CONTRIBUTIONS TO THE DEVELOPMENT OF DEVICES TO INCREASE SAFETY IN OPERATION OF THE ON-LOAD TAP-CHANGERS OF THE POWER TRANSFORMERS

Transcription

1 U.P.B. Sci. Bull., Series C, Vol. 73, Iss., 011 ISSN x CONTRIBUTIONS TO THE DEVELOPMENT OF DEVICES TO INCREASE SAFETY IN OPERATION OF THE ON-LOAD TAP-CHANGERS OF THE POWER TRANSFORMERS Tieriu CUJBĂ 1, Dorel CERNOMAZU În lucrare se analieaă influenţa olarităţii sau a succesiunii surselor e alimentare asura stailităţii servosistemelor. În veerea moelării matematice a olarităţii sau a succesiunii trifaate se aotă noţiunea e variailă efinită rin intermeiul algerei elementelor trivalente. Se stuiaă mai multe metoe entru contracararea influenţei variailei. Se oţine moelul matematic al convertoarelor e valenţă şi se reintă un stan exerimental entru stuiul mai multor variante originale e iscriminatoare e variailă. Prin utiliarea acestor tiuri e relee se oţine creşterea siguranţei în exloatare a comutatoarelor e reglaj su sarcină e la transformatoarele electrice e utere. This aer examines the influence of olarity or sequence on the staility of suly sources servo-systems. In the mathematical moeling of olarity or three hase sequence is aote the concet of variale efine y the algera of trivalent elements. Various methos to counter the influence of variale are stuie. Converters to otain the mathematical moel of valence an resents an exerimental stan for stuying several variants of the original iscriminatory variale. By using these tyes of relays we achieve imrovements of the safety in oeration of the on-loa-ta-changers of the electrical ower transformers. Keywors: on-loa-ta-changer, safety in oeration, the sequence hase, action evice 1. Introuction To etermine the conitions to increase safety in oeration of the on-loata-changers is necessary to stuy the factors an elements that can give inications aout the technical situation at a time. These factors are mainly mechanical an electrical in nature an shoul e stuie in the context of linking roviers with recommenations roose in technical ooks, for maintenance uring oeration. For examle, recent stuies at the University Politehnica of Bucharest [1] are ase on viration measurements, using an accelerometer an LaView rogram, to etermine the level of wear of the on-loa-ta-changer 1 PhD stuent, Faculty of Electrical Engineering an Comuter Science, University Stefan cel Mare Suceava, Romania, tieriuc@ee.usv.ro Prof., Faculty of Electrical Engineering an Comuter Science, University Stefan cel Mare Suceava, Romania, orelc@ee.usv.ro

2 5 Tieriu Cujă, Dorel Cernomau assemly. The on-loa-ta-changer equis 96% of over 10 MVA transformers. Measurements for etermining the level of wear or efects resulting on-loa-tachanger are as an oortunity ecause they are one of the major suassemlies of the transformers an auto-ower transformers, of the sustations an electrical networks, an statistical analysis of oerational ehavior inicates that the highest ercentage of failure or amage of the transformers an auto-transformers, accoring to research from ICMET Craiova []. Power suly of the action evices of the on-loa-ta-changer when the sequence is olarity reverse can cause amage in many cases, their situation eing further aresse in this article.. Preliminary consierations In Fig.1. it is resente scheule a tyical three-hase motor equie servo-system. It is note that if a normal iet, when oes BD utton an turns 1K contactor C1 cam will move the race L1 limiter, which limits the range of ajustment will lea to the outreak contactor 1K an thus lock the functioning of the action evice in the sense voltage orere y the BD. Consiering the same case, to suly the sequence of hases or incorrect olarity, if ush BD to close contactor 1K, which incorrectly ower suly, will cause y system ownmultilier rotating cam C1 to L limiter. But L limiter it isn t serial in 1K contactor coil circuit an cann t change its status. Therefore servo-system will not e stoe at the limit of travel controlle y BD utton, which causes follow: - reaking the noose kinematic elements (Fig. a); - the cage of some ortions of the regulating wining which will estroy the heat effect an ue to electro-ynamic forces eveloe etween turns, coils an winings (Fig. ); - artial an sometimes total estruction contacts (Fig. c). Fig. 1. Scheule a servo-system equie with a three hase motor

