Transmission overhead line is one of the main elements in electric power system. Electrical power system comprises of generation, transmission and distribution. For transmission lines, it is used to transmit electric power to large load center. Nowadays, double circuit transmission lines on the same tower with a different voltage are widely used. This paper present the studies of the effect on distance protection, when fault that occur in the transmission line that have different voltages in the same tower. In this situation, PSCAD/EMTDC software has been used to simulate the output current and voltages in order to see the fault effect on distance protection. In the other words, the PSCAD/EMTDC software is used in model and analysis of the effect of cross-country fault on distance protection. In this paper, the result of cross-country fault on distance protection with different voltage levels is presented

Abdul Karim, Sazali P.

Habi Buddin, Mohd. Hafiz

Mohd. Yusof, Alias

Mohd. Zin, Abdullah Asuhaimi

Omar, Nur Afifah

Universiti Teknologi Malaysia Institutional Repository

Effect of Cross-Country Fault on Distance Protection in Transmission Line with Different Voltage LevelsN.A. OmarFaculty of ElectricalEngineeringUniversiti TeknologiMalaysiaSkudai, Malaysiaeffa_fifa@yahoo.comA.A. Mohd ZinFaculty of ElectricalEngineeringUniversiti TeknologiMalaysiaSkudai, Malaysiaabdullah@fke.utm.myA. Mohd YusofFaculty of ElectricalEngineeringUniversiti TeknologiMalaysiaSkudai, Malaysiaaliasm@fke.utm.myM. H. HabibuddinFaculty of ElectricalEngineeringUniversitiTeknologi MalaysiaSkudai, Malaysiamhafiz@fke.utm.myS.P. Abdul KarimSenior TechnicalExpert TransmissionDivisionTenaga NasionalBerhadsazalipk@tnb.com.myAbstract — Transmission overhead line is one of the mainelements in electric power system. Electrical power systemcomprises of generation, transmission and distribution. Fortransmission lines, it is used to transmit electric power to largeload center. Nowadays, double circuit transmission lines on thesame tower with a different voltage are widely used. This paperpresent the studies of the effect on distance protection, when faultthat occur in the transmission line that have different voltages inthe same tower. In this situation, PSCAD/EMTDC software hasbeen used to simulate the output current and voltages in order tosee the fault effect on distance protection. In the other words, thePSCAD/EMTDC software is used in model and analysis of theeffect of cross-country fault on distance protection. In this paper,the result of cross-country fault on distance protection withdifferent voltage levels is presented.Keywords – Transmission Line, Cross-Country Fault, Fault,Distance Protection, Protection ZoneI. INTRODUCTIONThe purpose of a transmission network is to transfer theelectric energy from generating unit to distribution system [1-7]. Transmission lines also interconnect neighboring utilitiesnot only to economic dispatch of power during normalcondition, but also transfer power during emergencies[3,7,8,9]. When a fault occurs on transmission line, the voltageat the point of fault is suddenly reduced to a low value. Thus,fault is an abnormal flow of electric current [17-18].Faults on transmission lines must be detected correctly andquickly to prevent the disturbance or damage to system andmaintain security and reliability of supply [3-6]. This fault candamage the power system in several ways. To reduce theeffect of faults, distance protection relays are installed as apart of power system in order to protect the equipment fromdamages.As already known, a cross-country fault is one where thereare two faults occur at the same circuit, but in differentlocations and possibly involving different phases and voltages[8,12-14]. This type of fault can only occur at double or morecircuit in transmission line. In this case, the distance protectionmust trip only for fault that occurs in protected zone, butsometimes it may not trip the internal faults or trip the externalfaults incorrectly.To reduce the effect of fault, the distance protection hasbeen used in power system transmission line [15-17]. Distanceprotection is comparatively simple to apply and it can be fastin operation for faults located along the protected circuit[2,3,5,17,8,18].In this paper, the output of the simulation for the cross-country faults issues that affected the distance protection intransmission lines is presented. The theoretical analysis andthe PSCAD/EMTDC simulation results show that the locationof the fault was able to detect the high impedance ground faultin selective ways.II. POWER SYSTEM PROTECTIONA. BackgroundTransmission lines in power system exhibit the electricalproperties of the inductance, resistance, capacitance andconductors [3,16,14,19,18,10]. These parameters are essentialfor the development of transmission line models that are usedin power system analysis. The selection of the voltage levelfor transmission lines is based on the amount of the power andthe distance of the transmission line.Among the many cause of the fault, the cross-countryfault is the rare fault that occurs in power system. These faultsoften occur at the worst possible time and locations.Sometimes, it will occur with maximum amount of currentand cause big