Unit5.pdf

DESIGN, FABRICATION & TESTING OF A MAGNETIC AMPLIFIER EXCITATION SYSTEM FOR

SYNCHRONOUS GENERATOR

A DISSERTATION submitted in partial fulfilment of the requirements for the award of the Degree cf MASTER OF ENGINEERING in ELECTRICAL ENGINEERING OF R©©4WEt (Power System)1'~

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By

SURESH CHANDRA JAIN ''-

DEPARTMENT OF ELECTRICAL ENGINEERING UNIVERSITY OF ROORKEE ROORKEE (INDIA) 1975

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CERTIFIED . that the dissertation entitled "'DESI+GN, FABRICATION & ,TSSTING OF A MAGNSrIC. AMPLIFIER i^.

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EXCITATION SYSTEM FOR SYNCHRONOUS GENERATOR" rich is being sabmitted by Shri SURESH CHN+IDRA JAIN in partial fulfilment for the award of the degree of Master of Engineering In POWER SYSTEM( `ENGI iEERING of Electrical Engineering of the University of Roorkee, 'Roorkee, is a record of the student' e on vvrk carried out by him under our supervision and guidance. The matter embodied In this dissertation has not been submitted for the award..of any other degree or diploma. This is firther to certify that he has worked for a period of 7 months from March '75 to Sept. '75 for preparing this dissertation at this University, l ey

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(H. K. asenta) (3. M. Peers) Rea er *' Associate Professor Department of Suet. Engg• Department of Electrical Engineering University of Roorkee University of Roorkee Roorkee (U .P.) Roorkee (U.F .) Roorkee Dated 8 -1).. 1975.

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D0-8I1 917 i $

Tho ,ci hor istahos to cknox-flodSo his profound conac of gratitudo to Dr. S. r-, PorrCn l, Ascociato Profoaoor In L1octri eat t ngin ciring Dep ortment td Skirl M, IC,, Vnstrt o, focdor in Electrical RngInoortng Dpertmcnt s, University of

Roorltoo, for the!r export guidenuse, 1. adorn neouragemcnt accorded to him throughout tho period be has toon +marking on thi o di ssortation,. The cu.thor sincerely then cn Dr. To S. U. Rte Profoasor P- Head of Electrical 1nçinooring Departtcnt, t!nivorcity of Roorltoo, Roorkoo, for various focilitios provided in the complotion of the work. Tho author also tacos the opportunities to ox aroca his sincoro thcnks to Dr. X. Venksteocn, U.C. P.G. m/c Lab„ cnd Bonier ~ /c lob., Reader in Department of Rioctricel Engineering for giving their uaoful cuggostion. In tho laot r„lthor alco wichos to tb nk to Ur. Gcngo Rcn Vorme, P.S. Lab., '-1r, B. S. Vormo,, P.S. Lab* , Ur. J. P Sharman, Computer Lob. for Giving their valuable time for fabrication of the inotruments In connection with this dicser-

totion. UNIVERSITY 0? ROO TM EB

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mTnor3cTXoff .. .. 1. Typos of 1 xcitation Syaatom 2 9. l4odorn Excitation System 3.

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Cora,utor rcproscntation of 15

'Excitation By atoms

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APP EJDICES

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"An Excitation System is the source of field current for excitation of principal -electric machine, Including main s for its control". An excitation system, thoreforo, Includes all of the equipment requirod to supply field earrcnt to excite a principal electric machine Fhic . may be cn a. c. or d. c. machine End the regulating equipment to regulates or control the amount of field current. Basically it consists of xc'Eter Unit, field rheostat,, voltage regulator,, End field Eupprossion equipment. A msgoetic amplifier excitation system is a completely static excitation system 9 in htch the power required to excite the exciter is directly taken from the output of magnetic amplifier voltage regulator. A maen eti c ampli f9. er is nothing but simply a reactor rectifier combination, in thigh a small control currcnt can cont=l the large d, c. output power. The salient featuroc of this system over the conventional systems

1. System is completely static so components inherently

possess long life, mocbznical meintsntnee is absent. 2. Thoro Is no urnrmxp time, so that conversion equipment is ^vcilablo immodictoly. 3. Lesser floor space required and the weight is loft,

also thono are no foundation problems., 4. System is more reliable 5. High efficiency,, etc.

-21. TYPES OF EXCITATION SYST E 411 2 The principal types of excitation systeml now in use (having automatic voltage regulator) are the following $ 11 Self Excited Exciter and direct acting rheostatic type voltage regulator (Fig. 1.1). The voltage regulator changes the re si st erne n in the field circuit of the exciter. The voltage sensitive element of the regulator (for oxeaple, a solenoid) sets directly on the rheostat to very its resistance. This system is commonly used an the cmal1 s. c. generators. 1.2 Main cnd pilot excitors and indirect acting rhoostatic typo of voltage regulator (Fig. 1.2) then a small deviation of voltage occars, the voltage sensitive olenent of the regulator closes contests rich control a Qotor-driven snitch

L

itch raises or lowers the rest tanee of

the field rheostat of the main. exciter. If the voltage deviation is grestor, additional contacts are closed hich short circuit the field rheostat to produce a rapid bxiid up of the alternating voltage or contacts i►ro opened ich introduced the entire reststanco of the rheostat to produce rapid build..dot . This roguletor has the disadvcntege of a 'dead-band' i.e., a small rengo of valtogo in Lich no corrective action is produced. This dead zone roducos tho accuracy of voltage regulation and prevents the regulator from increasing steady state stability. 1* 3 Rotating ham Exciter with electronic Pilot exciter and Eloctronic Regulator

Tho electronic pilot exciter is a polyphase rectifier using thyritron tubes or the like.

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FIG. f.51 VOLTAGE CURRENT CHARACTERISTICS OF ELEMENTS USE C', N, IMPEDANCE TYPE VOLTAGE REGULATOR

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Thu a. c. supply of th€± rectifier may be either the main power system or a permanent magnot generator directly

connected to the main mac .ine. The electronic regulator controls The firing angle of the tube and thus varies the output voltage of the rectifier ich is impressed on the field r .nding of the mein exciter. No field rheostat is used. This system has been applied principally to synchronous condensers but also to some generators. 2.4 Electronic Mein Excitor and Electronic Regul ntc r: A six phase rectifier of larger cep acity, using ignitron tubes, supplios direct current to the field of the main generator. Again,9 the regulator controls the, firing a**lo of tho rectifier tubes. The anodes of each pair of tubes ore connected to their load through a tu.pole circuit breaker. _'hcn this breaker is opened, the load can be carried by the remaining four tubes. Thus # tubes c sn be replaced 4 thout shutting dotn the units. The poor supply for the rectifier is either the main a. c. generator or en Euxlll ary polyphase generator, usually direct driven. It the supply is from the main a. c. generator, series compensation may be employed to boost the voltage in proportion to the reactive current fed from the gcnoretor. Electronic main tnd pilot excitors have operated very satisfactorily but are not i.dely used because both their first cost and their m ntenanca cost have been found to be greater than for other tynos of excitation systrms.

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1.5 Hain Exciter,, Rotating Amplifier, cnd Static Voltage Regulator The main exciter is either an ordinary shunt,. vound -nochine or a shunt found machine with additional field winding ,. The rotating amplifier is a d.c. machine specially designed as a poorer amplifier. Such machines, knc,vra by the trade names of Amplidyne, Rototrol , or Pagulex. The important feature of such machines Is that a l arror output may be controlled by a few watt's input, ditch can be supplied by a static type of regulator having no dead bend and no moving parts. Such regulators are accurate and reliable. They are of either of tito types, electronic or impedsn.ce. The electronic regulator compares the constzt volts a drop across a glow tube or across a resistor In the plate circuit of a pentode with the rectified nitornating voltage being controlled,, the difference being applied to a control field winding of the emplifter, or each voltage being applied to one of a pair of such windings, the mmf' s of rhibh are opposed . The imp od n co typo regulator compares the current through a non..linear impedance (usually rn Iron..cored inductor) with that through a linear impedance (usually a capacitor) . See fig. 14 51. '!hcn the alternating voltage is correct, the rrent through the tvo Impeflicos are equal. ?}Yhcn the voltage is high or low, one current or the other predominates cad, D I r rectification, excites the control field winding (or windings) of the rotating amplifier. Insome cases, where the more power grin is required, a magnetic





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amplifier has been placed bat on the voltago regulator cad tho rotating amplifier. Several d.iffornt methods of excitingg the main exciter

arc used. One (fig. 1.52) i s to excite the main excitor separately from the output of. the rotating amplifier. Hovever, it is generally better to use some combination of coif end separate excitation of the main . exciter so th at the rotatingg amplifier can be removed from the service for meintcn ce vithout shutting don the generator unit. One such method is to connect the rota}ink; cmpl irior in oories with the self excited stunt field. (fig. i.5). ''ho f"i of d rh oo st at is so adjusted that ien amplifier voltage is zero the excitor operates self excited to supply the proper field current for average load on the a. c. generator. The voltngo on tho rmplifier eithor bucks or boosts that of the excitor armature as required for proper control of the alternating voltage. The amplifier may be disconnected by a tren sfer switch, the main excitor then being manunlly controlled. Mother method (fig. 1.54) is for the main exciter to hove ono shunt connected field winding iiith theostat adjusted to provide excitation for nvorage conditions end enothor field winding coparntcly excited by th(+ rotating emplifior, t tch either bucks or boosts the solf excitation an required* This motho6 has the advantage of having no s,.*itehin In the main field winding of the exciter., but has the disadvr►tage of

rcquiring a spoci of typo of excitor. Those achomos using rotating amplifier's have been extensively employed in recent years. 1.+6 Rotating Amplifier as Main Exciter and Static Regulator A to stage Retotrolhas been used as the main exciter. Tho Rototrol is similar in construction to as ordinary d. c. gcnorator except that the nagnotic circuit Is designod so that it does not saturate in the t'orking r~go. This mnchino has a self oxcitin g series field iindin g (connected in €cries ith tho armatures the load, end a 'tunning' resistor) and also has one more control field windings for acporoto excitation. •Ono advcntnae of this scheme is its rapid response becsso of The use of a cones field i tnding on ,the Rototrol. 1o 7 fain Bxci tor, 1 agn oti c Amplifier q tnd Static Regulator This schema, t.ihich is one of the newest,, is similar in general to schome 1.5 -k1ich to oxcitor c ith two field windings,, except that the rotating cnplificr is replaced by a magnetic amplifier.

