CA1175097A - Method for limiting voltage across series-connected thyristors of high-voltage rectifier - Google Patents
Method for limiting voltage across series-connected thyristors of high-voltage rectifierInfo
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- CA1175097A CA1175097A CA000387830A CA387830A CA1175097A CA 1175097 A CA1175097 A CA 1175097A CA 000387830 A CA000387830 A CA 000387830A CA 387830 A CA387830 A CA 387830A CA 1175097 A CA1175097 A CA 1175097A
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- Prior art keywords
- voltage
- thyristors
- series
- rectifier
- level
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Classifications
-
- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
- H02M1/00—Details of apparatus for conversion
- H02M1/08—Circuits specially adapted for the generation of control voltages for semiconductor devices incorporated in static converters
- H02M1/088—Circuits specially adapted for the generation of control voltages for semiconductor devices incorporated in static converters for the simultaneous control of series or parallel connected semiconductor devices
-
- H—ELECTRICITY
- H03—ELECTRONIC CIRCUITRY
- H03K—PULSE TECHNIQUE
- H03K17/00—Electronic switching or gating, i.e. not by contact-making and –breaking
- H03K17/08—Modifications for protecting switching circuit against overcurrent or overvoltage
- H03K17/081—Modifications for protecting switching circuit against overcurrent or overvoltage without feedback from the output circuit to the control circuit
- H03K17/0814—Modifications for protecting switching circuit against overcurrent or overvoltage without feedback from the output circuit to the control circuit by measures taken in the output circuit
- H03K17/08144—Modifications for protecting switching circuit against overcurrent or overvoltage without feedback from the output circuit to the control circuit by measures taken in the output circuit in thyristor switches
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- Engineering & Computer Science (AREA)
- Power Engineering (AREA)
- Power Conversion In General (AREA)
- Rectifiers (AREA)
- Heterocyclic Carbon Compounds Containing A Hetero Ring Having Oxygen Or Sulfur (AREA)
- Emergency Protection Circuit Devices (AREA)
Abstract
METHOD FOR LIMITING VOLTAGE ACROSS SERIES--CONNECTED THYRISTORS OF HIGH-VOLTAGE REC-TIFIER
Abstract of the Disclosure The method according to the invention for limiting vol-tage across series-connected thyristors of a high-voltage rectifier as a voltage surge is applied thereto consists in limiting voltage across groups of series-connected thyris-tors with a specified number of thyristors in a group, which is selected to suit the voltage surge parameters. For this purpose, voltage is measured across the thyristor next to the point to which the voltage surge is applied, and then across the following thyristors. When voltage across the first thy-ristor raises to a preset level, total voltage across the thyristors is successively measured, starting from the first thyristor, until it reaches a level equal to the ratio bet-ween the voltage surge amplitude and the total number of series-connected thyristors of the rectifier, multiplied by the number of thyristors giving the preset total voltage level which corresponds to the number of thyristors in the group.
Voltage across the group is limited to this level.
Abstract of the Disclosure The method according to the invention for limiting vol-tage across series-connected thyristors of a high-voltage rectifier as a voltage surge is applied thereto consists in limiting voltage across groups of series-connected thyris-tors with a specified number of thyristors in a group, which is selected to suit the voltage surge parameters. For this purpose, voltage is measured across the thyristor next to the point to which the voltage surge is applied, and then across the following thyristors. When voltage across the first thy-ristor raises to a preset level, total voltage across the thyristors is successively measured, starting from the first thyristor, until it reaches a level equal to the ratio bet-ween the voltage surge amplitude and the total number of series-connected thyristors of the rectifier, multiplied by the number of thyristors giving the preset total voltage level which corresponds to the number of thyristors in the group.
Voltage across the group is limited to this level.
Description
~7S~)9~
~it~e o~ the I~vention M~HûD ~OR ~IMITING VOI~AG~ ~ROSS S~I~ GO~;C~:13iD
~RIS~OP~S O~ HIG~I-VOI~[!AGE R~
Field of the In~erltion The inverLtion relates ~o con~erter equipment and, more particula;rly, to a method ~or limiting voltage a~ross ~sries--conn~cted thyristors OI a htgh-v~o~tage recti~ier.
The invexLtion is applicabic to the desi~Ling of high--voltage thsrristor reGtiIiers for d.c.tran~missîon li~es.
:E3aakgrowld of the In~entio:~
~ he n7~mber of serîes~conDected thyr~tors incorp~rated in a high-~oita~e th;~ristor rectifier is selected with du~
reg~rd for their charact~ristics and a maximum ~mplitude of a ~oltage surge which may ~ct upo~ tha rectifier i~ transient conditions arising whsn-'the 1~sulatio~ o~ a converte~ sub~
station o~ a d.c.transmission line breaks do~ ~nd the ~ino is short~d to the ~round.(c~ Ablaycv et al., ~'~lectriches-kiye stan~s~L, seti i ~ystemy. ûsno~niye technicheskiye p~o~
blemy peredachi electroenerghii postoyamlyrn tokom vy~okogo napryazheniya" /I'Power Stations,Networks ~nd Sgst~m~: ~he Ba-sic ~echnica~ ~robloms of High-~o~tage d~c.~ransmission~
Moscow,VI~I~I,1972,ppO158-159)0~h~ stra~ capacitan~ o~ the elements of the high-vo~tage recti:Eie.r iæ grounded~as a r~su~t, the amplitude of the ~ol~a~e sur~,e and the ra~e at ~l7h;c:h it irlcreases ar~ not egually dividcd betwee~ the thyristors, whereIore a voltage surge across a~ dividual thyxistors may be abo~e a permissible level~he greater ~ha ~umb~r o~
series-conn~cted thyristors a:rld the m~g~tude o~ stra;y capa-cita~ce OI the rectifier7 g e~eme~ts7 th~ mo:ca non-uniform ~L~lL75~9~
th~ division become~ (cf. ~corgil~et, 'IUpravlyayamige e~c-tricheski~e ~rentili i ikh primeneni~e" /"Contro~ed :E~ecti~iers and ~heir App~ications?'/, Moscow, 1971, pp. 153-155).
The ac~ion GI a vol~age surge upon thyristors is mitiga-ted by designing a recti:Eier so as to equalize the distributi-on of the amplibude o~ the voltage surge ana the rate of it~
i~crease among the iIldividual thyristors incorporated i~ the rectifier~ point to whirh volta~;e is ~pplied is an impor tant co~sideration in the se~ection of a recti~ier desig3:l.
In a multibridge rectifier, high~voltag~ rectifier ce~s of the upper bridge~ have to with~tatld the ~ ects oî pulsed vol-tage o~ both polarities both on the side OI the a~ode a~d c athode.
~ n incre~se i~ ~oltage a:nd a reduced number oî bridges in a d.c.transmission line ~ead~ to a~ increase in the amp~i-tude o~ puls~d ~oltage acting on the high volta~e rectifier~7 conseque~tly~ it necessita~es the U5~ 0~ a ~reat~r num~er o~
s~rie~-connected thyristor~ A good rectifier design provide~
~or a more or less uni~orm division of ~oltage among th~
thyri~tors, which, in tur~, mak~s it pos~ible to r~duce th~
number o~ thyristors.
