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MODELLING OF PHUNTSHOLING LOW VOLTAGE

 DISTRIBUTION NETWORK AND ANALYZING THE TECHNICAL LOSSES IN DIgSILENT POWER FACTORY SOFTWARE

Project Report

Submitted in partial fulfillment of the requirements

For the award of Bachelor of Degree In

Electrical Engineering

Submitted By:

   Mr. Sanga Chophel

   Mr. Pasang                                      

Ms. Pema Layzom

Ms. Sonam Paldon Dorji

    Under the guidance of: Mr. Roshan Chhetri

DEPARTMENT OF ELECTRCIAL ENGINEERING

COLLEGE OF SCIENCE AND TECHNOLOGY

PHUENTSHOLING, BHUTAN

June, 2017

ROYAL UNIVERSITY OF BHUTAN

COLLEGE OF SCIENCE AND TECHNOLOGY

DEPARTMENT OF ELECTRICAL ENGINEERING

CERTIFICATE

This is to certify that the project entitled 'MODELLING THE PHUNTSHOLING LOW VOLTAGE DISTRIBUTION NETWORK AND ANALYZING THE TECHNICAL LOSSES USING DIgSILENT POWER FACTORY SOFTWARE',which is being submitted by Mr. Sanga Chophel (02022013020), Ms. Pema Leyzom (02022013016), Ms. Sonam Paldon Dorji (EDE2012038), and  Mr. Pasang (EDE2012021) in partial fulfillment of the requirement for the award of the 'Degree of Bachelor of Engineering in Electrical Engineering' is a record of student work carried out at College of Science and Technology, Phuentsholing under my supervision and guidance.

                                                                                                         Mr. Roshan Chhetri

                                                                                                               Project Guide

Acknowledgements

The success and the final outcome of this project required a lot of guidance and assistance from many people and we are extremely fortunate to have got this all along the completion of our project work. Whatever we have done is only due to such guidance and assistance and we would like to thanks them.

We express our deep sense of gratitude to our guide Mr. Roshan Chhetri for his valuable help and guidance. We are thankful to him for the encouragement that he has given to us in completing the project.

Our project wouldn't have been come into picture without the idea of the topic. Thus we owe our profound gratitude to Mr. Kinzang Namgay, BPC Lhuentse for suggesting such an important project topic. We also thank him for providing necessary data and resources to start this particular project.

We also thank all BPC staff of Phuntsholing for kindly accepting us to get required data for our project. We thank Mr. Tsheltrim (Electrical Engineer) for guiding us in going through the data and accepting our helping call at any time.

We heartily thank Pema Wangchuk and Jurmey Tenzin of fourth year civil for accepting our request to go for our field survey to measure line length of selected network. We greatly appreciate their help and patience in doing the survey despite scorching sun.

We are also thankful to Mr. Tsheltrim (Electrical engineer in Phuntsholing BPC) and other staffs for their constant encouragement, support, suggestion and guidance which helped us in successfully completing our project work. Also, we would like to extend our sincere regards to all the non-teaching staff of electrical department for their timely support.

Abstract

Power loss in the Transmission/Distribution network is unavoidable, but must be contained to a manageable level. Energy losses in power system directly impact the efficiency of electricity transmission and distribution. The electrical energy losses in distribution system are given less importance until past few years. The distribution network in Bhutan has increased its size over a year and hence the electrical energy losses occurring in distribution network is more.

In this project the LV distribution network of Phuentsholing is taken under consideration to analyze different technical losses associated with it. Different technical losses in the network are theoretically calculated and also the losses are analyzed from network which is modeled in DIgSILENT power factory software. For reduction of energy losses in the system the battery storage was used. Analyzing of losses reduction was performed on the network model developed in the DIgSILENT power factory software.

Table of Contents

Acknowledgements i

Abstract ii

List of Abbreviations. v

List of tables. vi

List of figure vii

1 CHAPTER ONE: LITERATURE REVIEW. 2

2 CHAPTER TWO: INTRODUCTION 6

2.1 Objectives 7

2.2 Problem statement. 7

2.3 Project scope. 8

2.4 Methodology. 8

2.4.1 Collection data of existing Phuntsholing distribution network. 9

2.4.2 Mathematical calculation of different technical losses. 9

2.4.3 Modelling of Distribution network in DIgSILENT power factory and analyzing different losses. 9

2.4.4 Validation of technical losses from theoretical result with the result from DIgSILENT power factory software. 10

2.4.5 Assigning of effective mitigation techniques. 10

3 CHAPTER THREE: TECHNICAL LOSS IN DISTRIBUTION SYSTEM. 11

3.1 Technical loss 11

3.1.1 Distribution Line losses 12

3.1.2 Power transformer losses. 13

4 CHAPTER FOUR: STUDY OF EXISTING DISTRIBUTION SYSTEM IN PHUENTSHOLING. 16

4.1 Overview of 66/33/11kV Phuentsholing substation. 16

4.2 Details of outgoing feeder. 18

5 CHAPTER FIVE: METHODS TO REDUCE TECHNICAL LOSSES OF DISTRIBUTION SYSTEM IN PHUENTSHOLING. 29

5.1 Placing energy storage battery in the network. 29

5.2 Results. 33

6 Conclusion. 35

7 Recommendation 36

8 References 37

List of Abbreviations.

