INTERNATIONAL JOURNAL OF ENERGY RESEARCH
Int. J. Energy Res. (2009)
Published online in Wiley InterScience
(www.interscience.wiley.com). DOI: 10.1002/er.1573
Investigation of the distributed generation penetration in a medium
voltage power distribution network
G. N. Koutroumpezis, A. S. Safigianni,y, G. S. Demetzos and J. G. Kendristakis
Electrical and Computer Engineering Department, Democritus University Thrace, GR 67100, Xanthi, Greece
SUMMARY
This paper investigates the results of the distributed generation penetration in a weak medium voltage power
distribution network. The connected distributed generation resources are in their entirety small hydroelectric plants.
Their locations are predetermined. Specifically, the influence of distributed generation on the network branch currents
and voltage profile as well as on the short-circuit level at the medium voltage busbars of the infeeding substation are
examined using a commercial-grade software package. The arising problems are explored and alternative technical
solutions to deal with them are proposed. Finally, an initial proposal for an optimum distributed generation penetration
in the predetermined network positions is given. A real-world study case, rather than a simplified academic network, is
selected to be analysed in order to specify, as accurately as possible, the arising practical problems and to use this
experience in the future in the development of a fast and reliable method for the determination of optimal distributed
generation allocation in random network positions. Copyright r 2009 John Wiley & Sons, Ltd.
KEY WORDS:
distributed generation; medium voltage distribution network; short-circuit level; voltage profile
1. INTRODUCTION
Distributed generation (DG) is a new approach in
the electricity industry. In the literature, a large
number of terms and definitions are used in
relation to DG, such as ‘embedded generation’,
‘dispersed generation’ and ‘decentralised generation’.
As the analysis of the relevant literature shows,
there is as yet no generally accepted definition of
DG [1,2]. The different issues to be discussed [2] in
order to define DG more precisely are its purpose,
its location, its rating, the power delivery area, the
technology, its environmental impact, its mode of
operation, its ownership and its penetration.
A general definition for DG suggested in [2],
which is now widely accepted, reads as follows:
‘DG is an electric power source connected directly
to the distribution network or on the customer
site of the meter’. The distinction between
distribution and transmission networks is based on
the legal definition. The above definition of DG
does not define the rating of the generation source,
as the maximum rating depends on the local
distribution network conditions, e.g. voltage level.
*Correspondence to: A. S. Safigianni, Electrical and Computer Engineering Department, Democritus University Thrace, GR 67100,
Xanthi, Greece.
y
E-mail: asafig@ee.duth.gr
Copyright r 2009 John Wiley & Sons, Ltd.
Received 27 November 2008
Revised 27 April 2009
Accepted 9 May 2009
G. N. KOUTROUMPEZIS ET AL.
It is, however, useful to introduce categories of
different ratings of DG. The following categories
are suggested:
Micro distributed generation: 1 Watto5 kW;
Small distributed generation: 5 kWo5 MW;
Medium distributed generation: 5 MWo50 MW;
Large distributed generation: 50 MWo300 MW.
Furthermore, this definition neither defines the
area of the power delivery, the penetration, the
ownership nor the treatment within the network
operation. It also does not define the technologies
used, which can vary widely. The categories of
renewable and non-renewable DG are suggested as
possible.
DG is now being connected at distribution
level, which has led to the characteristics of the
network being changed [3]. Existing distribution
networks are passive in that they were designed
and built purely for the delivery of electricity to
customers. The introduction of DG is changing
the characteristics of the distribution networks. It
has led to increased and bi-directional active and
reactive power flows, along with wider variation in
voltage levels, both of which affect the operation
of equipment on the network and the extent of
losses.
Distribution networks are also characterised by
a design short-circuit capacity. As the level of
installed capacity increases, in the case of
DG penetration, it is a fundamental requirement
that the maximum short-circuit rating for all
equipment is not exceeded.