~ here i~ known a high-voltage t~yristox Dectifi0r ~cf~
A~Y~Stukachov et al~ E~ectriches~iye stantsii, s~ti i s~s~
t~ 13lectropereda~hi postojan~ym to~om ~.7ysokogo napryazhe--ni;ya'~ Power Stations, N~tworks a~d Systems~ Eigih-Voltag~ doc~
~ra~smission ~ es"/, ~oscow, VI~I~I, 1978/ p,. 44) wh~rei~
puls~d vo~tage i~ distributed among group~ o~ th;yrisl;~rs with the Qi~ of compensa-tio~ capacitors co~ected i:~ para~lel with ~ ~'7 the thyristors~ Within a group of thyri~tor~ th~ a~plitud~
o~ ~ol-tage acros~ the thyri~tors and tho ra~e of increase in the vo~tage are distributea with the aid o~ a reac-tor co~nec-ted ln series with the thyristors o~ the group and damping capacitors connec~ed in paral~el with each th~ris-torO B~cau-se o~ a small number of series co~nected thyristors in the group, the no~-uni~ormity o~ pu~sed vo~tag~ division is ncg-ligib~e.
With this mod~ of a doub~e voltage division, a minimum number of series-csnnected thyristors i~ calculated from this formula:
where E is the pulsea voltage amplitude;
U1 is the permissible ~oltage acros~ the thyristor;
is the vo~t~ge di~ision non-uni~ormitg;
E1 is a coef~ioien~ i~dicatin~ an incroa~e in ~oltage due to series con~ection of a reactor a~d damping capacitors in a group.
~ he rlumber of lih~yristors ca~culated from (1 ) is greater tharL the number of th;s~ristor~ in the case o:~ a uniform voltage distribution b~ an = U~ K1 ~ 1). In practice, ~ is in the rarlge o~ 101 ~ 1~72,~ a~d K1 is i~ the x~ge of ~1~.05 * '1.15.
~aking this into accou~t, olle can see ho~lv non-uniform voltag~
dlvisio~ determines the number of series-co~nected th~ristors, as compared to uni~orm voltage divisio~:
~, n ~ 15 ~ 3~3%~
~'75 0 ~ 7 Clearly~ such an increase in the num~er o~ th~ri~tors is a serious disadvanta~e o~ high~o~ta~e th~xistor recti~iers feat~ring a double division of pulsed voltageO
A high-voltage matri~ incoxporat~d in a high-~ol~ag~
th~ristor rectifier manu~actured by General Electric ~c~
U~ Patent Spe¢i~ication No 3,626,271 ~or a high-voltage d.c.
~tri~) ~imits voltage across the thgristors and protects them ~rom steep-edge voltages. ~he matrix contai~s ~our thyristors~
protective RC circuits and reactorsO One o~ the protectiYe elements is a capacitor which shunt~ some resistors i~ the RC ci-rcuits of the two middle th~ristor~ whene~er a dangerous vo~tage surge occurs.
~ gr~ater part o~ the pulsea voltage is ~pplied to ~he two extreme t~ristors o~ the matri~. As the vo~tage reaches a threshold le~el, these thyristors are switched on through the circuit in which the reactors are incorpo~ated. ~he s-teep--edge voltage a~ro~s the reactors is added to the pu~ed volta-ge acro~s the extreme thyri~tor~ w~ich are ~wi~ched, becauæe the rate o:f increase in the voltage across the~e thyri~tors i s above ~he critical 1eYe1. ~he numb~r o~ thyristors in a rectifier composed oî ~erie~-co~ected d.c.ma~rices correspond~
to a uniform pulsed volta~e distribution. How~er~ some o~ the thyristors are ~witched on at a ~imiti~g ~roltage level, wh~ch tells o~ the reliability oî thesa th~ri~tors~ ~oth~r disadv~-tages resides in the ~a¢t that th~ oth~r thyristor~ are ~witch ed on at a critical vol~age increase li!at~l9 d~J~dt. The th~srris-tors have to b~ highl~ sen~itive to dU/dt wi~h small dif~ersn-ces în thi~ respec~ bet~een individual thyristors. It is ~uite;
1~75~ 7 hard to meet thi~ condi~ion with a ~arge ~umber o~ thyristors.
The lat~t ~tudie~ of the dynamic ~tability o~ thyristor~ poin~
to a considerable increase in dU/dt; -thus it b~comes clear that dU/dt cannOt be u~ed, because it is extrem~ly difficu~t to co~trol this parameterO In the ~inal analysis, th~ protec-tion o~ a high~voltage rectifier from pulsed vo~tages is such that it leads to a switch-on of the whole recti~ier. HowevQr, a switching on o~ a rectifier at a wron~ moment af~ects normal switching o~ the con~rter brid~e and has an adverse effect on the power transmisqion line~-Thexe is known a device for protecting seri~s-connectQd thyristoes (cf. USSR Inventor~s Certi~icata ~o 244~489)o In this dJvice 9 each thyristor is conn~cted to a circuit compo-ssd o~ two ~valanche diodes connected in opposition~ Voltage surges acros~ the thyristor are limited by the avalanche diode~. It is highl~ probable, howe~er, that with a larg~
number o~ ~eries-connected thyristors some of them receive no con~rol pUlSe8; such th,yristors remai~ switGhed o~f, and the current o~ all the rectifier flows through their avalanche diodes. ~aturally9 this leads to a~ overheating and breakdo~n of the a~ala~che diodes, which ma~ turn9 lead to an igni~
tion o:~ the rectifier~ q!he avalanche diodes can be protected by using their aval~ncho current to driv~ the th~ristor~ which are out of control into conduction (c~. US Patent Speci~ication No 3,662,250 for a device to prot~ct thyristors from volta~;e surges)~ Howe~er, the number of th~i~tors has to be increased by a quanti-ty sufficien~ to rule out a switch~ng on of the -- 6 ~
S~7 rectifier in case o~ a voltage surge; the total number of th~ristors must also be increasea by a quan~ity which i9 SU~
cient to take care o~ the di~erences in the operation thre~holds of the avalanche diodes.
~ he same di~adv~tages are obse~ed in a thyristor cir-cuit (cf. US Pate~t Specificatioll ~o 394~7~261) in which pro-tection from vo~tage surges is ePf~cted with the aid o~ a ~ast-response discharger co~ected in p~rallel with each th~-ristor.
~ echnical literature (CI. Ab~a;ye~ et a~, "131ectriches-kiye stantsii, s~ti i systemy9 Osnovniy~ technichoskiye prob-lemy peredachi electroenergii pos~oyann~m tokom ~ysokogo ~apryazheniya" :"Power Stations~ Ne-two~ks and S~stem~ the Basic ~echnical Prob~ems o~ High-Voltage d.cO~ransmission"/, Mosoow, VI~I~Ig 1972~ de~cribes a re¢tifier in which voltage across the thyristors is ~imited by dividi~g RC circuits.
~hsse circuits ca~ be replaced by av~lanche diode~. A line reactor i~ cox~ected in series with the hi~;h-~roltage recti-~ier. Whe~ pulsed voltage i3 app~ied o~ the side of the re~c-tor, the latter reduces the rate o~ increase o~ voltage ac-ross the ractifier, whereb;y vo~tage is more uniform~y divided among the th~ torsl. However9 this lead~ to an i~craase of voltage dua ~o operation o~ the reactor a~d RC circuits co~-nected ther~toO Voltag~ can be reduced b3r a limiter coImected in paralle~ with the rectificr a~d having ~ upper opexation thre~hold egua1 to the puls~d vo:~tage a~p~itud~. In this case the coefficient ~ (1) is ~qual to U~lityj ~hersb~ the num~
ber OI thyristors i~ reduc~d b~ 5 to 15 per cent, a~ co~pared ~75~ 7 to the number OI thyristors rcquired when no ~imiter is used.
