Undelivered Energy Research Articles

Radial distribution network planning under uncertainty by implementing robust optimization

This paper presents a two-level robust optimal feeder routing model for the planning of radial distribution networks where power demand is uncertain. The robust model is solved by implementing the column and constraint generation strategy. The optimization goal is to find routes that provide minimal total annual costs that satisfy parameters for quality of supply and technical constraints under the worst uncertain power demand realization. The model incorporates annual capital recovery, energy loss, and undelivered energy costs. The column and constraint generation strategy was developed using a mixed-integer quadratically constraint programming model capable of obtaining a deterministic solution to the optimal feeder routing problem.

Rekonfiguracija i otočna kompenzacija u prisustvu distribuiranih izvora u razgranatoj distributivnoj mreži

Distribution utilities witness many changes nowadays. If the network voltages must be in 0.9-1.1 p.u. limits and grid input power factor greater than 0.85 all three modern strategies of smart distribution network as reconfiguration, capacitors switching and presence of distribution generation (DG) ought to be applied. Even in this case On Load Tap Changer (OLTC) in the supplying substation has to be used. In this paper, detailed technical analysis of 21 realistic operation cases is presented by hybrid algorithm of Minimum spanning tree (MST) plus Simulated Annealing (SA). MST is used for tackling reconfiguration first and SA for capacitor switching afterwards. Implemented transparent grafical Monte Carlo method for locating of distributed generators and capacitor banks is unique and simple. Assumption is that DG is already present. Gauss and Weibull changing nodal loads and wind generators output, respectively as well as daily load curves for working and weekend day with insolation of solar panels are included in analysis. The objective function comprising of the cost of power losses, price of capacitors and undelivered energy is minimized. IEEE 118 bus network is analyzed which has 118 nodes and 132 branches (15 ties), all of which can commutate, that is considered to be large scale. The basic switching logic of uniform distribution of wind generators to the nodes and capacitors in accordance with objective function, that changes every hour is unrealistic. More realistic one was issued with fixed nodes for allocation of DG and capacitors (the most frequently visited nodes). The programme final objective function indicates the price of peak power losses, losses of delivered electrical energy, of the banks, of undelivered electrical energy and commutations for the period of month and a half (1008 network operating hours).

On the MILP Modeling of Remote-Controlled Switch and Field Circuit Breaker Malfunctions in Distribution System Switch Placement

Installing sectionalizing switches and field circuit breakers (FCBs) is vital for the fast restoration of customer electricity supply in distribution systems. However, the high capital costs of these protection devices, especially remote-controlled switches (RCSs) and FCBs, necessitate finding a trade-off between their costs and financial benefits. In this study, we propose a mixed-integer linear programming (MILP) model for optimizing switch planning in distribution systems. The proposed model determines the optimal allocation of manual switches, RCSs, and FCBs to minimize the costs of switches and the reliability-oriented expenses. While the former includes the costs of installing and operating the switches, the latter consists of the distribution company’s lost revenue due to the undelivered energy and the regulatory incentives (or penalties) associated with service reliability indices. Two penalty-reward mechanisms are used to account for the financial benefits of increasing the service reliability through reducing the duration and frequency of interruptions. Proposing a novel reliability assessment model, we consider the possibility of malfunctions in both RCSs and FCBs in a highly efficient manner, which is a major contribution of this work. The proposed MILP model is applied to three test networks to validate its applicability and efficacy. The results show the importance of considering the possibility of switch malfunctions in distribution networks.

Rekonfiguracija distributivne mreže i otočna kompenzacija uz prisustvo vetro generatora i solarnih panela

Distribution utilities witness many changes nowadays. If the network voltages must be in 0.95-1.05 p.u. limits and grid input power factor greater than 0.85 all three modern strategies of smart distribution network as reconfiguration, capacitor switching and presence of distribution generation (DG) ought to be applied. Even in this case On Load Tap Changer (OLTC) in the supplying substation has to be used. In this paper, detailed technical analysis of eight realistic operation cases is presented by Simulated Annealing (SA) and by hybrid algorithm of Minimum spanning tree (MST) plus SA that works in shorter time. MST is used for tackling reconfiguration first and SA for capacitor switching afterwards that gives better results compared with SA alone. Implemented transparent graphical Monte Carlo method for locating of distributed generators and capacitor banks is unique and simple. Assumption is that DG is already present. Gauss and Weibull changing nodal loads and wind generators output, respectively as well as daily load curves for working and weekend day with insolation of solar panels are included in analysis. The objective function comprising of the cost of power losses, price of capacitors and undelivered energy is minimized. IEEE 69 bus network is analysed which has 69 nodes and 73 branches, all of which can commutate. The basic switching logic of uniform distribution of wind generators to the nodes and capacitors in accordance with objective function that changes every hour is unrealistic. More realistic one was issued with fixed nodes for allocation of DG and capacitors (the most frequently visited nodes). The programme final objective function indicates the price of peak power losses, losses of delivered electrical energy, of the banks, of undelivered electrical energy, OLTC and commutations for the period of month and a half.