The above changes to the use of the network
together with the potentially high penetration of
DG have led to the need for an effective and
easily used technique to optimise both the rating
and positioning of these generators within an
established network. The issues that need to be
considered in the choice of rating and positioning
of DG include both technical and commercial
factors [4–12]. The technical issues include the
adequacy of the network’s and associated plant’s
thermal rating, fault levels and sufficient voltage
support to insure both the security and quality of
electricity supply. The commercial issues include
the cost of DG, installation charges, operating
Copyright r 2009 John Wiley & Sons, Ltd.
costs, revenue expectations and the value of
reduced losses in the network. Specifically in [4],
the authors employ an optimal power flow
technique to maximise DG capacity with respect
to voltage and thermal constraints. In [5], genetic
algorithms were used to place generation
such that losses, costs and network disruption
were minimised and the rating of the generator
maximised. The constraints considered were voltage, the thermal short circuit and generator active
and reactive power capabilities. In [6], a determination of the allowable DG penetration level is
carried out based on the harmonic limit consideration, which is restricted to radial distribution
feeders with a uniform, linearly increasing or decreasing load pattern. The methodology of [7]
determines the optimal DG allocation with respect
to technical constraints such as voltage and
thermal current constraints, equipment ratings
and short-circuit levels. The basis for this methodology is in exploiting the interdependence, if any,
of the buses with regard to the constraints.
The constraints all have either linear or approximately linear characteristics with respect to increasing power injections, or they place a fixed and
independent limit on the power injection. The
authors of [8] apply tabu search techniques to locate DGs and minimise overall power losses. The
authors of [9] present a genetic algorithm approach that, for a defined planning horizon,
minimises the cost of network investment
and losses whilst meeting feeder thermal, voltage
profile and fault-level constraints. In [10], a
combination of fuzzy non-linear goal programming
and genetic algorithm techniques is used to locate
DGs and minimise overall power losses. In [11], the
authors use a heuristic approach to determine the
optimal DG size and site from an investment point
of view. In [12], a multi-objective procedure for
optimal DG siting and sizing is proposed. The goal
of the methodology is to establish the best
penetration level of DG, which maximises the
benefits of the presence of generators in a
distribution network as well as limits the network
performance deterioration due to DG not being
connected in optimal locations. Finally, [13]
describes a new model of energy infrastructure,
which consists of integrating different kinds of DG
Int. J. Energy Res. (2009)
DOI: 10.1002/er
INVESTIGATION OF THE DISTRIBUTED GENERATION PENETRATION
utilities in an energy (electricity and heat) generation
network controlled by a central energy management
system referred to as virtual utility.
This paper investigates the results of DG
penetration in a weak medium voltage (20 kV) network. The network is located in West Macedonia,
Greece. The connected DG resources are in their
entirety small hydroelectric plants with a total
capacity of about 11.5 MW. Their locations are
predetermined. Specifically, the influence of DG on
the network branch currents and voltage profile as
well as on the short-circuit level (SCL) at the
medium voltage busbars of the infeeding substation
are examined using a commercial-grade software
package. The arising technical problems are
explored and solutions (alternative DG connection,
reconductoring) are proposed. An initial proposal
for optimum DG penetration in the predetermined
network positions is also given. A real-world study
case, rather than a simplified academic network, is
selected to be analysed in this paper to specify,
as accurately as possible, the arising practical
problems and to use this experience in the future in
the development of a fast and reliable method for
the determination of optimal DG allocation in
random network positions.
2. TECHNICAL CONSTRAINTS
The following constraints are taken into account
during the investigation of DG penetration in the
examined network:
Thermal Constraint: the rated current of the
lines, Iirated, must not exceed
ð1Þ
Ii oIirated
where Ii stands for the current flowing at each
branch.
Transformer Capacity: the amount of generation connected minus the minimum load must
not exceed the rating of the transformer at the
higher voltage.
SCL Constraint: distribution networks are
characterised by a design short-circuit capacity,
i.e. a maximum fault current never to be exceeded, related to the rating of switchgear and
the thermal and mechanical endurance of all
Copyright r 2009 John Wiley & Sons, Ltd.
equipment and standardised constructions [14].
