A Reliability Impact and Assessment of Distributed Generation Integration to Distribution System

doi:10.4236/epe.2013.54B199

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Energy and Power Engineering, 2013, 5, 1043-1047

doi:10.4236/epe.2013.54B199 Published Online July 2013 (http://www.scirp.org/journal/epe)

A Reliability Impact and Assessment of Distributed

Generation Integration to Distribution System

Atthapol Ngaopitakkul1, Chaichan Po t hi s ar n1, Sulee Bunjongjit1, Boonlert Suechoey2,

Chaiyo Thammart2, Auttarat Nawikavatan2

1Department of Electrical Engineering, Faculty of Engineering, King Mongkut’s Institute of Technology Ladkrabang,

Bangkok, Thailand

2Department of Electrical Engineering, Faculty of Engineering, South-East Asia University, Bangkok, Thailand

Email: [email protected]

Received April, 2013

ABSTRACT

The main purpose of this paper is to study the reliability due to the employment of distributed generations (DG) inte-

grated to distribution system. The system under this study is from Provincial Electricity Authority (PEA) that is a part

of Thailand’s distribution system. Data of geographic information systems (GIS) including the distance of distribution

line and location of load that are parameter of PEA is simulated using digital simulation and electrical network calcula-

tion program (DIgSILENT) to analyze the impact of reliability with the installing DG into the distribution system. The

system average interruption frequency index (SAIFI), the system average interruption duration index (SAIDI) and in-

terruption cost are assessed as index of reliability by comparing the SAIFI, SAIDI, and interruption cost between the

base case (no DG) and the case that DG connected to the distribution system. The results can be summarized by focus-

ing on location of DG, the capacity of DG, the size of load, and the distance of load which are factors able to impact to

SAIFI, SAIDI, and interruption cost.

Keywords: Reliability; Distributed Generation; Interruption Cost; Distribution System; SAIFI; SAIDI

1. Introduction

Nowadays, the distributed generation (DG) is connected

into the distribution system; there are many issues [1-10]

that may cause the technical impacts to the distribution

system. Reliability is one of problems that are interested

based on studies research papers related to this subject.

In the literature [1, 2], this paper proposed a method to

analyze and evaluate the reliability of the transmission

equipment in the electrical system when installing the

generator to a distributed system as a case study. The

value of the damage (Failure Rates) is calculated in [3-8]

which analyzes and compares the reliability of the power

system in the different case studies. In the literature [9,

10], the authors use a Monte Carlo Simulation to random

the location of generator in distributed system, and then

determine the reliability of the power system.

The paper mainly focuses on analyzing and evaluating

the reliability in order to improve the reliability of power

system but not for analyzing in terms of the interruption

cost in case of power failure. This paper studies the im-

pact of reliability when a distributed generator (DG) is

installed into the distribution system. The system under

this study is from Provincial Electricity Authority (PEA)

that is a part of Thailand’s distribution system. DIgSI-

LENT power factory is employed to simulate and ana-

lyse the SAIFI, SAIDI and interruption cost when dis-

tributed generation (DG) is connected to 22kV distribu-

tion system.

2. Distribution Reliability Indices

Because of customer satisfaction, the utility of individual

customers to get the best service with the least amount of

power failure is important. The majority of customer

reliability problem is caused by distribution system. Util-

ities often monitor the reliability of customers by using a

reliability index. Therefore, calculating the reliability

index is interesting for their customers. The use of index

to indicate the average number of times of the power

failure and power outage per year per one customer

makes it possible to compare between different systems

and can also be targeted. The most common customer

reliability indices are:

System Average Interruption Frequency Index (SAIFI)

ASIFI ii





 (1)

A. NGAOPITAKKUL ET AL.

1044

System Average Interruption Duration Index (SAIDI)

SAIDI ii



 (2)

Interruption Cost



ECOST

nh nk

khk h

LC r





 (3)

where,

λ is the failure rate or interruption events

Ni is the number of customers served of node i

Ui is the restoration time or customer interruption

durations of node i

nk is the total number of load points in the study area

nh is the total number of outages that lead to power in-

terruption at load point k

Lk is the magnitude of the load curtailed in MW at

load point k

rh is duration of the contingency h

Chk is the cost of an outage contingency of duration rh

λh is the failure rate of the equipment

3. Power System Simulation using

DIgSILENT

The scheme under investigation is part of Thailand’s

electricity distribution system. DIgSILENT powerfactory

is employed to simulate and analyse the reliability when

distributed generation (DG) is connected to 22 kV dis-

tribution systems as shown in Figure 1. Data of geo-

graphic information systems (GIS) including the distance

of distribution line and location of load that are parame-

ter of PEA are shown in Table 1.

