Impact of rooftop photovoltaic penetration level on low

Ref. code: 25605622040581VOU

IMPACT OF ROOFTOP PHOTOVOLTAIC

PENETRATION LEVEL

ON LOW VOLTAGE DISTRIBUTION SYSTEM

BY

ORAWAN POOSRI

A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF

THE REQUIREMENTS FOR THE DEGREE OF MASTER OF

ENGINEERING (ENGINEERING TECHNOLOGY)

SIRINDHORN INTERNATIONAL INSTITUTE OF TECHNOLOGY

THAMMASAT UNIVERSITY

ACADEMIC YEAR 2017

Ref. code: 25605622040581VOU

IMPACT OF ROOFTOP PHOTOVOLTAIC

PENETRATION LEVEL

ON LOW VOLTAGE DISTRIBUTION SYSTEM

BY

ORAWAN POOSRI

A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF

THE REQUIREMENTS FOR THE DEGREE OF MASTER OF

ENGINEERING (ENGINEERING TECHNOLOGY)

SIRINDHORN INTERNATIONAL INSTITUTE OF TECHNOLOGY

THAMMASAT UNIVERSITY

ACADEMIC YEAR 2017

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ii

Acknowledgements

Firstly, the author would like to express her sincere gratitude and deep appreciation to her advisor, Assoc. Prof. Dr. Chalie Charoenlarpnopparut for his invaluable advices, enthusiastic guidance, and kind encouragement during the completion of this thesis. The author would like to give gratitude to the thesis examination committee, Asst. Prof. Dr. Prapun Suksompong, Assoc. Prof. Dr. Thavatchai Tayjasanant and Asst. Prof. Dr. Attaphongse Taparugssanagorn for their useful advices and suggestion.

Thanks to all faculties, staff and secretaries in School of Information, computer and Communication Technology for their assistance and encouragement. Grateful thanks to Provincial Electricity Authority for the great chance and scholarship to study at the Sirindhorn International Institute of Technology, Thammasat University (SIIT).

Thankful expression is given to her friends, for their help and moral support during the author study in SIIT. Furthermore, special thanks are given to MS. Kanokorn Luantungsrisuk for her helps and guidance.

Last but not least, deepest appreciation is expressed to her family for their utmost support and understanding during her study in SIIT.

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Abstract

IMPACT OF ROOFTOP PHOTOVOLTAIC PENETRATION LEVEL ON LOW VOLTAGE DISTRIBUTION SYSTEM

by

ORAWAN POOSRI

Bachelor of Engineering, King Mongkut's Institute of Technology, 2005 Master of Engineering (Engineering Technology), Sirindhorn International Institute of Technology, Thammasat University, 2018

Integration of increasing penetration level of rooftop photovoltaic in the next few years

may affect the quality of low voltage distribution system in Thailand. Harmonic current

injected from rooftop PVs may cause harmonic problem and affect power quality of

grid. Therefore, this research intends to study harmonic and unbalance voltage impact

of rooftop photovoltaic penetration level on low voltage distribution system (400/230V)

in urban area. DIgSILENT PowerFactory program is used to simulate and analyze the

impact of rooftop PVs which connected in different penetration level and two scenarios

of background system, such as balanced grid voltage, and polluted grid (with

THDv).The result of simulated model shows that the total harmonic distortion voltage

and the % Voltage Unbalance Factor of the network are over the standard when the

amount of PVs with inverter (which has THDi <2%) connected to the system is more

than 60% penetration of rated power of transformer. It would like to recommend PEA

for revise the number of rooftop PV into the LV distribution to be 15-50% of rating

transformer. However, it should be consider the other impact such as loss, power factor,

over voltage etc.

Keywords: Photovoltaic(PV), Rooftop PV, Distribution system, Distributed

generator, Harmonics Impact of Rooftop PV

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Table of Contents

Chapter Title Page

Signature Page i

Acknowledgements ii

Abstract iii

Table of Contents iv

List of Figures vii

List of Tables x

1 Introduction 1

1.1 Background 1

1.2 Statement of Problem 3

1.3 Objective 4

1.4 Significance 4

2 Literature Review 5

2.1 Impact of DG on distribution network 5

2.1.1 Voltage 5

2.1.2 Loss 7

2.1.3 Harmonic 8

2.2 Unbalance Voltage Calculation 9

2.2.1 NEMA Standards 9

2.2.2 IEEE Standards for Unbalance Power Phase 1 10

2.2.3 IEEE Standards for Unbalance Power Phase 2 10

2.2.4 Voltage Unbalance Factor 1 10

2.2.5 Negative Sequence Voltage Unbalance 11

2.2.6 Voltage Unbalance Factor 2 11

2.2.7 IEEE 1159 - 1995 14

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2.2.7.1 Voltage Unbalance Factor2 14

2.2.8 Symmetric Voltage 15

2.2.9 Calculate the voltage at various points in 17

the distribution system.

2.2.10 Three-phase power system 19

2.3 Harmonic 20

2.4 Related Standard 21

2.4.1 PRC(PEA Recommendation) 21

2.4.1.1 Voltage and Frequency Criteria 21

2.4.1.2 Electrical connection Criteria 22

2.4.1.3 Low Voltage and Over Voltage Criteria 24

2.4.1.4 Quality of Supply Criteria 24

3 Methodology 25

3.1 Simulated Model 25

3.1.1 Power Source 25

3.1.2 Distribution network 25

3.1.3 PV 26

3.2 Assumption 26

3.2.1 Residential Load Profile 26

3.2.2 PV Load Profile 26

3.2.3 Location of PV installation 27

3.3 Case Study 28

3.4 Computation hardware specification 34

4 Simulation Result and Discuss 35

4.1 Case-by-case discussion 35

4.1.1 Case Study 1 35



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4.1.10 Case Study 10 44

4.1.11 Case Study 11 45

4.1.12 Case Study 12 46

4.1.13 Case Study 13 47

4.1.14 Case Study 14 48

4.1.15 Case Study 15 49

4.1.16 Case Study 16 50

4.2 Overall discuss and comparison 51

4.2.1 PV1 @ each location type without harmonic background 51

4.2.2 PV1 @ each location type with harmonic background 52

4.2.3 PV2 @ each location type without harmonic background 54

4.2.4 PV2 @ each location type with harmonic background 55

4.2.5 PV1 and PV2 comparison @ each location type 57

4.2.5.1 Location of PV installation as Type A 57

4.2.5.2 Location of PV installation as Type B 58

4.2.5.3 Location of PV installation as Type C 59

4.2.5.4 Location of PV installation as Type D 60

5 Conclusion and Recommendation 61

5.1 Conclusion 61

5.2 Recommendation 62

References 63

Appendices 65

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Appendix A 66

Appendix B 67

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List of Figures

Figures Page

1.1 The generation of electricity from renewable energy sources 2

in 2007-2014.

2.1 Effects of PV generation - sunny day with high load. 5

2.2 Effects of DG to working characteristic of the compensator (a) and (b) 6

2.3 Effects of DG to working characteristic of the compensator 6

in the network with the recloser.

2.4 Voltage characteristics on low voltage feed line between light load 7

and nominal load under installation and non-installation of solar cells.

2.5 Annual energy losses (“three DGs” scenario). 8

2.6 Comparison of DG modeling (PQ or PV). 8

2.7 Asymmetric voltage in 3 phase system 9

2.8 The relationship between voltage unbalance factor and 13

NEMA standard at 2, 5, 10 and 20 percent unbalanced

2.9 Characteristics of unbalanced voltage at the wire to supply power 15

to the accommodation

2.10 Balance and imbalance 16

2.11 Symmetrical symmetry 16

2.12 Low voltage distribution system with radial connection 17

2.13 Voltage level Installed (a) Not installed (b) Installed DG 18

2.14 3-phase, 4-wire system 19

2.15 Phasor of the voltage 19

2.16 Connecting solar power system to distribution system 23

3.1 Single line diagram of PEA Low voltage distribution system model. 25

3.2 Daily load profile of household 26

3.3 Daily output power of rooftop PV 26

3.4 The length of feeder line a) and the zone of feeder b) 27

3.5 Type A: PV of Installation in feeder-by-feeder continuously 30

3.6 Type B: PV of Installation in the beginning zone of each feeder 31

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3.7 Type C: PV of Installation in the middle zone of each feeder 32

3.8 Type D: PV of Installation in the end zone of each feeder 33

4.1 Case Study 1 35

4.2 Case Study 2 36

4.3 Case Study 3 37

4.4 Case Study 4 38

4.5 Case Study 5 39

4.6 Case Study 6 40

4.7 Case Study 7 41

4.8 Case Study 8 42

4.9 Case Study 9 43

4.10 Case Study 10 44







4.17 Comparison, PV1 connected to grid without harmonic background 51

in each location type of PV installation.

4.18 Comparison, PV1 connected to grid with harmonic background 53


4.19 Comparison, PV2 connected to grid without harmonic background 54


4.20 Comparison, PV1 connected to grid with harmonic background 56


4.21 Comparison PV1 and PV2, when it connected to grid with/without 57

harmonic background in the location type of PV installation as Type A.


harmonic background in the location type of PV installation as Type B.

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harmonic background in the location type of PV installation as Type C.


harmonic background in the location type of PV installation as Type D.

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List of Tables

Tables Page

1.1 Status of renewable energy development in Thailand between 2012 1

and 2014

1.2 The target on using Renewable Energy at 30 Percent of Total Energy 2

Consumption by 2036

1.3 Building types, overall installed capacity and Feed-in-tariff rate 3

2.1 Comparison of Unbalance Voltage in Various Methods 12

2.2 Types and characteristics of electrical systems and electromagnetic 14

phenomena

2.3 PEA recommendation Harmonic voltage Limits for customers 20

at Point of common coupling (PCC)

2.4 IEEE Std. 519-1992 Harmonic Current Limits 21

2.5 Maximum and Minimum Voltage Levels of 22

Provincial Electricity Authority

2.6 The breakdown time when voltage is not in rated voltage range. 24

3.1 Case studies focused on this research 28

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Chapter 1

Introduction

1.1 Background

Globally, the trend of the electricity demand is higher actually. Most fuel used for generating the electric power such as coal, oil and natural gas, which are non-renewable fuel. The more expensive the cost of fuel, the higher price of the electricity power. Nowadays, many countries are interested the renewable energy thus the usage of renewable energy are increasing continuously and rapidly, because the advantages of renewable energy resource are clean, no pollution and low emission of greenhouse gases.

In Thailand, usage of Renewable energy is increasing as detail in Table 1. 1 show the status of renewable energy in end of 2012, 2013 and 2014 at 9. 95% , 10. 94% and 11. 91% respectively. The Ministry of Energy in Thailand emphasizes the renewable energy as the detail in Alternative Energy Development Plan (AEDP) 2015-2036 which set the target on using Renewable Energy at 30% of Total Energy Consumption by 2036 ( in form of electricity, heat and bio- fuel) as shown in Table 1. 2 [Alternative Energy Development Plan (AEDP), 2015].

Table 1.1 Status of renewable energy development in Thailand between 2012 and 2014 Types of Energy Unit 2012 2013 2014

Electricity* MW ktoe

2,786 1,138

3,788 1,341

4,494 1,467

Solar MW 376.72 823.46 1,298.51 Wind MW 111.73 222.71 224.47 Small Hydro Power MW 101.75 108.80 142.01 Biomass MW 1,959.95 2,320.78 2,451.82 Biogas MW 193.40 265.23 311.50 MSW MW 42.72 47.48 65.72 Heat ktoe 4,886 5,279 5,775 Solar ktoe 3.50 4.50 5.10 Biomass ktoe 4,346 4,694 5,144 Biogas ktoe 458 495 528 MSW ktoe 78.20 85 98.10 Biofuels ml./day

ktoe 4.20

1,270 5.5

1,612 6.10

1,783 Ethanol ml./day 1.40 2.6 3.21 Biodiesel ml./day 2.80 2.9 2.89 RE Consumption ktoe 7,294 8,232 9,025 Final Energy Consumption ktoe 73,316 75,214 75,804 Share of RE in Final Energy consumption

(%) 9.95 10.94 11.91

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* Including off grid power generation and not including power from the large hydro power plant

Table 1. 2 The target on using Renewable Energy at 30 Percent of Total Energy Consumption by 2036.

