POWER SUPPLIES FOR MAGNETS

R. A. Winje, P. J. ReardonNational Accelerator Laboratory':'

E. R. Schoop, W. A. ManahanTransrex Division, Gulton Industries, Inc.

Abstract

At the National Accelerator Laboratoryexcitation of magnets in the beam lines externalto the accelerator requires power supplies withwidely varying output ratings and a stablebehavior in non -Laboratory environments. Theproblem was solved by the design of a singlepower supply with nine different dc powerarrangements using the same primary acconnection. This paper contains a descriptionof this twelve phase 500 kW power supply inwhich the four internal 100 V, 1250 A half­wave units can be interconnected in differentways. This is followed by a description of thecomponents of the power circuit, the design ofthe regulator and the control system.

The paper concludes with a descriptionof the mechanical arrangement of the powersupply and a report of the performance obtained.

Introduction

Unlike the earlier proton acceleratorfacilities where the external proton beam linesand secondary particle beam lines weregenerally f?et up in large environmentallycontrolled experimental halls, the experimentalarea facilities at the National AcceleratorLaboratory mostly consist of long beam lineenclo,sures with small service buildings spacedfar apart (Fig. O. The power supplies provid­ing excitation current for conventional roomtemperature magnets for these beam lines arehoused both in the enclosures and in the servicebuildings; in some cases, under severeenvironmental conditions. These environmentalconditions plus the need for power supplyregulation of the order of 100 ppm establishesthe requirement for well regulated powersupplies.

In addition to stability, the fact that theprimary beam momentum will be varied irom50 GeV to 500 GeV with multiple momentumranges of the secondary beams at each of theprimary beam settings caused us to consider

power supplies with nexible arrangements foroutput currents and voltages. In order toconserve power we also decided that the suppliesshould be programmable and capable of followinguni -directional cur rent reference pulses similarto the main ring pulse but with a faster risetime and the same stability requirements on thenat top as they have in the dc mode of operation.

Another factor which was taken intoconsideration in the preparation of the initialrequest for proposals to build these powersupplies was that we wanted to limit the typesof power supplies to be employed in the experi­mental areas for improved interchangeability,ease of maintenance, and fewer spare parts.To some extent, our earlier deciSion to usemain ring type quadrupole and dipole magnetsand external proton beam quadrupole and dipolemagnets for the bulk of the beam transportneeds aided us in this and we could dictate thecurrent and voltage limitations for subsequentmagnets which were designed at NationalAccelerator Laboratory; but the problem ofpowering magnets brought to us by user groupswould still be with us.

Our request for proposals for the initialrequirement of high current power supplies wasprepared so that prospective suppliers wouldquote on two types of power supplies: 500 kWwith 5000 A and 350 kW with 5000 A each withfull current transformer taps at 1000/0, 700/0,and 40% to cor respond to the power settings wereqUired due to the various load impedances.The specifications for the power supplies werebased on using a six-phase rectifier system.We planned to order approximately 20 each ofthe two types of power supplies or 40 of thelarger type if the costs were comparable; withoptions for additional quantities if awarded bya certain time.

When the proposals were analyzed, itbecame clear that for a production run of about40 units, the cost for the 500 kW power supplywith different voltage settings comparedfavorably with the cost of twenty 350 kW supplies

':-Operated by Universities Research Association, Inc.under contract with the United States Atomic Energy Commission

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and twenty 500 kW supplies. The TransrexDivision of Gulton Industries was awarded thecontract and proceeded to design a prototypesix phase 500 kW supply. The tap settings werechanged to 1000/0, 50%, and 25% to obtain a betterbalance over the range of loads to be employed.

