Seminar Final Draft

8/2/2019 Seminar Final Draft

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[Type the document title]

Department of EEE,SREC

CONTENTS

CHAPTER NO. TITLE PAGE NO.1 Introduction

2 Historical background

3 Distribution generation technology

4 Power quality

5 Benefits and Issues

6 Impact of Distributed generation in Power losses


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ABSTRACT

The traditional energy structure of our country is single and theenvironmental pollution is serious. To a certain extent, it impeded the sustainable economic and

social development of any country. With the energy problems increasing seriousness, distributed

generation growing is growing a wide range of applications for the merits of small investment,

environmental protection, clean, reliable power supply and flexible generation manner, and so

on. However, a large number of distributed power poured into the grid change the grids

structure increase the randomness of system running, and impede the power system seriously.

Now a days the energy problems increasing seriousness,

distributed generation is growing a wide range of applications for the merits of small investment,

environmental protection, clean, reliable power supply and flexible generation manner, and so

on. However, a large number of distributed power poured into the grid change the grids

structure increase the randomness of system running, and impede the power system seriously.

There have been increased focus in the recent years on the

concept of smoothing intermittent output of distributed generation (DG) using energy storage.

DGs can be defined as the concept of connecting generating units of small sizes, between several

kW to a few MW.


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CHAPTER 1

INTRODUCTION


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INTRODUCTION

Definition:

Distributed generation is an electric power source connected

directly to the distribution network or on the customer side of the meter.

Most of the electricity produced today is generated in large

generating stations, which is then transmitted at high voltage to the load centers and transmitted

to consumers at reduced voltage through local distribution systems in contrast with large

generating stations, Distributed generation produce power on a customers site or at a local

distribution network. DG technologies include

>Engines

>Small hydro and gas turbines

>Fuel cells

>Photo voltaic systems etc

This thesis provides an overview of the impact that distributed

generation (DG) might have on the operation of power system. Issues like impact of DG on

losses, voltage control, power quality, short circuit power, and system protection are discussed.

Based on the discussion, it can he concluded that the impact of DG depends on the penetration

level of DG in the distribution network as well as on the DG technology. Furthermore, critical

issues, For example the impact of DG on the protection system, can he solved by using the right

technology and detailed studies beforehand. Also, new operation approaches, using IT

technologies, might help to integrate DG into the distribution network operation.

DG combines two or more power sources into one integrated system based on

renewable energy resources such as natural gas, wind, sun or Hydrogen, locating decentralized

power plants closed to power users. Thus, the DG systems are more efficient than traditional

power generation techniques .In design of distributed generation, all p. If DG is properly sized,


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sited, and selected in terms of technology, it can clearly provide benefits to control, operation

and stability of the power system. It should however be noted that distribution networks have

traditionally a rather inflexible design (e.g., a unidirectional power flow), which in principle can

cause integration problems with higher DG penetration levels or different technologies.

Nonetheless, those issues can usually be solved by modifying the distribution network, including

the control and/or operation approach, or by other technical means. Power sources units must be

connected into parallel.


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DIFFERENCES BETWEEN CENTRALISED AND DECENTRALISED

POWER SYSTEMS


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Transmission and Distribution losses for Countries(in percentage)

India 33

Nigeria 38

Nicaragua 30

Pakistan 26

Cameroon 26

Russia 12

UK 8

China 7

US 6

Japan 4

Germany 4


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CHAPTER 2

Historical Background


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HISTORICAL BACKGROUND

The importance of the impact that DG might have on the operation, stability, and

control of the power system has already been recognized in the late 1970s. One of

the most interesting publications on this subject was presented at the conference

Research needs for the effective integration of new technologies into the Electric

Utility held by the U.S. Department of Energy (DOE) in 1982 and was entitled

Impacts of new technology and generation and storage processes on power system

stability and operability . Over the last two decades the number of publications

discussing various areas of the interaction between DG and the utility has been

gradually increasing. Historically, until the 1990s the main focus of the research

was placed upon the impact that renewable power sources had on network

operation. However, also distributed generation in general was investigated. In the

late 1990s, this theme gained more interest in academia and industry, which

resulted in a large number of publications. Recently, also the results of two

extensive simulation case studies have been reported:

(i) Simulation of interaction between wind farm and power system, by theRusso National Laboratory, Denmark , and

(ii) DG Power Quality, Protection and reliability Case Studies Report, by GECorporate Research and Development.


