seminar report on optimal placement and optimal sizing of dg

Made by Khemraj Bairwa

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CHAPTER 1 INTRODUCTION DUE to uncertainty of system loads on different feeders, which vary from time to time, the operation and control of distribution systems, is more complex particularly in the areas where load density is high. Power loss in a distributed network will not be minimum for a fixed network configuration for all cases of varying loads due to dynamic nature of loads, When total system load is more than its generation capacity that makes relieving of load on the feeders not possible and hence voltage profile of the system will not be improved to the required level. In order to meet required level of load demand, DG units are integrated in distribution network to improve voltage profile, to provide reliable and uninterrupted power supply and also to achieve economic benefits such as minimum power loss, energy efficiency and load leveling and it has also some additional advantages like environmental friendly .It also promote the development in technologies for small scale generation .DGs are located to buses which are voltage sensitive. Thus allocation of these DGs at appropriate place increases the loadability and the voltage margin is also increased. Deregulation of electricity markets in many countries worldwide brings new perspectives for distributed generation of electrical energy using renewable energy sources with small capacity. Typically 5-kW to 10-MW capacities of DG units are installed nearer to the end-user to provide the electrical power. Since selection of the best locations and sizes of DG units is also a complex combinatorial optimization problem, many methods are proposed in this area in the recent past. The voltage instability in distribution network is referred as


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load instability. As the load demand on distribution networks are sharply increasing .hence the distribution networks are operating near to voltage instability. For an example a voltage instability problem in a distribution network, which was widespread to a corresponding transmission system caused a major blackout in the S/SE Brazilian system in 1997.So with an objective of improvement of voltage stability margin; DGs are placed in distribution network at appropriate place.


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CHAPTER 2 DISTRIBUTED GENERATION 2.1 Introduction to Distribution Generation

Distributed generation is an approach that employs small-scale technologies to produce electricity close to the end users of power. DG technologies often consist of modular (and sometimes renewable-energy) generators, and they offer a number of potential benefits. In many cases, distributed generators can provide lower-cost electricity and higher power reliability and security with fewer environmental consequences than can traditional power generators.

In contrast to the use of a few large-scale generating stations located far from load centers--the approach used in the traditional electric power paradigm--DG systems employ numerous, but small plants and can provide power onsite with little reliance on the distribution and transmission grid. DG technologies yield power in capacities that range from a fraction of a kilowatt [kW] to about 100 megawatts [MW]. Utility-scale generation units generate power in capacities that often reach beyond 1,000 MW.

Distributed generation, also called on-site generation, dispersed generation, embedded generation, decentralized generation, decentralized energy or distributed energy, generates electricity from many small energy sources. Most countries generate electricity in large centralized facilities, such as fossil fuel (coal, gas powered), nuclear, large solar power plants or hydropower plants. These plants have excellent economies of scale, but usually transmit electricity long distances and negatively affect the environment Distributed generation allows collection of energy from many sources and may give lower environmental impacts and improved security of supply


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figure 2.1 structure of system with distributed generation

2.2 Types of Distributed Energy Resources

2.2.1 SOLER ENERGY It has been estimated that technical solar energy has resource potential that far exceeds the total global energy demand. Solar energy is a kind of energy from the sun which can be converted to electricity using either photovoltaic system (PV) or solar power plant. Solar energy today is widely captured for electricity production using solar photovoltaic power system especially in sun rich countries. Early development of solar photovoltaic based power generation was operated in a very small-scale to supply electricity to single or cluster of small number of residential homes. Today, large solar power grid integrated systems have been developed. This rapid development in the solar technologies for electricity production has favored a drastic drop in the cost of procurement in the last few decades. buttress this fact by unveiling that the cost of high power band solar modules has decreased from about $27, 000/kW in 1982 to about $4000/kW in 2006; the installed cost of a