The plcture is guite di~er~nt when puls~d ~roltage is app7i-ed on the side opposite to the reactor. The reactor is remota ~rom the rectiIier' s circuit which is guite e ~*e~ded; for thes~ r~asons,, th~ reactor onl~ plays a minor ro~e in r~du-cing the rapidl~ incr~asing voltage; -this accou~s for a great non-uni~rmity OI dividing the pulssd voltage amplitude.
According to (1), such a situation necessitates the use of a greater numb~r o~ seri~s-connected thy~istors. I~ order ~o conEine voltage acros~ the th;yristors to permisæible levels, ~he operation throshold OI the limiter must be lower th n the pulsed ~a~e a~plitude. ~his condition c~not be me~, however, due to th~ effects UpOLl tho lim~ter o~' voltages across the rec-tiIier in normal and switching conditio~s.
US Patent Speci:Eication l~o 3,508,135 is conce~ned with a device wherein protection from pulsed vo~;~age is eIfect~d by ~imiting vo~tage across groups of series-cormected thyristor~
with the aid o~ avala~che diodes conrl~¢ted in ~ llel with the~e ~roups. Voltage limitation is e~fect~d at a ~e~l U
which i~ low~r than the sum to-tal o~ minimum switchin~ volta~e~
of ~ thyristor~, but greater than the ma~imum anode switching voltage o~ one thyristor of the group, i.e~
Um~ Umin~ (2) Thus it is assumed that an ~valanche diode, connected i~
~aral~l with a group of ~ thyristors and h~ving a ~o~tag~
limitatio~ level which satis~ies the condition of ~2), is a guarantee of permissible vo~tages across the th~ri~to~s of the ~'75 ~ ~7 group. However~ if pulsed voltage is applied to a high-voltage rectifier compri~ing s~veral hundred ~eries-connected thyxis-tors, the division o~ this voltag~ among the thyri~tors i~
~ery ~ar from being uniform. Volt~ges are above the permissib-le level at the thyristors close to the poi~t where pu~sed voltage is applied, whereas they are lowex acro~s o~her th~ris-tor~. At an in~tant voltage acros~ a group is limited by an a~alanche diode, the sum total of vo~tages across the th~ris-tors of -this group may be greater than a value a~ which volta-ges across the most heavily loaded thyristors are no-t in excess of permissible levels. ~et ot be assumed that a group o~ ~
thyri~tors i~ connected to a limiter with UII = 0.9-N-U1,which i~ in keeping with (2). The voltage scross the hea~iest-load thyristor is designated as UIIIO
UII
UIII = - 9 where ~ i~ the degree o~ ~on-uni~ormi~y 4~ voltage divi~ion.
With ~ = 1.2, U~ 1.08-UI, ~hich mea~s that U~
abo~e the permi~ible level and may be ~he cause o~ a breakdown of the -thyri~tor. ~o avoid ~uch a situation, one must eith0r increase the number Q~ th~ristor~ in the group or reduce the ~ol~age limita~ion level. On the other ha~d~ i~ limitation o~
voltage across the heavie~t-loadea th~ristors i~ con~ined to parmissible levels and if the number o~ th~ristor~ in ths group is selected at random, the protection level of the recti~ier must be equal to the total voltage limit~tion lev~l o~ the rectifier's diodesO It is commonly b~lieved th~t the prot~ction lsvel of a high-voltage recti~ier mu3t be equal to a maximum _ g _ s~
amplitude of a pulse wave which may act upon the rectifier. If the total limitation level of khe diodes is above the maximum pulse wave amplitude, this means that the rectifier is designed for higher voltages and is, t'nerefore, more expensive. It is impermissible that the total limitation level of the diodes should be below the maximum wave amplitude, because this may be the cause of breakdowns in long-term operation.
Thus the use o-E conventional methods for limiting voltage across a group consisting of any number of series-connected thyristors is no guarantee against thyristor breakdowns and against impermissibly high overvoltage protection levels.
It is an object of the present invention to provide a method for limiting voltage across series-connected thyristors of a high voltage rectifier, which would help reduce the number of series-connected thyristors, while maintaining the protection level of the rectifier.
It is another object oE the invention to provide a method for limiting voltage across series-connected thyristors of a high-voltage rectifier, which would improve the reliability of the rectiEier.
In accordance with a particular embodiment of the invention there is provided a method ~or llmit-ing voltage across series-connected thyristor,s of a high-voltage rectifier as a voltage surge is applied to the latter. The method includes the steps of measuring the voltage across the thyri.stor next ko the point where the voltage surge is applied across the following thyristors. The total voltage across -- 1~ --3L~75[)5~7 the thyristors is successively measured as voltage across the-first thyristor reaches a specified level.
The successive measuring is started with the first thyristor, and the measuring continues until ~he total voltage reaches a level equal to the ratio between the voltage surge amplitude and the total number of the series-connected thyristors of the rectifier multiplied by the number of thyristors giving the total voltage. Voltage across groups of series-connected thyristors is limited with a specified number of thyristors in each of the groups.
The number of thyristors in each of the groups is selected in keeping with the number of thyristors and the total voltage. Voltage across each-of the groups of thyristors is limited with the number of thyristors to the level.
The method according to the invention for limiting voltage across series-connected thyristors of a high-voltage rectifier makes it possible to reduce the number of thyristors and improves the reliability of rectifiers.
Other objects and advantages of the present invention will become more apparent from a consider-ation of the following detailed description of a preferred embodiment thereof, taken in conjunction with the accompanying drawings, wherein:
FIG. 1 is a time plot of voltages across a group of thyristors and each individual thyristor at a moment when the high-voltage rectifier is acted upon by a voltage surge, which plot also shows the level to which voltage across the yroup is limited through the use of the method according to the invention, 75~9~
~ IG~ 2 is a functional dia~am of a devic~ ~or carr~-ing out the method accordin~ to the inv~ntion for limiting voltage across series-connected -thyri~tors o~ a high-volta~a recti~ier;
FIG~ 3 ~s a plot o~ a pulse wave distri~ution among groups o~ thyri~tors o~ a hi~h-voltage xectifier whe~ ~oltage across the thyristors is limited by the m~tho~ according to the invention.