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CHAPTER 3

Distribution Generation

Technology


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DISTRIBUTED GENERATION TECHNOLOGY

Technologies for distributed generation:

TECHNOLOGY Typical available size module

1.Combined Cycle Gas 35-400MW

2.Internal combustion engines 5KW-10MW

3.Combustion turbine 1-250MW

4.Micro turbines 35KW-1MW

5.Small hydro 1-100MW

6.Micro hydro 25KW-1MW

7.Wind turbine 200W-3MW

8.Photo voltaic Arrays 20W-100KW

9.Solar thermal, Central receiver 1-10MW

10.Solar Thermal, Lutz system 10-80MW

11.Biomass Gasification 100KW-20MW

12.Fuel cells, Phos acid 200KW-2MW

13.Fuel cells, Molten Carbonate 250KW-2MW

14.Fuel cells, Proton exchange 1-250KW

15.Fuel cells, Solid Oxide 250KW-5MW

16.Geothermal 5-100MW

17Ocean Energy 0.1-1MW

18.Stirling Engine 2-10KW

19.Battery storage 0.5-5MW


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Table provides a brief overview of the most commonly used distributed

generation technologies and their typical module size. The technologies 5-11, 16 and 17 can be

considered renewable DG. The other technologies could also be called renewable DG if they are

operated with bio-fuels. Also fuel cells could be considered renewable DG if the hydrogen is

produced using renewable energy sources, e.g. wind power.

Similarly to the centralized generation, the following three generation technologies are normally

used for distributed generation: synchronous generator, asynchronous generator, and power

electronic converter interface. These DG technologies will now be briefly discussed.

Synchronous Generator:

The advantageous ability of the synchronous generator the primary generator technology for

centralized generation to produce both active and reactive power also provides benefits for

distributed generation applications. Synchronous generators are typically utilized by the

following DG applications if the generation capacity exceeds a few MW: biomass, geothermal,

diesel/gas engines driven generators, solar thermal generation, solar parabolic systems, solar

power towers, solar dish engines, gas turbines, and combined cycle gas turbines.

Asynchronous Generator:

In contrast to synchronous generators, asynchronous (induction) generators are only used for

distributed generation, but not for centralized generation. An asynchronous generator is basically

an induction machine which is connected to a prime-mover. When the generator is connected to

the power network, the mechanical power is converted into electrical power by the action of the

prime mover that drives the machine above synchronous speed. Hence, the asynchronousgenerator is not capable of operating independent from a relatively strong grid. Asynchronous

generators are used for many distributed generation technologies as long as the generation

capacity does not exceed a few MW due to its competitive price compared to synchronous

generators. Squirrel cage asynchronous generator used to be very common in the wind energy


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industry; however, this type of induction generator is now being gradually superseded by

asynchronous generators equipped with a converter, i.e., double-fed induction generators.

Power Electronic Converter:

Power converters normally use high power electronics to provide the desired power output. For

example, it is quite common that wind turbines use double-fed, variable speed induction

generators with an IGBT converter in the rotor circuit. Power electronic converters are also used

in photovoltaic systems, fuel cells, micro turbines, Sterling engine as well as battery storage, and

magnetic storage system.


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CHAPTER 4

Power Quality


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POWER QUALITY

From the CIRED (CIRED is the International Conference of Electricity Distributors). Some of

the European countries raise power quality as an issue in the current electricity marketevolutions. Depending on the aspect chosen, distributed generation can either contribute to or

deteriorate power quality. Here, we focus on some potential problems.