Subsequent to the award, it was recog­nized at National Accelerator Laboratory thatin the future, when upwards of 100 of theselarge power supplies were likely to be in servicesimultaneously, the power factor of the sixphase power supplies would in all likelihood below enough to require power factor correction.The problem was discussed with Transrex andthe system was changed to a 12 phase systemafter the completion of one supply with a sixphase system. Later on, as the requirementsfor the Proton Laboratory beam layouts becameclearer, there was pressure to change theearlier decision on limiting the types of suppliesin the experimental area and to allow two moretypes to be purchased; one to be approximatelya 2000 A, 150 V supply and the second to be a1200 A, 400 V supply. It was at this time thatwe came up with the idea that whereby inter­connecting the four 100 V, 1250 A half-waveunits, on our already existing 12 phase, 500 kWsupply, we could make a series parallelconnection to obtain 200 V, 2500 A, and in atotal series connection, we could obtain 400 Vand 1250 A. Since we planned to retain theprimary taps, we now would have what we werelooking for all along - - a very stable, program­mabIe power supply with flexible enough voltageand current arrangements to meet all of ourexperimental area requirements from 1000 Ato 5000 A and 25 V to 400 V. The proposedchanges were discussed with Transrex and thefinal detailed design of the new system was madeby them. The development of this flexible powersupply has been mutually accomplished byNational Accelerator Laboratory and Transrexand has worked out very satisfactorily in theProton Laboratory beam transport area and inthe Neutrino Laboratory. Additional supplieshave been installed in the Meson Laboratory andin the Proton Laboratory. They will all be inservice by the end of this year. We are nowconsidering the addition of reversing switchesand filters; although, as far as the latter isconcerned, our experience to date indicatesthat external filtering will not be required inmost cases. The cost of the power supplydescribed in this paper is approximately $35per kW.

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Description

The power supply is a 500 kW twelvephase unit with a unique arrangement of secon­dary connections, whereby the dc output of thepower supply is able to provide a wide range ofvoltages and currents. The output character­istics of the power supply are shown in Table I.

Rather than using the conventional wind­ing technique in the primary in which taps areadded at discreet points along the winding, thepower supply has a quadrifilar wound primary.This allows the primary to be reconnected tochange the basic power rating of the powersupply. The electrical equivalent to 25%, 50%and 100% full current, non-load changing tapsare available.

The rectification of the ac power and thecontrol of the resultant dc power is done byphase control of thyristors in a 12 phase, half­wave double star connection located on thesecondary side of the power transformers.Full current rated free wheeling diodes acrossthe power supply output are included.

Stability of the output current is obtainedby a self contained current and voltage regulatorshown in a simplified block diagram in Fig. 2.The regulator is designed to be stable over aload resistance range from two milliohms to1000 milliohms and time constants ranging from1/2 to 3 seconds. It was anticipated that theoutput current would be stable to better than0.01% long term in the presence +5%, -7o/r linevoltage changes and a 10% change in loadresistance.

The power supply is complete with itsown interlock chain with protective devicesinstalled to detect abnormal conditions, which,when activated will shut down the power supply.

Output

The basic power rating of the powersupply was determined by considering the typesand distribution of the magnet loads. Cur rentsapproaching 5000 A for some of the bendingmagnets and quadrupole magnets used in theexperimental area of the Laboratory arerequired during a 500 GeV operation. Likewise,some magnets in the high impedance range werealso contemplated for use in the experimentalarea. For' these magnets, currents approaching1200 A are required for maximum excitation.Typically up to five magnets can be seriesconnected to one power supply. In cases wheremore than five magnets are required to be series

TABLE 1. Output Characteristics

SecondaryConnections

Maximum dcVoltage

(100% Connection)(volts)

MaximumAvailable

Output Current(amperes)

Minimum &Maximum Load':'

(milliohms)

MaximumAvailable Power

Primary Connection25% 50% 100%

(kilowatts)

Parallel 100 5000 2. 5 - 20 125 250 500

Series -Parallel 200 2500 10 80 125 250 500

Series 400 1250 40 - 320 125 250 500

':'The minimum value of the range was determined by considering that the maximum output currentmay be drawn to 50% of the rated output voltage on each primary connection.

connected, up to three power supplies can beadded to achieve the higher voltage. In thismode of operation only one supply is currentregulated while the others are voltage regulated.In those cases where two or more power suppliesneed to be parallel connected to increase thetotal available current, an external currentsensor and regulator amplifier would need to beprovided. Then, the power supplies would beoperated as voltage regulated units. The openloop gain of the voltage amplifier is high enoughto insure stability and equal loading of the powersupplies.