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PV system declined from $16, 000/kW in 1992 to around $6000/kW in 2008. This landmark reduction in cost, climate change reductions obligation and policies, and Kyoto directives for clean development mechanism (CDM) are the basic vehicles envisaged to encourage more solar electricity generation across the globe. Currently, in developing countries like India, China and some other Southeast Asia, the uses of off-grid solar energy for combating rural energy deficiency is growing rapidly. In many other regions of the world, investment towards the development and promotion of solar power generation are being sustained using different workable policies. Some of the policies are fashioned towards exploring large scale of solar energy for either distributed electricity generation or grid-connected power supply. In the trend of future energy

Figure 2.2 solar energy


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2.2.2 Wind energy A wind power system is a device that converts the kinetic energy of blowing wind to alternating current electricity with the aid of an aero-wind turbine system illustrated in Figure-3. Power generated from wind was the fastest growing technology in the 90s and currently wind power doubles every 3 years and globally more efforts are being currently sustained to assess suitable sites for wind power generation. In 2010, the global capacity of wind power generation was estimated to be 196 GW with 1.9 TW forecasted by 2020. Apart from being used for onsite electricity generation, wind turbine systems in the form of large wind farms have also being used for grid connected supply of electricity especially in Europe, India, China and United States. The contribution from wind power system in these countries is significant especially as a means of cutting the emissions of carbon dioxide from thermal power generation. Therefore, apart from being used to solve rural energy problem, wind power system manufacturing in now a huge investment for some of these countries as the penetration of the system into power sector increases.

Figure 2.3 main components of wind turbines


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2.2.3 Solar Thermal Solar thermal systems generate electricity by concentrating the incoming sunlight and then trapping its heat, which can raise the temperature of a working fluid to a very high degree to produce steam and then generate electricity. Notice that this process is different from that of a photovoltaic panel where the sunlight is directly converted into electricity without the intermediate heat collection. Compared to solar photovoltaic, the solar thermal is more economical, as it eliminates the costly semiconductor cells. Applications of concentrating solar power are now feasible from a few kilowatts to hundreds of megawatts. Solar-thermal plants can be grid connected or stand-alone applications, for central generation or DG applications. They are suitable for fossil-hybrid operation or can include cost effective thermal storage to meet dispatch requirements

2.3 Potential Benefits of DG Systems

Consumer advocates who favor DG point out that distributed resources can improve the efficiency of providing electric power. They often highlight that transmission of electricity from a power plant to a typical user wastes roughly 4.2 to 8.9 percent of the electricity as a consequence of aging transmission equipment, inconsistent enforcement of reliability guidelines, and growing congestion. At the same time, customers often suffer from poor power quality—variations in voltage or electrical flow—that results from a variety of factors, including poor switching operations in the network, voltage dips, interruptions, transients, and network disturbances from loads. Overall, DG proponents highlight the inefficiency of the existing large-scale electrical transmission and distribution network. Moreover, because customers’ electricity bills include the cost of this vast transmission grid, the use of on-site power equipment can conceivably provide consumers with affordable power at


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a higher level of quality. In addition, residents and businesses that generate power locally have the potential to sell surplus power to the grid, which can yield significant income during times of peak demand.

Industrial managers and contractors have also begun to emphasize the advantages of generating power on site. Cogeneration technologies permit businesses to reuse thermal energy that would normally be wasted. They have therefore become prized in industries that use large quantities of heat, such as the iron and steel, chemical processing, refining, pulp and paper manufacturing, and food processing industries. Similar generation hardware can also deploy recycled heat to provide hot water for use in aquaculture, greenhouse heating, desalination of seawater, increased crop growth and frost protection, and air preheating.

Beyond efficiency, DG technologies may provide benefits in the form of more reliable power for industries that require uninterrupted service. The Electric Power Research Institute reported that power outages and quality disturbances cost American businesses $119 billion per year. In 2001, the International Energy Agency (2002) estimated that the average cost of a one-hour power outage was $6,480,000 for brokerage operations and $2,580,000 for credit card operations. The figures grow more impressively for the semiconductor industry, where a two hour power outage can cost close to $48,000,000. Given these numbers, it remains no mystery why several firms have already installed DG facilities to ensure consistent power supplies.

