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Fig. 1 Thyristor Divert Automatic Voltage Regulator

IN STR U CT!O NBOOK

Publication No. 95/2005

Issue: February 1984

Supersedes issue : October 1982

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CONTENTS

1.

2.

SECTION

INTRODUCTION

PRINCIPLE OF OPERATION2.1 The Compounding Circuit2.2 The Thyristor Circuit2.3 The Control Circuit2.4 The Stabilising Circuit2.5 The Frequency Cut-Off Circuit2.6 The Complete Circuit

PARALLEL OPERATION OFGENERATORS

DIODE FAILURE INDICATION(Brushless Machines Only) 6

OPTIONAL EXTRAS 65.1 Frequency Fall-Off Circuit5.2 Power Factor and Reactive

Power Control5.3 Astatic Parallel Operation5.4 Three-Phase Detector Unit5.5 Smooth Changeover

ARRANGEMENT OF THESTANDARD UNIT 8

INSTALLATION 8

COMMISSIONING 8

OPERATING INSTRUCTIONS 10

FAULT FINDING PROCEDURE 1010.1 Failure in the Auto Control Mode Only10.2 Failure in both the Auto and

Hand Control Modes

SETTING-UP PROCEDURE 1211.1 Calibration of the Voltage Control11.2 Optimum Stabilisation1 1.3 Ouadrature Droop Adjustment

EXCITATION DATA 13

RECOMMENDED SPARE PARTS 13

SPECIFICATION 17

LIST OF FIGURES

The Thyristor Divert AutomaticVoltage Regulator 1

Diagrams illustrating Principle ofOperation 3-4

Schematic Diagram of theT.D.A.V.R. 5Complete Excitation System as applied

to a Medium Voltage Generator 7lnternal Arrangement 8Complete Excitation System as applied

to a High Tension Generator IOutline Diagram of T.D.A.V.R. 11Simple Testing of a Thyristor 12Circuit Diagram of T.D.A.V.R. 15-16

LIST OF TABLES

Current RatingsTable of SparesList of Components

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10.

11.

12.

13.

HEALTH AND SAFETY AT WORK ACT 1974

This equipment has been designed and constructed so as to be safe and without risks to health when properlyused in accordance with the manufacturer's recommendations.

2. Use insulated meter probes.3. Use an insulated screwdriver for potentiometer adjustment where a knob is not provided.4. Wear non-conducting footwear.5. Do not attempt to modify wiring.6. Replace all protective covers, guards, etc. on completion.

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1. INTRODUCTIONThe Thyristor Divert Automatic Voltage Regulator,Fig, 1, is a static, compact, panel-mounting unit tocontrol the excitation of an exciter which in turnprovides the field current of an a.c. generatorThe exciter may be either a brushless or, in specialcases, a conventional d.c. generator.

The A.V.R. controls the output of a single phaserectifier supplied from a high impedance compound-ing circuit. The compounding circuit provides moreoutput than is required by the exciter under all con-ditions and the excess current is diverted from thefield windings through a thyristor, the gate of whichis controlled bl,the action of a sensing circuitn:oniiorirg the lir-^e voXtage and current.The compoundrng circuit consists of a choke whichhas a hig'r rrpecarce reiative to the exciter fieldresistance. ard ore cr i:,\o current transformers. Theadvantage oi rncl,cir:g ihe current transfor;irers isthat they siaole :"e :xciie iion to be sustained whenthe gene.at,c,r s sL.ji.:eC to a short circuit. Thecompo,;ncr:g ; r'c-it adcii:ionally constitLttes asuiieble sa-r::,1's,3a,r';or nand control which alsogir,,es a -ra:s,r'::'a-:c':atic compensation for loadcha-n=r

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Pnase eRectif ier conducts normally.Rectifier input current:rectifier output current:exciter field current which is approximately constantdue to its inductance. Current in choke L is there-fore substantially constant and the rectifier inputvoltage Vp is therefore equal to the supply voltage.Phase BThyristor conducts and hence diverts current fromthe exciter field by short circuiting the rectifier.

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1 Thynstor forward drop

2 Rectifier open circuit voltage

3 Rectaf ier forward drop

4 Mean ofVl5 Thyristor divert current

6 Rectifier free-wheeling currenl

_4Vollage waveforms

Current wavefornrs

Fig. 2 (a) Principle of operation, operational waveforms

The Thyristor Divert Automatic Voltage Regulatorhas several advantages over the more conventionalform of serles thyristor controller:1. The choke effectively isolates the thyristor from

the supply so that commutation of the thyristordoes not distort the voltage waveform.

2. Full-wave control is achieved by a single thyristorin place of two thYristors.

3. When applied to a generator', the excitation isable to build up of its own accord without theneed for a relay.

4. The exciter field current can be controlled downto near zero it necessary, thus reducing the riskof loss of control on leading power factor loads.

