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Hindawi International Transactions on Electrical Energy Systems Volume 2022, Article ID 8795100, 15 pages https://doi.org/10.1155/2022/8795100 Research Article Techno-Economic Assessment of Voltage Sags Mitigation in Distribution System Connected to DGs Elham M. Tantawy, Ebrahim A. Badran, and Mansour H. Abdel-Rahman Electric Engineering Department, Faculty of Engineering, Mansoura University, Mansoura, Egypt Correspondence should be addressed to Mansour H. Abdel-Rahman; email@example.com Received 7 January 2022; Revised 30 May 2022; Accepted 3 June 2022; Published 4 August 2022 Academic Editor: Ramesh Chand Bansal Copyright © 2022 Elham M. Tantawy et al. (is is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. (e penetration of DG in electrical distribution systems has many beneﬁts. (e paper highlights the impact of DG penetration at diﬀerent load centers and diﬀerent operating conditions in a distribution feeder. (e impact of DG penetration on feeder voltage proﬁle that depends on the size and location of DG in the system is illustrated. Mitigating methods are used to reduce the eﬀect of voltage disturbances. Economic assessment studies are used for assisting in the economic choice of mitigating methods. Economical aspects of distribution systems connected to DGs are considered through the analysis of the life cycle cost of these distribution generation sources. Maintenance strategies are illustrated and discussed to keep these sources always ready for operation regarding minimization of maintenance cost. Technical and economical assessments depend on the availability of historical data for disturbances cost including damages and cost of disturbance mitigation using diﬀerent mitigation methods. (ese data are diﬃcult to be available for diﬀerent types of loads. (erefore, load indices, K1, K2, and K3, are proposed in this paper for the diﬀerent loads as referring it to reference load has available data to overcome the challenge of data shortage. Also, a techno-economic assessment index F is proposed for the assessment of the impact of mitigating device improving cost and its feasibility. PSCAD/EMTDC simulation software package is used in this analysis. (e results show that the proposed techno- economic assessment methodology facilitates the decision of choosing the mitigation method for power quality problems and to overcome the challenge of data shortage in the techno-economic assessment. (e primary source of voltage sags observed on the 1. Introduction public network is the electrical short circuit occurring at Power quality is an important issue during the current any point in the electricity supply system. (e short circuit decades due to the mass use of electronic devices, and it’s causes a very large increase in the fault current, and this, more sensitive to voltage variations and the use of renewable in turn, gives rise to large voltage drops in the impedances resources for power generation . Electric power quality of the supply system. Short circuit faults are an un- disturbances are signiﬁcant economic consequences for avoidable occurrence on electricity systems. An example diﬀerent types of facilities. (e main terms that are used in of a voltage sag due to a downstream fault current is association with power quality are voltage sag, interruption, shown in Figure 2. long-duration supply interruption, transients, voltage un- (is results in some ﬁnancial compensation for parties balance, and harmonics [2–4]. incurring losses . Location of sag sources is crucial in Voltage sags are the most important power quality developing mitigation methods and deciding responsibili- ties. Technologies used for mitigating power quality are concerns for customers. According to IEEE standard 1159, Figure 1 illustrates deﬁnitions of voltage sags, swells, and translated in terms of cost and the expected improvements transients (IEEE 1159: 2009) as it is the RMS reduction in the in the system performance they can provide. (us, the AC voltage at power frequency from half of a cycle to a few improved performance is translated into economic beneﬁts. seconds’ duration. With the costs of the diﬀerent technologies and the expected 2 International Transactions on Electrical Energy Systems Transients Voltage swell Overvoltage 100 Normal operating voltage Transients Voltage sags Undervoltage Momentery Temporary Sustained interruption 10 ms 3 s 60 s Duration Figure 1: Denitions of voltage sags, swells, and transients (IEEE 1159: 2009). 