seminar report on optimal placement and optimal sizing of DG

Made by Khemraj Bairwa
1
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

2
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.

3
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

4
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

5
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

6
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

7
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

8
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

9
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,

10
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

11
 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.

13
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.

15
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

16
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 + Q2
lk.eff) Rk/V2
k
And the loss sensitivity factor is calculated (as given below)
,
=
2 ∗ , ∗
2
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.

20
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 =
, ∗ , ∗ ∗ cos( + , − , )
QGn,1 – C(n.4)*QDn,I = - ∑ , ∗ , ∗ ∗ sin( + , −
, )
And now branch current equations
In,ij= | | ∗ ( , )2 + ( , )2 − 2 ∗ , ∗ , ∗ cos( , − , )
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

21
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%
∑ . + ∑ ∗ , + ∑ ∗ , ≤
y*∑
Where y is maximum penetration ,which is assumed 30% of max. load.
CHAPTER 6

22
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

23
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.

24
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

25
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)

26
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.

27
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.

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seminar report on optimal placement and optimal sizing of DG