2. PRINCIPLE OF OPERATIONThe following explanation describes the operationand the interconnection of the sub-circuits. Referenceis made to the block schematic connection diagramshown in Fig. 3.

2.1 The Compounding CircuitThis circuit comprises the choke and currenttransf<.rrmer. The choke. having an impedance largerelative to the exciter field resistance draws a

current lp which lags the generator voltage Vt byapproximately 90", see Fig. 2. The current trans-former supplies a secondary current ICT which is

in phase with and proportional to the line current11. The field rectifier input current lF is the vectorsum of ln+lCt. The actual field current 11 is pro-portional to lp when the thyristor connected acrossthe rectifier does not conduct. l1 could be controlledto maintain the line voltage within 5% of nominal,by the compounding circuit alone. i.e. if this isemployed in accordance with the usual principlesof self-regulating generators. ln this applicationhowever, the compounding circuit is deslgned tosupply a current in excess of the field require-ments under all operating conditions, the surplusbeing diverted by the thyristor. ln this manner, a

closer control of the generator line voltage (within1%) is achieved.

ln practice, two current transformers in differentlines, with their secondaries connected in parallel,are normally used,

2.2 The Thyristor CircuitThe thyristor depends for turn-off upon the highinductance of the exciter field. Whilst the voltagereaching the exciter field consists of a series ofpulses at twice the supply frequency, the fieldcurrent l1 remains substantially constant during theperiods of a pulse. The current input to the fieldrectifier lF is approximately sinusoidal due to thehigh source impedance of the supply. and the exciterfield current will therefore free-wheel through thefield rectifier during that period of each half-cyclein which the instantaneous value of lF is less than li.During the free-wheeling periods the exciter fieldvoltage will 'become slightly reversed due to theforward drop in the rectifier, and the thyristor willtherefore turn off.The thyristor is triggered at an appropriate instantduring the normal conducting period of the rectifier,thereby short-circuiting the field winding for theremainder of the conducting period. Advancing orretarding the instant of firing will therefore vary thewidth of the voltage pulse and hence the mean valueof the voltage applied to the exciter field. The fieldcurrent l1 is proportional to the mean applied voltage.

2.3 The Control CircuitThe voltage across two lines of the generator isrectified to produce a d.c. signal dependent onthe line voltage, and a proportion of this signal iscompared with a stabilised d.c. reference. Thedifference or error signal is smoothed and amplified,and the amplified output voltage is fed to a capacitor.The time taken (from the instant at which voltagefirst appears on the thyristor) to charge this capaci-tor to a voltage sufficient to turn on a transistorin the firing circuit, and hence fire the thyristor, isproportional to the amplifier output voltage. .Thistime interval is in effect the width of the voltagepulses applied to the exciter field.

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Fig.2 Diagrams illustrating Principle of Operation

1 Current transformer

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2.4 The Stabilising CircuitThe stabilising signal is a voltage developed acrossa resistor connected in series with the exciterfield. This voltage is fed back through a seriesresistor and capacitor to the input of the transistoramplifier. Separate magnitude and phase controls(RV6 and RV5 respectively) are provided to optimisethe level of stabilisation. TheA.V.R. itself respondsvery rapidly but the generator response dependsupon its own characteristics together with those ofthe exciter and the compounding circuit. On applyingfull load kVA at a low power factor to a typical500 kVA set, nominal voltage should be restoredwithin one second.

2.5 The Frequency Cut-Off CircuitA circuit is included in the A.V.R. which preventsdamage to the machine or load for short duration,low speed operation, during run-up or shut-down.This circuit reduces the generator voltage when thefrequency of the generator falls below a pre-setlevel - approximately lOo/o below nominal. At thisfrequency the Frequency Cut-Off Circuit shortcircuits the input of the amplif ier, advancing the f iringangle of the thyristor and thereby diverting the entirefield current, causing the generator output voltageto fall rapidly. When the frequency has recovered toabove the preset level the short circuit is removedfrom the amplifier and the line voltage again buildsup to its nominal value.LK6 should be omitted on a 50 Hz machine to givecut off at 45 Hz (approx.)LK6 should be fitted on a 60 Hz machine to givecut off at approx. 54 Hz. The circuit can be inhibitedby removing LK4 and LKS, and this should be done ifthe unit described in Section 5.1 is fitted.

2.6 The Complete SystemThe complete excitation system as applied to amedium voltage generator is shown in Fig. 4, a

scheme for a high tension generator is shown inFig. 6. circuit details of the A.V.R. are not included.ln order to switch off the excitation, the exciterfield is simply short circuited via a discharge resistor.When operating on automatic control, the thyristoris connected across the output of the field rectifier.

