right4114800Impact of shunt reactor on long transmission line Industrial research Project submitted in partial fulfilment for the degree Baccalaureus Technologiae

right4114800Impact of shunt reactor on long transmission line
Industrial research Project submitted in partial fulfilment for the degree
Baccalaureus Technologiae (B-Tech) in Electrical (Power) Engineering
In the
Faculty of Engineering and Technology
By
Raselabe T.E
212088580
[email protected]
Mentor: Mr BJ Le Roux
Submission date: 13 September 2018
Vanderbijlpark
00Impact of shunt reactor on long transmission line
Industrial research Project submitted in partial fulfilment for the degree
Baccalaureus Technologiae (B-Tech) in Electrical (Power) Engineering
In the
Faculty of Engineering and Technology
By
Raselabe T.E
212088580
[email protected]
Mentor: Mr BJ Le Roux
Submission date: 13 September 2018
Vanderbijlpark
Mentor: Mr BJ Le Roux
Submission date: 13 September 2018
Vanderbijlpark
right-122872500
Declaration
I Raselabe Tshifularo Eric declare that this report is my own unaided work except where specific acknowledgement is made by name in the form of a reference. It is being submitted for the subject Industrial Project 4 (EPIPR4A) at the Vaal University of Technology, Vanderbijlpark. It has not been submitted before for any examination.

168592511493500T.E RASELABE 13 day of September 2018
(Researcher) (Signature) (Date)
Acknowledgements
I have taken efforts in this project. However, it would not have been possible without the kind support and help of my mentor Mr BJ LE Roux. I would like to extend my sincere thanks to all of them. I am highly grateful to my mentor for his help and constant supervision as well as for his support in completing this project.

I would like to express my gratitude and thanks towards my lecturers for their kind cooperation and encouragement which help me to complete my project. My thanks and appreciation to Mr Joules, Mr Kyere and my mentor of the project Mr BJ LE Roux for persevering with me as my supervisor throughout the time it took to complete this report of project.

Dedication
I would like to dedicate this project to my parents and my fellow students, that there is no doubt in my mind that without their support and counsel, I could have not completed my project.