Energy Share Energy of RE Final Energy Consumption

at 2036 Status

As of 2014 Target

by 2036 Electricity 9 15-20 27,789

Heat 17 30-35 68,413

Biofuels 7 20-25 34,798

Final Energy Consumption

12 30 131,000

The Ministry of Energy in Thailand has been promoting the production of electricity from renewable energy continuously since 1989. The proportion of electricity from renewable energy production from electricity generation system ( Including off grid power generation) for the whole country was at 4.3 percent in 2007 and it is increased to 9.87 percent in 2014 (excluding large hydro power plant).

Figure 1.1 The generation of electricity from renewable energy sources in 2007- 2014. [Alternative Energy Development Plan (AEDP), 2015].

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In 2013, the government of Thailand encourages residential and commercial units to install rooftop PVs for producing and selling electricity through feed- in- tariff ( FIT) which is proposed to attract many people for participation with this campaign as the detail in Table 1.3.

Table 1.3 Building types, overall installed capacity and Feed-in-tariff rate.

Building Type Installed Capacity (System Size)

Overall Installed Capacity

(Quota/Target)

Feed-in-tariff rate

(Bath/unit) (1) Residence Not exceeding 10 kWp 100 MWp 6.96 (2) Small Enterprise 10 – 250 kWp 100 MWp 6.55 (3) Medium-Large Enterprise/Industry

250 – 1,000 kWp 6.16

“MWp” means the maximum megawatt of photovoltaic panel at Standard Test Condition. “kWp” means the maximum kilowatt of photovoltaic panel at Standard Test Condition.

With aforementioned above, the amount of grid connected PV systems on the distribution system will be increasing in recently.

1.2 Statement of Problem

When a large number of Rooftop PV were connected to the distribution system, the operators may face the impact of PVs such as electric power loss, voltage fluctuation, power system reliability, harmonic, stability, voltage flicker, etc.

Power electronic inverter, in Grid connected PV systems for converting DC to AC, injects harmonic currents into power system. That may downgrade the quality of power grid and affect the reliability and safety of electrical equipment.

The impacts of harmonic currents to systems and equipment include: - Capacitor bank often explode or degenerate rapidly - Main Circuit Breaker often trip - Current flowing in neutral wire increase abnormally - Transformer is over heat though it supply load lower than its limit - Wire, bus bars, CB, motor, and electric equipment are high temperature

irregularly or damaged - Control devices malfunction or are damaged Harmonic problem is detrimental thus it is the worth for paying attention about

study and analysis impact harmonic of rooftop PVs on LV distribution network.

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1.3 Objective

The objective of this research include: 1. Study and analysis the impact of rooftop PV on the low voltage distribution

network in term of harmonic and unbalance voltage. 2. Evaluate the effect the power quality of the system (in term of harmonic and

unbalance voltage) when the different of PV penetration is connected on low voltage distribution network of Provincial Electricity Authority.

3. Recommend the guidelines and the regulation to the Provincial Electricity Authority for solar rooftop installed on the in the distribution system.

1.4 Significance

According the policy of the Government of Thailand to promote the renewable energy for generating the electric power, the large number of DG dispersed in the distribution network is multiplied in a few years. PEA, as the one of the electric utility of Thailand, will face the important issue about the impact of DG to the distribution network certainly. If the penetration of rooftop PV is high that mean the large number of inverters which cause harmonic current injected into grid and network. Utility may face an even larger problem in residential network. Its disadvantages cause some electric devices and the local equipment in distribution network ( like transformer, capacitor bank) malfunction or may be damaged. It is necessary that utility should be attention to study and analysis the power quality issues which may occur, the optimization of the penetration rooftop PV in LV distribution network that minimize the impact of rooftop PV.

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Chapter 2

Literature Review

2.1 Impact of Distributed generation on distribution network

In the traditional distribution, there are the power generators as a center of the network. The power flows out to the radial network, from the generator to loads. DG rarely is important for the traditional distribution system because of the low penetration of DGs in the network. Nowadays, the number of DG in the network is higher which can affect the power quality of the distribution network such as voltage, loss, harmonic, frequency, and robustness, etc.

2.1.1 Voltage

DGs are the power generators, which give the static power factor. Wherever DG is connected to the grid, the voltage at that point is risen. If DG is an induction generator, it will supply the real power to the grid and receive the reactive power from the grid at the same time. Whereas DG is a synchronous generator, it can adjust the power factor by either supplying the real power or receiving the reactive power. In the radial distribution without DG, the more that point is far from the power station, the lower the voltage of that point is measured. The problem can be resolved by the several methods such as changing the tap of the transformer, installation the capacitor or step-type voltage regulator (SVR) for improving the voltage of the distribution line. In the case that, the grid covers the wide area, the long distance of the distribution line or having the huge demand loads. If DG is connected nearby the loads, the voltage of the distribution line will be raised. M. Begovic studied the 69- bus system, in which there are DG as PV connected and voltage compensation with the shunt capacitor. In summer, the demand of system is high. DG as PV which operate at unity power factor, provide only the active power. In this studied, PV at any buses are represented the negative active load. The penetration PV is connected for 0% to 40% of the total load in the system [M. Begovic, 2001].

Figure 2.1 Effects of PV generation - sunny day with high load. PV provides only active power.

a) Active power at bus 53 b) Voltage at bus 53

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At bus PV connected, the active power demand from the grid will decrease and the voltage is raising thus the capacitor does not need to turn on. PV provide the peak power around at noon but the peak demand load is in the sunset. In that time, PV cannot operate and maintain the voltage of system. The capacitor will be turned on for improving the voltage profile of the system. It should have the battery for keeping the power PV generated for using in the cloudy day or at the evening. DG can improve the under voltage problem especially when it is installed near the huge load and far away from the substation. When DG, which is operated at unity power factor, is interconnected to the line at the back side of the capacitor, the voltage at the terminal will be higher. Moreover, if the capacitor is turned on for the voltage compensation, it will occur the overvoltage problem at the terminal line [Ensop (n.d.)]

Figure 2.2 Effects of DG to working characteristic of the compensator (a) and (b)

Figure 2. 3 Effects of DG to working characteristic of the compensator in the network with the recloser. Therefore, the setting of the compensator must be suitable for the variation of power flow, if DG connected to the system.

(a)

(b)

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If DG is installed at the secondary side of the transformer and the load demand of system is low. The customer will face the overvoltage problem. Figure 2.4 shows the voltage characteristics on the low voltage feed line, in case of low load and medium load under conditions installation and non- installation of solar cell on the roof. When the tap changing of transformer is not worked, Installation of solar cells under the condition that medium loads will remedy the falling of the voltage. In the case of low loads, to increase the problem that the voltage is raised in the system [Demirok et al., 2009].

Figure 2. 4 Voltage characteristics on low voltage feed line between light load and nominal load under condition installation and non-installation of solar cells. [Demirok et al., 2009] 2.1.2 Loss

According to DG provide the active power, it cause the power flow from the substation is less than. Thus, the current in the distribution line and the loss of the system are lower. If the position of DG in the system is near the load and the capacity of DG is approximate to the demand load, the total loss of the system will decrease actually. On the other hand, if DG is far away from the substation and generate the power to the substation, the total loss of the system will increase. V. H. Mendez studied the annual total losses of IEEE 3 4 - node, considering the difference of DG technology such as PV, Wind turbine, CHP, Mix CHP and Wind turbine and the different of penetration DG(0%-15%). The result was presented in the graph of annual loss plotted in U-Shape. The loss is the lowest when DG penetration is low. If DG penetration is more, the loss will be higher and it is possible that the loss may be higher than the system without DG. If DG can adjust the power factor which provide both active power and reactive power, the losses will decrease more than DG operate at unity power factor [V. H. M. Quezada, 2006].

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DG will be able to reduce the losses both transmission and distribution line if the capacity and position of DG in the system is proper. In case the capacity of DG is over the demand load, the loss of the system may be higher. 2.1.3 Harmonic

Among the sustainable energy sources, the research on photovoltaic generators has received much attention, especially the study of residential photovoltaic (PV) systems, which has potential of becoming a significant market. M.C.Benhabib and EPE/EPS group, studied the influence of the harmonic current generated by photovoltaic systems connected to the low voltage network and the interaction with other non-linear loads and the voltage of the network. Simulated Model is the LV network via a 10kV/400V transformer. The secondary of transformer has 2 feeders, in which 48 houses in each feeder and all houses were install PV system which PV inverter emit the output current harmonic distortion about 3.36%. There are three scenarios: in scenario1, each house contains a PV system and a linear load, in scenario2, each house contains a PV system and one nonlinear load (RL), and in scenario3, each house contains a PV system and four nonlinear loads (2 RL and 2 RC). The result shows the effect of these harmonic currents generated by big amount of photovoltaic systems and common electronic loads and the interaction between them. From these three scenarios, although there is no nonlinear load in the first scenario, the THDv is higher than 5%, because of the non-linearity of the transformer connected between each PV and the LV network, increasing of the current harmonics injected by each PV system itself. The second remark is that the introduction of only one nonlinear load in each house leads to an increase in the THD. This is worsened with the introduction of more non-linear load as. Moreover, the increase of the THD is observed not only in the currents but also in the voltages [M. C. Benhabib, 2007].

Figure 2.5 Annual energy losses (“three DGs” scenario).

Figure 2.6 Comparison of DG modeling (PQ or PV).

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2.2 Unbalance Voltage Calculation

The problem of unbalanced voltage in 3 phase power system is another important problem in power transmission. The unbalance voltage level causes that the current being supplied to 3 phase load is unbalance .due to power failure. The imbalance system may be possible from several causes like 3 - phase load unbalancing, unbalance of 1 -phase or 2-phase loads connection, and a short circuit or an asymmetric fault. Analysis of 3-phase electrical system in balanced condition can be analyzed as 1-phase circuit by writing 1-phase equivalent circuit (Single Phase Equivalent Circuit), because the voltage and current in each phase are equal. In case of the electrical system is unbalanced, it cannot be analyzed from a single-phase equivalent circuit in each phase. The direct analysis of the system circuits is quite mathematically complicated when the system is intricately linked. Symmetrical components are a way to separate the phase of an unbalanced system. N-phase is a balanced system of N components, which will make us to analyze 3-phase power system in unbalanced condition. By using the symmetric method, the system is divided into 3 balanced equilibrium systems, ie, positive, negative, and zero sequence. Most industrial load is balanced load and is connected to the 3 Phase system. An imbalance is generated because of the user in the 3 - phase 4 - wire system both single phase load and 3 phase load. The effect of 3 phase unbalanced voltage will affect to unbalance 3 phase current, that cause the temperature of the motor is higher [Kim et al., 2005].

Figure 2.7 Asymmetric voltage in 3 phase system

2.2.1 NEMA Standards Consider Unbalance Power Line (Line Voltage Unbalance

Rate)

It can be calculated from the most deviated line voltage and divided by the average line

voltage of all three phases, considering the size of the voltage. Do not consider the angle

of the voltage (ANSI / NEMA Standard, 1993) as in Eq. (1) - (2).

%LVUR= � Maximum�VAB-VAve(L-L) ,VBC-VAve(L-L) ,VCA-VAve(L-L) �VAve(L-L)

�×100 (1)

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VAve(L-L)=VAB+VBC+VCA

3 (2)

2. 2. 2 IEEE Standards for Unbalance Power Phase 1 ( Phase Voltage Unbalance

Rate 1)

It can be calculated from the most deviated phase voltage from the average phase

voltage and divided by the average phase voltage of the three phases, considering the

size of the voltage. Do not consider the angle of the voltage as in Eq. (3) - (4).

%PVUR1= �Maximum�VAN-VAve(Ph) ,VBN-VAve(Ph) ,VCN-VAve(Ph) �VAve(Ph)

�×100 (3)

VAve(Ph)=VAN+VBN+VCN

3 (4)

2. 2. 3 IEEE Standards for Unbalance Power Phase 2 ( Phase Voltage Unbalance

Rate 2)

It can be calculated from the phase voltage that deviates most during that phase and

then divided by the average phase voltage of the three phases, considering the size of

the voltage. Do not consider the angles of voltage (IEEE Standard, 1987) as in Eq. (5).

%PVUR2= �Maximum�Van,Vbn,Vcn�-Minimum�Van,Vbn,Vcn�VAve(Ph)

� ×100 (5)

2.2.4 Voltage Unbalance Factor 1

To be calculated from the ratio of the negative sequence voltage to the positive

sequence voltage, this measurements are the precise way. When the phase and

amplitude for the three phases are measured [ForTescue, 1918], as in Eq. (6) - (8).

