local relays complete the trip circuit andinitiate tone transmission to the remoteterminal where the tone receiver contactcompletes the trip circuit at that station.This is a high-speed sequential operationwhere the only delay is the operating timeof the tone equipment.

Another scheme for microwave trans-ferred tripping is shown in Figure 9 Inthis scheme, directional and overcurrentor distance relays at each line terminalare set to reach through the line section asshown. Operation of the relays startsthe tone (or tones), and reception of thetone completes the trip circuit. For anyfault in the line section GH, reception ofthe tone signal is necessary for high-speedtripping. For an external fault to theright of station H, the H terminal of lineGH will not trip since its directional con-tacts will be open. Station G will nottrip since it does not receive any tonesignal from station H. The operatingtime of either of these two schemes is ap-proximately 2 cycles. With this schemea tone is always necessary for tripping;thus taking the microwave out of servicewill disable the high-speed relaying.However, relay requirements are less ex-acting and, load conditions permitting,directional overcurrent relavs may beused in place of the distance relays.The relaying schemes described pre-

viously are basic in nature and do not in-clude out-of-step and backup relays. theapplication of these being a separateproblem.

Conclusions

1. Microwave systems may be used readilyto provide essentially the same type ofservices as obtained with power-line carrierbut in much greater numbers.2. The use of frequency-division multiplexoffers greater flexibility in "dropping" indi-vidual voice circuits and permits the use ofdirect modulation by high-frequency toneunits eliminating the need of a portion ofthe multiplexing equipment for applicationsinvolving telegraphic-type circuits.3. Due to the ease of obtaining telegraphic-type channels, supervisory control in mostcases should be of the single-station typeresulting in greater flexibility of operationand increased reliability.4. Microwave offers new relaying schemesdue to its independence from the trans-mission line and thus will stimulate newideas in the art of protective relaying.5. There is no special application probleminvolving emergency power supplies for anyof the services described except protectiverelaying where an interruption cannot betolerated.

References1. PRINCIPLES AND PROSPECTS OF MICROWAVECOMMUNICATION, F. S. Mabry. Westinighoutse

Enginieer (East Pittsburgh, Pa.), May 1949, pages74-77.

2. EcONOMIC AND ENGINEERING ASPECTS OFMICROWAVE AND CARRIER, F. C. Krings. Elec-trical World (New York, N. Y.), July 16, 1951,pages 99-102.

3. APPLICATION OF MICROWAVE CHANNELS, R. C.Cheek. AIEE Transactions, volume 70, part I,1951, pages 813-17.

4. MICROWAVE SYSTEM DESIGN FOR UTILITIES,C. M. Backer. Tele-Tech (New York, N. Y.),December 1951, pages 48-50.

5. THE COMBINATION OF SUPERVISORY CONTROLWITH OTHER FUNCTIONS ON POWER-LINE CARRIERCHANNELS, R. C. Cheek, W. A. Derr. ElectricalEngineering (AIEE Transactions), volume 64, May1945, pages 241-46.

6. BY A FLICK OF THE FINGER (SUPERVISORYCONTROL), W. A. Derr. Westinghouse Engineer(East Pittsburgh, Pa.), November 1949, pages162-67.

7. A HIGH-SPEED TELEMETERING SYSTEM WITHAUTOMATIC CALIBRATION, W. E. Phillips. AIEETransactions, volume 71, part II, pages 1256-61.

8. PROTECTIVE RELAYING OVER MICROWAVECHANNELS, H. W. Lensner. AIEE Transactions,volume 71, part III, 1952 (Proceedings 52-51).9. FIELD TESTING A MICROWAVE CHANNEL FORVOICE COMMUNICATION, RELAYING, TELEMETERING,AND SUPERVISORY CONTROL, D. R. Pattison, M. E.Reagan, S C. Leyland, F. B. Gunter. AIEE Trans-actions, volume 69, part II, 1950, pages 945-52.

10. A NEW HIGH-SPEED DISTANCE-TYPE CAR-RIER-PILOT RELAY SYSTEM, E. L. Harder, B. E.Lenehan, S. L. Goldsborough. Electrical Engi-neering (AIEE Transactions), volume 57, January1938, pages 5-10.

