ELECTRICAL FEATURES OF THE CHURCHILL FALLS DEVELOPMENTR. H. Stuart

Acres Canadian Bechtelof Churchill FallsMontreal, Quebec

S. E. GeshAcres Quebec LimitedMontreal, Quebec

C. H. BusbyBechtel Corporation

San Francisco, California

R. H. P. ThomChurchill Falls (Labrador)

Corporation LimitedMontreal, Quebec

ABSTRACT

This paper contains a brief outline of the principal elements ofthe 5225-MW Churchill Falls hydroelectric power development, to-gether with a review of the significant electrical features. It describesthe 500-MVA generating units, the arrangement of busses, trans-formers and 240-kV cables used to transmit energy from the under-ground powerhouse to the surface, the 735-kV switchyard, theauxiliary power system, protective relaying, control and annunci-ation schemes, and the data logging computer installation.

INTRODUCTION

The Churchill Falls, Development is situated on the ChurchillRiver in Labrador, some 1100 kilometers northeast of Montreal(Fig. 1). In this region, the river drops from the Central LabradorPlateau into a deep gorge through a series of rapids, including the75-meter high Churchill Falls itself. By diversion, the water can beretained on the plateau and channelled to a point approximately 2kilometers from the riverbed but over 300 meters above it. Thepower site is unusually attractive because of five factors which, incombination, are probably unique:

(1) The average flow is large - about 1370 m3 /s.

(2) The head is high - 324 meters.

(3) A very large amount of usable storage - over 31 billion cubicmeters - was developed simply by slightly raising the naturallevel of large lakes existing on the plateau.

(4) Most of the construction could be done in the dry.

(5) The reservoirs can be filled in a year.

Technological advances in EHV transmission during the early1960's, plus the rapidly growing demand for power in Quebec, madethe development of this remarkable but remote site economicallysound, and construction was started in 1967. By the mid-1970's,*when the last generating unit is completed, Churchill. Falls will beone of the world's major power stations with an installed capacity of5,225,000 kW and an annual output of approximately 34.5 billionkWh.5

Principal Elements of the Project

The arrangement of reservoirs, hydraulic control structures andspillways is shown in Fig. 2. These reservoirs are expected to provide

sufficient storage to permit utilization of approximately 98 percentof the long-term average flow.1

The powerhouse proper is carved out of rock 300 metersbeneath the surface.1 For large underground stations, there is a

strong incentive to choose the highest capacity machines feasiblewithin the limits imposed by power system reliability, manufacturingcapacity, transport facilities, and the state of the art. Taking all thesefactors into consideration, an installation of eleven 475-MW unitswas selected.2

The switchyard is located on gently sloping ground directlyabove the powerhouse complex. When completed, it will containfifteen 240-kV breakers, six 1 000-MVA, 236/71 5-kV transformerbanks, and twelve 735-kV breakers.

Power will be delivered ta the Hydro-Quebec system over three200-km, 735-kV transmission lines which, functionally, will be anextension of the Hydro-Quebec 735-kV system.3'4'6 In addition,two 230-kV lines are being constructed to supply approximately 250MW for mining operations in Labrador.

Paper C 72 264-0, recommended and approved by the Power GenerationCommittee of the IEEE Power Engineering Society for presentation at the IEEEPES Winter Meeting, January 28-February 2, 1973. This paper was upgraded totransactions status, T 72 264-0. Manuscript submitted February 1, 1972, madeavailable for printing April 4, 1973. Fig. 1. General location map.

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General Arrangement

The general arrangement of the powerhouse complex is shown inFigs. 3 and 4.

Each turbine is supplied through a 6.1-meter diameter inclinedconcrete penstock, steel-lined at the lower end. Early studies indic-ated that penstock valves would not only be costly, but would alsoinvolve a major extrapolation of existing experience, so it was decid-ed to omit them. To minimize wire drawing at the wicket gates, thepenstock is normally emptied when a unit is shut down (Fig. 7).