Hence, a basic requirement for permitting the
interconnection of DG is to ensure that the
resulting SCL remains below the network
design value (SCLrated). The SCL is highest
at the medium voltage transformer busbars
(SCLmax). The following relation gives the
constraint:
SCLmax oSCLrated
ð2Þ
Voltage Variation Constraint: when DG units
are connected at the distribution network, the
generator voltage will be the load/bus voltage
plus some value related to the impedance of
the line connecting them and the power flows
along that line [7,15]. The increased active
power flows on the distribution network have
a large impact on the voltage level because the
resistive element of the lines on distribution
networks is higher than other lines. The
following relation gives the constraint:
ei % ¼ Ui UT 100pjemax %j i8N
U
ð3Þ
mean
where ei is the voltage variation and Ui is the
voltage value at the ith bus, UT is the voltage
value at the substation busbars (UTmin for
minimum load and UTmax for maximum load,
determined by the marginal operation of the
transformer tap changer), Umean is the mean
voltage value at the substation busbars, emax
the permissible voltage variation and N is the
number of buses. The constraint is usually
examined for minimum load, as this is the
worst-case scenario for voltage rise.
3. NETWORK DESCRIPTION
Figure 1 shows the examined distribution network
with DG penetration. This network is situated in
West Macedonia, Greece. It is one of the main
medium voltage lines (named line 23) fed by a 25
MVA, 150/20 kV substation. There are also three
other main lines, which stem from this substation.
Line 23 is a radial network having mainly overhead
Int. J. Energy Res. (2009)
DOI: 10.1002/er
G. N. KOUTROUMPEZIS ET AL.
Figure 1. Network diagram.
lines. The main feeder consists mostly of 95 mm2
ACSR conductors, but there are also many lateral
branches consisting of 16 mm2 ACSR conductors.
The main buses such as lateral branch origins or load
positions are marked with the letter P in Figure 1,
whilst the letter S is used for the secondary buses. DG
units of a total power of about 11.5 MW are
connected in four network positions (P6, P19, P29
and P31). All these resources are small hydroelectric
plants.
Also given in Figure 1, except for the conductor
sizes, are the branch lengths and the installed maximum loads in Amperes, all coincident to the maximum load of the main feeder, which is equal to
110 A (or equally about 4 MVA). Analytical data
for all the network components are given in Table I.
4. NETWORK STUDY
Taking into account that the total DG penetration
is 11.52 MW or about 11.52/0.95 5 12.12 MVA
and that the minimum network load is about 20 A
or equally 0.706 MVA, their difference is about
11.5 MVA, which is smaller than the substation
rating (25 MVA). There is no DG penetration in
the other feeder stem from the 25 MVA substation.
So the second constraint of Section 2 (transformer
capacity) is not breached.
Copyright r 2009 John Wiley & Sons, Ltd.
The other constraints concerning the conductor
rated currents, the voltage profile of the network and
the SCLmax are examined by using the
NEPLAN software package [16] for power flow
analysis and short-circuit computation. Especially for
the SCL computation, the IEC60909 [17–20] is used.
First, power flow analysis is executed to calculate
the branch currents and the bus voltages of the
network given in Figure 1 for minimum load and
voltage supply (UTmin ¼ 20:4 kV). The results
of this analysis according to the branch currents
are that these currents are very small without DG
penetration. They become much bigger when the
DG units are connected to the predetermined
network buses, because of the increased power flow,
but they remain smaller than the rated conductor
currents. So the first constraint (thermal constraint)
of Section 2 is not breached.
The bus voltage variation is given in Table II
according to relation (3) for minimum load. As
Table II shows, the permissible voltage variation
(73% of the mean voltage value at the substation
busbars, which is equal to 21 kV, is the value which
the Public Power Corporation demands) is not
exceeded when no DG connection exists. But when
all the DG units are connected to the network
there is an impermissible voltage rise at the
buses of the route P4-P8, P9 and a marginally
Int. J. Energy Res. (2009)
DOI: 10.1002/er
INVESTIGATION OF THE DISTRIBUTED GENERATION PENETRATION
Table I. Network data.