3 Contriutions to the eveloment of evices to increase safety in oeration of the on-loa ta..53 a c Fig.. Damage to on-loa-ta-changer [6]: a) Breaking ro rive; ) Effects of short circuit current on the winings; c) Destruction of resistors, an contacts roken 3. Contriutions to the synthesis schemes rovie with the oortunity to eliminate the influence of ower suly on the correct oeration of servo-systems It s known that staility is etermine y arameters an servo-systems structure for the linear systems an inut arameters an the tye sie for the nonlinear systems [3]. Stuies on servo-systems oeration le to the fining that, esecially for those mounte on moile installations is conitional staility an olarity or three-hase sequence voltage ower suly to action evice. Aot a olar or three hase sequence incorrect result in overrunning extreme oerating range with sometimes serious consequences oth for watching an for installation. With reference to the loa switches tuning voltage of the ower transformers, amage cause y the choice of three hase voltage olarity or sequence of annual rises to values in the millions of lei. Mathematical moeling of three hase sequence of voltage olarity or ower is achieve y aoting the following notion of variale efine y the algera of trivalent elements as follows: Φ = Φ Φ = Φ( 1) = Φ( ) = Φ( 0) = 1 = = 0 - olarity or irect sequence - olarity or reverse sequence - ower is interrute Theoretically, the ossiility of trivalent conversion of variale is confirme y the ivalent Lagrange variale tri-valence [3]. In [4] were erive

4 54 Tieriu Cujă, Dorel Cernomau mathematical moels of the six ossile tyes of converter variale, as follows: = Φ1( 1) L1 = 1 ( ) ( ) = Φ ( ) L = 1 ( + ) Φ (1) 1 + 3( ) = Φ 3( 1) L1 + Φ 3( ) L = 4 ( ) = Φ 4 ( ) L = ( + ) 5 = Φ 5 ( 1) L1 = ( + ) Φ () Φ (3) Φ (4) Φ (5) ( ) = Φ L + Φ ( ) L = Φ (6) Tyes of converters 3 an 4, moele mathematically y functions Φ 3 an Φ are of great ractical. These converters ensures the correct installation, 4 even in terms of olarities or changing the sequence three hase ower suly. If DC sources these converters are mae on the asis of irect an reverse olarity selectors an for three hase source ase on irect sequence an reverse filters. If DC source, the function of the two tyes of converters can e achieve y a Graet rige, although their structure is aarently ifferent from that of converters tye 3 an tye 6 mae in classic fashion. This aer aims to emonstrate that theoretically an ractically, that a Graet rige recovery, can Φ. make a converter tye Φ ( ) an ( ) 3 4 Φ a Φ Fig. 3. Converter "variale " one with rectifier ioes Equivalence can e emonstrate exerimentally foun mathematically from the fact that the simle ioe rectifier is a circuit, Fig. 3, one of valence converter, whose inut sie is the variale associate with the tie at the entrance an exit where sie is a function Φ a, meaning that Φ associate current outut as shown in Tale 1.