The main powerhouse cavern, which accommodates the elevengenerating units, is 296 meters long, 25 meters wide and 47 metershigh. Unit protection and control boards, static excitation equip-ment, and unit service switchboards are arranged along the upstreamside of the top floor. Governor actuator cabinets and oil tanks, cool-ing water pumps, isolated phase bus coolers and generator terminalequipment are installed on the floor below. Auxiliary power andcontrol cables are laid in trays in a gallery on the upstream side, whileair and water piping is installed in a gallery on the downstream side.An unloading and storage area is provided at the west end and amachinery erection bay at the east end. A machine shop and a storagearea for small parts occupy the space beneath the east erection bay.

The powerhouse is served by two 400-ton cranes which, to-,gether, are capable of lifting a complete rotor. For security reasons,important facilities, such as auxiliary power substations, batteries, aircompressors and drainage sumps and pumps, are duplicated andinstalled at opposite ends of the powerhouse.

Immediately downstream of the powerhouse is a common surgechamber vented to the surface. Four sets of sectional draft tube gatesare provided and these are supplemented by temporary bulkheads setin the gate guides to protect the units still under construction. Twounlined tailrace tunnels, each 13.7 meters wide, 18.3 meters high and1692 meters long, lead from the surge chamber to the river.

After numerous schemes for bringing the power to the surfacehad been evaluated, the choice narrowed to two alternatives whichpromised similar reliability, costs, losses and reactance.

One proposal was to connect each generator directly to a1 5-735-kV transformer bank on the surface using isolated phase busin vertical shafts, while the other was to install unit-connected240-kV transformers underground, run 240-kV cables to the surface,and complete the connection to the 735-kV switchyard with236/71 5-kV autotransformers. The latter solution was eventually ad-opted on the basis that it permits simpler and more flexible operation.

Fig. 2. The reservoirs.

341

The main underground transformers are accommodated in agallery just upstream of the machine hall and connected to the gener-ators with isolated phase busses. To minimize fire hazard, each trans-former is located in a three-sided concrete cell fitted with an auto-matic deluge system and a crushed stone quenching pit.

For security reasons, not more than two 240-kV cable circuitsare run in one cable shaft; hence, six gunite-lined vertical cableshafts, each about 2.1 meters in diameter and 275 meters long, areprovided for the eleven cable circuits. Connections from the pot-heads at the top of each cable shaft to the switchyard are carriedoverhead.

The main control room is located in a relatively small controland administration building situated on the surface immediatelyabove the east end of the powerhouse. The above-ground location isbased on operator preference rather than cost or technical con-siderations.

A road and a 1616-meter long access tunnel provide access tothe powerhouse complex for heavy vehicles. Normal access for per-sonnel is by elevator from the control and administration building.

Generating Units

The Churchill Falls machines represent a significant extrapol-ation in hydraulic turbo-generator experience and, even though theywill be surpassed in rating and dimensions by the units now beingbuilt for Grand Coulee, they are still unique in the combination of'head, capacity and physical size.

At an early stage, a contract was negotiated with a consortiumof two major manufacturing organizations for the supply and instal-lation of turbines, generators, governors, excitation equipment andunit control boards. This not only permitted adequate time for thedesign and development, but also gave the machinery and stationdesigners a good opportunity to collaborate in optimizing key dimen-sions and other pertinent characteristics.

The underground powerhouse dictated a compact machine, andboth suppliers chose a configuration incorporating a conventionallyarranged turbine guide bearing, a thrust bearing supported on theturbine headcover, and a generator guide bearing mounted on anupper bracket attached to the top of the stator frame. The forgedshaft is relatively short and fabricated in one piece. The two makesof turbine and generator are physically interchangeable at any unitposition.

The turbines are Francis type, rated 648,000 hp at 200 r/minunder a net head of 313 meters. Calculated runaway speed is 305r/min for one design and 335 r/min for the other. Speed rise on fullload rejection is about 45 percent.

The governors are of the electrohydraulic type, arranged tocontrol each turbine through an individual 42 kg/cm2 (600 psig)oil-servo system. The hydraulic components, which include two pres-sure controlled 100-hp pumps and a 15-hp pump which runs con-tinuously, are located on the turbine floor, while the solid-stateelectronic components are built into the unit control boards. Allcontrols and adjustments to the response characteristics are madeelectrically, and the load settings on the individual governors can betied together in a joint control system.