Table of contents
Page
Declaration…………………………………………………………………………..ii
Acknowledgement………………………………………………………………….iii
Dedication…………………………………………………………………………..iv
List of Figures………………………………………………………………………vii
List of Tables……………………………………………………………………….vii
List of abbreviations and symbols…………………………………………………………viii
Chapter 1: Proposal
1Introduction1
1.1Background of the research1
1.2Purpose of the research3
1.3Significance of the report3
1.4Problem statement4
1.5Objectives4
1.5.1Specific research aim4
1.5.2Scope of the research5
1.5.3Limitation5
1.6Methodology5
1.7Budget forecast5
1.8Proposed time frame6
1.9 Outcome of the project…………………………………………………………….6
Chapter 2
2.1Introduction7
2.2Literature review7
2.2.1Application of shunt reactor7
2.2.2Switching in of reactor…9
2.2.3Shunt reactor disconnection…………………………………………….12
2.2.4Oil immersed shunt reactor protection…………………………………13
2.2.5Unsymmetrical faults and symmetrical components………………..13
2.2.6 Transmission line parameters and Ferranti Effect………….……….15
2.3 Summary…………………………….…………………………………….16
Chapter 3
3Introduction………………………………………………………………17
3.1Methodology……………………………………………………………..17
3.2Protection of the transmission line…………………………………….18
3.2.1Schweitzer SEL-751 relay for overcurrent and earth fault relay……18
3.2.2Distance protection on a transmission line……………………………18
3.3Calculations………………………………………………………………18
3.3.1RLC and ABCD Parameters of the transmission line………………..19
3.3.2 Transmission line parameters ABCD….………………………………19
3.3.3 Shunt reactor not connected under no-load condition…………….….20
3.3.4 Shunt reactor connected under no-load condition…………….………20
3.3.5 Faults at Bus bar 2 with Shunt reactor connected……………………20
3.3.5.1 Three phase fault……………………………………………………..….21
3.3.5.2 Single phase to ground fault………………………………………..…..22
3.3.5.3 Double line fault…………………………………………………….……22
3.3.5.4 Double line to ground fault………………………………………………22
3.4 Simulated results…………………………………………………..…….22
3.5 Phasor diagrams…………………………………………………..……..24
3.6 Table of results………………………………………………….………..24
3.7 Results discussion………………………………………………………..25
Chapter 4
4.1 Proposed further studies…………………………………………………27
4.2 Conclusion…………………………………………………………….…..27
4.3 Recommendation…………………………………………………….…..27
References
List of figures
Figure 1: Location of the shunt reactor on the network………………………………8
Figure 2a: Shunt reactor Phase Currents during Asynchronised Switching….9
Figure 2b: Shunt reactor neutral currents during asynchronised switching…..10
Figure 2c: Shunt reactor currents during synchronised witching…………………11
Figure 2d: Shunt reactor neutral currents during synchronised Switching……11
Figure 2e: Shunt reactor phase currents & voltages during synchronised Switching………………………………………………………………………………………. ….12
Figure 3: Connection for impedance………………………………………………………13
Figure 4a: Classification of line faults…………………………………………….14
Figure 4b: Symmetrical components from unsymmetrical network……………14
Figure 5: Ferranti effect in transmission lines……………………………………16
Figure 6: Zebra bundle conductor datasheet and tower structure design……19
Figure 7a: Transmission line with a disconnected shunt reactor………………22
Figure 7b: Transmission line with shunt reactor connected…………………….23
Figure 7c: Transmission line with shunt reactor connected with single line to
Ground fault and its overcurrent and distance time plot graph of Single Line
To ground fault…..………………………………………………………………..23-24
Figure 8: Phasor diagrams of long line with (green) and without (red)
shunt reactor…………………………………………………………………………24
List of tables
Table 1: Time schedule……………………………………………………………………….6
Table 2: Calculated results for a long transmission line under no load…………25
Table 3: Simulated results for a long transmission line under no load………….25
Table 4: Simulated and calculated results for the faults at bus 2…………………25
Table 5: Overcurrent and earth fault protection tripping times…………………….25
Table 6: Distance protection against faults with the tripping times…………….25
List of abbreviations and symbols
°- Degree
A- Ampere
ACSR- Aluminium Conductor Steel Reinforced
C- Capacitance
Cosph- power factor
CT- Current Transformer
F- Farad
G – Conductance
GMR- Geometrical Mean Radius
H- Henry
Hz- Hertz
I- Current
IF – Fault current
IR- Receiving current
IS- Sending current
K- Kilo
Km- kilometer
L- Inductance
L-L – Line to line
L-L-G- Line to line to ground
m – Meter
M- Mega
mm – millimeter
n- Nano
PC- Copper losses
PR- Receiving active power
Ps- Sending active power
pu – per unit
QR- Receiving Reactive power
Qs- Sending Reactive power
R- Resistance
s- Seconds
S- Siemens/ Apparent power
S-L-G- Single Line to Ground
t- Time
TMS- Time Multiplier Setting
V- Volts/ Voltage
VA- Voltage per Ampere
VA’r- Voltage per Ampere resistance
VF- Fault voltage
VR- Receiving voltage
VS- Sending voltage
VT- Voltage Transformer
W- Watt
X- Reactance
Y- Admittance
Z – Impedance
?- Beta
?- Phase
?- Ohms
Chapter 1
Introduction
1.1 Background of the research
In power systems transmission lines are conductors that are designed to carry high and extra high voltages to transmit power over a short, medium and long distance but, as the length of the line increases Ferranti effect occurs due to directly proportional of line length increases with the capacitance of the line. In power system, transmission lines plays critical role in the part of the economy, they increase the revenue of the active power and reduced the costs due to high reliability, low maintenance costs ; low internal losses that reduce the operating costs (ABB, 2017). Transmission lines are the sets of conductors that carry electrical power from the generating stations to the substations to deliver the power to the customers (Kalaga ; Yenumula, 2016).

Shunt reactors in power systems they are an investment for today and also for the future. A shunt reactor is commonly used for the compensation of reactive power in long high-voltage transmission lines and also in cable systems by controlling the line voltage (Sadhu ; Das, 2015). It is very critical for the voltage system profile to compensate the reactive power and this is helpful for the power factor improvement, decrease of losses and thus increasing the energy efficiency of the system (Nashawati, 2013).

In high and extra voltage, long and medium transmission lines they generate more reactive power due to their shunt capacitance that is proportional to length of the line (spring 2013). It is necessary to transmit power and to support voltage as reactive power at light/low loads have the undesirable effects such as: receiving end terminal voltage rises due to the ?ow of capacitive current through the line inductance, sending end terminal voltage due to ?ow of capacitive current through the impedance source, synchronous machines rises due with self-excitation in the event of load tripping (Sharma, 2013). It is not usual for power long lines and low short circuit power for voltage to increase by 20 percent. If not controlled the line overvoltage will minimise the life span of insulation material and results in system faults (Van Escudero ; Redfern, 2008).
Shunt reactors are located at the ends of high or extra voltage transmission lines, at some installations they are isolated during the period of high circuit loading. Shunt reactors they are classified into two types, dry type and oil immersed type reactors (Veerappan ; Krishnamurthy, 2009). Dry type reactors have lower operational costs and lower losses, usually they are installed to the tertiary winding of the transformer that is connected to the high voltage line to be compensated and their rated voltage is limited up to 24.5 kilo volts with also kilo-volt ampere rating. Oil immersed reactors mostly are connected to one or both ends of transmission lines and the voltage is not a limitation, as they are used for the line connection to control the voltage of the line (Blackburn ; Domin, 2014).