%VUF1 = �V2V1� ×100 (6)

V1= 13

(Va+aVb+a2Vc) (7)

V2= 13

(Va+a2Vb+aVc) (8)

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2.2.5 Negative Sequence Voltage Unbalance


sequence voltage. The results of this study are as follows:

%NSVU=�� 1-�3-6β1+�3-6β

�×100 (9)

𝛽𝛽= VAB4 +VBC

4 +VCA4

�VAB2 +VBC

2 +VCA2 �

2 (10)

2.2.6 Voltage Unbalance Factor 2


sequence voltage, this measurements are precis. When phase and amplitude for the 3

phases are measured (Kim et al.,2005), we get

%VUF2 = �V2V1� ×100 (11)

V1= 13�VA

' +aVB' e-jM2+a2VC

' e-jM3� (12)

V2 = 13�VA

' +a2VB' e-jM2+aVC

' e-jM3� (13)

V0 = 13�VA

' +VB' e-jM2+VC

' e-jM3� (14)

θ1' = cos-1 �VCA

'2 +VBC'2 -VAB

2

2VCA' ×VBC

' � (15)

θ2' = cos-1 �VAB

2 +VBC'2 -VCA

'2

2VAB×VBC' � (16)

θ3' = cos-1 �VCA

'2 +VAB2 -VBC

'2

2VAB' ×VCA

' � (17)

M1 = �180°- θ1' +θ2

'

2� (18)

M2 = �180°- θ2' +θ3

'

2� (19)

M3 = �180°- θ1' +θ3

'

2� (20)

VA' = VAB × �

sin�θ2'

2 �

sin(M1)� (21)

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VB' = VBC

' × �sin�θ1

'

2 �

sin(M1)� (22)

VC' = VCA

' × �sin�

θ3'

2 �

sin(M3)� (23)

Table 2.1 Comparison of Unbalance Voltage in Various Methods

Standard Phase Voltage Line Voltage Remark

%LVUR - 0.7014 ANSI/NEMA Standard

MG1-1993

%PVUR1 0.7014 0.9199 IEEE Standard 112,

1991

%PVUR2 1.9719 - IEEE Standard 936,

1987

%VUF1 0.746 0.7646

V1=219.5792 V1=380.3223

V2=1.6786 V2=2.9074

%NSVU - 0.7646

%VUF2 0.7646 0.7646 V1=219.59∠-0.0861°

V1=1.6789∠156.6036°

V1=0.8367∠-156.25°

Table 2. 1 shows the relationship of the percentage of unbalance voltage from each

measurement method. The value of %VUF2 are equal in both voltage which measured

by the phase voltage, and line voltage [Jong-Gyeum Kim., 2005].

Jong- Gyeum et al. focus on comparing the steps and how to calculate unbalance

voltage, phase voltage and the line voltage, in the condition as load unbalanced. For 3-

phase 4-wire systems, the system is not balanced due to the load and differential values

of the resistance. It make the size and phase of the voltage is not equal. To calculate

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13

with the line voltage will be closer to the actual value than the phase voltage [Jong-

Gyeum Kim., 2005].

Pillay and Manyage focus on comparison 3 standards of unbalance voltage standard.

The unbalance voltage can be measured in three ways. The result of the simulation is

the difference between The Line Voltage Unbalance Rate (NEMA) and the Voltage

Unbalance Factor are shown in Figure 2.8 and the unbalance voltage differs

approximately 0.8 percent, and it affect to the derating factor of motor slightly.

Figure 2.8 The relationship between Voltage Unbalance Factor and NEMA standard

at 2, 5, 10 and 20 percent unbalanced [Pillay and Manyage, 2001].

Thus the calculation with Voltage Unbalance Factor is close to the actual value. The

data used has to be high resolution and complicated. Unbalance voltage calculation

with Line Voltage Unbalance Rate is an alternative for measuring. Because of the

measured value is used to calculate, the result will be deviated from the actual value

slightly.

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2.2.7 IEEE 1159 - 1995

The voltage abnormalities can be classified according to IEEE standard. 1 1 5 9 - 1995

(Recommend Practice for Electric Power Quality Monitoring). This research reference

to the IEEE 1159-1995 standard for a measurement of abnormalities by studying the

voltage unbalance, The imbalance state of voltage in the standard defines from 0.5 to 2

percent under the steady state condition. The details are shown in Table 2. 2 [IEEE

Standard, 1995]

Table 2.2 Types and characteristics of electrical systems and electromagnetic

phenomena.

Type of PQ Phenomena Magnitude Duration Short Duration RMS Variations

Instantaneous 0.5-30 cycles

Interruption <0.1 pu

Sag -0.9 pu

Swell 1.1-1.8 pu

Momentary 0.5-30 cycles


Sag -0.9 pu

Swell 1.1-1.8 pu

Long Duration RMS Variations

Instantaneous >1 minute


Sag -0.9 pu

Swell 1.1-1.8 pu

Voltage Imbalance 0.5-2% Steady State

[IEEE Standard, 1995]

2.2.7.1 Voltage Unbalance Factor2

Unbalance voltage is the voltage size of a 3-phase power system in each phase varies

from 0.5 to 2 percent of the normal voltage, or the phase angle changed from 120

degrees, or both occur simultaneously. Sometimes, the unbalance voltage may be

defined by using the maximum deviation of the average three phase voltage per the

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average three phase voltage. The cause may be unbalanced of load in each phase. The

unbalanced voltage can be determined by the ratio of the negative sequence or the zero

sequence elements to the positive sequence component is shown in Figure 2.9. As a

result, the equipment, such as transformer motors, is shortened life time due to the effect

of heat [Dugan et al., 1996].

Figure 2.9: Characteristics of Unbalanced Voltage at the wire to supply the power to

the accommodation.[Dugan et al., 1996]

2.2.8 Symmetric Voltage

Symmetric system can analyze the system from a 1 - phase equivalent circuit because

the value voltage and current in each phase are equal to each phase. But it is different

at the angle of phase, each phase is apart 120 degrees. In the unbalance system, 1 phase

equivalent circuit analysis is not possible because the value of voltage, current and the

phase angle are not equal in each phase. To analyze directly from the 3 - phase system

under the condition as asymmetric system, it is difficult to mathematical calculations.

Due to, the circuit in the real system connected to each other [ForTescue, 1 9 1 8 ].

Fortescue use the applied theory to solve non- equilibrium N- phase problems with N-

phase analysis which is balance, it is called the symmetry element. The use of

symmetric theory apply to solve 3 - phase power equilibrium problems as shown in

Figure 2.10-2.11

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Figure 2.10: Balance and imbalance [ForTescue, 1918].

Figure 2.11: Symmetrical symmetry [ForTescue, 1918].

Positive-Sequence component contains 3 phasors which have the size in equally and

the angle of each phase is apart 120 degrees.

The Negative-Sequence component contains 3 phasors which have the size in equally

and the angle of each phase is apart 120 degrees.

The Zero-Sequence component consists of 3 phasors. The size of 3 phase is equal and

the phase angle is same, which can be expressed as in Eq. (24) - (29).

Va=V0+V1+V2 (24)

Vb=V0+a2V1+aV2 (25)

Vc=V0+aV1+a2V2 (26)

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�VaVbVc

� = �1 1 11 a2 a1 a a2

� �V0V1V2

� (27)

a = 0.5 - j0.866 (28)

a = -0.5 + j0.866 (29)

when

Va ,Vb ,Vc are the voltage of the electrical system.

V0 is a zero symmetric voltage.

V1 is a positive symmetric voltage

V2 is a negative symmetric voltage

From Eq. (24) - (26), the order of symmetry can be found from the voltage of an

unbalanced electrical system is as follows.

V0= 13

(Va+Vb+Vc) (30)

V1= 13

(Va+aVb+a2Vc) (31)

V2= 13

(Va+a2Vb+aVc) (32)

�V0V1V2

� = �1 1 11 a a2

1 a2 a� �

VaVbVc

� (33)

2.2.9 Calculate the voltage at various points in the distribution system.

From the article Cobben, Calculation the voltage level in low voltage and medium

voltage system is a radial connection as shown in Figure 2.12 [Cobben, 2007].

Figure 2.12 Low voltage distribution system with radial connection [Cobben, 2007].

Medium voltage level at the bus station of the power station is the constant voltage. It

will changes in case of the voltage variation in the medium voltage network (ΔUM) as

shown in Eq. (34) - (37)

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∆UM=∑ ��∑ Pj

UL,j×√3NMj=1 �×R(M,j->j-1)+ �∑

Qj

UL,j×√3NMj=1 �×X(M,j->j-1)�

NMi=1 (34)

The variation of transformer voltage (∆UT)

∆UT= ��∑ Pj

ULL×√3NTj=1 �×RT+ �∑

Qj

ULL×√3NTj=1 �×XT� (35)

The variation of the voltage in the low voltage network (∆UL)

∆UL=∑ ��∑ Pj

UL,j×√3NLj=1 �×R(L,j->j-1)+ �∑

Qj

UL,j×√3NLj=1 �×X(L,j->j-1)�

NLi=1 (36)

Consider the voltage transformer ratio between the lines at the NL spot

UNL= 1T

×(UM-∆UM)-∆UT-∆UL (37)

when

ULL = Line voltage at low voltage side of the transformer.

UM = Line voltage at low voltage busbar in sub-station

P = active power at each connection point.

Q = reactive power at each connection point.

RM = Resistance at the medium voltage network

XM = Inductance at the medium voltage network

RL = Resistance at the low voltage network

XL = Inductance at the low voltage network

T = Transformer Ratio (UMV/ULV)

RT = Transformer resistance (UMV/ULV) Low voltage Side

XT = Transformer Inductance (UMV/ULV) Low voltage Side

ULj = Line voltage at each connection point.

Figure 2. 13 shows the deviation voltage situation in the distribution system has been

partially offset the location of the transformer and the deviation voltage situation in the

network. Some of the locations of the transformer and the installation of the DG have

been partially compensated and the voltage raised [Cobben, (2007].

Figure 2.13: Voltage level Installed (a) Not installed (b) Installed DG[Cobben, 2007]. (a) (b)

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2.2.10 Three-phase power system

Figure 2.14 3-phase, 4-wire system

Phase voltage (Vp) is a three-phase electrical system, the voltage balance between the

phase can be shown as in Eq. (38) - (40):

Van=Va=Vp∠0° (38)

Vbn=Vb=Vp∠-120° (39)

Vcn=Vc=Vp∠+120° (40)

The VLL voltage is expressed as:

Vab=Va-Vb=VLL∠+30° (41)

Vbc=Vb-Vc=VLL∠-90° (42)

Vca=Vc-Va=VLL∠+150° (43)

Eq. (38) - (43) can be written as a phasor, as shown in Figure 2.15

Figure 2.15 Phasor of the voltage [Cobben, 2007]

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Determine the resistance is the balance that is connected to the system for the Wye

connection Figure 2.15 and the resistance value connected. Z∠ψ can find the current

from Eq. (44).

Ia= VZy

= Vp

Zy∠(0°-ψ) (44)

When ψ is between -90° and 90° for ψ larger than 0°.

Inductance (Ia lagging Va) for ψ smaller than 0° load capacity (Ia leading Va)

Phase current in the 3-phase system is as follows:

Ia=Ip∠(0°-ψ) (45)

Ib=Ip∠(120°-ψ) (46)

Ic=Ip∠(-240°-ψ) (47)

2.3 Harmonic

Total Harmonic Distortion, THD: The ratio of Root- Sum- Square of RMS of the harmonic component and RMS of the fundamental component in the percentage as the total harmonic distortion current ( THDi) and the total harmonic distortion voltage ( THDv) in Eq. ( 48) and ( 49) respectively.

THDi(%) = �𝐼𝐼22+𝐼𝐼32+𝐼𝐼42+⋯

𝐼𝐼1× 100 (48) THDv(%) =

�𝑉𝑉22+𝑉𝑉32+𝑉𝑉42+⋯

𝑉𝑉1× 100 (49)

Table 2. 3 PEA recommendation Harmonic voltage Limits for customers at Point of common coupling (PCC)

PEA recommendation IEEE Std 519-1992

THDv less than 5% Odd less than 4% Even less than 2%

THDv less than 5% Individual THD less than 3%

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Table 2.4 IEEE Std. 519-1992 Harmonic Current Limits

2.4 Related Standard

2.4.1 PRC(PEA Recommendation)

We study the connection of the solar power system to the distribution system of the Provincial Electricity Authority. Therefore, we have studied the details of associated standards and guidelines, as follows:

2.4.1.1 Voltage and Frequency Criteria Consider the system voltage and frequency guidelines, the power generation of a very small power producer ( VSPP) must be compatible with the PEA's power distribution system. The power supplier shall design the power supply control system in parallel with the generator at the point of connection ( PCC) , the power network shall be in accordance with the standard of maximum and minimum voltage of the Provincial Electricity Authority as shown in Table 2. 5. The frequency of the electrical system is 50 ± 0.5 Hz. In case of the malfunction in the electrical system, if the system frequency is not in range 48 - 51 Hz over 0.1 second, the circuit breaker must be disconnected at the access point automatically. The PEA's power system planning is based on the voltage table shown in Table 2.5.