System Frequency

Imbalances between demand and supply of electricity cause the system

frequency to deviate from the rated value of 50 Hz. These deviations should be kept within very

narrow margins, as the well functioning of many industrial and household applications depends

on it. In economic terms, system frequency can be considered as a public good. As a

consequence, the transmission grid operator is appointed to take care of the system frequency as

well as of other services with a public good character that need to be provided.

The installation and connection of distributed generation units is also

likely to affect the system frequency. These units will free ride on the efforts of the transmission

grid operator or the regulatory body to maintain system frequency. The latter will probably have

to increase their efforts and this could have an impact on the efficiency of the plants and on their

emissions. Therefore, the connection of an increasing number of distributed generation units

should be carefully evaluated and planned upfront.

Voltage level

According to Ackermann et al. (2001), the impact of distributedgeneration connected to the distribution grid on the local voltage level can be significant. A same

reaction was noted through the CIRED (1999) questionnaire, where, next to the general impact

on power quality, a rise in the voltage level in radial distribution systems was mentioned as one

of the main technical connection issues of distributed generation. The IEA (2002) also mentions

voltage control as an issue when distributed generation is connected to the distribution grid. This


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does not need to be a problem when the grid operator faces difficulties with low voltages, as in

that case the distributed generation unit can contribute to the voltage support. But in other

situations it can result in additional problems.

Connection issues

Change in power flow

Power can flow bidirectional within a certain voltage level, but it

usually flows unidirectional from higher to lower voltage levels, i.e. from the transmission to the

distribution grid. An increased share of distributed generation units may induce power flows

from the low-voltage into the medium-voltage grid. Thus, different protection schemes at both

voltage levels may be required.

Protection

Distributed generation flows can reduce the effectiveness of protection equipment. Customers

wanting to operate in islanding mode during an outage must take into account important

technical (for instance the capability to provide their own ancillary services) and safety

considerations, such that no power is supplied to the grid during the time of the outage. Once the

distribution grid is back into operation, the distributed generation unit must be resynchronized

with the grid voltage.Reactive power

Small and medium sized distributed generation units mostly use asynchronous generators that are

not capable of providing reactive power. Several options are available to solve this problem. On

the other hand, DG units with a power electronic interface are sometimes capable to deliver a

certain amount of reactive power.

Power Conditioning

Some distributed generation technologies (PV, fuel cells) produce direct current. Thus, these

units must be connected to the grid via a DC-AC interface, which may contribute to higher

harmonics. Special technologies are also required for systems producing a variable frequency


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AC voltage. Such power electronic interfaces have the disadvantage that they have virtually no

inertia, which can be regarded as a small energy buffer capable to match fast changes in the

power balance. Similar problems arise with variable wind speed machines.


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CHAPTER5

Benefits and Issues


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BENEFITS AND ISSUES

Voltage level at grid connection

Although some authors allow distributed generation to be connected to thetransmission grid, most authors see distributed generation as being connected to the distribution

network, either on the distribution or on the consumers side of the meter. In all cases, the idea is

accepted that distributed generation should be located closely to the load. The problem is that a

distinction between distribution and transmission grid, based on voltage levels, is not always

useful, because of the existing overlap of these voltage levels for lines in the transmission and

distribution grid. Moreover, the legal voltage level that distinguishes distribution from

transmission can differ from region to region. Therefore, it is best not to use the voltage level as

an element of the definition of distributed generation. It would be more appropriate to use the

concepts distribution network (usually radial) and transmission network (usually mashed) and

to refer to the legal definition of these networks as they are used in the country under

consideration.

Generation capacity (MW)

One of the most obvious criteria would be the generation capacity of the units installed.However, the short survey of definitions illustrated that there is no agreement on maximum

generation capacity levels and the conclusion is that generation capacity is not a relevant

criterion. The major argument is that the maximum distributed generation capacity that can be

connected to the distribution grid is a function of the capacity of the distribution grid itself.