Figure 1. A simple radial system with DG connected.

Table 1. The length of transmission line and load in each

bus which is connected in distribution syste m.

Bus Distance (km) Load (MW)

Substation and 1 4.4 0.14

1 and 2 16.6 2.47

1 and 3 13 1.11

2 and 4 28.5 1.35

4 and 5 16.87 1.42

4 and 6 18 0.62

5 and 7 10 0.58

6 and 8 18.52 0.69

From Figure 1, it can be seen that there are 8 buses

from substation (Sub_Chokchai) and load of each bus

that is connected between distribution lines. To study the

reliability, simulations were performed with various

changes as follows:

- A number of distributed generators are no DG and

with DG.

- The location of distributed generators are designated

on any bus of distribution system and installed between

buses of distribution system.

- The capacity of DG is 2 MVA, 4 MVA, 6 MVA, and

8 MVA installed at the distribution system.

4. Impact of DG for Reliability

The objective of this paper is to study the impact of reli-

ability when distributed generation is connected to dis-

tribution system. The impact of DG is divided into 3 in-

dices in order to evaluate the reliability of system. The

SAIFI, SAIDI and Interruption cost of the base case (no

DG) and with DG is compared. The results are shown in

Table 2 and Table 3.

The first index, the SAIFI of base case (no DG) is

16.7464 times/customer/year while the SAIFI of PEA

regulation must be changed lower than 17.34 times/cus-

tomer/year. So the SAIFI will be compared with DG at

each bus as shown in Table 2. The results shown that,

when location of DG is considered by installing at bus 1,

2 and 3, the SAIFI is equal to the case of the base case

(no DG). Likewise, when the DG is installed at bus 4,

bus 5, bus 6, bus 7, and bus 8, it can be seen that the

SAIFI decreases. This indicates that utility has benefit

from employing DG.

In addition, when capacity of DG is considered with 2

MVA, 4 MVA, 6 MVA and 8 MVA that is installed at

each bus, the SAIFI is lower than the base case (no DG)

except for the case that the capacity of DG is 8 MW and

installation location is at bus 5 and bus 7. It is noticed

that, when the capacity of DG is increased, SAIFI tends

to decrease so reliability of distribution system will be

A. NGAOPITAKKUL ET AL. 1045

improved. This also indicates that capacity of DG and

location of DG play an important role for reliability in

such a system.

Table 2. The reliability index in case of DG installed at any

buses of distribution system.

Case SAIFI

(times/year)

SAIDI

(hour/year)

Interruption

Cost ($)

no DG 16.7464 21.064 147,351

Bus 1

2 MVA 16.7464 21.055 150,904

4 MVA 16.7464 21.05 148,641

6 MVA 16.7467 21.044 150,863

8 MVA 16.7462 21.039 148,608

Bus 2

2 MVA 16.7464 20.104 161,765

4 MVA 16.7464 19.316 149,031

6 MVA 16.7464 18.52 156,261

8 MVA 16.7462 18.233 137,887

Bus 3

2 MVA 16.7464 21.055 147,958

4 MVA 16.764 21.05 147,819

6 MVA 16.7464 21.044 148,095

8 MVA 16.7462 21.039 147,595

Bus 4

2 MVA 16.7464 19.629 157,973

4 MVA 12.15112 12.412 105,919

6 MVA 12.15112 11.776 103,279

8 MVA 12.15094 11.582 94,909

Bus 5

2 MVA 15.137 18.29 143,088

4 MVA 10.2316 10.763 90,727

6 MVA 10.1089 10.217 87,322

8 MVA 29.6436 35.897 287,294

Bus 6

2 MVA 15.5458 18.69 148,283

4 MVA 10.9371 11.529 98,434

6 MVA 10.9371 10.494 95,722

8 MVA 10.9369 10.722 87,345

Bus 7

2 MVA 15.1368 18.315 143,182

4 MVA 9.6705 10.03 83,771

6 MVA 9.5021 9.695 80,711

8 MVA 29.1259 35.202 293,903

Bus 8

2 MVA 15.5457 18.699 148,379

4 MVA 10.3671 10.831 90,350

6 MVA 10.3677 10.505 88,827

8 MVA 10.3677 10.303 83,115

Table 3. The reliability index in case of DG that is installed

between buse s of distr i bution system.