12 24 36 48 60 72 84 96 108 120 132 144 156 168 180 192 –5 –10 –15 –20 Time [ms] Figure 2: Example of a voltage sag due to a downstream fault current (voltage waveform and RMS plot). benets, comparison of the dierent technologies yields the 2. In Section 3, the voltage sag analysis is introduced with best return on investment . explaining of losses, mitigation methods, and its economic e use of distributed generation (DG) as a source of considerations. For the techno-economic assessment, the active power in the system is eective to mitigate the voltage main challenge is the shortage of data. erefore, to over- regulation problems. e DG size and location in the system come this shortage, indices are proposed in Section 4. e validity of the proposed indices is tested via an electrical are important; otherwise, adverse eects, such as misoper- ation of protection relays, may occur [6, 7]. DG is used at distribution system. e techno-economic assessment is dierent positions and with dierent ratings. carried out using the proposed indices in both steady-state is paper introduces a technical and economical as- and fault conditions using PSCAD/EMTDC in Section 5. sessment of the voltage sag eect in the distribution system Finally, the main conclusions are given in Section 6. connected to DG. Life cycle cost analysis for mitigating equipment and renewable energy source is to be made to 2. Distributed Generation Background assist in the study of the economic assessment and taking the decision of choosing a mitigating method. erefore, the 2.1. Renewable DG Integration. Distribution generation is presented work proposes a fast preliminary assessment of “small-scale generating units located close to the loads that the economic and technical assessment of voltage sag are being served.” It can be classied as nonrenewable and mitigation. us, fast and eƒcient tools are necessary to renewable energy resources . e former includes re- analyze the feasibility of these systems in the most eective ciprocating engines, micro-turbines, combustion gas tur- and accurate way. Financial assessment is achieved when bines, fuel cells, and micro-combined heat and power (CHP) both the return on the total capital invested and the return plants. e latter includes biomass, wind, solar PV, geo- on the paid are at a suƒcient level of innovation. e study is thermal, and tide power plants . carried out in steady-state and fault conditions using Solar PV technologies require high capital investment PSCAD/EMTDC. cost. It has the advantages of long-life service and silent e paper is organized by starting with a background of operation. It requires low maintenance but is redundant . DG in electrical distribution systems in Section 2. en, the Wind turbine is classied as vertical axis wind turbines life cycle cost (LCC) model for main renewable DG tech- and horizontal axis wind turbines. It is characterized as nologies (solar and wind) energy is explained also in Section emissions-free and requires no fuel . Volt [V] Voltage (%) International Transactions on Electrical Energy Systems 3 Table 1: (e cost of renewable DG technologies [10, 11]. Capacity Capital cost Fuel cost Operation and maintenance cost Service life (kW) ($/kW) ($/kWh) ($/kWh) (years) Solar photovoltaic 100.0 6.675 0 0.005 20.0 Small-size wind turbine 10.0 3.866 0 0.005 20.0 Large-size wind turbine 1000.0 1500.0 0 0.005 20.0 Comparing DG with centralized generation, DG has the maintenance, spare parts, and overheads. Finally, the advantage of lower capital cost because of its small size, it can decommissioning stage has two choices either removing the be easily assembled and installed within a short time, and the turbines or replacing them with newer technology. (ere- power delivered can be increased or decreased by additional fore, the LCC model of wind farm is divided into four or removing modules . Also, DGs are connected very categories as wind turbines cost C , civil work and in- WT close to the load. (erefore, reduction in the cost of building stallation C , electrical apparatus C , and operation and civil Elec new transmission and distribution lines can be achieved. maintenance costs C as follows: O&M Additionally, the closeness to the load reduces the price of LCC � C + C + C + C . (2) WT Elec Civil O&M transporting electrical power to the load. When the DGs have excess power not needed by the load, the excess power is delivered to the grid. Table 1 illustrates the summary of 3. Voltage Sag Analysis some renewable DG technologies costs . (e characteristics of voltage sag are the voltage reduction magnitude and its duration. For single-phase systems and 2.2. Life Cycle Cost for Main Renewable DG Technologies. three-phase balanced systems, this characterization is ﬁne Life cycle cost (LCC) is important to assess the economic . Whereas for three-phase unbalanced sags, the three feasibility of engineering systems. Electrical energy systems individual phases would be aﬀected diﬀerently; hence, three require more capital investment and more operating costs diﬀerent magnitudes and three diﬀerent durations are found compared to other systems. Renewable energy sources such and the most aﬀected phase is taken as a measure of sag. (e as wind energy and solar energy have an important role in performance of voltage sags is obtained by the following: energy production scenarios. (e cost of energy systems includes the initial cost of delivering components of the (a) Long-term monitoring of voltages at system buses system, fuel, maintenance, wages, and other costs. (erefore, [15, 16]. It provides information about the expected the cost of kWh of electricity is determined. However, many severity and frequency of voltage disturbances. Also, it allows the utility to study the power quality level diﬀerent energy technologies exist for generating electricity (coal-ﬁred steam power plants, gas turbine combine-cycle and guide in a realistic way the investment in using devices for voltage sag mitigation [1, 6]. power plants, fuel cells, hydropower power plants, wind power, solar, and many others), and comparison between (b) Fault positions method which is a commonly used these diﬀerent technologies needs economic assessment for method for voltage sag estimation. Large number of each of these technologies . faults are generated throughout the power system, and corresponding magnitude and duration of sags are measured and computed. 