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2.1 A High Initial Response Bruahleas Excitation System # A high initial response excitation system retaining the advantages of the absence of comnutators, collectors and brushes - uhile responding with the speed of electronic exciter has been developed* This system provides fast response by means of high forcing and reduction of the time constant of the rotating exciter and voltage regulator# The basiC.brushloss excitation system is sho.n In fig. 2.1. This system includes an alternator reoti tier main exciter and a permanent magnet generator pilot exciter both directly driven from the synchronous machine rotor. The main (brushless) exciter has a stationary field and a rotating armature ihich is directly connected through silicon rectifiers to the synchronous machine field without commutator., collectors and brushes. Field power for the brushless exciter is supplied from the PMQI, having rotating permanent magnets attached to the shaft end a stationary three phase armature. The a. c. output of PMG is converted to d. c. by phase controlled, three phase, Rill wave,, thyriaters bridges. in this system, base excitation and manual control of synchronous machine voltage is provided by an adjustable d.c.



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also serves all, of the voltage regulator logic circuiting. This bru.chless oxcitattbn system sues designed to have some special characteristics to meet the high initial response requirement, 2.2 A Rotating Thyrister Excitation System for Hydrooloctri c Generators. A block diagram of the excitation sy stern is shore in fig. 2.2. The section enclosed by dashed lines i s the rotating portion of the system. The remainder is divided into tvv independent regulating system* The exciter regulator maintains the exciter a.c. torminol voltage at a nearly constent level corresponding to ceiling voltage. The exciter output is then used to power the entire excitation system effectively isolating its opor ,tion from outside disturbsncos. Voltage buildup cAn be accomplished using only the residual excitor flux.. For convenience end to shorten the build up time, flashing from the station battery supply is also incorporated. The generator rogulator to Maintain the generator ter+ntnn voltage at a nearly constant level determined by the voltage adjuster setting end modified by the under-excited limit,, line compensation (or droop depending on the desired connection) and a stabilizing signal derived from generator power.

9 The excitor has a rotating armature end a atationpry fiold windinC6 Typical excitor frcqucncies renge from 16 to O9►j. tith a coiling voltage of 1.5 p.0 field voltage.

based on generator rated

The generator field rectifier t13 a double c ay thyri s#or bridge circatt etpable of inverting to reduce the generator . 1 field current. Since the voltage supplying th thyri s}er bridge is the coiling voltage, so that the sppod of response is a function of that coiling voltage, Tho po,trer supply End rectifier control included as a

part of the rotating olemant produce the necessary phase controlled trigg-nring simal.s in response to a d. c. control 1.ovo2 supplied by the voltage rogulator. Ofnorator field carrcnt me surem=nt + s obtained from currcnt trrnsformerc located in the a. c. side of the gcnorntor field rectifier. The oxciter a. c. voltage is averaged, compared against the exciter voltago reference, and applied to the rectifier

control end roctifier in such a mcnnor as to maintain the excitor terminal, voltage at the dosirod levdI. Log-.lend coui'cnoation is uard to stabilize the voltage control. A current lieait to provided in tho oxcitor field control to protect the system.

Stcndtrd potential and cu.rrcnt trcacformors are used for sensing the acnorctor terminal. conditions. The potcnti al signal Is averaged and compared directly with the operators voltage adjustment (voltage reference) in the automatic mode of operation. The potential and current signals are combined in a cot of transducers to produce the watt and var signals for the complimentary functions. These complimentary signals are then added in proper phase and polarity to modify the basis voltage regulation. In tho manual mode of operation, the gcnerator fie d current is compared with a separate manual voltage adjustment (reference) cud spoly to the rotating thyrictors bridge through separate regulating elements. The gc orstor regulotor has lag-lead compensation to provide stoble, rosponsfvo operation. Not show in Fig.2 2 'S an over voltarto protection control filch to combined i th a field discharge resistor to protect the system In the event of out-of-stop operation. The control and rest stor provide full protection independent of the excitation system operation.

2.3 flercury Are Rectifier Excitation System? ~lorcury arc rectifiers are suitable for an excitation installation which is economical from the point of view of prime cost cnd maintenance. Mercury are rectifiers have satisfactory behaviour under instantaneous over loads.

11 _ Comperod t4th them, somiconducor rectifiers arc more t i; An over voltage t ich is too high, or en excess cairrcnt for too long period Q may spoil the semi Conductor rectiftorq while in the caco of mercury are rectifier they till cca so only a flash back„ xhich is not serious. 17

A typical schematic dicgrnm for the multi mode mercury are rectifiers is shot in fig. 2. . This arrtngomcnt does not provid a for negative field current tit does pornit a negative field voltage of a mcgnitude approaching the positive coiling. As the field volt go can bo changed almost inctn_ teneou.hly both increases sad decreases in Held currcat can bo extremely rapid. If an are back occurs,, one bf the valves conducts In the reverse direction and short circuits to phases of the rectifior trsn sformcr, U ith the ilti.-anode rectifier, arc-backs are cupprosscd by phesinc back {h-P grid control so the tube cannot fi-Vc.for the soversl cycles. At the end of this fixed period f normal firing control is resumed and usually the rectifiers will rocsmo normal operation. As the outside source of supply for most of generating stations is over n sincle 2213.4cV lino, it eras considered assn+i al that the generators bo able to start up without supply from outside the station. This is accomplished by supply initial gccorator excitation from the 125 volts station bettory ihich is ].sr used for tho other control and alarm functions. 0





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-12-. On startup s contractors are cl000d to connoct the station brttory acroas the gen orator field through a diode, as shox-sl in fig. :. t?h n the generator voltage reaches 50 to 751 of rated value s depending on the particular excitation systo-i9 the main rectifiers takos over. The diode prevents the reverse current flowing in to the bottc?y. This start up procedure requires only about flee seconds co that the drain on the battery is only a fraction of rat ampere-hour. The firing control and the control elements of the voltage roulator are static elemcnto. Trcneistorizod a lifiers having negligible time delays are employed In th control circuits. Much of the control switching is porformod by ti tic switching dovico~s. 2.4 SCR Excitation Cystc i7 A schematic diagram of tho SCdt oxcitation systrm3 is sho,,,n in fig. 2, 4. In common norcury are roct i fi or excitation systems this system does not provide negative field curry-fit cnd start,xp ics accomplished using the station battery to provide the initial gcnerator field current. The rectifiers are connected in parallel to obtain sufficient Qzarrent carrying ccpactty. 'rho mnin po -r rectifiers are housed in 11 trays *rith one bridge of 11 CCI;' a in each tray. Each l rg of the rectifier bridges is protoctod with series fuises9 =rge protection, end a f ilt indicating light. Also each lag is provided ,tth a

s©rios-connacted, air corn roactor to insure a propor bal rn co in loading batom the parallel rectifiers. Ratings of the compcncnts permit carrying twice rated field current for 3) second$. If one of the roctifidr fuses blows, the excitation ccn operate contincously at rated fiold current. Blowing of additional fuses i-All result in cutornatic shut don. A soy-called crowbar circuit is provided to protect the rectifiers end generator egninst the effect of cn oxcosstve negative voltage -hich cgn occur if tho generator fells out of stop. If a negative voltage exceeding n preset value occars, tho roctifiere are turned off cad mn SCR, connected across the field so as to posit the flo~r of negative field current, is turned on. 2.5 A. C. Exciter/Static Rectifier Excitation Sy stom8 Tho basis schemo of a typical voltage regilator for a 510 1T't' Cen.crater is siovn in fig. 2.5 share thyristors control the excitation of tho main a. c. exciter d achieve a fast response owing to the forcing avail able from the constant voltage high frequency pilot exciter. This faster response of the semiconductor o. v,. r. compared with p roviou s a. v. r. s. using manotie cxplifiora, results in a bettor system response. The main points specified for such a rectifier are as follows :

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(ii) Tho rectifier *ia11 be rated for cn output of not loss than 110`"' in voltage n d currant in terms of the roquironents of the gcnorntors thcm they are operating at rated output. (b) in the static rectifier scheme, the conventional fl old cult oh End suppression circuit shnil be retained for the usual purpose* Cc) The rectifier shrll be cepble of ulthctrndin g any voltage and current surges art sing from the gen erator during sy at ci feilts. The rectifier is gcnorellp asso:.iblod in a numbor of cubiclos~, oech cubicle being a complete '.-phaso bridge connected unit. The cubicles are then connected in parallel to provide the required current capacity. R

3,

99MRITTERR 'RESIN R OF EXCITATIQN SY ►T21 I

A sub-committee of the IEEE has defined four excitation systems types to be used in computer representation. These should be adequate to represent all modern systems. Some older systems must be approximated with one of the four types or it must be assumed that machine has fixed excitation. In the development of excitation system,, systemblock diagrams, it has been necessary to establish a per unit voltage base. For the following discussion, one per unit generator voltage is defizfed as rated voltage. One per unit exciter output volatage is that voltage required to produce rated gen erator voltage on the generator air gap line. 3.1 Type 1 - Contineousl r Acting Re lstor send 'Exciter i~ nr irrr.~~~..wr■ _

The excitation system designated type I is shorn in fig. 3.1(a)w The type I excitation system is representative of the majority of modern systems now in service and presently being supplied. This includes most contineousfy acting systems with rotating exciters.

