Brückner, A

Labeye, J F

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'·'I .. I ' PS/6624 A RESONAN'l' CHARGING PULSED HIGH VOLTAGE POW-ER S1JPPLY A. Brticki1er, J. F. La be ye SI/Int. r·1AE/ 68-6 27.6.68 1, Summary 1.1. Applications 1,2. Advantages - 2-2, Principle Functio~~Qircuit Layout 2.1. Circuit 2.2. Functions 2.3. Layout of Circuit Elements 2.4. Characteristic Impedance, Charging Time and Current values 3. An example of a 45 kV - 100 ~oule uni,i PS/6624 - 3-1. Sur:nna:r.y The described H. V. Pm-rer Supply uses a 10 ms charging line for any H. V. capacity to be cr.targed periodically. The r·epetition rate can, 1vi thout difficulties, tJe increased till approximately 10 p.p. s. The only H. V. element of the supply is its H. V. pulse transformer. All.~.-~:-- -regulations are done on the lCI"l voltage side. The amplitude stability for aconstant charge-capacity is about c1oe (thermal drift). The H.Ve output is short-circuit proof at any moment of the charging period. Special protection ar1d interlock circuits are not necessary. 1.1. Applications This type of Po1ver Supply can only be used when the times of the discha:cge can be related to the Power Supply charge command signal by an interval of greater than 10 ms. Using two independent low voltage-systems and a H. V. transformer l'rith a double primary coil, positive and negative charge is possible, even ~>Tith a different polarity from pulse to pulse. The polarity must, at least, be known 30 ms before charging. Ii these application condi.ions are fulfilled, the pulsed H.V. su~ply is a cheap charging system. For charging voltag8 below 10 kV and an energy per charge-pulse smaller than 20 joules it should not be used ~·rithout reducing drastically the electronic steering system. From 20 joules up to 300 joules charge enorgy, a single thyristor low voltage system, and from 300 joules ••• 600 joul&s, a double thyristor system may be used. From 600 joules up1vards igniters may be used instead of thyristors. From 4000 joules upwards, the electromechanical forces in the primary circuit must be observed. PS/6624 - 4 -1.2. Advantages Compared ivith conventional Povl"er Supply types, the greatest advantage is an electrically rigid construction; there is no direct voltage on the H.V. capacitive load (useful for sorios ope:r·ation of capacitors for instance). Vlhon tho systom is svJitched off, the H.V. capacitor will be disci.1arged automatically. Thore are no H.V. electronic elements in this supply. It will not produce X-rays. The electronic steering system is small and the whole supply cheap. A 200 joule - 45 kV supply can be ple.ced in 3/4 of a rack, a 500 joule -90 kV supply in 1+ racks. The proper material costs were 2.500.- respectively 5.000.-SFr. To get the ·complete costs, iJOrking time included, one should multiply these values by 3. 2. Principle Functions and Circuit laJ[out 2.1. Principle circuit The principle circuit is shmm in fig. 1: Electrolytic Capacitor PS/6624 r Fast Impulse SvJi tch Transformer t< -, .) CJ _L -c 3 I --Transformer Protection (t ~ 3 ).!.sec) y-- ·-- - -et.. --Cable or lin8 to be charged. Capacity:C2 '· ._ ~------~....__ - 5 -2.2. Function First the capacitor c1 must be charged to a voltage u1 and the transformer should be pre-magnetized to allow a L'llfequal to tvlice the saturating flux t L'I'I'=Il' :::2'¥ >[ udi pp p::: Both auxiliary circuits are not shmm here. When the fast switch (thyristor or ignitron) is fired, the primary voltage "u 11 of the transformer· jumps up to "u.." whilst the secondary voltage "u " p ~ s reaches the top voltage in half a period of a cosinus oscillation. (See fig. 2) The primary and secondary current behave like half a sinus period. The voltage ~ of the primary capacitor drops from lOo% to 7o% of the charging voltage. When the top voltage at the secondary capacitor c2 is reached the current in the primary circuit goes through 0. The thyristor does not conduct inverse current, so the oscillation is stopped at the top voltage and immediate discharge will not happen. The voltage 1-rill stay near the top voltage until the transformer saturates and d~scharges the capacitor c2 by free non-linear oscillations, The capacitor c2 shall bo discharged by another system.before tho transformer reaches saturation. (e.g. kicker magnet or spark chamber). w~en the power supply is pushed to the limit of its capabilities, the ratio between flat top time and charging time becomes smaller and smaller. If it is overcharged, the thyristor may never stop conducting current till an auxiliary protection circuit breaks the current for a short moment. Fig. 2 {..C-1 (Capacitor lovJ voltage) t.A.f (transformer, primary winding) t'\. (transformer, secondary v.rinding) primary current • l.p Ls secondary current PS/6624 - 6-1-----4----, '-...., ""~-._____ . ! I ----r---·-----t---+--I ---~------~----~-~-;~t I ' ! I ··1\· I \ I )\ \ (a) (b) (c) (d) (e) - 7-2.3. Lay-<?2~ _ _9!