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Table 2.5: Maximum and Minimum Voltage Levels of Provincial Electricity Authority (Volt)

Voltage Level Normal Emergency Maximum Minimum Maximum Minimum

115,000 120,700 109,200 126,500 103,500 33,000 34,700 31,300 36,300 29,700 22,000 23,100 20,900 24,200 19,800

380 418 342 418 342 220 240 200 240 200

[Provincial Electricity Authority, 2016]

2.4.1.2 Electrical connection Criteria Electrical connection standards determine the total installed capacity of the power system connected in the low- voltage transformer shall not exceed 15% of the transformer size. If the total installed capacity of the power system is fully connected, the 15% limit of the transformer size is already set. Power producers must be connected in a 22 or 33 kV distribution system. The power supplier must supply transformers, distributors and protective equipment in accordance with the standards of the Provincial Electricity Authority. [Provincial Electricity Authority, 2016]

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M1 M2

CB-A

CB-B CB-C CB-D

INVERTER

SOLAR PANEL

Utility’s distribution line

Utility’s distribution transformer

Utility’s low voltage distribution line

Part of utility’s responsibilityPart of Customer’s responsibility

50/51 50N/51N

Figure 2.16: Connecting solar power system to distribution system 1. M1 means the meter where the power user buys electricity from the regional power. 2. M2 means the meter to measure a power unit from the production of electricity on solar rooftop. 3. In case of Customer’s transformer, part of customer responsibility is at the position after the protection device or switch. 4. In case of capacity of solar rooftop systems over 250 kW. One set of electrical quality meters must be installed. 5. Solar Rooftop systems must not have an energy storage system installed for selling the electricity to Provincial Electricity Authority. [Provincial Electricity Authority, 2016]

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2.4.1.3 Low Voltage and Over Voltage Criteria The power system of a very small power producer will have to be disconnected from the power grid, if the Line to Neutral voltage in the grid system is out of range specified in Table 2.6 Table 2.6 The breakdown time when voltage is not in rated voltage range.

Voltage level at PCC breakdown time (Second) 50%V < 0.3

50% 90%V≤ < 2.0 90% 110%V≤ ≤ Continuous

110% 120%V< < 1.0 120%V ≥ 0.16

[Provincial Electricity Authority, 2016]

2.4.1.4 Quality of Supply Criteria Quality of Supply Criteria which PEA needs to be considered 1. Rapid Voltage Change: By changing the voltage of the low- voltage distribution system must not exceed 5 percent.

2. Harmonic Voltage Distortion: The third harmonic of the system must not exceed 8 percent.

3. Voltage Unbalance: Under normal conditions, in the high- voltage and low-voltage distribution system, the unbalance voltage must not exceed 2 percent.

4. System Frequency: The system frequency can be changed in the range of 50 ± 0.5 cycles per second.

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Chapter 3

Methodology

3.1 System Model

System model consist of 3 parts as Nakhon Pathom LV network shown in Fig. 3.1

Figure. 3.1 Single line diagram of PEA Low voltage distribution system model.

3.1.1 Power Source

In system model, the first part is 3 phase distribution transformer ( DTR) which is connected between the medium- voltage bus 22kV and the low voltage network for adjusting the voltage level from 22 kV to 400 kV. The sizing of distribution transformer is 250kVA; and the type of connection is Delta-Wye connection.

3.1.2 Distribution network

The secondary side of transformer is the residential low voltage networks which

compose of four wires with radial topology. There are 3 feeders consisting of 159

households as detailed:

Feeder 1: there are 24 households and the length of feeder is 134 meter.

Feeder 2: there are 73 households and the length of feeder is 398 meter.

Feeder 3: there are 62 households and the length of feeder is 180meter.

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0.00.20.40.60.81.01.2

0:00

1:30

3:00

4:30

6:00

7:30

9:00

10:3

012

:00

13:3

015

:00

16:3

018

:00

19:3

021

:00

22:3

0

Pow

er(p

.u.)

Time(hr)

Residential Load Profile

3.1.3 PV

Single phase PV sizes 3 kW with 2 types of inverter as PV1 and PV2 (1) PV1 is represented rooftop PV with inverter type 1 release the current distortion (THDi) less than 2% (2) PV2 is represented rooftop PV with inverter type 2: release the current distortion (THDi) more than 5%

3.2 Assumption

3.2.1 Residential Load Profile PEA load profile of a residential customer at the Central Region 3 [Provincial Electricity Authority, 2015] during 24 hours is shown in Fig. 3.2. Peak load are in during 18:00 -23:00 and 00:00-06:00.

Figure. 3.2 Daily load profile of household

3.2.2 PV Load Profile

Power output of Rooftop PV during 24 hours is shown in Fig. 3.3.

Figure. 3.3 Daily output power of rooftop PV

0

0.2

0.4

0.6

0.8

1

1.2

0:00

1:30

3:00

4:30

6:00

7:30

9:00

10:3

012

:00

13:3

015

:00

16:3

018

:00

19:3

021

:00

22:3

0

Pow

er(p

.u.)

Time(hr)

Output power of Rooftop PV

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3.2.3 Location of PV installation

In this research, Rooftop PV will be installed at feeder- by- feeder continuously, the beginning zone, the middle zone, and the end zone of each feeder. The beginning zone of feeder is the distance from the beginning of feeder to the position 1/3 of feeder. The middle zone of feeder is the distance from the position at 1/ 3 of feeder to the position at 2/3 of feeder. The end zone of feeder is the distance from the position at 2/3 of feeder to the terminal of feeder.

a) The length of each feeder .

b) The zone of each feeder can be divided to 3 zone

Figure 3.4 The length of feeder line a) and the zone of feeder b) by assuming the length of feeder equal to L meter. The beginning zone of feeder line is from 0 to 1/3 L, the middle zone of feeder line is from 1/3L to 2/3 L and the end zone of feeder line is from 2/3L to L. Remark: Phase connection of each PV is randomized using normal random distribution function.

Begin Zone End Zone

Middle Zone

0 1/3 L 2/3 L L

Feeder 1 ≈ 134 m

Feeder 2 ≈ 398 m

Feeder 3 ≈ 180 m

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3.3 Case Study

There are 16 case studies focused on this research as detailed in the table below: Table 3.1 Case studies focused on this research Case study Current distortion

of PV Harmonic

Background Location of

PV installation Penetration

of PV

1 < 2% No Type A 10%-80% 2 < 2% Yes Type A 10%-80% 3 < 2% No Type B 10%-50% 4 < 2% Yes Type B 10%-50% 5 < 2% No Type C 10%-80% 6 < 2% Yes Type C 10%-80% 7 < 2% No Type D 10%-50% 8 < 2% Yes Type D 10%-50% 9 > 5% No Type A 10%-80% 10 > 5% Yes Type A 10%-80% 11 > 5% No Type B 10%-50% 12 > 5% Yes Type B 10%-50% 13 > 5% No Type C 10%-80% 14 > 5% Yes Type C 10%-80% 15 > 5% No Type D 10%-50% 16 > 5% Yes Type D 10%-50%

Remark: all case studies are considered at loading level, 25%, 50% and 80% of transformer power ratings 1) Harmonic Background: The total harmonic distortion of the network is

nearly 2% at the LV bus.

2) Type definition

- Type A: Install PV feeder-by-feeder continuously

- Type B: Install PV at the beginning zone of each feeder

- Type C: Install PV at the middle zone of each feeder

- Type D: Install PV at the end zone of each feeder

3) Penetration level of Rooftop PV

Penetration level of Rooftop PV is the proportion of power solar rooftop installed with the rated power of transformer

%PV Penetration =

Total PowerPV

Rated Power of TR

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Rooftop PVs will be installed to distribution system with 10% to 80 % PV Penetration (step size 10%)

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Feeder 1

42 41 40 39 27 26 25 24 23 22 21 20 19 18 17 16 15

1 2 3 4 5 6 7 8 9 10 11 12 13 14

36 35

2838 37 29 30 31

34 33 32

114115118 117

119 116

26121120

1 2 3 4 5 6

23 22

7 8 9 1025 24

21 20 19 18 17 16 15 14 13 12 11

2927 28 30

113 112 111 110 109 108 107 55 54 53 52 49 47 46

35 3736

38 39 40 41 42 43 44 45

34 32 106 105 104103 102

101 100

99 98

79

97 96 95

6256 57 58 59 60 61

94

80 81

78 77 76 75 74 73

63 64 65

72 71

66

70 69

67 68

93 92 90 89

82 878385

84

91

86 88

Feeder 2

1

3 2

4

5

93

6

92 91

7

90 89

8 9

43 42

10

41 40

39 38

11

35 34

37 36

12

33 32

31 30

13

27 26

29 28

14

25 24

23 22

15

19

21 20

16

18

17

44

88 87

45 46 47

51

50 49

52

808182 83 84

86 85

48

53

78 77

79

54

74

76 75

55

73 72

71

56

69 68

70

58

65

59

64 63

60

62

6157

67 66

Feeder 3

250 kVA

HV Bus22 kv

LV Bus400v

51 50 48

Install PV Feeder-by-feeder continuously10% PV Penetration Installed bus20% PV Penetration Installed bus30% PV Penetration Installed bus40% PV Penetration Installed bus50% PV Penetration Installed bus60% PV Penetration Installed bus70% PV Penetration Installed bus80% PV Penetration Installed bus

Figure 3.5 Type A: PV of Installation in feeder-by-feeder continuously

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Feeder 1

42 41 40 39

1 2 3 4

36 35

28

38 37

114115118 117

119 116

26

121 120

1 2 3 4 5 6

23 22

7 8 9 1025 24

21 20 19 18 17 16 15 14 13 12 11

Feeder 2

1

3 2

45

936

92 917

90 898 9

43 42

4488 87

Feeder 3

250 kVA

HV Bus22 kv

LV Bus400v

The Beginning Zone10% PV Penetration Installed bus

20% PV Penetration Installed bus




Figure 3.6 Type B: PV of Installation in the beginning zone of each feeder

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Feeder 1

27 26 25 24

5 6

29 30 31

34 33 32

2927 28 30

113 112 111 110 109 108 107 55 54 53 52 49 47 46

35 3736

38 39 40 41 42 43 44 45

34 32

106 105 104 103 102

101 100

99 98

79

97 96 95

6256 57 58 59 60 61

94

80 81

Feeder 2

10

41 40

39 3811

35 34

37 3612

33 32

31 3013

27 26

29 2814

25 24

23 2215

19

21 2016

18

17

45 46 47

51

50 49

52

808182 83 84

86 85

48

53

78 77

79

54

74

76 75

Feeder 3

250 kVA

HV Bus22 kv

LV Bus400v

33 31 50 4851

The Middle Zone10% PV Penetration Installed bus20% PV Penetration Installed bus30% PV Penetration Installed bus40% PV Penetration Installed bus50% PV Penetration Installed bus60% PV Penetration Installed bus70% PV Penetration Installed bus80% PV Penetration Installed bus

Figure 3.7 Type C: PV of Installation in the middle zone of each feeder

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Feeder 123 22 21 20 19 18 17 16 15

7 8 9 10 11 12 13 14

78 77 76 75 74 73

63 64 65

72 71

66

70 69

67 68

93 92 90 89

82 8783

85

84

91

86 88

Feeder 2

55

73 72

76 71

56

69 68

70

58

65

59

64 63

60

62

6157

67 66Feeder 3

250 kVA

HV Bus22 kv

LV Bus400v






The End Zone

Figure 3.8 Type D: PV of Installation in the end zone of each feeder

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3.4 Computation hardware specification

1. Personal computer: Corei5 2.4Ghz 8GB-Ram 2. Operation System: MS-Window 8.0 3. Simulation Program: DIgSIENT Power Factory v.14.0 for load flow and harmonic load flow calculation [Grainger et al., 1994]. 4. Analytic Program: Microsoft Excel 2016

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0.0

5.0

10.0

10% 20% 30% 40% 50% 60% 70% 80%

%THDv in Case Study 1 (TypeA: Feeder-by-feeder)Loading 25% Loading 50% Loading 80%

%THDv : < 5%

0.0

2.0

4.0

NO PV 10% 20% 30% 40% 50% 60% 70% 80%

%VUF in Case Study 1 (TypeA: Feeder-by-feeder)Loading 25% Loading 50% Loading 80%

%VUF : < 2%

Chapter 4

Simulation Result and Discuss

4.1 Case-by-case discussion

4.1.1 Case Study 1 : PV1,which inject the output current distortion(THDi) nearly 2%, were installed in the low voltage distribution network without the harmonic background. Starting PV1 installation on feeder 1 with 10% PV penetration and increasing PV1 installation to 20% PV penetration on feeder1 and feeder2. To repeat with increase PV1 installation until % 80 PV penetration on feeder1, feeder2 and feeder3 in order continuously. The result of simulation following in case study 1 show the relationship between the total harmonic voltage distortion in the LV distribution network and % PV penetration increasing on the network as Fig 4.1 a). The more PV1 installation increase on feeder-by-feeder continuously, the more THDv of the network add up. When PV were installed more than 60 % PV penetration, THDv in the network will be over the standard (THDv must be not over 5%). Although the loading of transformer will differ as 25%, 50% and 80%, the THDv still increase in the same trend. Not only will it affect the total harmonic distortion voltage, but also the voltage unbalance as Fig 4.1 b). The most PV1 installation is increasing on feeder-by-feeder continuously, the most voltage unbalance factor (%VUF) in the network is adding. When PV were installed more than 50 % PV penetration, the voltage unbalance in the network will be over the standard (%VUF must be not over 2%)

Figure 4.1 Case Study 1, PV1 connected to grid with 10-80% PV Penetration.