Power recovery of the PV arrays under partial shading by a power electronic compensator

The partial shading phenomenon in some modules of the PV arrays limits the total current of the series modules and reduces the total output power. In this paper, a power electronic compensator with a multi-winding transformer is presented to recover the undelivered energy of the shaded modules. The proposed configuration compensates reduced currents due to the partial shading on the series modules by injecting the required currents into parallel circuits of the shaded modules. The unshaded modules provide the compensatory currents by creating a common flux into the core of the multi-winding transformer. The average current and the output power of the PV array are considerably improved under partial shading conditions. The proposed configuration has a very simple and sensorless control structure, and its power electronic elements are less than other improving configurations. The simulation and experimental results confirm the presented analytical relations and desirable performance of the proposed configuration to recover the undelivered energy of the PV array under the partial shading conditions.

An Enhanced MILP Model for Multistage Reliability-Constrained Distribution Network Expansion Planning

Reliability is an essential factor in distribution networkt expansion planning. However, standard distribution reliability assessment techniques rely on quantifying the impact of a pre-specified set of events on service continuity through the simulation of component outages, one at a time. Due to such a simulation-based nature, the incorporation of reliability into distribution network expansion planning has customarily required the application of heuristic and metaheuristic approaches. Recently, alternative mixed-integer linear programming (MILP) models have been proposed for distribution network expansion planning considering reliability. Nonetheless, such models suffer from either low computational efficiency or over-simplification. To overcome these shortcomings, this paper proposes an enhanced MILP model for multistage reliability-constrained distribution network expansion planning. Leveraging an efficient, yet accurate reliability evaluation model, proposing a customized technique for effectively imposing radial operation, as well as utilizing pragmatic measures to model reliability-related costs are the salient features of this work. In this respect, practical reliability-related costs are considered based on reliability incentive schemes and the revenue lost due to undelivered energy during customer outages. The proposed planning approach is tested on four networks with 24, 54, 86, and 138 nodes to illustrate its efficiency and applicability.

OPTIMAL DISTRIBUTION NETWORK SWITCH PLANNING CONSIDERING MALFUNCTION OF SWITCHES

Sectionalising switches play a crucial role in the post-fault reconfiguration of distribution networks. In this paper, we propose a mathematical model for the switch placement problem, through which the optimal configuration of manual and remote-controlled switches (MSs and RCSs) as well as field circuit breakers (FCBs) can be determined. The objective is to minimise the installation and operation costs of switches together with the reliability-oriented costs, which include the distribution company's lost revenue due to the undelivered energy and the regulatory incentives (or penalties) associated with service reliability indices. To determine the regulatory incentives (or penalties), two reward-penalty mechanisms are applied to the system average interruption frequency index (SAIFI) and system average interruption duration index (SAIDI). Also, a new reliability assessment model is developed in this paper to quantify SAIFI, SAIDI, and expected energy not supplied. In this model, we consider the possibility of malfunctioning in RCSs and FCBs, which has a high occurrence probability, especially in severe weather conditions. The proposed switch optimisation model is implemented on a test network to validate its applicability. The results reveal the importance of considering the placement of FCBs and the possibility of switch malfunctions in switch placement models.

Market-Based Energy Management Model of a Building Microgrid Considering Battery Degradation

This article presents a model for energy management system of a building microgrid coupled with a battery energy storage. The model can be used to dispatch the battery as a flexible energy resource using a market-based setting. The battery is modeled considering battery degradation and real-life operation characteristics derived from measurements at a residential building. The performance of the model was evaluated first with simulations and integrated afterwards to an energy management system, which was demonstrated at a real residential building (HSB Living Lab) equipped with photovoltaic and battery storage systems. The simulation results showed that the building owner, and subsequently the residents, could benefit from the proposed model in reduced annual cost up to 3.1% under the considered pricing scheme. The demonstration results showed that dispatch under the measurement-based model could decrease the undelivered energy over the daily requested amount from the battery from 13.3% to 3.7%. Thus, the proposed model, which couples the measurement-based dispatch with battery degradation, can lead to a more accurate estimation of the building operation cost and an improved overall performance of battery as a flexible resource in building microgrids.

