Harmonic enhancement in microgrid with applications on sensitive loads

International Journal of Electrical and Computer Engineering (IJECE)
Vol. 9, No. 2, April 2019, pp. 826~834
ISSN: 2088-8708, DOI: 10.11591/ijece.v9i2.pp826-834  826
Journal homepage: http://iaescore.com/journals/index.php/IJECE
Harmonic enhancement in microgrid with applications on
sensitive loads
Montaserbillah Hafez, Hussein El-Eissawi, Nabil Ayad
Egyptian Atomic Energy Authority, Nuclear Research Center, Cairo, Egypt
Article Info ABSTRACT
Article history:
Received Aug 9, 2018
Revised Nov 2, 2018
Accepted Nov 23, 2018
Power quality issues are an important and growing problem in microgrid.
There are two reasons; the more active consumer is participating in the
power sector, the use of renewable energy which having a great impact on
voltage variation. This paper discusses power quality disturbance and
especially harmonic distortion issues in microgrid, and suggests a solution to
maintain the operation of the distribution system within power quality
standard. To protect sensitive loads from harmonics produced by the grid and
by renewable energy sources, passive harmonic filter has been proposed in
this paper. The electrical system of a nuclear research reactor as sensitive
loads is designed by using Electrical Transient Analyzer Program (ETAP)
software. The results show these technical issues are presented with their
influence on electrical voltage and harmonic specter.
Keywords:
ETAP
Harmonic distortion
Microgrid
Passive filter
Power quality Copyright © 2019 Institute of Advanced Engineering and Science.
All rights reserved.
Corresponding Author:
Montaserbillah Hafez,
Egyptian Atomic Energy Authority,
Nuclear Research Center, Cairo, Egypt.
Email: eng.mon@hotmail.com
1. INTRODUCTION
The modern microgrid has brought large challenges to controlling the power quality. Because of the
demands for extremely efficient consumption, the diversity of loads, in addition to the use of renewable
energy source (Photovoltaic (PV), biomass, wind, etc.) generation source, and grid connection technology
through the power electronics borders [1], [2].
The Electrical Power Quality is the supply of reliable power to its customer at designed rating of
voltage and frequency with ideal sinusoidal voltage and current waveform [3], it is affected due to various
reasons in modern power electronic world because of the usage of power electronic semiconductor based
devices and power quality disturbances [4], [5].The definition of Power quality according to the IEEE
Standard “The concept of powering and grounding electronic equipment in a manner suitable to the operation
of that equipment and compatible with the premise wiring system and other connected equipment” [6].
Power quality problem include phenomena such as voltage fluctuation, voltage unbalance, very short
interruptions, voltage sag, and harmonics distortion [7], [8]. This paper deals with reduction of devastation
effects caused by harmonics which is type of power quality problem.
Harmonic distortion causes some unexpected conditions on the electrical system. Harmonic
distortion can decrease the accuracy of the electrical meter. Harmonic distortion may also cause excessive
dissipation of electrical equipment so as to increase the cost of the bill [9], [10]. Furthermore, harmonic
distortion causes electrical equipment not to work on the specified power quality standards causing a
decrease in the lifetime of the electrical equipment [11], [12]. The harmonics generation from renewable
energy source depends on the type of inverters will be divergent. In Photovoltaic depends on the type of
control strategy and the size of PV systems and also on the grid voltage harmonics [13]. In wind energy,
the converter is used to convert variable voltage from the induction generator to DC voltage, just like that
producing DC power. The DC voltage is converted to AC voltage that is suitable for electrical operations in