Network Feeder Q
UnQ 5 150 kV, SCLQ 5 197 MVA, RQ/XQ 5 0.1
Network Transformer
SCLrated 5 250 MVA, SrT 5 25 MVA, tr. 5 150/20 kV, UTmax 5 21.4 kV, UTmin 5 20.4 kV, UmeanE21 kV
HEP West Greece Participations S.A. 1, 1.66 MW
Generator G1
Synchronous, PELTON, PrG1 ¼ 1:66 MV, UrG1 ¼ 660 V, x00d1 ¼ 0:131 p.u.,
xd1 ¼ 2:39 p.u., cos jrG1 ¼ 0:95 (inductive)
Transformer T1
SrT1 ¼ 2 MVA, trT1 ¼ 20=0:66 kV, ukrT1 ¼ 5:66%, uRrT1 ¼ 1%
HEP West Greece Participations S.A. 2, 2 1.58 MW
Generators (G2, G3)
Synchronous, PELTON, PrG23 ¼ 1:58 MW, UrG23 ¼ 660 V, x00d23 ¼ 0:133
p.u., xd23 ¼ 2:4 p.u., cos jrG23 ¼ 0:95 (inductive)
Transformers T2,T3
SrT23 ¼ 2 MVA, trT23 ¼ 20=0:66 kV, ukrT23 ¼ 6:25%, uRrT23 ¼ 1%
PPC Renewables S.A., 1.5 MW13.2 MW
Generator G4
Synchronous, PELTON, PrG4 ¼ 1:5 MW, UrG4 ¼ 660 V, x00d4 ¼ 0:14 p.u.,
xd4 ¼ 1:5 p.u., cos jrG4 ¼ 0:95 (inductive)
Generator G5
Synchronous, FRANCIS, PrG5 ¼ 3:2 MW, UrG5 ¼ 6:3 kV, x00d5 ¼ 0:23 p.u.,
xd5 ¼ 2:5 p.u., cos jrG5 ¼ 0:95 (inductive)
Transformer T4
SrT4 ¼ 2 MVA, trT4 ¼ 20=0:66 kV, ukrT4 ¼ 6:0%, uRrT4 ¼ 1%
Transformer T5
SrT5 ¼ 4 MVA, trT5 ¼ 20=6:3 kV, ukrT5 ¼ 6:0%, uRrT5 ¼ 1%
HEP Distratou, 2 MW
Generator G6
Synchronous, PrG6 ¼ 2 MW, UrG6 ¼ 690 V, x00d6 ¼ 0:133 p.u., x0d6 ¼ 0:24 p.u.,
xd6 ¼ 1:77 p.u., cos jrG6 ¼ 1
Transformer T6
SrT6 ¼ 2 MVA, trT6 ¼ 20=0:69 kV, ukrT6 ¼ 5:0%, uRrT6 ¼ 1%
Medium Voltage Lines
Overhead lines
ACSR 16 mm2: RL20 C ¼ 1:098 O=km, XL 5 0.393 W/km, Irated 5 127 A
ACSR 35 mm2: RL20 C ¼ 0:52 O=km, XL 5 0.369 O/km, Irated 5 197 A
ACSR 95 mm2: RL20 C ¼ 0:192 O=km, XL 5 0.336 O/km, Irated 5 400 A
Bunched cable 3 150 mm2: RL20 C ¼ 0:2375 O=km, XL 5 0.125 O/km,
Irated 5 280 A
Underground cable
XLPE (3 240125)mm2: RL20 C ¼ 0:127 O=km, XL 5 0.115 O/km, Irated 5 410 A
Additional data
Minimum Network Load: 20 A, Maximum Network Load: 110 A, Load power factor: cos j 5 0.9, inductive,
Permissible voltage variation: emax% 5 73%
impermissible voltage rise at the bus P19, as the
greyscale cells in Table II show. The problem is
significant at the route P4-P8, P9 and taking into
account that the fourth constraint (the voltage
variation constraint) of Section 2 is breached, the
question is whether the connection of the DG units
of PPC Renewables SA to bus P6 is possible
without using a voltage regulator.