3. PARALLEL OPERATION OF GENERATORSThe facilities necessary for a number of generatorsto run in parallel and supply a common load areprovided by the Ouadrature Droop Circuit. Aninstrument current transformer (usually included inthe switchgear) can be employed to provide thenecessary supply. A preset potentiometer, O. Droop(RV1 ) incorporated in the A.V.R., enables the voltagedroop characteristic to be adjusted to a maximum of10% of the selected operating voltage for full loadreactive kVA. ln principle. a voltage proportionalto and in phase with the Iine current is added to thedetector line voltage vector so that the generator isgiven a drooping Voltage/kVAr characteristic.Alternatively, the A.V.R,'s may be interconnectedwithin an Astatic Loop to eliminate the voltagedroop; see Section5.3.

4. DroDE FATLURE INDICATOR (BRUSHLESSMACHTNES ONLY)

Fuses are provided in the rotating rectifier assemblyof Brush brushless generators to ensure that if adiode fails, that arm of the rectifier bridge becomesopen circuit. ln this condition the exciter can continueto function and provide full load excitation. Thechange in ripple content of the exciter field currentcan be detected and used to provide an indicationof diode failure.The Diode Failure lndicator comprises a currenttransformer, the primary winding of which is con-nected in series with the exciter field, and a neonlamp which responds to the ripple induced in theexciter field. The neon lamp is shunted by a resistorto reduce the sensitivity of the indicator so that itdoes not respond to the inherent ripple during normaloperation. The indicator can be checked duringnormal operation by depressing a 'test' push-button.The circuit is a standard feature on brushlessqenerators of 25O kVA and above, and an optionalextra on smaller machines. Alternatively. a diodefailure relay can be supplied to give a remote signalIn the case of diode failure. For further detailsrefer to the appropriate CG series publication.

5. OPTIONAL EXTRAS5.1 Frequency Fall-Off Circuitln certain applications (e.9. load shedding to preventengine stalling) it is necessary to attain a moreaccurate rate of line voltage reduction with fallingfrequency.A unit which reduces line voltage to half nominal at75% (or 50%) nominal frequency can be provided,if necessary.For detailed description of the Frequency Fall-OffCircuit, refer to the CG series publication.

5.2 Power Factor and Reactive Power ControlWhen accurate control of power factor or reactivepower is desirable, the Excitation Bias Unit isavailable for interconnection with the T.D.A.V.R.

5.3 Astatic Parallel OperationBy interconnecting the Ouadrature Droop circuitsof a number of A.V.R.'s, it is possible to eliminatethe droop in busbar voltage normally associatedwith parallel running. achieve more accuratereactive load sharing and replace the single/parallelrunning switch by circuit breaker auxiliary contacts.Direct interconnection between sets of quadraturecurrent input terminals may not be possible becauseof earthing of the instrument current transformersecondary windings. To overcome this, an additionalwinding is provided on the internal quadraturedroop transformer and brought out to extra terminals.These windings are then connected in series toform the astatic loop on all the sets to be paralleled.For detailed description of parallel operation, seeBrush Publication No. 11/1009, available on request.

5.4 Three-Phase Detector UnitTo maintain the mean voltage of all three phasesa Three-Phase Detector Unit is available.Basically, this unit takes the other two Iinevoltages and provides a d.c. signal which is addedto a proportion of the d.c. signal originally producedfrom one line voltage. A signal proportional to themean of all three line voltages is thereby obtained.

5.5 Smooth ChangeoverFacilities can be provided which enable a SmoothChangeover from 'Auto' to 'Hand' operation (andvice versa) to be achieved. This involves the in-clusion of an Ammeter (if one is not already used)and the fitting of a four position Smooth Changeoverswitch. For further detalls refer to the appropriateCG series publication.

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6. ARRANGEMENT oF THE STANDARD UNITThe physical arrangement of the standard unit isshown in Fig. 1 . It is designed for flush mountingon a switchboard. The Nominal Voltage Control isaccessible through an aperture in the front of theunit.The internal arrangement is shown in Fig. 5. Withthe exception of the thyristor and diode bridgeassembly, the circuit elements are mounted on aprinted circuit board which can be hinged out at thefront, either to give access for testing purposes or tofacilitate complete replacement. All preset adjust-ments are accessible when the front cover is removed.

7. INSTALLATIONThe A.V.R. is designed to be mounted on the frontpanel of a larger cubicle. The necessary apertureshould be cut 374 mm high and 171 mm wide, seethe dimensioned outline diagram, Fig. 7. For ade-quate air circulation, it is recommended that a freespace of 305 mm be made available above and below,and at least 102 mm at each side and to the rear of the

unit. Firm anchorage for the A.V.R. is provided bythe L-clamps supplied for each vertical edge; theseare screwed to the rear of the mounting surface onthe customer's panel. The necessary power con-nections to the A.V.R. are made to the MO terminalson the right-hand side looking at the rear; all otherconnections are made to the screw terminal blockson the bottom surface located immediately behindthe front panel.