11. A DISTANCE RELAY WITH ADJUSTABLE PHASE-ANGLE DISCRIMINATION, S. L. Goldsborough.Electrical Engineering (AIEE Transactions), vol-ume 63, November 1944, pages 835-38.

12. A NEW CARRIER RELAYING SYSTEM, T. R.Halman, S. L. Goldsborough, H. W. Lensner,A. F. Drompp. Electrical Engineering (AIEETransactions), volume 63, 1944, pages 568-72.

No Discussion

S. M. DENTONMEMBER AIEE

THE Davis Dam power development islocated on the Colorado River 65

miles downstream from Hoover Dam andis one of a series of hydroelectric and ir-rigation projects extending from HooverDam to the Gulf of California. Seventy-five miles below Davis is Parker Dam andPower Plant, built by the Bureau of Rec-lamation, with an installed capacity of120,000 kw. Parker Dam was completedin 1938 and power generation started in1942. Other dams below Davis on the

Paper 52-249, recommended by the AIEE PowerGeneration Committee and approved by theAIEE Technical Program Committee for pres-entation at the AIEE Pacific General Meeting,Phoenix, Ariz., August 19-22, 1952. Manuscriptsubmitted March 26, 1952; made available forprinting July 3, 1952.

S. M. DENTON and H. 0. BRITT are with the Bu-reau of Reclamation, Denver, Colo.

H. 0. BRITTASSOCIATE MEMBER AIEE

Colorado River include Laguna and Im-perial Dams, both of which are for diver-sion only, and Headgate Rock Dam builtby the Office of Indian Affairs, which hasa power potentiality of 40,000 kw. Atnormal water surface elevation LakeMohave, which is the 1,800,000-acre-footreservoir formed by Davis Dam, will ex-

tend to the tailrace of Hoover PowerPlant. The first of five 45,000-kva gen-

erators at Davis Power Plant was placedin service on January 5, 1951. Since thattime the four remaining units have gone

into operation bringing the total capacityto 225,000 kw. The power plant will gen-

erate from 800,000,000 to 1,000,000,000kilowatt-hours annually with power ratescomparable to those established forParker Dam Power Project. The power-

producing and transmission facilities areintegrated with the extensive system ofthe Southwest, supplying power toArizona, Southern California, and South-ern Nevada.

Purpose

In addition to power generation, theDavis Dam Project will operate to betterconserve the water of the Lower ColoradoRiver and to service the Mexican WaterTreaty. Normal water releases at HooverDam and Power Plant are governed pri-marily by power demands in the marketareas of Southern California. During theperiods, when the water releases for powerat Hoover exceed the downstream irriga-tion requirements, the excess water es-capes to the Gulf of California. Thestorage reservoir created by Davis Dampermits closer regulation of the river bypermitting release of water for down-stream requirements at the most favorabletimes, utilizing water which otherwisewould be wasted. The Mexican Water

Denton, Britt-The Davis Dam Power Development

The Davis Dam Power Development

OCTOBER 1952 917

Figure 1. Map of the Colorado River below the Grand Canyon

Treaty, which became effective in 1943,governs the division of the Colorado Riverwaters between the United States andMexico. In return for certain considera-tions from Mexico, the treaty obligatedthe United States to construct Davis Damwithin 5 years from date of treaty rati-fication. Servicing of this treaty is oneof the major purposes of the Davis DamProject, and in this connection the dam

will serve as a metering and regulatingpoint for delivery of water to Mexico.

Basic Arrangement of ProjectFeatures

The principal features of the projectare the dam, spillway and outlet struc-ture, power plant, switchyards, and about900 miles of transmission lines with sub-

station facilities. The dam is an earthand rock-fill embankment and has astructural height of 200 feet. In order toreach bedrock for a concrete dam founda-tion at this site would have required theexcavation of sand, gravel, and silt in theriver bed to a depth of 200 feet. A costanalysis eliminated a concrete dam infavor of an earth and rock-fill dam par-tially due to the nature of the founda-