The NEPLAN software package was also used to
examine whether the network satisfies the third constraint (the SCL constraint) of Section 2 for maximum
voltage supply (UTmax 5 21.4 kV). The result is that
DG penetration causes a significant increase in
SCLmax (229 MVA instead of 197 MVA without DG
connection), as the level of installed capacity increases,
but without exceeding SCLrated 5 250 MVA, given in
Table I. So the third constraint is not breached.
Copyright r 2009 John Wiley & Sons, Ltd.
5. ALTERNATIVE PROPOSALS
The connection of the DG units of the PPC
Renewables SA to bus P6 leads to an unacceptable network voltage profile, as ascertained in
Section 4. Two alternative proposals were examined in order to solve this problem:
First proposal: connection of the DG units of
the PPC Renewables SA to bus P24 instead of
bus P6. This connection can be realised via an
existing line having an ACSR 95 mm2 conductor
7 km in length. A relative analysis shows that the
thermal constraint is not breached. The SCLmax
decreases (226 MVA instead of the initial
SCLmax 5 229 MVA). This is to be expected as
the distance of the new connection point of the
Int. J. Energy Res. (2009)
DOI: 10.1002/er
G. N. KOUTROUMPEZIS ET AL.
Table II. Bus voltage variation ei% for minimum load.
ei% with DG
ei% with DG
Bus
ei% without
DG
Existing
DG
First
proposal
Second
proposal
P1
P2
P3
P4
P5
P6
P7
P8
P9
P10
P11
P12
P13
P14
P15
P16
P17
P18
P19
P20
P21
P22
0.00
0.43
0.46
0.68
0.72
0.76
0.77
0.85
0.80
0.44
0.48
0.60
0.83
0.89
0.99
0.65
0.68
0.73
0.74
0.65
0.79
0.88
0.00
0.03
0.77
6.19
7.49
9.80
9.80
9.72
9.78
0.02
0.07
0.18
0.42
0.47
0.57
0.28
0.76
2.06
3.51
0.29
0.15
0.06
0.00
0.62
0.66
0.88
0.91
0.96
0.97
1.05
1.00
0.63
0.68
0.79
1.03
1.08
1.18
0.54
0.06
1.25
2.71
0.54
0.68
0.77
0.00
0.06
0.08
0.28
0.33
0.45
0.44
0.37
0.42
0.07
0.02
0.09
0.33
0.38
0.48
0.37
0.85
2.15
3.60
0.38
0.24
0.15
PPC Renewables SA units from the network
origin increases. The bus voltage variation when
one of the two alternative proposals is adopted is
also given in Table II. With the presumed DG
connection, the network acquires a very good
voltage profile and so the relative constraint
concerning the permissible voltage rise is no
longer breached.
Second proposal: conductor replacement at the
route P2-P6 with ACSR 95 mm2 conductors
(of about 12 km). With the implementation of
this proposal, the thermal constraint is satisfied.
SCLmax, which is now equal to 232 MVA,
remains smaller than SCLrated, even if it is
increased (because the route P2-P6 acquires
bigger conductors) compared to the initial
SCLmax, (229 MVA). The proposal improves
remarkably the network voltage profile, as
Table II shows. Only the problem related
to bus P19 remains, but this is marginal.
The implementation of this proposal gives the
possibility to supply increased loads to the route
P2-P6.
Copyright r 2009 John Wiley & Sons, Ltd.
Bus
ei% without
DG
Existing
DG
First
proposal
Second
proposal
P23
P24
P25
P26
P27
P28
P29
P30
P31
S01
S02
S03
S04
S05
S06
S07
S08
S09
S10
S11
S12
0.93
0.94
0.94
1.00
1.00
1.08
1.08
1.03
1.03
0.43
0.46
0.43
0.52
0.65
0.67
1.00
1.06
1.02
1.08
1.08
1.08
1.13
1.13
1.16
1.10
1.64
2.34
2.35
1.89
2.05
0.03
0.77
0.03
0.10
0.23
0.32
1.10
2.13
1.72
2.35
2.41
2.56
0.63
0.70
0.66
0.60
1.14
1.85
1.86
1.39
1.55
0.62
0.66
0.62
0.71
0.84
0.51
0.60
1.63
1.22
1.86
1.92
2.06
1.22
1.22
1.25
1.20
1.73
2.43
2.44
1.98
2.14
0.06
0.08
0.06
0.01
0.14
0.41
1.20
2.22
1.81
2.44
2.50
2.65
Both the proposals solve the original problem.