Detailed Description of the Invention he method according to the invention for ~imiting ~ol-tage across ~eries-connected thy~istors of a high-vo~tage recti~ier co~sists i~ limiting voltage across groups o~ series--connected thyristor~ with a speci~ied number of th~ristors in each group. ~he number OI thyristors in a group is æe~ected to suît voltage surge paramebers. ~or this purpose, voltag~
i5 measured acrosæ the thyris~or ne~t to the poi~t w~ere a vo}tage surge is applied. When voltage acroæs the ~irst thyristor raises to a speci~ied level, total ~oltag~ acro~s the thyristor~ is succe~lv~y measured, startlng ~rom the first th~ristor, until it reaches a ~evel equal to the ratio be~ween the volta~e ~urge amp~itude and the total number o~ s~rie~-connected thyristors of the rscti~i~r, mu~tiplied b~ the number o~ thyri~tor~ giving th~ speci~ied total voltage corresponding to the num~er of th~ristors in the group. Vol-tage across the group is th~ limitaa to this ~avel, In most cases vol~age e, ~hich ~cts upo~ the xacti~ier,may be rsprese~ted to a csrtain degr~e o~ appro~imation by a wave with a known amplitude ~ (curve I o~ ~IG~ 1) a~d a dura-tion ~ o~ lts obliqu~-angled ed~e~ Curve II repre~c~t~ vol-tage across a group of ~ thgristors. C~urves III, IV ... ~T
represen-t voltage acros~ individual thyristo~s of the group~
A speci~ied voltage UI acros~ the hea~iest-loaded thyris~
tor is reached at a~ in~tant to (curv8 III). As poi~ted out abovea at this instant one calculates the sum total o~ vo~ta-ges acros~ the thyri~tors, ~tarting from the first o~e. I~
U~ ~ E ~ ~, where n i5 the total num~er of thyristors is the rectifier~ voltage is limited acro~s a group of 1~ thy-ri~tor~. ~ha limitation ~e~el is equal to tha wave amplitude divided b~ the number ~n of the groups. This rules out a si tuation when ~ UN ~ En ~ N~ i~e. when voltage across the hea~iest-loaded thyristor i~ above a permi~siblY level~ In addition, the total ~imitation lavel guarantee~ a reoti~ier protaction level equal bo the pulse wave amplitude.
~ he ~ollowing description re~ers to a pre:farred embodi-ment o~ the mqthod according to the i~vantio~, app~ied to a recti~ier int~nded for d~c. tran~mi~sio~ ~he xectl~iex comp-rises n ~erie~-conne¢ted thyrlstors 11~ 12~ , each connected ~n parallel with a respecti~e damping RC circuit 21 - 319 22 ~ 32' - 2~ - ~. An anode reactor * i~ connec-ted in serie~ with t~e rectifier. ~he circuit cont~ining th~
rectifier and reactor 4 is a~ arm of a co~erter bridge.
A non-line arre~t~r 5, ~hich det~rmine~ the protect~on l~vel of the rectifierf is connocted in parallel with the abo~e-men-tion~d bridge ~rm. Conn~cted ~ par~llel with the xectifier is an arrester whlch in the simp~e~t ca~e compri~es ~imitsrs - ~3 -V~l7 61~ 62~ ha ope~atio~ threshold o~ aach o~ th0limiters 61 through 6~ i~ selected to bs equa~ to E/~.
Outputs o~ the limiters 61 through ~ are connected to (n - 1) input~ of a switchi~g unlt 7 which in the gener~
case may have ~ - 1) outputsO ~ccording to the inve~tion, the ~.~umber o~ thyrîs~ors in a group and ~he lev~l to which vol~age acros th~ group i8 limited are detsrmin~d a~
~ollows~
Vo~tmeters 81~ 82~ o~ measure ~o~tages across tho thyrist~xs 11, 12, ..., 1N and s~d signals to a switching unit 9 which con~ects outputs of the voltmeters 81t 82, -, 8N to i~puts o~ a computing unit 10 whan volta$e across the heaviest-~oaded thyristor 11 raisès to a specified lev21.
~ h~ computing unit 10 calculate~ the num~er ~ of thyri-stors, the sum total ~ of voltages across -khe th~ristors a~d UII = E N; it also comp æes th~e valu~s. If these va~ues are equal ~a certain speoified degree of error is not exc~uded)~
a si~nal i~ produced whi¢h is proportional to the numb~ N of thyristors. ~he ~ignal is tr~nsmit~ed ~o the switching unit 7 which connects outputs o~ groups of ~ ~imit~r~ ~o those oP th~
groups of ~ th~ristors. ~he vol~meters 8~, 8~, ..., ~ , the witching units 7 ~nd 9 a~d th~ computing unit ~0 may be of type k~own to those s~illed i~ the art.
~ he method acco~din~ to the i~ven~ion make~ it possible to divide a r~ctifier înto ~ groups o~ thyristor~. ~IG~ 3 showæ a distribution o~ a pul~e w~ve e amon~ groups o~
thyristorsO The pulse wave e is applied on the side opposite .. ~ 1*
5~
to the reactor 4 (FIG. 2~ h~ r~actor 4 i re~ote ~rom the poi~ ~v which the pulse wave i~ app~ied7 50 ib~ e~ct on the wave di~tribution is insigni~ica~t. ~h~ pulsed vol-tage is represented by an oblique-angled wave with an ampli-tude E (~I~. 3) and edge duration ~. During the tim~ int~r-~al O~ ~, voltage across several groups o:~ th~ristors, for example, U1 and U2, reache~ the limitation le~ /Mo Accor-ding to ~IG. ~, the limitars of the ~'irst an~ ~¢ond group~
are actuated at insta~s t1 and t2. Operation of the limi-ters lasts ~or only ~ ~raction o~ ~ ~ Within the time i~t~r-val O~ ~ voltage across other remote groups9 ~u¢h as UM (~IG.
3), does not reach the limitation level. ~rom instant ~9 ~oltages U1 and U2 drop below the E/~ level which is r~ached again duri~g the time in~erval tM ~ t~'o Without tho limiters 61 (~IG. 2), 6~ olta~e across the groups would change as shown by the broken lines in FIG. ~. At instant ~, voltagos U1 and U2 would be above the limitation level~ ~he increase in voltag~ could only be compensated by increasi~g the number o~ th,yristors. A slngle ~-~evel limiter connected in parallel with the rectifier as a whole cabbot reduce U1 and U2, because at instant ~ vo~tage UB acro~s the recti~ier is be~ow the limitatio~ level El Such a limit~r on~y e~imina~
tes an i~crea~e of ~oltage across the recti~ier due to read-justme~ts in the ~ loop~ A ~imita~ion level below E is impermissible i~ long-term operation~
~ he method according to the invention ~or ~imiti~g vol-ta~;e across series-connected th~ristors OI a hig~L-voltage recti~ier o~ a d.c. transmission line, makos it possible to 5~5~7 reduce thQ number of thyristors in a recti~ier co~plet~ hcontrol~ protection, sign~ling and cooling system~ ~he method improves the reli~ y of recti~iers~ because vo~-tage across the thyristors can nev~r rise abo~ the permis-sible leve~O In addition~ the method according to the i~Yen-tion ~or limiting voltage across ~roups o~ thyristors is such that a rsctifier can n~ver be ~wit¢hed on at a volt~ge surgz amplitude, which would otherwisq affsct normal switching of a converterls recti~ier~:
~it~e o~ the I~vention M~HûD ~OR ~IMITING VOI~AG~ ~ROSS S~I~ GO~;C~:13iD
~RIS~OP~S O~ HIG~I-VOI~[!AGE R~
Field of the In~erltion The inverLtion relates ~o con~erter equipment and, more particula;rly, to a method ~or limiting voltage a~ross ~sries--conn~cted thyristors OI a htgh-v~o~tage recti~ier.
The invexLtion is applicabic to the desi~Ling of high--voltage thsrristor reGtiIiers for d.c.tran~missîon li~es.