The generators are air-cooled machines of modern but fairlyconventional design. The main characteristics are specified asfollows:

Rated capacityPower factorVoltageWinding temperature (max.)

Synchronous reactanceTransient reactance (unsaturated)Inertia constant (H)Rotor diameterRotor weightStator core depth

500,000 kVA0.9515 kV1150CWith cooling water 1 50C100%33%3.59.0 m600,000 kg3.0m

Voltage, reactance, inertia and temperature rise were determinedin consultation with the generator designers, with the intention ofachieving sound mechanical design and satisfactory electrical per-formance at the most favourable overall project cost.

The stators are piled and wound at site to permit the use of acontinuously stacked core. Windings consist of six parallel circuitsmade up of single-turn coils employing "Roebel"-type bars havingepoxy-mica insulation. A novel feature of the winding is that theneu: als of the six circuits are made independently around the peri-

Fig. 3. General arrangement plan.

342

phery of the stator, thus eliminating heavy, costly neutral end con-nections. The six neutrals are interconnected with 1 5-kV No. 2 AWGcable, and grounded through a 75-kVA askarel-type distributiontransformer and resistor sized for a one-minute rating.

Six sets of neutral current transformers per phase for differentialprotection are mounted on the stator frame, and one current trans-former is installed to detect any significant unbalanced current flow-ing in the neutral connection between two groups of three circuits.

The rotor rims are built up of high tensile-strength steel selectedso that, at runaway speed, the stress will not reach 75 percent ofyield. Non-continuous amortisseur windings are fitted.

The generators, are cooled by a simple closed air-circulatingsystem, using air-to-water heat exchangers mounted on the statorframes. There is no requirement for bleeding off air for powerhouseheating; hence, automatic temperature regulators are unnecessary.

Although the maximum winding temperature is specified as1 15°C with cooling water at 150 C, the water will seldom reach thistemperature, and it is expected that for over 90 percent of the time,the winding temperature will be less than 1 100 C.

One manufacturer employs a spring-mounted thrust bearing,while the other uses a bearing similar in principle but utilizinghydraulic load cells in place of mechanical springs.

A high speed static excitation system was specified to assist inmaintaining stability over the long 735-kV transmission system.Performance characteristics are as follows:

IN

IN

II INCLINED PENST

CONSTRUCTION

6 CABLE

Operating voltageOperating frequencyCeiling voltage

Regulator time constantStabilizing signalSwitching surge withstandMaximum dynamic overvoltage

30-150% rated90-150% rated6.4/unit on no-load air gapline field voltageLess than 0.03 secDerived from watt transducer2.75/unit1.7/unit

Switching surge and impulse tests have been performed to provethe design.

Physically, the excitation equipment consists of thyristors sup-plied from a transformer connected directly to the generator term-inals. The 3524-kVA, three-phase, askarel-filled transformer is fittedwith grounded aluminum barriers between phases to minimize therisk of phase-to-phase faults. The rectifier package is throat-connected to the transformer, and contains the air-cooled thyristors,the voltage regulator, the field breaker and a discharge resistor. It wasenvisaged that dust might cause problems, particularly during thelong powerhouse construction period; hence, a closed ventilatingsystem was selected, with duplicate fans 4nd an air-to-water heatexchanger. The voltage regulator is designed so that joint var controlcan be added in the future.

Main Transformers

The initial concept foresaw the use of 167-MVA single-phaseunits throughout in order to keep the shipping weight within the127,000-kg limit imposed by the then existing transport facilities.Further studies, however, showed that substantial savings could be

;SHAFT

SHAFT

I~~ VEN V~~~-u-],I1

RIVER

Fig. 4. General arrangement cross section.

343

realized through the purchase of 500-MVA, three-phase, 240-kVtransformers, along with 333-MVA, single-phase, 735-kV units, eventhough considerable expenditures would be required for cranes andtransporters to handle loads of up to 226,500 kg (250 tons).

Site assembly of transformers was contemplated but deemedtoo risky in view of the strict control of cleanliness necessary for thesuccessful manufacture of EHV equipment and the importance ofmaintaining schedule.

In establishing ratings, two factors were considered of specialimportance. First, the transformers must have ample capacity so thatthey do not become limiting on station output, and second, theimpedance between generator terminals and the 735-kV bus mustnot exceed 25 percent for system stability reasons.