2.2.1. LCC Model of Solar PV System. (e LCC model of solar PV system composed of the following cost categories: Voltage sags can be calculated and analyzed utilizing two planning C , PV panels C , electrical apparatus C , main types of simulation tools: custom-made tools usually Dev Panel Elec mounting structure and civil work C , in addition to Civil developed on commercial software platforms and general- operation and maintenance C  as follows: O&M purpose simulation packages, e.g., PSCAD/EMTDC. LCC � C + C + C + C . (1) panel Elec Civil O&M 3.1. Voltage Sag Losses. (e total losses caused due to voltage sag can be expressed according to the following equation: 2.2.2. LCC Model for Wind Farm. (e life cycle of wind farm Total losses � production losses passes through four stages: development stage, imple- + restart losses + losses of spoiled materials mentation stage, operation stage, and decommissioning stage . (e development stage starts by ﬁnding suitable + cost of damage + other costs. site that has suitable wind characteristics. (en, starting the (3) design, prepare the equipment and construct it where the whole capital is used. Next is the operation stage which is the (e nominal loss value of an industrial process “maxi- longest stage; hence, the design continues to last for 20 to mum loss value” is deﬁned as the ﬁnancial loss incurred due 25 years during this, and the costs are distributed on to process interruption during peak production period 4 International Transactions on Electrical Energy Systems [9, 17, 18]. Two main parameters are needed to estimate (e payback period measure shows the period (e.g., ﬁnancial loss caused by voltage sag and short interruption number of months) of beneﬁts required for the project to which are the nominal loss value and process failure risk. It is break even . It is calculated for a voltage sag mitigation given  by the following equation: solution as follows: (IC × 12) Expected Financial Loss per Sag � Nominal Loss PP � . (8) (A − AOC) × Process failure Risk. Generally, a solution having the least payback period is (4) mostly preferred. (e nominal loss for existing customers in the system is determined from customer surveys. Having analyzed the 3.3. Voltage Sag Mitigation. As the electrical loads in the results from the survey, three categories of voltage sag proﬁle electrical distribution systems include electronic devices and were resulted as most meaningful for estimation of costs components, power quality is to be improved by using which are as follows : suitable fast response compensator as Static VAR Com- (1) Group A includes 10 or less voltage sags per year pensator (SVC), thyristor control series compensator with residual voltage less than 40% of nominal for (TCSC), and UPFC (Uniﬁed Power Flow Controller), sag duration shorter than 100 ms STATCOM, and (DVR) dynamic voltage resistor. (e major (2) Group B includes 10 or less voltage sags per year with technologies available for voltage sag mitigation are [7, 24] residual voltage less than 40% of nominal for sag Uninterruptible Power Supplies (UPS), Static Transfer duration shorter than 100 ms and 5 or less voltage Switch (STS), Sag Prooﬁng Transformer, Dynamic Voltage sags per year with residual voltage less than 70% of Restorer (DVR), and STATCOM. nominal and duration ranging from 100 ms to Equations (9)–(12) illustrate the cost functions for SVC, 300 ms TCSC, and UPFC and STATCOM in $/kVAR . Also, Table 2 illustrates a sample of data for cost of some miti- (3) Group C includes 1 interruption with duration of 3 gation devices. minutes or more ∗ 2 ∗ � 53.2 S + 5.856 S + 220.22, STATCOM STATCOM STATCOM 3.2. Voltage Sag Economic Analysis. Economic analysis for (9) any investigated system can be evaluated using the net ∗ 2 ∗ present value method [19, 20]. (e mathematical expression (10) C � 53.2 S + 7.833 S + 0.33894, SVC SVC SVC to evaluate the NPV is reported [21, 22] as follows: ∗ 2 ∗ C � 0.0015 S − 0.713 S + 153.75, (11) TCSC TCSC TCSC NPV � − C , (5) (1 + i) y�1 ∗ 2 ∗ C � 0.0003 S − 0.2691 S + 188.22. (12) UPFC UOFC UPFC where C is the cash ﬂow when the time is zero, C is the year 0 y Economically, the value of the service provided is the cash ﬂow, i is the interest rate, and y is the year of most important parameter in voltage sag management given investment. by equation (13). (e positive value indicates a gain in return (us, the NPV sign positive or negative indicates the of investment for voltage sag mitigation. Maximizing the feasibility of the investment and therefore the economic “value of service” brings maximum proﬁt . convenience. Beneﬁt-cost ratio (B/C) and payback period (PP) are two Optimum case � Min.