Int J Elec & Comp Eng ISSN: 2088-8708 
Harmonic enhancement in microgrid with applications on sensitive loads (Montaserbillah Hafez)
827
the grid. However, the use of converters injects a high intensity of current harmonic low frequency content
into the power system [2].
Employing active and passive filters can improve the power factor and minimize harmonic currents.
Active filters are highly flexible, but they increase system complexity and costs [14]. Passive filters are
simpler and more economic, offering both the power-factor correction and high current-filtering
capacity [15]. They also reduce harmonic voltages in installations where the supply voltage is disturbed [16].
Various methods have been proposed for designing the passive filters [17]-[20]. The goal is to minimize the
harmonic impedance at specific frequencies and to maximize the fundamental frequency impedance of the
filter for minimizing losses. However, re-calculations are required for each load change [16].
In this research, the nuclear research reactor is the case study to reduce the harmonic distortion.
The authors design of single-tuned passive filter for suppressing the harmonic currents. Two types of
harmonics produced by the grid and by renewable energy sources are modeled using ETAP. The limitation of
harmonics pollution present at the point of common coupling (PCC) had been control by IEEE Std. 519 to
improve the power quality, which widely accepted in nuclear research reactor.
2. PASSIVE HARMONICS FILTERS
For mitigating the harmonic distortion passive filtering is the simplest conventional solution [21].
Passive elements like resistance, inductance and capacitance are used by the passive filters to control the
harmonics. Common types of passive filters and their configurations are depicted in Figure 1.
Figure 1. Passive power filters
The shunt connection of passive filters with the power system provides least impedance path to the
harmonic current at tuning frequency. As compared to the shunt filter series filter is designed to carry full
load current therefore they need over current protection devices. Whereas shunt passive filter carries a
fraction of series filter current. The series filter is relatively more expensive hence shunt passive filter is
commonly used as harmonic filter. Furthermore it also provides reactive power at system
operating frequency.
The most use of passive filter is a Single Tuned Filter (STF). The most commonly used passive filter
is the single-tuned filter. This filter is simple and least expensive as compared with other means for
mitigating the harmonic problems [22], [23]. The LC STF (Single Series Filter) is most common and
inexpensive type of passive filter. This filter is connected in shunt with the main distribution system and is
tuned to present low impedance to a particular harmonic frequency. Therefore; harmonic currents are
diverted from the least impedance path through the filter. For designing the single tuned filter it is essential to
select the appropriate capacitor value that enables good power factor at system frequency. Placing these
filters in close proximity to the disturbing devices is a more expensive solution, but it is a solution that
provides reduced losses in the power network [24], [25].
3. ETAP SIMULATION AND MITIGATION OF HARMONICS
3.1. Brief introduction of ETAP software
ETAP is a comprehensive analysis tool for power system design and testing developed by
OTI company. ETAP is enterprise software with fully graphical interface. It can switch multiple functional
interfaces in the same program and the operation is very convenient. The ETAP harmonic analysis module
can simulate various power components and devices accurately. The module has two analysis methods:
harmonic wave power flow and harmonic frequency scan. In order to explore the harmonic distortion and

 ISSN: 2088-8708
Int J Elec & Comp Eng, Vol. 9, No. 2, April 2019 : 826 - 834
828
diffusion characteristics in the nuclear research reactor, this paper conducts the analysis and calculation using
the harmonic analysis tool in ETAP. This tool, which complies with IEEE 519 standards, embedded the
power flow algorithm of Newton- Raphson and Gauss-Seidel and can customize the harmonic source model,
is able to evaluate the distortion rate and system resonance quickly.
3.2. ETAP simulation of electrical system for nuclear research reactor
In this paper, the microgrid of nuclear research reactor is simulation by ETAP 12.6. A feeder with
short-circuit power Ssc=65 MVAsc connected to the 11 kV bus, bus 2 (PCC) connected to the 11 kV bus via
500 kVA (11/0.4 kV) transformer. There are four lumped loads (two static loads and the other two are motor
loads), 100 KVA each. In addition, the Renewable energy source contains photovoltaic panels (150 KVA)
and wind turbines (400 KVA) are connected to bus 3. Lumped load 5 is an external load. The circuit diagram
is shown in Figure 2, and the relevant element parameters are shown in the diagram. There are two study
cases of source of harmonic and effected on PCC.
Figure 2. Circuit model in ETAP 12.6
Case 1: Harmonic from Grid:
The source of harmonic is the grid and effect on the PCC, bus 3 is disconnected. First step in this
study was to assess the harmonic distortion of the PCC without any technical solution addition, for distortion
mitigation. After performing the harmonic power flow simulation is shown in Figure 3, the results of THD
values of the buses. IEEE 519 standard of limits of harmonic voltage are shown in Table 1.
Figure 3. Harmonic flow simulations without filters