:E3aakgrowld of the In~entio:~
~ he n7~mber of serîes~conDected thyr~tors incorp~rated in a high-~oita~e th;~ristor rectifier is selected with du~
reg~rd for their charact~ristics and a maximum ~mplitude of a ~oltage surge which may ~ct upo~ tha rectifier i~ transient conditions arising whsn-'the 1~sulatio~ o~ a converte~ sub~
station o~ a d.c.transmission line breaks do~ ~nd the ~ino is short~d to the ~round.(c~ Ablaycv et al., ~'~lectriches-kiye stan~s~L, seti i ~ystemy. ûsno~niye technicheskiye p~o~
blemy peredachi electroenerghii postoyamlyrn tokom vy~okogo napryazheniya" /I'Power Stations,Networks ~nd Sgst~m~: ~he Ba-sic ~echnica~ ~robloms of High-~o~tage d~c.~ransmission~
Moscow,VI~I~I,1972,ppO158-159)0~h~ stra~ capacitan~ o~ the elements of the high-vo~tage recti:Eie.r iæ grounded~as a r~su~t, the amplitude of the ~ol~a~e sur~,e and the ra~e at ~l7h;c:h it irlcreases ar~ not egually dividcd betwee~ the thyristors, whereIore a voltage surge across a~ dividual thyxistors may be abo~e a permissible level~he greater ~ha ~umb~r o~
series-conn~cted thyristors a:rld the m~g~tude o~ stra;y capa-cita~ce OI the rectifier7 g e~eme~ts7 th~ mo:ca non-uniform ~L~lL75~9~
th~ division become~ (cf. ~corgil~et, 'IUpravlyayamige e~c-tricheski~e ~rentili i ikh primeneni~e" /"Contro~ed :E~ecti~iers and ~heir App~ications?'/, Moscow, 1971, pp. 153-155).
The ac~ion GI a vol~age surge upon thyristors is mitiga-ted by designing a recti:Eier so as to equalize the distributi-on of the amplibude o~ the voltage surge ana the rate of it~
i~crease among the iIldividual thyristors incorporated i~ the rectifier~ point to whirh volta~;e is ~pplied is an impor tant co~sideration in the se~ection of a recti~ier desig3:l.
In a multibridge rectifier, high~voltag~ rectifier ce~s of the upper bridge~ have to with~tatld the ~ ects oî pulsed vol-tage o~ both polarities both on the side OI the a~ode a~d c athode.
~ n incre~se i~ ~oltage a:nd a reduced number oî bridges in a d.c.transmission line ~ead~ to a~ increase in the amp~i-tude o~ puls~d ~oltage acting on the high volta~e rectifier~7 conseque~tly~ it necessita~es the U5~ 0~ a ~reat~r num~er o~
s~rie~-connected thyristor~ A good rectifier design provide~
~or a more or less uni~orm division of ~oltage among th~
thyri~tors, which, in tur~, mak~s it pos~ible to r~duce th~
number o~ thyristors.
~ here i~ known a high-voltage t~yristox Dectifi0r ~cf~
A~Y~Stukachov et al~ E~ectriches~iye stantsii, s~ti i s~s~
t~ 13lectropereda~hi postojan~ym to~om ~.7ysokogo napryazhe--ni;ya'~ Power Stations, N~tworks a~d Systems~ Eigih-Voltag~ doc~
~ra~smission ~ es"/, ~oscow, VI~I~I, 1978/ p,. 44) wh~rei~
puls~d vo~tage i~ distributed among group~ o~ th;yrisl;~rs with the Qi~ of compensa-tio~ capacitors co~ected i:~ para~lel with ~ ~'7 the thyristors~ Within a group of thyri~tor~ th~ a~plitud~
o~ ~ol-tage acros~ the thyri~tors and tho ra~e of increase in the vo~tage are distributea with the aid o~ a reac-tor co~nec-ted ln series with the thyristors o~ the group and damping capacitors connec~ed in paral~el with each th~ris-torO B~cau-se o~ a small number of series co~nected thyristors in the group, the no~-uni~ormity o~ pu~sed vo~tag~ division is ncg-ligib~e.
With this mod~ of a doub~e voltage division, a minimum number of series-csnnected thyristors i~ calculated from this formula:
where E is the pulsea voltage amplitude;
U1 is the permissible ~oltage acros~ the thyristor;
is the vo~t~ge di~ision non-uni~ormitg;
E1 is a coef~ioien~ i~dicatin~ an incroa~e in ~oltage due to series con~ection of a reactor a~d damping capacitors in a group.
~ he rlumber of lih~yristors ca~culated from (1 ) is greater tharL the number of th;s~ristor~ in the case o:~ a uniform voltage distribution b~ an = U~ K1 ~ 1). In practice, ~ is in the rarlge o~ 101 ~ 1~72,~ a~d K1 is i~ the x~ge of ~1~.05 * '1.15.
~aking this into accou~t, olle can see ho~lv non-uniform voltag~
dlvisio~ determines the number of series-co~nected th~ristors, as compared to uni~orm voltage divisio~:
~, n ~ 15 ~ 3~3%~
~'75 0 ~ 7 Clearly~ such an increase in the num~er o~ th~ri~tors is a serious disadvanta~e o~ high~o~ta~e th~xistor recti~iers feat~ring a double division of pulsed voltageO
A high-voltage matri~ incoxporat~d in a high-~ol~ag~
th~ristor rectifier manu~actured by General Electric ~c~
U~ Patent Spe¢i~ication No 3,626,271 ~or a high-voltage d.c.
~tri~) ~imits voltage across the thgristors and protects them ~rom steep-edge voltages. ~he matrix contai~s ~our thyristors~
protective RC circuits and reactorsO One o~ the protectiYe elements is a capacitor which shunt~ some resistors i~ the RC ci-rcuits of the two middle th~ristor~ whene~er a dangerous vo~tage surge occurs.
~ gr~ater part o~ the pulsea voltage is ~pplied to ~he two extreme t~ristors o~ the matri~. As the vo~tage reaches a threshold le~el, these thyristors are switched on through the circuit in which the reactors are incorpo~ated. ~he s-teep--edge voltage a~ro~s the reactors is added to the pu~ed volta-ge acro~s the extreme thyri~tor~ w~ich are ~wi~ched, becauæe the rate o:f increase in the voltage across the~e thyri~tors i s above ~he critical 1eYe1. ~he numb~r o~ thyristors in a rectifier composed oî ~erie~-co~ected d.c.ma~rices correspond~
to a uniform pulsed volta~e distribution. How~er~ some o~ the thyristors are ~witched on at a ~imiti~g ~roltage level, wh~ch tells o~ the reliability oî thesa th~ri~tors~ ~oth~r disadv~-tages resides in the ~a¢t that th~ oth~r thyristor~ are ~witch ed on at a critical vol~age increase li!at~l9 d~J~dt. The th~srris-tors have to b~ highl~ sen~itive to dU/dt wi~h small dif~ersn-ces în thi~ respec~ bet~een individual thyristors. It is ~uite;
1~75~ 7 hard to meet thi~ condi~ion with a ~arge ~umber o~ thyristors.