Because this latter capacity can differ widely, it is not possible to include it as an element of the

definition of distributed generation. However, this does not imply that the capacity of the

connected generation units is not important.

Services supplied

Generation units should by definition at least supply active power in order to be

considered as distributed generation. The supply of reactive power and/or other ancillary services

is possible and may represent an added value, but is not necessary.


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Generation technology

In some cases, it can be helpful to clarify the general definition of distributed

generation by summing up the generation technologies that are taken into account. It would

however be difficult to use this approach to come to a definition because the availability of

(scalable) technologies and of capacities, especially in the field of renewable, differs between

countries. Also conventional systems such as gas turbines are available over wide ranges (a few

kW to 500 MW).

Sometimes, it is claimed that distributed generation technologies should be

renewable. However, it should be clear from section 1 that many small-scale generation

technologies exist not using renewable as a primary source. On the other hand, not all plants

using green technologies are supplying distributed generation. This would, for example, depend

on the plant size or on the grid to which the installation is connected (transmission or

distribution). Should a large offshore wind farm of 100 MW be considered as distributed

generation? And what about a large hydro power plant located in the mountains?

Operation mode

Ackermann et al. (2001) do not consider the operation mode (being scheduled, subject

to pool pricing, dispatchable) as a key element in the general definition of distributedgeneration. This is a correct view, but at the same time it must be recognized that many of the

problems related to distributed generation, essentially have to do with the fact that these

generation units are beyond control of grid operators. So, it can be meaningful to use (elements

of) the operation mode as a criterion to narrow the definition.

Power delivery area

In some cases, distributed generation is described as power that is generated and consumed

within the same distribution network. As correctly stated by Ackermann, Andersons et al.

(2001), it would be difficult to use this as a criterion, even for a narrowed definition, because it

requires complex power flow analyses.


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Ownership

Ackermann et al. (2001) do not consider ownership as a relevant element for the definition of

distributed generation. Thus, customers, IPPs and traditional generators can own distributed

generation units.


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CHAPTER6Impact of Distributed

Generation in power losses


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THE IMPACT OF DG IN POWER LOSSES

In this section we present the results of the study of the impact of DG

connection on the power losses in the distribution network. We evaluated the power losses overone year for different scenarios. The aim will be to know whether DG increases or decreases

power losses, depending on the configuration of the network and on the technology used by

generators and the level of penetration of DG.

The power losses depend on factors such as demand, DG production and the network operation.

Therefore, to study the power losses, it is not enough to study

the network in extreme conditions, as it has been done in the previous section.

We use profiles for power demand and power generation with a resolution of half an hour, and

duration of one year. The DG generation profile is of wind type. These profiles have been

obtained from. With these data we have analyzed the effect on power losses caused by variation

in the demand and generation profiles.

We have defined two different scenarios to assess the impact of different network configurations

in the power losses. The first scenario is the one presented in previous section without control


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strategies. In the second one, we have included the control strategies previously explained. We

have simulated the connection of different inductive wind DG units. Next we present the results

obtained using different configuration cases for the DG unit, in the first scenario. The cases are

as follow: case 1: No DG unit installed;

case 2: One DG unit installed, with a maximum capacity of 0.575 MW

operating at a PF of 0.8;

case 3: One DG unit installed, with a maximum capacity of 1 MW, with

active power output limited to 0.575 MW operating at a PF of 0.8;

case 4: One DG unit installed, with a maximum capacity of 0.35 MW

operating at a unity PF;

case 5: One DG unit installed, with a maximum capacity of 1 MW, with

active power output limited to 0.35 MW and operating with

unity PF.

The case 1 presents losses close to 6%. For Case 2, losses increase slightly to

6.48% because the flows during the year are higher. These results are influenced by the fact that

bank capacitors are active for a smaller number of iterations. Case 3 presents losses of 8.58%.

