numerical distance protection and teleprotection testing with

Numerical Distance Protection and Teleprotection Testing withComparative Practical Result

MOHAMED BOUCHAHDANE1, AÎSSA BOUZID2

1Institute of Electrical Engineers and Electronics, University of Boumerdes2Department of Electrical Engineering, University of Constantine 1

[email protected], [email protected]

Abstract: - Any kind of power system shunt fault results in customers being disconnected if not quickly cleared.Distance protection meets the requirements of speed and reliability needed to protect electric circuits, thusdistance protection is used to a large extend on power-system networks. It is a universal short-circuit protection.Its mode of operation is based on the measurement of electrical quantities (current and voltage) and evaluationof the impedance towards the fault, which basically is proportional to the distance to the fault. Numericaldistance protection is the utilization of microprocessor technology with analogy to digital conversion of themeasured values (current and voltage), computed (numerical) distance determination and digital processinglogic. Present paper aims to show Numerical Distance Protection Testing using NETSIM. Good comparativeresults have been obtained. Absolute selectivity and short tripping times of the line protection in meshednetworks can be achieved by using line distance protection with teleprotection schemes.

Key-Words: - Distance protection, netsim, short cirtcuit, teleprotection, testing

1 IntroductionThe principle of distance protection involves theratio between the voltage and the measured currentat the relaying point. The calculation of the apparentimpedance is compared with the reference (reachimpedance). If the measured impedance is less thanthe reference impedance, it is assessed that faultoccurs within the protected line. Testing theimpedance characteristic is the way to prove theoperation of the relay whether it is ready to operateor not[1][2][3].

In this work, we shall see the differentsimulations led through the Netsim (NetworkSimulation) compared to practical testingconducted in the 60 kV substation of Bouira(Algeria) as follow:• Injection of a fugitive default in zone 1 withinphase L3.• Injection of a permanent default in zone 1within phase L2.• Injection of a default in zone 2 within phase L1according to two different conditions whetherTeleprotection is activated or not.

2 Protection System Definition

2.1 Introduction

International Commission for Electrotechnics(I.C.E) defines protection as a collection ofdisposals allowing the detection of defaults andabnormal situations within the nets in order tocontrol the release of one or more circuit-breakersand, where necessary, elaborate other signalingorders[4] [5].

2.2 Protection FunctionsProtection functions are realized by relays ormultifunction-devices. Initially, relays of protectionwere of a analogical type and mainly could onlyperform one single function. Currently, numericaltechnology is the most operational. It helps inconceiving functions increasingly progressing andthe same device generally performs severalfunctions.

3 Malfunctions

3.1 Origin of FaultsVarious network components are designed,constructed and maintained to achieve the bestcompromise between cost and risk of failure. Thisrisk is not zero and incidents and faults disrupt theoperation of electrical installations[6][7].

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• Airlines: are subject to atmospheric disturbances(thunders, storms, etc.).,. Mountainous regions, forexample, are such much more likely than others tolightning.• Underground Cables: are exposed to externalaggressions (mechanical earthmoving gear, forexample) that systematically result in permanentfaults.• Equipment networks and substations: includeinsulators (solid, liquid or gas) composed of more orless complex connections placed between energizedparts and ground. Being degraded insulators, leadingto isolation faults isolates.

4 Faults Characteristics

4.1 Nature of Fault• Fugitives Faults: Fugitives faultsa require a veryshort break from the power supply (on the order of afew tenths of a second).• Permanent Faults: These faults cause a definitivetrigger that requires intervention operational staffintervention to locate the fault and restart thehealthy part.• Self-extinguishing Faults: it is those whospontaneously disappear within a very short timewithout causing discontinuities in the electricalenergy supply.• Semi-permanent Faults: These faults require to getremoved, one or more relatively long interruptionsof the power supply (on a few tens of seconds order)without the need for intervention by the operatingstaff.

4.2 Fault CurrentA perfect fault current of a voltage generator is, intheory, infinite. Fortunately, in practice, the value ofthe fault current is finite, limited by the internalimpedance of the source, the various line sectionsand components placed on the path of the current.

Faults are transitory electromagnetic phenomena.They appear when the insulation between twoconductors of different voltages or between a liveconductor and earth broke.