__~:::_"i_:.~:.._?1G~~p.ts First the cho.rging voltnge u2 eh for the load capacity c2 must be given. Secondary charging energy: c2 2 E2 = -2 u2 eh Secondly th<J ropoti tion ro. to and a convenient primry voltage shc'lll be knm·m. '.'le get a \·Jell optimised system (See fig. 1), when observing the follovring points: 2. 3 .1. The Pt:_imnr:v COJ)o_cit or C 1 may be an electrolytic, surge proof type. It is better to drive many small capacitors in parallel than to have ono largo capacitor, because a small capacitor can normally be discharged faster th'.ln a big ono. The stored primary energy: Reason: - Lovwr influence of primo.ry capacity variations on secondary cbarging voltage due to tenporo:ruro effects ( ~· 500ft only) Longer life of the electrolytic capacitors Better recharging efficiency in the lovr voltage system. ( 6('J{o • • • 80/o instead of 50% wJ..an E1 = E2) vl e find then: (r = turns ratio of the transformer) 2.3.2. The primar<J swit£h The circuit needs a unidirectional primary switch such as a thyristor or an igni tron. The available primary sNitch is th<; element which determines most the convenient prionry voltage. A good value is e.g. ~eh 300 ••• 430 v. In this case ono, can >"iell op. . .irate a 600 V- thyristor 1-rith 500/550 V electrolytic capacitors for cl. \fuen the H. V. systol"~ is earthed and the switch erronGously fired the primar'J current reaches about 210% of the nominal value. (Oscillation between c1 and 11b of the transformer) (Seo also 2.4) PS/6624 - 8-'i.'he nom.ino.l pco.k current ior the switch must uhereforo be chosen uS: Jl ~ 0 ,ll-8 J nom surge As c.. rough indication 1ve r.YJ.y tnke: 1 Siemens thyristor BSTN 02-60 ::ill E2 = 200 joules 2 Po.rc..llel thyristors BSTN 02-60 till E2 == 400 joules \'/hen three; or moro thyristors are needed it is better to use one igni tron which co.n be driven by a nedil:lLl pm,rer thyristor. 2. 3. 3. The H. V,, -Tr!:_l:tWfOrJJLor is the most critical olw.ent of the circuit. It seems reasonable to use norme.l 50 H z -H.V. Transformers. The cho.rging times then become about 5 ••• 15 ns and the primary currents stay in reasonable order of magnitude. In this application the nominal 50 H power of the transformer is z defined as follows:--the inductive primary.voltage at nominal current and secondary short circuit is ~ 5% of noninal voltageo - the resistance losses shall be smaller than 3%. the nominal volto.ge u must be defined so that the transformer does not so.turate at r 1,30.U • n All calculations are made in order that the transformer will need its nominal flux during the charging time and tho difference between saturation and nominal flux is left available for the flat top. So the flat top at nominal conditions reaches 15% ••o 2o% of the charging time. Using an over dim.ensioned11 transformer, the ratio of flo.t top to cho.rging tine becones noro fo.vouro.ble, but possibly the primary switch must stand higher currents. The ins~lo.tion level 1nay be chosen so that the nomino.l 50 H ros volto.ge z is 6o% of the nominal charge voltage. N2 The turns is chosen r == 0,96 PS/6624 u ~ ~eh ratio r ==-- (N: number of spires priuo.ry/socondary) Nl -1 12~3 - 9-(Under this condi ticm~ tho pcmer supply 't~ill really reach a nininuo flat top of 15% of the charging time). e.g. s n 1200 V'l ~·T}l:;l1 p -- 100 joules "· .. J,~ '~ .