Distributed Generation in Electric Power Systems:
An Overview and Important Issues
RUDY GIANTO, M. IQBAL ARSYAD, PURWOHARJONO, FITRI IMANSYAH, K. H. KHWEE
Department of Electrical Engineering,
University of Tanjungpura,
Jalan Prof. Dr. H. Hadari Nawawi, Pontianak 78124,
INDONESIA
Abstract: - This paper discusses distributed generation (DG) in electric power systems. Various popular DG
technologies that are currently used are also described, along with brief explanations of their working
principles. It has been acknowledged that the integration of DG with renewable energy sources in power
systems is increasing and will grow further. The main reason for this growth is the rising cost and
environmental concerns of non-renewable energy sources (fossil fuels). Furthermore, DG offers some
advantages, such as reducing power losses in transmission and distribution lines and improving power supply
security. However, the increasing DG penetration brings technical implications for the power system to which
the DG is connected. These critical issues are also highlighted in the present paper.
Key-Words: - distributed generation, electric power system, distributed generation technologies, renewable
energy sources, distributed generation effects
Received: August 22, 2022. Revised: August 19, 2023. Accepted: September 16, 2023. Published: October 26, 2023.
1 Introduction
The typical structure of an electric power system is
given in Figure 1. Conventional power generating
stations (for example, steam, hydro, and nuclear
power plants) are generally large and can have a
power rating of up to 1000 MW. These power
generation stations are usually located far from load
centres. Thus, the generated electrical power must
be delivered through some long transmission lines.
Because the generator voltage is typically low (6 to
24 kV), the generator voltage is increased using a
power transformer to a higher voltage level
(transmission voltage level). The higher voltage
level is intended to increase the transmission line
capacity and reduce power losses in the
transmission line. The voltage reduction from the
transmission voltage level is first carried out at the
transmission substation, where the voltage is
reduced to a lower voltage (sub-transmission
voltage level). Then, a second reduction is carried
out at the distribution substation, where the voltage
is further reduced to a distribution voltage level.
Generators in conventional electric power
systems generally use energy from fossil fuels (non-
renewable energy). It has been well acknowledged
that the extensive use of fossil fuels will
significantly affect global climate conditions due to
environmental pollution. Furthermore, because the
electrical power must be delivered through long
transmission and distribution lines, there will be
significant power losses in these lines. These power
losses are estimated at around 4 – 5% in
transmission lines and 10 – 15% in distribution
lines, [1].
Fig. 1: Electric power system structure
Another disadvantage of the conventional
electric power system is that the electric power
flowing in the transmission line will also increase
with the growth of the system load. If the power
flow exceeds the line capacity, it needs to be
improved by replacing or adding a new transmission
line. This improvement will require quite significant
investment costs.
WSEAS TRANSACTIONS on POWER SYSTEMS
DOI: 10.37394/232016.2023.18.18
Rudy Gianto, M. Iqbal Arsyad,
Purwoharjono, Fitri Imansyah, K. H. Khwee
E-ISSN: 2224-350X
172
Volume 18, 2023
The disadvantages of conventional power
systems described above are the main reason for the
increasing installation of distributed generation
(DG) in electric power systems. DGs are power
generation plants located close to load centres (in
the distribution or sub-transmission systems). DG
has a smaller capacity compared to conventional
generators (Table 1), [1], [2]. Some of the DG
technologies that are currently popular include wind
power, solar photovoltaic, fuel cells, gas turbines,
and microturbines, [1], [2].
Table 1. DG capacity
No
DG
Capacity
1
Micro
< 5 kW
2
Small
5 kW – 5 MW
3
Medium
5 MW – 50 MW
4
Large
> 50 MW
In Figure 2, DGs of the form wind power plants
are installed in the distribution systems (primary and
secondary distribution systems). Because it is close
to the load centre, no power is lost in the
transmission line (or the total power loss in the
transmission line can be reduced). Furthermore,
with the presence of DG, power flow in the
transmission line can also be reduced, and the line
capacity may not need to be improved if there is an
increase in system load.
