Cong 2008005

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Abstract - The controlled switching of circuit breakers has shown

to have a highly satisfactory performance for the reduction ofelectric transients in the electrical grid while maneuvering circuit

breakers. A controlled switching device was developed for theutilization in the energization and de-energization of unloaded

transmission lines as well as in the disconnection and subsequentenergization of unloaded power transformers. The device was

developed using a DSP (Digital Signals Processing) system whichresulted from an R&D project between the University of SãoPaulo and the Electric Power Utility Company ECTE (EmpresaCatarinense de Transmissão de Energia S.A.) that belongs to the

TBE (Transmissoras Brasileiras de Energia) group.

Index Terms – Circuit breaker controlled switching, Trans-

former Inrush Currents Elimination, Overvoltage, COMTRADE,DSP

I. INTRODUCTION

Controlled switching is usually utilized by electronic devicesso as to facilitate the contact operations of the switchingequipment on a predetermined point in relation to a referenceelectric signal.The monitoring of the opening refers to the contact separationcontrol technique of each pole of the circuit breaker in relationto the current phase angle, thus, controlling the arc time tominimize the stresses in the power system components.Similarly, these stresses can be minimized by using the con-trolled switching for monitoring the closing time in relation tothe system voltage waveform.Such controllers are used for the interruption of small induc-tive currents, switching of capacitor banks and transmissionlines as well as in the energization of power transformers.This paper will deal with the closing time control of circuitbreakers for the maneuvers described next:

• energization and de-energization of the 525 kV transmis-

sion line linking Blumenau and Campos Novos;• energizaton of the third 525/230 kV Blumenau transformer.

In the cases of energization and de-energization of transmis-

J. A. Jardini – Polytechnic School of Universidade de São Paulo, Depart-

ment de Engineering, Energy and Electric Automation – ( [email protected])Ronaldo P. Casolari – Polytechnic School of Universidade de São Paulo,Department de Engineering, Energy and Electric Automation –([email protected])

Gerson Y. Saiki – Polytechnic School of Universidade de São Paulo, De-partment de Engineering, Energy and Electric Automation –([email protected])

Mario Masuda – Polytechnic School of Universidade de São Paulo, De-partment de Engineering, Energy and Electric Automation – ([email protected])

L. C. Magrini – Polytechnic School of Universidade de São Paulo, De-partment de Engineering, Energy and Electric Automation –([email protected])

Rogério M. Jacobsen - Transmissoras Brasileiras de Energia (TBE)([email protected])

sion lines, the objective of the controlled switching is to re-

duce the overvoltages resulting from those maneuvers. As forthe power transformers energization, the objective is to reducethe inrush currents that appear following its energization.Also, the basis and development specification of a controlledswitching device utilizing a digital signals processing (DSP)system will be presented.The controlled switching device was developed for the Blu-menau substation at ECTE. The system components in redcolor, shown in Fig. 1, pertain to the ECTE Company.

Figura 1 -

ECTE System (C. Novos/Blumenau 525 kVTransmission Line and the third power transformer)

A. Energization of the Transmission Line

The controlled switching device will be used for energizationof unloaded transmission line. The studied line links Blu-menau and Campos Novos and has 252.5 km of extension at525 kV. The circuit breaker used in the substation of Blu-menau is monopolar.The time when the voltage passes through zero, will presentthe least overvoltage in the circuit breaker.

B. De-energization of the Transmission Line

The system used for the de-energization of unloaded transmis-sion line was the same case of line energization (figure 1).As there are no special devices to drain the residual load at the

opening of the transmission line, the maneuvering is made inpresence of residual loads in the three phases. After the open-ing of the transmission line, the device determines the polarityof the residual loads in each individual phase. The best de-energization times are the voltage peaks at the source side.The polarity of those peaks must be the same as the residualload in each individual phase.