5 Contriutions to the eveloment of evices to increase safety in oeration of the on-loa ta..55 Values associate with "variale Tale 1. Meaning current Current Value variale 1 0 Value function Φ a Φ a ( 1 ) = 1 Φ a ( ) = 0 Φ a ( 0 ) = 0 Value function Φ Φ ( 1 ) = 1 Φ ( ) = Φ ( 0 ) = 0 Starting from the ossile values of the function Φ an Φ alying the generalie formula of Lagrange interolation is otaine: = Φ ( 1) L = 1 ( + ) = Φ (7) a a 1 + = Φ ( ) L = ( + ) = Φ (8) + Given the relations (1)-(6) that which Φ a = Φ1 an Φ = Φ shows that a ioe rectifier, eening on connection moe 4 circuit, the converter can erform the functions of the valence converter of tye 1 resectively tye 4. In Fig. 4. is shown the rincile scheme of a recovery Graet rige which is owere y a DC motor. a y Searate excitation D1 a M D D3 D4 ( ) ( ) a Fig. 4. Recovery Scheme Graet: a) Schematic iagram; ) Exerimental Stan If an automatic control system to ower an electric motor three hase as variale acts irectly on the action evice an its control scheme, stuy its influence has focuse on these two items, which are use in any servo-

6 56 Tieriu Cujă, Dorel Cernomau systems. For analysis consiers simlifie scheme of Fig.7. extening the notion of staility of this scheme, the staility conition is limite to the existence of a erfect corresonence etween orer an effect. Electric engine status is shae y trivalent variale Z efine as: 0 Z= 1 engine ile engine rotates to increase the sie of the execution engine rotates execution of ecreasing sie Engine status is a function of state contactors 1C an nc lock moel variale y ; an as the variale. 0 Y= 1 1C an nc contactor triggere 1C lug, nc triggere 1C triggere, nc lug Block contacts status is suject to state control uttons BD an BC shae y trivalent variale ; efine as: when the transfer of energy to 1C an nc contactors coils is interrute 0 = 1 when the transfer of energy to one of the contactors coils 1C or nc is y utton or contact BC when energy transfer to one of the contactors coils 1C or nc is mae with utton or contact BD The utton or contact BC is to increase the sie of the orer of execution, an the BD for the uroses of this ecrease. Status utton can e moelle y BC ivalent variale c = { 0;1 }, an the state of BD y ivalent variale = { 0;1 }, where value 1 corresons to the state in which the two switches or contacts are riven. It notes that: ( y) ( ) Z = f, (9) y = f y = (10)

7 Contriutions to the eveloment of evices to increase safety in oeration of the on-loa ta..57 Accoring to reviously estalishe staility conition reuces to the relationshi: Z = (11) Setting conitions imose scheme of Fig. 5. leas to the next area of Z = f, y ossile values of the function ( ) f (, y) f f f ( 1,1 ) = 1; f ( 1,) = ; f ( 1,0) = 0 (,1) = ; f (,) = 1; f (,0) = 0 ( 0,1) = 0; f (,) = 1; (,0) = 0 f (1) R S T IC nc IC-1 IC- IC-3 BC BD nc-1 nc- nc-3 SM Fig. 5. Simlifie scheme of a ower servo-system Alying the interolation generalie formula of Lagrange: f ( x x... x ) f ( α, α... α ) Lα ( x ) Lα ( x )... Lα ( x ) 1, n 1 n 1 1 αi = 0,1, = n n (13) where f ( α 1, α... α n ) is the ossile values of function f ( x1, x... x n ) an is the olynomial form of Lagrange: L L L 0 1 ( x1 ) = x1 + 1; L0 ( x ) = x + 1;... L0 ( xn ) = xn + 1 ( x1 ) = x1 + x1; L1 ( x ) = x1 + x1;... L1 ( xn ) = x1 + x1 ( x ) x1 + x1; L ( x ) = x1 + x1;... L ( xn ) = x1 + x1 (14)