Fig, 3.1 shows the significant transfer functions rhich should be included for satisfactory representation In computer studies. Many other system types may be represented it excitetion system ceiling voltage is assumed to be Independent of generator terminal conditions.



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FIG.3.2 TYPE Ii EXCITAf ION SYSTEM REPRESENTATION ROTATING RECTIFIER SYSTEM

Tho transfer finctiona and womenclatur© of typo t

will be described in dotai7 , reforring to fig. 3.1. Vim. Is the generator terminal voltage applied to the regulator Input. The first transfer f znction is a simple time constt it ~'g represent&tin g regulator input filtering. For most systems, T R is very .smell end may be considered to be zero. The first summing point compares the regulator roforcnee egith the output of the input filter to determine the voltage error input to the regulator amplifior. Float computer programmes do not require an input of VRpp,, but rather intornally calculate the proper value by assuming V~ at t = o is at a proper value. Thc second summing point combines volt n°-e error input tAith the excitation major damping loop si al . Tho -Bain regulator transfer ft nction is represented as a gain X. and a time connttrit T. Follotitng this,, tho maximum and minimum 11 mi t s of the regulator are imposed so that large input error st gn al s cannot produce a regulator output r, i ch exceeds practical limits. The next summing point aubtr©cts a signal 01ich rep roacnt: the saturation fznction, 3*, = f(FpD) y, of the 14 ea- cxcitor. Thnt ins exciter output voltage (or generator Yield volt ago ''PD) is zultipl ind by a nonlinear saturation function cud subtracted from the regulator output signal.

. 17

The rocult nt is appliedd to the exciter trsn sfor f incll on 1/ (Kg thhcn self excited shunt field Is used, KE represents the setting of the shunt field rheostat and provides a positive feed back of excitor output, To establish Initial conditions E R Is often choose s'ic9i that it is equal in magnitude to the saturation fh4ction at a Initial value of E. At t1ni s .value, the shunt field exactly compensates for excitor saturation end no regulator output is required to establish the initial value of E.D. For those systems with a scparately oxcitod excitor0 regulator output is rcqutrod to supply tho excitor field end oat •- bli sh the initiall value of EFD. Major loop danptng Is provided by the feedback tr€n afer function s1/( fi dFp) from exciter output SM to the first summing point. It should be emphasized that there i s el interrel ation bot ioen exciter ceiling E'Pi max, regulator coiling V max' oxcitor saturation S$, cud 'KB, The following expression must bo satisfied under steady state conditions° VR - (ICE c SE) 0 9P EFD min 4 'RF Egg) max - m (1) (The sign of K R is negative for a self excited shunt field) At ceiling, or RF _ EI.'p max VR max , (I{ a SE max ) ipi max = 0

o'. •' (~"1

K$ is always ssecified, either as input data or program logic, to permit automatic calculation. In addittên,, of the remaining three constants V. max* 3g max and EPD max' the specification of any two establishes the third. Since different programs may use different input data, care should be taken to make sure that (3) is satisfied. Par some systems employing noncomzTutating type exciters, the minimum value of E Is zero and cannot be negative. Saturation Function -. The exciter saturation fanction 9]j is defined as a multiplier of exciter output gFD to represent the increase in exciter excitation requirements beceaae of saturation. Fig. 3el(b) illustrates the calculation of a particular value of S. At a given exciter output voltage, the quantities A and. are defined as the exciter excitation to produce the eutput voltage on the constant rest stance load saturation curve and air gap line, respectively 8 .:.A. g B The exciter constant rest stance load saturation curve has been in this definition of fig. Different computer programs have represented exciter saturation in different ways but, in general, the saturation function can be defined by two points. To be con si stant , the

.. 19 procedure suggested is to establish two voltages at .rich to specify Sp and use them as data for computer input. The fbrm of the saturation function is not defined here, but rather considered to be a part of the particular computer program used.

•

3.11 Type 1$ - Controlled Rectifier Systems with terminal potential. supply only

A special case of type 1 is a system employing an

excitation source from terminal voltage with controlled rectifiers only. A system of this type respondd quickly, tut With ceiling voltage procortione], to generator terminal voltage. Referring to fig. p.1, VR max is not assamed constent but rather is computed as a proportion of terminal voltage. VR max : lc.p VT In general., the constants for this type of system are such that K.g =1f TB=0 ! end S3 =0, 3.2 Type 2 -. Excitation system - Rotating Rectifier System The type 2 system,. Fig, 3, 21, applies for units with the major damping loop input from the regulator output„ An example is the vesting house bruahless system put into service upto and including 1966. The transfer function includes one additional time constant to compensate for the exciter t1mtdi is not included within the damping loop. Other characteristics of type 2 systems are similar to type 1.

3.3 Typo 3 Excitation system - Static t-Ath terminal potcntiel and current supplies Some static systems can not be represented by type 1 or 1$ because generator terminal current is used iith potential as the excitation source. An ox iple bf such a system is the General Electric SCPT. The type - 3 system has been developed to represent this particular static systom. Fig. 3.3 givos the Qren ofor functions mating up a typo 3 system. The rogul ater tr n sfor functions are simil er to typo 1, upto zd -including the regul ator output 1imitor (V R max - VR min ) • The folio 9.ng summing points combines the rcSulator output with the signal representing the self oxcitation from tho generator terminals. Kp is thin coofficbent of the shunt excitation supply proportional to terminal volt ago. Similarly, K is the coefficient of the supply obtained from the terminal current trrnsformor. The multiplier (WNLT) accounts for the variation of solf-oxcitati n with change in the regular relation of field current iFD end self oxcitotion vbltago VTR EV. The V

ma limiter acts the excitation system output B to zoro tkicn to > 1 4 that is,, then the field current exceeds tho o rcitation output current. Sxcoss gcn oration field aarrcn►t by posses the excitation supply by flowing through the output recta. fi ore

2l..

Tho tranafor f inctior~i 1/LIC E • FE) represent ot the constents of tho excitation trsnsformor. Damping is provided by.fiold. back trensfor function s%/(1 e drF) 3.4 Typo 4 - Excitation System.. Iloncontinuously Acting The cyotcros dtseussod previously are representative of the modern high gain, fast acting oxcit ation sources. The typo 4 systo- is used to ronresent the other systems,,, In particular thoso that wore usod immediotoly boforn the developmcnt of tho continuously acting oxeitntion systems, General Blectric Hosting house

GFt 4 roerul ntor B3 30 rogul ato r

Theso systems respond at basically to differcnt speeds, depending upon tho magnitude of the voltogo error. Far small errors, ad juatmcnt is made dth a motor-oporatod rheostat. Larger errors ecuso rooiators to be quickly shorted or Inserted cad a strong forcing of gad cppl iad to the excitor. Fla. 3.4 illustrates this action, The excitor representation is similar to the previously described systems except that no major dompIng loop is represented. Dcponding upon the m itudo of voltage error A VT different rogulator modes are spoel.fied. If voltage or^or is larger the tho fast raice/lowor contact setting R,~. (typically five porcont€ago), V maw or VR min is applied to the excitor,

.. 22 ..

depending upon th© sign of the voltage orror. For a voltage error loss then Kyv the exciter Input equals the rheostat setting V,,„ The zboostst setting is adjusted up or dorm depending upon the sign of the error. The time con ntEt representing the slow adjustment or excitor field voltage is T. Nomenclature $ VT

-

generator terminal voltage.

TR

,.

Regulator input tutor time constant

,~

Regul ate r ro form co volt age setting

VREP a

Regul ator

gain

Rogilator amplifier time constvnt SE

..

Exciter saturation function

EFD

--

Exciter output voltage

Kg

excitor con stEx t related to self--oxcitod field

T8 Kp

40 .~

Excitor time constant Regulator stabilizing circuit gain

Tyr

.•

Regulator stabilizing circuit time constant

Vg

..

Regulatorr output voltage Potential Circuit gain of typo 1 S or typo 3 system

5 K1

-

Current circuit gain of typo 3 system

IF

-

Ocnorator field constant

AVT

..