A Ampere

ACSR Aluminum conductor Steel reinforced

BB Battery Bank

BPCL Bhutan Power Cooperation Limited

CTC Continuously transposed conductor

DG Distributed Generator

DNR Distribution network reconfiguration

DT Distribution transformer

GPS Global positioning system

GW Giga Watt

GWh Giga Watt hour

HMI Human Machine Interface

IDMT Inverse definite minimum time

ISO International organization for standardization

kV Kilo volt

kVAR Kilo Volt Ampere reactive

kWh Kilo Watt hour

LED Light emitting diode

LV Low voltage

MATLAB Matrix laboratory

MVA Mega volt ampere

MVAR Mega volt ampere reactive

MW Mega Watt hour

MWh Mega Watt hour

PLC Programmable logic controller

PSO Particle swarm optimization

RTU Remote terminal unit

SCADA Supervisory control and data acquisition

SF6 Sulphur Hexa-fluoride

SPSO Selective particle swarm optimization

List of tables.

Table 3.1: Table showing DIN4250 standard transformer losses at 100% loading. 15

Table 4.1 Outgoing feeder details of 66/33/11kV substation, Phuentsholing. 21

Table 4.2: Table showing the result of theoretical losses and the losses obtained from DIgSILENT power factory. 28

List of figure

Figure 2 1 the diagram showing the methodology of project. 8

Figure 3 1 the diagram showing fish bone analysis: Cause of loss. 12

Figure 4 1 Average peak load in January month of all feeder. 22

Figure 4 2 PWD feeder modelled in DIgSILENT power factory software. 24

Figure 4 3 Ashi Bangalow feeder modelled in DIgSILENT power factory software. 25

Figure 4 4 Ramitey feeder modelled in DIgSILENT power factory software. 25

Figure 4 5 Water Booster  feeder modelled in DIgSILENT power factory software. 26

Figure 4 6 Tading rural feeder modelled in DIgSILENT power factory software. 26

Figure 4 7 BPC colony feeder modelled in DIgSILENT power factory software. 27

Figure 4 8 Comparison between theoretical loss calculated and losses obtained from DIgSILENT power factory. Error! Bookmark not defined.

Figure 5 1 Showing one day load curve of three feeders. 30

Figure 5 2 Showing the battery bank installed in BPC colony feeder. 30

Figure 5 3 Showing battery storage installed in Tading rural feeder. 31

Figure 5 4 Showing battery storage installed in Ashi Bangalow feeder. 31

Figure 5 5 showing Battery storage installed in Ramitey feeder. 32

Figure 5 6 showing battery storage installed in RWD feeder. 32

Figure 5 7 Showing battery storage installed in Water Booster feeder. 33

'

CHAPTER ONE: LITERATURE REVIEW.

The technical loss and its analysis in selected distribution network are performed using PSS/Adept program. In the evaluation of losses, the result of theoretical losses was compared with the result obtained from practical measurement. It was found out that low-voltage transformer and distribution line losses constitute maximum value at around 18.72% of the total losses [1]. The proper selection of distribution component and to investigate cost analysis is the major controlling factor in order to reduce those technical losses.

An analysis of technical and non-technical losses and its impact on the power sector was done in India owing to their power sector being characterized by inadequate and insufficient power supply [2]. The huge amount of energy is lost in the Transmission and distribution system by the technical and non-technical losses. Thus this paper analyzes technical and nontechnical losses and its impact on power system by case study and MATLAB Simulation in power system.

In India, due to continued rising trend of losses in distribution network, study on technical and non-technical losses done in Ambattur industrial Estate-SS distribution network (India) fed from a main intake of 110 KV which is fed to two main loads to zones of 33KV for Industrial User & 11KV for residential users using ETAP (Electrical transient analysis program) shows that there were total losses of 3.6kW of base losses and 9.52kW of studied losses. The technical losses caused by material properties and its resistance to the flow of electrical current in distribution was analyzed and simulated through electrical transient analysis program. It was also found out that transformer having the maximum losses of 8.9kW. Installation of capacitor banks, relocation of distribution transformers, ensuring a constant Power Factor to industrial users, avoiding overloading of transformers and resizing of conductors are some of the recommended mitigation techniques [3].  

A study on technical and non-technical losses for loss reduction in distribution systems have been initiated in Mazoon Electricity Company (MZEC) due to the increasing cost of supplying electricity, the shortage in fuel with ever-increasing cost to produce more power, and the global warming concerns. Reduction of the technical losses were studied and the following projects were examined:(a) installing parallel feeders for overloaded feeders according to the approved security standard, (b) introducing transformer(s) for overloaded substation, (c) installing more capacitor banks at the primary feeder which will help in boosting the voltage and improving the power factor as well as reducing there active power losses, and (d) introducing more links between the feeders to facilitate load sharing. Results revealed that there was a little decrease in the active power but the reactive power decreases considerably. On the other hand, the losses were dramatically reduced and voltage profiles were improved to be within the standard tolerance ''6 %.