A dry type reactor it fails to operate due to the faults, phase to phase faults on tertiary bus results in high magnitude phase currents, phase to ground faults results in low magnitude ground current as this fault depends on the size of resistor and grounding transformer, turn to turn faults occurs within a reactor and it results in a very small reactor change phase current (Sarma ; Vedam, 2008). A line or bus connected and oil immersed reactors can also failure due to the failure of the equipment such as bushing and insulation failure because they results in large changes in phase currents magnitude, a turn to turn faults within the reactor winding as the results in small change in current, change in impedance reactor, increasing operating temperature, internal pressure tank and gas accumulation, lastly a low oil and loss of cooling are miscellaneous failures (Anderson, 2012).
Protection of the shunt reactor is similar to that of transformer with the size and is very critical in power systems including the reactor electrical protection and the reactor non electrical protection. Reactor primary protection includes both overcurrent and differential protection (Das, 2017). High impedance differential protection is differential protection scheme and is connected to dedicated Current Transformers, this primary protection it does not detect interturn faults but it prevents faults from the winding to the core, faults between the winding of different phases and winding to winding faults. Turn to turn protection scheme is directionalised to see zero sequence current flow into reactor, the relay device cannot operate for external faults. This relay setting ranges between 5 to 10 percent of the reactor rating and its tripping cycles is delayed by 15 cycles (Meliha ; Selak, 2012).

Phase distance relay compares the ratio input current and voltage to balance the relay its setting is applied in zone 1, zone 2, zone 3, overreaching tripping and reverse blocking. Zone 1 relays they detects faults on the first 80 to 90 percent of the protected line and they operate with no time delay. Zone 2 relay detects faults anywhere on the protected line and relay need to be set at minimum of 125 percent of the protected line impedance. Zone 3 is set to detect close-in faults on lines at terminals remote line and the setting is at 150 percent of the protected line impedance (Sleva, 2009). Detecting the ground faults on the transmission line, a directional time and instantaneous overcurrent relays are used. Directional are used because lower fault clearing times can be achieved by installation of relays that can distinguish between reverse and forward directions short circuits. Instantaneous overcurrent ground relays need to be set above maximum fault current that is flowing through fault line in order to limit fault conditions since they are not obvious (Singh, 2009).

1.2 Purpose of the research
Purpose of this research is to investigate the impacts of shunt reactors in long transmission line and how to write the technical report. This research it must include three B-Tech subjects in order to do power flow, protection setting and fault analysis on the network system. The research will focus mainly on the no load or open circuit condition since the shunt reactor is only needed during this condition.

1.3 Signi?cance of the report
The gap between the existing knowledge and the proposed research is that, as the length of the line increases in high voltage long lines of more than 200 kilometres the Ferranti effect occurs under no load or light load condition. Therefore it is very important to install shunt reactors to eliminate the Ferranti effect along the lines (Aung ; Min Oo, 2014). This research will ?ll the gap on how the exceeded inductive VAR’s consumed and operate at light loads, as it causes voltage to increases with higher insulation level and results in bigger problem. The proposed research and existing knowledge are related since Eskom Company will reduce Ferranti effect and the operation cost during the variation of load.

1.4 Problem statements
A long transmission line draws high charging current and at no load condition and the supplied reactive power exceeds the consumed reactive power, this leads to Ferranti effect. The excessive voltage at receiving end may cause operative ratings of the terminal and it may leads to insulation breakdown resulting in minimizing their lifespan and damaging the equipments.

1.5 Objectives
1.5.1 Specific research aim
The specific aim of this project is to:
Investigate the impact of shunt reactor on long length transmission line to reduce the Ferranti effect using DigSilent Powerfactory software.
Varying the transmission line lengths to compare the sending end voltage and receiving end voltage to investigate Ferranti effect profile.

Impact of varying the loads to avoid the Ferranti effect, as the sending end voltage is lower than receiving end voltage.

Determining the shunt reactors ratings for the compensation of the reactive power, as the minimum reactors ratings are maintained to optimise ratings at the terminal receiving end.

1.5.2 Scope of the research
Proper selection of the conductors, equipments and protecting them against faults.

Long transmission line under light or open circuited load at receiving end because Ferranti effect occurs more across the entire length of the line.

Designing the single line diagram to be able to interpret the load flow and power analysis using DigSilent Powerfactory as is the most usable software in the industry.

Limiting the flow of short circuit current of the system in order to eliminate the risk of damaging the equipments and power interruptions or safety implications.