Case SAIFI

(times/year)

SAIDI

(hour/year)

Interruption

Cost ($)

no DG 16.7464 21.064 147,351

Bus 1 - Bus 2

2 MVA 16.7464 20.087 163,000

4 MVA 16.7464 19.316 160,038

6 MVA 16.7464 18.545 156,858

8 MVA 16.7462 18.233 138,892

Bus 1 - Bus 3

2 MVA 16.7464 21.055 147,881

4 MVA 16.7464 21.05 147,760

6 MVA 16.7464 21.044 148,122

8 MVA 16.7462 21.039 147,536

Bus 2 - Bus 4

2 MVA 16.7464 21.064 150,918

4 MVA 13.1397 15.377 119,819

6 MVA 12.4914 14.301 112,710

8 MVA 12.1509 13.845 102,520

Bus 4 - Bus 5

2 MVA 16.7464 19.633 158,115

4 MVA 12.1511 12.4 106,089

6 MVA 12.511 11.795 103,250

8 MVA 12.509 11.582 94,909

Bus 4 - Bus 6

2 MVA 15.5458 18.689 148,267

4 MVA 10.9506 11.557 98,669

6 MVA 10.9505 10.95 95,723

8 MVA 10.9504 10.729 87,430

Bus 5 - Bus 7

2 MVA 15.1368 18.301 143,122

4 MVA 10.4714 11.081 92,509

6 MVA 10.0205 10.181 86,285

8 MVA 35.624 44.109 352,909

Bus 6 - Bus 8

2 MVA 15.5458 18.695 148,322

4 MVA 10.937 11.522 98,166

6 MVA 10.8112 10.88 94,342

8 MVA 10.5175 10.413 84,228

The second index, the SAIDI of base case (no DG) is

21.064 hour/customer/year while the SAIDI of PEA reg-

ulation must be changed lower than 19.55 hour/cus

-tomer/year. Similarly, capacity of DG and location of

DG is considered so the behavior of SAIDI is shown in

Table 2. The results show that, when location of DG is

considered by installing at bus 1, 2 and 3, the SAIDI is

equal to the case of the base case (no DG). Likewise,

when the DG is installed at bus 4, bus 5, bus 6, bus 7 and

bus 8, it can be seen that the SAIDI is also decreased as

A. NGAOPITAKKUL ET AL.

1046

same as SAIFI. This indicates that utility has still benefit

from employing DG.

The capacity of DG is also considered; it is noticed

that when the capacity of DG is increased, SAIDI tends

to decrease as same as SAIFI. This also indicates that

capacity of DG, location of DG, location of load, and

size of load play an important role for reliability.

The third index, the interruption cost of base case (no

DG) is 147,351 U.S. Dollar /year. Similarly, capacity of

DG and location of DG are also considered; the obtained

results for interruption cost are given in Tabl e 2.

The results show that, when capacity of DG and loca-

tion of DG is considered by installing at bus 1 to bus 3,

the interruption cost is increased and more than the base

case (no DG) due that the size of load is large so average

hours service availability of customer is decreased and

the failure rate of the equipment (λ) in equation 3 will be

increased. Likewise, when the DG is installed at bus 4,

bus 5, bus 6, bus 7 and bus 8, it can be seen that the in-

terruption cost is decreased except for the capacity of DG

is less than 2 MVA. This also indicates the slight mis-

match between DG capacity and size of load. It is clearly

seen for the cases that, when interruption cost is consid-

ered and the capacity of DG is 8 MVA which is installed

at bus 7 and the size of load is 0.58 MW, the interruption

cost is significantly increased.

From Table 3, it can be seen that the reliability index

obtained from the base case as same as case of DG is

installed on any bus will be compared with DG that is

installed between bus. The first index, the SAIFI of base

case (no DG) is still 16.746 times/customer/year and the

SAIFI of PEA regulation is also 17.34 times/customer/

year. The results show that, when location of DG is con-

sidered by installing between bus 1-bus 2, bus 1-bus 3,

the SAIFI is equal to the base case (no DG) and case of

DG installed on any bus. Likewise, when the other case

of DG in Table 3 is considered, it can be seen that the

SAIFI is decreased and less than the base case but has

value nearby the case of DG installed on any bus for the

most cases except for the case that the capacity of DG is

8 MW and DG location is between bus5-bus 7 with load

of 0.58 MW. This also indicates that capacity of DG,

location of DG, location of load, and size of load play an

important role for reliability.

The second index, the SAIDI of base case (no DG) is

still 21.064 hour/customer/year while the SAIDI of PEA

regulation is also 19.55 hour/customer/year. Similarly,

capacity of DG and location of DG are considered and

the behavior of SAIDI is shown in Table 3. The results

show that, when location of DG is considered and in-

stalled at bus 1, 2 and 3, the SAIDI is equal to that of the

base case (no DG). Likewise, when the DG is installed at

bus 4, bus 5, bus 6, bus 7 and bus 8, it can be seen that

the SAIDI is also decreased as same as SAIFI. This indi-

cates that utility has still benefit from employing DG. In

addition, when capacity of DG is considered, it is noticed

that when the capacity of DG is increased, SAIDI tends

to decrease as same as SAIFI.