Their simulation results have shown that the implementation of these projects leads to a significant improvement in voltage profile, and reduction in the active and the reactive power losses.  The economic analysis was also done and had revealed that the implementation of the proposed projects in MZEC leads to an annual saving of about US$ 5 million. The study is still in progress to investigate the effect of using distributed generation (DG) on losses reduction before and after implementing the aforementioned projects [4].

The different loads (residential, commercial and industrial) can be used for calculations through load factor improvement and simulation (DIgSILENT) methodologies in order to develop accurate and authentic results. The results were further analyzed to develop an optimum solution. Those solutions are mainly aimed at improving the load factor with battery energy storage by peak shaving. It focuses on improving technical losses caused by circulating current (I2R), thereby improving the overall energy efficiency when a battery energy storage is involved. The battery energy storage system has indicated positive response and the load factor have shown improvement [5].

Implementation of DG at the different location and the variation of power losses with changed in location has been simulated and analyzed using DIgSILENT PowerFactory software in Turkey [6]. It was observed that the DG in the network and other power source can improve the losses in the network significantly thereby increasing its efficiency.

Theoretical analysis has been carried out to estimate the losses involved in transformers in Pune, India and found out that total losses due to transformer in the feeder is 8.57% of the total input to the substation [7]. An assessment and minimization of distribution transformer loss is done in detail with help of ETAP software simulation from the past data in MAMBALAM substation and found out the total losses due to transformer in the feeder is 0.71% of the total input to the substation [8]. A proper maintenance and a lower kVA ratings of the transformer can save the losses occurring in the network.

Reduction of the distribution losses in a commercial section are its main aim. The first step that they have used in power loss minimization procedure is loss calculation as it is a common tool to optimize the design, operation and planning of the electrical network [9]. They have used these two methods and compared for power loss calculations between field measurement and simulation results. Here the technical loss was minimized by complete removal of low voltage network and considered that the reduction of power loss as the proper planning of network. It has observed that the distribution losses as 23.17 % and after adopting various mitigation techniques the losses was reduced to 3.85%.

The optimal planning and reduction of technical loss in distribution network was its main objectives. The selection of optimal conductor size and the placement of capacitor in radial distribution network was considered to be practical planning [10]. Here the technical operational constraints are available conductors and capacitors, voltage limit, maximum permissible carrying current of conductors. It uses particle swarm optimization (PSO) to solve power loss minimization.  By applying this method, they have observed reduction in final cost of network planning, losses and their cost are considerably reduced and improved voltage profile was achieved.

The capacitor placement and distribution network reconfiguration (DNR) are two useful methods in reducing the power losses of distribution networks [11]. This paper proposes a selective particle swarm optimization (SPSO) to solve the optimal capacitor placement problem, the optimal feeder reconfiguration problem, and the problem of a combination of the two. The problem is posed as an optimization problem with an objective to maximize the loss reduction and improve the voltage profile. The proposed method has been implemented on two distribution systems published in the literature. The simulation results have indicated that the proposed method is reliable, easy to implement and can be used as an advantageous alternative in the comprehensive optimization for power loss reduction in distribution networks. Furthermore, when simultaneously account both feeder reconfiguration and capacitor placement, the loss reduction is much higher than considering them separately.

The above presented papers and other related papers has given us profound ideas in understanding different technical losses that are present in distribution networks. Moreover it has provided us with different methodologies to calculate technical losses with much efficient and accurate way. Furthermore, we were gained lot of knowledge to reduce or mitigate various technical losses that are present in existing distribution networks. Thus those literature has helped us in understanding more about our project topic and thus help us to proceed further with our project.

'

CHAPTER TWO: INTRODUCTION

Efficient use of energy has become one of the most effective methods to go for sustainable usage of already exhausted energy resources. Studies carried out to identify viable options to combat climate change have revealed that improving energy efficiency measures are more effective in preventing climate change than developing energy supply technologies (regional report).  Royal government of Bhutan has already planned to phase out the use of inefficient high power consuming incandescent light by providing subsidized light emitting diode (LED) (Kuensel 2016).

When government is taking keen initiative even in reducing inefficient energy consumption, we cannot effort to neglect the losses that are occurring in electricity transmission and distribution system. The power loss is associated in the process of transferring the power to customer and performance of the utility largely depends upon the level of power loss in the network. The losses not only affect utility performance of customer but also reduces the income generation of respective company.

The losses in transmission and distribution system of electricity is considerably large in magnitude and causes inefficiency in the system which need to be analyzed and mitigated. Though certain losses in the system may be allowable but the losses in the system sometime goes beyond the allowable range which should be contained. Ideally, losses in an electric system should be around 3 to 6%. In developed countries, it is not greater than 10%. However in developing countries, the percentage of active power losses is around 20% [3]. Therefore, it is important to reduce losses in system to increase efficiency of energy usage of available resource.

The losses which are associated in transmission of electricity in Bhutan was already analyzed by group of student from college of science and technology in collaboration with Rostock University. Loss analysis in distribution system especially in Bhutan is also equally important as it will contribute significant knowledge to respective sector in taking measures to reduce losses. Technical losses are one of the most predictable and can be contained to minimum amount if it is mitigated properly.