1.5.3 Limitations
High and extra voltage in long and short length transmission lines
Power flow studies
Fault analysis
Protection settings
1.6 Methodology
The project will commence with an overview of the problems encountered with High or Extra High Voltage long transmission line. This will be followed by literature review that covers up the background theories of the research with the helps, journals and articles. All the conditions stated under the specific aims will be achieved by designing and simulating the network system using DigSilent powerfactory software. The simulation and calculation models will be performed and their results will be compared and discussed in details.

1.7 Budget forecast
No materials will be bought since there will be no practical model performed. The project is based on the simulation model and it will be performed at VUT E102 simulation laboratory.

1.8 Proposed time frame
Table 1: Time schedule
Task Week Week Week Week Week
Chapter 1 5 April Chapter 2 4-7 June Chapter 3 30july-2 August Chapter 4 27-30 August Final report 13 September
Presentation To be discussed
1.9 Outcome of the research
Technical report
Simulated network
Hand calculations and simulated results
Protection against three phase, single line to ground, line to line and double line to ground faults.

Chapter 2
2.1 Introduction
Transmission lines physically integrate the generating plants output and requirements of the customers by supplying the energy flow among the different circuit in power systems. For a power system transmission line is considered to have sending and receiving end, and to have series resistance, inductance and shunt inductance and the conductance as primary parameters. The long transmission is more than 250 km and it has uniformly distributed parameters (El-Saadawi, 2015).

Transmission line transmits bulk electrical power from sending end to receiving end stations without supplying to any consumer and it can be divided into two main parts primary and the secondary. The transmission voltage is boosted by the step-up transformer to a voltage of 132 kV or 400 kV or 765 kV and when the electricity reaches its destination at the receiving substation the voltage is stepped down for distribution to 66 kV or 33 kV or 22 kV or 11 kV. The secondary transmission it forms the link between the main receiving end substations and secondary substations. In the transmission line the voltage can varies as much as 10 percent or even 15 percent due to variation of loads (Eskom).

2.2 Literature review
2.2.1 Application of shunt reactor
Shunt reactors are used in high voltage and extra high voltage to limit the overvoltage due to generation of the capacitive reactive power in cables and long overhead lines. The shunt reactors are normally connected as a star either fixed or switched at the following location as shown in figure 1.

Directly or with disconnect switches to a line
With circuit breakers to a line
With circuit breakers to a power transformer tertiary winding
The shunt reactor neutral it can be directly grounded or grounded via neutral a neutral reactor. When connected to power transformer tertiary winding, the neutral is normally ungrounded or grounded through the impedance (Asea, 2009).

Figure 1: Location of the shunt reactor on the network
Transmission line voltage rises of 20 percent are not unusual for systems with low short circuit power and long lines. If it is not controlled, a lifespan of insulation materials will be reduced by line overvoltage and will results in system fault, compromising both system availability and security. The excess generated of reactive power by high voltage and extra high voltage overhead line or cable need to be drawn out to keep voltage within the acceptable limits. The variation of desired voltage under normal conditions usually ranges between 5 and 10 percent, general during heavy loading than under light loading (Anderson, 2012).

Shunt reactors as they are used in long transmission lines or even shorter if they are supplied by weaker system for reactive power compensation, voltage control and occasionally for synchronous stability improvement. A line shunt reactor that are permanently connected allows a reduction in line insulation level. The possibility of great interest at the early stages of development of transmission systems due to the availability of short circuit power as it is relatively low, so the overvoltage condition achieved by the reactors is very critical and the line loading is usually well below Surge Impedance Loading, for which a continuous connection of a shunt reactor is tolerated. High degrees of shunt compensation can limit the stability limits when the line loading is increased the total reactive power (generated-losses) is reduced and in some cases, shunt reactors they need to be disconnected to avoid the excessive voltage drop. It’s not unusual to use a combination of fixed and switched reactors to overcome this problem (Van Escudero ; Redfurn, 2008).

2.2.2 Switching in of reactor
The switching in of a reactor gives rise to inrush current, a transient phenomenon similar to saturation in the shunt reactor magnetic circuit. In principle, it is the same thing as transformer inrush current but there are differences. A reactor core keeps no remanence, due to air gaps that makes the whole thing easier. The damping of asymmetric condition, DC component is slow because of the inherent low losses in a shunt reactor. It is important to keep this phenomenon when designing protection system relay for high voltage shunt reactors. The instantaneous current values during switching in of shunt reactors are shown in figure 2a.

Figure 2a: Shunt reactor Phase Currents during Asynchronised Switching (Gaji?, Hillström ; Meki?, 2011: 7)
Without saturation, the first peak of the current with full dc offset would be 2×square root of 2 = 2.82 times the rated current. The actual peak current may rise to a value between 3 and 5.5 times depending on the design details of the shunt reactor. The time of reactor when it reaches saturation is circled in figure 2a. The combination of individual phase current offsets will result in neutral current harmonics and with dc offset from the zero as shown in figure 2b.