The ratings of all the components of thepower circuits meet the NEMA standards foroverload conditions; that is, 120% for two hours.Also, the power supply may be pulsed to 7000 Aon a 50% duty cycle.

Conversion Frequency

The choice of the conversion frequencywas made by considering the overall effects ofmany of these power supplies operating simul­taneously on our primary ac distribution system.At the Laboratory, the primary power to theequipment areas is fed by buried 13.8 kV.3 phase feeders to strategically located. outdoortype unit· substations of the 1500/1900 kVA.480 V. 3 phase class. Several power suppliesare connected to a single' unit substation. thusraising the possibility of power supply inter­actions. or cross talk. The severity of thisproblem can be reduced. although probably noteliminated. by operating at a high conversionfrequency. This improvement occurs becausethe input line currents contain less harmoniccurrents at the higher conversion frequencies.Therefore. selective filtering of the acsynchronizing voltages for the thyristors gating

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amplifiers can be done without incurring largephase shifts at the primary voltage frequency.Additional benefits arise because the overallconversion efficiency is improved. In manycases the higher conversion frequency has alsoeliminated the need for filtering of the outputof the power supply.

Our choice was then the twelve phase(720 Hz) conversion frequency over the moreconventional six phase (360 Hz). In some powersupply designs. this decision could have resultedin twice as many thyristors as the six phasedesign; however, in our case the same numberresulted due to the basic 5000 A output currentrequirement.

Input Power

The input to the power supply is theutility standard 460 V. 3 phase. 60 Hz power.This is fed to the internal circuitry through a1000 A molded case. air insulated circuit breakerwith a 35,000 A interrupting capacity.

Power Conversion

Circuit

In the original stages of design it wastempting to consider obtaining the 720 Hz outputripple by utilizing only one rectifier transformerwith four zig-zag secondary Windings displacedby 150 • Careful study of the mechanical inter­connections required showed that it would bemore economical to utilize two transformerswith identical secondaries but with theirprimaries shifted by 300 • Therefore. theprimaries were designed to be delta in onetransformer and wye in the other. In additionto the 720 Hz output ripple. it had been decided

to provide four separate and distinct 100 Vsections

leach one with a capability of 1250 A.

It became evident that the best rectifier circuitto obtain these outputs was a six phase star withinterphase transformers (Fig. 3). One half ofeach secondary would then provide the required100 V at 1250 A.

The four separated 100 V power sectionsare then added in a series connection l keepingthe two interphase transformers in the circuit l

to achieve 400 V at 1250 A. Paralleling the twosecondary halves of each power transformerand adding them in series gives an output of200 V at 2500 A. Likewise paralleling bothpower transformer sections through the thirdinterphase transformer gives an output of 100 Vat 5000 A.

The primary winding of the two powertransformers are wound as four separate, butparalle11 windings. Thus l through a convenient­ly located tap board l the four primary windingscan be connected either in series l series­parallel l or all in parallel to obtain the 250/0,50%1 and the 100% connections. This providesthe flexibility to properly match the powerrequired by the load to the rating of the powersupply, thereby minimizing the installationcosts. The basic power rating of the powersupply is 500 kW when all the primary windingsare connected in paralleL It can be changed to250 kW in a series-parallel connection or to125 kW when all the windings are seriesconnected.