2.4 Why Not Use More DG Technologies

There are a mulitude of impediments to using DG technologies. A combination of social, scientific, and technical impediments prevent a transition to a more friendly DG future. Both proponents and opponents of DG technologies acknowledge that economic considerations such as


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capital costs, utility preferences, and business practices tend to deter people from investing in such technologies. DG systems are believed to have higher, comparative capital costs (in dollars per kilowatt) than other generators, which places many smaller, decentralized systems out of the price range of most residential consumers. Moreover, entrepreneurs and business owners argue that the comparative higher capital cost convinces them that investing in renewable or distributed systems is too expensive and deviates from the core mission of their corporate goals. Even electric utility managers generally shun renewable energy technologies, thinking that their power output is more intermittent than their fossil-fueled and nuclear alternatives, thus making them less viable providers of base-load and peaking power. Finally, since renewable and distributed energy systems, by their very nature, are more diverse and context dependent, transmission and distribution operators argue that they tend to be more difficult to permit, monitor, interconnect, and maintain.

Furthermore, many analysts believe that the strong political support for DG technologies, after the energy crisis of the 1970s, inflated expectations among the public that the use of renewable energy resources would grow rapidly. Yet a number of unforeseen events occurred: the Reagan administration shifted the energy policy of the country, fossil fuel prices fell in the 1980s, and conventional technologies continued to improve. Advocates of DG suggest that voters and politicians became disillusioned with renewable energy, and relinquished whatever social capital they achieved after the energy crises to utility managers and system operators. After the 1970s, when the country shifted completely back into the fossil fuel paradigm, inconsistent political support for tax credits created great uncertainty regarding DG technologies. This uncertainty deterred industry investment in renewable and distributed energy systems. As a result,


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strong utility bias became reflected in numerous state and federal regulations.

2.5 Integration with the grid

For reasons of reliability, distributed generation resources would be interconnected to the same transmission grid as central stations. Various technical and economic issues occur in the integration of these resources into a grid. Technical problems arise in the areas of power quality, voltage stability, harmonics, reliability, protection, and control. Behavior of protective devices on the grid must be examined for all combinations of distributed and central station generation. A large scale deployment of distributed generation may affect grid-wide functions such as frequency control and allocation of reserves.

2.6 Advantages of Distributed Generation:

Distributed Generation technologies include generation sources such as Solar, Wind, Fuel cells, Biomass, IC Engines. The rating of the power generation sources will be from few kW to MW.

Distributed Generation increases the reliability of power supply to the consumers. As these generating units are at the load side in the power system, this significantly reduces Transmission and Distribution losses

The connection of distributed generation sources to the power system will improve the voltage profiles, power quality ans supports the voltage stability of the system. This allows the system to withstand higher loading conditions and reduce the cost of Infrastructure for building the transmission and distribution systems


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Distributed Generation technologies can be made part of the smart grid or micro grid to improve the efficiency of the system.

Compared to other conventional plants, these plants require less time for commissioning and payback period is also less compared to conventional plants.

Some Distributed Generation Technologies are flexible in operation, size and can also easily extendable.

Some distributed Generation technologies have higher overall efficiency and low pollution such as combined heat and power (CHP) and some micro turbines

The right type of generating source suitable at that location can be installed and can generate power at cheaper cost.

2.7 Disadvantages of Distributed Generation:

Distributed Generation technologies have some negative impacts on the environment as well as economic aspect

Wind turbines will have visual, acoustic and bird life impact Wind farms and PV systems require large area compared to the

conventional technologies for the same installed capacity Small hydro, tidal and wave power plants may influence the

ecosystem and fishery Biomass may produce unpleasant emissions in case of incomplete

combustion The output of some of the renewable energy sources such as wind,

PV are variable and difficult to predict. Connecting the Distributed Generation sources to the grid is

complex. Protection design requires good communication between Distributed Generation project developer and Grid authorities. during the design process


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The main technical issue for connection of Distributed Generation to the grid relate to reliability, quality of supply, protection, metering and operational protocols for connection and disconnection, islanding and reactive power management

Connecting Distributed Generation to distribution network in the power system will introduce a source of energy at the point. This increases the fault level in the network and may complicate the fault detection and isolation.