Thus we will model the LV distribution network of Phuntsholing in DIgSILENT power factory and analyze the technical losses occurring in the system.  

This project enables us to calculate total technical losses in the network and identifies different mitigation techniques. It can improve utility performance of the customer and helps respective company to distribute electricity in most effective and efficient way. Therefore it is worth modelling and analyzing the technical losses in distribution networks.

Objectives

To collect various information about main distribution network component of different feeders which are there in existing Phuntsholing LV distribution network.

To do theoretical calculation of technical losses exist in different feeders.

Model the existing distribution system in DIgSILENT power factory and analyze different technical losses associated with different distribution components (such as power transformer, distribution lines and etc.) and to find the total technical losses.

Evaluate the various mitigation techniques.

Problem statement.

The losses which occurs in distribution networks may be small yet it is undesirable in this modern era and it must be studied thoroughly and can be contained to considerable amount. Bhutan Power Corporation limited (BPCL) has not done any analysis on technical losses which are occurring in distribution network. Moreover the distribution networks are not yet modelled in DIgSILENT power factory for different analysis such as to calculate different technical losses. This projects introduces to the implementation of this software find various technical losses which occurs in distribution network. Moreover it also analysis the different mitigations of various technical losses in the networks.

Project scope.

This report covers the theoretical calculation of technical losses in Phuentsholing distribution network also the modelling of network DIgSILENT power factory software with the data obtained from Phuentsholing BPCL. The load flow analysis was done based on peak load of 2016 January month. The result obtained from DIgSILENT power factory was validated with the result that we got from theoretical calculation. The various mitigation techniques to reduce different technical losses are also analyzed and presented

Methodology.

Collection data of existing Phuntsholing distribution network.

Various data required in modelling the distribution network was collected from both upper BPC substation and lower substation. The data which we got from Phuentsholing substation are the single line diagram of distribution network,  peak load of every feeder, the number transformer connected in each feeder and their ratings and we also collected its networks drawn in GPS. We couldn't get the exact length of various section line and load of each transformer connected in the feeders.

In this project, the section lengths are calculated from the GPS networks upon confirming its accuracy. It was observed the length that we got from field survey and the one from GPS is almost equal, thus we can rely on the section length that we get from GPS network.

The load of every transformer was estimated from the peak load of each feeder by calculating its percentage load of total transformer kVA rating. Thus it is considered that all transformer are loaded equal percentage of their total kVA rating.

Mathematical calculation of different technical losses.

The mathematical calculation of different technical losses are theoretically calculated for both transformer and lines. The formulae to calculate different losses are as given in literature review under the following section.

Modelling of Distribution network in DIgSILENT power factory and analyzing different losses.

This report presents the modelling of modelling of Phuntsholing Distribution Network in DIgSILENT power factory software. The modelling of network and studies can be done using various software/tools, however the DIgSILENT software is being used here because of more tools and functions. Before starting the project, DIgSILENT software have been studied in previous semester in power system analysis and also we did through revision during project. Furthermore we seek help from those students who is doing project in collaboration with one of the German university.

Validation of technical losses from theoretical result with the result from DIgSILENT power factory software.

The technical loses results from the DIgSILENT power factory was compared with the result that are obtained from theoretical calculation.

Assigning of effective mitigation techniques.

The various affective and applicable mitigations for different technical losses in the distribution network are presented. The mitigation analysis was performed in DIgSILENT power factory software.

'

CHAPTER THREE: TECHNICAL LOSS IN DISTRIBUTION SYSTEM.

Technical loss

The amount of power (kW or MW) that is lost in the distribution network either during transportation or during delivery is known as the power loss. The factors on which the power losses depends are network configuration, power factor, load profile, power factor, and materials of the network and the length of network. Power loss can be also transformed to the energy loss as kWh, MWh or GWh and it indicates the power lost over the period of time.

Technical loss occurs in winding, conductors or work parts in transformer and other electric instrument. Technical loss in power system are transformer line loss, power transformer losses, distribution line losses and LV transformer and distribution line losses [1].

Except for the fixed load, current flowing through the line/network changes with the change in load. The loss in the network, therefore, varies with the current. For the varying load, Average Technical Loss can be determined from the Peak Load by considering LOAD FACTOR and LOSS LOAD FACTOR as explained hereunder.

Distribution Line losses

The line losses depend on the types of conductor being used and the load that are there on the feeders. The line loss is directly proportional to the product of square of current and the resistance of the conductor. The current in the line increases with the increase in the load and vice versa and thus the line losses varies throughout the day. Though line lasses in the network are also contributed by other factors like inductance of the line and extra, this project only considers the line losses that are contributed by current and conductor resistance. The equation given below are adopted to estimate the line losses that are there in the network.

Distribution Line Losses(kWh)=Loss factor ''Line Losses''period

Where                                      Loss Factor=0.33LF+'0.67LF'^2

                                    Load factor (LF) =(Average Load(kWavg))/(Peak Load (kWpeak))

Power transformer losses.