Thyristors

The thyristors were selected to providea 25% junction temperature margin and 200%rated-to-applied inverse voltage rating. Coolingwater was available at 1130 F, maximum l withflow up to 8 gpm at differential pressures to150 psig l maximum. The PSI H1400 (1400 Arms) provided a single device with adequateratings to meet all the requirements.

This large area thyristor (48 mm diam­eter) requires hard firing of the gate to maxim­ize its dII dt rating. A gate firing circuit usingcapacitor discharge provides about 20 V opencircuit l 2 A short circuit with a rise time ofO. 15 microsecond. This peak gate pulse decaysto 400 mA in 50 microseconds and continues fora total width of about 1 millisecond. The gatecircuit electronics was located close to thethyristors and includes the resistance­capacitance dV / dt networks l transient voltagesuppressors, and the output isolated pulsetransformer.

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Firing circuits located in the electronicsassembly transmit the 24 V peak triggeringpulses on coaxial cable to the gate firing circuits.The firing circuits employ a linear ramp whichis compared to the control input signal to triggera monostable multivibrator to produce the firingpulse. The ramp is gated on-and-off by a phaserelated 50 V ac line signaL The high amplitudeof this line signal, plus some filtering l ensuresa noise free l 180 degree ramp. The ramp hasa peak amplitude of 10 to 12 V so the inputcontrol signal range must be zero to 11 V.This high amplitude improves tolerance tosignal harmonics as well as noise.

Free Wheeling Diodes

The freewheeling diodes were originallyselected to carry 5000 A continuous dc with a25% temperature safety margin. This reqUiredusing three PSI-HD2500 diodes in parallel.The reconnectable secondary configuration usedone freewheeling diode in each of the four half­wave star sections so the diode might have beenchanged to a HD2000 1 but use of the HD2500continued in the production run. This providesa derated l continuous current capability of6400 A.

Power Transformers

The nominal rating of each transformeris 350 kVA; however, this rating is misleadinginasmuch as the transformer should includeother sources of unusable kVA, mainly low line,stray losses and tertiary currents. Of theseelements the most difficult to reconcile with theoverall design is the stray loss element. It isa function of not only load conditions but alsoconductor size and shape. By careful selectionof conductor, stray losses can be reducedconsiderably. On the other hand, a poor choicecan result in losses that are, in magnitude,even as high as the normal conductor I2R losses.Another important aspect is the 180 Hz currentcomponent. To reduce this current l a tertiarywinding is required in the wye primarYI doub1e­wye secondary transformer.

To obtain outputs of 25%1 50%, and 100%of full voltage l it was decided to quadrifilarwind the primaries of the transformers. ThatiS I each primary is wound with four insulatedconductors. These conductors can be connectedin series l series -parallel, or parallel to obtainthe desired outputs. The advantages of thismethod of winding over the inclusion of discreettaps on the windings far outweigh the disadvan­tages. Among the benefits is the fact that theabsolute value of the leakage impedance remains

constant at any tap. Another advantage is thatbecause the winding is symmetrical, all thewindings carry the same current for a givenload current regardless of the tap. Still anotheradvantage, tap changing is done in the primarywhere currents are lower and no overwinding isnecessary. The only major disadvantage ofthis arrangement is caused by the fact that undercertain connections the voltage gradient betweenturns can be very high and thus extreme careis required in the design and construction of theprimary windings.

voltage which supplies ac power to the powersupply also is characterized by both fast andlong term changes. At the Laboratory, 5%changes are not uncommon. The line voltagecan be seen to dip by about O. 5% just due to theoperation of the accelerator alone.

Although most of the copper conductorsin the magnets are water cooled, they stillexhibit a change in resistance due to the changein temperature. This change can be as muchas 10 to 15%.

TABLE II. Regulator Design Parameters

The regulator design parameters areshown in Table II below.