8. coMMrssroNrNGOn arrival at site the equipment should be examinedand any damage reported immediately to the manu-fa ct u re rs.lnstallation and wiring should be completed asdetailed in Section 7.

/y'ore.'When the A.V.R. is to be used on machineswith a no load exciter f ield voltage of less than 15volts, removal of the link 'R34' on the printed circuitboard is recommended.

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Fig. 5 Front view and internal arrangement of a thyristor divert automatic voltage regulator

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ln order to check the operation of the equipment:1. Connect an ammeter (if one is not fitted) into the

Thyristor Divert Circuit. (See Fig.4).2. Run the generator up to speed with the offlHand/

Auto switch in the 'OFF' position and with theHand Controller set to the minimum volts position.

3. Switch the OfflHand/Auto switch to the'HAND'position and increase the Hand Control Regulatorsetting until nominal voltage ls attained.

4. Set the front panel VOLTAGE control (RV3) toNOMINAL and switch the OfflHand/Auto switchto 'AUTO' position.Note: lf a Smooth Changeover switch is provided,follow the procedure (detailed in Section 9) forchanging from'HAND' to'AUTO'.

Current ratings of the various circuits are shown inTable 7.1 .

Figs. 4 and 6 are general connection diagramsfor medium voltage and high tension generators.Care should be taken to observe that the terminalsof the potential transformers are connected strictlyin accordance with the circuit diagram providedwith the contract. A copy of the drawing is includedin the Generator lnstruction Manual (if applicable)and its number is given in Appendix'A' of Section Nof the manual.Any schematic or wiring diagrams supplied bythe Switchgear manufacturer should be carefullychecked to ensure that the connections correspondwith those shown on the circuit diagrammentioned above.

Table 7.1 Current Ratings

CABLE IDENTIFICATION CURRENT RATING

Exciter Field to Terminals21 and25 Advised per Contract*

Excitation C.T.s to Terminals22 and 33 Advised per Contract *

Choke Circuit (between lineand Terminal 23) Advised per Contract*

Hand Control Regulator Circuil Advised per Contractx

Divert Circuit(Terminals 24 and 25) Advised per Contract*

OCC lnjection(Terminals 9 and 10) 5 amps

Astatic I nter-connection(Terminals 6 and 16) 100 mA

External Rheostat (Voltage) 20 mA

Sensing lnput (Terminals 7 and 8) 100 mA

*Normally 15 A maximum

WARNING: IT SHOULD BE NOTED THAT HEAT-SINKS ARE CONNECTED ELECTRI-CALLY TO THE EXCITER SUPPLYAN D ARE TH EREFORE LIVE I

5. Check that the range of adjustment covered bythe VOLTAGE control is satisfactory. lf neces-sary, the range can be shifted by trimming thepreset control labelled V.TRIM (RV4). Also checkthat the Thyristor Divert Current at nominalvoltage complies with the specified value. (SeeSection 1 2).Load can now be applied to the generator asrequired and the Divert Current again checked.After having proved the excitation system, the

OfflHand/Auto switch can be left in the 'AUTO'position - in which case the generator voltagewill automatically build up as the set is run up tospeed.Note: lf the A.V.R. is unstable or the response isvery sluggish refer to Section 1 1.2.

9. oPERATING INSTRUCTIoNSStandard facilities are provided for both autoand hand operation of the voltage regulator: ingeneral, auto operation is the more likely requirement.With the set running, the panel control labelledVOLTAGE (RV3) is adjusted until the requiredgenerator line voltage is displayed on the voltmeter.ln the event of a fault on the A.V.R., continuity ofoperation can be maintained by selecting the'Hand'control position on the selector switch. The com-pounding circuit provides a measure of voltagecontrol, i.e. typically i1lYo for a fixed position of theHand Control Regulator. The excitation can betrimmed by adjusting the Regulator to maintain therequired voltage for a particular load.lf the optional extra, Smooth Changeover facilityis incorporated, the following procedure should befollowed:Smooth Changeover - HAN D to AUTO1 . Adjust Voltage Setting Rheostat to maximum.2. Switch Oft/Hand/Transfer/Auto switch to'Trans-

fer'.3. Reduce Voltage Setting Rheostat until divert

current just starts to flow.4. Switch OfI/Hand/Transfer/Auto switch to'Auto'.Smooth Changeover - AUTO to HAND1. Adjust Hand Control Regulatorto maximum.2. Switch Off/ Hand/Transfer/Auto switch to 'Trans-

fe(.3. Reduce Hand Control Regulator until divert

current is reduced to zero.4. Switch OfI/Hand/Transfer/Auto switch to'Hand'.

10. FAULT FINDING PROCEDUREln general. conditions which indicate failure of theequipment can be classified as follows:(a) Failure of the system excitation in the auto

control mode, but not in the hand control mode.(b) Failure of the system excitation in both the auto

and hand control modes.