Figure 2b: Shunt reactor neutral currents during asynchronised Switching (Gaji?, Hillström ; Meki?, 2011: 8)
The time for more or less fully balanced operation is around zero flux in the core may be fairly long often in order of seconds, but for a such condition there is no harm for the shunt reactor itself. In recent years, the points on wave closing relays are available from switchgear manufacturers. By using these relays switching of different of different power system devices, including shunt reactors they can be performed without a disturbance to the rest of the power system. Typical current waveforms during synchronized shunt reactor switching are shown in figure 2c, 2d ;2e.

Figure 2c: Shunt reactor currents during synchronised witching (Gaji?, Hillström ; Meki?, 2011: 8)

Figure 2d: Shunt reactor neutral currents during synchronised Switching (Gaji?, Hillström ; Meki?, 2011: 9)
Shunt reactor switching and circuit breaker poles must be precisely closed in three consecutive phase voltage peaks in order to obtain such disturbances as shown in figure 2e.

Figure 2e: Shunt reactor phase currents ; voltages during synchronised Switching (Gaji?, Hillström ; Meki?, 2011: 9)
2.2.3 Shunt reactor disconnection
Disconnection of small reactive current at one time regarded as a hazardous operation due to the risk of current chopping and resulting in overvoltage switching. Modern surge arresters are fully capable of managing this condition, and besides, the circuit breaker and its tendency to chop the reactor current is not so pronounced for typical high voltage and extra high voltage shunt reactor rated current values. The primary current chopping causes another, and maybe less known, transient effect, which appears in the CT secondary circuit. This effect is manifested as an exponentially decaying dc current component in the CT secondary. This effect is explained as a discharge of magnetic energy stored in the current transformer magnetic core. The secondary discharge currents are typically very small for shunt reactors and cause no effect on the reactor protection schemes with numerical relays (Bashar ; Thompson, 2013).

2.2.4 Oil immersed shunt reactor protection
Faults that produce large magnitudes of the phase currents for relay protection is generally a combination differential, overcurrent and distance relaying. Each of these protection schemes they have their own limitations. Turn to turn fault cannot be detected by differential relay and overcurrent relay must be set above normal load current to detect faults. Shorted turns can be detected using relay impedance as there is significant reduction in 50 Hz impedance of shunt reactor under such condition. Mechanical failure or low-level faults protection it involves the oil system by temperature and pressure devices similar to those of the transformer (Horowitz ; Phadke, 2014). Impedance relay (device 21) connection is shown in figure 3.

Figure 3: Connection for impedance (Horowitz ; Phakde, 2014: 247)
2.2.5 Unsymmetrical faults and symmetrical components
Unsymmetrical faults in three phase system are fault that leads to unequal current with unequal phase shifts. These faults occur in the system due to short circuit or open circuit of transmission or distribution, it can be caused by abnormal weather conditions (ice loading on lines, heavy wind, lightening strokes and other natural disasters) or manual errors (www.chegg.com). The open circuit or short circuit of transmission and distribution line as they leads to unsymmetrical or symmetrical faults and these line faults are classified as:
Single line to ground fault (L-G fault)
Double line fault (L-L fault)
Double line to ground fault (L-L-G fault)

Figure 4a: Classification of line faults (www.chegg.com)
The unsymmetrical network can be expressed in terms of symmetrical components which are positive, negative and zero sequence component.

Figure 4b: Symmetrical components from unsymmetrical network (www.chegg.com)
Matrix formula for unbalanced voltages to symmetrical components (first equation). Symmetrical components to unbalanced voltages (second equation).

182816524765000
2.2.6 Transmission line parameters and Ferranti Effect
Transmission line parameters are A, B, C and D, their purpose is for the analysis of an electrical network. They are also used to determine the input, output voltage performance and current of the transmission network. The ABCD parameters and receiving ; sending voltages and currents formulas are:
A = D = coshyl………………………………………………………………………………….1
B = Zc×sinhyl……………………………………………………………………………………2
C = sinhyl / Zc……………………………………………………………………………………3
VS = VR.A + IR.B…………………………………………………………………………………4
IS = IR.A + VR.C………………………………………………………………………………….5
VR = VS.A – IS.B………………………………………………………………………………….6
IR = IS.A – VS.C………………………………………………………………………………….7
Ferranti effect as it occurs due to overvoltage of the receiving end voltage being higher than the sending end voltage during light load or open circuit condition. It is illustrated with the help of phasor diagram as shown in figure 5. Both the inductance and capacitive have effect on the transmission line for occurrence of Ferranti effect. Equation 8 shows the receiving end voltage under light load or open circuit.