The lat~t ~tudie~ of the dynamic ~tability o~ thyristor~ poin~
to a considerable increase in dU/dt; -thus it b~comes clear that dU/dt cannOt be u~ed, because it is extrem~ly difficu~t to co~trol this parameterO In the ~inal analysis, th~ protec-tion o~ a high~voltage rectifier from pulsed vo~tages is such that it leads to a switch-on of the whole recti~ier. HowevQr, a switching on o~ a rectifier at a wron~ moment af~ects normal switching o~ the con~rter brid~e and has an adverse effect on the power transmisqion line~-Thexe is known a device for protecting seri~s-connectQd thyristoes (cf. USSR Inventor~s Certi~icata ~o 244~489)o In this dJvice 9 each thyristor is conn~cted to a circuit compo-ssd o~ two ~valanche diodes connected in opposition~ Voltage surges acros~ the thyristor are limited by the avalanche diode~. It is highl~ probable, howe~er, that with a larg~
number o~ ~eries-connected thyristors some of them receive no con~rol pUlSe8; such th,yristors remai~ switGhed o~f, and the current o~ all the rectifier flows through their avalanche diodes. ~aturally9 this leads to a~ overheating and breakdo~n of the a~ala~che diodes, which ma~ turn9 lead to an igni~
tion o:~ the rectifier~ q!he avalanche diodes can be protected by using their aval~ncho current to driv~ the th~ristor~ which are out of control into conduction (c~. US Patent Speci~ication No 3,662,250 for a device to prot~ct thyristors from volta~;e surges)~ Howe~er, the number of th~i~tors has to be increased by a quanti-ty sufficien~ to rule out a switch~ng on of the -- 6 ~
S~7 rectifier in case o~ a voltage surge; the total number of th~ristors must also be increasea by a quan~ity which i9 SU~
cient to take care o~ the di~erences in the operation thre~holds of the avalanche diodes.
~ he same di~adv~tages are obse~ed in a thyristor cir-cuit (cf. US Pate~t Specificatioll ~o 394~7~261) in which pro-tection from vo~tage surges is ePf~cted with the aid o~ a ~ast-response discharger co~ected in p~rallel with each th~-ristor.
~ echnical literature (CI. Ab~a;ye~ et a~, "131ectriches-kiye stantsii, s~ti i systemy9 Osnovniy~ technichoskiye prob-lemy peredachi electroenergii pos~oyann~m tokom ~ysokogo ~apryazheniya" :"Power Stations~ Ne-two~ks and S~stem~ the Basic ~echnical Prob~ems o~ High-Voltage d.cO~ransmission"/, Mosoow, VI~I~Ig 1972~ de~cribes a re¢tifier in which voltage across the thyristors is ~imited by dividi~g RC circuits.
~hsse circuits ca~ be replaced by av~lanche diode~. A line reactor i~ cox~ected in series with the hi~;h-~roltage recti-~ier. Whe~ pulsed voltage i3 app~ied o~ the side of the re~c-tor, the latter reduces the rate o~ increase o~ voltage ac-ross the ractifier, whereb;y vo~tage is more uniform~y divided among the th~ torsl. However9 this lead~ to an i~craase of voltage dua ~o operation o~ the reactor a~d RC circuits co~-nected ther~toO Voltag~ can be reduced b3r a limiter coImected in paralle~ with the rectificr a~d having ~ upper opexation thre~hold egua1 to the puls~d vo:~tage a~p~itud~. In this case the coefficient ~ (1) is ~qual to U~lityj ~hersb~ the num~
ber OI thyristors i~ reduc~d b~ 5 to 15 per cent, a~ co~pared ~75~ 7 to the number OI thyristors rcquired when no ~imiter is used.
The plcture is guite di~er~nt when puls~d ~roltage is app7i-ed on the side opposite to the reactor. The reactor is remota ~rom the rectiIier' s circuit which is guite e ~*e~ded; for thes~ r~asons,, th~ reactor onl~ plays a minor ro~e in r~du-cing the rapidl~ incr~asing voltage; -this accou~s for a great non-uni~rmity OI dividing the pulssd voltage amplitude.
According to (1), such a situation necessitates the use of a greater numb~r o~ seri~s-connected thy~istors. I~ order ~o conEine voltage acros~ the th;yristors to permisæible levels, ~he operation throshold OI the limiter must be lower th n the pulsed ~a~e a~plitude. ~his condition c~not be me~, however, due to th~ effects UpOLl tho lim~ter o~' voltages across the rec-tiIier in normal and switching conditio~s.
US Patent Speci:Eication l~o 3,508,135 is conce~ned with a device wherein protection from pulsed vo~;~age is eIfect~d by ~imiting vo~tage across groups of series-cormected thyristor~
with the aid o~ avala~che diodes conrl~¢ted in ~ llel with the~e ~roups. Voltage limitation is e~fect~d at a ~e~l U
which i~ low~r than the sum to-tal o~ minimum switchin~ volta~e~
of ~ thyristor~, but greater than the ma~imum anode switching voltage o~ one thyristor of the group, i.e~
Um~ Umin~ (2) Thus it is assumed that an ~valanche diode, connected i~
~aral~l with a group of ~ thyristors and h~ving a ~o~tag~
limitatio~ level which satis~ies the condition of ~2), is a guarantee of permissible vo~tages across the th~ri~to~s of the ~'75 ~ ~7 group. However~ if pulsed voltage is applied to a high-voltage rectifier compri~ing s~veral hundred ~eries-connected thyxis-tors, the division o~ this voltag~ among the thyri~tors i~
~ery ~ar from being uniform. Volt~ges are above the permissib-le level at the thyristors close to the poi~t where pu~sed voltage is applied, whereas they are lowex acro~s o~her th~ris-tor~. At an in~tant voltage acros~ a group is limited by an a~alanche diode, the sum total of vo~tages across the th~ris-tors of -this group may be greater than a value a~ which volta-ges across the most heavily loaded thyristors are no-t in excess of permissible levels. ~et ot be assumed that a group o~ ~
thyri~tors i~ connected to a limiter with UII = 0.9-N-U1,which i~ in keeping with (2). The voltage scross the hea~iest-load thyristor is designated as UIIIO
UII
UIII = - 9 where ~ i~ the degree o~ ~on-uni~ormi~y 4~ voltage divi~ion.
With ~ = 1.2, U~ 1.08-UI, ~hich mea~s that U~
abo~e the permi~ible level and may be ~he cause o~ a breakdown of the -thyri~tor. ~o avoid ~uch a situation, one must eith0r increase the number Q~ th~ristor~ in the group or reduce the ~ol~age limita~ion level. On the other ha~d~ i~ limitation o~
voltage across the heavie~t-loadea th~ristors i~ con~ined to parmissible levels and if the number o~ th~ristor~ in ths group is selected at random, the protection level of the recti~ier must be equal to the total voltage limit~tion lev~l o~ the rectifier's diodesO It is commonly b~lieved th~t the prot~ction lsvel of a high-voltage recti~ier mu3t be equal to a maximum _ g _ s~
amplitude of a pulse wave which may act upon the rectifier. If the total limitation level of khe diodes is above the maximum pulse wave amplitude, this means that the rectifier is designed for higher voltages and is, t'nerefore, more expensive. It is impermissible that the total limitation level of the diodes should be below the maximum wave amplitude, because this may be the cause of breakdowns in long-term operation.
Thus the use o-E conventional methods for limiting voltage across a group consisting of any number of series-connected thyristors is no guarantee against thyristor breakdowns and against impermissibly high overvoltage protection levels.
It is an object of the present invention to provide a method for limiting voltage across series-connected thyristors of a high voltage rectifier, which would help reduce the number of series-connected thyristors, while maintaining the protection level of the rectifier.
It is another object oE the invention to provide a method for limiting voltage across series-connected thyristors of a high-voltage rectifier, which would improve the reliability of the rectiEier.