10.1 Failure in the Auto Control Mode OnlySuch a condition infers that a fault may be locatedeither with the thyristor or in the control electronics.Typical symptoms would be:(a) A high surge current in the thyristor when the

mode of operation is changed from hand to autocontrol, followed by a collapse o{ the generatorterminal voltage. Alternatlvely, failure of theexcitation when the set is running in the autocontrol mode.

(b) Absence of thyristor current in the 'Auto' mode,causing overvoltage and possibly rupturing ofthe excitation and voltage detector fuses.

(c) Oscillation of the generator voltage, which can-not be eliminated by adjustment of RV5 and RV6.

(d) Voltage regulation in excess of t 1o/o of nominal.(e) A change in the generator voltage which cannot

be compensated by adjustment of RV4.(f) Poor on load response,Symptoms (a) and (b) could result from a faulteither with the thyristor or in the control electronics.

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Symptoms (c) to (e) inclusive must be due primarilyto a fault within the control electronics, althoughpoor regulation can be caused by stabilising controlRV6 being set too far clockwise. Refer to Section11.2.Before attempting to test the thyristor. check theconnections to the ammeter and the excitation switchexternal to the A.V.R., also check the thyristor con-nections inside the A.V.R. lf all the connections aresound, the thyristor itself should be checked, seeFig. 8.

1 Resistor47ohms2 Battery 4 5 volts at 1 amp short-term rating

3 0-l amp d.c. ammeter

Fig. 8 Simple Testing of a Thyristor

Remove all electrical connections from the suspectthyristor, and connect the thyristor (which mayremain fixed in its heat-sink) into the simple testcircuit shown in Fig. 8.

(a) lnitially, with the switch S open and not havingpreviously been closed, ensure that theammeter registers zero current.

(b) Close S and observe that the ammeter nowregisters approximately 0'75 amp.

(c) Reopen S and observe that the ammeter con-tinues to register - ideally as in (b) above.

lf any one of these three tests is not satisfied, thethyristor should be replaced, and the originalsubjected to more rigorous tests on an approvedThyristor Characteristic Test lnstrument before it isfinally discarded.

Note;Io reduce the whole anode current to zero aftera serviceable thyristor has been triggered - as in (b)above - the battery circuit must be disconnected -e.g. by disconnecting one side of the ammeter.lf the thyristor is not faulty, check the voltagesensing supply at terminals 7 and 8 on hand control ;also, check the fuses on the printed circuit board.Should the supply be present and the fuses intact,the fault must lie within the electronics. The A.V.R.must then be replaced by a spare and the faulty unitshould be returned to the manufacturers for furthertesting and repair.

10.2 Failure in both the Auto and Hand ControlModes

Typical symptoms:(a) Failure to excite.(b) lnability to supply higher loads at rated power

factor accompanied on auto control by zerodivert current and on hand control by maximumsetting of hand control regulator.

Symptom (a) infers that the compounding circuitis not supplying current to the exciter field.First therefore, check all external connections to theA.V.R. The transformer windings of the diode failureindicator and also the choke winding should bechecked for continuity.A check should be made of all internal connectionsto the compounding circuit rectifier. Each individualdiode of the rectifier bridge should be checked bymeans of a resistance test-meter. Low resistance inboth directions or high resistance in both directionsindicates a faulty diode which must be replaced.lf it is necessary to replace power diodes or thethyristor, silicone grease should be used to ensurea good thermal contact between thedevice and heat-sink and, when tightening the device, the torquevalues given in Table 13. 1 should not be exceeded.Suitable silicone grease is recommended in sectionsG and S of the Generator lnstruction Manual.Symptom (b) indicates incorrect phase relationshipbetween choke and excitation C.T.'s. Confirm thatconnections are as shown on contract circuitdiagram. C.T. polarity is important.

1 1. SETTING-UP PRocEDURE

11.1 Calibration of theVoltage ControlWith the Voltage control (RV3) set to its mid-position, 'nominal' voltage can be calibrated bymeans of V. Trim (RV4). RV4 therefore affords com-pensation for long term voltage drift.

1 1.2 Optimum StabilisationTwo potentiometers are provided in the stabilisingnetwork:RV6 - Ouantity. This varies the amplitude of thefeedback signal.RVs - Phase. This varies the time constant of thenetwork.With RVO fully anti-clockwise the voltage controlsystem is unstable and becomes progressively morestable as the potentiometer is turned clockwise. lnthe fully clockwise position responses tend to be'slugged', the line voltage taking a relatively Iongtime to recover to its final value.With RVs too far anti-clockwise'load on' responsestend to have excessive voltage dips and the regula-tion of the A.V.R. may deteriorate due to the A.V.R.amplifier being driven into saturation by a large'ripple'signal from the feedback network.With RVs too far clockwise responses tend to beoscillatory.lf incorrect settings are suspected, the followingprocedure is recommended.1. Set RV5 one-third clockwise and RV6 fully

anti-clockwise.2. Switch the excitation to auto control - the voltage

control system will be unstable.3. Turn RV6 slowly clockwise until the oscillation

is just damped out.4. Rapidly adjust the voltage control potentiometer

(RV3 or RV4) or preferably throw load on andoff the set and observe the response with a lowinertia meter (e.9. AVO).