VR = VsA……………………………………………………………………………………………8

Figure 5: Ferranti effect in transmission lines
2.3 Summary
The project prescribes the impacts of shunt reactor on the high voltage and extra high voltage long transmission lines. Shunt reactor has two types but the oil immersed is the chosen one because it is used in high voltage and extra high voltage, its protection and location has also been discussed. Faults that occur on the transmission lines were studied to provide adequate protection scheme. Since both the inductance and capacitance are responsible for Ferranti effect, shunt reactor is the best equipment to solve this phenomenon.

Chapter 3
3.Introduction
In a long transmission line during light load or no load condition there is over-voltage at the receiving end voltage and is greater than the constant sending end voltage due to the shunt capacitance that generates more reactive power in the line, this phenomenon is called Ferranti effect. Therefore, shunt reactors are needed to overcome this problem during no load condition and to find the specific rating of the reactor to be installed at the receiving to obtain acceptable terminal voltage and also absorbing the reactive power (Tarannun and Singh, 2017). The network system will be simulated under no load condition with and without the shunt reactors to compare the sending and receiving voltages and also the VA’r compensation.
For a fault analysis the three phase, single line to ground, double line and double line to ground faults will be calculated and simulated and also with the aid of the phasor diagrams. This chapter it will cover the RLC of the line and ABCD parameters of a transmission line with selection of the equipments and protection devices. Protection settings it will include the overcurrent, earth fault and the distance protection of the transmission line.

3.1Methodology
A 50MVA grid of 0.8 lagging power factor is connected to 400 kV bus1, a tower of rated 1.297 kA two Zebra ACSR parallel bundle conductors of 342 km long transmission is connected between bus 1 and bus 2. A shunt reactor of 243.7MVA’r is connected at the receiving end of a long transmission line at bus 2, between bus2 and bus3 a step down transformer 1 of 400/132 kV j10% is connected. A short transmission line of 1.5 km is connected to bus 3 and bus 4, a transformer 2 with the rating size of 132/22 kV j6% is connected to bus 4 and bus 5 to the MV load.

Design the circuit using Digsilent software as stated above and simulate the circuit under no-load with shunt reactor connected and also with reactor not connected. When shunt reactor is connected a three phase, single line to ground double line and double line to ground faults are simulated. Protection of the line against faults is performed using the overcurrent and earth fault protection relay Schweitzer SEL751 and for the distance protection relay Schweitzer SEL241 is used.
3.2Protection of the transmission line
3.2.1Schweitzer SEL-751 relay for overcurrent and earth fault relay
This relay it can be used for directional and non-directional overprotection to protect transmission lines, power system circuit or transformers. The characteristics choices of this relay are for the element time-overcurrent and the overcurrent elements of this relay they detect ground faults (Schweitzer Engineering Laboratories, 2013). The normal inverse 51P1 of phase current relay has current setting of 3.2 sec.A with the time dial of 0.1, and 50P1 of pickup current of 10.38 sec.A with 0.05s TMS. The normal inverse 51G1 of earth fault current relay has current setting of 1 sec.A with the time dial of 0.1 and 50G1 of pickup current of 7 sec.A with 1 TMS.

