investigation on protective relays testing methods

5/28/2018 Investigation on Protective Relays Testing Methods

24th Intern ational Spring Seminar on Electronics TechnologyMay 5-9 2001 Calimanesti-Caciulata, Romania

Investigation on Protective Relays Testing Methods

Stefan Ovcharov, Stanimir Vichev, Peter YakimovFaculty of ElectronicsTechnical University of Sofia1797 Sofia, BulgariaPhone i-359 2 965-32-65 E-mail: pij @vm ei.acad.bg

AbstractThis article describes some methods, used in protective relay testing. Protective relay is a veryimportant part of the energy system. Its purpose is to find out the fault and to switch off a circuitbreaker in order to prevent the non-affected part of the power network. Modeling the energysystem is needed not only to test and evaluate the action of the protective relays but for personneltraining in conditions similar to these in real networks as well. Because of that the model must bemore realistic and has to per orm au lts in real time. A various of parameters of the signals mustbe simulated to pegor m situations, occur in real networks. The paper shows some methods fo rprotective relays static and dynamic testing. These methods require generating signals withvariable parameters for every different application. The paper describes some signals used inresearch and ma nufacturing of relay equipment and fo r field tests of protective relays too. Tosatisfy these requirements there is a need of a simulator which is able to generate waveforms notonly with the main frequen cy but including higher harmonics. The paper describes the blockdiagram and the characteristics o a portable protective relays test set, designed in Bulgaria andits possibilities for protective relays static and dynamic testing in comparison to the simulators,designed by ABB R elay Division in Sweden and Texas A M University in USA.

1. INTRODUCTIONAs power grids get bigger and carry more power,the need for quick, reliable disconnection when faultsoccur becomes more and m ore urgent. The purpose ofprotective relay equipment is to sense fault states andtrip circuit breakers. If a fault is not corrected early,personal injuries and serious damage can occur.Disconnection must take place selectively, i.e. it mustbe limited to the faulty part of the power grid. This iswhy the protective relay equipment must be able todistinguish between permissible heavy load conditionsand hazardous operational disturbances. T o avoid

unjustifiable interruptions, the protective relayequipment must not react to disturbances beneath aspecified level called the pick-up value [11, [ 3 ] .

Protective relay equipment must sometimes handleunusual faults that involve distortion, transients andharmonics. These unusual disturbances can behandled by test equipment having a DC-coupledamplifier and a program that generates suitabledisturbances or plays back information previously

stored on a disturbance recorder. This permits nearlyall forms of waveforms and transients to be generated.Since automatic testing proceeds at high speed andcan be conducted repeatedly in exactly the same way,the time and effort devoted to preparations made

before the first test are well worth wh ile.Simulating is a very important part of the

personnel training. It allows creating situations,similar to those appearing in the real networks. Thishelps operators to improve their skills in safetyconditions and does not require disconnection ofpower plants and big loads in the power system.

2. TESTING RINCIPLESElectric power grid protection systems guard

exJemely valuable equipment, and protective relayequipment plays a vital role in this protection chain.To ensure consistent reliability, protective relayequipment must be checked by testing at regularintervals. These tests must make certain that the

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24th International Spring Sem inar on Electronics TechnologyMay 5-9, 200 1 Calimanesti-Caciulata, Rom aniaprotective relay equipment is operating according toits preset settings. The test equipment supplies therelay protection equipment with inputs thatcorrespond to different faults and different operatingsituations. Pick-up values are ap proached by graduallychanging the magnitudes of these inputs. Quick,selective disconnection in the event of a fault alsorequires correct operating times. These can bemeasured by sup plying the protective relay equipmentwith inputs that exceed by a wide margin the pick-upvalue while simultaneously measuring the time thatelapses prior to tripping. There are two mainprinciples for testing protective relay equipment. Forprimary injection testing, high current is injected onthe primary side of the current transformer. T he entirechain - current transformer, conductors, connectionpoints, relay protection and sometimes circuit breakersas well - is covered by the test. The system beingtested must be taken out of operation during primary

- injection testing (usually conducted in connectionwith commissioning and also when secondary circuitsare not accessible). For secondary injection testing,the protective relay equipment is disconnected fromthe measuring transformers and the circuit breaker.Current is fed directly to the protective relayequipment, and the system being tested does not haveto be taken out of operation. If a relay'scurveskharacteristics are to be tested at many pointsor angles, repeated manual adjustment of the testequipm ent is time consuming . Test equipment that cancondu ct a test automatically in accordanc e with a plandrawn up in advance is much faster and far moreconvenient. Moreover, the time during which theprotective relay equipment is out of operation isminimized and the test can be conducted in exactly thesame way every time it is run.2.1. Achievements in testing

The latest achievem ents use digital technologies indesign of simulators for protective relays testing andmodel the power network and the faults withelectromagnetic transient programmes. This offers theuser flexibility and accuracy in testing. Texas A&MUniversity d esigned su ch a simulator, working in realtime and modeling transients, similar to thoseoccuring in real networks. It allows changes intopology of the network after receiving the trippingsignal from the relay [2]. Such simulators are veryexpensive and may be used in the research andevaluation in the field of power systems, not only forprotective relays testing.