Transformer losses are divided into two main components: no-load losses and load losses. Every kind of transformer has such kind of losses despite their different applications and rating.

Though there are other losses such as losses created by harmonics in larger transformer and also the losses caused by its auxiliary parts such as cooling equipment like fans and pumps.

No load loss or Core loss

No-load losses are present in the transformer core whenever the transformer is energized. No load losses are also known as iron losses or core losses. This losses constant despite varying load.

They are composed of:

Hysteresis losses, caused by the frictional movement of magnetic fields in the core laminations when it is magnetized and demagnetized by alternation of the magnetic field. It depend on the type of material used to manufacture the core. Silicon steel was observed to have lower hysteresis than normal steel and amorphous metal possess better performance than the silicon steel.

Eddy current losses, is caused by varying magnetic fields inducing eddy currents in the laminations as a result the huge amount of heat is produced. Such losses can be reduced by building the core from thin laminated sheets insulated from each other by a thin varnish layer to reduce eddy currents.

Transformer No load loss or Core loss= Core losses from the Test Report of manufacturer.

Load loss or Winding Losses

These losses are known as copper losses or short circuit losses. Load losses vary with the variation of transformer loading.

They are composed of:

Ohmic heat loss or sometimes it is referred to as copper loss, since this resistive component of load loss dominates. This loss occurs in transformer windings and is caused by the resistance of the conductor used. The magnitude of these losses increases with the square of the load current and is proportional to the resistance of the conductor winding. It can be reduced by increasing the cross sectional area of conductor or by reducing the conductor winding length.

Conductor eddy current losses. Eddy currents, due to magnetic fields caused by alternating current, also occur in the conduction windings. This loss can be reduced by reducing the cross-section of the conductor as it reduces eddy currents, so stranded conductors are used to achieve the required low resistance while controlling eddy current loss. Effectively, this means that the 'conductor winding' is made up of a number of parallel windings. Since each of these windings would experience a slightly different magnetic flux, the voltage developed by each would be slightly different and connecting the ends would result in circulating currents which causes loss. This is avoided by uisng continuously transposed conductor (CTC), in which the strands are frequently transposed to average the flux differences and equalize the voltage.

The winding losses are estimated by using the equation given below.

Winding Losses=('MVA'^(2 )''Load Losses''Loss Factor)/('MVA'^2 peak )

Loss factor=K''LF + 0.8LF2

Where K = constant and the value for K are:

0.2: for distribution system and

0.3: for transmission system.

Load losses= Copper Losses from the report test

TABLE for STANDARD of TRANSFORMER LOSSES

SL.No kVA rating At 100 % Loading

Wi (Watt) Wc (Watt)

1 10 70 190

2 16 75 300

3 25 125 425

4 50 210 1250

5 100 340 2150

6 200 570 3600

7 250 610 4450

8 315 720 5460

9 400 850 6450

10 500 1000 7800

11 630 1200 9300

12 800 1420 11000

13 1000 1750 13500

14 1250 2100 16400

15 1600 2550 19800

Table 3.1: Table showing DIN4250 standard transformer losses at 100% loading.

The above standard transformer losses for different rating was used in the theoretical calculation of transformer losses. It is standard approved by international organization like ISO and other. The losses for transformer which are not there in above are obtained by interpolation and the extrapolation of above data and the transformer losses are calculated.

'

CHAPTER FOUR: STUDY OF EXISTING DISTRIBUTION SYSTEM IN PHUENTSHOLING.

 Overview of 66/33/11kV Phuentsholing substation.

Phuentsholing under Chhukha Dzongkhag is one of the biggest city in Bhutan and has people working in different private and government organization. It is also the biggest business center for both commercials as well as the industrial. It is therefore very important to study and analyze the distribution network. The Phuntsholing city is supplied power through a 66/33/11 kV substation located at Dhamdara. This substation is one of the oldest substation in Bhutan which was built in 9180s mainly to import power from India to use power during construction of Chhukha Hydro Project. It was then used to export power to India after the completion of Chhukha Hydro Power plant. Today, with Tala Hydro Power Plant, the power exported to India is very bulk and hence new substation of higher capacity is established at Malbase.

There are two incoming feeder 66kV feeder from Malbase and another 66kV line from Chhukha. There are three power transformers of 10MVA and one 3MVA transformer. There are nine outgoing feeders from these substation three 33kV feeders and six 11kV feeders. The details of those feeders which are considered for our study will be discussed later in this section.

Equipment of the Phuntsholing Substation.

Bus-Bar: The bus-bar arrangement of this substation is single bus-bar system with sectional bus isolator. By keeping the sectional bus isolator open, one section can be in service while the other can be taken for maintenance or extension without shutting down the substation. There are four buses one 66kV bus, one 33kV bus and two 11kV buses. The 66kV is provided with the bus sectional isolator. Two 11kV buses are coupled using the bus coupler.

Power transformer: The power transformer is used in the substation to step up or step-down the voltage. In this substation there are four power transformers manufactured by AREVA and VOLT-APMS. There are two 10MVA (66/55kV) transformers which feeds the 33kV feeders, one 3 MVA (66/11kV) and 10/12.5 MVA (66/11kV) transformer which feeds 11kV feeders. All are three phase transformers because of its advantageous over using single bank transformer. The third transformer is dedicated for Druk Iron Steel feeder.