(Sag financial loss (13) economic measures used for the optimal selection of voltage + Cost of Mitigation), sag mitigation solutions [19, 23]. (e beneﬁt-cost ratio (B/C) is an economic measure that illustrates the feasibility of Value of service � Initial financial losses using the voltage sag mitigation solution. It is given by  − (Cost of mitigation + Resideual losses). B A × W × T (6) � , (14) C IC + AOC × W × T T − t 1 + I (7) W � , 3.4. Economic Analysis of Voltage Sag Mitigation. To make economic study for voltage sag mitigation technologies, cost where A is the saved annual cost accumulated/year after of equipment operation and maintenance is a major item to employing a mitigation solution, W is the present worth be considered. Maintenance is deﬁned as a combination of factor, I is the annual interest rate, t is the time period in all technical, administrative, and managerial actions during years, AOC is the cost of the annual operation, IC is the cost the life period of equipment. For example, the annual cost of of investment solution, and T is the mitigation devices’ maintenance for STATCOM s is 5% of its capital cost per lifetime. kVA . However, maintenance and operation cost for International Transactions on Electrical Energy Systems 5 Table 2: e cost of voltage sag mitigation devices . Typical cost Mitigation device Equipment cost ($) Operating and maintenance cost ($) of initial cost per year Facility protection (2–10 MVA) DVR (50% voltage boost) 300.0/kVA 5.0% Static switch (10 MVA) 600,000 5.0% Fast transfer switch (10 MVA) 150,000 5.0% Failure starts Potential to occure Failure P Preventive scheduled maintenance Preventive condition based maintenece Function Faiure F F Corrective maintenance Gradual failure PF interval Time Time (a) (b) Figure 3: System condition during its life period with adopting maintenance . wind energy and PV energy as a renewable energy source is combination of all technical, administrative, and managerial actions during the life period of an item intended to retain it more than STATCOM [14, 15]. or restore it in a state in which it can perform the required function . 3.4.1. Life Cycle Costing (LCC) Model for Equipment. As previously mentioned in Section 2.2.2, the LCC model of 3.4.2. Maintenance Types. Maintenance is essentially clas- equipment is also divided into four categories: development sied as preventive maintenance and corrective mainte- costs C , equipment C , installation C , and operation Dev eq in nance. Preventive maintenance is classied as preventive and maintenance costs C . scheduled maintenance and preventive condition-based LCC C + C + C + C . (15) Dev eq in. M maintenance . (a) Preventive maintenance e condition of any equipment and its components with its operation during its life period can be represented as Preventive maintenance (PM) is dened as the illustrated in Figure 3. As shown in Figure 3(a), any maintenance, which is carried out before failures equipment starts its operation in new condition. As the time occur. It is divided into the following: of its operation increases, its eƒciency begins to decrease, (i) Preventive scheduled maintenance: it is carried and as the time of operation passed, its condition is dete- out according to an established time schedule riorated, and this can be represented by a decaying curve (ii) Preventive condition-based maintenance: it is (condition versus time). is curve may be straight line or in based on the performance and parameter system general as shown in Figure 3(b). After a certain time interval, components monitoring for the prediction when it becomes in condition less than new and some spare parts maintenance is needed  require replacement, and this is represented at the rst point on the curve (failure starts to occur). As the time of oper- (b) Corrective maintenance ation increases more, the equipment condition will be less Corrective maintenance (CM), which is the main- till the indicated potential failure point, repair is required at tenance carried out after fault to put the item into a the indicated functional failure F, and the equipment re- state to perform components required function . quires major maintenance or to be replaced. Figure 3(b) shows system condition during its life period with adopting preventive and corrective maintenance according to the 3.4.3. Maintenance Cost Optimization. e main objective system time schedule. for maintenance optimization is as follows : To put the system and its components in a ready state of (a) e total costs for maintenance must be minimized operation during its life period, the following maintenance types are made and scheduled. Maintenance is the main (b) e maintenance should be done to have high factor that any system will be in a ready state for operation availability and safety operation