This value is due to a high consumption of reactive power by the DG unit when the generation of

active power is high. For the cases 4 and 5, losses are reduced significantly thanks to the activepower production of the DG unit, eliminating the need to import this power. Connection of a DG

unit has a very positive effect in reducing the number of iterations in which there are violations

of lower voltage limits. This is due to the power saving which results from not needing to import

power from the head feeder in power networks with low X/R ratio.

For the second scenario, the cases are the following:

case 6: no DG unit installed;

case 7: one DG unit installed, with a maximum capacity of 0.39 MW

operating at a PF of 0.8;

case 8: one DG unit installed, with a maximum capacity of 1 MW, with

active power output limited to 0.39 MW operating at a PF of 0.8;

case 9: one DG unit installed, with a maximum capacity of 0.246 MW

operating at a unity PF;


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case 10: one DG unit installed, with a maximum capacity of 1 MW, with

active power output limited to 0.246 MW and operating with

unity PF.


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Worldwide installed capacity (GW)

Region Thermal Hydro Nuclear Others Total

North America 642 176 109 18 945

Central & South America 64 112 2 3 181

Western Europe 353 142 128 10 633

Eastern Europe 298 80 48 0 426

Middle East 94 4 0 0 98

Africa 73 20 2 0 95

Asia 651 160 69 4 884

Total 2,175 694 358 35 3,262

Percentage 66.6 21.3 11.0 1.1 100


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ADVANTAGES:

1) Useful addition for a large power grid2) Can make up the deficiency of large power grids stability3) Need not build power transformer and distributed station4) High efficiency and environmental protection.5) Can achieve load power demand in remote areas.

CHALLENGES IN TECHNICAL ASPECTS:

1) Penetration levels2) Location sizing3) Optimizing the location of DG4) Islanding scenario5) Line losses reduction

CATEGORIZATION:

One can further categorize distributed generation technologies

as renewable and nonrenewable. Renewable technologies include:

Solar, photovoltaic or thermal

Wind

Geothermal

Ocean.


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Nonrenewable technologies include:

Internal combustion engine, ice

combined cycle

Combustion turbineMicroturbines

Fuel cell.

Distributed generation should not to be confused with renewable generation. Distributed

generation technologies may be renewable or not

It can be understood that the impact of DG on operational aspects of the

distribution network depends on the penetration of DG well as on the DG technology.

Furthermore, critical issues, for example the impact of DG on the protection system, can be

solved by using the right technology and detailed studies beforehand. Also, new operational

approaches for distribution network, using IT technologies, might help to integrate DG better

into distribution network.


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CONCLUSION

It is economically nonsensical to pursue two strategies at thesame time, for both a centralized and a decentralized energy supply system, since both strategies

would involve enormous investment requirements. I am convinced that the investment in

renewable energies is the economically more promising project. When we make additional

investments in the electricity grid, we should no longer be spending money on the 20th century

grid system, but should instead focus on the 21st century paradigm of distributed generation. The

centralized model no longer fits the inherently decentralized nature of renewable energy supply.

The grid must change


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rEFERENCES:

1. Puttgen, H. B., Macgregor, P. R., and Lambert F.C., Distributed Generation: SemanticHype or the Dawn of a New Era?,IEEEPower & Energy Magazine.

2. A. M. Borbely.Distributed Generation: The Power Paradigm for the NewMillennium. CRC Press, 2001.

3. Liang Caihao, Duan Xianzhong, "Distributed Generation and its Impact on PowerSystem", Automation of Electric Power Systems, VoI.2S, pp.53-S6, Dec. 2001.

4. ACKERMANN, T., ANDERSSON, G., and SDER, L., (2001), Distributed generation:a definition,Electric Power Systems Research, vol. 57, p. 195-204.

5. Stan Mark Kaplan, Fred Sissine,(ed.) Smart grid: modernizing electric powertransmission and distribution... The Capitol Net Inc, 2009

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