Effects of integration of distributed generation on reliability in distribution system

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INTRODUCTION
Every power utility's primary goal is to offer electricity to customers in a way that is both economical and reliable.The cost of power supply interruptions to customers will decrease as a result of effective planning and maintenance of a reliable energy supply.Reliability plays a critical role in planning and design of a distribution system, which will function cost-effectively with few interruptions to customer loads [1].According to the reports that have been published in the literature, distribution system failures are responsible for around 80% of customer interruptions.As a result, both from a technical and financial standpoint, the reliability of distribution networks is regarded as one of the most major challenges.For this reason, to be in competition, the service company will see for means to reduce expenses and also supply the suitable level of reliability for its consumers [2].The main function of electrical utility company operating in Int J Pow Elec & Dri Syst ISSN: 2088-8694  Effects of integration of distributed generation on reliability in distribution … (Rudresha Sogilu Jayappa) 499 a deregulated atmosphere is to rise the market value of facilities it offers to customers.This can be done by building new, more affordable electrical infrastructure and offering reliable electricity at lower operational and maintenance costs [3].All of these aspects will contribute to lower customer billing, which is likely to increase customer satisfaction.One of the ways by which above objective can be met is integration of distributed generation (DG) [4].Many researches are done to find the benefits of DG integration into the electrical system [5].Presently, DG technology is inviting the power engineer as a substitute for the conventional central power supply, to reduce voltage drop, losses and recover the reliability in the system.DG is also known as dispersed generation, is a kind of small generation that is primarily linked at the distribution system's end user.To ensure a more reliable supply, DG will be easily accessible during system failure [6].
Doung et al. [7] ideal position and size of solar units in radial distribution systems (RDS) is explained.Using the power stability index to identify key buses, the best DG placements are discovered in [8].To locate and raise the voltage profile in the system, modified voltage index is employed in [9], and mixed-integer nonlinear programming is used to explain the optimization problem.The researcher [10] a broad analysis of the voltage stability indices is given.The words in [11] the various optimization techniques are explained and in [12] a cuckoo search algorithm is used to resolve the best DG location difficulty.The authors in [13]- [15] a various solution to multi-objective optimal placement DG problem of power distribution networks is addressed.
A number of reliability indices, including the system average interruption duration index (SAIDI), customer average interruption duration index (CAIDI), average service availability index (ASAI), system average interruption frequency index (SAIFI) and average service unavailability index (ASUI) [16] are used to estimate the system's reliability.The studies of power system reliability employs a variety of methodologies [17].Mathematical models are used in analytical methodologies to measure the reliability of electrical distribution systems.In addition to thermal overloads, the analytical method based on emergency enumeration can detect voltage collapse issues.However, the enumeration approach must make a number of simplifying assumptions because it is unable to describe a broad range of operational situations [18].
For evaluating the system's reliability, Monte Carlo simulation has a number of benefits that become more obvious when DGs are heavily integrated into the system.The various operational problems that DGs pose are avoided using Monte Carlo simulation.However the transmission outages, voltage drop and voltage collapse issues is not possible to model in this technique [19].The significant assistances of this paper depend on development of loss sensitivity factor (LSF) based method for optimal DG incorporation and reliability analysis based on following important issues: − A position of DG is considered in distribution system to reduce the overall losses, which intern reduces the cost in the system.− Voltage at various buses in the distribution system is considered.− Reliability indices of the system are considered.− The proposed method's ease of use, accuracy, and suitability for use in practical distribution systems must be considered.
The next part of the paper is organized as follows: i) Section 2 gives the definitions of reliability indices; ii) Section 3 presents the problem statement; iii) Section 4 provides the proposed DG placement and sizing approach; iv) Section 5 gives simulation results and discussion; and v) The conclusions and remarks are given in section 6.

RELIABILITY INDICES
The distribution system's main goal is to provide the consumer with continuous power supply.The frequency of interruptions, the length of each interruption, and overall power lost throughout the interruptions are used to evaluate the power system's reliability indices.The commonly used distribution indices comprise SAIDI, SAIFI, CAIDI, ASUI and ASAI and are described below [20]