The power transformers are installed upon lengths of rails fixed on concrete slabs having foundation 1 to 1:5 m deep. For rating up to 10 MVA, oil immersed transformers are used. For higher ratings, the transformers are generally air blast cooled.

Relays: In Phuntsholing substation two different types of relays are in use, over current relays and earth fault relays. Both the relays are of inverse definite minimum time (IDMT), electromagnetic disc rotating type. These relays are used for the protection of the feeder lines. In these types of over current relays the operating time is inversely proportional to the operating current.

Circuit breaker: A circuit breaker is the equipment which can open or close a circuit under normal as well as fault conditions. It can be so designed that it can be operated manually (or by remote control) under normal conditions and automatically under fault conditions. For later operation, relay circuit is used with a circuit breaker.

In Phuentsholing substation SF6 circuit breakers are used for protection of lines and transformers associated with voltage level of 66 kV. For lower voltages, 33kV and 11 kV, the vacuum circuit breakers are used.

Isolating switches: In substations, it is often desired to disconnect a part of the system for the general maintenance and repairs. This is accomplished by an isolating switch or isolator. An isolator is essentially a knife switch and is designed to open a circuit under no load.

Current Transformer: A current transformer is a step down transformer which steps down the current to a known ratio. The primary of this transformer consists of one or more turns of thick wire connected in series with the line. The secondary consist of a large number of fine wires and provides for the measuring instruments and relays a current which is a constant fraction of the current in the line.

Voltage transformer: It is essentially a step down transformer and steps down the voltage to a known ratio. The primary of this transformer consist of a large number of turns of fine wire connected across the line. The secondary winding consists of a few turns and provides for the measuring instruments and relays a voltage which is known fraction of line voltage.

Metering and Indicating Instrument: There are several metering and indicating instrument (e.g. ammeter, voltmeter, energy meters etc.) installed in a substation to maintain watch over the circuit quantities. The instrument transformers are invariably used with them for the satisfactory operation.

Miscellaneous equipment:

Fuses

Carrier-current equipment.

Sub-station auxiliary supplies.

Details of outgoing feeder.

There are nine outgoing feeder under operation out of which only six 11 kV feeders are taken in consideration.

Sector II Feeder:

This feeder has two parallel 33kV lines coming from the Phuntsholing Substation. This feeder supply power to the Sector II substation located at the ground floor of the BPCL office, Phuntsholing. From this sector II substation there are three more outgoing feeders, namely water booster feeder, RSA feeder and PWD feeder. This substation is controlled automatically by SCADA system.

The SCADA system stands for supervisory control and data acquisition. The basic components of this system are:

Human Machine Interface (HMI): this is the apparatus which presents process data to a human operator, and through this, the human operator monitors and controls the process.

The supervisory (control) system, gathering (acquiring) data on the process and sending commands (control) to the process.

Remote Terminal Units (RTUs) connecting to sensor in the process, converting sensor signal to digital data and sending digital data to the supervisory system.

Programmable Logic Controller (PLCs) used as field devices because they are more economical, versatile, flexible and configurable than special purpose RTUs.

Communication infrastructure connecting the supervisory system to the Remote Terminal Units.

The outgoing feeders from this substation supply mainly to the town areas. There are total of 3614 customers connected to this substation with the help of above mentioned three feeders. The feeders from this substation are placed with unitized substation wherever necessary and the conductor used is mostly the underground cables. The fault rarely occurs in this feeder and the most common fault is earth fault. The line length of the feeder is about 10 kilometers.

Druk Iron Steel Feeder:

Under Phuntsholing Distribution system, Druk Iron and Steel feeder is dedicated feeder which means the whole feeder maintenance is done without involvement of BPC. It takes voltage of 33kV from 10 MVA transformers from Phuntsholing substation and extends up to 2.838 km from the BPC Substation. There are three transformers connected in feeder with a total load of 8200kVA. From feeder fault report data, we have found out that the monthly peak load of feeder is about 7.15MW.

The feeder runs through the steep slope, which is covered by trees and bushes from the base of Phuentsholing till the customer terminal at Druk Iron & steel premises.

Kabray- Ramitey Feeder:

Kabray and Ramitey feeder have a line length of 9.498km and its voltage level is 11kv. There are 12 transformers connected with the total rating of 2506 kVA.  The feeder construction type is overhead and the conductor used is Rabbit. This feeder serves a total customer of 389. The Ct ratio is 100/1 A. Since this feeder is an 11kV feeder the circuit breaker in use is vacuum circuit breaker.

TADING RURAL FEEDER:

Tading feeder is 11kV rural feeder which runs all the way from Dhamdara substation to Tading and serves a total of 377 customers. It extends up to 20.48249 km. As per the feeder data the monthly peak load is around 0.22MW. The conductor in used is ACSR (rabbit).