of the equipment. during its life period. Maintenance is dened as a Maintenance cost must be as low as possible Condition Condition [%] 6 International Transactions on Electrical Energy Systems (c) e equipment after maintenance should have a long lifetime Total cost Hence, it is required to balance between preventive and Cost for preventive maintenance corrective maintenance regarding the relationship between those maintenance types. Figure 4 illustrates the total cost Cost for corrective maintenance required in relation with maintenance. Minimization of total maintenance cost through Amount of maintenance equipment life period and due to its use and operation is Figure 4: Balance between preventive and corrective maintenance required, as it deteriorates, as shown in Figure 4. is de- [10, 17]. terioration is measured as the increase in the operation and maintenance (O&M) costs . ese costs will reach a value at which it is preferred economically to replace the equip- (c) Annual cost of system voltage disturbances after ment. is requires to have an optimal replacement policy mitigation is computed. for total cost minimization. e equipment components (d) e total annual cost improvements of electrical should be replaced by an identical one to return the system performance are obtained. equipment in new condition after replacement. erefore, the techno-economic assessment requires comparison between costs associated with the impact of 4. Techno-Economic Assessment for Voltage disturbance (damages and costs associated with interrup- Sag Mitigation tion) and the cost of equipment required to improve the technical performance. Figure 5 illustrates annual outages Techno-economic assessment for voltage sag mitigation and its cost on the right side, and the left side represents the depends on the availability of historical data for disturbances cost of mitigating equipment. en, cost-benet analysis cost including damages and cost of disturbance mitigation (comparison between these two costs) is considered to have using dierent mitigation techniques. ese data are diƒcult the feasible techno-economic solution. to be available for dierent types of loads. 4.2. Proposed Load Indices. e main challenge for good techno-economic assessment is the availability of data. 4.1. Requirements of Techno-Economic Assessment. e re- erefore, it is proposed in this paper to formulate load quirements for adopting any techno-economic assessment indices for any load data depending on the reference load depend on data collection, data analysis and report, and data. erefore, it is proposed to use the following proposed project formulation. indices as given in the next sections. Technical assessment is carried out according to the e proposed indices are used to overcome the shortage following: of data for dierent electrical loads. e proposed strategy (a) e electrical distribution system is simulated for techno-economic assessment of DG in electrical distri- bution systems started with data collection for the distur- (b) e bus voltages are obtained by running load §ow bances occurred in the dierent industries and the outages analysis occurred. Field data are collected from project owners, (c) Dierent FACTS are considered with dierent size construction industry consultants, contractors, and working and the voltage proles are obtained engineers. e collected (quantitative) data were gathered by (d) e electrical losses are calculated for each value of face-to-face interviews, online contact, mail, and phone. DG at each bus In Figure 6, the electrical loads are classied into dif- (e) e impact of mitigating device is given by the ferent sectors such as industrial and commercial. Each sector analysis and comparison with the obtained results concerns dierent types of loads, e.g., industrial sector in- cludes paper industry, textile, and chemical. (f) e impact of DG penetration is given by the analysis and comparison with the obtained results (g) Technical system improvement in voltage system 4.2.1. Reference Load Data. Load indices are dened as the prole is given by system electrical losses and system ratio between certain reference energy consumption of disturbances after mitigation is obtained dierent types of events (categories A, B, and C) for resi- dential, commercial, industrial, ..., etc. Economical assessment is carried out according to the Semiconductor industrial load is taken as reference load following: as shown in Figure 6 as it has complete and enough historical (a) Annual cost of system voltage disturbances before data about system supply interruption cost, and disturbances mitigation is computed cost is taken as the annual reference load energy con- (b) Mitigating devices that include annual initial in- sumption which is (Y) MWh. erefore, load in the same reference load sector suers from shortage in data and has an vestment cost, annual repair, and maintenance cost are determined. annual load energy consumption of (X) MWh. Cost International Transactions on Electrical Energy Systems 7 Techno-economic assessment analysis Annual process outage Mitigation methods Annual cost