829
Table 1. Voltage Distortion Limits
Bus voltage V
at PCC
Individual harmonic
(%)
Total harmonic distortion THD
(%)
V ≤ 1.0 kV 5.0 8.0
1 kV < V ≤ 69 kV 3.0 5.0
69 kV < V ≤ 161 kV 1.5 2.5
161 kV < V 1.0 1.5
It can be seen that there are a serious harmonic pollution in bus 2 (PCC) complies with IEEE 519
standards. Figure 4 represents the value of harmonic spectrum for the voltage of the PCC.
Figure 4. Harmonic spectrum of the PCC without filters
In the harmonic spectrum, there are significant levels of harmonic ranks 5th, 7th, 11th, 13th.
Figure 5 presents the voltage waveforms distortion of the PCC without any technical solution addition.
Figure 5. Voltage waveforms of the PCC without filters
The second step in the simulation is to solve the issue caused by the grid. The solution is to connect
a passive harmonic filter in the PCC bus to reduce this order. The harmonic analysis simulation is presented
in Figure 6 and the results for THD. The next table shows the data of harmonic filter:
Table 2. Data of Harmonic Filter
5th 7th 11th
L(uH) 157.24 82.44 33.42
C(uF) 2741 2741 2741
0
1
2
3
4
5
6
7
8
9
10
1 3 5 7 9 11 13 17 19 23 25
VoltageSpectrum(%)
Harmonic Order
Without
STD
-150
-100
-50
0
50
100
150
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1
Voltage(%)
Time (Cycle)

 ISSN: 2088-8708
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Figure 6. Harmonic flow simulation with filters
Figure 6 shows the THD values, which have a large decrease in bus 2 after connected the filters.
Figure 7 represents the harmonic spectrum level of the voltage waveform of the PCC with single-tuned
passive filter.
Figure 7. Harmonic spectrum of the PCC with filters
In the harmonic spectrum, there are found significant decrease for the values of harmonic ranks.
Figure 8 presents the voltage waveforms distortion of the PCC with filters.
Figure 8. Voltage waveforms of the PCC with filters
0
0.5
1
1.5
2
2.5
3
3.5
4
4.5
5
1 3 5 7 9 11 13 17 19 23 25
VoltageSpectrum(%)
Harmonic Order
-150
-100
-50
0
50
100
150
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1
Voltage(%)
Time (Cycle)

831
In Figure 8, there are improved voltage waveforms, a profile which resembles much to the
sinusoidal. This smoothness is created by connecting harmonic filters after identifying the issues caused by
grid.
Case 2: Harmonic from Renewable energy:
The source of harmonic in renewable energy is the wind and Photovoltaic (PV) and effect on the
PCC, and the grid is disconnected. The harmonic power flow simulation is shows in Figure 9.
Figure 9. Harmonic power flow simulation without filters
It can be seen that there are a serious harmonic pollution in bus 2 (PCC) complies with IEEE 519
standards. Figure 10 represents the level of harmonic spectrum for the voltage of the PCC of the distribution
system.
Figure 10. Harmonic spectrum of the PCC without filters
Figure 11. Voltage waveforms of the PCC without filters

 ISSN: 2088-8708
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In the harmonic spectrum we have significant values of harmonic ranks 5th, 7th, 11th, 13th.
Figure 11 presents the voltage waveforms distortion of the PCC without any technical solution addition.
Figure 12. Harmonic flow simulation with filters
The solution is to connect a passive harmonic filter in the PCC bus to reduce this order.
The harmonic flow simulation is presented in Figure 12.
Figure 12 shows the THD values, which have a large decrease in bus 2 after connected the filters.
Figure 13 represents the harmonic spectrum level of the voltage waveform of the PCC with passive filters.
Figure13. Harmonic spectrum of the PCC with filters
In the harmonic spectrum, there are found significant decrease for the values of harmonic ranks.
Figure 14 presents the voltage waveforms distortion of the PCC with filters.
In Figure 14, there are improved voltage waveforms, a profile which resembles much to the
sinusoidal. This smoothness is created by connecting harmonic filters after identifying the issues caused by
renewable energy.

833
Figure 14. Voltage waveforms of the PCC with filters
4. CONCLUSION
Power quality and especially harmonic issues in the microgrid is presented. A single-tuned Passive
Harmonic Filter is used to mitigation of harmonics in the nuclear research reactor from grid and from
renewable energy source was proposed. The measurements show increasing in the 5th, 7th, 11th, 13th.
Harmonics level above their permissible limits which resulted in a failure of some devices. The test system is
simulated in ETAP software environment with the measured harmonic content. The proposed passive filter
does not create resonance with system and offers low impedance track to harmonic current. Moreover, it
yields good results in terms of total voltage and current harmonic distortion when compared with IEEE 519-
1992 standard.
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