Fig. 2: DG in electric power system
Energy sources in DG generally come from
renewable energy sources (for example, wind or
solar) and, therefore, will not affect global climate
conditions. This paper discusses DG in electric
power systems. Various popular DG technologies
that are currently used are also described and briefly
explained. Important issues related to DG
penetration in power systems are also given in the
present paper.
2 DG Technologies
As mentioned before, some of the DG technologies
that are currently popular include wind power, solar
photovoltaics, fuel cells, gas turbines, and
microturbines. Table 2, Table 3 and Table 4 show
comparisons of these DG technologies, [1]. It can be
seen from Table 2 that fuel cells, gas turbines, and
microturbines have higher efficiencies than wind
powers and solar photovoltaics. Meanwhile, Table 3
shows that the installation and maintenance costs of
solar photovoltaics are higher than other DG
technologies. However, these DG technologies (and
also wind power) are relatively clean as they do not
produce pollutant emissions (Table 4).
Table 2. Comparison of DG technologies (power
output and efficiency)
Power Output
Efficiency (%)
300 kW – 5 MW
20 – 40
300 kW – 2 MW
5 – 15
1 kW – 20 MW
80 – 90
15 kW – 50 MW
80 – 90
25 kW – 500 kW
80 – 85
Table 3. Comparison of DG technologies
(installation and maintenance costs)
Technology
Installation Cost
($/kW)
Maintenance Cost
($/MWh)
Wind Power
1,000 – 5,000
1 – 4
Solar
Photovoltaic
6,000 – 10,000
10
Fuel Cell
1,000 – 5,000
5 – 10
Gas Turbine
400 – 1,200
3 – 8
Microturbine
5 – 10
5 – 10
Table 4. Comparison of DG technologies (pollutant
emissions)
CO2 (kg/MWh)
NOx (kg/MWh)
0
0
0
0
430 – 490
0.005 – 0.01
580 – 680
0.3 – 0.5
720
0.1
2.1 Wind Power
The basic principle of a WPP (Wind Power Plant)
system is based on the following two processes:
conversion of kinetic energy from moving air
(wind) into mechanical energy and conversion of
mechanical energy into electrical energy. The
conversion of kinetic energy into mechanical energy
WSEAS TRANSACTIONS on POWER SYSTEMS
DOI: 10.37394/232016.2023.18.18
Rudy Gianto, M. Iqbal Arsyad,
Purwoharjono, Fitri Imansyah, K. H. Khwee
E-ISSN: 2224-350X
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is carried out by a wind turbine, while the
conversion of mechanical energy into electrical
energy is carried out by an electric generator.
Figure 3 briefly explains the process of electric
power generation by the WTG (Wind Turbine
Generator) unit in the WPP system. The turbine
blades will start to spin when exposed to wind, and
it will, in turn, rotate the generator rotor. The turbine
rotor is usually coupled to a gearbox, and the
gearbox shaft is connected to the generator rotor.
The gearbox is needed to convert the turbine rotor's
low speed to the higher speed required by the
generator to generate electrical power. A WPP
usually contains a group of WTG units. A collection
of WTG units located in one area to produce
electrical power is referred to as a wind farm or
wind park (Figure 4).
Fig. 3: WTG unit
Fig. 4: A wind farm
Based on the rotational speed, WPPs can be
divided into two groups, namely: (i) fixed or near
fixed-speed WPPs, and (ii) variable-speed WPPs. In
fixed-speed WPP, the system frequency to which
the WPP is connected will determine the rotational
speed of the WPP generator. Therefore, the
generator speed of this type of WPP is only allowed
to vary at very narrow intervals (typically around 1
– 2% above synchronous speed). Fixed speed WPP
generally utilizes a SCIG (Squirrel Cage Induction
Generator) to convert wind energy to electrical
power. Since fixed-speed WPP only operates at 1 –
2% above synchronous speed, the conversion of
wind energy to electric energy will not be optimal.
This disadvantage has recently resulted in the
increasing use of variable-speed WPPs, [3], [4].
In variable-speed WPPs, wind energy conversion
to electrical power is usually carried out using a
DFIG (Doubly Fed Induction Generator) or PMSG
(Permanent Magnet Synchronous Generator).