Generator tors anal voltago error

ITV

-

Fact raiae/lo r contact setting type 4 system

23 -

T E - Rh eo st at time constant type 4 eY stem. "

Voltage obtained by vector vam of potential *d current signals, type 3 system,

V - Field rheostatt setting

I,~ .. Generator terminal current

24 4. EXCIT AT ION SY ST E1 WITH M A(N TTI C AUTOMATIC VOLT AGE UkO The magnostat voltage regulator, as spplied to the control of large generators being menu facturod indi geneou sly by CIS, , Bhopal comprises a voltage respon so circuit, a tupotngo magnetic amplifier, Ed a high sensitivity exciter phi ch controls the main oxcitor on the generator set. The flinction of the regulator is to adjust the generator excitation automatically In recpon ae to deviations in bi c-.bar voltage detected by the voltage sensitive circuit. Suitable cnplificotion to provided by the megnotic amplifior to cncaro that the voltage is held vithin close limits for my load from zero to full load. The zraltogo recpon no circuit and magnetic Cpl if for are eitiroly static devicoc, end no moving contacts are employed in the roaulating circuit. Rend control of the genorator for starting end the emergency purposes ( .th the voltage regulator out of sorvico) is by mr-en s of the conventional bend or motor operated excitor field rheostat. betas are provided of predetermining the rogulntor and rbooatat settings, in order to tnnvaro smooth change-over botuQon hid cnd automatic control of the generator.





r

+:

1

A, a, ~I A $ s'~E q^ar

uI

rlhvi

-.

[.

O , P,.IP(ER — FIRST STAGE

lL4NER

FIG l ZENN~R HUE COMPARIM ,~~ C ~I;,i, i CI^C[. NHARACI N16%

'

u

r

_i

A MRt — r laa.,. fl

L _. .

1 ~ _..~_ I - -

_ .._~ L

V-

1tia~~

1ST 5TA4[

AAGNfi''r. T Y

VCLTAGE '; _J

c

TYPICAL

5WT!_H 5'Y!/ I

G~M701A~(M1'Lj

URLL1

R IO1 ' r ---1

r

r

-- .L.

0

_4

AI . X X' ( •

I

"

iY

EX ,:"1T " ;ti S'fM M7H MAGNETIC AUTOMATIC VOLTAGE REGUI ATOW

' r1~'

L~ .1Q R~?~ RJr



~RIOS

..._~...

L.. ..._._ .. VGt*AGf

rEA ,v4

25~.

A protectivo relay to provided to remove the rogul ato r from service in the ovents of incorroct oporrxtion. Under this fcalt condition tho generator is cutomatically returned to bond control. A cot p unding circuit of quadretum in jection type is included In the voltage regulator to satobilise the reactive KVA loading of the gonorator eh cn operation in parallel vith other gonorating pleat. D1SCRIPTION O F CIRCUITS

x

Tho operation of the voltage regulator may be follorcd in dote-il by reference to simplified diagram. Fig* •.4x.45 COLT AGE S F!N SI TI V.I CIRCUIT s Tho three-Pbnse generator terminal voltage from the voltago tresformor (VT) is cpplied to the trcnsformor TI. The secondary voltage from TI first rectified in MRI end omoothonod in chot L1, is then applied to the voltage sensitive bridge,, v1hich comprises volts' o reference diodes ZI to 28 cnd resistors R R crad R4 (fig. 4). The diodes are spoct l silicon devices operated at the reverse voltage brealcdovn (or Zcnor) points,, tk ore the voltage across the diode is conatc t within close limits over a itdo rrngo of current. At normal gcnorntor voltages across resistors R 3 and H 4 are equal. to those across the reference diodes rnd the bridge to balcncod,, cb that the output voltage botveon

points 23 and 15 is zero. It the generator voltage alters, the bad.ence of the bridge vill be disturbed end an output voltage iI11 result, the magnitude depending on the generator voltage deviation from normal. The bridge output from points 23 and 15 is applied to the control winding of the first

stage magnetic amplifier.

L IFZ!R The main elements of the amplifier,, rich is of the tuo-stage magnetic type, are the saturable reactor SRI end rectifiers MR2 and MR3 in the first stage and SR2, MR4 and MK.5 in the second stage. The first stage of the amplifier (fig. 43) receives its a.c, supply from the generator potential transformer at points 25 end 26 end gives a d.c. output at print a 29 and 34 to control winding A3- A4 of saturable reactor SR2 on the second stage inplIfIer. The second stage receives its s.c. supply from the generator potential transformer and gives a d.c. output to the ' unpiidyne' exciter control field. The amplifier d epertda for its action on the principle of saturable reactor, a high degree of amplification is achieved by the use of special magnetic material, for the core,. Potentiometer RY1 is used to adjust the gain of the amplifier to the desired valve by controlling the amount of positive or negative feedback applied to the first stage. It will be observed that over the eking portion of the characteristics, the d-c. output current from each amplifier stage is directly prepotanti al to the d. e. control current. To ensure that the

Vilifier stages operate over the required portion of their characteristics, the second state has a bias-winding A1--A2 supplied from the pilot exciter ad is stabilised by tenor diodes. EXCITATION Si'ST)4S s

When on eutometic control, the main exciter field is supplied from en ' emplieyne' exciter %hose fields are controlled by the magnetic amplifiers, Field Xi.X2 is a positive bias field carrying a d. c. current derived from the pilot exciter, Field X?-X4 is a negative control field and carries the amplifier output as previously described. Under normal condi•. tions the excitation produced by X3.X2 exceeds that dia to XS-X4 by an amount sufficient to provide normal excitation of the main exciter and alternator. If the generator voltage falls (for example,, due to on Increase in load) the action of the voltage sensitive end amplifier circuits will cease the current in field X3-X4 to fall # thus giving a net increase in excitation to the generator set and consequently restoring the voltage to normal, Conversely a rise in the generator voltage results in reduction of excitation and restoration of voltage to normal. ANTIHUNT

$ The voltage regulator circuit described above, in

common with the other sensitive regulating devices, requires

stabill sing to prevent hunting and to ensure satisfactory

..28.0 recovery following ridden load changes. In this case stabilisation is achieved by transient negative feedback of the main exciter and afiidyne exciter armature voltages Into the amplifier. Adjustable components are used to enable the regul ator to be matched to any generator set, Mn additiin el stabil ising voltage is obtained from a small winding on the quadrature axis of the a rplidyne, it is applied to the amplifier and assets in atabili sing the exciter voltages. RAND gQNTF43L

When the regulator is out of service during starting or for maintenance purposes the generator excitation ca1 be controlled manually by means of rheostat LW 101. This rheostat is ' potentiometer ' connected across the rectified output of the pilot alternator and supplies excitation to amplidyne field X5-X6. To reduce the effects of residual. magnetism in the exciters end to give a satisfactory control characteristic on hand-control, a portion of the amplidyne armature voltage Is 'fed-back' into the circuit of field X5.X6 through resistance divider R 102, 106, 107, 109. H ARZAMT0 c AN GT 0 VFR

s

Ch Changeover bet wean hand sad sato control of the generator is by means of switch SW2,, the contacts of mbich connects amplidyne fields X1-X2 and X2..X4 to the voltage regulator for ,auto control * end field X5-X6 to rheostat RV101 for hand control. 'he appropriate control (R'V7 or RV 101) is adjusted to give zero reading on balance meter M2 before

switch SWW2 is changed over, thereby ensuring that the regulator voltage adjustment or field rheostat position is correctly set to take over control without Bch a go in generator a xci t at ion. MOTS „AMELX YN E 5 ,r s

The emplidyne exciter end pilot alternator are driven by induction motor supplied from the low voltage A.C. system through a direct on line contactor starter. The oniplidyne is • form of d.c, generator having the special features of quick response and very low excitation power. The high power gain is obtained by means of 'crass field' excitation. The pilot exciter is a small permanent magnet machine and is overhung on the end of the set. This generator has no brushes or weeding pert. A fly%beel is provided on the motor amplidyne set to maintain the set speed and prevent loss of excitation on the main generator under conditions of momentory loss of low voltage s. c. supply.

CHAPTER . II

1. ERROR DETECTORS 12 The different tykes of error detectors are desor bed below s1.11 Bridges using Saturated Diode Valves In this bridge the variable element is varied as a result of variations in filament temperature and not as a result of variations in the voltage applied to the bridge circuit itself. A circuit is shorn in fig. i.1) (s) Uh i ch consists of three linear resistors R1, R 2 and R4 and a saturated diode V1. The valve may be considered as acting as a variable resistor, its value being controlled by the voltage applied to its filament. Increasing the filament voltage increases the emission end reduces its resistance. Characteristics of a tube of this type are shown in fig. 1.11(b), It Iss seen that the resistance dicreases rapidly as the filament voltage increases but that this rest stance also depends on the en ode voltage. Since the anode-voltage/anode current characteristic of a diode is nonlinear the balance of the bridge will change If the supply to the bridge changes, independent of any change of filament voltage. This is important If the bridge is fed from eq pipply derived from the input to the stabilizer end it is preferable to feed the bridge from a constant voltage source.