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CHAPTER 3 VOLTAGE STABILITY 3.1 Introduction Voltage stability of a distribution system is one of the keen interests of industry and research sectors around the world. It concerns stable load operation, and acceptable voltage levels all over the distribution system buses. The distribution system in a power system is loaded more heavily than ever before and operates closer to the limit to avoid the capital cost of building new lines. When a power system approaches the voltage stability limit, the voltage of some buses reduces rapidly for small increments in load and the controls or operators may not be able to prevent the voltage decay. In some cases, the response of controls or operators may aggravate the situation and the ultimate result is voltage collapse. Voltage collapse has become an increasing threat to power system security and reliability. Many incidents of system blackouts because of voltage stability problems have been reported worldwide. In order to prevent the occurrence of voltage collapse, it is essential to accurately predict the operating condition of a power system. So engineers need a fast and accurate voltage stability index (VSI) to help them monitoring the system condition. Nowadays, a proper analysis of the voltage stability problem has become one of the major concerns in distribution power system operation and planning studies. 3.2 Types of voltage stability 3.2.1 Static voltage stability 3.2.2 Dynamic voltage stability

3.2.1 Static voltage stability - This is a stability phenomenon, where the power system loses its ability to control load bus voltage due to various


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reasons. This phenomenon can lead to failure of the total or partial power system due to interventions of various control and protection actions.

The reasons for voltage instability could be - Failure to provide necessary power support to the loads as a consequence of power transfer limit. The power transfer limit is determined not only by the bus voltage phase angle, but also by bus voltage magnitude - Failure to meet power requirements due to equipments reaching

their control and operating limits. Examples are transformer tap limits, generator reactive power supply capabilities.

- Inconsistency in the load power requirements as function of bus voltage and power supply characteristics.

Static technique can be used to analyzed the power system, which holds a relationship between the received power and voltage at certain bus in the system which is known as P-V curve or nose curve and this curve is obtained by applying continuous power method.


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Figure 3.1 V-k curve

3.2.2 Dynamic voltage stability- The dynamic behavior of power systems subjected normal power impacts is influenced by the following factors:

The system load level. The network characteristics. The Generator and its controller characteristics. The load characteristics.

The system is dynamically stable if the oscillatory response following a perturbation quickly settles down to a new stable operating point without sustained oscillations. These studies are typically carried out using linearized model of the system.

3.3 Impact of DG installation on voltage stability


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Figure 3.2 impact of DG unit on max.loadability and voltage stability margin As DG is installed on certain bus. It improves the maximum ability of that bus and voltage stability margin. Stability margin can be defined by the MW distant from operating point to the critical point. In above given diagram, λ is scaling factor of factor of load demand which varies from 0 to λmax(maximum loading). When number of DGs connected to a bus increases than the voltage profile is improved.

Figure 3.3 impact of DG installation on voltage profile Stability margin can be increased or decreased depending upon operation of DG at unity, leading and lagging power factor (as shown in figure)


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Figure 3.4 impact of power factor on voltage profile


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CHAPTER 4 SELECTION OF CANDIDATE BUSES Distribution Buses at which DGs are going to installed, is known as candidate bus. And the selection of candidate is done with help of voltage sensitivity analysis. In addition to this the candidate buses should be located on the main feeder of the system. Sensitivity analysis is used to compute sensitivity factors of candidate bus locations to install DG units in the system. Estimation of these candidate buses helps in reduction of the search space for the optimization procedure. Consider a line section consisting an impedance of Rk+jXk and a load of Plk,eff +jQlk,eff connected between k-1 and k buses a given below

The active power loss in the kth line between k-1 and k is given by Plosses = ( P2

lk,eff + Q2lk.eff) Rk/V2

k And the loss sensitivity factor is calculated (as given below)

휕푃푙표푠푠휕푃푙푘, 푒푓푓

= 2 ∗ 푃푙푘, 푒푓푓 ∗ 푅푘

푉2

And now this is arrange in descending order for all buses of the given system. This factor decides the sequence in which buses are to be considered for DG installation.