C. Transformer Energization

The controlled switching of transformers has the objective ofreducing the inrush currents that appear when the transformer

Point-on-Wave Controller Developed for

Circuit Breaker SwitchingJ. A. Jardini, R. P. Casolari, G. Y. Saiki, M. Masuda, , L. C. Magrini, R. M. Jacobsen

978-1-4244-1904-3/08/$25.00 ©2008 IEEE

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is energized. By choosing appropriate times for energizationof the transformer, there will be a great reduction of thosecurrents that are responsible for the harmonic generation,stress in some equipments and bad operation of protectionsystems.The present project used the energization strategy that takesinto account the residual flux resulting from the precedentopening. Within that strategy, the delayed energization wasused. The first phase to be energized is the one with greaterresidual flux in absolute value. This is advantageous because itallows the energization at low values of the source voltage,imposing a less voltage stress in the transformer at the energi-zation time. That phase is energized at the time in that theresidual flux is equal to the prospective flux of that phase. Theprospective flux is the one that would exist in each phase incase of absence of the desenergization.For the remaining phases, different approaches can be used toreduce or to eliminate the core saturation, taking the net andthe circuit breaker characteristics into account. An approachthat has been studied and applied with success is the closing ofthe two remaining phases at the same time, some half-cyclesafter the passage through voltage zero of the first phase, once

the residual flux in the other two phases is eliminated quicklyin some cycles and a flux occurs called dynamic, which is theflux generated by the energization of the first phase. In a realapplication, a delay of 4.5 cycles has been used with success.Based on the methodology of the delayed energization, theproject adopted as follows:"Initial Energization of the phase with greater residual flux (inabsolute value) at the time in that the residual flux is same asthe prospective one. The 2 remaining phases will be closedafter 4.5 cycles, simultaneously, when the dynamic flux is thesame as the prospective one."The residual and dynamic fluxes are obtained through thevoltage integration beside the 525 kV of the transformer soon

after the circuit breaker. Thus, the prospective flux is obtainedthrough the voltage integration beside the source, in otherwords, before the circuit breaker.

II. CONTROLLED SWITCHING DEVICE

A. Hardware Architecture

The selected hardware for the controlled switching device has,as a basic characteristic, the capacity to support the acquisitionand treatment of at least 320 samples per cycle of six analogi-cal channels in a way to provide an inferior error to 20 electricdegrees.

Those requirements are not complied by most of the com-

mercialized industrial computers, which led to the develop-ment of a hardware based on the C6000 technology of TexasInstruments. From that DSPs family, the TMS320C67x gen-eration was chosen, whose 32-bit processor operates at 225MHz and incorporates resources of floating point. The manu-facturer commercializes a "starter kit" denominatedTMS320C6713 DSK, which was used as a basis for the hard-ware development.

This TMS320 family is built on the VelociTI architecture.It presents a high performance architecture and very longinstructions (VLIW) developed by Texas Instruments, which

make of these devices an excellent choice for multichanneland multifuction applications, ideal for applications of highperformance through a parallelism growth increase.

The CPU core of the TMS320C6713 platform consists of 8functional units (two multipliers and six ULAs) and 32 generalpurpose recorders with words of 32 length bits. These devicesare developed with a data memory and with an on-chip pro-gram that can be set up as cache memories. The peripherals

include improved controllers for direct access to the (EDMA)memory, power-down logic, interfaces for external memories(EMIF), multichannel buffered serial ports (McBSP), hostinterface (host-port) (HPI) and timers.

The TMS320C6713 DSK kit has 16 Mbytes of SDRAMand 512 Kbyte flash and has a dedicated busbar (busbarEVM), through which several input and output peripherals canbe linked. Through this busbar high-speed AD converters canbe linked operating at up to 2Mhz of acquisition per channel,and up to four channels. Specific circuits with several ADconverters can also be mounted as well as digital inputs, digi-tal outputs, and also interfaces of serial communication ofhigh-speed.