Pepsi-Bhutan Dairy Feeder

This feeder is the 11kV outgoing feeder which is located near the Phuntsholing Substation. The feeder is connected to a total of 140customers. It feeds to places like CHPC colony, Drangchu, Dairy, B/ply, FCB, BWPI, Packaging, Darla, GWMC, City water pump and BPC colony. A total of 10 numbers of transformers are connected to each of the places resulting in 5060kVA of connected load of the feeder. The total line length is 1.806 km from the BPC and the conductors used for the line is mainly HV ABC cables.

Industrial Area Feeder

Industrial feeder has the line length of 0.946 km and the number of the customers connected to the feeder is 21. It consumes the voltage of 11kV, three types of conductor are used in this feeder namely cable, dog and HV ABC. There are 8 transformer connected to this feeder and these transformers have the total capacity of 3683kVA.

8 Hospital Feeder

Hospital feeder is 11kV outgoing feeder which is nearest to the Phuntsholing substation with a line length of 0.112 km.  The feeder is under the service for all the hospital residing customers which is collectively referred as one customer. There is only one transformer connected through the line with a rating of 750 kVA. The conductor used for the line is cable and a vacuum circuit breaker is also connected in the line.

Sl.no Name of the feeder Voltage level No. of customers Types of conductor used Length of the conductor Connected load No. of transformers

Sector II feeder

Water booster feeder

11kV

3596 Cable 5.138km 7840 kVA 14

HV ABC 0.053 km

RSA feeder

11kV Cable 0.121km 2750 kVA 4

HV ABC 0.369 km

PWD feeder

11 kV Cable 2.453 km 6704 kVA 15

HV ABC 2.453 km

Rabbit 0.396 km

Tading rural feeder

11 kV 394 Rabbit 20.48249 km 2043 kVA 32

Kabray Ramitey Feeder

11 kV 389 Rabbit 9.498 km 2007 kVA 14

Serena Bosokha feeder

33 kV 92 Dog 9.498 km 186 kVA 4

Druk iron and steel feeder

33 kV 1 Dog 2.839 km 8200 kVA 3

Industrial area feeder(Ashay Bangalow)

11kV 21 Cable 0.313 km

4118 kVA 8

Dog 0.482 km

HV ABC 0.151 km

Pepsi-Bhutan Dairy feeder(BPC colony)

11kV 139 Cable 0.419 km 5060 kVA 10

HV ABC 1.387 km

Hospital feeder

11kV 1 Cable 0.122 km 750 kVA 1

Substation feeder 11 kV 1 Cable 0 km 300 kVA 2

Table 4.1: Outgoing feeder details of 66/33/11kV substation, Phuentsholing.

In our study we have included only six 11 kV feeders to do through modelling and study of technical losses in the network. Those feeders are as listed below.

PWD feeder.

Ashay Bungalow.

Ramitey Feeder.

Water Booster feeders.

Tading Rural feeder.

BPC colony (Pepsi-Bhutan dairy feeder) feeder.

Average peak load for the January month.

Figure 4 1:  Average peak load in January month of all feeder.

Detail of different rated transformer used in different feeders.

BPC Colony feeder.

SL.No. Transformer kVA rating Quantity Total kVA

1 250 2 500

2 315 2 630

3 500 2 1000

4 630 1 630

5 750 2 1500

6 800 1 800

Total overall Transformer kVA 10 5060

Tading rural feeder.

SL.No. Transformer kVA rating Quantity Total kVA

1 16 7 112

2 25 13 325

3 63 7 441

4 125 2 250

5 250 1 250

6 315 1 315

7 350 1 350

 Total overall Transformer kVA 32 2043

Ashi Bungalow.

SL.No. Transformer kVA rating Quantity Total kVA

1 63 1 63

2 125 1 125

3 250 1 250

4 500 1 500

5 630 1 630

6 750 1 750

7 800 1 800

8 1000 1 1000

Total overall Transformer kVA 8 4118

Ramitey Feeder.

SL.No. Transformer kVA rating Quantity Total kVA

1 63 9 567

2 125 1 125

3 250 2 500

4 315 1 315

5 500 1 500

 Total overall Transformer kVA 14 2007

PWD Feeder.

SL.No. Transformer kVA rating Quantity Total kVA

1 16 1 16

2 63 1 63

3 125 1 125

4 250 4 1000

5 500 3 1500

6 750 4 3000

7 1000 1 1000

Total overall Transformer kVA 15 6704

Water Booster.

SL.No. Transformer kVA rating Quantity Total kVA

1 125 1 125

2 250 1 250

3 315 1 315

4 400 1 400

5 500 3 1500

6 750 7 5250

Total overall Transformer kVA 14 7840

PWD.

Figure 4 2: PWD feeder modelled in DIgSILENT power factory software.

Ashay Bungalow.

Ramitey Feeder.

Water Booster.

Tading Rural Feeder.

Figure 4 6: Tading rural feeder modelled in DIgSILENT power factory software.

BPC Colony Feeder.

Figure 4 7: BPC colony feeder modelled in DIgSILENT power factory software.

Losses obtained from DIgSILENT power factory software and theoretical calculation.