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CHAPTER 5 DG PLACEMENT PROBLEM FORMULATION The study of placement of DG unit is demonstrated in five scenarios

Scenario 1 – this is base case in which no DG is connected to the system.

Scenario 2 - only dispatchable DGs(non renewable DG) are connected

Scenario 3 – only wind based DG is connected Scenario 4 – only photovoltaic DG is connected Scenario 5 – a mix of dispatchable , wind , pv DG units are

connected. In the formulation of DG, the following assumptions are considered

More than one type of DG can be installed at same candidate bus. The DG units are assumed to operate at unity power factor. All buses are subjected to same solar irradiation and wind speed. The penetration level is equal or less than 30% of maximum load.

The DG placement method is carried out as follows

A year is divided into four seasons and each season is represented by any day within that season.

The day which represents a season, is further divided into 24 1hour time segments each referring to particularly hourly interval of the entire season. So for a year there are 96 time segments (24*4).

Mean and standard deviation are calculated for each time segment. Beta and weibull probability density function are calculated for each time segment.

And this density function is divided into states to incorporate the power output of the solar DG and wind based DG units.


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Here Vn is voltage at certain bus during n state and VP is the voltage profile with DG and without DG is considered. The following equation can be modified to include the probabilistic nature of the DG generation as in

Maximize where n= 1, 2 ….N (no of buses). The highest value of Vindex means best location for DG installation.

The power flow equations with consideration of DG installation are given below. PGn.1+ C(n,1)*PDG,Di +C(n,2)*PDG,Wi +C(n,3)*PDG,Si – C(n,4)*PDi =

푉푛, 푖 ∗ 푉푛, 푗 ∗ 푌푖푗 ∗ cos(휃푖푗 + 훿푛, 푗 − 훿푛, 푖)

QGn,1 – C(n.4)*QDn,I = - ∑ 푉푛, 푖 ∗ 푉푛, 푗 ∗ 푌푖푗 ∗ sin(휃푖푗 + 훿푛, 푗 −훿푛, 푖) And now branch current equations In,ij= |푌푖푗| ∗ (푉푛, 푖)2 + (푉푛, 푗)2− 2 ∗ 푉푛, 푖 ∗ 푉푛, 푗 ∗ cos(훿푛, 푗 − 훿푛, 푖) In,ij = feeder current in connecting buses i, j during state n. The voltage and angle for slack bus are Vn,1 =1.025 , δn,1 =0.0


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Voltage limits for other buses 0.95 < Vn,i< 1.05 Feeder current capacity 0< In,ij <Iijmax

The maximum penetration on each bus can not be more than 10MW for the candidate bus. For system maximum penetration is only up to 30% ∑ 푃푑푔.퐷푖 + ∑ 퐶퐹푤 ∗ 푃푑푔,푊푖 + ∑ 퐶퐹푠 ∗ 푃푑푔, 푆푖 ≤ y*∑ 푃퐷푖 Where y is maximum penetration ,which is assumed 30% of max. load. CHAPTER 6


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RESULTS

6.1 Results of candidate buses for the DG units installation Selection of candidate buses is done by developing 26 case studies, where cases numbers are equal to the number of the system buses (located at main feeder). In each case DG is installed at certain candidate buses and changes in the system voltages are observed. The installed DG is of 4.5MW at unity power factor. And penetration level is assumed 30 % of maximum demand of that bus.

Figure 6.1 results of voltage sensitivity analysis Form this figure buses from 19 to 41 can improve the voltage profile better than the buses from 1 to 18. And the order of sensitive buses can be determined by

The more sensitive buses are 40,39,38,37,35,33,32,23,24,19,26,28


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6.2 Result of the impact of the DG units on voltage stability We know that as a DG is installed on certain bus, it improves the voltage stability margin and maximum loadability. The DG is installed at certain bus. It affects the voltage stability margin and maximum loadability.