The underground generatorforced-oil water-cooled type withrated as follows:

CapacityTemperature RiseVoltageBILImpedance

transformers are three-phase,thermally upgraded insulation

500 MVA at 0.95 PF lagging650C with cooling water 25°C14.75-240 kV with no taps900 kV12% maximum

The capacity is 550 MVA with 150C cooling water and 375MVA with one oil pump out of service.

A computer study showed that adequate surge protection isprovided by 192-kV lightning arrestors connected to the cable term-inals on the surface, so it was possible to reduce clearances and thedimensions of the transformer gallery by enclosing the 240-kV bush-ings and cable potheads in an oil-filled compartment mounted on thetransformer.

The 1 000-MVA transformer banks in the switchyard are madeup of forced-air-forced-oil-cooled, single-phase autotransformer unitsrated as follows:

vision for adding generator surge protection should experienceindicate a need for it. Current transformers are mounted inside thebus housing and near the generator terminals, there are links whichcan be removed and replaced with a short-circuiting bar to facilitatetesting the machines.

The hexagonal aluminum conductors have welded joints, exceptat the terminals where silver-plated bolted connections are provided.Housings fabricated from heavy aluminum-formed plates continuous-ly welded together are used to achieve a degree of shielding adequateto eliminate problems of magnetically induced overheating in nearbysteel work.

Air is blown into the middle phase housing and returns to thecooling unit via the outer phases. Each cooler is equipped with twofull capacity fans and an air-to-water heat exchanger supplied fromthe unit cooling water system. Normally, one of the fans runs andthe other is a standby arranged to start automatically should the firstfan fail.

240-kV Cables

The connections from the underground 14.75-240-kV unittransformers to the surface consist of single conductor, paper-insulated, oil-filled, aluminum-sheathed, polyethylene-jacketed cablesrated 1500 amperes, 245 kV, 1050 kV BIL.

The copper conductor is 1150 mm2 (2250 MCM) constructedof six segments wound around a helical hollow core (Milliken type).Nominal insulation thickness is 17 mm and the extruded aluminumsheath is 4.3 mm thick. The overall diameter of the cable is 97 mm.

The pothead at the lower end is designed to take the full statichead as stop joints are not used. Type tests were performed on thepotheads at 42 kg/cm2, which is approximately 60 percent morethan the maximum service pressure. Pressurized oil reservoirs arelocated on the surface close to the upper potheads.

CapacityTemperature RiseVoltage (bank)Tertiary voltageBILSwitching surge withstandPower frequency withstandImpedance

333 MVA at 1.0 PF650C236/715 kV no taps13.8 kV1950 kV1425 kV850 kV rms12% maximum

The tertiary windings are fitted with internal reactors to limitthe short circuit level to 500 MVA and they are suitable for supply-ing a load of 30 MVA. Except where connected to an externalsystem, the tertiaries are grounded at one corner through a distrib-ution transformer and resistor.

Isolated Phase Bus

The connections between generator terminals and the14.75-240-kV step-up transformers are made with forced air-cooledisolated phase bus rated 22,500 amperes, 15 kV, 110 kV BIL. Theself-cooled rating is 10,000 amperes and, in the event of failure ofthe cooling system, the bus is capable of carrying full generatoroutput for 15 minutes without exceeding 1250C.

Tap connections are provided for potential transformers, excit-ation transformers and unit service transformers, and there is pro-

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The cables are supported in the vertical shafts by flexible alum-inum clamps at 9.2-meter spacing. Between clamps, the cable run isslightly curved, thus allowing a small amount of movement to relievestresses caused by thermal expansion. The sheaths are solidly ground-ed at the surface and grounded through 3-kV distribution-type light-ning arrestors at the transformer end.

A fan at the head of each shaft cools the cables by blowing airdown the shaft. The cooling system is monitored by pressure andtemperature sensors, and it includes a standby fan which will startautomatically should the air flow become inadequate. Thermostatic-ally-controlled electric heaters maintain the incoming air above 0°Cto prevent freezing and spalling of the shaft lining.

Tests were performed in accordance with IEC requirements and,in addition, both a load cycle test on 27 meters of cable in thevertical position and a sheath fatigue test were carried out.