3.2.2Distance Protection on a transmission line
Distance relay is classified into two main parts, ground and phase relays. Three phase and double line fault for a transmission line are protected by the phase relays, with the single line to ground and double line to ground fault a ground relays are used to protect these faults (Padmin, 2013). When the fault occurs, the fault classification (single phase to ground, phase to phase, double phase to ground or three-phase fault) the function and fault location are activated. The function of fault location is to predict distance from relay to the fault point (Ismail and Hassan, 2013). Transmission line has three different zones, zone 1 covers the distance of 60%, zone 2 covers between more than 60% to 100% and zone till upto 120%.
3.3Calculations
Arrangement in bundle per phase of the stranded conductors can be two, three and four. The three arrangements are used for a voltage that is above 345kV to limit the corona effect. In figure 6 a zebra bundle conductor ACSR 54/7 of stranded conductors is used.
Figure 6: Zebra bundle conductor datasheet and tower structure design
3.3.1RLC and ABCD Parameters of the transmission line
R= 0.0674?/ km
Dbs= 1.0940.7788rd3 = 1.0940.7788×14.31mm×(0.45)3 = 0.195m
Deq= 3(8.5)2×17 = 10.709m
L= 2×10-7lnDeqDbs = 2×10-7ln10.7090.195 =0.80117mH/km
Dbsc= 1.094rd3 = 1.09414.31mm(0.45)3 = 0.207m
C =2?EolnDeqDbs = 2?×8.85×10-12ln10.7090.207 = 14.091nF/ km
3.3.2Transmission line parameters ABCD
The length of the long transmission is 342km
Z= R + jXL = (23.051+j86.08) ?
y= G+j2?fC = j2?×50×342×14.091nF/ km = 1.514m?90?S
ZC= Zy= 242.609?-7.5??
yl = zy = (0.048+j0.364)
?= 0.364×180°? = 20.86?
A = D = Coshyl= 0.9357?1.05?
Sinhyl = 0.3593?82.83?
B = ZC× Sinhyl = 242.609?75.33??
C = SinhylZc = 1.481m?90.33?S
3.3.3Shunt reactor not connected under no-load condition
IR = 0A
VR = VsA = 400?0?0.9357?1.05? = 427.487?-1.05? kV
IS = VRC = 427.487?-1.05? kV × 1.481m?90.33?S = 633.108?89.28?A
PR = VRXVSCOS(B-?)B-AxVR2COS(B-?)B= 400X427.487COS(75.33-1.05)242.609-0.9357X427.4872COS(75.33-1.05)242.609 = 0MW
QR = VRXVSsin(B-?)B- AxVR2sin(B-?)B = 400X427.487sin(75.33-1.05)242.609-0.9357X427.4872sin(75.33-1.05)242.609 = 0MW
PS= 1.732VS IS cos (V-I) = 1.732×400×.633108 cos (-89. 28?) = 5.512 MW
QS= 1.732VS IS cos (V-I) = 1.732×400×.633108 sin (-89.28?) = 438.583 MW
3.3.4Shunt reactor connected under no-load condition
IR = QR1.732VR = 243.7MVAr1.732×400kV = 351.751A
3.3.5 Faults at Bus bar 2 with Shunt reactor connected
Transformer 1 Transformer 2
Rpu= Pc/S Rpu= Pc/S
= (10.5×103) / (150×106) = (7.5×103) / (80×106)
= 7×10-5 p.u = 9.375×10-3 p.u
XT (OLD) =(0.1)2-(7×10-5)2 XT (OLD) =(0.06)2-(9.375×10-3)2 =j0.1 p.u = j0.0593 p.u
XT (NEW) =j0.1×50MVA150MVA = j0.033p.u XT (NEW) =j0.0593×50MVA80MVA = j0.033p.u
Line 1;2 Line 3
Distance= 342km Distance= 1.5km
R= 0.0674?/km R= 0.0674?/km
L= 0.8116mH/ km L= 0.8116mH/ km
C= 14.091nF / km C= 14.091nF / km
Z= 342 0.0674+j87.21-660.514×50MVA4000002 Z= 1.5 0.0674+j0.252×50MVA4000002
X= -j0.179 p.u X= j0.0004688 p.u
=97.931? XREACROR (up) = 645.5463200 = j0.205 p.u
ZGRID (p.u) = ZactZbase
= 97.9313200= 0.0306 p.u
Zeq1= XT1+XL3+XT2=j0.072p.u
Zeq2= (Xgrid+XL1;L2)// Reactor =j0.027p.u
Fault= j0.0194p.u
Abase = S3×V = 50MVA3×400KV = 72.169AIF(p.u) = VfZfault = 1j0.0194 =51.546?-90?p.u
3.3.5.1 Three phase fault
I3Ø= Ibase X IF(p.u) = 3720.023A
3.3.5.2 Single line to ground fault
IF(p.u) = 3×VfZ1+Z2+Z0 = 3×1j0.0194+j0.0194+j0.0194 = 51.546?-90?p.u
IFAIFBIFB= 51.546?-90?p.u00p.u=3720.023?-90?00 A
3.3.5.3 Double line fault
IFa1 (p.u) = – IFa2 (p.u = VfZ1+Z2 = 1j0.0194+j0.0194 = 25.773?-90?p.u
IFAIFBIFB=044.64?180?44.64?0?p.u= 03221.624?180?3221.624?0? A
3.3.5.4 Double line to ground fault
IFa1 (p.u) = VfZ1+(Z2//Z0) = 1j0.0194+(j0.0194//j0.0194 = 34.364?-90?p.u
IFa0 (p.u) = IFa2 (p.u = -IFa1(p.u)×Z1Z0+Z2 = 3×1j0.0194+j0.0194+j0.0194 = 51.546?-90?p.u
IFAIFBIFB=051.546?150?51.546?30?p.u = 03720.023?150?3720.023?30? A
3.4 Simulated results

Figure 7a: Transmission line with a disconnected shunt reactor

Figure 7b: Transmission line with shunt reactor connected
The circle graph is for distance protection with three zones, a fault is in zone2 as shown in figure 7c below which is the ground relay with a tripping time of 0.195s. IDMT curve is for overcurrent protection with the phase current and earth fault current relays. 51G1, 51P1 and 50G1 tripping times are 0.334s, 0.908s and 0.04s respectively.

Figure 7c: Transmission line with shunt reactor connected with single line to ground fault and its overcurrent and distance time plot graph of Single Line to ground fault.