Faults cause very high currents in the constituentelements of the network and the current fault(Three-phase) is an essential element for thedimensioning of electrical equipment.

Faults can cause economic damage if they arenot removed quickly by protection systems [8][9].

Fig. 1. Fault current curve type.

4.3 Statistics FaultsAt the network air transport level in SONELGAZ(The Algerian: National Company for Electricityand Gas) short circuits statistics are:• Fugitive : 70% to 90%

• Semi-permanent: 5 to 15%

• Permanent 5-15%Note: On underground electrical networks (Cable)faults still are ongoing.

5 Faults Impact on the GridFaults in electrical networks have adverseeffects[6][10]:

5.1 Functioning of the Electrical NetworksThe adverse effects of short circuits are especially tobe feared on the THT electric network on whichdebit strong power generator groups.

Short circuit, polyphase ones in particular andnear the power plants lead to a decrease of torque(Cr) into the machines and therefore a disruption ofthe balance between it and the engine torque (Cm).If they are not quickly removed, they can lead to theloss of stability of groups of generators as todesynchronized operations that may harm materials.

Time for removal short-circuits in the order of100-150 ms are generally considered not to exceedvalues on electrical networks THT.

5.2 Maintenance of EquipmentFaults cause overcurrents in case of a three-phasefault. The fault current can be exceeded by 20 to 30times the rated current (In). These overcurrentsbring two types of constraints:• Thermal constraints: due to release of Joule heat(RI2) in electrical conductors.• Mechanical Constraints: due to electrodynamicsforces, they cause particular sway over the airlinesconductors and the displacement of the windings oftransformers.


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If these efforts exceed the permissible limitsduring construction, they are likely to cause seriousdamages.

Moreover, electric arc resulting from a defectinvolves an important local energy release whichcan cause important damages to the equipment andbe hazardous to staff working nearby.

5.3 Quality of SupplyFor users, defects result in a drop voltage whoseamplitude and duration are function of efferentfactors such as the nature of the short circuit, thenetwork structure made, ground method, operatingmode, performance protection ... etc..

5.4 Circuits of TelecommunicationsThe presence of a asymmetrical fault between oneor two phases of a power line and earth causes theflow of a homopolar current that flows to groundthrough the neutral points of the networks.

A longitudinal voltage induced, proportional tothis current, appears on the telecommunication lineswhich have a parallel path to the electric energy.This voltage can reach hazardous values as well asto staff and telecommunication facilities.

5.5 Staff SafetyThe inadvertent powering of the masses, elevationspotential linked to the flow of fault currents to earth,drivers fell to the ground….etc…are situationswhich may present risks to safety. Groundingneutral points mode thus plays an essential role.

6 Additional Constraints forProtectionElectrical protection must not restrict normaloperation of electrical networks, in particular [12][13].1 They should not limit the flexibility of theprotected network by prohibiting certain operatingpatterns (Curly Networks, mesh, radial).2 They must remain stable in the presence ofphenomena others than defects:

• When operating maneuvers, during transientsubsequent to blank switching on or off of linestransformers.

• In presence of permissible variations in voltageand frequency.

• In case of overloads and imbalances enteringinto the operating margin of electrical networks.

• In the presence of oscillations resulting fromtransient generators.

• Under the influence of an anomaly of themeasuring circuits.

7 Main Qualities of Protection

7.1 Quick Removal of FaultsFaults are incidents that must be removed as soon aspossible, it is the role of the protections which thatof speed operation and performance priorities.

Fault clearing time has two main components:• Operating time protection (tens of milliseconds).• Opening time of circuit breakers with moderncircuit breakers (SF6 or vacuum), they are between1 and 3 periods.

7.2 Selective Elimination of FaultsSelectivity is an ability of a set of protections todistinguish between the conditions for whichprotection must operate and those where it does notwork.

The different ways that can be implemented toensure good selectivity in the protection of anelectrical network. The most important are thefollowing three types:• Current discrimination by currents.• Time discrimination by time.• Selectivity exchange of information, called logicselectivity.