A necessary feature in phased controlledrectifier systems to which inductive loads areconnected is a two loop regulator. The innerloop is a voltage regulator in which the rawoutput voltage of the power supply is stabilizedprimarily against fast line voltage changes.The voltage loop is generally characterized bya modest open loop gain and a large bandwidth.The outer loop in the power supplies has theoutput current as the controlled parameter.The function of this loop is to regulate theoutput against load changes which generallyoccur slowly. Therefore, the current loop ischaracterized by a high open loop gain, butwith a restricted bandwidth.

A first order control system is desirablein both the current and voltage regulators. Thistype of control system is characterized by anopen loop response that has a -6 dB I octave rolloff. The overshoot in the response of the systemis therefore minimized when the input undergoesstep changes. This feature is reqUired whenthe power supply is to be programmed. It is

The water cooled secondary windingsare wound over the electrostatic shields. Thesesecondary windings are wound bifilar (two inhand) and insulated from each other. Eachwinding represents one half (line to neutral) ofone three phase system. To obtain as muchbenefit from the water cooling as possible,primary and secondary are tightly coupled and,therefore, the leakage reactance is low.

Interphase Transformers

There are two 180 Hz, 1250 A and one360 Hz, 2500 A transformers. All of them arewater cooled. Because there is a full thyristorphase back requirement and also because therectifier transformer leakage reactance is low,the 180 Hz units are designed to support avoltage time integral of about 300 V msec. The360 Hz unit is designed for about 70 V msec.Additional important considerations in thedesign of interphase transformers are straylosses, audible noise and dc unbalance. Audiblenoise is reduced by careful arrangement of coreclamping devices and proper selection of corematerial and shape. The unbalance effects ofthe dc component of the current are minimizedby the inclusion of an air gap in the magneticpath. This gap is designed for approximately20% unbalanc e.

Regulators

Design

The output current of power suppliesused in particle physics applications must haveexcellent stability in both the short term andlong term. As a design objective, a stabilityof O. 01% of full output was chosen. Thisfigure is achievable in phase controlled systemsproviding that the regulator design is carefullydone.

The power supplies are generallyoperated in buildings where the ambienttemperature may change by 40 0 C. The line

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Voltage loopopen loop gainclosed loop bandwidthclosed loop gain

parallel connectionseries and series­

parallel connection

Current loopopen loop gainunity gain closed loop

bandwidthclosed loop gain

Loop Stabilization

50 dB10 Hz

20 dB40 dB

80 dB5 Hz

o dB

necessary to adjust the frequency response ofthe current regulator to match the variousmagnet resistances and time constants to achievethe desired response.

Voltage Loop

A detailed block diagram of the regulatorsystem is shown in Fig. 4. By means of theswitch at the input of the voltage regulator it ispossible to operate the power supply as a voltageregulated or current regulated system or tooperate from an external analog signal.

The voltage regulation mode loop remainsclosed as an inner loop when the system isoperated in the current mode. This featureprovides fast correction for such disturbancesas line transients. In addition, the inner voltageloop provides a constant gain over the entirecontrol range.

Series operation of the power supplieswith grounded controls requires either isolateddetection of output voltage or a high commonmode rejection (CMR) circuit. The CMR ap­proach chosen uses a Type 741 operationalamplifier with both null and CMR adjustments.This circuit provides 0 - 10 V de for either the100, 200, or 400 V de outputs.

Because no power filters are used in thesupply, the voltage loop requires a filter for the720 Hz and higher frequency noise. The activefilter employed provides typically 50 dBattenuation of the 720 Hz ripple. The phasecontribution of this filter at 60 Hz is only -600

typically. This small phase shift allows thevoltage loop to be closed with a corner frequency(-3dB) in excess of 10 Hz. This provides aresponse time to correct line disturbances ofabout 20 milliseconds. The loop gain of thevoltage loop provides regulation of betterthan:!:.O.l%.