I o

+----o o-t

C VO'AC

f2 ;

I

FIG 1.11 ) SATURATED DIODE MEASUH

-

.-..-

lil

T

I

FV Ii

'R. OF E) 1. VAi TtPi :ANCE V. :

I-,

- 31 1.12 Other Types of Measuring Units In certain types of regulating and controlling units (e,g., the Metadyne end the Trensductor) it is not necessary to feed a single signal in to the device. Instead a number of signals may be applied and a device operates according to the algerbie sum of the signals,, i.e. the magnetic field produced is a result of the ampere-turrns produced by a number of control windings, each being fed with a particular current. A number of measuring units have been devised for use with these units. The simplest arrangement (which is really a referencecurrent measuring unit) is to feed one winding with a constant direct current (the reference current), end to feed the other winding with a direct current prepotional to the output voltage of the regulator. The consti* t current may be obtained from a direct current source or from a alternating currant source (such as the output) and rectified by a suitable rectifier. The current may be maintained constant by any suitable device such as a barrer. The current proportional to the out put Is obtained from a rectifier, usually a full wave bridge rectifier as shown in fig. 1.12(a) . The to control windings are arranged to oppose each other so that, at one particular output voltage, there are no re ultannt ampere-turns produced by these windings. By arranging that the amp ore- turns of each winding are large, a small change of output voltage will causee a

FCR

AJ..\C

PJ VOTACf TO MEASURING UN.T



CONTROL WINCAC

L

I ti

(C) cc

VG'

V? V1

FIG. 1 I? BALANCE CURRENT TYPE MEASURING UNITS rc NPL'

--0

TO I

ME ASLtRINC, s u -,7

OL'PL' To

C DNTRt.

1 —---

C

.

(L )

A

To CON T ROL CIRCUIT

..-

HG 113 THk PHASE SATURATED TRANSFORMER MEASURING UNITS

32.. rolativo large change of rociitc t amporo-turns. Thia orrrngo-. mcnt is simple and is not affected by frequency chnngoa of the supply voltage. Another arrangement which may bo considered as similar to a non..linear bridge measuring unit its shown in fig. 1.12(b). In this coos one winding is fed throu.6a a resistor R (or a linear reactor) and rectifier REi so that the current in the windings is proportional to the output voltage1 so shorn by the straight line for current it in fig. 1.12(c). The other finding is fed through a non linear device,, usually o saturatod reactor L, end rectifier RE2, the current i2 in this winding opposing that of ii in the other .1nding. Due to saturation,, the irront 12 is not proportional to the output voltage bit incr©acec more rapidly: as eho'n by tho curve of fig. 3.12(c). fit a valtcgo V1 the two currents are equal rnd, assuming equal turns on the two .ndin gst the ampere 'Earn c are zero. If the voltage drops to p?4 12 is reduced more than i t end a result nt current AB is now available to produce control emnere turns.

This arrcn gem€nt has the disadvantage that since the current 12 is approximately inversely proportional to frequency, The balcnce voltage V, varies ?.with frequency. An unu ni al moosuring unit for operation of threw-phase supply is shovn in Fia. £.13(a). The primary winding of a throe-pbaoo tren sformer is connected in star to the output voltage

-33-

of the roguintor, vhilo the secondary is connected in mesh to the control circuit, commonly the control cl.nding of is magnetic amplifier. Due to the saturation of iron core s in order to obtain a sinusoidal flux, a third harmonic magnetizing current must flow. Since it ccn not flow in the star primary it flows In the mash secondary. The magnitude of the current depends on the saturation of the core cnd hence on the voltage applied to the primary,, as chow in fig. 1.13(b) . The dicadvcntage of this arragemcnt is that it is ern sitive to froqucncy. If this is importcnt the frequency compenantod circuit chosen in fir„ 1.13(c) may be used. As tho frequency is incro asod o higher voltage is applied to the primary of the transformer so maintaining the flux don atty 9, and thoroforo output t rnproximrltoly constsnt. The eompcnsction varies t4th c~aplied voltage Fmd to only correct at one volve9 but it Is con sidorable important on the uncorpcncatod typo.

do

34

i

2. DRSIW 0 I I'RRDR ,. DITECTORS 2.1 DQSIgU of Error-Detector - I A Complete schematicc diagram ehovn In fig. 201. This arrsngomcnt 18 to food one finding 'ttth a con stvxt current of 10 mA (the reference current) cnd to feed other finding v4th a direct current of 14 mA proportional to the output voltage of c.c,, goncrator. Both the direct currents are obtained from the €~1toz sting eurrcnt source (ouch as tho output of the o. c. gcnoretor) , htch to first stepped don by transformer 4Y)/100 volts ,Gnd then rectified by the suitable rectifiers. The current obtainod is consttrat by the scnor_diode. The Current proportional to tho output voltage of o. c. genorator is also obtained from the aarzxo courdo. Rating of the zenor is 10 V rid 10 mA, so that the current in the zenor circuit should not be oxcoodod more then 1A mA. This value of current to obtained by putting cuitablo reeistsncoo R l cad R2. 2.2 Do ai off Error Doctor .- 2 Another err, n gomont Of error- deto etc r I. s ton in Fig. 2.`3(o).

In this orrr~ gom2nt one grin din g is food through a linear trtri sformor T1 (400/100 volts) rn6 a roet2fi.or bridge RF1, so that the direct current in GVi winding in proportional to the



0

h

f

o0-—

4OO / !OO V

3

-f

3Aa

RECTfFIER

FIG. 2.1

L

IfL

ERROR DETECTOR--- 1

T

w,, :

RE

I

L*i

I

– – L

400 PTV.

TRANSFORMER

~

_ZY

is kV

0--

0--

•

0_-._

T 2

AEz

FIG.? 2 (a) ERROR DETECTOR-•2

C L1- NT

i

-

Vz

V1

VOLTAGE ---~

FIG.2.2(b) CHARACTERISTIC OF ERROR DETECTOR

-35output voltage of a. c. genorator, as shoun by the straight line for current 9.I in fig. 2,2(b). The othor in ding C! 2 is fad through a non-linear device, I. e, non-lin©ar transformer T 2 and rectifier RE2, and this current i2 in this *winding opposing that of i t in the other winding. Due to saturation,, the current i2 is not proportional to the output voltage,, but increases more rapidly, as shovn by the curve in ft g, 2.2(b), At a voltage V1 the two currents are equal and assuming . equal turns on the to windings, the ampere.-turns are zero. If the voltage drops to V2, i2 is reduces more then 11 Fnd a resultant current AB is nc>w available to produce control amp c►re- to TT) s. For the details of the design of the transformers and rectifiers for reference See appendices I and 2 respectively.

3. THEORY OF MAteETIC AMPLIFIER A magnetic amplifier consists essentially of a saturable reactor end a semiconductor rectifier, when connected to a cyan st en t voltage a, c. source, it forms an ad ju stabl e voltage source of d. c. voltage. It can be used as a power conversion unit of an adjustable voltage system for d. c. motor control, or as a regulator,, or as ass excitation system fbr the control of dec. r/c field or power conversion units of adjustable voltage systems„ The function of the saturable reactor is based on the to inductcnco theory as explained in fig. 3.1. The diffor ntisl permeability is ideally infinite in the unsaturated region of SR S and honco the inductance of SR is ideally Infinite. As a result, the inductance is infinite, the fill absorption voltage All be appeared across the SR. If it is switched to differentia]. permeability is idoolly zero, thus

giving ideally zero inductance, thus the full absorption voltage will bo appeared across the load. In the following theory, the SR is viewed as an inductance hib, during the steady state onorationn, is very high (ideally bfinite) throughout one part

of the half cycle of the supply voltage and very low (ideally zero) throughout the rest of half cycle. Thus the operating region of SR iu betuacn zero to infinite impedance, and hence react an cc.

TB! TGY BTZC AMPLIFIER t7E?RR

The heart of magnotjc amplifier, ed the source of its name, is tho magnetic core. The study of the nature of the core to be used %All therefore be of considerable relevi ce. The requirements for a transductor core are specified herein by cammari E1ng the desirable footuros cnd the particular way lb .ich each one infiuocees the overall performenco. ( a)

Slh erpn 088 o f B..H Curve'

The non!..Unoarity of the magnetization carvo is the basis reason for trrnsduetor operation. Unloss this non. linearity is pronounced the linear operating region of the tranoductor *411 bo small tnd emplificcition loin,

(b)

Slope in Unsaturated Region

~rir.~~~r•u.rrrrri...~~rrr~ r~,r.rrr

If the slope of the magnetization curve in large in the unsaturated region this loads to a high gain and smell standing current A th the ro cul t in g stability of the characteri sties.

(c)

Iran Losoes,

I xcosaivo iron losses educe reduced gain and increased zoro drift. They do not seriously limit the thermal rating bocauao thcn tho iron loaaos are maximum the coppor louses are negliQiblo r_ud tho tvD are never a m aximam at the some time,

Cry)

3 aturntion Plux Dc n nIt

¶hic should bo as largo as possible In order to onable the a. c, rinding s to 'support a largo supply voltage for a given, number of turns, Co)

Rolativo bportrnco

of various factors

Unfortunately the loss otpenoive corn materials ore notably Inferior in may respect, thus ailiebn-.iron, t ►ic to relatively dhoc5 has a cow nrativoly lots permeability together with a saturation ubi ch is not particularly c'A arp. It alga suffers from the dfoadvcitego of having htgior loacos thin the nicltel-iron Coro, the l ottor hotovor, are reach morn e cn oleo. rlbon dooling Frith ?Or' nickol-irons (cxaotci, pox rub C g etc.) tho pormoabiitty to high, the losses ore lou tmd tho kaaoo of tho characteristic is relatively sharp. Yho cost of thrso materials, hocrovor, Is very high tad rho saturation flux density. to bn] y about on o..h ai f of that for silicon iron. Thiss toads to incroaoo the toigbt of ffiunetai rcquired fbr a given output %& ic'b ro gi It o in a farther Increase of costs. 1 ur et el is therefore generally confined to moll or units or first ate.. oo rcquirina a high Grin. iho 5P nieltol irons (fl.C.R. Doltrmoxv orthonci) have a hips saturation induction but the loc oa are higher that in zsarnotoi. Eorly trcn eduetors omployod cores aoco!blod fron leminat ton o 6f tho typo commonly uood In t ran otormora. But

v• - e m, s' (wt + 0) FIG- 3.1

FIG. 3. ACTUAL HYSTERISIS LOOP OF RECTANGUL AR

LOOP MATERIALS b

ul

FIG. 3.3 ASSUMED HYSTERISIS LOOP FOR RECTANGUI.s-R LOOP MATERIALS

uuuuuuouu ----- --~ VA

FIG,3 4

Ii

r

t

SERLE. S CIRCUIT CONSISTING OF A RESISTANCE ARC A SUITABLE CORE REACTOR

t icn used for trcnoductors they give rice to profbund non.