Switchyard

The single-line diagram is shown in Fig. 5. The criteria used inestablishing the scheme of connections are similar to those employedby Hydro-Quebec and can be summarized as follows:

(1) A transmission line should not be lost due to a fault in anyapparatus other than equipment connected directly to the line;

(2) No more than one transmission line should be lost due to a faultin equipment connected directly to the line;

(3) It should be possible to perform maintenance on equipmentwithout interruption of service;

(4) Busses should be limited to two levels only to keep the height ofstructures reasonable;

(5) Requirements for costly 735-kV breakers should be kept to aminimum;

(6) Unit breakers should be provided to simplify the switchingrequired when starting and stopping the generators;

(7) The 735-kV rings interconnecting the 735-kV lines and trans-former banks should remain closed under normal operatingconditions.

It will be noted that transverse 230-kV busses are provided tosupply the 230-kV lines and to facilitate making emergency connec-tions in the event of a transformer failure.

Insulation levels for the 735-kV system were determined fromthe results of studies carried out by Hydro-Quebec using analoguecomputer facilities.7 These studies showed that maximum switchingsurge overvoltages can be limited to 1.8 per unit through the use ofclosing resistors on the line circuit breakers, and indicated that themaximum 60-Hz overvoltage on load rejection will not exceed 1.45per unit.

Based on the foregoing, the insulation values for 735-kV trans-formers and shunt reactors were specified as follows:

Basic impulse level withstandSwitching surge withstandPower frequency withstand (wet)Lightning arrestor rating

1950 kV1425 kV850 kV565 kV

For other switchyard equipment, a BIL of 2100 kV wasselected.

Minimum electrical clearances are as follows:

735 kV phase-to-phase735 kV phase-to-ground735 kV above-grade230 kV phase-to-phase230 kV phase-to-ground230 kV above-grade

10.70 meters5.50 meters10.70 meters3.66 meters2.28 meters6.71 meters;

Low level 735-kV busses are fabricated from 154-mm diameteraluminum tubing, while high level strain busses comprise two bundle2050-mm2 aluminum conductors spaced at 380-mm centres.

The galvanized steel structures for the high level busses consistof 'A' frames fabricated from wide flange beams supporting con-ventional lattice-type cross arms.

All the high voltage breakers are air-blast type, with a maximumfault clearing time of 0.05 seconds.

The 735-kV breakers have an interrupting rating of 25,000MVA symmetrical and the line breakers are fitted with 400-ohmclosing resistors to limit switching surges. The 230-kV breakers havean interrupting rating of 15,000 MVA symmetrical. High pressure airis supplied from a central compressor station.

Fig. 5. Single-line diagram (arrangement of generator, transformers and switchyard).

345

(3) A recording instrument board;

For the common station services such as lighting, ventilating,heating, drainage systems, elevators, cranes, compressors, batterychargers and hydraulic gates, together with local loads such as thetownsite and the airport power is obtained from tertiary windings ontwo of the main 236/71 5-kV transformer banks. Two 1 5-MVA auto-transformers with automatic on-load tap changers regulate the volt-age. Primary distribution is at 13.8 kV, except for a 66-kV woodpole line which serves the airport and the four distant hydrauliccontrol structures. For all important loads, duplicate 1 3.8-kV feedersand step-down transformers are provided, together with automatictransfer on loss of voltage.

Generating unit auxiliaries are normally fed from 1 000-kVAtransformers connected directly to the generator terminals. When aunit is shut down, those auxiliaries required for restarting are auto-matically transferred to the common station service supply.

In the event of a complete shutdown, two 500-kW diesel-drivengenerators at the control and administration building can furnishsufficient emergency power to maintain essential services and startone of the main units. Emergency diesel generators are also installedat the outlying hydraulic control structures.

Control

The control system is arranged to permit normal operation ofthe entire power complex from the control room, using the followingfacilities:

(1) A main benchboard from which the units can be started,synchronized or stopped automatically; the load can be con-trolled and normal switching operations can be performed;

(2) A supervisory control board for remote control of the outlyinghydraulic control structures;

(4) Lamp-type annunciators;

(5) A console and automatic typewriters for a data loggingcomputer;

(6) A large operator's desk on which telephones for the variouscommunications systems are mounted.