However, DFIG is currently more popular because
the price is cheaper. Compared to fixed speed WPP,
DFIG-based variable speed WPP can operate at a
much wider rotation speed range. The generator
speed of this type of WPP can vary between 40%
below synchronous speed and 30% above
synchronous speed. This wider speed range
operation is the reason why DFIG-based variable
speed WPP can extract more wind energy than fixed
speed WPP, [4].
2.2 Solar Photovoltaic
PV (Photovoltaic) cells in an SPV generator utilize
semiconductor material (usually in the form of
silicon cells) for directly converting solar radiation
to electrical energy. These PV cells are generally
connected in series and referred to as a PV module.
This series connection is made so that the PV
module can produce voltage with a desired
magnitude. An SPV generator typically consists of
several PV modules connected in a series-parallel
combination, as shown in Figure 5. This series-
parallel combination of PV modules is known as a
PV array and is intended so that the SPV generator
can generate the required voltage and power. Figure
6 presents a basic configuration of an SPV
generator. Figure 6 shows that the main components
of an SPV generator include the PV array, VSC
(Voltage Source Converter), and filter.
2.3 Fuel Cells
Fuel cell (FC) directly converts the chemical energy
contained in fuel (for example, hydrogen, natural
gas, methanol, gasoline, etc.) into electrical energy.
Figure 7 shows the basic configuration of a single-
cell FC. As shown in Figure 7, a single cell FC
contains two electrodes, namely a negative electrode
(anode) and a positive electrode (cathode). An
electrolyte separates the two electrodes. The fuel
(e.g., hydrogen) is supplied at the anode, and the
oxidant (usually air or oxygen) is supplied at the
cathode. Oxidation and reduction processes will
occur on the two electrodes and will produce an
WSEAS TRANSACTIONS on POWER SYSTEMS
DOI: 10.37394/232016.2023.18.18
Rudy Gianto, M. Iqbal Arsyad,
Purwoharjono, Fitri Imansyah, K. H. Khwee
E-ISSN: 2224-350X
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electric current. The process that occurs at these
electrodes can be accelerated by using a catalyst.
Fig. 5: PV array
Fig. 6: SPV generator
Fig. 7: Single-cell FC
A single-cell FC can only produce an electric
voltage of less than 1 Volt. Higher voltage can be
obtained by arranging several single-cell FCs in
series, as shown in Figure 8. In multi-cell FCs, each
cell is usually separated via a bipolar separator
plate. The number of cells arranged depends on the
desired power output and performance of each cell.
Because FC does not have a hydrocarbon
combustion process, it does not produce pollutant
emissions such as COx and NOx, so it can be
considered clean from an environmental point of
view. Based on the electrolyte material used, FC can
be classified into PEMFC (Proton Exchange
Membrane Fuel Cell), DMFC (Direct Methanol
Fuel Cell), PAFC (Phosphoric Acid Fuel Cell), AFC
(Alkaline Fuel Cell), MCFC (Molten-Carbonate
Fuel Cell ), and SOFC (Solid Oxide Fuel Cell).
Fig. 8: Multi-cell FC
2.4 Gas Turbine and Microturbine
The basic configuration of a gas turbine that drives
an electric generator is shown in Figure 9. It can be
seen that the gas turbine system consists of three
main components, namely: compressor, combustion
chamber, and turbine. The incoming air is
compressed in the compressor to increase its
temperature and pressure. This hot, high-pressure air
is mixed with fuel (usually natural gas) and burned
in a combustion chamber. This combustion causes
the gas volume to increase and be expanded into the
turbine so that the turbine produces mechanical
power to rotate the electric generator. In Figure 9, it
can be seen that the turbine is also used to rotate the
compressor. The power required to rotate the
compressor is usually around 40% - 80% of the
turbine power output. A microturbine is a smaller-
scale gas turbine. The microturbine components are
often made from the same materials as the gas
turbine.