The selection of one or the other is a matter of
financial evaluation, the possibility of implementation and general Public Power Corporation policy.
6. OPTIMUM DISTRIBUTION FOR
MAXIMUM DG PENETRATION
The problems arising from an almost arbitrary
DG penetration in predetermined buses of a power
distribution network were examined in the previous sections and possible ways to deal with them
were proposed.
This section examines the case where the previously mentioned four buses are possible DG
connection points and the determination of an optimum distribution for maximum DG penetration in
these positions is desirable without breaching the
technical constraints given in Section 2 and also
without any network modification.
The problem is examined by exploiting the
method of [7] and also taking into account the
Int. J. Energy Res. (2009)
DOI: 10.1002/er
INVESTIGATION OF THE DISTRIBUTED GENERATION PENETRATION
thermal constraint given in Section 2. The general
idea of the above method is the maximisation of an
objective function, expressing DG capacity subject
to the technical constraints mentioned in Section 2.
The basis for the methodology is in exploiting the
interdependence, if any, of the buses with regard to
the constraints. So the constraints all have either
linear or approximately linear characteristics with
respect to increasing power injections, or they
place a fixed and independent limit on the
power injection. Table III gives the resulting DG
penetration as well as one that can be practically
realised using the standardised DG units for each
position with the technical data given in Table I
(the last column of Table III). The higher DG
penetration in the last case is due to the fact that
the DG units connected to bus P29 are working at
cos j 5 1 instead of cos j 5 0.95, as the initial
theoretical computation considers.
As Table III shows, the calculated optimum
total DG penetration (theoretical and practical) is
higher than the existing one and it has a quite
different distribution. After the connection of the
standardised DG units given in the last column of
Table III, the branch currents remain smaller
than the rated conductor currents and the SCLmax
(now equal to 229 MVA) is almost the same
compared to the initial SCLmax. The network
voltage profile for minimum voltage is very good
and it is much better than that corresponding to
Table III. Optimum DG penetration.
Optimum DG
penetration
with
standardised
DG units
Node
P19
P31
P06
Existing DG
penetration
[MW]
1.66
3.16
4.7
(Inadmissible
voltage level)
P29
2
Total 11.52
[MW]
Optimum DG
penetration
DG
[MW]
[MW] units
1.7
5.1
1.5
1.66 G1
6.32 4 G2
1.5 G4
4.25
12.55
4
2 G6
13.48
Copyright r 2009 John Wiley & Sons, Ltd.
the existing DG penetration, as a comparison
of the relative columns of Table IV shows. So all
the technical constraints given in Section 2 are
satisfied and the network acquires a very good
voltage profile as well.
The penetration of DG units having usual sizes
in a distribution network with the usual prices of
cos j causes a voltage rise. So the examination of
the network voltage profile for minimum load
is essential in order to avoid an impermissible
voltage rise. But when the DG penetration is
relatively high and cos j is inductive (even if it is
almost equal to the unit), as relevant investigation
proves, a voltage drop instead of a voltage rise
may appear. For this reason, the examination of
the voltage profile of distribution networks with
particular DG penetration for maximum load is
advisable. Table IV also shows the voltage profile
of the network given in Figure 1 for maximum
load, with the existing DG penetration and for the
optimum DG penetration given in the last but one
column of Table III. In the relative columns
of Table IV, the buses with an impermissible
voltage drop are shown in greyscale. The proposed
optimum DG distribution improves the voltage
profile of the examined network during the hours
of maximum load, particularly at the route P4-P9,
in comparison with the existing DG penetration,
as Table IV shows. The network voltage profile
for maximum load after the connection of the
DG units (existing or optimum DG penetration)
is generally improved in comparison with the
situation without DG penetration, which is an
expected result because of the increased active
power flows on the distribution network.