Denton, Britt-The Davis Dam Power Development OCTOBER 1952918

Generating Units

tion. The selection of an earth and rock-fill type of dam dictated a channel-typespillway outside the river channel. Dueto the nature of the terrain and theamount of floodwater to be considered, achannel spillway on the left side of theearth-fill dam was selected. Originalstudies of the power plant location con-templated a site on the right bank of theriver. This site, however, required a con-siderable amount of excavation and in-volved the use of long penstocks whichwould require surge tanks to provide ac-ceptable operation of the units. Fur-ther study indicated some savings in costand improved operating conditions for thepower plant could be realized by combin-ing the spillway and outlet structure withthe power plant intake structure, consid-erably shortening the penstocks, andeliminating the surge tanks. This ar-rangement was adopted and designs pro-ceeded on this basis. Further investiga-tion of the foundation conditions in thevicinity of the forebay structure necessi-tated a movement upstream of the intakestructure for the power plant, leaving thepower plant itself in its original location.The earth and rock-fill-type dam is ap-proximately 1,600 feet long at the crest.The combined spillway and forebay chan-nel is cut through the rock for about 4,000feet around the left abutment of the dam.The spillway structure is placed across theend of this channel with the intake struc-ture for the power plant paralleling thechannel and normal to the spillway. Thepower plant joins the intake structure at

the downstream end but is separated fromthat point by an angle of 30 degrees fromthe intake structure. This split arrange-ment was dictated by foundation condi-tions. The spillway has a dischargecapacity of 175,000 cubic feet per secondand is provided with radial gates withinthe structure to supplement water re-leases over the spillway and through thepower plant.The Davis Power Plant is of the semi-

outdoor type with the building enclosingthe generators but without a superstruc-ture. The five generators are serviced bya gantry crane on the roof by means ofhatches above the generating units.

TURBINES

The turbine installation for the plantconsists of five vertical-shaft Francis-type94.7-rpm hydraulic turbines with rivetedplate-steel spiral scrollcases and elbow-type draft tubes. Each turbine has acapacity of 62,200 horsepower at full gateand 120 feet net head and is designed forbest efficiency operation at 127 feet nethead. The expected efficiency at thisbead is 90 per cent. The normal net ef-fective head on the turbines may vary be-tween 100 and 130 feet, and the extremerange between 89 feet and 136 feet. Whenoperating at a net head of 120 feet withfull gate opening, the five turbines willdischarge a total of 26,000 cubic feet ofwater per second.The turbine runners are of cast steel in

one piece with a diameter across the topof 17 feet. They are designed to with-stand safely the stresses due to operationat runaway speed at maximum head, in-cluding pressure rise, with the turbinegates wide open and with no load on thegenerator.Each turbine head cover is provided

with an automatically operated air valveto improve turbine operation at partgate. The valve is operated by the gateshifting ring and is adjusted to admit airto the draft tube at certain preset valuesof gate opening. In addition, a smallerair valve is provided for use when thegenerators are operating as synchronouscondensers. This valve is actuated bythe gate shifting ring and admits com-pressed air to the draft tube at zero gateopening as part of the mechanism to de-press the water in the draft tube to anelevation below the turbine runner.

Denton, Britt-The Davis Dam Power Development

Figure 2. Aerial view of Davis Dam, Power Plant, and switchyard areas

Figure 3. Davis Power Plant and intake structure looking downstream

OCTOBIER 1952 919

The plant is constructed so that afterremoval of the intermediate shaft be-tween the turbines and generators, all re-

movable parts can be raised from the tur-bine pit and moved along the gallery bymeans of the govermor gallery travelingcrane. The turbine parts then can behoisted through the hatchways betweenunits by the 325-ton gantry crane withoutdisturbing the generators. When the gen-

erator is dismantled, the turbine partsmay be hoisted through the generatorstator, using the 325-ton gantry crane.

GOVERNORSThe governors for regulating turbine

speed are of the oil-pressure, cabinet-actuator type with electric-driven speed-responsive elements. The speed-respon-sive elements are actuated by permanent-magnet generators connected to the up-

per ends of the generator shafts. Thegovernors control the wicket gates bymeans of oil pressure applied to the servo-

motors and are designed to operate theturbine gates through a complete closingor opening stroke in 4 seconds with a nethead of 127 feet on the turbines. Theactuator main relay valve is adjustable tolimit the rate of movement of the tur-bine gates between 4 and 12 seconds forfull gate-opening or gate-closing stroke.For normal operation, the actuators willbe adjusted for an 8-second rate of travel.