One of the best known systems used not only forfield tests of protective equipm ent but for research aswell is the computer-aided relay testing andsimulation system FREJA [3]. It combines the safe,well-proven and rugged hardware design needed forfield use over a wide temperature range with the

possibilities of intelligent software to perform rapidtesting, simulation and analysis for power systemprotection.

FREJA can generate three voltages and threecurrents, or with the optional external amplifier, sixcurrents. Each ou tput can be varied independently andup to three frequencies can be superimposed inamplitude and phase. Both static and dynamic testingcan be performed such as pre-fault and faultgeneration, simultaneous ramping of several quantitiesand waveForm editing. As a simulator FREJA cangenerate the standard simulations of the FREJA SIMDatabase l ibrary or use e.g. EMTP or COMTRADEfiles as well as edit the wave forms. Several unitsFREJA can be synchronized to simulate a T-l ine orperform end-to-end testing. O ne of the most importantadvantages with FREJA is the user-friendly softwarewhich allows you to select the optimum test procedurefor each type of relay and application. Fo r both simpletesting and comprehensive investigations it isnormally best to test manually or in semi automaticmode. But for protection which requires a largenumber o test points and test loops, i.e. overcurrentprotection and d istance protection, the fully automatictest procedure of FREJA will save both time, troubleand money.2.2. End-to-end testing of protective relay systems

Programma has evaluated a test method for anentire protective relay system. It is d one by connectinga FREJA to each end of one or two power lines, andsynchronize the generation using satellite receivers.The test method was used primarily to verify thecommunication link between items of protective relayequipm ent in the field. It comp rises a fibre optics link,electrical transmission via a route-switchedtelecommunications network or a radio link. Themethod can also be used simultaneously to verifyprotective relay system functions. The method isespecially promising because it can verify modernprotective relay systems that provide longitudinaldifferential protection in situations where thecommunication link is a route-switchedtelecommunication network. T he new method makesit possible to study the behaviour of a protective relaysystem using the communication link's actual settingsand actual time delays. Test results show that the newmethod is very time-effective, and it is considered anexcellent systems-engineering tool for new systems.Moreover, it supports advanced troubleshooting andverification of functions - features heretoforeunavailable in conventional sys tems [3].

3 SOME rESTING METHODSIn static tests. generating sine w ave signals of

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24th International Spring Sem inar on Electronics TechnologyMay 5-9, 2001, Calimanesti-Caciulata, Romania

voltages an d currents with previously set values of theamplitude, phase angle and frequency startsimmediately after the initiating signal and continuesup to the end of the testing without any chan ges.automatically in a previously set.

Overcurrent relays are tested to determine thepickup and dropout values and to measure their triptime. For the first test must be defined the values ofISTART, STOP nd the speed. The current will nowslowly increase until the Pickup value, then thecurrent will dec rease until the Dropou t value, and thenthe hysteres will be calculated.

In the time test first must be selected the fault typewhich will be tested (1-, 2- and 3-phase). Start andstop values of th e current have to be s et too. Then therelay must be fed with the start value of the current,either until the relay trips or until the time has beenelapsed. Then the current increases and the aboveprocedure is repeated, until the current has reached thestop value.

A similar method is used to test a distance relay. Itrequires to choose max impedance IZI, number ofzones, A q for the ramps, start and stop q and the zonetimes. With the start of the test q increases and all thezone boundaries will then be found automatically

In dynamic tests all parameters can be changed

using the time-saving search-half method [3].Point TimePoint Pass

Fig.1Distance relays can also be tested easily andquickly using the RX-instrument. An impedance planethat shows R and X is provided here. Here, the currentand phase angle are previously set and then theimpedance level is varied to see how the protective

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relay reacts. Then the measured time can be read.Each individual measurement can be flagged with aspecial symbol (fig. 1).The so-called whirlwind is an advanced feature ofthe RX-instrument. When activated, the whirlwindscans the entire impedance plane automatically, andeach individual measurement is flagged with a sy mbolwhose appearance depends on the tripping time(fig.2).