The load details of every feeders are taken from the PBIS report of January month of 2015 and during this calculation the load are taken as the average peak load of that month. The percentage loading of each transformer are considered to be equal depending upon their ratings. The losses obtained from different methods are as given in the table below. The losses include both transformer and line losses.

SL.No. Feeder  name Losses From DIgSILENT (kW) Theoretical Losses (kW)

1 BPC Colony    17.26 16.18189

2 Tading Rural Feeder 19.98 19.47128

3 Ashi Bungalow 8.28 8.19380

4 Ramitey Feeder 17.01 15.23194

5 PWD feeder 22.53 25.77693

6 Water booster 25.04000 22.71972

Table 4.2: Table showing the result of theoretical losses and the losses obtained from DIgSILENT power factory.

'

CHAPTER FIVE: METHODS TO REDUCE TECHNICAL LOSSES OF DISTRIBUTION SYSTEM IN PHUENTSHOLING.

There are many methods which can be applied in distribution network to reduce technical losses to considerable magnitude. One of the most durable mitigation technique which we can adopt in such network is by placing the energy storage battery in different locations. We can also analyze the losses reduction by replacing the conductors with one which has lowest resistances.

Placing energy storage battery in the network.

In the resent years much of the focus on the development of electric storage technology has been given on the battery storage which reduces the power losses in the network. There is a numerous variety of battery types serving different purposes in power system network. Generally, energy storage system enhances power system reliability and power quality, minimize the power loss and improve the voltage profiles, reduces the power system cost and control high cost energy imbalance charges.

In this project, we placed different rating of energy storage battery in different location in distribution network model which was developed in DIgSILENT power factory. The battery capacity of 0.02 to 0.2 MW with reactive power ranging from 0.02 to 0.2 MVAR was implemented. The battery increases the voltage in different node and reduces the technical losses which are there in the network.

The storage may be charged from main grid during base load generation which is when the load demand is low and is typically during early hour of the day and towards midnight of that day as indicated by available load profile of different feeders as given in figure below.

Figure 5 1 Showing one day load curve of three feeders.

The different storage incorporated in the distribution feeders are as given in the following figures.

BPC Colony.

Figure 5 2 Showing the battery bank installed in BPC colony feeder.

Tading Rural Feeder.

Figure 5 3 Showing battery storage installed in Tading rural feeder.

Ashi Bangalow.

Figure 5 4 Showing battery storage installed in Ashi Bangalow feeder.

Ramitey Feeder.

Figure 5 5 Showing Battery storage installed in Ramitey feeder.

PWD Feeder.

Figure 5 6: showing battery storage installed in RWD feeder.

Water Booster.

Figure 5 7 Showing battery storage installed in Water Booster feeder.

Results.

It is observed that the technical losses can be reduced by installing battery storage system in the network. When battery storage in installed in network, the reduction of current is observed and thus the technical losses values are also reduced. The reduction of losses improves further with the increase in the number of battery storage in the system. The result obtained is given in the table below as compared to the result obtained without the battery storage.

Feeder Losses From DIgSILENT before battery bank (kW) Loss after installing Battery Bank(kW) Percentage reduction of losses (%).

BPC Colony    17.26 17.1 0.92

 Tading Rural Feeder 19.98 12.62 36.84

Ashi Bungalow 8.28 7.37 10.99

Ramitey Feeder 17.01 13.89 18.34

 PWD feeder 22.53 15.47 31.34

Water booster 25.04 24.87 0.68

Table 5.1: Table showing losses comparison between before and after installing the battery bank in the system of different feeder.

Figure 5 8: Histogram of losses obtained before and after installation of battery bank.

'

Conclusion.

This project work 'Modelling of Phuentsholing Low Voltage distribution network and analyzing technical losses using DIgSILENT power factory software' had aims and objectives to study different methodology to calculate technical losses in distribution system, study the existing Phuentsholing distribution network and to find the technical losses in the system. Furthermore it also finds the different mitigation techniques to reduce losses in the system.

In this project the losses are analyzed for LV distribution network or feeder (i.e 11 kV line) which are fed from upper and lower substation of Phuentsholing. The load data year 2015 from PBIS were used for calculation as well as for modelling in DIgSILENT power factory.

The losses in network were calculated theoretically as well as it was obtained from DIgSILENT power factory. The two results were compared and the mitigation for technical losses was identified. In this project the battery storage system was used for mitigation of technical losses and it was observed that battery storage works well in reducing losses in the system.

The energy demand in the world is increasing and while Bhutan harnesses clean and renewable energy, losses are unavoidable but it needs to be managed to a minimum level. Losses can be reduced to a large extend in the upcoming distribution systems by installing proper transformer ratings with low resistance conductors. As for the already existing distribution network various mitigation techniques are available and cost analysis of each can be done.  

'

Recommendation

Losses analysis using only and feeder and incorporating all major and minor equipment in the network must be analyzed.

Few energy storage can be installed upon its cost analysis to reduce technical losses in distribution system.

The rating of transformer must be properly selected according to the consumer load.

Optimization of correct size and the location of the battery storage in the system should be taken in account.

The appropriate transformer ratings must be used according to the load in future planed network to prevent losses.

Use conductors with lowest resistance as far as possible in future.

References

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