1 noority half tray up tho mngnoti notioon chzPactoristie. Toroidal cores givo the b.ighact cpltttcation cnd grontost stability In all cocoa. The offoctivo clopo of the notnotination curvo is greater th * that of flat l zinatod corn rid Individual coros are more conciatrnt. Tho chief difft4mltios 110 in the cost of it.nding, tho poor vinding saoco fcctor9 partirular]ly in small units, ci d the rathor n cord €hmo c 4ch door not rowdily tcnds it colt to ocoy cl ampi ig or ftttin g compactly into ergo ipmcnt tcro op coo zict be con corvodm TPI r I Y ' BE3Ts LOOP

The actual bystoro is loop for nickel-4.ron raloys corr only 'hnovn as roctcngulor loop or cc&uaro loop actortol s i C)otfl in fig. 8.2e Loop 1% in this ftQurio rcproac2t o tho major hyotorocis loop. B roproocnto tho minor hyotorocic loop cad 9.s obtainod t icn a vol tago incfficicft to antu.rato the cure t. o cppliod to it. Tho minor hyatorr~to loop is symmetric about the vortical nxt a, i tg. 3.3 rcproccnt s the eocieod hyst.erocin loop for tho rectcngulnr loop untorinls, flora 8 % ,lo-11'8 rcpr000iata the r tnor hyntoronia loop, tiboroao 1 4&G.'7- roproccnto the major hystorosia loop. In tho oubacqucnt trootmcnt tho hyatoroaia loop of fie. P.2. hn7.1 bo tho basi s of c alya-a.

n~at,LYat8 Ci? -A SIt PLt SLRIES CIfl:UIT

si~tor a simple caries circuit of fig, 34 ditch consists of a resistance (load) cnd a saturable core reactor connected across a time varylba voltage source VW* Prom basis *ircuit theory,, it fo ,love that a

or VA z=V,.. iR, V1 = 11,E dt

Toro I is the numbor of turaa in tho aatura11a core rosetor„ Ito have three distinct otntos of oporotion. (a)

Under rsccitod State Horn the induced valtago across tho saturable core

roactor is zero, cnco d l / dt to zero. The current in tho circuit shall lio botuon -o- I x cnd I=. ihore Ix i s the Qoa otising currcnt,o

co V1

= a

V

(b) Excitation Poriod The conditions during the period cc'i be summari zod aathomctiozaily an fbllona s VA a i Ir

Nor lot VA -7 a end lot the current l be at the vnjuo I 3„ If the coro goes in exciting period at tho 4netint t rri d if the f1u r in core, at the said in of r r t ho at tho vlua

,'j, then the value of core flux 9r, at a ltittor inotrat

t2 to gi vcn by tho fbllo win g relation a t ~2

a

1 p - VA dt tl tt oacoo may ariso s (a)

''2 ,~Q'c

s In this csso the excitation period

to not over at the in ct tt t2. Tho current in the c'i rea it cln t In oou c to remain at 4 I X4

(b) '2 79'0 -- This is phy stcolly iraoosiblef bocaa co tho core flux ccnnot incronso above the coturation level. ihoroloro in Coco (b) , the oacitin ported e, me, s to C end o the fnatent t og t < tg so9 Iva a~ Q'l — dt0 t3. A



42 r

When the voltage applied is sinusoidal, certain assumption and approximations can be made in the aelysis. Let the. voltage applied be i V = 'gym Sin ' at.

At time t = 0, the voltage V is zero end is increasing in the 'direction . Let it be assumed that the load resistence R L G .-.~. . Let the flux be zero et 4, = 0. Ix

First there must be an onderazcitod period- with the flux remaining at zero and with the circuit current R i art 1.R s pa 1 L Thus underexeitod period viii come to an end Then i =i-t at the Instant t = t* C t* > 0), Let Mt* - 0*, then V

Vm

I x Sin wt* -n - - sine. lit L I x Ry, Sin G* Vm

?he first approximation can be made. Im that the underexcitid period is very nnch small compared to 1/4th, of

43

the cyclo crid thoroforo 'Chia ported ccn bo nogloctod, According, it is oasamod that the crarrent I chr_ngoB from .zero to • I.. or - I tnstc tcncouoly. So the ozciting interval. starts at t = 0, During this Interval V i a positive end I a ~a I X" Nov, VA

= V - 1z 1L U Vm sinVt-in RL

^zcept as t - ' O. for ell other tiaos V "7 7 In R L The oocond epproxination to that during tho exciting ported the wboio of the supply voltog4 t.o c plioc9 ocroan tho anturoblo core reactor.

1Jhcn the core

octurotoc,

VA = 0, 4 = + 00

F So I = ...V .. .... ..... Sin wt RL RL

In tho okotch of I va t, if , o roaconablo cealo to to bo cho ocn , tho ozc ittn g current could bo cc approaching zoro comp arod to tho maxiaim volu o of the load current. ?ho maxi iim voluc of the capply voltage that ctf bo cppl iod to tho eoro9 to that it oporatc u in tho un ootu r©tod Steicy rogion all throur tho cyclo undor otoady c condition I o cailod the abcorption voltodo. 'rhio ccn bo found out by condidoring that the core vzrka bottroen the flux limite of

M Am

cw 06 and - 0113 g during one half cyclo of period T/2„ xharoforo, 'toa T/2 4 0 = 4 111 V.dt

a

l~ (Vm Sian ) a t 2O vu s

IN

e

a w Vm rx 3, 4 5'o

if the poior is to be cupplisd to tho load,, the soturoblo core reactor must be saturable. This ct be Bono in to 1O7V I.. (i) By applying a voltage greater that tho abcorption voltage of the saturable core reactor. This typo of reactor is called tho oaturstfng reactor,, (ii) By applying a voltage c ual to the absorption voltage of tho core cfld saturating the S.C.R. by applying additional d. c. magnetizing mint from a sop crate winding bound on the saturable core reactor. This is called a saturable reactor. This ccn be dons no shot in fig.S.S. rho arrrigocCZIt d1ota An fig, 3.5 Guffors from the follosing to Gioadvcntagos $ 1, ?horn is a transformer action bot cn the control circuit and load circuit* if the control circuit restotenco

46_ RC to lour the SR bob twos as n tronaformor iith tort circuitod socondery. A very small d. c9. valteco 1C provides a very forgo control mnf under stoody state conditions. '11th. tho result 1R grill be operating in the saturation level ell through the cycle. Therefore the pour doll vorod to the lord o. rinot bo controlled. To provcnt tho coupling botu cn tho bond circuit and control circuit, we have to have o, vary hgah control circuit resistrnco M. But In this case to drive a cont'ol current , i c , c very brae d. c. voltage source is noeonenry ( 1;c = To R0) with the result the potter rcquiroa nt In the control circuit becomes oxromoly high in comparicon with the potor doll verod to the toad. , In foot, there to no cmp1 iftc rt ton. P.. ':%on using the obovo ©rrcnr omcnt ulth high control circuit rocistcnc ,*9 aaturotion only occurs onco ovary cicle Cnd this thcroforo forma the basis of a hrlf..wovo trtnoductor olcnrnt. 13tcn used In conjunction with rectifiers it cgn bo node to give useful rain q othort,ioo tho circuit is of littlo value. Thoroforo, to oliotn mto the two dioedvrnt ages mentioned above of En ordinary $R circuit, we .solo use of tvo identtcQl cotu"abio rooctors, each having load uinding of rT1 turns and control trin din g of g c turns (ft g. ?. f ) e Tho control win ding of thoco ter ccturnblo rooctors ore elwoys connected in series olding. The lord ,indinga of these saturable reactors can be connected in different ways frith or ,ithout roctifioro to give difforcnt magnetic amplifier circuits.

5 A SATURABLE DETECTOR

_

x;

FIG 3. b TWO SUITABLE REACTORS FOR MAG AMP.

1

f

NON

IL



-- —

POL ARILS D CONTROL CHARACTERISTIC

tN

r; Vn -a

c

t')

FVI i 3

f- v-•

- t7 1N d

IAGtETIC AMPLIFIER CIRCUIT

SERIES

,x1

s

I i ° ~ X

_s

e ti

a

FIG. .5 9

I

I

fir?