process outage Cost of mitigation Cost beneﬁt analysis Best techno-economic solution Figure 5: Major aspects to nd the best techno-economic solution. Electrical loads Load sector K1 , …... Industerial Commercial Residential Load Type K2 Semiconductor Chemical Paper Textile , …... Figure 6: Distribution system electrical loads. Table 3: Weighting factors for dierent categories of voltage sag [5, 21]. Event category Interruptions Category A Category B Category C Weight of disturbance 1 0.8 0.4 0.1 4.2.2. Še Proposed Load Sector Index (K1). It is proposed 4.2.4. Še Proposed Disturbance Type Cost Index (K3). that k1 is the ratio between the annual energy consumption Due to the common availability interruption event cost in of the load, and the annual energy consumption in the electrical loads, K3 is the voltage sag event cost referred to reference load (X/Y) is the load sector index. erefore, the voltage sag event interruption cost. erefore, annual energy consumption of the load Voltage sag Event cost K1 . K3 . (19) annual energy consumption of the refrence load Voltage sag Event Interruption cost (16) Table 3 gives the weighting factors for the cost of the voltage sag event that are expressed in per unit of the cost of en, the load sector index can be used to dene the cost the interruption. e weighted events can then be assumed of interruption of certain load through the following . K3 is used to calculate the number of equivalent in- equation: terruptions to get the total cost of all the events using the Interrupion cost event in certain load interruption cost. Table 3 illustrates an example of the (17) weighting factors or dierent voltage variations referred to K1 interruption cost of refrence load. as interruption [5, 21]. For the dierent types of loads of the dierent load sectors, it is proposed that 4.2.3. Še Proposed Load Type Index (K2). It is proposed that interrupion cost event of certain load K2 is the load type index, which is the ratio between the ∗ ∗ annual energy consumption of the load sector and the K1 K2 equivalent interruption disturbances (20) annual energy consumption in the reference load sector. interruption cost of refrence. erefore, annual energy consumption of this load sector K2 . 4.3. Še Proposed Methodology of System Data Preparation. annualenergy consumption of the reference load sector Using the proposed indices given in Section 4.2 (K1, K2, and (18) K3), the required data can be calculated to overcome the 8 International Transactions on Electrical Energy Systems Technical and Economical assessment data Input system data Yes Data known No Input reference system data Select type of load and load sector and calculate K1 and K2 annual energy comsumption of the load K1 = annual energy comsumption of ref.load annual energy comsumption of this load sector K2 = annual energy comsumption of reference load sector Calculate the equivalent interruption disturbances by K3 Voltage sag Event cost K3 = Voltage sag Event Interruption cost Input interruption cost interruption cost event in certain load = K1 K2 equivalent interruption disturbances interruption cost of reference load * * * Calculate losses Input Mitigation devices data Select Mitigation device and calculate the annual cost of the selected device Apply next mitigation device No Techno-economic assessment index < 1 Yes Accepted choice Figure 7: e §owchart of the proposed techno-economic assessment. International Transactions on Electrical Energy Systems 9 Bus 1 Bus 2 Bus 3 Bus 4 Load 1 Load 2 Load 3 Load 4 0.5 MW 1.0 MW 1.5 MW 4 MW (a) RL RL RL RL 0.5 [MW] 1.0 [MW] 1.5 [MW] 4 [MW] (b) Figure 8: e test system. (a) e radial distribution test system; (b) test system model in PSCAD/EMTDC. 1.022 1.03 1.02 1.01 1 0.991 0.99 0.977 0.973 0.98 0.97 0.96 0.95 0.94 Bus 1 Bus 2 Bus 3 Bus 4 Figure 9: e distribution’s network voltage prole without DG. 1.005 1.015 1.01 1.005 0.995 0.99 0.995 0.985 0.99 0.985 0.98 0.98 0.975 0.975 0.97 0.97 0.965 0.965 Bus 1 Bus 2 Bus 3 Bus 4 Bus 1 Bus 2 Bus 3 Bus 4 4 MW 6.5 MW 4 MW 6.5 MW 5.5 MW 7 MW 5.5 MW 7 MW (a) (b) 1.02 1.04 1.03 1.01 1.02 1.01 0.99 0.99 0.98 0.98 0.97 0.97 0.96 0.96 0.95 0.95 0.94 Bus 1 Bus 2 Bus 3 Bus 4 Bus 1 Bus 2 Bus 3 Bus 4 4 MW 6.5 MW 4 MW 6.5 MW 5.5 MW 7 MW 5.5 MW 7 MW (c) (d) Figure 10: e distribution network voltage prole with connected DG. (a) DG is connected at bus 4; (b) DG is connected at bus 3; (c) DG is connected at bus 2; (d) DG is connected at bus 1. Voltage [PU] Voltage [PU] Voltage [PU] Voltage [PU] Voltagr [PU] 10 International Transactions on Electrical Energy Systems Table 4: Summary of simulation results of dierent values of DG at dierent places. Voltage level (PU) DG location DG value (MW) Bus 1 Bus 2 Bus 3 Bus 4 No DG 0 1.022 0.991 0.977 0.973 4 1.002 0.982 0.979 0.986 5.5 1 0.981 0.98 0.988 Bus 4 6.5 0.99 0.98 0.98 0.99 7 0.995 0.98 0.981 0.993 4 1.008 0.988 0.984 0.98 5.5 1.006 0.987 0.986 0.981 Bus 3 6.5 1.005 0.987 0.987 0.983 7 1.003 0.988 0.99 0.985 4 1.015 0.996 0.981 0.977 5.5 1.015 0.997 0.981 0.978 Bus 2 6.5 1.014 0.998 0.983 0.979 7 1.014 1 0.984 0.98 4 1.024 0.994 0.979 0.975 5.5 1.027 0.997 