The location of PV installation is as Type A: Feeder-by-feeder continuously.

a) %THDv

b) %VUF

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0.00

1.00

2.00

3.00

4.00

NoPV 10% 20% 30% 40% 50% 60% 70% 80%

%VUF in Case Study 2 (TypeA: Feeder-by-feeder)

Feeder1 Feeder2 Feeder3

%VUF : < 2%

0.00

5.00

10.00

NoPV 10% 20% 30% 40% 50% 60% 70% 80%

%THDv in Case Study 2 (TypeA: Feeder-by-feeder)


%THDv : < 5%

4.1.2 Case Study 2 :The LV distribution network with harmonic background is nearly 2% at LV bus, because of harmonic loads installation on feeder1. Without PV installation in the network, the max total harmonic distortion voltage is about 8% on feeder1, and 2% on feeder2&3 respectively. Starting PV1 installation on feeder 1 with 10% PV penetration and increasing PV1 installation to 20% PV penetration on feeder1 and feeder2. To repeat with increase of PV1 installation until % 80 PV penetration on feeder1, feeder2 and feeder3 in order continuously. The result of simulation following in case study 2 show the relationship between the total harmonic voltage distortion in the LV distribution network and % PV penetration increasing on the network as Fig 4.2 a). The trend of THDv on feeder 2 will increase clearly. Until %PV penetration more than 60% THDv on feeder2 will be over the standard limitation. On the other hand, THDv on feeder 1 and feeder 3 increase slight because the number of households and PV1 installation on feeder 2 are rather than feeder1 and feeder 3. The amount of %THDv on feeder 3 is lower than the other feeders because feeder 3 is so far from feeder1. The relationship between the voltage unbalance in the LV distribution network and % PV penetration increasing on the network is shown as Fig 4.2 b). The trend of VUF on feeder 1 and feeder 2 will increase clearly. Until %PV penetration more than 50%, the %VUF on feeder1 and feeder 2 will be over the standard limitation. On the other hand, %VUF on feeder 3 increase slight because the number of households and PV1 installation on feeder 3 are much less quantity than feeder1 and feeder 2.

Figure 4. 2 In Case Study 2, PV1 connected to grid (harmonic background) with 10-

80% PV Penetration. The location of PV installation is as Type A: Feeder-by-feeder

continuously.

a) %THDv

b) %VUF

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0.0

0.5

1.0

1.5

10% 20% 30% 40% 50%

%THDv in Case Study 3 (TypeB:Beginning Zone)

Loading 25% Loading 50% Loading 80%

0.0

0.2

0.4

0.6

0.8

NO PV 10% 20% 30% 40% 50%

%VUF in Case Study 3 (TypeB:Beginning Zone)Loading 25% Loading 50% Loading 80%

4.1.3 Case Study 3: PV1 (THDi ≈2%) is installed in the low voltage distribution network without the harmonic background. The location of PV installation is the beginning zone of each feeder. (Due to the number of households on the beginning zone of all feeder are only 41 households, PV installation will be possible with 10-50% PV penetration.) Starting PV1 installation with 10% PV penetration and increasing PV1 installation to 10% PV penetration in each round until % PV penetration is equal to 50%. The result of simulation following in case study 3 show the relationship between the total harmonic voltage distortion in the LV distribution network and % PV penetration increasing on the network as Fig 4.3 a). The amount of %THDv will increase when PV penetration in the network add up. Although PV1 will be installed to 50% PV penetration, The amount of %THDv still under the standard limitation. Whereas PV installation in the LV network with the location as Type B (only the beginning zone of each feeder) does not influence to the voltage unbalance as shown in Fig 4.3 b). The amount of %VUF will change slightly in each level of PV penetration because the location of PV installation is spread in each phase of each feeder. But the factor, which influence to the amount of %VUF, is the loading of transformer.

Figure 4. 3 In Case Study 3, PV1 connected to grid with 10- 50% PV Penetration.

The location of PV installation is as Type B: the beginning zone of each feeder.

a) %THDv

b) %VUF

Ref. code: 25605622040581VOU

38

0.00

0.50

1.00

1.50

2.00

NoPV 10% 20% 30% 40% 50%

%VUF in Case Study 4 (TypeB:Beginning Zone)Feeder1 Feeder2 Feeder3

0.00

2.00

4.00

6.00

8.00

10.00

NoPV 10% 20% 30% 40% 50%



4.1.4 Case Study 4: The LV distribution network with harmonic background nearly 2% at LV bus, because of harmonic loads installation on feeder1. Without PV installation in the network, the max total harmonic distortion voltage is about 8% on feeder1, and 2% on feeder2&3 respectively. The location of PV installation is the beginning zone of each feeder. Starting PV1 installation with 10% PV penetration and increasing PV1 installation to 10% PV penetration in each round until % PV penetration is equal to 50%.(Due to the number of households on the beginning zone of all feeder are only 41 households, PV installation will be possible with 10-50% PV penetration.) The result of simulation following in case study 4 show the relationship between the total harmonic voltage distortion in the LV distribution network and % PV penetration increasing on the network as Fig 4.4 a). When the level of PV penetration add up, the amount of %THDv on feeder2 and feeder3 will increase slightly from 1.8% to 2.2%.The relationship between the voltage unbalance in the LV distribution network and increasing % PV penetration on the network is shown as Fig 4.4 b). At 10% PV penetration, it occur the voltage unbalance on feeder2 and feeder3 but it still under the standard limitation (<2%). It does not have a tendency for the variation of the voltage unbalance because of the several factors like the amount of loads, phase connection of loads, distance of loads, etc.


50% PV Penetration. The location of PV installation is as Type B: the beginning zone

of each feeder.

a) %THDv

b) %VUF

Ref. code: 25605622040581VOU

39

0.0

0.5

1.0

1.5

2.0

NO PV 10% 20% 30% 40% 50% 60% 70% 80%

%VUFin Case Study 5 (TypeC: Middle Zone)Loading 25% Loading 50% Loading 80%

0.0

1.0

2.0

3.0

4.0

10% 20% 30% 40% 50% 60% 70% 80%

%THDv in Case Study 5 (TypeC: Middle Zone)Loading 25% Loading 50% Loading 80%

4.1.5 Case Study 5: PV1 (THDi ≈2%) is installed in the low voltage distribution network without the harmonic background. The location of PV installation is the middle zone of each feeder. Starting PV1 installation with 10% PV penetration and increasing PV1 installation to 10% PV penetration in each round until % PV penetration is equal to 80%.The result of simulation following in case study 5 show the relationship between the total harmonic voltage distortion in the LV distribution network and % PV penetration increasing on the network as Fig 4.5 a). The more PV1 installation increase in the network, the more THDv of the network add up. Although the level of PV penetration will be higher to 80%, The THDv of the network still be under the standard limitation. As the spread of PV1 installation is widely on each feeder. The relationship between the voltage unbalance in the LV distribution network and % PV penetration increasing on the network is shown as Fig 4.5 b). At any level of PV penetration, it has a chance of occurring the voltage unbalance (0.5-2%) on each feeder but it still under the standard limitation (<2%). It gives the some trend for the variation of the voltage unbalance because of the several factors like the amount of loads, phase connection of loads, distance of loads, etc.


The location of PV installation is as Type C: the middle zone of each feeder.

a) %THDv

b) %VUF

Ref. code: 25605622040581VOU

40

0.00

0.50

1.00

1.50

2.00

NoPV 10% 20% 30% 40% 50% 60% 70% 80%

%VUF in Case Study 6 (TypeC: Middle Zone)


0.00

2.00

4.00

6.00

8.00

10.00

NoPV 10% 20% 30% 40% 50% 60% 70% 80%

%THDv in Case Study 6 (TypeC: Middle Zone)


%THDv : < 5%

4.1.6 Case Study 6: The LV distribution network with harmonic background is nearly 2% at LV bus, because of harmonic loads installation on feeder1. Without PV installation in the network, the max total harmonic distortion voltage is about 8% on feeder1, and 2% on feeder2&3 respectively. The location of PV installation is the middle zone of each feeder. Starting PV1 installation with 10% PV penetration and increasing PV1 installation to 10% PV penetration in each round until % PV penetration is equal to 80%.The result of simulation following in case study 6 show the relationship between the total harmonic voltage distortion in the LV distribution network and % PV penetration increasing on the network as Fig 4.6 a). The more PV1 installation increas on feeder-by-feeder continuously, the more THDv of the network add up. Although the level of PV penetration will be higher to 80%, The THDv of the network still be under the standard limitation. As the spread of PV1 installation is widely on each feeder. The relationship between the voltage unbalance in the LV distribution network and % PV penetration increasing on the network is shown as Fig 4.5 b). At any level of PV penetration, it has a chance of occurring the voltage unbalance (0.5-2%) on each feeder but it still under the standard limitation (<2%). It does not trend for the variation of the voltage unbalance because of the several factors like the amount of loads, phase connection of loads, distance of loads, etc.


80% PV Penetration. The location of PV installation is as Type C: the middle zone of

each feeder.

a) %THDv

b) %VUF

Ref. code: 25605622040581VOU

41

0.0

0.5

1.0

1.5

2.0

NO PV 10% 20% 30% 40% 50%

%VUFin Case Study 7 (TypeD: End Zone)


0.0

1.0

2.0

3.0

4.0

10% 20% 30% 40% 50%

%THDv in Case Study 7 (TypeD: End Zone)Loading 25% Loading 50% Loading 80%

4.1.7 Case Study 7: PV1 (THDi ≈2%) is installed in the low voltage distribution network without the harmonic background. The location of PV installation is the end zone of each feeder. Starting PV1 installation with 10% PV penetration and increasing PV1 installation to 10% PV penetration in each round until % PV penetration is equal to 50%.(Due to the number of households on the end zone of all feeder are only 37 households, PV installation will be possible with 10-50% PV penetration.) The result of simulation following in case study 7 show the relationship between the total harmonic voltage distortion in the LV distribution network and % PV penetration increasing on the network as Fig 4.7 a). The amount of %THDv will increase when PV penetration in the network add up. Although PV1 will be installed to 50% PV penetration, The amount of %THDv still under the standard limitation. The relationship between the voltage unbalance in the LV distribution network and % PV penetration increasing on the network is shown as Fig 4.7 b). At any level of PV penetration, it has a chance of occurring the voltage unbalance (0.5-2%) on each feeder but it still under the standard limitation (<2%). It does not trend for the variation of the voltage unbalance because of the several factors like the amount of loads, phase connection of loads, distance of loads, etc.