Current Loop

The current loop uses a type 725':'operational amplifier for very low noise andtemperature coefficients but very high gain.A two stage, resistor gain control is used tosimplify gain changing and minimize parameterchanges seen by the operational amplifier. Thebasic lagging corner frequency (0.00045 Hz) ofthe current loop is set by feedback on thisamplifier with a 20 megohm resistor and 18microfarads capacitor. Its first order gainroll off ("integrating") continues until a leadingcorner frequency is reached that matches themagnet load time constant lag frequency (Fig. 5).

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This assures a first order, stable systemthroughout the system bandwidth. The loopgain, which always exceeds 10, 000 (80 dB),provides a gain bandwidth of 5 Hz.

Total system regulation and stability ofbetter than + 0.01% in an ambient environmentspecified fr-;m 15 to 55 0 C is achieved by use ofan oven. The oven contains the precisioncurrent amplifier and the active references aswell as additional regulators for the amplifierand an active filter with notches at 240 Hz and720 Hz for operation into resistive loads orvery low time constant magnets.

Reference Voltage Supply

The precision reference supply provides10 V de to a 1000 ohm externally connectedpotentiometer. Therefore, the reference wasmade short circuit proof by using a type 723':'monolithic voltage regulator. The 723 is usedwith a precision reference diode to improve itsstability.

Measurements of overall system warmupand temperature stability indicate a two-sigmatemperature coefficient of -0. 00 lo/al °c for 90%of the power supplies. Part of this negativecoefficient is probably due to component agingand should be halved after about 200 hours ofoperating time. The oven regUlates the steadystate operating temperature to less than + O. 20 C,so the system temperature stability is approxi­mately :t.0.0002%.

T ransductor

The transductor used to measure theoutput current is a unique patented Transrexdesign that employs a seven core sensing head.Two sets of three cores respond to load currentin a differential manner and a feedback Windingmaintains a constant ampere-turn operatingcondition with a very high gain amplifier. Thefeedback current is an exact ratio of Windingturns, and this current of about 1 A at fulloutput current is read with an array of precisionresistors.

The differential connection of the sensehead eliminates the need of pre regulating theinput ac power to the head. The seventh corein the head provides direct high frequencyresponse to load current changes. The charac­teristics of the transductor are listed in Table III.

':' Fairchild Semiconductor, Mountain View,California.

Power Control

Protection

TABLE III. Transductor Characteristics

Control System

be performed. These functions include ON-OFFcontrol and monitoring, fault monitoring andreset, and output current and voltage control andmonitoring.

The components of the power supply arehoused in a steel frame, free-standing structuredesigned for indoor use. Steel panels with frontdoor accessibility cover the unit giving dripproof construction (Fig. 6). The dimensions ofthe power supply are 122 em x 122 cm x 183 emhigh (48 in. x 48 in. x 72 in. high) and theweight is 2700 kg (5900 lb). All power connec­tions (ac and de) are made at the top. Watersupply and return connections are also madeat the top.

Mechanical

The power supply output is controlled bymeans of a reference voltage which is applied tothe input of either the current loop or voltageloop amplifier. The output of the internalprecision reference voltage supply is appliedto the power supply input by means of apotentiometer driven by a pulse controlledstepping motor. The stepping motor and themulti -turn potentiometer were chosen to providea resolution of at least 100 ppm. Applicationof 5 V, 50 microsecond pulses to the cw(increase) or ccw (decrease) inputs of the motorlogic are reqUired for operation of the motordriven potentiometer.

The power supply may also be pro­grammed either by means of a remotely locatedwaveform generator or an optional ramp andflat -top generator which may be added to thepower supply. In either case, the rate ofchange in the output is generally dependentupon the time constant of the load and theavailable output voltage; and to a lesser degree,the speed of response of the power supply.

500 A/V

5 ppm/% change1 ppm/oC1000 Hz

SensitivityCoefficients

line voltagetempe rature

Frequency Response(Nominal, - 3 dB)

The power supply contactor is energizedby means of a relay-based interlock and controlsystem. All fault signals are connected intothe control chain through auxilliary contacts ofthe sealed-in relays of the protective devices.