damages [5].In this situation, the distance protection is used to detectthe fault and prevents it from causes a big damage. Thesedistance protections detect the fault and closed the system,cleared the fault that occurred in transmission line and afterthat it will enable the system to function as usual.B. Power System ConfigurationPower system is a complex system in the world. Doublecircuit transmission lines are being used more widespread asthey increase the power transmission capacity and increase thereliability of the system [7,15-17,8,12-14,19]. Double circuittransmission lines are defined as lines that share the samestructure or right of way for all, or a portion of, their length. Itmay enhance the transmission capacity of each way, other thanto reduce the use of ground and can save cost.Faults have two types which are symmetrical andunsymmetrical faults [1,4,8]. Single line to ground fault is themost common fault while the three phase short circuit fault isthe most severe faults. Whenever the fault occurs, the loss ofsupply will be faced by the consumers. Cross-country fault canbe defined as a fault that is possibly involving different phaseand occurring at two different locations in power system[1,2,4,7,14-17].To protect the components in transmission lines fromdamages, distance protection relays are used and operatedwithin a certain distance. In transmission system, distanceprotection works by utilizing the fact that the measuredimpedance from a point is directly proportional to the distance.If the apparent impedance is less than the impedance-reach,then it is concluded that a fault has occurred in the protectedline between the relay location and the impedance reach of therelay. Combination of an impedance reach and its associatedtime delay is known as a protection zone. It is common toprovide distance relays with three protection zones but,depending on the application, extra zones can be included in therelay. The incidence of a fault within a protection zone of adistance relay must initiate and complete the operation of therelay.For this research, PSCAD/EMTDC software has been usedto simulate the system in order to generate the current andvoltages during cross-country fault condition. Based on thesimulation, the result will be compared with fault and cross-country fault.III. POWER SYSTEMNETWORKThe steps for the simulation are:A. System StudiedFigure 1 shows that the system that has been used in thesimulation which is based on the single line diagram of thepower system for two terminals with different type of voltagesin a transmission line system.B. Power System ModellingIn this paper, the result and analysis have been done usingPSCAD/EMTDC software in order to generate the current andvoltages during cross-country fault condition.  From thisFigure 1, the output for current and voltages during cross-country fault can be determined.In this analysis, if there is a fault occurs in line, the tripsignal will be sent to trip the circuit breaker. The trip signal ismeasured at the secondary side of distance protection relaymodule. In order to determine the trip signal, the apparentimpedance of each phase and ground element is calculated asshown in Table 1:TABLE I: APPARENT IMPEDANCEElement Apparent Impedancea-bb-cc-aa-gb-gc-gThe calculation for apparent impedance cannot be obtaineddirectly from the network. Both of the voltage and current haveto pass through Capacitive Voltage Transformer (CVT) andCurrent Transformer (CT). After that, the signal is reduced bythe turn ratio and sent to Fast Fourier Transform Module (FFT)in PSCAD/EMTDC [14].Figure 1 shows that the simple model transmission line thathas been designed to represent the real system. Thetransmission line is represented by using the Bergeron linemodel system which is available in the software and thegenerators is represented by using the equivalent potentialsource and equivalent source impedance. The bulk of data aregenerated using multiple run component of PSCAD/EMTDCsoftware. With this, the variable parameter in PSCAD can beused in designing the model.C. System MethodologyThe cross-country fault can be defined as a fault that ispossibly involving different phases and occurring at twodifferent locations and voltages simultaneously in powersystem. Based on this research, the effect of cross-countryfault on distance protection will be determined by usingPSCAD/EMTDC software.  By using this software, the outputcurrent and voltage will be identified and the result of cross-country fault will be calculated. By using the simulation fromPSCAD/EMTDC, the comparison between ordinary fault andcross-country fault can be done.PSCAD/EMTDC is used to generate fault current andvoltage signals under cross-country fault scenarios [9,21-23].The transmission line in the system is being represented usingthe Bergeron line model. In order to get a better result, theanalysis has been done on every kilometer of the transmissionline.After that, the analysis are needed to be done in order tofind the suitable distance relays protection for every differenttype of cross-country fault that occur. In this paper, the analysiswill focus on Mho distance relay characteristics only.D. System Modelling and AnalysisThe transmission line network in this paper