In accordance with a particular embodiment of the invention there is provided a method ~or llmit-ing voltage across series-connected thyristor,s of a high-voltage rectifier as a voltage surge is applied to the latter. The method includes the steps of measuring the voltage across the thyri.stor next ko the point where the voltage surge is applied across the following thyristors. The total voltage across -- 1~ --3L~75[)5~7 the thyristors is successively measured as voltage across the-first thyristor reaches a specified level.
The successive measuring is started with the first thyristor, and the measuring continues until ~he total voltage reaches a level equal to the ratio between the voltage surge amplitude and the total number of the series-connected thyristors of the rectifier multiplied by the number of thyristors giving the total voltage. Voltage across groups of series-connected thyristors is limited with a specified number of thyristors in each of the groups.
The number of thyristors in each of the groups is selected in keeping with the number of thyristors and the total voltage. Voltage across each-of the groups of thyristors is limited with the number of thyristors to the level.
The method according to the invention for limiting voltage across series-connected thyristors of a high-voltage rectifier makes it possible to reduce the number of thyristors and improves the reliability of rectifiers.
Other objects and advantages of the present invention will become more apparent from a consider-ation of the following detailed description of a preferred embodiment thereof, taken in conjunction with the accompanying drawings, wherein:
FIG. 1 is a time plot of voltages across a group of thyristors and each individual thyristor at a moment when the high-voltage rectifier is acted upon by a voltage surge, which plot also shows the level to which voltage across the yroup is limited through the use of the method according to the invention, 75~9~
~ IG~ 2 is a functional dia~am of a devic~ ~or carr~-ing out the method accordin~ to the inv~ntion for limiting voltage across series-connected -thyri~tors o~ a high-volta~a recti~ier;
FIG~ 3 ~s a plot o~ a pulse wave distri~ution among groups o~ thyri~tors o~ a hi~h-voltage xectifier whe~ ~oltage across the thyristors is limited by the m~tho~ according to the invention.
Detailed Description of the Invention he method according to the invention for ~imiting ~ol-tage across ~eries-connected thy~istors of a high-vo~tage recti~ier co~sists i~ limiting voltage across groups o~ series--connected thyristor~ with a speci~ied number of th~ristors in each group. ~he number OI thyristors in a group is æe~ected to suît voltage surge paramebers. ~or this purpose, voltag~
i5 measured acrosæ the thyris~or ne~t to the poi~t w~ere a vo}tage surge is applied. When voltage acroæs the ~irst thyristor raises to a speci~ied level, total ~oltag~ acro~s the thyristor~ is succe~lv~y measured, startlng ~rom the first th~ristor, until it reaches a ~evel equal to the ratio be~ween the volta~e ~urge amp~itude and the total number o~ s~rie~-connected thyristors of the rscti~i~r, mu~tiplied b~ the number o~ thyri~tor~ giving th~ speci~ied total voltage corresponding to the num~er of th~ristors in the group. Vol-tage across the group is th~ limitaa to this ~avel, In most cases vol~age e, ~hich ~cts upo~ the xacti~ier,may be rsprese~ted to a csrtain degr~e o~ appro~imation by a wave with a known amplitude ~ (curve I o~ ~IG~ 1) a~d a dura-tion ~ o~ lts obliqu~-angled ed~e~ Curve II repre~c~t~ vol-tage across a group of ~ thgristors. C~urves III, IV ... ~T
represen-t voltage acros~ individual thyristo~s of the group~
A speci~ied voltage UI acros~ the hea~iest-loaded thyris~
tor is reached at a~ in~tant to (curv8 III). As poi~ted out abovea at this instant one calculates the sum total o~ vo~ta-ges acros~ the thyri~tors, ~tarting from the first o~e. I~
U~ ~ E ~ ~, where n i5 the total num~er of thyristors is the rectifier~ voltage is limited acro~s a group of 1~ thy-ri~tor~. ~ha limitation ~e~el is equal to tha wave amplitude divided b~ the number ~n of the groups. This rules out a si tuation when ~ UN ~ En ~ N~ i~e. when voltage across the hea~iest-loaded thyristor i~ above a permi~siblY level~ In addition, the total ~imitation lavel guarantee~ a reoti~ier protaction level equal bo the pulse wave amplitude.
~ he ~ollowing description re~ers to a pre:farred embodi-ment o~ the mqthod according to the i~vantio~, app~ied to a recti~ier int~nded for d~c. tran~mi~sio~ ~he xectl~iex comp-rises n ~erie~-conne¢ted thyrlstors 11~ 12~ , each connected ~n parallel with a respecti~e damping RC circuit 21 - 319 22 ~ 32' - 2~ - ~. An anode reactor * i~ connec-ted in serie~ with t~e rectifier. ~he circuit cont~ining th~
rectifier and reactor 4 is a~ arm of a co~erter bridge.
A non-line arre~t~r 5, ~hich det~rmine~ the protect~on l~vel of the rectifierf is connocted in parallel with the abo~e-men-tion~d bridge ~rm. Conn~cted ~ par~llel with the xectifier is an arrester whlch in the simp~e~t ca~e compri~es ~imitsrs - ~3 -V~l7 61~ 62~ ha ope~atio~ threshold o~ aach o~ th0limiters 61 through 6~ i~ selected to bs equa~ to E/~.
Outputs o~ the limiters 61 through ~ are connected to (n - 1) input~ of a switchi~g unlt 7 which in the gener~
case may have ~ - 1) outputsO ~ccording to the inve~tion, the ~.~umber o~ thyrîs~ors in a group and ~he lev~l to which vol~age acros th~ group i8 limited are detsrmin~d a~
~ollows~
Vo~tmeters 81~ 82~ o~ measure ~o~tages across tho thyrist~xs 11, 12, ..., 1N and s~d signals to a switching unit 9 which con~ects outputs of the voltmeters 81t 82, -, 8N to i~puts o~ a computing unit 10 whan volta$e across the heaviest-~oaded thyristor 11 raisès to a specified lev21.
~ h~ computing unit 10 calculate~ the num~er ~ of thyri-stors, the sum total ~ of voltages across -khe th~ristors a~d UII = E N; it also comp æes th~e valu~s. If these va~ues are equal ~a certain speoified degree of error is not exc~uded)~
a si~nal i~ produced whi¢h is proportional to the numb~ N of thyristors. ~he ~ignal is tr~nsmit~ed ~o the switching unit 7 which connects outputs o~ groups of ~ ~imit~r~ ~o those oP th~
groups of ~ th~ristors. ~he vol~meters 8~, 8~, ..., ~ , the witching units 7 ~nd 9 a~d th~ computing unit ~0 may be of type k~own to those s~illed i~ the art.
~ he method acco~din~ to the i~ven~ion make~ it possible to divide a r~ctifier înto ~ groups o~ thyristor~. ~IG~ 3 showæ a distribution o~ a pul~e w~ve e amon~ groups o~
thyristorsO The pulse wave e is applied on the side opposite .. ~ 1*
5~
to the reactor 4 (FIG. 2~ h~ r~actor 4 i re~ote ~rom the poi~ ~v which the pulse wave i~ app~ied7 50 ib~ e~ct on the wave di~tribution is insigni~ica~t. ~h~ pulsed vol-tage is represented by an oblique-angled wave with an ampli-tude E (~I~. 3) and edge duration ~. During the tim~ int~r-~al O~ ~, voltage across several groups o:~ th~ristors, for example, U1 and U2, reache~ the limitation le~ /Mo Accor-ding to ~IG. ~, the limitars of the ~'irst an~ ~¢ond group~
are actuated at insta~s t1 and t2. Operation of the limi-ters lasts ~or only ~ ~raction o~ ~ ~ Within the time i~t~r-val O~ ~ voltage across other remote groups9 ~u¢h as UM (~IG.