The location of PV installation is as Type D: the end zone of each feeder.

a) %THDv

b) %VUF

Ref. code: 25605622040581VOU

42

0.00

0.50

1.00

1.50

2.00

NoPV 10% 20% 30% 40% 50%

%VUF in Case Study 8 (TypeD: End Zone)Feeder1 Feeder2 Feeder3

0.00

2.00

4.00

6.00

8.00

10.00

NoPV 10% 20% 30% 40% 50%

%THDv in Case Study 8 (TypeD: End Zone)Feeder1 Feeder2 Feeder3

%THDv : < 5%

4.1.8 Case Study 8: The LV distribution network with harmonic background is nearly 2% at LV bus, because of harmonic loads installation on feeder1. Without PV installation in the network, the max total harmonic distortion voltage is about 8% on feeder1, and 2% on feeder2&3 respectively. The location of PV installation is the end zone of each feeder. Starting PV1 installation with 10% PV penetration and increasing PV1 installation to 10% PV penetration in each round until % PV penetration is equal to 50%.(Due to the number of households on the end zone of all feeder are only 37 households, PV installation will be possible with 10-50% PV penetration.) The result of simulation following in case study 8 show the relationship between the total harmonic voltage distortion in the LV distribution network and % PV penetration increasing on the network as Fig 4.8 a). When the level of PV penetration add up, the amount of %THDv on feeder2 and feeder3 will increase slightly from 1.8% to 2.2%.The relationship between the voltage unbalance in the LV distribution network and % PV penetration increasing on the network is shown as Fig 4.8 b). At any level of PV penetration, it has a chance of occurring the voltage unbalance (0.5-2%) on each feeder but it still under the standard limitation (<2%). It does not trend for the variation of the voltage unbalance because of the several factors like the amount of loads, phase connection of loads, distance of loads, etc.


50% PV Penetration. The location of PV installation is as Type D: the end zone of each

feeder.

a) %THDv

b) %VUF

Ref. code: 25605622040581VOU

43

0.0

5.0

10.0

15.0

10% 20% 30% 40% 50% 60% 70% 80%

%THDv in Case Study 9 (TypeA: Feeder-by-feeder)


%THDv : < 5%

0.0

1.0

2.0

3.0

4.0

NO PV 10% 20% 30% 40% 50% 60% 70% 80%

%VUF in Case Study 9 (TypeA: Feeder-by-feeder)Loading 25% Loading 50% Loading 80%

%VUF : < 2%

4.1.9 Case Study 9: PV2,which injects the output current distortion(THDi) more than 5%, is installed in the low voltage distribution network without the harmonic background. Starting PV2 installation on feeder 1 with 10% PV penetration and increasing PV2 installation to 20% PV penetration on feeder1 and feeder2. To repeat with increase PV2 installation until % 80 PV penetration on feeder1, feeder2 and feeder3 in order continuously. The result of simulation following in case study 1 show the relationship between the total harmonic voltage distortion in the LV distribution network and % PV penetration increasing on the network as Fig 4.1 a). The most PV2 installation is increasing on feeder-by-feeder continuously, the most THDv in the network is adding. When PV were installed more than 30 % PV penetration, THDv in the network will be over the standard (THDv must be not over 5%). Although the loading of transformer will differ as 25%, 50% and 80%, the THDv still increase in the same trend. Not only will it affect the total harmonic distortion voltage, but also the voltage unbalance as Fig 4.1 b). The most PV2 installation is increasing on feeder-by-feeder continuously, the most voltage unbalance factor (%VUF) in the network is adding. When PV were installed equal or more than 50 % PV penetration, the voltage uabalance in the network will be over the standard (%VUF must be not over 2%)

Figure 4.9 In Case Study 9, PV2 connected to grid with 10-80% PV Penetration.

The location of PV installation is as Type A: Feeder-by-feeder continuously.

a) %THDv

b) %VUF

Ref. code: 25605622040581VOU

44

0.00

1.00

2.00

3.00

4.00

NoPV 10% 20% 30% 40% 50% 60% 70% 80%

%VUF in Case Study 10 (TypeA: Feeder-by-feeder)


%VUF : < 2%

0.002.004.006.008.00

10.0012.0014.00

NoPV 10% 20% 30% 40% 50% 60% 70% 80%

%THDv in Case Study 10 (TypeA: Feeder-by-feeder)Feeder1 Feeder2 Feeder3

%THDv : < 5%

4.1.10 Case Study 10: The LV distribution network with harmonic background is nearly 2% at LV bus, because of harmonic loads installation on feeder1. Without PV installation in the network, the max total harmonic distortion voltage is about 8% on feeder1, and 2% on feeder2&3 respectively. Starting PV2 installation on feeder 1 with 10% PV penetration and increasing PV2 installation to 20% PV penetration on feeder1 and feeder2. To repeat with increase PV2 installation until % 80 PV penetration on feeder1, feeder2 and feeder3 in order continuously. The result of simulation following in case study 10 show the relationship between the total harmonic voltage distortion in the LV distribution network and % PV penetration increasing on the network as Fig 4.10 a). The trend of THDv on feeder 2 will increase clearly. Until %PV penetration more than 30% THDv on feeder2 will be over the standard limitation. On the other hand, THDv on feeder 3 increase slightly because the number of PV2 installation on feeder 3 are rather than feeder1 and feeder 2. The relationship between the voltage unbalance in the LV distribution network and % PV penetration increasing on the network is shown as Fig 4.10 b). The trend of VUF on feeder 1 and feeder 2 will increase clearly. Until %PV penetration more than 50%, the %VUF on feeder1 and feeder 2 will be over the standard limitation. On the other hand, %VUF on feeder 3 increase slightly because the number of households and PV2 installation on feeder 3 are much less quantity than feeder1 and feeder 2.

Figure 4. 10 In Case Study 10, PV2 connected to grid (harmonic background) with

10-80% PV Penetration.The location of PV installation is as Type A: Feeder-by-feeder

continuously.

a) %THDv

b) %VUF

Ref. code: 25605622040581VOU

45

0.0

1.0

2.0

3.0

10% 20% 30% 40% 50%



0.0

0.2

0.4

0.6

0.8

NO PV 10% 20% 30% 40% 50%

%VUF in Case Study 11 (TypeB:Beginning Zone)Loading 25% Loading 50% Loading 80%

4.1.11 Case Study 11: PV2(THDi < 5%) is installed in the low voltage distribution network without the harmonic background. The location of PV installation is the beginning zone of each feeder. Starting PV2 installation with 10% PV penetration and increasing PV2 installation to 10% PV penetration in each round until % PV penetration is equal to 50%.(Due to the number of households on the beginning zone of all feeder are only 41 households, PV installation will be possible with 10-50% PV penetration.) The result of simulation following in case study 11 show the relationship between the total harmonic voltage distortion in the LV distribution network and % PV penetration increasing on the network as Fig 4.11 a). The amount of %THDv will increase when PV penetration in the network add up. Although PV2 will be installed to 50% PV penetration, the amount of %THDv still under the standard limitation. Whereas PV installation in the LV network with the location as Type B (only the beginning zone of each feeder) does not influence to the voltage unbalance as shown in Fig 4.11 b). The amount of %VUF will change slightly in each level of PV penetration because the location of PV installation is spread in each phase of each feeder. But the factor, which influence to the amount of %VUF, is the loading of transformer.


The location of PV installation is as Type B: the beginning zone of each feeder.

a) %THDv

b) %VUF

Ref. code: 25605622040581VOU

46

0.00

0.50

1.00

1.50

2.00

NoPV 10% 20% 30% 40% 50%

%VUF in Case Study 12 (TypeB:Beginning Zone)


0.001.002.003.004.005.006.007.008.009.00

NoPV 10% 20% 30% 40% 50%

%THDv in Case Study 12 (TypeB:Beginning Zone)Feeder1 Feeder2 Feeder3

%THDv : < 5%

4.1.12 Case Study 12: The LV distribution network with harmonic background is nearly 2% at LV bus, because of harmonic loads installation on feeder1. Without PV installation in the network, the max total harmonic distortion voltage is about 8% on feeder1, and 2% on feeder2&3 respectively. The location of PV installation is the beginning zone of each feeder. Starting PV2 installation with 10% PV penetration and increasing PV2 installation to 10% PV penetration in each round until % PV penetration is equal to 50%.(Due to the number of households on the beginning zone of all feeder are only 41 households, PV installation will be possible with 10-50% PV penetration.) The result of simulation following in case study 12 show the relationship between the total harmonic voltage distortion in the LV distribution network and % PV penetration increasing on the network as Fig 4.12 a). When the level of PV penetration add up, the amount of %THDv on feeder2 and feeder3 will increase slightly from 1.8% to 3.4%.The relationship between the voltage unbalance in the LV distribution network and increasing % PV penetration on the network is shown as Fig 4.12 b). At 10% PV penetration, it occur the voltage unbalance on feeder2 and feeder3 but it still under the standard limitation (<2%). It does not trend for the variation of the voltage unbalance because of the several factors like the amount of loads, phase connection of loads, distance of loads, etc.


10- 50% PV Penetration. The location of PV installation is as Type B: the beginning

zone of each feeder.

a) %THDv

b) %VUF

Ref. code: 25605622040581VOU

47

0.0

2.0

4.0

6.0

8.0

10.0

10% 20% 30% 40% 50% 60% 70% 80%

%THDv in Case Study 13 (TypeC: Middle Zone)


%THDv : < 5%

0.0

0.5

1.0

1.5

2.0

NO PV 10% 20% 30% 40% 50% 60% 70% 80%

%VUFin Case Study 13 (TypeC: Middle Zone)


4.1.13 Case Study 13: PV2 (THDi >5%) is installed in the low voltage distribution network without the harmonic background. The location of PV installation is the middle zone of each feeder. Starting PV2 installation with 10% PV penetration and increasing PV2 installation to 10% PV penetration in each round until % PV penetration is equal to 80%.The result of simulation following in case study 13 show the relationship between the total harmonic voltage distortion in the LV distribution network and % PV penetration increasing on the network as Fig 4.13 a). The more PV2 installation increase in the network, the more THDv of the network add up. When the level of PV penetration more than 40%, The THDv of the network will be over the standard limitation. The relationship between the voltage unbalance in the LV distribution network and % PV penetration increasing on the network is shown as Fig 4.13 b). At any level of PV penetration, it has a chance of occurring the voltage unbalance (0.5-2%) on each feeder but it still under the standard limitation (<2%). It does not trend for the variation of the voltage unbalance because of the several factors like the amount of loads, phase connection of loads, distance of loads, etc.


The location of PV installation is as Type C: the middle zone of each feeder.

a) %THDv

b) %VUF

Ref. code: 25605622040581VOU

48

0.001.002.003.004.005.006.007.008.009.00

NoPV 10% 20% 30% 40% 50% 60% 70% 80%

%THDv in Case Study 14 (TypeC: Middle Zone)Feeder1 Feeder2 Feeder3

%THDv : < 5%

0.00

0.50

1.00

1.50

2.00

NoPV 10% 20% 30% 40% 50% 60% 70% 80%

%VUF in Case Study 14 (TypeC: Middle Zone)


4.1.14 Case Study 14: The LV distribution network with harmonic background is nearly 2% at LV bus, because of harmonic loads installation on feeder1. Without PV installation in the network, the max total harmonic distortion voltage is about 8% on feeder1, and 2% on feeder2&3 respectively. The location of PV installation is the middle zone of each feeder. Starting PV2 installation with 10% PV penetration and increasing PV2 installation to 10% PV penetration in each round until % PV penetration is equal to 80%.The result of simulation following in case study 14 show the relationship between the total harmonic voltage distortion in the LV distribution network and % PV penetration increasing on the network as Fig 4.14 a). The more PV2 installation increase in the network, the more THDv of the network add up. The THDv on feeder 2 and on feeder 3 will be over the standard limitation, when the level of PV penetration on feeder 2 and on feeder 3 are more than 40% and 70% respectively. The relationship between the voltage unbalance in the LV distribution network and % PV penetration increasing on the network is shown as Fig 4.14 b). At any level of PV penetration, it has a chance of occurring the voltage unbalance (0.5-2%) on each feeder but it still under the standard limitation (<2%). It does not trend for the variation of the voltage unbalance because of the several factors like the amount of loads, phase connection of loads, distance of loads, etc.