is used togenerate the fault current and voltage during cross-countryfault. The system studied is composed of a double-circuittransmission lines that are connected to the sources at eachend as shown in Fig. 1.Fig. 1. Simple Single Line Diagram ModelingAll components are modeled by PSCAD/EMTDCsimulation software such as different fault on transmissionline, fault timing and fault position that is adjusted manuallyby dividing the line into two part of required length. Thetransmission line is simulated using distributed parameter linemodel. Fig. 1 shows that the different circuit with differentvalue of voltages.Fig. 2. Time Occur and Trip SignalThe data for this analysis is collected for one cycle offault and the time for fault occur is fixed at 0.2 sec for theduration of 0.05 sec as shown in Fig. 2. The simulation isbased on different types of fault including three phase fault,phase to phase fault, phase to phase to ground fault and singlephase to ground fault.Fig. 3. Output Voltage and Current (Fault in NormalCondition)(a) (b)Fig. 4. Distance Protection Relay (Fault in Normal Condition)a) Impedance Z b) ResistanceFig. 3 shows that the output for voltage and currentwaveforms from the simulation. where since there is no faultsoccur in the system, so it works as in a normal condition.Therefore, there is no effect to the distance protection asshown in Fig. 4.From this analysis, the first fault analysis is for single lineto ground fault that occurs simulteneously which involvesdifferent voltages level. Fig. 5 shows the output voltage andcurrent for single line to ground fault.Fig. 5.Output Voltage and Current (Single Line to GroundFault Condition)In the Fig. 5, it can see that the output for voltage andcurrent change when the fault occur on the system. During thattime, the circuit becomes unstable and will not operate untilthe fault has been fully cleared.(a) (b)Fig. 6.Distance Protection Relay (Single Line to Ground FaultCondition)a) Impedance Z b) ResistanceWhen the fault occurred in transmission line, distanceprotection on the system will interrupt. Fig. 6 shows that theoutput for distance protection relay during single line toground fault that occur in the system. When the R-XTrajectory of the impedance has crossed the reach zone (usingzone 1), it shows that the single line to ground fault at thissituation is still in protected zone and will operate normallyafter the fault has been cleared.Fig. 7.Output Voltage and Current (Line to Line FaultCondition)Different effect for different kinds of fault that occurredin transmission line system can be found. When the line to linefault occurred, the voltage and current waveforms are asshown in Fig. 7. From the observation, voltage and currentfrom the line are interrupted and this will make the systembecome unstable.(a) (b)Fig. 8.Distance Protection Relay (Line to Line Fault Condition)a) Impedance Z b) ResistanceThe simulation output for distance protection relay isshown in Fig. 8. From the analysis, the fault that occurred inthis system is still in protected zone. When the R-X Trajectorysignal is detected, the tripping signal will be sent to trip thebreaker. The tripping signal at breaker can be verified from thephase and ground element that can be identified during theabnormal condition in Polarised Mho Distance Relay.IV. CONCLUSIONFault always occurs in different ways and different types. Inthis paper, the effect of the voltage with different type of faultthat occurred in the transmission line is determined. Based onthe theoretical part before, there are types of fault that couldpossibly occur in transmission line. But in this paper, it onlyfocuses on the effect of the single line to ground fault and lineto line fault on transmission line. From this analysis, it showsthat the output for current and voltage are still in protectedzone when the faults occurred. This analysis is done usingPSCAD/EMTDC simulation software. The cross-country faultcan also be analyzed based on the sampled output voltage andcurrent waveform. From this analysis, it shows that theamplitude and phase angle of the faulted current and voltagesignals are obtained from FFT Module that are provided insidethe simulation software. From here, the R-X Trajectory canidentify the cross-country fault that occurred in transmissionline system and for the calculation of the apparent impedance,it needs the output current and voltage that obtained from FFTModule. It is concluded that the cross-country fault thatoccurred in transmission line can be detected by using thesimulation software in distance protection either it still inprotected zone or not in order to protect the component intransmission line from damages.ACKNOWLEDGMENTThis project is supported by Universiti TeknologiMalaysia (UTM) and Malaysia Ministry of Higher Education(MOHE) under RUG VOT no 03H45REFERENCES[1] N. A. Omar. A. A. M. Zin, A. M. Yusof and S. P. A. 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Effect of cross-country fault of distance protection in transmission line with different voltage levels

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Effect of cross-country fault of distance protection in transmission line with different voltage levels

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