Complete controls for the units are also provided on the unitcontrol boards adjacent to the generators. These facilities can be usedto operate the machines locally during commissioning, testing, main-tenance, or in an emergency.

The normal starting procedure is to fill the penstock by crackingthe headgate, which takes about 20 minutes, then open the headgatefully, start the unit auxiliaries, release the brakes, open the wicketgates, allow the machine to run up to speed, flash the field from thestation battery, build up voltage, close the motor-operated 230-kVdisconnect, and synchronize by closing the unit 230-kV breaker. Theautomatic starting sequence is described in more detail in Fig. 6.

The normal stopping procedure is to unload the machine, tripthe 230-kV breaker, close the headgate and allow the penstock todrain through the wicket gates, which are held at the speed no-loadposition. When the penstock empties, and the unit slows down, thewicket gates are closed, the brakes are applied, and the auxiliaries areswitched off. Fig. 7 shows this sequence in greater detail.

Pushing an emergency stop button on the unit control board willdrop the headgate and trip the 230-kV breaker immediately. It is alsopossible to close the headgate and trip the 230-kV breaker directlyfrom the control room.

On each unit control board, there is an automatic synchronizer,plus a set of instruments for manual synchronizing. When the mach-

NORMAL START

1. MANHOLE COVERS ON2. DRAFT TUBE GATE REMOVED STARTING TIMER ON3. ALL RATER. DRAIN, OIL AND AIR VALVES SET 2 230 KY CIRCUIT BREAKER OPEN4. 230 KV GROUNDING SWITCH OPEN 3 230 KV MOTOR OPERATED DISCONNECT SWITCH OPEN

MMANUAL DISCONNECTING SWITCHES CLOSES 4 WICKET GATES CLOSED6. NO ALARM SHOWING ON ANNUNCIATOR CABINET 5 GATE LIMIT A30VE SPEED NO LOAD

7. BRARES ON H. SHUTDOWN SOLENOID LATCHED UP8 GOVERNOR OIL PRESSURE NORMAL i FIELD BREAKER CLOSED9. AUXILIARIES ANO TRANSFER SWITCHES ON AUTO 8 VOLTAGE REGULATOR SWITCH IN ON POSITION

10. SHUTDOWN RELAYS NOT ENERGIZED 9 EXCITATION CONTROL SET AT NO LOAO11 EXCITATION FAN SELECTOR SWITCH CLOSED O. BRAKE PRESSURE NORMAL12- BREAKERS FOR AUXILIARIES CLOSED,' 1. GOVERNOR TRANSFER SNITCH ON AUTO13. FUSES I DUAMY FUSES INTACT

1. START THRUST BEARING OIL LIFT PUMP0. START TRANSFORMER OIL PUMPS CEHRELEASE ARAKES CEKRELEASE +NTSASIS. START ONE WATER POMAP RETRACT CREEP DETECTOR SHUTDOWN SOLENI UNIiSTRTV. START ISOLATED PHARSE BUS FAA

1. THRUST BEARING OIL LIFT PUMP ON2. THRUST REARING WATER FLOW ON3 TURBINE SHAFT SEAL WATER FLOW ON4. TURBINE AIR HEAR SEAL WATER FLOW ON5. GOVERNOR PRESSURE NORMAL LRAKES OFF

AT 951SPEED START TRANSFER UNIT SERVICEI. STOP THRUST REARING EXIAINTO UNIT TRANSFORMER STARSTSPTSTARTINGYNTIMER

OIL LIFTPOMP FRIATNO 1. START SECOND WATERPUNP20LS 3 HOSSNCIGSIC TR UOAI YCRAON

2 FLASh FIELODF

2. START TURAINE AERATION COMPRESSOR

CLOSE 230 KV :B=E:=K:-R~S~ 1. RELEASE SPEES NO LOAD SOLENOIDCLOSEODOI BREAERS 2. DE-ENERGIZE AUTO SYNCHRONIZER LOV UIT

Fig. 6. Semi-automatic starting sequence.