V rt t f

PARALLEL MAGNET;; AMP!. IFIFR CIRCUIT

r

0D T P L CI AR AC T CTtt S I C 017 0 r -1-1 -M1 - -MC EIPLI VI P;

tontrol ch nrnetert stt c of o magnotie pl ifior is ct curro s1aoiririg the vortation of ov©rogo load current (1v) iittb control current (to) for a fixed load, Dcepcndtog upon the tray two load ndingo of SPA and B nro connected tith ro pcot to

oacb othor, difforcrt types of control characteristics aro obtainod• aI I A IOU O J3 ' T tai: ' t'I i`RS A11 the baste maCflotic cpliftors can bo dividod Into

t to vain Croup a v vt ?. (1) Uon-polhori rod aognot1c c iltfiora circuits giving nony.pol eri zod control ah aractori ati cs. (ii) Polarized nagnot tc Ali fi er giving pol on cob control ch nracteri atic a. It to clear from tho abovo the basic moanotic califiaro

are divided into to Croup o In cccordcnco tyith. their control characteristics. (i)

non-rolariood ='1atotic Aoltficrs and their

Tho nc -pol oricod control characteristic Xll be ate shorn in fig. .7. The characteristic is non-polarised b ,coi co the load circuit to not ocnsitivo to control signal polarities. Tharp era tt booic zaM of is argil iti or circuits coning under thi o group,

Vi?.

(a)

Sories meiotic affil itior ci rc.iit (fig. 8)

(b)

Parallel magnetic amplifior circuit trig, ;.M).

As the na o noggosts in S.!4. A& circuit the tta load winding of SR 'A' and SR ' ' are cornoctod in series In such a iioy that the total indtucod voltage across control windings

(i.e. across 3'1 - Y,4 In fig. 3.8) is zero, v-bon to reactors are operating in unsaturated region. Similarly in the case of a parallel. taagnoti c calf firer circuits,, tho to load d24gs Xl .. X cd X 3 ~- X. are connected In parallel in such a crap that the indu cod voltage across Y1 -- Y of fig. .E' 3 a ri(3ain cord, under unnaturatod operating conditions of S1 'A' cad SR 'B' * One more point has to bo noted horn. in tho case of a P $l. t. circuit,# the supply voltage to bo cppl iod is cqu r~l to the obcorpt ton voltogo of 'oseb R.R. t~iilo In the case of a C.M.A. circ-uit,a tho voltage that has to bo aspltod to cqurl to twico the absorption voltage of each core.

Tho polarized control chnractoricti c will be as sboin in P'i g. 3.11). Cho characteristic is called pol ari sod c araetoriaitc boccnao tho load circuit is sensitive to control uignrl polarit ic~ti. Thc1 basic magnetic ttmpltfioro coming under this group, vir. (a) Series mo otic ampitfiorn with

external fco d back - series sol f- ozci tod naEngttc crplifiers (fig. 3.13),

VIZ, 3.10 POLARIZED CONTROL CHARACTERISTIC: r

•Nj

hI

Nl

_

4J

F:G 3.1I SERIES SELF EXCITED MAGNETIC AMPL IFIER

-.

~a NF ; I L +•

k1

LL C

I

I

i

1 i

i

I

FIG-3 12 PARALLEL 5 SELF EXCITEC MAGNE- TiC AMPLIF- !ER

aT i

~

L

3

~

it

L

_

FIG ;LS

.

W:-i!":GE. AMP! !TAT

FO 0 C

L OA[

a VI

r 48g.

(b) Parallel magnetic amplifiers with external teed back . parallel self-excited magnetic amplifiers (fig. 3.i). Cc) Bridge amplistat circuit (Fig. 3.13} for d. c. toad. The first tea► are self-~explanstory. The shape of control characteristic can b• changed depending upon the mount of feed-back m.m, t. (t f N f) Bridge empli stet circuit is storm In fig, 3.12, This type of connection of saturable reactors requires for the d. e. load. The load winding of B.R. 'A' and S.R. 'B' are connected in parallel. Fill wave rectification is obtained by the full wave bridge rectifiers.

4. fir F 'ALT R 12 T iQt! s•Ts^ Tai n^ ~i .~?

PQP_2KUZ34a I

A mognotic oxnpliflor orcitation systom Is sho-tn In Pig. 4, is cpplios to the control of nync ironous gc orators, comprises a orrbr•detoctor circuit, o single stage magnetic ocplifior,, itch controlo the main oxcitor on the gonorator oct. The fur etion of the rogulntor is to adjust the gcnerr►tor oucitntion catomoticclly. Suitoblo t+plificotion is providod by the magnetic aaplifinra to cf .pro thrt tho volto(o is hold crithin close limits for eny load from Eoro to fill loam. Tho error detector r-nd nrigtetic a"plifior circuits, ore cnntirely static doaicon d no mooring contain are r_^nloyod in tho roaxleting circuit. The operation of the circlit may ho follot~od In dot ,,i2 by roforcnco to dinarca fig. 4. Tho throo ph coo gcnorator terminal vlta o is replied to voltsao ocn sitive circuit i. o.. , error detector unit. This arrr-naomont is to food one control -aInding of tho mogn&i c li'ior Eritb a conotcnt direct currcnt (the roforcnce carrcnt) rnd to food the other control finding with a direct currcnt proportional to tho output of ae c. gonorator. Tho con strt currcnt In obtainod from the alternating currcnt courco (cch as tho output of a. c. gcnerator) and then roctifted by the roctiftorn. Thic current is 12 maintain consttnt by zcnor diode Zn 2. The carrcnt it proportional fbr the output of o.c.

! c

4

a: 0 Li Z" Li

0 0 kf

>L,l7

0

Li U) >U)

O

m

0

U x Li U Li

L

(Ccnorator is obtained from tho armo courco. Thneo two control windinga are arrcngod to oppose each other so that at particular output there is no recu.ltent ampere-turns produced by these 7inding s, The main elements of the magnotic amplifier are the saturable reactor end rcctifiors. The magnetic amplifier rocoivos its a. c. supply from the separate a. e. source at points 1..21 cd it givos d, c, output at points 34. Tho output of the nognotic r,: pliffor is directly connoctod to the field of the excitor ;g®norator sot. If the Qcnorotor voltage falls (duo to ran increase in toad) the action of error dotoctor circuit ,t11 ccu so the currcnt in tho vindina CW*i fills, giving a not increaso in o tcitntion of excitor-gcnarator sot end eoncoquen iy restoring the volto to normal. Conversely a rise in generator voltage results 0 In reduction of excitation restoration of voltage to normal. Detailed npocificetions of I1.G. !.th exciter are gtvczz In the cppendix '?.

/o&y 33 ESITUL LIV"~."Y 0W{YERS~ Y OF ROORKEE ROORREE

PIFRFOR44IJC9 QF MAGNSTIC 64PLI1IIER EXCITATIONSYJt1-1

The various .ozperim€nts performed as a part of the fabrication r rk, era doccribod baby z 1. erimcnt i .. To obtn1n th ch~n~ractor1atics ~.~ror ~rrww~s~~ rrw_r~~i~_ ri~+rrir

ot . mm r dnt r rto xe

Tho oxporimontal sot up for both typos of error detectors are shoe in Chmtor II Rig., 2.1 and 2d (a) ro poc. tivoly. The cb araetoristics of error detectors is take by varying the input voltage, The output currents 11 end 19 are noted In thn control tilndthgri C"T1 and Ct-Y2 respectively. Tho rnadings for those systems ere to'bulotod in the T ablos 1 tnd 2 rospoctivoly X2d they characteristicap are ahoy in fig. 1 end 2. rospoctivoly. 2* E on at tt . 2.1 To obtnin the I nMoti sntion curve (Volt-. Amg ) o f thc~ gR mat o i x The ozorimcnta1 sot up chown In the fig. 2.1. The voltngo VL applied to the core in varied and the corresponding valuoa of the currct tL are notod. Tho roadings for a roproocn.. tativo core ter- tabilatod in table 4 cnd magnetisation charootoristic is shomm In 1t r. 1(o) .

C)

E

1

501

Q Li)

21

E

[~

d

E~

mss- - ---i

rWE >

« c1 cu

V

C'V

i

62..

2. ! e iraont tIt - To obtain the c*inrnctoria'•ics ,pf # circuit The circuit arrxigoment for this o pon mcn t 9. s to .► in fig. 2.?. Apply 50 volts s. c. across the torminalo 3.4. Peed d.c. mmf to the control uindtng from a doe* source across the points 1-2. A double pots tiomotro arrcngomnt I s used for smooth cri_ci accurate control of control currant I .

KOC-p 1r

at

any ;?* 6!) ohms, Th o o. c. €apply is 50 volts across points V..4. Tho load current IL Must be round about WA/2L, Vbcn 'I,c = 0. The control cu.rrcnt I C is incroasod ,''Iov&y. If the loed c'4irrcnt IL is al co incronsec then 10 is in tho positive mmf direction. The value of TL Is noted for different value of t in tho positive end reactive anmf' diroction. The readings aro tabul otod in the ta'Ao 4 and tho control characteristic is ziot1 in fig.2(b) .

3.