7.2.1 Ampere-metrical selectivity• Principle: It is based on the fact that in a network,the fault current is even lower than the fault is closerto the source.• Operation: An Ampere-metrical protection isarranged at the start of each section: a threshold isset to a value below the minimum value fault causedby a defect on the section monitored and exceedingthe maximum value of current caused by a faultdownstream (beyond the monitored area).• Benefits: Thus set, each protection works only fordefects located immediately downstream of itsposition inside the monitored area, it is insensitiveto defects appearing beyond.


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Fig. 2. Operation of a current discrimination.

7.2.2 Time clock selectivitySelectivity wherein protections sought are organizedto operate in a manner offset in time. ClosestProtection to the source to the longest timing.• Operation: Thus, in the diagram, the default hasbeen represented by all the protections (A, B, C, andD). Protection delay D closes its contacts installedfaster than C itself faster than the installed B ...

After opening the circuit breaker D and thedisappearance of the fault current, protections A, B,C are no longer requested, return to their standbyposition.

The difference in operating time between twosuccessive protections ΔT is the interval selectivity.

Fig. 3. Principle of time discrimination.

7.3 Sensitivity of ProtectionProtection must operate in very broad currents ofshort circuits between:• The maximum current is determined by the designof facilities and is well known.• A minimum current whose value is very difficultto assess and which corresponds to a fault occurringin often exceptional cases.

The concept of sensitivity of protection is oftenused in reference to the lowest fault current forwhich protection is able to function.

7.4 Protection reliabilityThe terms and definitions given here are widelyinternationally used in practice.1 Protection has a proper operation whentransmitting a response to a fault on the network atany point in line with what expected.2 In contrast, incorrect operation, it has two aspects:

• The malfunction or non-operation: when theprotection that would function does not work.

• The unwanted operation: which is an unjustifiedoperation, either in the absence of a fault or afault for which protection would not work.

3 Reliability of a protection which is the probabilityof not having a malfunction (avoid nuisancetripping), is the combination of:

• Safety: Which is the probability of not having amalfunction.

• Security: which is the probability of not havingundesired operation.

8 The Principle of Distant Protection

8.1 IntroductionThe most used worldwide type of distant protectionis the distant protection (in particular because of itstotal autonomy that requires no connection betweenthe two ends of the line to be protected), it ischaracterized by two features [11] :• The relationship between the fault distance andtime triggering the relay.• The electrical variables to measure the distance tofault (U and I).• The maximum current is determined by the designof facilities and is well known.

Distance protection is selectively sensitive toexternal faults, operating out of synchronism of thenetwork and to variations in the voltage, it can be


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used on lines whose length is between 10 and 300km and the voltage higher 30 kV.

The distance relays of the voltage and currentmatch, i.e. the impedance at the relay location.Impedance per mile is fairly constant and theserelays respond to the distance between the relay andthe fault point.

As power systems become more complex andthe fault current varies with changes in generationand system configuration, directional over currentrelays become difficult to implement for alleventualities, while the distance relay is set for aconstant wide variety of external changes to theprotected line.

We have U = Z. I, if there is a fault then Iincreases, U decreases which makes Z decreases.These relay call minimum impedance. The principleof distance protection is based on Ohm's law Z = U /I, with Z = RL + j XL.We note that the line resistance (RL) is proportionalto the length (L), so to determine the length wherethe problem is, we just have to know the impedanceie the image of the voltage and the current fromtransformers CT and VT measurements.

8.2 Different Types of Distance RelaysThe relays are widely used for protection of electriclines and apply as easily to the case of electricaltransmission lines as that of the sections. As theshortest delay always corresponds to the shortestdistance, one of the most answered in this type ofequipment is:• Impedance relay.• Admittance relay.• Reactance relay.

8.3 Highlights Distance Protection

8.3.1 Relationship between time – distance:Time discrimination of the protection is given by thetiming of tripping time as a function of the distancebetween the measuring point and the fault.

At SONELGAZ level we must chose three areasin downstream area and a lover as follows:• The first downstream area covers about 80% of theprotected line AB, and triggered the circuit breakerin T1.• The 2nd zone extends downstream to 100% of theprotected line AB + 20% of the adjacent lineshorter, and tripped the circuit breaker in T2.

• The 3rd Zone extends downstream to 100% of theprotected line AB + 40% of the adjacent line thelongest, and caused the circuit breaker to T3.• The 4th Zone is an area lover of 60% of theprotected line AB and the breaker tripped T4.