346

Auxiliary Power

ines are being placed on line from the control room, only automaticsynchronizing is used. Closing of the 735-kV breakers is supervisedby synchronism check relays, and there will be instruments in thecontrol room for manual synchronizing of the line breakers.

As auxiliary power systems and other services such as drainageand compressed air normally operate automatically, they are onlymonitored from the control room. In all cases, though, there isprovision for local manual control should the automatic equipmentfail.

Protective Relaying

The protective relaying systems are designed on the basis that tomaintain system stability, major faults must be cleared in 0.1 secondand no single contingency fault should result in the loss of more than1000 MW of generation.

The protection for the generating units, the isolated phase bussesand the generator transformers is comprehensive but conventionaland generally in accordance with current North American practice.The combination cable and overhead line circuits between the under-ground transformers and the switchyard are protected by duplicatesets of pilot wire relaying, and the 230-kV busses have high speeddifferential protection.

The 236/71 5-kV transformers are provided with two sets of highspeed harmonic restraint type differential relays supplemented by

sudden gas pressure relays. The 735-kV busses, also, are protected bytwo separate sets of high speed differential relays. Instantaneousovercurrent-type ground fault detectors are used with the 735-kVcurrent transformers, and local breaker failure back-up relaying isincluded.

The shunt reactor protection consists of differential, sudden gaspressure, phase overcurrent and ground overcurrent relays operatingthrough lockout relays to trip the line breakers at Churchill Falls,and send transfer trip signals to the far end of the line.

The 735-kV line protection comprises two independent relaysystems, each of the directional comparison permissive underreachingtype. One system utilizes phase and ground distance relays operatingthrough a power line carrier link, while the other uses distance relaysof a different design, operating through a microwave-troposcatterlink. Overvoltage tripping and provision for future automatic re-closing are included.

The various relay systems all employ tried and proven electro-mechanical relay elements, tripping through pairs of multicontactauxiliary tripping relays, connected in parallel to improve reliability.Relays for the generating units are mounted on the unit controlboards in the powerhouse, whereas the line and switchyard relays aremounted on duplex switchboards housed in a prefabricated steelbuilding in the switchyard. An automatic oscillograph is installed inthe switchyard relay board specifically to assist in analyzing the per-formance of the switchyard and transmission line protection.

NORMAL STOP1T ENERGIZE SPEEE NO LOAT SOLENOID2. OPEN 230 KV D ISCONNECT

WATERv KE50 TR IPEXCITATNON71 STOP EXC ITAT ION FAN

9. STOP TRANSFORMER 01IL PUMPS10. STOP SOLATED PHASE BUS FAN

ATI RPUFAINGOLLF T7 P ALN21.STOPANSER CONIT SERYIER ST1RT THUS BEAINGOILLIFZA SHUT-DWNFALLNOI AT 60 RPM FALLING 1. APPLY CREEP DETECTOR

0-L0. DISCONNECT HIBRATION DETECTOR 02 ENERGIZE TIME RELAY APPLY B. STOP SETUND CEOLING OATER PUMP

LOCKOUT TRIP OR EMERGENCY STOP

ENERGIZE SHUT-DOWN SOLENOID2. TRIP 230 KV BREAKER3. SUPPRESS FIELD4. TRIP FIELD BREAKER

TRIP LOCKOUT RELAY 5. STOP EXCITATION FAN6. TRIP INTAKE GATE7. ANNUNCIATE8. SENS SIGNAL TO COMPUTER9. BLOCK STARTING

AT 170 RPM FALLING

OPEN 230 Kv DISCONNECT 1. TRANSFER UNIT SERVICE 1. START THRUST BEARING OIL LIFT2. BLOCK SOME ANNUNCIATION POINTS TO COMMON SUPPLYE PUMP3 STOP TRANSFORMER OIL PUMP 2. STOP ONE COOLING WATER 2. DISCONNECT VIBRATION DETECTOR4. STOP ISOLATED PHASE BUS FAN PUMP

AT 75 RPM FALLING AT AS RPM FALLING 1. APPLY CREEP DETECTOR_ L * AT 60 RP F LL NG 02. STOP SFCONO COOLINGNWTER PUMPENERGIZE TIME RELAY APPLY BRAKES 3. STOP THRUST BEARING OIL LIFT PUMP

NON LOCKOUT TRIP

1. ENERGIZE SPEED NO LOAD SOLENOID2. TRIP 230 KV BREAKER3. SUPPRESS FIELD4. TRIP EXCITATION

TRIP NON-LOCKOUT RELAY 5. TRIP FIELD BREAKER6. STOP EXCITATION FAN7. ANNUNCIATE9. SEND SIGNAL TO COMPUTER.9 BLOCK START ING

1. TRANSFER UNIT SERVICETO COMMON SUPPLY

.2 STOP ONE COOLING WATERPUMP

Fig. 7. Stopping sequence.