0.981 0.978 Bus 1 6.5 1.026 0.995 0.98 0.977 7 1.027 0.996 0.981 0.978 Table 5: System losses of dierent values of DG at dierent locations. Losses (PU) DG location Bus 4 Bus 3 Bus 2 Bus 1 0 MW 1.02 4 MW 0.35 0.36 0.515 0.99 DG value 5.5 MW 0.37 0.303 0.503 0.99 6.5 MW 0.0864 0.0121 0.2 1.02 7 MW 0.33 0.225 0.4 1.02 Losses 1.2 0.8 0.6 0.4 0.2 0 MW 4 MW 5.5 MW 6.5 MW 7 MW DG Value Bus 2 Bus 4 Bus 1 Bus 3 Figure 11: System losses due to dierent values of DG at dierent locations of the system. problem of data shortage. Figure 7 shows the §owchart for the total annual cost of each scenario for voltage sag miti- the steps adopted for preparing the data used in techno- gation and its corresponding net annual cost of improve- economic assessment for voltage sag mitigation in distri- ments are computed, the analysis and comparison of the bution systems which suer from shortage in historical data obtained results illustrate the impact of the mitigating device about cost of voltage sag disturbances. and its feasibility. cost of voltage sag improvement F . (21) 4.3.1. Še Proposed Techno-Economic Assessment Index (F). the annual cost of mitigation scenario used It is proposed that the techno-economic assessment index is the cost of voltage sag improvements referred to the annual erefore, for feasible solutions F, it is more than 1, and for nonfeasible solutions, it is less than 1. cost of mitigation scenario used as given in equation (21). As Losses [PU] International Transactions on Electrical Energy Systems 11 Table 6: Summary of simulation results of diﬀerent values of DG and places when three-phase fault happens at each bus. Fault at bus 1 Fault at bus 2 Fault at bus 3 Fault at bus 4 DG value MW Bus1 Bus2 Bus3 Bus4 Bus1 Bus2 Bus3 Bus4 Bus1 Bus2 Bus3 Bus4 Bus1 Bus2 Bus3 Bus4 (PU) (PU) (PU) (PU) (PU) (PU) (PU) (PU) (PU) (PU) (PU) (PU) (PU) (PU) (PU) (PU) DG 0 0.594 0.588 0.585 0.575 0.596 0.591 0.58 0.582 0.635 0.59 0.586 0.59 0.627 0.6 0.59 0.588 location 2 0.601 0.593 0.591 0.6 0.602 0.592 0.593 0.6 0.609 0.592 0.592 0.605 0.636 0.6 0.592 0.598 DG at bus 4 0.597 0.591 0.595 0.604 0.599 0.59 0.593 0.605 0.611 0.592 0.594 0.605 0.637 0.597 0.593 0.6 4 5.5 0.598 0.59 0.595 0.605 0.597 0.591 0.595 0.605 0.611 0.593 0.595 0.607 0.644 0.601 0.592 0.603 7 0.602 0.595 0.6 0.611 0.602 0.596 0.601 0.609 0.612 0.595 0.596 0.612 0.645 0.603 0.594 0.606 2 0.605 0.595 0.596 0.593 0.603 0.595 0.595 0.593 0.611 0.595 0.597 0.593 0.645 0.597 0.594 0.592 DG at bus 4 0.604 0.595 0.597 0.595 0.603 0.595 0.599 0.596 0.613 0.592 0.6 0.597 0.642 0.601 0.595 0.593 3 5.5 0.603 0.596 0.601 0.596 0.602 0.594 0.601 0.596 0.613 0.594 0.601 0.597 0.643 0.602 0.596 0.593 7 0.605 0.597 0.605 0.604 0.604 0.595 0.604 0.602 0.614 0.596 0.603 0.601 0.645 0.604 0.599 0.596 2 0.607 0.6 0.591 0.587 0.608 0.595 0.59 0.591 0.619 0.600 0.591 0.591 0.65 0.608 0.592 0.591 DG at bus 4 0.608 0.6 0.593 0.59 0.606 0.599 0.591 0.589 0.620 0.601 0.592 0.592 0.651 0.612 0.593 0.592 2 5.5 0.605 0.603 0.592 0.59 0.608 0.599 0.593 0.59 0.619 0.601 0.593 0.592 0.653 0.615 0.595 0.594 7 0.608 0.606 0.595 0.593 0.609 0.601 0.596 0.593 0.621 0.603 0.594 0.594 0.656 0.616 0.595 0.595 2 0.613 0.595 0.585 0.583 0.609 0.594 0.586 0.584 0.627 0.598 0.591 0.591 0.659 0.609 0.592 0.591 DG at bus 4 0.614 0.594 0.587 0.584 0.611 0.594 0.585 0.585 0.63 0.599 0.592 0.593 0.66 0.610 0.593 0.592 1 5.5 0.615 0.594 0.586 0.585 0.614 0.595 0.587 0.583 0.632 0.6 0.592 0.592 0.662 0.611 0.595 0.593 7 0.615 0.596 0.589 0.586 0.615 0.596 0.589 0.591 0.636 0.601 0.593 0.593 0.663 0.612 0.596 0.595 12 International Transactions on Electrical Energy Systems Fault at bus 1 Fault at bus 2 0.62 0.62 0.61 0.61 0.6 0.6 0.59 0.59 0.58 0.58 0.57 0.57 0.56 0.56 2 4 5.5 7 2 4 5.5 7 2 4 5.5 7 2 4 5.5 7 2 4 5.5 7 2 4 5.5 7 2 4 5.5 7 2 4 5.5 7 DG at bus 4 DG at bus 3 DG at bus 2 DG at bus 1 DG at bus 4 DG at bus 3 DG at bus 2 DG at bus 1 Bus1 Bus3 Bus1 Bus3 Bus2 Bus4 Bus2 Bus4 (a) (b) Fault at bus 3 Fault at bus 4 0.64 0.68 0.66 0.62 0.64 0.62 0.6 0.6 0.58 0.58 0.56 0.56 0.54 2 4 5.5 7 2 4 5.5 7 2 4 5.5 7 2 4 5.5 7 2 4 5.5 7 2 4 5.5 7 2 4 5.5 7 2 4 5.5 7 DG at bus 4 DG at bus 3 DG at bus 2 DG at bus 1 DG at bus 4 DG at bus 3 DG at bus 2 DG at bus 1 Bus1 Bus3 Bus1 Bus3 Bus2 Bus4 Bus2 Bus4 (c) (d) Figure 12: Voltages for each bus of dierent values and dierent places of DG when three-phase fault happens at dierent buses. (a) DG is connected at bus 1; (b) DG is connected at bus 2; (c) DG is connected at bus 3; (d) DG is connected at bus 4. Figure 9 shows the voltage for the system buses without 5. Application of the Proposed Techno- DG connection. Figures 10(a)–10(d) illustrate the system Economic Assessment Method buses voltages with dierent values of DGs connected at For the validity of the proposed strategy, a radial distribution buses 1, 2, 3, and 4, respectively. feeder, shown in Figure 8(a), is used. e feeder feeds four Simulation of results indicates that the connected DG electrical loads which are part of IEEE 34 electrical bus dis- shares the responsibility of supplying the required demand with the substation. e summary of the simulation