The TMS320C6713 DSK kit incorporates besides the proc-essor, devices required by DSP, such as, feeding circuit, tim-ers, external memory, among others, providing the possibilityof optimized execution of the project. This processing plat-form also includes audio input and output, connected to a 16bits audio codec, parallel port for communication with thecomputer and connectors for the connection of expansionplates.

They were incorporated to the analogical and digital inter-face plates kit that provides six inputs under voltage (0 to130Vac) and six isolated current inputs (4 to 20ma) besidessixteen opto-digital inputs coupled dry contact type, and sixdigital voltage outputs implemented through IGBT's (InsulatedGate Bipolar Transistor). These six outputs power the openingreels and closing of each circuit breaker poles.

The IGBTs are interconnected to the DSP through opticalcoupling, which should be connected to an external source ofup to 125Vcc for powering of loads with current of up to 25Amperes. The IGBT switching time is about 50 to 100 micro-seconds, however the time in order for the operation current toset down depends on the load to be energized.

B. Software Architecture

The programming is made in C language, through a tool ofthe manufacturer denominated Code Composer. This tool runsin MS Windows environment enabling the development and

debugging of the code in high environment level, with re-sources for compilation of the code source developed andunloading of the binary code generated for the DSP via USBport.

The developed software uses functional parameters, con-stant and processing keys that are stored in flash and are re-covered in the beginning of the processing. It was developedin Visual Basic; a set-up tool that enables the user, in a laptopor interlinked PC to the DSP via serial port, to consult or alterany values of the parameters or coefficients of the formulaswithout the need to understand the DSP particularities nor its

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memory mapping (figure 2).The openings or closings led by the equipment have an al-

gorithm summary, as well as the wave form of the voltagesand currents along the maneuvering, registered for later analy-sis. The wave form can be later extracted and saved inCOMTRADE format, in the user's machine, through the set-upprogram.

Figura 2 -

Set-up program screen

C. Algorithm

In order to minimize the transitories resulting from the cir-cuit breakers powering maneuvers, there is a need that theyoccur in certain intervals of voltage angle (for each phase).The first parameter considered in the algorithm of the systemis the interval of the angle of the voltage of each phase, so thatthe switching time of each pole of the circuit breaker is locatedwithin the intervals of the voltage angle. For the powering tooccur within these specified intervals, the opening and closing

times were considered (operation times) of the circuit breakerssupplied by the manufacturer.Additionally, the circuit breakers operation time, independ-

ent of the interruption system and of the type of operationmechanism, varies depending on certain service parameters:• With the control voltage reduced in the reel of the circuit

breaker, there is less available energy to change the com-mands of electric control for a mechanical action. The op-eration is prolonged independently. (Valid for all types ofdrivers);

• Altering the hydraulic pressure in the hydraulic drivers, a

change in the available energy occurs in order to executethe switching movement;

•

The environment temperature is the most complex influ-ence parameter. The electric resistance of the operationreels, the viscosity of the oil and the SF6 gas pressure aredependent of the temperature. Besides, there is expansionof the powering rods and porcelains. All these parametersinfluence the operation time of different modes.

In an extreme condition, each of these 3 parameters can al-ter the operation time in milliseconds order. The compensationof the variation of these parameters was also considered in thealgorithm of the system. Each of these parameters is moni-tored through sensors associated to the system.

In regard to the energization algorithm of the transmissionline, as verified in simulations to the 3 phases, they should beclosed in the interval of the voltage wave within -30º and +30ºof each phase, central value equal to 0º, in other words, at thetime in which the voltage in each phase is going through zero(sinusoidal wave). For the identification of the passagethrough zero, with positive derivative, the moment in that an nreading is bigger than zero and the readings n-1 and n-2 are

smaller or same to zero is identified.The powering of the circuit breaker can be requested in anypoint of the voltage wave, through an external command.Starting from this command, the system will identify the mo-ment of the passage through zero of the voltage wave of oneof the system phases beside the source. In relation to this in-stant, the moment in that the circuit breaker must be poweredwill be calculated, taking the circuit breakers nominal opera-tion time into consideration, compensated with the serviceparameters presented previously. The nominal operation time,corrected according to the current conditions, can be consid-ered as a delay that should be counted so that the opening orclosing is really concluded at the moment of the passage

through zero of the voltage wave. The same procedure is madefor the other phases taking the difference in phases of 120º and240º into account.