3.5Phasor diagrams

Figure 8: Phasor diagrams of long line with (green) and without (red) shunt reactor
3.6 Table of results
Table 2: Calculated results for a long transmission line under no load
With Shunt reactor disconnected
VS (kV) VR (kV) IS (A) IR (A) PS (MW) QS(MVAr) PR (MW) QR(MVAr)
400 427.487 633.108 0 5.512 -438.595 0 0
With Shunt reactor connected
400 400 351.75 351.75 0.04 -240.78 0 -243.7
Table 3: Simulated results for a long transmission line under no load
With Shunt reactor disconnected
VS (kV) VR (kV) IS (A) IR (A) PS (MW) QS(MVAr) PR (MW) QR(MVAr)
400 428.14 725.21 0 4.96 -502.42 0 0
With Shunt reactor connected
400 400 348.7 351.75 0.04 -241.62 0 -243.7
Table 4: Simulated and calculated results for the faults at bus 2
Single line to ground (A) Double line fault(A) Double line to ground fault (A) Three phase fault (A)
Simulated Calculated simulated calculated simulated Calculated Simulated Calculated
3622.206 3720.023 0 0 0 0 3628.881 3720.023
0 0 3189.46 3221.624 3665.56 3720.023 3628.881 3720.203
0 0 3189.46 3221.624 3641.71 3720.023 3628.881 3720.203
Table 5: Overcurrent and earth fault protection tripping times
Fault type 51P1 (sec) 50P1 (sec) 51G1 (sec) 50G1 (sec)
S-L-G 0.906 0.334 0.04
D-L-F 1.091 0.93 D-L-G-F 0.912 0.35 0.35
3 phase 0.906 Table 6: Distance protection against faults with the tripping times
Fault type Z3MP Z2MG Z1MG
S-L-G 0.195 D-L-F 0.915 0.195 D-L-G-F 0.915 0.195 3 phase 0.915 3.7 Results discussion
In long transmission line during no-load, constant voltage at the sending end is less than the receiving end voltage as compared in both simulation and calculated. Both the simulated and calculated results they are almost equal meaning the project is running successful. In short transmission line that is connected to between bus 3 and bus 4, Ferranti effect does not occur due to the capacitance value that is almost equal to 0. Shunt reactor is connected to the receiving end of the long line during no load condition to absorb reactive power and to avoid the occurrence of Ferranti effect. All types of faults of simulated and calculated results are approximate. Overcurrent and distance protection were simulated accurately because the relays are tripping according to the protection.

Chapter 4
4.1Proposed further studies
The project is very useful in the industry, most people can learn more about the short, medium and long transmission line and impact of shunt reactors. Understanding more on how to select proper transmission line parameters ; ratings and determining shunt reactor ratings, protection of the equipments against all the types of faults as it is very critical to protect them using correct CT’s, VT’s and relays from being damaged. Company such as Eskom can benefit a lot from this project as it supplies electricity to the consumers and during light or no load by switching in the reactor they can save more costs as the will be no occurrence of Ferranti effect.

4.2Conclusion
A long transmission line draws high charging current and at no load condition the supplied reactive power exceeds the consumed reactive power, this leads to the elevated voltage levels. From the power flow studies during no load, the receiving end current (IR) is zero amperes and the ratio of receiving voltage to sending voltage to be 1/A where A is 0.9357?1.05° and this equal to 1.069 or approximately 9.4 percent higher than the sending voltage. When the shunt reactor is connected the sending end voltage becomes equal the receiving end voltage.
In short transmission line the charging current and capacitance are negligible resulting in sending voltage equals or greater than the receiving voltage therefore Ferranti effect does not occur as shown in simulated results between bus 3 and bus 4 unlike in long transmission line where capacitance increase with the length of the line between bus 1 and bus 2. In short transmission line shunt reactors are not needed as there is no increase in voltage line.

The technical report was done accordingly with the assistance from the mentor and simulated network were constructed using Dig-silent powerfactory to achieve the specific aims of the project also with the help of the B-Tech subjects (Power systems, Electrical Protection and Protection Technology).
4.3Recommendation
This project is environmental friendly and it does not cause any environmental concerns, water, air, noise level and soil. The Ferranti effect occurs in High voltage and Extra High voltage in medium and long lines except in short lines. When the transmission line receiving end voltage is greater than the sending end voltage, the increase in voltage may cause operative ratings of the terminal and it may leads to insulation breakdown resulting in minimizing their lifespan and damaging the equipments. To maintain the level of the voltage profile along the line, a circuit breakers that are connected to the variable shunt reactors are switched in during light or no load condition even this solution is costly because the load fluctuates randomly as the power generated cannot be planned exactly due to sudden tripping of the loads.
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