Trip times T1, T2 and T3 correspond to the fourdifferent operating zones and a selective interval.

Protections A1, B1, A2 and B2 have similarsettings and a directional function indicated by thearrows, for example, the distance protection instation A (A1) set to protect the power line AB.

When a fault d1 between the line AB and thenearest station A less than 10% of the length of theline, both A1 and B1 protections at the end of theline AB are detected but the fault time differs.

The A1 distance protection detects the fault inthe first zone and triggered downstream circuitbreaker Q1 and distance protection zone B1detected in the 2nd and triggered downstream circuitbreaker Q2.

When a defect d2 between the line AB and thenearest station B lower than 10% of the length of theline, the two relays A1 and B1 at the end of the lineAB, the distance protection A1 detected the defectsecond downstream area and triggers the circuitbreaker protection and T2 B1 distance first detecteddownstream area and triggered the circuit breakerQ1. The third area downstream area as a backup forprotection A1. The 4th lover Zone as an area foremergency protection A2 and B2.

Fig. 4. Chronometric selectivity of distanceprotection.

Fig. 5. Distance protection zones.


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8.4 Distance Protection With QuadrilateralCharacteristic (Optional)The distance protection has a polygonal trippingcharacteristic. Depending on which version wasordered.In total there are five independent and oneadditional controlled zone for each fault impedanceloop. Figure 6 shows the shape of the polygons asexample. The first zone is shaded and forwarddirectional. The third zone is reverse directional.In general, the polygon is defined by means of aparallelogram which intersects the axes with thevalues R and X as well as the tilt ΨDist. A load trapezoid with the setting RLoad and ΨLoad may be used to cut the area of the load impedance out of thepolygon.

The axial coordinates can be set individually foreach zone; ΨDist, RLoad and ΨLoad are common for all zones. The parallelogram is symmetrical withrespect to the origin of the R–X–coordinate system;the directional characteristic however limits thetripping range to the desired quadrants (refer to„Direction determination“ below).

Fig. 6. Polygonal characteristic (setting values aremarked by dots)

Fig. 7. Directional characteristic in the R-X-diagram

Figure 7 shows the theoretical steady-statecharacteristic. In practice, the limits of thedirectional characteristic when using memorizedvoltages is dependent on both the source impedanceand the load transferred across the line prior to faultinception.

Accordingly the directional characteristicincludes a safety margin with respect to the bordersof the first quadrant in the R–X diagram (Figure 7).

Since each zone can be set to Forward, Reverseor Non-Directional, different (centrically mirrored)directional characteristics are available for Forwardand Reverse.

A non-directional zone has no directionalcharacteristic. The entire tripping region applieshere [14][15].

Fig. 8. Connection for Siemens 7SA6x V4.7Line[16].


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9 Results

9.1 Simulation 1

9.1.1 Theoretical result:We simulated a fugitive short circuit on phase L3 inzone 1 using the Netsim. The theoretical results areas shown below.

Fig. 9. Time signal Graph.

9.1.2 Practical result:We injected a similar defect using OMICRONsecondary injection test sets and measurementdevice (CMC 356). We have obtained practicalresults as shown below.


Table 1Successful Sequence

CycleEvent /Time Mode Ttheor Tgap Treal Result

1 Trigger. Expected n/a n/a 16,50ms +

Timeout Time 1,200s100,0ms 1,229s +

FinalTrigger

3pNot

Expected n/a n/a n/a +

Fig.9 and Fig.10 show the appearance of thesingle line-to- ground fault as well as the dropvoltage V within phase L3.

In the meantime, this will have as a directconsequence the simultaneous starting of thedownstream protection of distance. Later on, L3release is to occur. Logical signals would then showthe elimination of the fault and the time for openingthe circuit breaker. At last, L3 reset is ordered.

9.2 Simulation 2

9.2.1 Theoretical result:We simulated a permanent short circuit on phase L2in zone 1 using the Netsim. The theoretical resultsare as shown below.


9.2.2 Practical result:We injected a similar defect using OMICRONsecondary injection test sets and measurementdevice (CMC 356). We have obtained practicalresults as shown below.