results is tribution system . e system is simulated by PSCAD/ EMTDC as shown in Figure 8(b). e simulation is veried by given in Table 4. Table 5 and Figure 11 illustrate the system losses for dierent values of DG at dierent locations. It can comparing the results of studying the system operation at normal condition with that published in . e close be seen that the DG reduces the losses due to close proximity to loads. Installing DGs close to loads and in modular sizes agreement between both results is achieved. Dierent oper- ating scenarios with DG of less than 10 MW capacity con- matches the local load or energy requirement of the cus- tomer, and reduction of transmission and distribution losses nected directly at the dierent system buses are considered. is achieved. Also, simulation is run considering cases of three-phase 5.1. Results of Voltage Sag Technical Assessment with DG fault through resistance at dierent buses at dierent lo- Connected. e simulation is carried out in the following cations. Table 6 illustrates the summary of simulation results cases: of dierent values of DG and places when three-phase fault happens at each bus. Figure 12 shows the relation of bus (a) Without inserting the DG into the system and the voltages for dierent values and dierent locations of DG voltage at each bus is measured when three-phase fault occurs at the dierent system buses. (b) With implementing the DG with dierent values and It is noticed that the least electrical losses and best voltage at the dierent buses and the voltage at each bus is prole occur at bus 3 with DG value of 6.5 MW. It is clear measured that the implementation of DG as an active power source has (c) With implementing the DG with dierent values and an impact on improving the buses voltage in the distribution at the dierent buses with three-phase faults through network. resistance at dierent buses and the voltage at each A number of cases of technical studies are simulated on bus is measured radial distribution system while the change of the size and Voltage [PU] Voltage [PU] Voltage [PU] Voltage [PU] International Transactions on Electrical Energy Systems 13 Table 7: Data of the system events. Total equivalent Event Interruptions Voltage sag category A Voltage sag category B Voltage sag category C events Annual events 4 5 7 2 11 K 1 0.8 0.4 0.1 Equivalent event of 4 4 2.8 0.2 interruption Table 8: Data of the reference and other loads investigated. Ref. load data Load 1 Load 2 Load Industrial Industrial Commercial Load sector Semiconductor Semiconductor — Electrical annual energy consumption 100 MWh 35 MWh 20 MWh k 1 1 0.2 K 1 0.35 — Table 9: Improvement cost of the disturbances. Equivalent interruption Disturbances cost Improvement cost System events 11 192500 — 20% improvement 8.8 154000 38500 $ Table 10: (e total cost per year for each diﬀerent types of mitigation device. Cost through 5 years $ O & M cost/year $ Cost/year $ Total cost/year $ DVR 3000000 150000 600000 750000 Static switch 600000 300000 120000 1500000 Fast transfer switch 150000 75000 30000 375000 STATCOM 5598.78 279.93 1119.75 1399.69 SVC 5398.66 269.93 1079.73 1349.66 TCSC 149440.75 7472.03 29888.15 37360.18 UPFC 27497.22 1374.86 5499.44 6874.30 Table 11: (e saving due to the use of the diﬀerent mitigation devices in case of 20% improvement. Saving $ Techno-economic assessment index F Feasible Not feasible DVR − 711500 <1 x Static switch − 1461500 <1 x Fast transfer switch − 336500 <1 x STATCOM 37100.31 >1 x SVC 37150.34 >1 x TCSC 1139.82 >1 x UPFC 31625.7 >1 x location of DG in the system occurred. DGs connected very the data of the reference load, L1 and L2. K3 is calculated close to the load are the best case. (ey reduce the losses and with the total number of events based on interruptions in cost of building a new transmission and distribution lines. Table 3. Load indices K1 and K2 are calculated and given in Also, DG improves power quality and reliability. Table 8 from equations (17) and (20). (e cost per one event of interruption is 50000 $ for the reference load as it is a semiconductor industrial load with 5.2. Results of Techno-Economic System Assessment. For data electrical annual energy consumption of 100 MWh . (e preparation of the system studied shown in Figure 8, as- improvement cost of 20% improvement is illustrated in suming load 1 is a semiconductor industrial load has 18 Table 9. (e equivalent interruption event is improved from events of voltage sag disturbances per year which are clas- 11 events to 8.8 events and the disturbance cost from 192500 siﬁed as illustrated in Table 7. Based on the disturbances $ to 154000 $. weights index K3 given in Table 3, the system equivalent It is assumed that the 20% improving in this system events are 11 interruption events per year. Table 8 illustrates required 10 MVA, and the total cost per year for each 14 International Transactions on Electrical Energy Systems mitigation device is calculated from Table 2 and equations References (9)–(12) as illustrated in Table 10.  I. Leisse, O. Samuelsson, and J. 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