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Annunciation and Data Logging

A solid-state lamp type annunciator system, together with a datalogging computer, provide an audible and visual indication plus aprinted record of abnormal conditions throughout the power com-plex. To avoid having an excessive number of annunciator windows,the visual alarms have been grouped to indicate the location andnature of the trouble, whereas the computer prints out a record ofprecisely which alarm contact operated.

Generating unit alarms are shown on an 80-point annunciatormounted on each unit control board. In addition, they are groupedand displayed on individual 12-window unit annunciators located onthe main benchboard in the control room. Alarms associated withpowerhouse services underground are connected to two 40-pointannunciators, one at the east end of the powerhouse and one at thewest end. These alarms, too, are grouped and displayed in the controlroom, along with alarms pertaining to service facilities located aboveground. About 450 switchyard alarm contacts are wired to anelectronic cabinet in the switchyard relay building, grouped, anddisplayed on a 160-window annunciator in the control room.

When all eleven units are installed, operation of the plant willrequire monitoring of about 1650 alarms and over 300 indicatinginstruments. To record and assess all this data manually is a form-idable task; hence, it was felt that the plant could be operated moreefficiently with the aid of a data logging computer which couldautomatically scan and log all these quantities as required, as well ashighlight abnormal conditions for the operators. It was recognized,however, that computer installations are subject to teething troublesand outages for maintenance and repair, so it was agreed that thecomputer should supplement rather than replace conventionalinstrumentation and annunciation.

The main computer is installed immediately beneath the controlroom. The heart of the system is a central processor with an all-corememory of 28-k 16-bit words and a full cycle time of 3 micro-seconds. Data retrieval from the powerhouse and switchyard areas isaccomplished with the aid of four remote computer interfaces, eachof which scans, multiplexes and transmits signals to the central com-

puter over a pair of wires. Trip alarms, however, are hardwired to thecomputer to permit a resolution time of 4 milliseconds.

In addition to automatically printing out operating reports andalarm histories, the computer can be used to display analogue valueson call, and print out trend patterns over a 15-minute period. Initial-ly, the computing function will be limited to calculating water dis-charge through the turbines, but it is expected that, in time, moreuse will be made of this feature to assist in optimizing unit loadingsand water control.

REFERENCES

(1) D. Wermenlinger, J. G. S. Thomson4 J. M. Gardiner, "ChurchillFalls Power Facilities", Journal of the Power Division Proceed-ings of the American Society of Civil Engineers, pp. 515-537,March 1971.

(2) J. L. Haydock, J. G. Warnock, "Giant-Sized Hydraulic Tur-bines", presented at the American Power Conference, April 24,1968.

(3) R. Fournier, D. McGillis, J. C. Roy, "Planning of 735-kV Exten-sion to Hydro-Qu6bec System to Incorporate Churchill Falls in3300-Mile Network", Report No. 42-02, 1968 CIGRE.

(4) G. W. Clayton, D. McGillis, "Preliminary Studies of PowerTransmission from the Churchill Falls Development", presentedat the American Power Conference, Chicago, 1967.

(5) Gordon D. Friedlander, "Power from Labrador: The ChurchillFalls Development", IEEE Spectrum, pp. 81-91, February 1971.

(6) W. S. Price, G. G. Sauv6, "Insulation Coordination and Con-ductor Selection for the Churchill Falls 735-kV TransmissionLines", presented at the IEEE EHV Conference, Montreal, 1968.

(7) Jean-Guy Ren6 and W. E. Feero, "Switching Surge Studies Set735-kV Insulation for Quebec", Electrical World, pp. 26-28,September 23, 1968.

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