5. lf responses are too oscillatory, turn RV6 clock-wise by a small amount and repeat test 4.

When response to a particular load change iscritical it becomes advisable to use a U.V. recorderor similar instrument to record line voltage and theunit should be set up with that particular load change.If, for instance, very good recovery of voltage isrequired after the application of a short durationoverload (e.9. motor start) then when this responseis obtained, responses with the set lightly loadedmay tend to be under damped.

V,

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To optimise the response it may sometimes benecessary to make small adjustments of RVsrepeating the procedure outlined above at eachsetting until optimum settings are arrived at.The stability controls also affect the degree ofvoltage overshoot on build up of excitation. lf it isexcessive compromise stability settings must bearrived at.It is important that the A V.R. choke (voltagetransformer, if fitted) and C.T. feeds are connectedexactly as shown on the contract circuitdiagram. lncorrect phasing of the C.T.'s relative tothe reactor supply can seriously impair the transientperformance of the regulator.Poor on load response can be caused by incorrectphase relationship between C.T.'s and choke. Con-firm that connections are as shown on contractcircuit diagram, C,T. polarity is important.Link LK8 is normally fitted and should beremoved in instances when a laminated exciter(i.e. Type XL) is used and stabilising problemsare encountered.

1 1.3 Ouadrature Droop AdjustmentThe quaclratui'e droop adjustment, O. Droop (RV1 ),provides a maximum voltage droop of 10%of nominalvoltage when the rene!'ator supplies full load re-active kVA. For normal parallel operation RV'l shouldbe set at 30% of its maximum clockwise rotation. ltis essential, for satisfactory reactive load sharing,that RV1 on each unit to be paralleled is adjustedfor the same perce;rtage droop.lf astatic parallei operation is employed, all RV1controls should be set fully clockwise for maximumdroop.

12. EXCITATION DATAFor details of Excitation and Divert currents, etc.,refer to Appendix'A' in Section 'N' of the appropriateBrush Generator I nstruction Manual.

13. RECoMMENDED SPARE PARTSTable 13.1 gives a list of recommended spare partsrequired to service the A.V.R. in the event of a failuredue to faults of a simple nature.To facilitate component identification an internalcircuit diagram of the A.V.R. is given in Fig. 9 and a

list of components is given in Table 1 3.2.Circuit references correspond to those given on theschematic diagram of Fig. 9.

Table 13.1 Table of Spares

*1 lb. ft 0.14 kg, m.

1. The power diodes listed above replace directlyMullard BYX52 900 & BYX52 900R which in turnreplaced lnternational Rectif ier Co. diodes 40H F 100and 40H F R 100. Early A.V. R.'s were fitted with

Mullard BYYl5 and BYY16 diodes which are nowobsolete.When ordering replacement diodes in this caseplease state if these are fitted, as an adaptor is re-quired to enable the present device to be fitted inthe original tapped hole in the heat sink.

2. The A.V.R. rating, i.e., 1 or 2 kW, is indicated onAppendix 'A' of section N of the Generator Instruc-tion Manual.For comprehensive spares requirements, it isrecommended that a complete unit should be held asa spare.ln cases of difficulty or doubt, and for furtherinformation, contact:

Product Support GroupBrush Electrical Machines LtdLoughboroughLeicestershireTelephone: Loughborough (0509) 61 1511Telex: 341091 (Brulob G)

lnstructions given in this publication are given forinformation and guidance, and the Company cannotaccept responsibility for the manner in which theyare observed, nor for any consequences thereof.

The design and manufacture of BRUSH electricalequipment are subject to constant improvement andt.herefore the specifications and illustrations may varyin some details from the product supplied.

Com-po n ent

Fuses

PowerD iodes

Th yri sto r

ldentificationor Type

500 mA Cartridge

1.25 2.5 Westcode SW10 PCN 040

28428/181

284281 1 95

Westcode SW10 PCR 040

unit I BTY91 -800R

2 kW I Mullardunir I ervgs-soon

,

13

Resistors

Capacitors

Diodes

Surge Suppressors

Zener Diodes

Transistors

Thyristor

Transf ormers

Table 13.2 List of components for T.D.A.V.R. See circuit diagram Fig. 9

CIRCUITREF.