En orit t IV - To obtain the otQt dy_ atntg_ stnfio voltrho ratulction Tho osrporimcntal. cot up is thot to the Chcpter It

Fig. 4. Tho throo phase load to tppliod to tho Ccnorator terminal Is variod ctid corrocponding values of voltage drop are notode Tho readings for a rcprosontativo system are tcbulotod in table 6 end tho characteristic is abo f n fig. „ At 6 crnporoa load -10 load voltug .. o ... 40 V ii11 load voltage 375 volt,. ..0

52Thus the percentage pf regulation con be calculated as p ercen.tage yr -....,.. Nonlo vla - ll votge l..,.~,._. Fu otge _., load ...Y.....~,«...,... '~...-......,...~....~.. ~ regulation Full toed volt age 4' O 975

275 .

xc 100 s~ 6.6

The regiletion of the e, c. generator without using the magnetic amplifier excitation system is calculated at 6 aup

toad. No load voltage

40'V

all load voltage ,.. ...

V

Percentage of regulation

25 Thus the percentage of regulation'4th using the designed c4r&it has been reduced to 18.4°x.

T ebI a Ch,r cteristi cs of erro! detector o

Input voltage Current it Current 12 volts In CW3. in mA In CW2 in mA

25

0.5

1

50

1.5

2.25

75

2.0

4.17

100

2.0

5.00

151

4.5

7.5

2fo

6.0

10.0

250

7.5

10.0

300

9.0

10.0

350

Io. 5

10.0

400

12.0

10.0

410

12.5

10..0

4 55 ..

T abi e — 2 Charecter1 tie of error detector of Chanter II ficz 2.11 put voltage volts 0

Current ii C Jj InmA

Current 12 CW2 in ®A

0

0

12)

55

2)

1.64

80

40

20!7

95

65

240

112

90

28 0

125

110

lBO

135

125

300

142

1~8

320

1517

148

340

160

162

250

172

178

375

3.80

1885

390

185

19+)

410

190

210

4 t i u Chi pct ri stie o f Ami,jostrt

Volt ago Vt volts

L irrent IL m4 23

38*5 54

73 10r 55-) 33gl 3 95,0

Table •- 4

c (_.)

'L

Ic (*)

11

0

2.2

0

2

22

2

4

2.0

4

$

1.5

$

1*)

1.0

10

12

0.53

12

14

0.16

20

36

.0.3.5

20

18

0.155

40

2d

0.165

53

25

0.185

80

30

0.210

70

40

0.0

as

l•

50

O.0

9n

'*

60

0 IqB0

10

0.410

80

0.460

90

0.52

100

0.53

.

100

2.12

2.23.

2.25

2.20

F4

R

V0 ,taxE3 c*

twig LOSd 3Y Amp s. e r 8 c► r t rn in 400

0

397

2

390

4

ZBO

5.5

:'75

6.0

370

7400

C

o

0 0

or 4

LL

C,

1---

-

tf

--4

Li (-) a: (-)

2

3-

LU

Ll

- i

- I -....

C)

C)

Es

1 14

so nog; (-) -0•— I c - -4► (+)

FIG. 2 (b)

CONTROL CHARACTERISTIC OF MAC. Aiv'~Ir

J

r m

I-

b

FIG 3 ST A STATE VOLTAGE R[GUATON C-1ARACTERTiC OF THE SYSTEM

C

B AP P. f .. IV

C fl I! C LU S I 0 tI ?bin 11cgnotio HAnpli fior oszcitotion oy ctom to

cpplio6

for ozcitatlon of small oynchronoua gcnoroto , Tho cyatoo 4a having poculiar choroc'torto.►

tics of Error-Dotoctor cnd Uagnottc Ammplifier* As tho c ►aractoriu*tc of orror datoctor, ich inittrlly givoa total negative orror oignola to tho control t .nding of DafJflOttc amplifior, then tho gcnorator Is running on no load. Alhcn tho load to cppliod to tho acnorntor tort

n ob a, tornin ni volt ago iiiill fail thcn tho orro r-

dotoetor trill diva pomitivo error aiCflalc cnd thus it mointaingod tho o not tation volt ,ago con cttnt d hcnco tho torrin nil voitaao of gcnorator. Boocuao tho oyotcm to eorplotoly static s

it Givoc bettor porforinc oo on tho convcnttonc1. cyotcrn bit it In in Porto r tbcn tho th yri oto r s oxcit otion Oy ot c. 0.

The percent age voltage regulation of the system amn bg 4creased by increasing the gain of magn4.. tic anl1fi er. This can be increased by in creasing the number of turns of control windtng of magnetic amplifier or by intrroducing the solid state amplifier betareen magnetic amplifier and error-detector units or by using one more magnetic amplifier circuit in series with this magnetic amplifier.

61 ~. RAF ER E 0 CLs

1.

E 7. Kiinbork, "Poor Syatom Stability a Synchronous Machines" Book, Volume III.

2.

V. Eatorn, "Excitation or L argo.Turbo. Genorctors" Proc. ISE, June 1964, pp. 1040„

3. To L. D111mm,, J,'7* Slwoglund, P.W. K any, 3. B. South and C. Raczouski, "A Riah Initial Response Bruci1ass Excitation Sy stem". I EE! ' ron a., Vol. P AS 90, Sept. /V ct. 1971, pp.

2089s.

4, tfriaht, 1, r., Ha loy, R, tad Dineley, J. L. " 3rush1oss Thyristor Excitation System", IE~E Trans. on PAs, Scpt./Oct.- 1972g. pp, 1848,

5. D, C. thitn.oy, D. Bo Hoover, P.O. Bibo., "tn Electric Utility Brushloss Excitation Syofom", Trans. AIEF on PAS Nos. 47-51, Fob. 1980, pp. 1821. 6.

Be C. Bartung, E,R, LtnfLst, E'nd Go R. t4etoy, "A Rotating thyri stor Excitation System for Hydro.Electric Generators" T'rcno. IEEE on PAS, VOl. PAS ,. 9, Sept, /Oct. 1972% pp. 2171.

7.

K. A. T7c Clynaont, Q. r nchur, R.J. Rose, and Li. !!ilson, "D poricnco ciith High Spood Dictifior Excitation Systems" Trans. IEM on PA39 Vol. PAS..87, June 19O, pp* 1964. .

8.

Rev, H.J. $umbtrios, Dipl. BL.S. and t , Fairecy, 3.Sc,, "Excitation Rectifier Schemes for largo goneratory&' Trans. I EEC on PAS, Vol. 119, 11c. 6, June 1972 pp.661.

9. "Computor Ropr000ntotion of Excitation 8yotaa~' a Co!ltttoo roport, TREE PAS..87, Juno 1938. pp. 1460. 100

''Dchsr Pouor Plc t Excitation Characteristic or 8cn crator" Bees Construction Board FMarno Nose 105•BLD/IR, 15 . BL 1) end

11.

Smith, I . R, , ,i d ' 1 an 1n g B. D" , 'Rru shl o s s Synchronous Generator with Rotating ?hyristors E~rcitntion". Proc.. ICE, Vol. 12, N'o. 8, Aug. 197?, pp. 27:.

12.

0. N. Pa'ehctt g ''Automatic Voltage Regulators snd Stabiltzors" (Book).

13.

Ii. F. Storm, '~i-4 cgn of i c Ampl i Fi ar s 0 (Book).

14.

Sidnoy Platt, ''i1namctic Ampltfi"rc Theory tnd Ippl1cation" (Book) .

15.

H. P. S orn, "i-lognotic Amplifiers with Inductive D.C. Load",, AIBE ?rcns. Vol. 7, pt. I, Nov. 1954, pp. t56.

15. A, Go filnoo "Trcanoductoro ix d £4 ci untie Aw,lif1.ors" (Book). 17. R. H. Frost Stith,, "the Theory end Decign of 14cgnotic AmpliPiera" (Nook).

4PP WDIX f It Tho throe single phase tr nsfor fors of equal ratings are designed. The design of ouch trastormer

220/55 volts C,O. f b0 . core Flux density 1.3

Area of cross section •.. 14.4 cm2 primary Nos of turn ... 520 using 21 S.tr G. Cu. wire Secondary go. of turn ... 13' using 22 °,'~„C. Cu . ,jt ro

By connecting each trcoformor In star, a throe phase star countod trrnsformar is available. Do 4in H ofNon Linnnr Trnncformorn

Tho three oing1c.-ph000 trenfoancrs of equal ratings ore do signed. 220/55 volts, Iron core

Flux density ... •,. 3.6 trb/m2 Area of cross section ...0, 1444 cm2

Primary No. of turns ... 401 of 22 S,",',4. Cu,a~riro Secondary No. of turns ... 100 of 18 S.1-'. G. Cu. rO Each transformer primary tnding is conne ctod In dolts, c d ooccndnry winding is connected in series. By c plying 444 volts on primary, the core All get saturate , this the output voltage of cones winding vill be third harmonic voltage. The wave shape of third harmonic voltage is shoe in the fig. 1s

APP R DI X _ • II AgrInGO OF R3§TIFIj;

These are the silicon diodes of 400 Ply end 3 Amps. current rating. L

APPWDIX •~ II'i• SPRCiFT CAPICNR OF T XCITXR

D.C. Generator 40 volts - 8.7 Amps • 35 KW -- 1&Y rpm BPr;I1IIO 9QF 01 `' A'GR

A.C. 21 phase Generator Star connected 400 V, 10.8 A Cost 0.8 7.5 K VA 1600 rpm 50 Hi z 9PFCIFICNrIONS OF MOTOR

DsC, Motor 223V 8 IKW

42A 15x30 rpm