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1 Trigger. Expected n/a n/a 17ms +


FinalTrigger

3p Expected n/a n/a 15.9ms +

Imp.Clos.CB

NotExpected n/a n/a n/a +

Fig.11 and Fig.12 show the appearance of thesingle line-to- ground fault as well as the dropvoltage V within phase L2. This will have as adirect consequence, as shown in meantime, thesimultaneous starting of the downstream protectionof distance. Later on, L2 release is to occur. Logicalsignals would then show the elimination of thedefect and the time for opening the circuit breaker.L2 reset is then ordered .In this particular casewhere defect is to persisting, the Protection-relayorders a definitive disconnection of the line.

9.3 Simulation 3We undertook the same simulation but in zone 2 onphase L1 with both deactivated and activatedTeleprotection.

9.3.1 Before activating Teleprotection:• Theoretical result


• Practical result



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FinalTrigger

3p Expected n/a n/a 322,8ms +

Imp.Clos.CB

NotExpected n/a n/a n/a +

The particularity in this simulation held in zone2is (the Teleprotection being deactivated) that theelimination time of the default was longer to acertain extent.

9.3.2 After activating Teleprotection:• Theoretical result


• Practical resultTable 4

Successful Sequence




Final Trigger 3p Expected n/a n/a n/a +


In that case where simulation still was held inzone 2 but with the Teleprotection activated, theelimination of the default is, on the contrary, veryfast and hardly instantaneous.

10 ConclusionNumerical Distance Protection has as a fundamentalbenefit to ensure a real and effective liability andconstancy of the system as it clearly discernsbetween fugitive and permanent defaults .This, withregard to an optimal management of the domesticand economic field. In an other hand, we may takeinto consideration that Teleprotection whenactivated shows a high potentiality in terms offastness in detecting the different faults and defectsthat may occur within a line considered. We wouldalso say that practical simulating tests led in asubstation were accurately confirmed whencompared to the results obtained through theNetsim.


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References:[1] Harker Keith, Power system commissioning

and maintenance practice,Institution ofElectrical Engineers, London, 1998.

[2] Glover J. Duncan, Overbye Thomas Jeffreyand Sarma Mulukutla S, Power systemsanalysis and design, 4th ed, Thomson 2007,2008.

[3] Nagsarkar T. K and Sukhija M. S, Powersystem analysis, Oxford University Press,2007.

[4] Chapman Stephen J , Electric machinery andpower system fundamentals, Boston :McGraw/Hill 2002.

[5] M. Lami ,Protection and monitoring of theelectrical energy transmission networks -Volume 1, Grenoble University , 2003.

[6] Horowitz Stanley H and Phadke Arun G,Power system relaying, Taunton , New York :Research Studies Press : Wiley 1992.

[7] J.M. Gers, E. J. Holmes, ”Protection ofElectricity Distribution Networks”, TheInstitution of Electrical Engineers, London,U.K. 1998.

[8] A. Apostolov, and, B. Vandiver, MaintenanceTesting of Multifunctional Distance ProtectionIEDs, Transmission and DistributionConference and Exposition, IEEE PES,OMICRON electronics, Los Angeles, CA USA, 19-22 April 2010.

[9] P.M. Anderson, “Power System Protection”,The Institute of Electrical and ElectronicsEngineers Inc, New York, U.S.A, 1999.

[10] M. P. Ransick, “Numeric protective relaybasics”, Proceedings of the 33rd IAS AnnualMeeting (The IEEE 1998 Industry ApplicationsConference), 1998. Vol. 3,12-15 Oct 1998,pp(s): 2342 -2347.

[11] G.I. Atabekov, “The Relay Protection of HighVoltage Networks”, Pergamon Press Ltd,London, 1960.

[12] B. de METZ-NOBLAT , F. DUMAS, C.POULAIN, " Cahier technique n° 158 Calculdes courants de courtcircuit " SchneiderElectric, CT 158 édition septembre 2005.

[13] Omicron Measurement Package Softwaremanual.

[14] NetSim ,Introductory Examples, Omicronelectronics, Klaus 2001.

[15] Distance Protection 7SA6, SIEMENS.SIPROTEC, V4.61 and higher, Manuel 2005.

[16] Siemens 7SA522 7SA6x V4.7 Line PTT UserManual, V1.000 OMICRON PTL.


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numerical distance protection and teleprotection testing with

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