As for the de-energization of the transmission line (WithoutReactor) the best times for de-energization occur when thevoltages in the side source, in each phase, reach the values ofthe residual voltages of the respective phases, with an accept-able interval of ±30º around this excellent value. In this casethe voltage of a system phase is monitored beside the source,as well as the voltages in the three phases of the system besidethe line (before and after the LT opening). Based on this prem-ise, the controller calculates the necessary delay times for eachphase to be de-energized in the excellent point of the voltagewave. Also taking into account the additional times related tothe circuit breaker operation and to the operation voltagevariations of the closing reel, the oil pressure and of the envi-ronment temperature.

In the Transformer Energization, the excellent moment oc-curs when the magnetic fluxes beside the transmission line(prospective) and beside the transformer (residual) are thesame, for the phase that presents larger residual flux in abso-lute value. And the two remaining phases should be energized4.5 cycles after the first phase, simultaneously.

The magnetic flux is proportional to the integral voltage, toavoid displacement in relation to zero. The voltage integration

must start at the moment in that it is at its maximum, and,therefore the magnetic flux is zero. For the identification ofthe maximum voltage instant, a similar function to the identi-fication function of the passage through zero is used. Thefunction basically determines the moment in which the signalpresents a superior value to 90% of the maximum value veri-fied in the previous cycle, and in which the voltage (n+1)<voltage (n) and voltage (n-1) <voltage (n).

The calculation of the excellent instant also takes into ac-count the additional times related to the operation of the cir-cuit breaker and to the variations of the voltage of the closing

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reel operation, the oil pressure and the environment tempera-ture.

D. Acquired signals

The DSP analogical ports are connected to the followingsubstation signals:

• Voltage in Pole A, in busbar B of the substation be-

side the Transmission Line• Voltage in Pole A, in busbar beside the high voltage

of the transformer• Voltage in Pole B, in busbar beside the high voltage

of the transformer• Voltage in Pole C, in busbar beside the high voltage

of the transformer• Signal AC representing the unloaded current of the

transformer in phase A.• Signal DC from 4 to 20mA representing the hydrau-

lic pressure in Pole A• Signal DC from 4 to 20mA representing the hydrau-

lic pressure in Pole B•

Signal DC from 4 to 20mA representing the hydrau-lic pressure in Pole C

• Signal DC from 4 to 20mA representing the envi-

ronment temperature• Signal DC from 4 to 20mA representing the Auxil-

iary Service Voltage.

The voltage inputs and alternating current are acquired at a20 kHz rate per channel, while the ones from 4 to 20 MA areswept at a 1 kHz rate per channel.

The following digital information is collected at a 1 kHzfrequency per channel;

•

Contact Condition 52A (NA) of the Circuit breaker• Contact Condition 52B (NF) of the Circuit breaker• Contact Condition 52A (NA) of the Circuit breaker

• Contact Condition 52A (NF) of the Circuit breaker

• Closing Command Condition given by the User to

the Circuit Breaker• Closing Command Condition given by the User to

the Circuit Breaker

The developed equipment also offers a port for synchroni-zation with a unique time base according to the IRIG B stan-dard.

III. TESTS

Initially powering simulated tests in laboratory, without thephysical presence of a circuit breaker, stimulating the switch-ing device starting from a giga of tests, and using some of thedigital inputs of the device to indicate the change of conditionof the opening and closing IGBT outputs. These inputs wouldbe normally used to verify the status of the circuit breakers.

Once linked to the equipment, the developed software iscontinually collecting all of the analogical and digital signals,

but only save the samples once the circuit breaker poweringcommand is detected.