I l l I I I I I I

Fig.2

4. RESULTSAs a result of the investigation have beenformulated requirements for design a test unit whichcan perform regular tests of protective relays but it has

to be used in the field of research too.The purpose of the paper is to present the

possibilities of the designed unit in static and dynamictests.The simulator is controlled by a Central ProcessorUnit (CPU), based on the microprocessor MC68008.There is a module D/A consisting six digital-to-analog converters which output signals drive threepower voltage amplifiers and three power currentamplifiers. The tested relay is fed by the outputs ofthese amplifiers. There is a module Digital inputs andoutputs which receives the tripping signal from the

relay. The values of the necessary parameters can beset by the Display module on the front panel of theunit or by a PC via interface Rs232. The blockdiagram of the unit is shown on fig.3.

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24th International Spring Seminar on Electronics TechnologyMay 5-9,2001, Calimanesti-Caciulata. Rom ania

Fig.3In dynamic testing the unit can perform a cycle

consist ing four programm ed segments [4]. For everysegment is necessary to set information for the voltageand current outputs and for the digital inputs andoutputs (fig.4).

Fig.4There are two condit ions for jump to a new

segment:- end of the programmed time duration of the

previous segment (TM);- execution of previously set condition for the

digital inputs.The execution of the programmed cycle startsfrom the segment SI after pressing the button Startfrom the front panel of the u nit. The cycle stops after:- pressing the button Stop from the front panel;

- reac hing a se gm ent with TM =O- execution of the fourth segment.The testing unit offers possibilities for static anddynam ic tests in the following modes:1. Symm etrical system of voltages and currents.In this mode is possible linear or step variation of the

amplitude and phase angle of the three voltages and

three currents sim ultaneously (fig.5).

Fig.52. Non-symmetrical system of voltages and

currents.In this mode is possible linear or step variation of theamplitude and phase angle of every output signalindepend ently (fig.6).

t

Fig.63. Linear or step variation of the frequency of the4. Generation of delta voltage.5 Generation parameter impedance of the6. Generation parameter power.These modes are mostly used for secondary fieldtests at regular intervals during the explo itation of the

relay equipment. For tests in the period of research ofprotective relays and evaluation of a new equipmentare proposed the nex t possibilities allowing simu lationof unusual faults that involve distortion, transients andharmonics:7. Generation of one phase current with anaperiodic component.

output signals.

transmission line.

_i t )= - I cosy exp ~ u I cos@* -vu30 1 I A20

-10-20-30

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24th International Spring Seminar on Electronics TechnologyMay 5-9, 2001, Calimanesti-Caciulata, RomaniaTau is the aperiodic time constant.w s the angle of the p hase voltage.8 . Generation of voltage or current with sine-

quin s the initial value of the phase angle of theF,,, modulation frequency.voltage.

shaped sweepin g of the amplitude.

Protective relay is a part of great importance in thepower system. The reliable function of the systemsin{2nF,,,t arcsin[2Ui,, /(U,,,,, - U m i n ) n / 2 depends strongly on the accurate and selectivereaction of the relay equipment. To ensure thereliability protective relays must be tested regularly, insituations similar to those appearing in real powersystems. Simulators have to feed the inputs of therelays with testing quantities which parameters canvary in wide limits. One of the best devices used allover the world is FREJA. Th e testing unit presented i nthe paper aims to cover many of the functions ofFREJA. In addition its outputs can feed the inputs ofthe older electromechanical relays as well as theinputs of electronic ones. .

U,,, nitial value of the voltage;F,, modulation frequency.80 u,v

-809. Generation of voltage or current with sine-shaped sweeping of the phase angle.

S

REFERENCES[ G.Nimmersjo, Birger Hillstrom, Odd Wemer-Erichsen, GeorgeD.Rockefeller, Digitally-Controlled Real-Time Analog PowerSystem Simulator for Closed Loop Protective Relaying Testing,IEEE Transactions on Power Delivery, Volume 3, Number I ,January 1988[2] M.Kezunovic, et al., Transients computation for Relay TestingIn Real-Time , 9 3 SM-383-0 PWR D IEEE Transactions on powerDelivery, Volume 9 Number 3, July 1994[3] http://www programma se/FREJA3OO Pdf[4] Ovcharov St., St. Vichev, V. Velikov, P. Yakimov, ProtectionRelays Static and Dynamic Testing, Proceedings of the SeventhInternational Conference Electronics'98 , September, 23-2.5.Sozopol, Bulgaria, Book 3, pp.108-113

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