R1

R27R3, R4, R35

R5, R7R6, R43-45

R8R2, R9

R10R1 1

R12R13R18

R20. R46R21

R22, R23,)yR41 )

R24a,R24b)R25a, R25b iR26a, R26bl

R28R29R34R42R36

RV1, RV6RV3

RV4, RVs

c1, c17c2

IDE NTIFICATION

RESISTOR 1 '8 KOHMS *1o/o 2 WAfT metal oxide filmRESISTOR 820 OHMS t2o/o L\NA11 metal oxide filmBESISTOR 4.7 KOHMS +2% + WATT metal oxide filmRESISTOR 1 MOH M +5% + watt carbon filmRESISTOR 100 KOHMS *5o/o*watt metal oxidefilmRESISTOR 2.7 KOHMS a2o/o lwatt metal oxide {ilmRESISTOR 3.3 KOHMS l2o/o 2wan metal oxide filmRESISTOR 22 KOHMS *2o/oLwatt metal oxidefilmRESISTOR 470 OHMS *2o/o \ wafi metal oxide filmRESISTOR 220 OHMS !2o/olwatt metal oxidefilmRESISTOR 15 OHMS *5% l watt metal oxide filmRESISTOR 3 9 KOHMS *2% Lwau metal oxide filmRESISTOR 1 KOHM +2%2watt metal oxidefilmRESISTOR 8'2 KOHMS +Zyo+watt metal oxidefilm

RESISTOR 2.2 KOHMS *2o/otwatt metal oxide film

RESISTOR 680 OHMS --596 12 watt

RESISTOR 0.68 OHM 90 watts Berco type KTVWURESISTOR 100 OHMS t2o/oZwafi metal oxidefilmRESISTOR O OHMS (LINKED OUT)RESISTOR 220 KOHMS =2%)watr metal oxide filmRESISTOR 0 5 OH L4 50 wattPOTENTIOMETER 50 OHMS :10% 1 watt COLVERN CLR 1206POTENTIOMETER 250 OHMS !101k1 watt COLVERN CLR1206POTENTIOMETER 5 KOHMS -10%1 WAtt COLVERN CLR1206

CAPACfTOR 22 MFD :209:35 v D.C. tantalunl electrolyticCAPACITOR 6 8 M FD +20,'L 35 v D.C. solid tantalum

CAPACITOR 0.22 MFD :-9; 160 \, D.C. I\4etalli"ed filmpolyester. Wima Tropy{ol M

CAPACITOR 0'1 MFD :59; 160 v D.C. Metallised f ilmpolyester. Wima Tropy4ol MCAPACITOR 1 0 MFD !596 160 r.'D C. l,'ietalliscd fil:npolyester. Wima Tropyfol MCAPACITOR 250 M FD 'l 5 v D.C. tania;ur eiectrolyticCAPACITOR 0 047 N4FD r50%-25:" Erie'Transcap'ceramicCAPACITOR 0'047 MFD L20dA 25C '' D.C. Merallised filmpolyester. Mullard C280AE P4 7K

DIODE 1A. 600PlV silicon. Type lN 4005

DIODE 70A, 1O00PlV silicon. Westcode type SW10 PCN 040DIODE 70A, 'l000PlV silicon. Westcode type SW10 PCR 040

SURGE SUPPRESSOR - 2'4 kVY secs - Westlnghouse typec1 86L 1 5A

ZENER DIODE 12v *5o/o 1 5 w. Mullard type BZY95-C12ZENER DIODE 5'6 v *5%O'4 w. Mullard type BZY88-C5V6ZENER DIODE 9 1 v *5o/oO'4 w. Mullard tvpe BZY88-C9V1

VTI-4 VT6 I TRANSISTOR 500 mA,25 v. Ferranti rypeZT8-lvTs I f nnrustsfoR 500 mA, 25 v. Ferranti typeZT187

THYRISTOR 11 '5 A 960 PRV Mullard BTY91 -800R-1 kW AVR32.5 A 960 PRV Mullard BTY95-800R-2 kW AVR

CURRENT TRANSFORMERVOLTAGE TRANSFORMERPULSE TRANSFORMER

F1, F2 FUSELINK.500 mA BRUSH SIZE 0

BRUSHREF. NO.

26388-27926384-27126384-28926284-57326386-32126384-28326384-28526384-30526384-26526384-25726386-22926384-28726384-27326384-295

26384-281

26412-669

2661 6-40626384-249

26386-32926457-25226631 -7 1726631-72726631 -7 43

26827-49326827-484

26863-1 09

26863-1 07

26863-1 1 3

26829-53626175-1 4426863-305

28226-301

28232-86524232-466

281 1 8-51 0

28256-1 0028255-20528255-602

28363-42328333-844

28428-18728428-195

25124-210c.942269225124-735

9871 586/02

c3, c4, c8,c11, C13c14, C'19c5, c12 Ic18 ic6

c7c10

c15, C16

Z7z8212

D7, ID31-33 I

D1 5-D221D3-D6, I

D8, DgJD23, D25D24, D26

K1

THI

XIx2X4

Y

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Fuses

14

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/;\\7-r- IIA Po--

LK7(J'l--

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t4?ts.o.T

LL-

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Iz6P3 F.1

Key : (Circled numerals)1 P.T. supply2 Three phase detector3 Astatic connection4 C.T. supply5 Voltage detector circuit6 Raise volts