10-80% PV Penetration. The location of PV installation is as Type C: the middle zone

of each feeder.

a) %THDv

b) %VUF

Ref. code: 25605622040581VOU

49

0.0

2.0

4.0

6.0

8.0

10% 20% 30% 40% 50%

%THDv in Case Study 15 (TypeD: End Zone)Loading 25% Loading 50% Loading 80%

%THDv : < 5%

0.0

0.5

1.0

1.5

2.0

NO PV 10% 20% 30% 40% 50%

%VUFin Case Study 15 (TypeD: End Zone)


4.1.15 Case Study 15: PV2 (THDi>5%) is installed in the low voltage distribution network without the harmonic background. The location of PV installation is the end zone of each feeder. Starting PV2 installation with 10% PV penetration and increasing PV2 installation to 10% PV penetration in each round until % PV penetration is equal to 50%.(Due to the number of households on the end zone of all feeder are only 37 households, PV installation will be possible with 10-50% PV penetration.) The result of simulation following in case study 15 show the relationship between the total harmonic voltage distortion in the LV distribution network and % PV penetration increasing on the network as Fig 4.15 a). The amount of %THDv will increase when PV penetration in the network add up. When PV2 were installed up to 30% PV penetration, The amount of %THDv will be over the standard limitation. The relationship between the voltage unbalance in the LV distribution network and % PV penetration increasing on the network is shown as Fig 4.15 b). At any level of PV penetration, it has a chance of occurring the voltage unbalance (0.5-2%) on each feeder but it still under the standard limitation (<2%). It does not trend for the variation of the voltage unbalance because of the several factors like the amount of loads, phase connection of loads, distance of loads, etc.


The location of PV installation is as Type D: the end zone of each feeder.

a) %THDv

b) %VUF

Ref. code: 25605622040581VOU

50

0.00

0.50

1.00

1.50

2.00

NoPV 10% 20% 30% 40% 50%

%VUF in Case Study 16 (TypeD: End Zone)Feeder1 Feeder2 Feeder3

0.00

2.00

4.00

6.00

8.00

10.00

NoPV 10% 20% 30% 40% 50%

%THDv in Case Study 16 (TypeD: End Zone)


%THDv : < 5%

4.1.16 Case Study 16: The LV distribution network with harmonic background is nearly 2% at LV bus, because of harmonic loads installation on feeder1. Without PV installation in the network, the max total harmonic distortion voltage is about 8% on feeder1, and 2% on feeder2&3 respectively. The location of PV installation is the end zone of each feeder. Starting PV2 installation with 10% PV penetration and increasing PV2 installation to 10% PV penetration in each round until % PV penetration is equal to 50%.(Due to the number of households on the end zone of all feeder are only 37 households, PV installation will be possible with 10-50% PV penetration.) The result of simulation following in case study 16 show the relationship between the total harmonic voltage distortion in the LV distribution network and % PV penetration increasing on the network as Fig 4.16 a). When the level of PV penetration add up, the amount of %THDv on feeder2 and feeder3 will increase slightly from 1.8% to 2.2%.The relationship between the voltage unbalance in the LV distribution network and % PV penetration increasing on the network is shown as Fig 4.16 b). At any level of PV penetration, it has a chance of occurring the voltage unbalance (0.5-2%) on each feeder but it still under the standard limitation (<2%). It does not trend for the variation of the voltage unbalance because of the several factors like the amount of loads, phase connection of loads, distance of loads, etc.


10-50% PV Penetration. The location of PV installation is as Type D: the end zone of

each feeder.

a) %THDv

b) %VUF

Ref. code: 25605622040581VOU

51

0

2

4

6

8

NoPV 10% 20% 30% 40% 50% 60% 70% 80%

%THDv Comparison PV1 @Loading 50% (each location type)

Feed-by-feeder Beginning Zone Middle Zone End Zone

THDv: < 5%

0.000.501.001.502.002.503.003.50

NoPV 10% 20% 30% 40% 50% 60% 70% 80%

%VUF Comparison PV1 @Loading 50% (each location type)


%VUF : < 2%

4.2 Overall discuss and comparison

4.2.1 PV1 @ each location type without harmonic background

PV1, which inject the output current distortion nearly 2%, were installed in the low voltage distribution network (without harmonic background) at the different location as 4 types:

A. Feeder-by-feeder with PV penetration 10-80% B. Beginning zone with PV penetration 10-50% C. Middle zone with PV penetration 10-80% D. End zone with PV penetration 10-50%

The simulation result of each location type focuses on the amount of %THDv and %VUF as shown in Fig. 4.17 a) and b). Only the location as type A (Feeder-by-feeder) the amount of %THDv will be over the standard limitation, when %PV penetration more than 60 % and the location of PV installation must be as Type A(Feeder-by-feeder continuously). By the way, the amount of %VUF will be over the standard limitation, when %PV penetration more than 50 % and the location of PV installation must be as Type A(Feeder-by-feeder continuously). Due to the location of PV installation with type A, PV will adhere massively thus the current distortion will be reinforced and it effect to the amount of THDv in the network. The other location types, the amount of %THDv trend increasing but it still under the standard limitation. It has a chance of occurring the voltage unbalance (0.5-2%). It does not trend for the voltage unbalance.

Figure 4.17 Comparison, PV1 connected to grid without harmonic background in

each location type of PV installation.

a) %THDv (without harmonic background)

b) %VUF (without harmonic background)

Ref. code: 25605622040581VOU

52

0.0001.0002.0003.0004.0005.0006.0007.000

NoPV 10% 20% 30% 40% 50% 60% 70% 80%


%THDv Comparison on Feeder2, PV1 @Loading 50% (each location type)

%THDv : < 5%

0.0

1.0

2.0

3.0

4.0

5.0

NoPV 10% 20% 30% 40% 50% 60% 70% 80%


%THDv Comparison on Feeder3, PV1 @Loading 50%

4.2.2 PV1 @ each location type with harmonic background

PV1(THDi ≈2%) is installed in the low voltage distribution network (with harmonic background nearly 2% : harmonic loads were installed on feeder1) at the different location as 4 types. The simulation result of each location type focus on the amount of %THDv and %VUF on feeder 2 and feeder 3 are shown in Fig. 4.18 a) and b). Only the location as type A (Feeder-by-feeder), the amount of %THDv on feeder 2 will be over the standard limitation, when %PV penetration more than 60 % and the location of PV installation must be as Type A(Feeder-by-feeder continuously) as Fig.4.18 a). By the way, the amount of %VUF on feeder 2 will be over the standard limitation, when %PV penetration more than 50 % and the location of PV installation must be as Type A(Feeder-by-feeder continuously) as Fig.4.18 a). Due to the location of PV installation with type A, PV will adhere massively thus the current distortion will be reinforced and it effect to the amount of THDv in the network. The number of PV installation on feeder3 is less than feeder2 and feeder 3 is so far from feeder1. This affect to the amount of %THDv and %VUF on feeder 3 is lower than feeder2 as Fig.4.18 c) and d) respectively.

The other location types, the amount of %THDv trend increasing but it still under the standard limitation. It has a chance of occurring the voltage unbalance (0.5-2%). It does not have a tendency for the voltage unbalance.

a) %THDv on Feeder2 (with harmonic background)

b) %THDv on Feeder3 (with harmonic background)

Ref. code: 25605622040581VOU

53

0.0

0.2

0.4

0.6

0.8

1.0

NoPV 10% 20% 30% 40% 50% 60% 70% 80%


%VUF Comparison on Feeder3, PV1 @Loading 50% (each location type)

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

NoPV 10% 20% 30% 40% 50% 60% 70% 80%


%VUF Comparison on Feeder2, PV1 @Loading 50%

%VUF : < 2%

Figure 4. 18 Comparison, PV1 connected to grid with harmonic background in each

location type of PV installation.

c) %VUF on Feeder2 (with harmonic background)

d) %VUF on Feeder3 (with harmonic background)

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%THDv Comparison PV2 @Loading 50% (each location type)


THDv: < 5%

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%VUF Comparison PV2 @Loading 50% (each location type)


%VUF : < 2%

4.2.3 PV2 @ each location type without harmonic background

PV2, which inject the output current distortion more than 5%, is installed in the low voltage distribution network (without harmonic background) at the different location as 4 types: The simulation result of each location type focus on the amount of %THDv and %VUF as shown in Fig. 4.19 a) and b). Among the location as Type A (Feeder-by-feeder), Type C (middle zone) and Type D (end zone) the amount of %THDv will be over the standard limitation, when %PV penetration more than 40 % ,50% and 30% with the location of PV installation as Type A (Feeder-by-feeder), Type C (middle zone) and Type D (end zone) respectively. Another location type, the amount of %THDv trend increasing but it still under the standard limitation.

By the way, the amount of %VUF will be over the standard limitation, when %PV penetration more than 50 % and the location of PV installation must be as Type A(Feeder-by-feeder continuously). Another location type, It has a chance of occurring the voltage unbalance (0.5-2%). It does not have a tendency for the voltage unbalance.

Figure 4.19 Comparison, PV2 connected to grid without harmonic background in

each location type of PV installation.

a) %THDv (without harmonic background)

b) %THDv (without harmonic background)

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4.2.4 PV2 @ each location type with harmonic background

PV2(THDi >5%) is installed in the low voltage distribution network (with harmonic background nearly 2% : harmonic loads were installed on feeder1) at the different location as 4 types. The simulation result of each location type focus on the amount of %THDv and %VUF on feeder 2 and feeder 3 as shown in Fig. 4.20 a) and b). On Feeder2, Among the location as Type A (Feeder-by-feeder), Type B (beginning zone) and Type D (end zone), the amount of %THDv will be over the standard limitation, when %PV penetration more than 40 % ,50% and 30% with the location of PV installation as Type A (Feeder-by-feeder), Type C (Middle zone) and Type D (End zone) respectively as Fig.4.20 a).Another location type, the amount of %THDv trend increasing but it still under the standard limitation. On Feeder3, only the location as Type C (Middle zone), the amount of %THDv will be over the standard limitation, when %PV penetration more than 70 % as Fig.4.20 b). The other location types, the amount of %THDv trend increasing but it still under the standard limitation.

By the way, On feeder 2, the amount of %VUF will be over the standard limitation, when %PV penetration more than 50 % and the location of PV installation must be as Type A(Feeder-by-feeder continuously) as Fig.4.20 c). The other location types, they have a chance of occurring the voltage unbalance (0.5-2%). It does not trend for the voltage unbalance. On feeder 3, the amount of %VUF at each location types still under the standard limitation as Fig.4.20 d).

a) %THDv on Feeder2 (with harmonic background)

b) %THDv on Feeder3 (with harmonic background)

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%VUF : < 2%

0.0

0.2

0.4

0.6

0.8

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Figure 4. 20 Comparison, PV2 connected to grid with harmonic background in each

location type of PV installation.

c) %VUF on Feeder2 (with harmonic background)

d) %VUF on Feeder3 (with harmonic background)

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%THDv Comparison (Type A: Feeder-by-feeder)Case 1 Case 9 Case 2 at F2 Case 10 at F2

THDv: < 5%

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%VUF Comparison (Type A: Feeder-by-feeder)Case 1 Case 9 Case 2 at F2 Case 10 at F2

%VUF : <

4.2.5 PV1 and PV2 comparison @ each location type

4.2.5.1 Location of PV installation as Type A

Comparing 4 cases: Case1 and Case 9 as PV1 and PV2 respectively, which were connected with the location as feeder-by-feeder continuously in the grid without harmonic background. Case2 and Case 10 as PV1 and PV2 respectively, which were connected with the location as feeder-by-feeder continuously in the grid with harmonic background nearly 2% at the LV bus. The case studies herein were focused on the %THDv of feeder2 and feeder3, so that the impact may be result from harmonic on feeder1 and %PV penetration adding on feeder2 and 3.

The result of simulation show that the %THDv value of 4 cases tend to increase according to the level of %PV penetration in the network as Fig.4.21 a). In the grid with harmonic background, the %THDv will be higher than another. The %THDv is over the standard limitation in case10, case9, case2 and case1 at the level of PV penetration is equal to more than 30%, 30%, 60% and 70% respectively.

In the part of %VUF as Fig.4.21 b), all cases have a tendency the %VUF value add up when the level of PV penetration in the network is higher. The %VUF is over the standard limitation in case1, case9, at the level of PV penetration is equal or more than 50% and more than 50% for case2 and case10. The cause of %VUF is higher due to adding up PVs connected in the feeder 1 and 2 which are higher than feeder 3.

Figure 4. 21 Comparison PV1 and PV2, when it connected to grid without/with

harmonic background in the location type of PV installation as Type A.

a) %THD

b) %VUF

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%THDv Comparison (Type B: Beginning Zone)Case 3 Case 11 Case 4 at F2 Case 12 at F2

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%VUF Comparison (Type B: Beginning Zone)Case 3 Case 11 Case 4 at F2 Case 12 at F2

4.2.5.2 Location of PV installation as Type B

Comparing 4 cases: Case3 and Case 11 as PV1 and PV2 respectively, which were connected with the location as the beginning zone of each feeder in the grid without harmonic background. Case4 and Case 12 as PV1 and PV2 respectively, which were connected with the location the beginning zone of each feeder in the grid with harmonic background nearly 2% at the LV bus. The case studies herein were focused on the %THDv of feeder2 and feeder3, so that the impact may be result from harmonic on feeder1 and %PV penetration adding on feeder2 and 3.