8 58 Tieriu Cujă, Dorel Cernomau Otain the following equation of state: ( y) = y Z = f, (15) Analying the equation of state (15) aout the conition of staility (11) are foun uner the influence variale, staility can e achieve in two cases namely: - case I, when ower suly is associate with a variale ivalent efine on the fiel = { 0;1 }; - case II, variale ' trivalent efine on the fiel '= { 0;1; } is sustitute y a ivalent function of the form Φ( ) = = { 0;1 }, where equation of state ecomes: ( y) = Φ y Z = f, (16) Bloc for eveloment control '= ( 0;1 ) y = f ( ) = ( 0;1; ) y f = ' y SM Case I = ( 0;1; ) φ = ( 0;1 ) Bloc for eveloment control y = f ( ) = ( 0;1; ) y f = φ y SM Case II Fig. 6. Logical schemes for the two cases The function Φ ( ) = is a hysical moel y converting the variale element in a trivalent '= { 0;1; } an ivalent variale = { 0;1 } is aote the name of the converter valence tri-ivalent. Logical schemes for the two cases are resente in Fig. 6. With reference to case 1, the ower sources, the only that suort an association with variale ivalent are the single hase sources in which case the variale ' is efine as: ' 0 1 for lack of ower suly for the resence of ower suly

9 Contriutions to the eveloment of evices to increase safety in oeration of the on-loa ta Counter influence variale using three-ivalent valence converters It is note that in relations (1)-(6), for trivalent variale, functions Φ ; Φ Φ can take only 0 an 1 values while functions ( ) 3( ) ; Φ5 ; 6 1 ; Φ 4 Φ only values 0 an. For the rolem consiere, is ractical imortant only the first three tyes of converters, whose state equations can e written as: Φ1 = [ ( + )] = [ δ1 ϕ ] Φ ) = [ ( + ) ] = [ δ ϕi ] = [ ( + ) + ( + )] = [ δ ϕ + δ ϕ ] 1 (17) ( (18) Φ i (19) Exressions (17)-(19) assing at the structural form: Φ1 = [ δ1 ϕ ] (0) Φ = [ δ ϕi ] (1) Φ = δ ϕ δ () ( ) [( ( )) ( ( ))] 3 1 ϕ A logical scheme which are shown in Fig. 7, Fig.8 an Fig.9. In the revious exressions δ are trivalent constant efine as: δ 1 = 1 δ = δ δ 3 = 0 when shaing a ortion of the circuit, the energy transferre without shae or olarity three hase sequence of voltage network when a ortion of the circuit moel, which transferre ower without olarity or shae-hase sequence voltage network when a ortion of the circuit is interrute or when circulate homo-olar sequence currents Consiering the values an functions ϕ ( ) an = otain: ϕ for = 1 an ϕ () 1 = 1 ; ϕ ( ) = 0 ; ϕ i( 1 ) = 0 ; ϕ i( ) = 1. Therefore it is conclue that the element shae function ϕ = +, an the element shae function = + is a iscriminating variale = 1 ϕ is a iscriminating variale =. These are iscriminating variale P simle action equie with only one inut an only one outut control (Fig.8 an Fig.9). i

10 60 Tieriu Cujă, Dorel Cernomau Functions ϕ ( ) an ϕ no hysical sense for = 0 a fact confirme i y ractice. Analying the mathematical moel of the converter tye valence 3, that it is equivalent to two transucers of tye 1 an oerating in arallel, which is exresse y: ϕ3 = ϕ1 ϕ (3) The aove equalliy is ossile ecause of its roerties of the Lagrange formula. for trivalent variale. A tye 3 converter can e achieve either y two searate iscriminating in which one for variale = 1 an another for variale = or acting with a iscriminatory with comine action (equie with only one imut an two outut control), wich encomassing the functions of the two iscriminating with a simle action (Fig.9). φ1 ( ) δ ϕ = 1 ϕ = + δ1 =1 δ1 ϕ Fig. 7. Valence converter tye 1 φ δ ϕ = i ϕ i = + δ = δ ϕ i Fig. 8. Valence converter tye

