalanced Fault Detection using Soft Open Point in an Electrical Distribution Network

Soft open point (SOP) is a power electronic device that installed in place of normally open points in distribution networks. This paper investigates the performance of SOP under an unbalanced line to ground (L-G) fault in a medium voltage (MV) distribution network. A method to detect unbalanced grid side AC faults was developed using positive and negative sequence currents injected into the feeder by the SOP. Simulations were carried out on a network model developed in PSCAD/EMTDC. Local measurements at SOP grid connection point were used to define a fault index. Results show that the fault index, based on the values of positive and negative sequence currents, is able to effectively detect the presence of an unbalanced fault in a MV distribution network.

Impact of Distributed Generation on the Reliability of Local Distribution System

With the growth of distributed generation (DG) and renewable energy resources the power sector is becoming more sophisticated, distributed generation technologies with its diverse impacts on power system is becoming attractive area for researchers. Reliability is one of the vital area in electric power system which defines continuous supply of power and customer satisfaction. Around the world many power generation and distribution companies conduct reliability tests to ensure continues supply of power to its customers. Uttermost reliability problems in power system are due to distribution network. In this research reliability analysis of distribution system is done. The interruption frequency and interruption duration increases as the distance of load points increase from feeder. Injection of single DG unit into distribution system increase reliability of distribution system, injecting multiple DG at different locations and near to load points in distribution network further increases reliability of distribution system, while introducing multiple DG at single location improves reliability of distribution system. The reliability of distribution system remains unchanged while varying the size of DG unit. Different reliability tests were done to find the optimum location to plant DG in distribution system. For these analyses distribution feeder bus 2 of RBTS is selected as case study. The distribution feeder is modeled in ETAP, ETAP is software tool used for electrical power system modeling, analysis, design, optimization, operation, control, and automation. These results can be helpful for power utilities and power producer companies to conduct reliability tests and to properly utilize the distributed generation sources for future expansion of power systems.

Scale Formation and Corrosion of Drinking Water Pipes: A Case Study of Drinking Water Distribution System of Shiraz City

<p>Due to increased consumption of drinking water in the world, there are attempts to apply new solutions for<br />accessing sufficient amounts of water with proper quality. In addition, efficient usage of energy and finding a<br />solution for reducing the scale-related problems in drinking water pipes are among major concerns of urban<br />water supply. Annually, significant budgets are assigned for removing the scale of pipes as well as home and<br />industrial devices. The present study endeavors to examine the scale-formation and corrosion potential of<br />drinking water in drinking water distribution network of Shiraz City (south of Iran). This study is of descriptive<br />type conducted through Langelier, Puckorius, Ryznar, Larson and aggressive indices and taking 144 samples of<br />different sources and points of distribution network. The results showed that the mean values of LI, RI, LS and<br />AI were 0.07 (slightly scale forming), 7.1 (non-scale forming), 1.2 (corrosive) and 14 (non-corrosive),<br />respectively. The mean of scale formation rate value in Shiraz drinking water pipes was 0.26 mm/y. Accordingly,<br />zones located in east, southeast and south of Shiraz have more problems of scale formation. Scale composition of<br />33 home pipe samples and 8 network pipe samples were analyzed by X-ray diffraction method. Results indicated<br />that main compositions in scale samples were calcium carbonate, calcium sulfate, magnesium carbonate,<br />magnesium sulfate, hematite, maghemite, magnetite, goethite, zinc oxide, gypsum, vivianite, dolomite,<br />hydroxyapatite and troilite. Main elements in scale samples were magnesium, silicon, phosphorus, sulfur, zinc,<br />copper and lead.</p>

A Fault Location Method in Distribution Network Based on Firefly Algorithm

In the distribution network fault location, the impact of information distortion needs to be to focus on, especially when the short-circuit current is used as the fault information. Considering the distortion or failure of real-time information and other issues, the quick location method of the failure point in distribution network is analyzed. Based on the mathematical model of distribution network fault location, firefly algorithm is applied. According to the characteristics of fault location objective function in distribution network, convergence criterion is proposed, which is suitable for fault location mathematical model.

A Modified Proportional Fair Scheduling Algorithm for the Electric Power Wireless Private Network

With the development of smart grid, the requirements of high speed, low delay and better coverage have motivated a electric power wireless network that bridge the communication gaps between the transmission system and the load. In this paper, we introduce a new electric power wireless communication network, and give a general overview of studies on the major characters of communication such as wide coverage, a lot of measurement points in distribution networks as well. In order to improve the communication performance, the paper proposes a modified proportional fair algorithm, which allocates the radio resources by introducing a Quality-of-Service (QoS) scale factor. By comparing with the proportional fair algorithm, we get the conclusion that the modified algorithm is more suitable for the electric power wireless private network.

Effect of Load Models on Probabilistic Characterization of Aggregated Load Patterns

This paper presents a comprehensive approach to probabilistic characterization of aggregated load pattern of low-voltage consumers. Different from previous methods, consumer load patterns obtained from load survey are converted to empirical cumulative density functions. The functions are then used to address stochastic nature of load pattern in any given point of distribution network. The proposed approach is adopted to investigate the effect of load models on the characterization of aggregated load patterns. In addition, a goodness-of-fit analysis has been carried out to show that the load models can significantly affect the accuracy of aggregated load modeling. It is demonstrated that the constant power (real and reactive) load model which is normally adopted in most distribution network management studies may lead to misleading results compared to the actual network. Case studies are presented and discussed with reference to a real distribution network. The results verify that the proposed method is accurate and flexible, and the voltage-dependent load model is the most promising solution for the aggregated load modeling.