Figura 3 -

Test in the Blumenau substation

The analogical and digital greatness of interest are regis-tered starting from the command for the beginning from themaneuver up to the alteration of the contacts 52 a and b of thecircuit breaker, which signalize the end of the operation.

Later tests were made in field, in the Blumenau substation,with the objective of verifying the precision of the algorithmsof the system during the opening and closing operations of thecircuit breaker DJ1050 (Alston FX500KV) that belongs to theTransmission Line that links Blumenau to Campos Novoscircuit breaker and half set-up). This test was made with theunloaded circuit breaker, in order to avoid that bad eventualoperation of the device that could cause disturbance in the

substation.In a first moment the measures made by the sensor ones

were validated comparing them with the values originatingfrom other sensors already existent in the substation. Severaltests were accomplished for gauging the mathematical modelsthat determine the times of closing and opening of the circuitbreaker in real conditions of operation in field.

As example one of the tests is introduced for the closing ofthe circuit breaker. In figure 1, the times corrected for theclosing of each of the poles are presented, calculated by thedevice.

After verifying the coherence between the closing andopening times, calculating from the greatness measured by thesensors, a closing test was accomplished for the verification ofthe powering instants of the IGBTs, and the results registeredin the COMTRADE file, susceptible to be analyzed by anysoftware and upon the oscillographics produced by otherequipments of SE.

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Table 1- Powering Times

Greatness Device

Pressure in Phase A (Bar) 361,9258

Pressure in Phase B (Bar) 356,1741

Pressure in Phase C (Bar) 360,9806

Auxiliary Service Voltage (V) 132,26

Environment Temperature (Celsius) 32,58

Phase A Closing Time (µs) 19340,14

Phase B Closing Time B (µs) 19650

Phase C Closing Time (µs) 19274,17

Figure 4 presents the oscillographics regarding the accom-plished test, the tables presented are related to phase A voltage(the source side); voltages of phases A, B and C (the transmis-sion line side); hydraulic pressures of the poles of phases A, Band C; environment temperature and feeding voltage of circuit

breakers powering reels. As onc can observe in the oscil-lographics related to the test, after the duration of the maneu-ver calculated for pole A (19.34 ms), a passage through volt-age zero occurred in pole A. The duration has as an initialreferential, the powering instants of the IGBT's, which werehighlighted in the oscillographics presented. Regarding theother phases the respective powering difference in phases of120º and 240º were verified.

As one can observe in the oscillographics regarding thetest, after the duration of the maneuver calculated for pole A(19.34 ms), it happened a passage for the voltage zero in thepole A. The duration has as an initial referential the poweringinstants of the IGBT's, which were highlighted in the oscil-lographics presented. Regarding the other phases the respec-tive powering difference in phases of 120º and 240º wereverified. .

IV. CONCLUSIONS

The project of circuit breakers powering lasts for fouryears, which is in the beginning of the third year, with thedevelopment and tests of the device prototype for closingmaneuvers. The equipment is being submitted to performancetests and validation to evaluate the adherence of the imple-mented mathematical models. The subsequent phase of the

project will contemplate maneuvers of the circuit breaker innormal operation conditions, complementing the necessaryrequirements for complete approval of the powering device.

Figura 4 -

Circuit breaker closing test

V. REFERENCES

[1] WG 13.07 “Controlled Switching of HVAC Circuit Breakers: Guide forApplication Lines, Reactors, Capacitors, Transformers”, Part 1,ELÉCTRA No. 183, Pages 43 – 73, 1999.

[2]

WG 13.07 “Controlled Switching of HVAC Circuit Breakers: Guide forApplication Lines, Reactors, Capacitors, Transformers”, Part 2,ELÉCTRA No. 185, Pages 35 – 37, 1999.