PROBLEM STATEMENT
This manuscript examines a real-world distribution feeder that runs from the 110/11 KV Alkola substation near Shivamogga in Karnataka.The feeder contains 41 distribution transformers and a maximum load of 1.987 MW and 0.626 MVAR.As the population grows, the demand on the distribution system also grows over time, this result in rise of system loss and fall in voltage in system.The purchaser at the end bus will experience a low voltage issue, where the voltage is below the permitted boundary as a result supply to the customer gets affected, which results in interrupted power supply to the consumer.By placing DG at the user end, the voltage at the buses will be improved, and the system's overall loss will be reduced, which further provides the reliable supply to the consumer [21], [22].
This study investigates the major uncertainties faced by the customer in the real-world distribution feeder, which are low voltage level and more system losses.The voltage in the practical feeder is shown in Figure 1 and its daily load curve is shown in Figure 2. According to standard rule, we used 6% variable voltage throughout analysis, which corresponds to Vmin = 0.94 pu and Vmax = 1.06 pu.In subsequent section we'll demonstrate how the best DG size and placement affect the voltage level at the various buses in the power system, which intern affect the reliability of the distribution system.Effects of integration of distributed generation on reliability in distribution … (Rudresha Sogilu Jayappa) 501 system.The formula to determine the loss sensitivity factor (LSF) for a particular system after the size of the DG is changed from PDG1 to PDG2, and resulting variation in power loss is from PL1 to PL2 and is given by [23].
In this study, the Sensitivity factor is determined for each bus by applying above equation.The bus with the greatest sensitivity is then identified, and other buses with sensitivity factor that are extremely close to the highest value are chosen for study.Then, change the DG size with high values at each of these chosen buses to determine power loss.The best position is on the bus that has the lowest loss for each DG size, and the ideal DG size corresponds to that generation [24], [25].The Computational procedure for the Proposed Methodology is shown in Figure 3.

RESULTS AND DISCUSSION
− Case-1: Analysis of practical system without DG One of the 11 KV practical distribution feeder from Alkola substation in Shivamooga, Karnataka, is having 41-bus is simulated in PWS software.The reliability analysis of this feeder is studied without and with position of DG.Excluding DG, active-and reactive-power loss is 0.1334 MW and 0.096 MVAR respectively and lowest system voltage is 0.8978 pu at maximum load.− Case-2: Analysis of practical system with Incorporation of DG unit (solar PV unit) The simulation model of practical feeder using PWS is displayed in Figure 4.The projected LSF method is used to discover best place and size of DG.The best location attained in this process is at bus 18 and DG size is 30% of whole generation without DG.The ideal DG position and size found in this technique is bus-18 and 0.633 MW respectively.In this case the solar PV module can be used as a DG unit which can supply power from morning 9 am to 5 pm in load curve, which will reduce the burden on the central grid and will improve the reliability of the system.
The outcomes, obtained with and without DG employment, are presented in Table 1.After DG employment the active power loss is decreased to 0.0783 MW, reactive power loss is condensed to 0.0589 MVAR and lower most system voltage is enhanced to 0.9405 p u from 0.8978 pu.The Figure 5 shows improve in voltage profile with DG placement.The active and reactive power losses for various scenarios are depicted in Figures 6 and 7 respectively.The figure demonstrates that adding DG to the distribution system results in a greater decrease in actual and reactive power losses.Figure 5 compares the voltages for a 41-bus actual distribution system with and without DG placement.The customer data of practical distribution system without DG for reliability analysis is given in Table 2 and reliability indices with and without DG in the practical system is given in Table 3.As observed in Table 3 the performance of reliability indices is improved with DG integration into the distribution system.The reliability of the system before and after DG is shown in Figures 8 and 9 respectively.As observed in the figures the reliability of the system is improved after location of DG in the practical distribution system and is shown in Figure 9.

CONCLUSION
In This work the effect of DG on the reliability of a distribution network is examined, for this practical feeder is taken and is modeled in PWS software.The progress in entire system after DG integration units has indicated by reliability indices values.After applying proposed method, the optimum position of DG is obtained at bus 18 with 0.633 MW of DG size.The real and reactive power loss reduction are 41.30% and 38.64 % respectively, lowermost bus voltage is enhanced to 0.9405 p u and the reliability indices are also improved.The reliability indices became better with DG when compared in the system without DG.The addition of DG units into practical feeder resulted into reliability improvement of the system, therefore it is suggested that practical distribution feeder which comes under Mangalore electricity supply company (MESCOM) should install DG units into their network to assure the electricity requirement of their consumers.

Figure 2 .
Figure 2. Daily load curve of practical feeder

Figure 3 .
Figure 3. Step by step computation of proposed methodology

Figure 4 .
Figure 4. 41-bus practical distribution feeder is modelled in PWS with DG

Figure 5 .Figure 6 .
Figure 5. 41-bus practical distribution-system voltage profile with and without DG

Figure 8 .Figure 9 .
Figure 8. Reliability Indices without DG placement in the system

Table 1 .
Loss analysis in the system

Table 3 .
Reliability Indices with and without DG in the system