- kVA ~·Jl'!Ol1 J p .u,, = 410 joules L 240 kY0. ~·JhCJl'l 1il ""2 :::: 20 k-joules The trc.nefor:21m' is designGd in tl1is chnpter for nominal op0ration. If, fo:o:- tooting oquip:::1ent n higher voltage thrm no:winal voltage is. required, this r::.o.y ho o1:/ccined 7 ;.rLcn the secondnry charge capacity c2 is reduced. RGd.ucing drast:i.cc,lly c2 and keeping u1 eh constant, one can at maximum increase u2 at l'iv%" Reducin~_;' c: 2 at 5Cf/o o.nd increasing ~ eh at 130% one oay get an increase of u2 till 150?s. Fe:;_~ i'lm~ calculation in the transforoer, one Tiay count during the. charging tine T under noTiinal c~:1di tions u flux in the iron correspondent to the product. q.r charging timE: = 0,64 • T • u2 chq,rge 2 (For nn ider,·. c}fiansfornor without arw renisti vo losses, the factor would be integral u 2 ( t) d;C 'trould lead to a value of about 'I' 2 = 0, 56 T • u2 . o f:L1 Cl1 whilst the. integral / t1 1 ( t) dt vTO\lld lead to about'I' 2 = 0, 70 T • u2 0,50. eh Tho eh" The .Jq .1 differences be~veen tnese fcvr fo.ctors are due to the damped half oscillation of tho charging period and to the resi;:Jti ve voltage losses in tho primry and secondary:_ vrindings of the t;ransfornor). The prcr.JLlgnetisation current through the transfor.Cler shall at lonst be equal to t1'1'ice th'3 :peo.k vnlue of the 50 H r:1agnetisntion current at nooino.l voltage. z 2.3.4. Tr.<:m.~:fgTP!1::...._Protection circuit R,_Q3 The tro.nsformor oust be protected against nanosecond kicks, when coorging a thyristor or spuTlc g:~p circuit. The tin.:: constant 't' == n3 c3 ""' 4 f.1Sec is sufficient for 50 Hz HV transfornorso Thu resistor rr3 sh~ll be s~qller than 50/o of the secondary copper resistance. PS/6624 - 10 -2.4. Chnr~cteristic i~~9Sk~l92L-cha~ging_tipe and ue~k v0lues of currents ]'ron fig. 1 we derive o. prio.nry replacing circuit: _Fig. 3a L. r/ 1 ,------~~-__,:.--yy-y-·L_ ___ _ l lC"' -~ ~ c 1 C ?. -··2 'r Fia. 3b L. c3 ,~. c2, n~gligible, L,,.l1 c; = 0,4 c1J ._ _____ ('/")''"\..--.... ____ _ .l. --1 --· 1 --::; PS/6624 - ll -2.4.2. Charge time 2.4 • .3. 2.4.4. T h == rr /1 • o.71c2 1 == 2.65 /1 c1 -c "' 0'1 ~ 01 2 Under normal conditions with a 50 H transformer, the charge time ID.ll z be about 10 ms. Primary nomi:r~.al Eea:k ou~ , 2 u2ch ~ 0.6 ulch J ~1( . c2 r -·l 1 2 r Tch z 0 Prima£:2: Short Circuit Peak Current u J C ~ 0,8 1Ch ~ 2,1 J 1 ~-~ 1 ,j La1 /C1 ~ J 1 c <Jta1 /C1 when no resistance losses in transformer a:re on sidered - 12 -3. An Exar.lPle of a. 45 kV-100 .ioul..9 uni·~ Fig. 4 shows the complete Block-Diagrruo: the recharging current for th0 low voltage ntorage capacitor (3r:ili') flovm in th(~ invorse sense through tha.. primary coil of the H.V. transformer. When the charge regulator (4) stops the charging of the capacitor, lA remains on the primary coil of the transformer to keep it premagnetised. (flowing back to the de. supply at 450V). When the higher circuit (3) fires the main thyristor BSTN 02-60 the charging circuit (2) with.the BTY 87-600 will interrupt the charging current for 10 ns to give a better flat top. Inmediately after each charging pulse the system (2) gets the B1Y 87-600 continuously conducting again. The relay (1) opens the current circuit, when the nain tbyristor accidentally does not stop conducting. (e.g. when the supply is shorted on the H.V. output or if a H.V. break-down happens before the flat top is reached). The relay (5) discharges the storage capacitor, when the 220 V line is interrupted. The H.V. transformer is largely overdimensioned. (1,1 kVA ivould be sufficient in this case). With a few modifications in capacitors and resistors this supply nay be improved till 300 joule per pulse. A circuit of the same principle with two thyristors BSTN (02-60) and a stronger transformer has been built for 600 joules and 90 kV. PS/6624 r·····-·· .. ·-·J ·) >· . -~·...-· CL •. I .1~.~ I I ,,.~, ' 'I ~~ ·~"-· ·+-:r ~;~ -+ .... 13 4CO r-~Jo ........... i ~:~;~.~-~· ~ ..• , ·-·--~:: .: ·-~, •••. J , e; :r ·'! + 01 ' ·;·-f··-i 0~ ........... ,...J ----····--·----·-·-i l·-~[--c3 ··-·--··::-·-·1··-·--.. ' ~· ·. 1 r1 ;:. -[>I----.J--·------c--~--~-----· ~··~l J ~ I __ • .Jl , ... .:T . -------··------~ ,. ... J ' '"' '~ \) --~ ~. .. v <J <! •:) <;]._ LJ \J .. ---[ }--·--·- c~ 8 "''·~ ~ .. :r \}"". ' ...... ' 1r ~~""{-· .. - 14 -Fig. 5a/5b shmr the H.V. at c 1% connection of tho transformer and the current at ~tduring a charging pulso. Load capacity c2 = 115 nF energy E2 = 117 joule at 45 kV fig. 5a/5b charge at 41 kV 5b damped non linear oscillations fig. 5c increasing flat top time with decreasing voltage More detailed circuits are available for those interested, PS/6624 - 15 -SIS/A/15930 Fig. 5a 10 kV/div 1 ms/div 50 A primary/div or 0,5 A secondary/div Fig. 5b 20 kV/div 5 ms/div 100 A primary/div 1 A secondary/div or 1 A secondary/div Fig, 5c 20 kV/div 1 ms/div increasing flat top with decreasing voltage 

A resonant charging pulsed high voltage power supply

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