[3] H. Ito “Controlled Switching Technologies, State-of-the-Art”, Transmis-sion and Distribution Conference and Exhibition 2002: Asia Pacific.IEEE/PES, Pages 1455 – 1460, Vol. 2, 2002

[4] J. H. Brunke, K. J. Fröhlich “Elimination of Transformer Inrush Cur-rents by Controlled Switching. Part I: Theoretical Considerations”, IEEETransations on Power Delivery, Volume: 16, Issue: 2 ,April 2001,Pages: 276 – 280.

[5] J. H. Brunke, K. J. Fröhlich “Elimination of Transformer Inrush Cur-rents by Controlled Switching. Part II: Application and Performance

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Considerations”, IEEE Transactions on Power Delivery, Volume: 16, Is-sue: 2, April 2001, Pages: 281 – 285

[6]

Rocha, A. C. Carvalho, J. L. Távora “Manobra Controlada: Modelagemda Suportabilidade Dielétrica do Disjuntor Durante a Operação deFechamento”, XIV SNPTEE, Belém, Brasil, 1997

VI. BIOGRAPHIES

José Antonio Jardini (M’ 1966, SM’ 1978, F’ 1990) was born in São Paulo,Brazil, on March 27th, 1941. He graduated from Escola Politécnica daUniversidade de São Paulo in 1963 (Electrical Engineering). From the sameinstitution he received the MSc, PhD, Associate Professor and Head Professordegrees in 1971, 1973, 1991 and 1999, respectively. For 25 years he workedfor Themag Engenharia Ltda., a leading consulting company in Brazil, wherehe conducted many power systems studies and participated in major powersystem projects such as the Itaipu hydro plant. He is currently Head Professorat Escola Politécnica da Universidade de São Paulo, where he teaches powersystem analysis and digital automation, and where he leads the GAGTDgroup, which is responsible for the study and development of automationsystems in the fields of generation, transmission and distribution of electricity.He represented Brazil at SC-38 of CIGRÉ and is a Distinguished Lecturer ofIAS/IEEE.

Ronaldo Pedro Casolari graduated in Electric Engineering at the Escola deEngenharia Mauá in 1972. He received the MSc in 1996 at the Polytechnic

School of São Paulo University. Had his professional development at consult-ing companies, with projects in the area of power electric systems for compa-nies as Itaipu, Eletronorte, Furnas, Chesf, Cesp and others, with systemsplanning, coordination of insulation and electric transitory. At present worksas a consultant at Sao Paulo University with electric transmission and distribu-tion projects.

Gerson Yukio Saiki was born on March 30, 1970, graduate in electricalengineering for the Polytechnic School of the University of São Paulo in1997. He obtained his title of Master in electrical engineering for the sameinstitution in 2001. Currently he works in “GAGTD – Group of Automationof the Generation Transmission and Distribution of Electric Power”, in theDepartment of Energy and Automation of the Polytechnic School of theUniversity of São Paulo.

Mario Masuda was born on June 25, 1948 in Tupã, São Paulo, Brazil. Hereceived his B.Sc. degree in Electrical Engineering from the Polytechnic

School at the University of São Paulo, in 1973. From 1973 to 1991, he waswith Themag Eng. Ltda working in the area Power Systems and Automation& Transmission Lines projects. From 1991 to 1997, he worked independentlyexecuting projects, supervising and teaching courses related to the installationof fiber optic cables in transmission lines (OPGW). From 1997 to 2002, heworked at Furukawa and Constructions Ltd., with the latter activities.Presently, he works as a researcher at GAGTD in the Polytechnic School atthe University of São Paulo.

Luiz Carlos Magrini was born in São Paulo, Brazil, on May 3 rd, 1954. Hegraduated from Escola Politécnica da Universidade de São Paulo in 1977(Electrical Engineering). From the same institution he received the MSc andPhD degrees in 1995 and 1999, respectively. For 17 years he worked forThemag Engenharia Ltda, a leading consulting company in Brazil. He iscurrently a researcher at Escola Politécnica da Universidade de São Paulo -GAGTD group.

Rogério Moreira Jacobsen not avaible.

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