11 Contriutions to the eveloment of evices to increase safety in oeration of the on-loa ta..61 φ [ δ ϕ + δ ϕ ] 3 = 1 i ϕ = + δ 1 =1 δ1 ϕ OR ϕ i = + δ = δ ϕ i Fig. 9. Valence converter tye 3 6. Conclusions 1. Recovery scheme Graet connecte etween a DC ower suly an DC motor ensure its correct olarity regarless of the fluctuation of ower suly olarity.. In Fig. 10. is resente a servo-system equie with relay for a correct three hase voltage suly, ase on mathematical moel of valence converter tye 3 (logical scheme of Fig.9), which was conucte in laoratory EMAD of University Ştefan cel Mare Suceava [6]. There is an electromagnetic relay of variale with action comine [7], that imroves the simlifie scheme of a ower servo-system resente in Fig. 7. With this moel, the irection of rotation, of the evice a Fig. 10. Servo-system equie with relay for a correct three hase voltage suly: a) Schematic iagram; ) Exerimental Stan.

12 6 Tieriu Cujă, Dorel Cernomau of the on-loa-ta-changer of the ower transformer, remains unchange if the ower suly three hase sequence change. We create an other moels of the relays for a correct three hase ower suly, for examles in [8] an [9]. Notice, making the electronic rotection relay [9], we use, among other comonents, two triggers Schmitt ecause the outut of the Schmitt trigger remains constant if the inut stays elow (or aove) some critical threshol (thanks to Otto Schmitt an American scientist, he invente a simle electronic circuit) [10] an [11]. R E F E R E N C E S [1] S. D. Grigorescu, Cercetări rivin iagnoa reventivă a comutatoarelor e reglaj su sarcină in transformatoarele e mare uterere (Research on reventive iagnosis uner on-loa-tachangers in high ower transformers) Raort e cercetare, Universitatea Politehnică Bucureşti, Revista e Politica Ştiinţei şi Scientologie, Număr secial, 005 [] D. S aceroţianu, Contriuţii la erfecţionarea echiamentelor şi tehnologiilor e monitoriare şi iagnosticare a transformatoarelor e utere (Contriutions to the imrovement of equiment an technologies for monitoring an iagnosis of ower transformers), Teă e octorat, Universitatea in Craiova, Facultatea e Inginerie în Electomecanică, Meiu şi Informatică Inustrială, 010 [3] I. Bejan, Gherghina Balaan, Automatiări şi telecomeni în electroenergetică (Automation an remote control in the electricity), Eitura iactică şi eagogică, Bucureşti, 1976 [4] N.V. Boţan, Comana sistemelor e acţionare electrică (Buy electrical rive systems), Eitura tehnică, Bucureşti, 1977 [5] D. Cernomau, Contriuţii la realiarea unor transformatoare entru reglarea continuă a tensiunii su sarcină (Contriutions to achieving continuous regulation of voltage transformers for loa), Teă e octorat, I.P.Iaşi, Facultatea e Electrotehnică, 199 [6] T.O. Cujă, Contriuţii teoretice şi exerimentale reliminarii în omeniul creşterii siguranţei în exloatare a transformatoarelor electrice e utere (Contriutions heoretical an exerimental reliminaries on imroving safety in oerating ower transformers), Referat II în carul stagiului e regătire entru octorat, Universitatea Ştefan cel Mare Suceava, Facultatea e Inginerie Electrică şi Ştiinţa Calculatoarelor, 010 [7] T.O. Cujă, D. Cernomau, Releu e rotecţie entru alimentarea cu tensiune trifaată corectă (Relay rotection for ower suly the correct hase), Cerere e Brevet e invenţie A/00694 in , OSIM Bucureşti [8] T.O. Cujă, D. Cernomau, Releu e rotecţie îmotriva alimentării cu tensiune trifaată incorectă (Relay rotection against incorrect hase voltage suly), Cerere e Brevet e invenţie A/00696 in , OSIM Bucureşti [9] T.O. Cujă, Releu electronic e rotecţie (Electronic rotection relay), Cerere e Brevet e invenţie A/00695 in , OSIM Bucureşti [10] Otto Schmitt, A Thermionic Trigger, Journal of Scientific Instruments 15 (January 1938), University College Lonon,. 4-6 [11]