Figure 6.2 impact of the size of the DG units on maximum loading

This result only represents one size and location. In case DG unit is varied from 0 to 16 MW. And penetration level is up to 100% for study of the impact of DG size on voltage stability. This is also shown in given figure. And impact of the DG location study is achieved by developing 26 cases (the cases are equal to the number of the system buses which are located in main feeders). In each case a DG is installed at a certain bus and maximum loadability is observed. The installed DG is assumed to generate constant power of 4.4MW. in both cases, DG unit is operated at unity power factor; the system load demand is taken at the peak value.


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Figure 6.3 impact of the location of the DG units on max. loading Placing a DG unit in bus 40 improves the stability margin more than the other buses because this bus is more sensitive to real power. And if DG is placed on bus 28, the feeders will gain less capacity. And when two DG units are installed, the downstream feeders (23 to41) and the upstream feeder gain more capacity. This will increase in the voltage stability margin. However, this result is still lower than that of installing one DG unit at bus 40.

6.3 Result of the DG size and location

The results of five scenarios are listed in table given below.

Candidate buses

Scenario 1 Scenario 2 Scenario 3 Scenario 4

19 0 0 0 0 23 0 0 0 0 24 0 0 0 0


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26 0 0 0 0 28 0 0 1.1MW 1.55MW 32 0 0 0 0 33 0 0 0 0 35 0 0 0 0 37 0 0 0 0 38 0 0 2.2MW 1.92MW 39 0 0 0 0 40 0 4.5MW 6.6MW 9.47MW Total size 0 4.5MW 9.9MW 12.94MW Table 6.1 results of the DG location and size, scenarios (1-4)

The first column of this table is the candidate buses for DG installation, which are obtained from sensitivity analysis. And other column shows the sizing and sitting of DG units in each scenario.

Candidate buses Scenario 5(wind)

Scenario 5(solar)

Scenario 5(dispatchable)

19 0 0 0 23 0 0 0 24 0 0 0 26 0 0 0 28 0 0.87MW 0 32 0 0 0 33 0 0 0 35 0 0 0 37 0 0 0 38 0 0 0 39 0 0 0 40 3.3MW 3.38MW 1.2MW Total size 3.5MW 4.25MW 1.2MW Table 6.2 results of the DG location and size, scenarios (5)


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In above given two tables DG units are placed and sized on buses 40, 38, 28. In all scenarios the highest rating of DG is installed in bus 40 because bus 40 is located at far end of distributed system and has lower voltage profile.

Scenario Type of DG Location (bus no.)

Rating MVA Power factor

1 Base case 2 Dispatchable 40 4.5 0.95 leading 3 Wind 19

40 8.8 1.1

0.95 leading Unity

4 Solar 19 28 40

9.7 1.06 2.38

0.95 leading Unity Unity

5(mix) Dispatchable Wind Solar

40 19 19

0.82 3.3 4.2

0.95 leading 0.95 leading 0.95 leading

Table 6.3 results of the DG location and size, scenarios when DG units operated between 0.95 lead or lag power factor

In above table results are obtained for fixed power factor. The highest rating of DG units is placed in bus 19. Because sensitivity analysis shows that bus 19 is less sensitive to the real and reactive power injection compare to bus 40. The rating of DG units in scenario 5 is lesser than other scenarios.


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CHAPTER 7

CONCLUSION In the report ,a method of allocation for DG is studied with aim of improving of voltage stability margin. Here load is modeled by IEEE-RTS system. While renewable DG resources are modeled with historical data. Nature of load and renewable DG generation are considered as probabilistic nature. The selection of candidate buses is done by help of sensitivity analysis. Results show that installation of DG at appropriate place with appropriate size, have positive impact on voltage stability margin without violating he constrains of system. When DG is operating at unity power factor than it is recommended that DG should be placed at most sensitive buses in order to improve the voltage stability margin without violating the system voltage and current limits. And as results show that high rating of DGs are installed at upper stream feeder in order to keep the voltage and current rating in limited region.