Stochastic optimization of comfort-centered model of electrical water heater using mixed integer linear programming

This paper introduces a new strategy for controlling electric water heaters (EWH) using mixed-integer linear programming (MILP). It has two major contributions: 1) To balance between cost savings and the discomfort (cold water) that Demand Response (DR) could bring, the discomfort is modeled as undelivered energy in the objective of the problem rather than a thermal constraint. This improves both sides of the cost-saving Vs. User-comfort trade-ff. 2) in EWH control, many previous works only rely on electricity prices for scheduling. However, this work is among the very few works that also consider consumption for scheduling. Further, by treating the hot water withdrawal pattern as a random variable, the algorithm finds the best setpoints for EWH via stochastic optimization over a range of possible hot water withdrawal patterns, rather than requiring perfect foresight of withdrawal. The result of these changes is an algorithm that can let the temperature fall below minimum when probability of energy usage is low without affecting user comfort while other methods always keep the temperature above minimum. The effectiveness of this approach on improving both sides of the cost Vs. discomfort trade-off and the effectiveness of stochastic approach is confirmed by comparison with two other methods.

Investigation of high voltage ACSR transmission line dead end connector fault

Transmission line plays important roles in delivering electric energy from generation site closer to the customer. Failure of a transmission line can cause significant economic loss due to undelivered energy and may lead to catastrophic system black out. One critical part of transmission line is dead end connector, thus ensuring good condition of transmission line dead end connector is critical to avoid extensive losses. This paper investigates the cause of failure of dead end connectors that were installed in 150 kV ACSR lines. The failed connectors were examined and tested to find out the cause of the breakdown. Several samples of suspected bad connectors are also tested for comparison. Simulations using finite element software were conducted to provide broader insight on failure propagation. The investigation found that the dead end connectors were failed due to high current flowing through the steel part of the conductor which is caused by high contact resistance between the aluminium part of the conductor and the connector. Further study is needed to mitigate similar condition to occur in the dead end connector installation.

MILP Model of Electricity Distribution System Expansion Planning Considering Incentive Reliability Regulations

This paper aims at proposing a mixed-integer linear formulation to incorporate reliability-oriented costs into the expansion planning model of electricity distribution networks. In this respect, revenue lost associated with the undelivered energy caused by network interruptions as well as costs incurred by the widely used reward–penalty regulations is considered as the major reliability-related costs from distribution companies point of view. A set of mixed-integer linear equations is proposed to calculate the most common distribution system reliability indices, i.e., expected energy not served, system average interruption frequency index, and system average interruption duration index. It is found that these equations can also facilitate the formulation of radiality constraint in the presence of distributed generation units. Moreover, application of the proposed method is investigated through various case studies performed on two test distribution networks with 24 and 54 nodes.

A Method for Assessing the Risk of Accidents in 10/0.4-kV Electrical Networks

То improve the conditions of interdistrict 10/0.4-kV electrical networks, their condition was assessed according to such criteria as risk of electrical networks, risk assessment of power lines and transformer substations, and average undelivered energy, for which a method of assessment and calculation of the risks of accident of the power supply system was developed. Components of interdistrict electrical networks affect the occurrence of dangerous technogenic situations, creating risk-forming factors that can have different dimensions (rubles, W, MW h, etc.); may contain both numerical values and terms of the form “often,” “periodically,” “rarely,” and so on; and, therefore, are difficult to be take into account when working out the integral risk. This problem can be solved with the use of fuzzy logic—in particular, on the basis of the Fuzzy Toolbox 0.4.6 package. A point-linguistic system of risk factor assessment, a hierarchical structural scheme of an expert system for the assessment of dangerous technogenic situations as concerns power lines and substations, and a fuzzy inference system for the assessment of dangerous technogenic situations in relation to electrical installations of the Slavgorod interdistrict electrical networks were developed.

Impact of Q(U) and P(U) PV plants characteristics and power storage on connectable power in LV distribution networks

This study deals with autonomous voltage control in low-voltage (LV) networks using Q/U and P/U functions of inverters. The influence of Q/U and P/U parameterisation on connectable photovoltaic (PV) power plants power within the frame of medium-voltage/LV transforming station is analysed on a model of LV network. For the P/U control, an estimation of undelivered energy for 1 year due to power restriction in the modelled network is calculated. In variants with Q/U control, network losses are calculated for different characteristics. The next option for increasing PV power plants integration is considering the accumulation. On the basis of calculations performed, risk connected with autonomous PV power plants operation in LV networks was identified.