The third index, the interruption cost of base case (no

DG) is still 147,351 U.S. Dollar/year. Similarly, capacity

of DG and location of DG are also considered and the

obtained results from interruption cost are shown in Ta-

ble 3. The results show that, the interruption cost tends to

decrease as same as the case of DG installed at bus.

However, when the interruption cost is compared be-

tween DG installed at bus and installed between buses, it

can be seen that the interruption cost of DG installed

between buses is lower than that of the DG installed at

bus. This also indicates the slight mismatch between DG

location and size of load.

5. Conclusions

This paper focuses on the analysis of reliability with the

inclusion of DG. The system average interruption fre-

quency index (SAIFI), the system average interruption

duration index (SAIDI), and interruption cost are as-

sessed as index of reliability by comparing the SAIFI,

SAIDI, and interruption cost between the base case (no

DG) and the case that DG connected to the distribution

system. The results can be summarized by focusing on

the location of DG, the capacity of DG, the size of load,

and the distance of load which are factors able to impact

to SAIFI, SAIDI, and interruption cost as shown in Ta-

bles 2-3. Both the location of DG and the capacity of DG

must take into account to reach optimal condition in or-

der to create the suitability and fairness for both utility

and DG.

6. Acknowledgements

The authors wish to gratefully acknowledge financial

support for this research from the King Mongkut’s Insti-

tute of Technology Ladkrabang Research Fund, Thailand

and the energy policy and planning office (EPPO), Min-

istry of Energy, Thailand. They would like also to thank

for the DIgSILENT presented in this paper which is

supported by Provincial Electricity Authority (PEA).

REFERENCES

[1] M. Fotuhi-Firuzabad, “An Analytical Method to Consider

DG Impacts on Distribution System Reliability,”

IEEE/PES Transmission and Distribution Conference and

Exhibition: Asia and Pacific, 2005, pp. 1-6.

[2] I. K. Tarsi, A. Sheikholeslami, T. Barforoushi and S. M.

B. Sadati, “Investigating Impacts of Distributed Genera-

tion on Distribution Networks Reliability: A Mathemati-

cal Model,” Electric Power Quality and Supply Reliabil-

ity Conference (PQ), 2010, pp.117-124.

A. NGAOPITAKKUL ET AL.

1047

[3] H. Falaghi and M. Haghifam, “Distributed Generation

Impacts on Electric Distribution Systems Reliability:

Sensitivity Analysis,” The International Conference on

Computer as a Tool (EUROCON), Vol. 2, 2005, pp.

1465-1468.

[4] Y. Yue, K. J. Qian and C. K. Zhou, “The Effect of Dis-

tributed Generation on Distribution System Reliability,”

42nd International Universities Power Engineering Con-

ference (UPEC), 2007, pp. 911-916.

[5] S. X. Wang, W. Zhao and Y. Y. Chen, “Distribution Sys-

tem Reliability Evaluation Considering DG Impacts,”

Third International Conference on Electric Utility De-

regulation and Restructuring and Power Technologies

(DRPT), 6-9 April 2008, pp. 2603-2607.

doi:10.1109/DRPT.2008.4523850

[6] N. Chaiyabut and P. Damrongkulkamjorn, “Impact of

Customer Scattering on Distribution System Reliability

with Distributed Generation,” IEEE Region 10 Confer-

ence (TENCON), 2010, pp. 568-573.

[7] A. C. Neto and M. G. da Silva, “Impact of Distributed

Generation on Reliability Evaluation of Radial Distribu-

tion Systems Under Network Constraints,” 9th Interna-

tional Conference on Probabilistic Methods Applied to

Power Systems (PMAPS), 11-15 June 2006, pp. 1-6.

doi:10.1109/PMAPS.2006.360421

[8] A. A. Chowdhury, “Reliability Modeling of Distributed

Generation in Conventional Distribution Systems Plan-

ning and Analysis,” IEEE Transactions on Industry Ap-

plication, Vol. 39, No. 5, 2003, pp. 1493-1498.

doi:10.1109/TIA.2003.816554

[9] In-Su Bae and Jin-O Kim, “Reliability Evaluation of Dis-

tributed Generation Based on Operation Mode,” IEEE

Transactions on Power Systems, Vol. 22, No. 2, 2007, pp.

785-790. doi:10.1109/TPWRS.2007.894842

[10] A. M. Abdullah, “New Method for Assessment of Dis-

tributed Generation Impact on Distribution System Reli-

ability: Islanded Operation,” IEEE Innovative Smart Grid

Technologies – Asia (ISGT Asia), 2012, pp. 1-5.