7 Trim voltsB Ouadrature current compensation9 Frequency cut-off

'l 0 Stabilisation quantity1 1 Stabilisation phase12 Main printed circuit board13 Voltage control (External) o

14 Divert connection1 5 Field connection16 A.C, field supplyR42a, R42b selected on 1

f Pl,2, etc, Test PointsLKl, 2, etc. Links

@ External connectionsO lnternal connections

-y

T.D.A.V.R.LIN K/CONNECTION REOUIREM ENTS

Voltage Setting(i) lnternal : Betain RV3. Terminals 11 & 12 to be

open circuit.(ii) External : Remove RV3. Terminals 1 1 & 12 to

external potentiometer.

Supply Voltage(i) H.T. System : V.T. to Terminals 7 & 8.

Transformer 110 V.(ii) L.T. System : V.T. to Terminals 7 & 8.

Transformer41 6/227 V.

4R4G

R.9

Frequency cut-off (See Section 2.5) I(i) 60 Hz operation : Fit link 6 \ Retain link 4

I

(ii) 50 Hz operation : remove link 6.,;[ I link 5. I

Three-Phase Detector (See Section 5.4)Remove link 1. Fit link 3. Omit link 2.Frequency Fall-off (See Section 5,'l )Remove link 4r5 & 7.Single-Phase SensingFit link 1 & link 2.

Stabllisjng (See Section 1 1.2)Link 8 normallY litted.

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RASA9 B

LK8z5

iu

3

* Link I only fitted for special applications

Fig.9Drawing No. B 9419357Circuit diagram of T.D.A.V.R.

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G l{here separation between AVR andrheostat exceeds 1m of wirinSuse screened cable with the screentaken to terminal 2l of the AVR.

CAU[CF'|: THIS TERIIINAL 1S tfVE.

t{-r(13)

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Power Handling

Exciter Field Voltage

Voltage Regulation

Operating Voltage Range

Line Voltages

Power Consumption

Parallel Operation

Leading Power Factor Operation

SPECIFICATION

500-1000 or 1000-2000 watts continuous f ield power depend-ing on the type of thyristor f itted.

100 volts maximum continuous.

The generator voltage is maintained within +1% of the selectedoperating voltage subject to the following conditions :

1 . The output power must not exceed the rated value.

2. The ambient temperature does not deviate from the initialconditions by more than t1 5"C.

3. The frequency variation does not exceed t5% of thenominal f requency (50 Hz, 60 Hz).

Should the frequency deviate progressively beyond these limits,gradual change in the generator voltage takes place. Theexcitation equipment will not suffer damage if it is left in circuitwhilst the set is running at reduced speed.Should the frequency fall to approximately 1O% below nominal,the generator voltage falls rapidly to below half of its nominalvalue. The output voltage is automatically restored when theoperati ng f requency recovers.

An adjustment of L7'5% of the nominal voltage is provided bythe Voltage Control potentiometer.

Three transformer taps are provided for nominal line voltageswithin *6% and -10% of 110 v,227 v and 416 v. An internalpotentiometer on the voltage detector if fined in order to set themid-position of the Nominal Voltage control to correspond tothe chosen nominal voltage.

Consumption f rom the Potential Transformer (Secondary,1 10 volts) does not exceed 5 VA.

The Ouadrature Droop Circuit may be operated from a suitableinstrument current transformer having a 5 amp secondarywinding. The additional burden on the C.T. is 1 VA. A separatesingle pole switch is required to eliminate the Ouadrature DroopCircuit when the generator is single running.

Satisfactory operation on leading power factor loads, subject tothe normal stability limitations of the generator, is inherent inthe control since the diverting action of the thyristor can decreasethe excitation system output to near zero if necessary.

Operating : -2OoC to +65"C. (Within the immediate vicinity' of the A.V. R.).

Storage : -40oC to *100'C

374 mm high x 1 71 mm wide.

The design and manufacture of BRUSH electricalequipment are subfect to constant improvement andtherefore the specifications and illustrations may varyin some details from the product supplied.

€- Ambient

Panel Cut-Out for

Temperature Range

Mounting Purposes

Weight 8'2 ks (1 8 lb).

Overall Dimensions 440 mm high X 197 mm wide x235 mm deep.

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HAWKER SIDDELEY

BRUSH ELECTRICAL MAGHINES LTDP.O. Box 18 Loughborough Leicestershire [E11 iHJTelephone: Loughborough (0509) 611511

Telefax: OSO9 6lo4qTelex: 341091 (Brulob G)

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