The result of simulation show that the %THDv value of 4 cases trend to increase according to the level of %PV penetration in the network as Fig.4.22 a). In the grid with harmonic background, the %THDv will be higher than another. The %THDv is under the standard limitation in 4 cases

In the part of %VUF as Fig.4.22 b), they do not change when the level of PV penetration in the network is higher. The cause of %THDv under the standard and no changing of %VUF may be result from the maximum of %PV penetration in the beginning zone is only 50% according the number of household is 41 households, PVs the location of PVs were scattered in the beginning zone of each feeder and phase connecting randomly.


harmonic background in the location type of PV installation as Type B.

a) %THDv

b) %VUF

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%THDv Comparison (Type C: Middle Zone)Case 5 Case 13 Case 6 at F2 Case 14 at F2

%THDv : < 5%

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%VUF Comparison (Type C: Middle Zone)

Case 5 Case 13 Case 6 at F2 Case 14 at F2

4.2.5.3 Location of PV installation as Type C

Comparing 4 cases: Case5 and Case 13 as PV1 and PV2 respectively, which were connected with the location as the middle zone of each feeder in the grid without harmonic background. Case6 and Case 14 as PV1 and PV2 respectively, which were connected the location as the middle zone of each feeder in the grid with harmonic background nearly 2% at the LV bus. The case studies herein were focused on the %THDv of feeder2 and feeder3, so that the impact may be result from harmonic on feeder1 and %PV penetration adding on feeder2 and 3.

The result of simulation show that the %THDv value of 4 cases trend to increase according to the level of %PV penetration in the network as Fig.4.23 a). In the grid with harmonic background, the %THDv will be higher than another. The %THDv is over the standard limitation in only case13 and case14 at the level of PV penetration is equal to more than 40%.

In the part of %VUF as Fig.4.23 b), all cases have a tendency occurring the voltage unbalance when PV penetration are connected in the network. The %VUF still under the standard limitation. The cause of %VUF does not have a tendency due to the location of PVs were scattered in the middle zone of each feeder and phase connecting randomly.


harmonic background in the location type of PV installation as Type C.

a) %THDv

b) %VUF

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%THDv Comparison (Type D: End Zone)Case 7 Case 15 Case 8 at F2 Case 16 at F2

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%VUF Comparison (Type D: End Zone)Case 7 Case 15 Case 8 at F2 Case 16 at F2

4.2.5.4 Location of PV installation as Type D

Comparing 4 cases: Case7 and Case 15 as PV1 and PV2 respectively, which were connected with the location as the end zone of each feeder in the grid without harmonic background. Case8 and Case 16 as PV1 and PV2 respectively, which were connected with the location the end zone of each feeder in the grid with harmonic background nearly 2% at the LV bus. The case studies herein were focused on the %THDv of feeder2 and feeder3, so that the impact may be result from harmonic on feeder1 and %PV penetration adding on feeder2 and 3.

The result of simulation show that the %THDv value of 4 cases trend to increase according to the level of %PV penetration in the network as Fig.4.24 a). In the grid with harmonic background, the %THDv will be higher than another. The %THDv is over the standard limitation in only case15 and case16 at the level of PV penetration is equal to more than 20%.

In the part of %VUF as Fig.4.24 b), all cases have a tendency occurring the voltage unbalance when PV penetration are connected in the network. The %VUF still under the standard limitation. The cause of %VUF does not have a tendency due to the location of PVs were scattered in the end zone of each feeder and phase connecting randomly. The maximum of %PV penetration in the beginning zone is only 50% according the number of household is 37 households

Figure 4. 24 Comparison PV1 and PV2, when it connected to grid with/without

harmonic background in the location type of PV installation as Type D.

a) %THDv

b) %VUF

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Chapter 5

Conclusions and Recommendations

5.1 Conclusion

This research has investigated the impact of solar rooftop PV penetration to the low voltage

distribution system of Provincial Electricity Authority. In this paper focuses on the total

harmonic distortion voltage and the voltage unbalance in the network when rooftop PV

with inverter 2 type (which has THDi<2% and >5% in PV1 and PV2 respectively) were

installed in the LV network with 10-80% PV Penetration. Although PV1 will inject the

output current distortion (THDi) less than 2%, if PV1 installation in the network with more

than 60% PV penetration of the rated power of the distribution transformer, it effect to the

THDv of buses in system over the standard limitation. Moreover, if PV2 installation in the

network will effect to the THDv of buses in system over the standard limitation when %PV

penetration is more than 30%.

The amount of %THDv depend on the location of PV installation, if PVs connected

to the network adhere massively, the amount of %THDv will add up. Nevertheless, in the

condition %THDv under the standard, the location of PVs disperse all over the feeder

(as the location of PV installation is Type B, C and D), the level of PV penetration in

the network may be more than PV installation gathered (as the location of PV

installation is Type A). Besides, harmonics background in network should be measured

and taken into account before high penetration PV will be integrated to LV network. When

PVs were connected to the polluted grid, both THDi of PV inverter and harmonics

background may affect THD of network to increase or higher the standard. The number of

PV installation in the polluted grid, while THDv still under the standard limitation, will be

less than the grid without harmonic background as if PV1 installation in the polluted

network with not exceed 50% PV penetration of the rated power of the distribution

transformer.

Not only the harmonic impact, but also the amount of % voltage unbalance factor

was influenced from PV penetration. The amount of %VUF depend on the location of PV

installation and phase connecting, if PVs connected to the network adhere massively(as the

location of PV installation is Type A), the amount of %VUF will add up and over the

standard limitation when %PV penetration is equal or more than 50%. Whenever, PV

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penetration connected in the network, it has a chance occurring the voltage unbalance but

the amount of %VUF still under the standard limitation in case of dispersed PV

installation (as the location of PV installation is Type B, C and D) and phase connection

randomly. Considering system loading level at 25%, 50%, and 80% it affect to THDv and

%VUF of system slightly.

5.2 Recommendation

This research simulates the low voltage distribution system of PEA with the 250

KVA distribution transformer supplying the area of a village. Nevertheless, this

simulation model can adjust the input data or factor of model if whoever is interested

in other areas, or other load profiles which the simulate result may be differ depend on

the assumption of the model.

This research can be used as the data for revise the criteria of rooftop PV

installation on the PEA distribution system. At present, PEA specifies the number of

single phase rooftop PV at 15% of rating distribution transformer. The result of this

research shows that PV penetration about 50% in the system will not affect to the

voltage unbalance and harmonic voltage distortion. PEA will be able to revise the

number of rooftop PV into the LV distribution to be 15-50% of rating transformer for

the distribution system as this research. However, it should consider other impacts such

as loss, power factor, over voltage etc.

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References

Books and Book Articles

Grainger, J.J. and Stevenson, W.D.(1994). Power System Analysis. McGraw-Hill

R.C. Dugan, M.F. McGranaghan, and H.W. Beaty. (1996). Electrical Power Systems

Quality. New York: McGraw-Hill.

Articles

Cobben, J.F.G. (2007). Power Quality Implications at point of connection. Ph.D. Thesis,

Techische University.

Electronic Media

M. C. Benhabib, J. M. A. Myrzik and J. L. Duarte. Harmonic effects caused by large

scale PV installations in LV network. 2007 9th International Conference on

Electrical Power Quality and Utilisation, Barcelona, 2007, pp. 1-6.

E. Demirok, D. Sera, R. Teodorescu, P. Rodriguez and U. Borup. Clustered PV

inverters in LV networks: An overview of impacts and comparison of voltage

control strategies. 2009 IEEE Electrical Power & Energy Conference

(EPEC), Montreal, QC, 2009, pp. 1-6.

V. H. M. Quezada, J. R. Abbad and T. G. S. Roman. Assessment of energy distribution

losses for increasing penetration of distributed generation. IEEE

Transactions on Power Systems, vol. 21, no. 2, pp. 533-540, May 2006.

Jong-Gyeum Kim, Eun-Woong Lee, Dong-Ju Lee and Jong-Han Lee. Comparison of

voltage unbalance factor by line and phase voltage. 2005 International

Conference on Electrical Machines and Systems, Nanjing, 2005, pp. 1998-

2001 Vol. 3.

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C. L. Fortescue. Method of symmetrical co-ordinates applied to the solution of

polyphase networks. Proceedings of the American Institute of Electrical

Engineers, vol. 37, no. 6, pp. 629-716, June 1918.

P. Pillay and M. Manyage. California Electricity Situation. IEEE Power Engineering

Review, vol. 21, no. 5, pp. 10-12, May 2001.

Other Materials

IEEE Std. 1995. IEEE Recommend Practice for Monitoring Electric Power Quality

(IEEE Std.1159-1995).

IEEE Std. 1992. IEEE Recommended Practices and Requirements for Harmonic

Control in Electrical Power Systems (IEEE Std. 519-1992).

Ministry of Energy (2015). Alternative Energy Development Plan 2015 September

2015,www.dede.go.th/download/files/AEDP2015_Final_version.pdf

PRC-PQG-01/1998. (1998). Regulation of harmonic on power system for business and

industry.

Provincial Electricity Authority (2016). Regulation on the Power Network System

Interconnection Code 2016, www.pea.co.th/Portals/0/Document/vspp/PEA

Interconnection Code 2016.pdf

Provincial Electricity Authority (2015). Load Profile. Retrieved from March 10, 2015,

www.amr.pea.co.th

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Appendices

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Appendix A

Example of phase connection of each PV in Case Study 1

Case study 1 with 80% PV penetration @ Location TypeA

PV No. Connected Bus and Phase

PV No. Connected Bus and Phase

1 Bus1_017A 35 Bus2_076A 2 Bus1_018B 36 Bus2_077B 3 Bus1_019B 37 Bus2_078B 4 Bus1_020A 38 Bus2_085A 5 Bus1_021A 39 Bus2_089A 6 Bus1_022C 40 Bus2_090A 7 Bus1_023C 41 Bus2_091A 8 Bus1_024B 42 Bus2_092C 9 Bus1_025B 43 Bus2_093B 10 Bus1_026A 44 Bus2_094A 11 Bus1_027A 45 Bus2_095B 12 Bus2_011C 46 Bus2_096C 13 Bus2_021C 47 Bus2_097B 14 Bus2_024A 48 Bus2_098A 15 Bus2_025A 49 Bus2_099A 16 Bus2_034A 50 Bus2_100B 17 Bus2_036A 51 Bus2_101B 18 Bus2_046C 52 Bus2_102C 19 Bus2_047A 53 Bus2_103C 20 Bus2_048A 54 Bus2_104A 21 Bus2_049A 55 Bus2_105A 22 Bus2_050A 56 Bus2_106A 23 Bus2_051B 57 Bus2_107B 24 Bus2_052B 58 Bus2_108A 25 Bus2_053B 59 Bus2_109A 26 Bus2_054C 60 Bus2_110A 27 Bus2_055C 61 Bus2_111B 28 Bus2_069A 62 Bus2_112B 29 Bus2_070A 63 Bus2_113A 30 Bus2_071B 64 Bus2_119A 31 Bus2_072B 65 Bus3_021A 32 Bus2_073C 66 Bus3_051C 33 Bus2_074C 67 Bus3_088A 34 Bus2_075A

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Appendix B

Example of The top twenty of maximum THD at any bus

The top 20 bus which has the %THDv in Case study 1 with 80% PV

penetration @ Location Type A

Rank Max THDv (%) Name_Bus 1 5.811674 Bus2_087A 2 5.811674 Bus2_087A 3 5.811446 Bus2_090A 4 5.811296 Bus2_089A 5 5.725806 Bus2_086A 6 5.725525 Bus2_091A 7 5.64848 Bus2_084A 8 5.648213 Bus2_085A 9 5.637689 Bus2_070A 10 5.637636 Bus2_069A 11 5.596903 Bus2_076A 12 5.596777 Bus2_075A 13 5.566187 Bus2_094A 14 5.478113 Bus2_099A 15 5.478031 Bus2_098A 16 5.30505 Bus2_104A 17 5.304948 Bus2_105A 18 5.21314 Bus2_048A 19 5.213115 Bus2_050A 20 5.213087 Bus2_047A

Name_Bus definition:

Bus2_087A is represent Bus no.87 on feeder2 and phase connection is phase A

Documents

Impact of rooftop photovoltaic penetration level on low