7. CONCLUSIONS
DG penetration in distribution networks causes
changes to their characteristics. These changes are
unacceptable, as basic technical constraints do not
apply.
This paper, exploiting a commercial-grade
software package, examines the results of concrete
DG penetration on branch currents, the voltage
profile and the short-circuit level of a realistic
medium-voltage distribution network. Problems
related to a voltage rise arose and different ways
Int. J. Energy Res. (2009)
DOI: 10.1002/er
G. N. KOUTROUMPEZIS ET AL.
Table IV. Influence of the optimum DG penetration on the bus voltage variation ei%.
ei% for minimum load
ei% for maximum load
Bus
Existing
DG
Optimum
DG
Existing
DG
Optimum
DG
P1
P2
P3
P4
P5
P6
P7
P8
P9
P10
P11
P12
P13
P14
P15
P16
P17
P18
P19
P20
P21
P22
0.00
0.03
0.77
6.19
7.49
9.80
9.80
9.72
9.78
0.02
0.07
0.18
0.42
0.47
0.57
0.28
0.76
2.06
3.51
0.29
0.15
0.06
0.00
1.31
1.04
0.79
1.22
2.01
2.00
1.92
1.98
1.34
1.39
1.50
1.74
1.80
1.90
1.78
1.30
0.03
1.51
1.79
1.93
2.01
0.00
1.57
0.94
3.46
4.57
6.64
6.59
6.22
6.47
1.60
1.83
2.44
3.71
3.99
4.51
2.21
2.35
2.62
2.71
2.22
2.94
3.41
0.00
1.96
1.85
0.99
0.73
0.14
0.20
0.60
0.32
2.00
2.24
2.86
4.16
4.45
4.98
2.73
2.88
3.16
3.24
2.74
3.49
3.96
(an alternative DG connection, reconductoring)
to deal with them were proposed. The above
mentioned problems are due to the fact that the
existing DG penetration is arbitrary to a point,
and they can be avoided if a relative study precedes
the DG installation in predetermined positions, as
the previous section clearly shows.
The method applied in the previous section for
the determination of optimum DG penetration
gives satisfactory results for small distribution
networks, a small number of predetermined DG
connection points and for DG units with the same
features. But in cases of large networks, random
penetration points (a marginal case assuming that
all the network buses are possible DG locations)
and a mix of generator technologies, the method is
laborious and time consuming. It also adopts
simplifications, which in some cases may lead to
incorrect results or perhaps to the failure to find a
solution. Therefore, the development of a new,
more accurate, fast and flexible method, working
for every size of distribution network and giving a
Copyright r 2009 John Wiley & Sons, Ltd.
ei% for minimum load
ei% for maximum load
Bus
Existing
DG
Optimum
DG
Existing
DG
Optimum
DG
P23
P24
P25
P26
P27
P28
P29
P30
P31
S01
S02
S03
S04
S05
S06
S07
S08
S09
S10
S11
S12
1.13
1.13
1.16
1.10
1.64
2.34
2.35
1.89
2.05
0.03
0.77
0.03
0.10
0.23
0.32
1.10
2.13
1.72
2.35
2.41
2.56
1.59
1.59
1.56
1.62
0.97
0.06
0.04
0.49
0.16
1.36
1.07
1.36
1.47
1.6
1.86
1.62
0.35
0.83
0.04
0.07
0.32
2.50
2.51
2.50
2.80
2.29
1.91
1.89
2.15
2.02
1.57
0.94
1.57
2.03
2.71
2.23
2.8
2.02
2.27
1.89
1.83
1.69
2.66
2.67
2.64
2.95
2.03
0.93
0.91
1.66
1.37
1.96
1.85
1.96
2.45
3.14
2.76
2.95
1.27
1.94
0.91
0.79
0.51
solution for the optimum DG allocation without
fail is necessary.
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