Fig. 9: Gas turbine and generator configuration
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DOI: 10.37394/232016.2023.18.18
Rudy Gianto, M. Iqbal Arsyad,
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3 Impacts of DG on Power Systems
3.1 Load Flow and Voltage Profile
Traditional distribution systems are designed to
receive electrical power from the transmission
system and distribute it to customers (loads). Thus,
electrical power will flow from a higher to a lower
voltage level. However, with the presence of DG in
the distribution system, the power flow direction can
be reversed, as shown in Figure 10. In this case, the
distribution network will no longer be a passive
circuit that supplies loads, but it will be an active
system where the DG will also determine the power
flows and system voltage profile. Changes in power
flow due to the DG will have technical and
economic implications for the power system to
which the DG is connected, [1], [2], [5].
(a)
(b)
Fig. 10: (a) Passive network, (b) Reverse power
It is also to be noted that with the presence of
DG, the power flow in a distribution system
component can increase beyond the component's
thermal limit (or current carrying capacity).
Furthermore, the presence of DG can increase the
system voltage. This voltage rise can be a problem
because the voltage in distribution networks is
usually specified at ±5% of the nominal or working
voltage, [2].
3.2 Short-Circuit Fault Level
In a traditional distribution system, the short circuit
current will only flow from the transmission system
to the fault point. DG installation will cause the fault
current to increase due to the additional contribution
of fault current from the DG (Figure 11). This
increase in fault current can cause the fault level (or
short circuit rating) designed for distribution system
protection devices to be exceeded. If this happens,
the short circuit rating of the protection devices
must be increased, which, of course, requires quite a
considerable cost, [2], [5].
Fig. 11: DG effect on fault level
3.3 Harmonic Distortion
Harmonics can cause the voltage wave to no longer
be sinusoidal. DG equipped with power electronic
equipment (VSC) can generate harmonics in the
electric power system. These harmonics can become
problematic if the voltage wave distortion is outside
the allowable tolerance, [2], [5].
3.4 Protection System
DG can have an impact on the protection system of
the electric power distribution network. Protection
problems arising from DG's presence in the
distribution system include blinding of protection,
false tripping, islanding, and auto-reclosing issues,
[2], [5], [6].
3.4.1 Blinding of Protection
The blinding of protection problem can be explained
by looking at Figure 12. Figure 12 shows that if
there is no DG, relay R detects a fault current equal
to the current drawn from the transmission system
(IG). However, in the presence of DG, relay R
cannot detect the contribution of fault current from
DG (IDG). In other words, relay R is blind to the
contribution of the fault current from DG, while the
magnitude of the fault current is IG + IDG.
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Rudy Gianto, M. Iqbal Arsyad,
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Fig. 12: Blinding protection
3.4.2 False Tripping
Figure 13 shows two feeders (Feeder 1 and 2) of a
distribution network wherein one of the feeders
(Feeder 1) has a DG. Both feeders are protected by
overcurrent relays R1 and R2. If, for example, a
fault occurs at Feeder 2. The fault current supplied
by DG (IDG) can cause R1 to trip or operate before
R2. In turn, this unnecessary trip operation will
cause the healthy feeder (Feeder 1) to be
disconnected. False or sympathetic tripping is likely
if the relay is a non-directional overcurrent. This
type of relay cannot detect the direction of the fault
current, so it cannot distinguish whether the fault is
in the forward or reverse direction.
3.4.3 Islanding
An 'islanding' condition occurs when the power flow
from the transmission system is disconnected,
causing the DG and local loads to be separated from
the system. This condition can be explained by
looking at Figure 14. If there is a fault at the feeder,
the feeder CB will open to isolate the fault. Opening
the CB results in disconnecting the power supply
from the transmission system, and the DG (along
with local loads) will be separated from the system.
This condition is undesirable and can be dangerous.
To anticipate this, the DG must be designed to
disconnect from the system (or shut down) if the
power supply from the transmission system is lost.
The exception is for feeders that supply essential
local loads (e.g., hospitals). In this case, DG can be
designed to operate both in on-grid and standalone
conditions. In VSC-based DG, islanding can be
detected using a harmonic distortion-based
technique.