The ON-OFF control and the resetfunctions can either be operated locally orthrough a set of remotely located relay contacts.Local monitoring of the status of the interlockchain and fault indicators is provided.

The power supply is completely selfprotected against ac overloads and currentunbalance, dc overloads and over temperature.The power thyristors and free wheeling diodesare protected against over temperature bymeans of bi -metallic thermostats placed oneach device. In addition each power thyristoris protected by a Carbone-Ferraz 1250 A fuse.The operation of any of the protective deviceswill cause the interruption of the gate pulsesto the thyristor as well as the opening of theprimary ac contactor. Provisions are alsoincluded for remote load fault sensing.

Ground faults are detected by means ofa current sensitive trigger fuse. Upon acti-vat ion, the firing circuit input is shorted andthe primary contactor is de-energized. Theload is protected from. excessive instantaneouscurrents by a 200 ohm. current limiting resistor.

The control of the protective devices areincluded in sealed -in fault indication and controlrelays. The operation of the protective devicewill remain indicated until the operator, throughthe control system, resets the power supply.

Computer Control

In addition to the local control a limitednumber of remotely controlled operations can

All the electronics for the power supply,with the exception of the transductor electronics,are mounted in a NIMBIN assembly which islocated on the front of the power supply.(NIM: AEC Standard TID-20893, NuclearInstrumentation Module) The heavy dutycomponents such as the main circuit breakerand contactor are mounted on an insulatedpanel board located about 36 em (14 in) behindthe front door.

The two main power transformers arelocated in the lower half of the power supply.Primary connection changing is done from thefront. Each power transformer assembly alsocontains its own double wye interphase trans-

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TABLE IVHarmonic Analysis of the Input Line Current

operating on the 1000/0 primary connection. Theload was a 95 milliohm water cooled resistor.The results of this analysis, presented inTable IV, demonstrate the benefit of operatingat the higher conversion frequency. The totalharmonic content was about 4. 4%. It would beexpected that with an inductive load the harmoniccurrents would be smaller.

former. The combining interphase transformerfor the delta -wye unit is located on the left sideof the power supply, immediately behind thepanel board.

The secondary series-parallel connec­tions are made with water cooled links. Thelinks are accessible through the side panels.About 8 links are required to be moved inchanging from one connection to another. Expe­rienced technicians can change the connectionsin about one hour.

The thyristors and free wheeling diodesare located at the rear of the power supply(Fig. 7). There are four separate assemblies,one for each half-wave star section. Eachassembly is complete with its own free wheelingdiode. The bus-bar from the power transformersecondary is connected to the thyristor heatsink through the current limiting fuse.

HarmonicNumber

11113232535

FrequencyHz

60660780

138015002100

Harmonic Current(% of fundamental)

100.03.71.51.00.50.5

The transductor head and its electronicsare located at the top of the power supply.Access to the transductor is through hingedpanels on the top and side of the power supply.

Cooling

All major heat dissipating elements arecooled by a three branch water system. Waterenters and leaves the power supply throughconnections made on the top of the unit. Thethyristors, freewheeling diodes and all themagnetics are water cooled. A total flow of4-1/2 gpm at a pressure drop of les s than55 psig for ambient temperatures to 400 C isrequired. For ambients to 550 C, 5-1/2 gpmflow with a 100 psig pressure drop is required.

Conclusion

A total of 85 500 kW power supplies areon order, 45 of which are of the type describedin this paper. About 25 of the 45 units have beenreceived and about 20 of these are now in routineoperation, using various connections, in theNeutrino, Meson and Proton area beam linesand in other parts of the external beam transportsystem.

In addition to the standard factory testswhich were made at the time the equipment wasdelivered, some additional tests have been madeboth at the Laboratory and at the manufacturingfacility of Transrex.