Path-set based optimal planning of new urban distribution networks

This paper presents a method for optimal planning of new urban distribution networks based upon the selection of the best subset of paths providing back feed from the entire path set generated for the available cable routes. The optimal solution is the path subset providing minimum total annual cost including capital recovery, loss and undelivered energy costs while satisfying all technical constraints. The impacts of distributed generator units, if available, can be also taken into account in the optimization flow. The reliability requirements are additionally assured by introducing SAIFI and SAIDI constraints. The method allows for common trenches for cables and different sizes of feeders depending on their loads. The planner is allowed to choose the concept of back feed, through only feeders interconnecting source nodes, ring feeders or by the best combination of these two structures. During the optimization process the optimal distribution system trees are generated providing minimum loss operation. The search for the optimal network is conducted using the simulated annealing algorithm.

Probabilistic evaluation of failure risk of transmission line surge arresters caused by lightning flash

Transmission line surge arresters (TLAs) are vital elements for protection of power networks against the lightning surges. The proper selection of TLAs leads to a reduction of the lightning-related outages as well as the costs imposed to the power utility, because of the undelivered energy and damage to the equipment. The selection of the optimal arrester depends on how well its stresses can be estimated. Although a ground flash very frequently consists of multiple strokes, it is usual to consider only a single lightning stroke to calculate the lightning-related failures. A probabilistic method is presented for risk calculation that considers multiple strokes of each lightning flash to estimate the annual outage rate of TLAs. In the presented method, once the equivalent wave of the flash is computed, the probability of arrester failure is estimated by means of two indices, including total charge and maximum energy stress by the flash, separately. The energy stress caused by the flash is calculated using a few electromagnetic transient program (EMTP) simulations. Then, the obtained results from EMTP simulation are utilised to estimate the probability of failure. The accurate evaluation of failure probability of arresters permits the power utility to select the optimal arresters, considering a desirable average life.

Reliability Assessment of EHV Gas-Insulated Transmission Lines: Effect of Redundancies

This paper deals with the reliability analysis of gas-insulated transmission lines (GIL). Two scheme alternatives of a GIL system have been investigated from a reliability standpoint. These configurations are of basic interest since they recognize how reliability performance may be improved by introducing redundancies at either the system level or at the unit level. Of course, reliability can only be increased with higher investment costs: these can be justified when a high level of transmission-line reliability is required. For the connection of a new powerplant to a node of the existing electric grid, the cost of undelivered energy can play a key role. Therefore, in the context of an electric energy market where the transmission grid ensures the efficient matching of demand and supply, a tool for evaluating the availability of a transmission line may be extremely important.

Optimal Planning of Radial Distribution Networks by Simulated Annealing Technique

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> A method for optimal planning of radial distribution networks is presented in detail based upon a combination of the steepest descent and the simulated annealing approaches. The object of investigation is the complete network of available routes and the optimization goal is to find the routes that provide the minimal total annual cost. The minimum capital cost oriented solution created by applying the steepest descent approach is used as the initial solution for the optimization procedure that is further improved by simulated annealing to obtain the minimum total cost solution. The method takes into account the capital recovery, energy loss and undelivered energy costs. </para>

Asset management of wood pole utility structures

This paper describes two probabilistic approaches for evaluating the economic impacts of alternative maintenance strategies, design strategies (design load), and compensation fees for undelivered energy. The first approach is based on simulating as function of time the statistical expected value of the number of pole replacements in each year due to climatic damage and maintenance replacements at regular inspection intervals. The second approach calculates the number of failed poles due to single large storms (wind, ice). Calculated examples show that the introduction of compensation fees for undelivered energy gives a strong incentive to carry out live line maintenance, and to design and construct mechanically stronger lines.

A Risk Management Procedure for Supply Restoration in Distribution Networks

A procedure for supply restoration in distribution networks based on fuzzy risk management is proposed in this paper. The introduction of fuzzy logic enables more realistic modeling of uncertainty in the acquaintance of network load and payback effect, while risk management provides higher quality of decision-making in the restoration process in such an uncertainty environment. The proposed algorithm is tested on several real-life distribution networks. The obtained results show that acceptance of a certain risk provides a reduction of expected costs due to undelivered energy during the process of supply restoration.

Technical and economical optimisation of overhead power distribution line lightning protection

The existing methodology for overhead line lightning protection design does not take into account customer and utility costs of line outages. In the paper a new concept of line lightning protection design based on economic optimisation is presented. Different tower types are analysed and for various undelivered energy participation factors optimal line design suggested. In line lightning flashover rate estimation both direct and induced surges are analysed.