Fig. 13: False tripping
Fig. 14: Islanding
3.4.4 Auto-Reclosing Problems
ARR is commonly used in medium voltage
distribution networks to anticipate temporary
(transient) faults. However, the presence of DG in
the distribution network can disrupt the operation of
ARR, which can be explained by looking at Figure
15. Figure 15(a) shows the network without DG.
When a fault occurs, ARR will send a signal to CB
to open its contacts to isolate the fault. After some
time delays, ARR will send a signal to CB to close
its contacts. When the fault has disappeared
(temporary fault), the CB will remain closed, and
the system will return to normal operation.
However, if the fault still exists (permanent fault),
ARR will again send a signal to CB to open its
contacts. If the ARR is single-shot reclosing, the CB
will remain open. However, if the ARR is multi-shot
reclosing, the CB reclosing process can occur more
than once.
With DG installation in the distribution network,
as shown in Figure 15(b), there will be two
problems. The first problem is the presence of DG
fault current (IDG), even though the CB operation
has cut off the fault current from the transmission
system (IG). This DG fault current causes the fault
arc to persist, and in turn, it will convert the fault
into a permanent fault (ARR detects that the fault is
not temporary). The second problem is that if the
ARR closes the CB after a fault, the DG may not be
in sync with the transmission system, and loss of
synchronism may occur.
WSEAS TRANSACTIONS on POWER SYSTEMS
DOI: 10.37394/232016.2023.18.18
Rudy Gianto, M. Iqbal Arsyad,
Purwoharjono, Fitri Imansyah, K. H. Khwee
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(a)
(b)
Fig. 15: Auto-reclosing problem
4 Conclusion
In this paper, DG in electric power systems has been
discussed and presented. Various popular DG
technologies that are currently used (i.e., wind
power, solar photovoltaic, fuel cells, gas turbines,
and microturbines) have also been described and
briefly explained. Critical issues related to DG
penetration in power systems are also given in the
present paper. These issues include system voltage
profile, fault level, and harmonic distortion. DG can
also impact the protection system of the electric
power distribution system to which the DG is
connected. Protection problems arising from DG's
presence in the distribution system include blinding
of protection, false tripping, islanding, and auto-
reclosing issues. These issues have also been
highlighted in this paper.
References:
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[2] N. Jenkins, J.B. Ekanayake, and G. Strbac,
Distributed Generation, The Institution of
Engineering and Technology, 2010.
[3] R. Gianto, and M. Rajagukguk, Integration of
PMSG-Based Wind Turbine into Electric
Power Distribution System Load Flow
Analysis, WSEAS Transaction on Power
Systems, Vol.17, 2022, pp. 45-52.
[4] R. Gianto, Steady-State Model of DFIG-Based
Wind Power Plant for Load Flow Analysis, IET
Renewable Power Generation, Vol.15, No.8,
2021, pp. 1724-1735.
[5] L.I. Dulau, M. Abrudean, and D. Bica, Effects
of Distributed Generation on Electric Power
Systems, Procedia Technology, Vol.12, 2014,
pp. 681-686.
[6] S.K. Salman, and A.T. Johns, Digital
Protection for Power Systems, The Institution
of Engineering and Technology, 2022.
Contribution of Individual Authors to the
Creation of a Scientific Article (Ghostwriting
Policy)
The authors equally contributed to the present
research, at all stages from the formulation of the
problem to the final findings and solution.
Sources of Funding for Research Presented in a
Scientific Article or Scientific Article Itself
No funding was received for conducting this study.
Conflict of Interest
The authors have no conflicts of interest to declare.
Creative Commons Attribution License 4.0
(Attribution 4.0 International, CC BY 4.0)
This article is published under the terms of the
Creative Commons Attribution License 4.0
https://creativecommons.org/licenses/by/4.0/deed.en
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WSEAS TRANSACTIONS on POWER SYSTEMS
DOI: 10.37394/232016.2023.18.18
Rudy Gianto, M. Iqbal Arsyad,
Purwoharjono, Fitri Imansyah, K. H. Khwee
E-ISSN: 2224-350X
178
Volume 18, 2023