The harmonic content of the input linecurrent was measured on a power supply witha series-parallel connected secondary and

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The stability of the output current withthe regulator in the current mode was measured.A Leeds and Northrup precision shunt, traceableto the National Bureau of Standards, was usedto measure the current. The total change incurrent from a cold start was 600 ppm whilethe long term stability was 20 ppm. Themeasured short term stability was 40 ppm.

The output current ripple is dependentupon the time constant of the load and theamplitude of the ripple voltage from the powersupply. The ripple current was measured on apower supply connected to a series arrangementof two National Accelerator Laboratory TypeB2 magnets and one Type B 1 magnet. The powersupply was connected as a 100 V, 5000 A unitand the ripple current was measured at about45% of the maximum output voltage which wasthe worst case. The time constant of the loadwas about one second. The ripple currentmeasured at 60 Hz was 0.011% of the averagevalue (1830 A) and was 0.003% at 720 Hz.

The operation of the power supply in thepulsed, current regulated mode was demonstra­ted and the results shown in Fig. 8. In thistest a power supply was operated with thesecondary in a parallel connection and theprimary in the 100% connection. The load forthe power supply consisted of three seriesconnected type B2 bending magnets. Theconnected load resistance was 25 milliohm andthe inductance was 24 mH, giving a timeconstant of 0.96 sec. From the current pulseshown in Fig. 8, the initial rate of rise of thecurrent is 3300 AI sec which gives an inductive

voltage of 79 V. The maximum resistivecomponent voltage was 34 V. Because thepower supply was voltage limited to 100 V thecurrent pulse becomes rounded after O. 3 sec.Within the limits of the bandwidth of the currentregulator and the available output voltage, theoutput current settled to the basic steady-statestability, characteristic of the power supply inabout one second.

Acknowledgements

The authors wish to express theirappreciation to Mr. Jan Ryk, NationalAccelerator Laboratory, for providing thestability and ripple current data and toMr. Eugene Woods for providing assistancein obtaining the pUlsed operation data.

1--1000' -----tSCALE

0=NEUTRINO LABORATORY

I

V30" B~BLECHAMBER

HADRON BEAMS

/WONDERBLDG.(E·21)

CHICAGO CYCLOTRON

TARGET HALL ENCL 100 /MUONI5~::~~::6)

I. CHAMBER

_--------- MU\ON BEAM LAB 'c'(E\ IA)

---------\----- ;. 1NEUTRINO BEAM

L1NACBOOSTER

Fig. 1. Neutrino beam line. Many of the power supplies described are in the service buildings andequipment enclosures located along these beam lines. Similar conditions exist for theMeson beam line (to the left of the Neutrino beam line) and for the Proton beam line (to theright of the Neutrino beam line).

Fig. 2. Simplified Block Diagram

4S0Vaf

Fig. 3. Power Circuit. The thyristors shownare PSI Type H1400 and the diodes arePSI Type HD2500.

672

100.,.---r-...,...,.,,..,.,.---r-,,,,,,,,,,"""-r-...,...,.,,..,,,-r-"""""Tn,,-r-I'""TT"TTTTl

_.O+_.......JL......J'-'-.u.......,f---'---'-.J...l.J.Ll"'l-_.L-..L..J.::>ol=......-'-'--L:.......1.I.I:-----'----'-J...L...,.."{.001 .01 0.1 1..0 10 tOO

HI

".&INETTM: CONITANT..KIi··..'

.. __ MINIMUM

00

.0

IOOO.A

-10

GAIN

db +--!~V~0~LT~.:.~.~••~.~U~L.~T~0~.!....~ ....::::;:s::;:======:::::=- 1CLOSED LOOP RESPONK10

=:-~III

Fig. 4. Regulator System block diagram.

Fig. 6. Power Supply - Front View, external Fig. 7. Power Supply - Rear View, internal

Fig. 8. Output Current Pulse.Horizontal - 1 sec / emVertical - 250 A/em

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