3), does not reach the limitation level. ~rom instant ~9 ~oltages U1 and U2 drop below the E/~ level which is r~ached again duri~g the time in~erval tM ~ t~'o Without tho limiters 61 (~IG. 2), 6~ olta~e across the groups would change as shown by the broken lines in FIG. ~. At instant ~, voltagos U1 and U2 would be above the limitation level~ ~he increase in voltag~ could only be compensated by increasi~g the number o~ th,yristors. A slngle ~-~evel limiter connected in parallel with the rectifier as a whole cabbot reduce U1 and U2, because at instant ~ vo~tage UB acro~s the recti~ier is be~ow the limitatio~ level El Such a limit~r on~y e~imina~
tes an i~crea~e of ~oltage across the recti~ier due to read-justme~ts in the ~ loop~ A ~imita~ion level below E is impermissible i~ long-term operation~
~ he method according to the invention ~or ~imiti~g vol-ta~;e across series-connected th~ristors OI a hig~L-voltage recti~ier o~ a d.c. transmission line, makos it possible to 5~5~7 reduce thQ number of thyristors in a recti~ier co~plet~ hcontrol~ protection, sign~ling and cooling system~ ~he method improves the reli~ y of recti~iers~ because vo~-tage across the thyristors can nev~r rise abo~ the permis-sible leve~O In addition~ the method according to the i~Yen-tion ~or limiting voltage across ~roups o~ thyristors is such that a rsctifier can n~ver be ~wit¢hed on at a volt~ge surgz amplitude, which would otherwisq affsct normal switching of a converterls recti~ier~:
Claims
1. A method for limiting voltage across series-connected thyristors of a high-voltage rectifier as a voltage surge is applied to the latter, comprising the following operations:
measuring voltage across the thyristor next to the point where the voltage surge is applied, across the following thyristors;
successively measuring, as voltage across said first thyristor reaches a specified level, the total voltage across said thyristors, starting with said first thyristor, until said total voltage reaches a level equal to the ratio between the voltage surge amplitude and the total number of said series-connected thyristors of the rectifier, multiplied by the number of thyristors giving said total voltage;
limiting voltage across groups of series-connected thyristors with a specified number of thyristors in each of said groups;
selecting the number of thyristors in each of said groups in keeping with said number of thyristors and said total voltage;
limiting voltage across each of said groups of thyristors with said number of thyristors to said level.
measuring voltage across the thyristor next to the point where the voltage surge is applied, across the following thyristors;
successively measuring, as voltage across said first thyristor reaches a specified level, the total voltage across said thyristors, starting with said first thyristor, until said total voltage reaches a level equal to the ratio between the voltage surge amplitude and the total number of said series-connected thyristors of the rectifier, multiplied by the number of thyristors giving said total voltage;
limiting voltage across groups of series-connected thyristors with a specified number of thyristors in each of said groups;
selecting the number of thyristors in each of said groups in keeping with said number of thyristors and said total voltage;
limiting voltage across each of said groups of thyristors with said number of thyristors to said level.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| SU803224740A SU982505A1 (en) | 1980-12-26 | 1980-12-26 | Method of limiting high-voltage thyristor rectifier voltage |
| SU3224740 | 1980-12-26 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1175097A true CA1175097A (en) | 1984-09-25 |
Family
ID=20934464
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000387830A Expired CA1175097A (en) | 1980-12-26 | 1981-10-13 | Method for limiting voltage across series-connected thyristors of high-voltage rectifier |
Country Status (9)
| Country | Link |
|---|---|
| JP (1) | JPS57110075A (en) |
| CA (1) | CA1175097A (en) |
| CH (1) | CH663119A5 (en) |
| DE (1) | DE3146555A1 (en) |
| FR (1) | FR2497417B1 (en) |
| GB (1) | GB2090482B (en) |
| IT (1) | IT1168460B (en) |
| SE (1) | SE446920B (en) |
| SU (1) | SU982505A1 (en) |
Families Citing this family (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPH01103171A (en) * | 1987-10-15 | 1989-04-20 | Toshiba Corp | Power converter |
| DE102006046040A1 (en) * | 2006-09-28 | 2008-04-03 | Siemens Ag | Thyristor valve of a HVDC system |
Family Cites Families (6)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CH470799A (en) * | 1967-01-02 | 1969-03-31 | Asea Ab | Thyristor valve circuitry with overvoltage protection for high voltage |
| US3508135A (en) * | 1967-11-21 | 1970-04-21 | Philips Corp | Device comprising a plurality of series-arranged,semiconductor controlled rectifiers |
| US3662250A (en) * | 1970-11-12 | 1972-05-09 | Gen Electric | Thyristor overvoltage protective circuit |
| DE1952828C3 (en) * | 1969-10-16 | 1979-10-11 | Licentia Patent-Verwaltungs-Gmbh, 6000 Frankfurt | Circuit arrangement for protecting series-connected thyristors against overvoltages |
| US3962624A (en) * | 1973-06-28 | 1976-06-08 | Allmanna Svenska Elektriska Aktiebolaget | Thyristor rectifier |
| CH576205A5 (en) * | 1974-07-11 | 1976-05-31 | Gni Energetichky I Im G M Krzh | HV inverter thyristor overvoltage protection - has controllable overvoltage suppressor regulated by current detector signals |
-
1980
- 1980-12-26 SU SU803224740A patent/SU982505A1/en active
-
1981
- 1981-10-08 GB GB8130419A patent/GB2090482B/en not_active Expired
- 1981-10-09 FR FR8119086A patent/FR2497417B1/en not_active Expired
- 1981-10-13 CA CA000387830A patent/CA1175097A/en not_active Expired
- 1981-11-13 JP JP56181251A patent/JPS57110075A/en active Pending
- 1981-11-18 IT IT41693/81A patent/IT1168460B/en active
- 1981-11-24 DE DE19813146555 patent/DE3146555A1/en not_active Withdrawn
- 1981-12-15 CH CH8009/81A patent/CH663119A5/en not_active IP Right Cessation
- 1981-12-21 SE SE8107664A patent/SE446920B/en not_active IP Right Cessation
Also Published As
| Publication number | Publication date |
|---|---|
| SU982505A1 (en) | 1984-12-15 |
| FR2497417A1 (en) | 1982-07-02 |
| SE8107664L (en) | 1982-06-27 |
| GB2090482B (en) | 1984-03-21 |
| FR2497417B1 (en) | 1985-08-02 |
| CH663119A5 (en) | 1987-11-13 |
| IT8141693A0 (en) | 1981-11-18 |
| JPS57110075A (en) | 1982-07-08 |
| IT8141693A1 (en) | 1983-05-18 |
| SE446920B (en) | 1986-10-13 |
| DE3146555A1 (en) | 1982-09-09 |
| GB2090482A (en) | 1982-07-07 |
| IT1168460B (en) | 1987-05-20 |
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