GENERATORS

The generators are rated at 45,000 kva,unity power factor, 3 phase, 60 cycle,13,800 volts, 94.7 rpm. They are of con-

ventional design with the thrust and

upper guide bearings located above therotor and with a lower guide bearing be-low the rotor. Both the stators androtors have class B insulation. The de-sign value of rotor WR2 is 75,000,000pounds at a radius of 1 foot. This valueof WR2, which is considerably higherthan normal, was required to improve theregulating characteristics of these generat-

ing units.The generators are totally enclosed and

are air-cooled with eight surface air coolersequally spaced around the periphery

of the stator frame. Rated outputmay be delivered with one air cooler outof service without exceeding the 40-de-gree-centigrade temperature limit forcooling air entering the generator. Thegenerator housings are sufficiently air-tight to insure proper operation of theautomatic carbon-dioxide fire-extinguish-ing system. This equipment releasescarbon dioxide into the generator uponoperation of the generator differential re-lays or whenever temperature within thehousing reaches a predetermined level.

In order to supply the high-chargingcurrent required by the extensive trans-mission system to which the generatorsare connected, they were designed with ashort-circuit ratio of 2. Subject to ther-mal limitations, the maximum line-charg-ing capacity of each machine, whenoperating at normal rated voltage andfrequency is 72,000 kva, and the calcu-lated value of rated current direct-axistransient reactance is 28 per cent. Amor-tisseur windings on the rotors are designedto give a 1.29 ratio of quadrature-axissubtransient reactance to direct-axis sub-transient reactance.The thrust bearing is located above the

rotor to facilitate bearing maintenance.This bearing carries the entire weight ofthe rotating parts of the generator andturbine plus the unbalanced hydraulicthrust which amounts to a total load of1,270,000 pounds. The thrust and up-per guide bearings are located in a com-mon oil reservoir and are cooled by watercirculated through coils inside the oil res-

Figure 5. Artist's drawing showing section through Davis Power Plant and intake structure

Denton, Britt-The Davis Dam Power Development

Figure 4. Davis Dam, Power Plant, and spillway

920 OCTOBER 1952

Figure 6. Davis PowerPlant. Plan showingpower plant deck andtransformer installationon intake structure.Generators are servicedthrough circular hatches.Turbine parts may be re-moved through rec-tangular hatches be-

tween units

ervoir. The lower guide bearing is aself-cooled bearing.Each generator is equipped with air-

operated brakes capable of bringing therotating parts of the generator and tur-bine to a stop from one-half normal speedwithin 71/2 minutes after the brakes areapplied. The brakes are mounted on thelower bearing bracket and bear against aplate mounted on the under side of therotor. The brakes also may be used asjacks for lifting the generator and turbine

N4

rotating parts a sufficient distance to pro-vide for removal or adjustment of thethrust bearing. A motor-operated high-pressure oil pump supplies the pressurefor jacking.

Generator excitation is from direct-connected 330-kw 250-volt main excitershaving a speed of response of 0.5, anddirect-connected 12-kw 250-volt self-excited pilot exciters. Both main andpilot exciters have class A insulation. Inorder to allow for some variations from

Denton, Britt-The Davis Dam Power Development

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OCTOBER 1952 921

operation at unity power factor, the main Figure 7. Davis Powerexciter capacity is 10 per cent in excess ofthat required for operation at name-platerating.

VOLTAGE REGULATION

Each generator is equipped with anautomatic voltage regulator, a main ex-citer field rheostat which is motor-oper-ated from the regulator, a pilot exciterfield rheostat, and a voltage adjustingrheostat. The alternating voltage is con-trolled by adjusting the field current ofthe main exciter by means of the motor-operated field rheostat, with the pilotexciting voltage maintained at a constantvalue. A manually controlled switch isprovided for adjusting the position of therheostat during testing and servicingperiods, but the voltage is normally con-trolled by the automatic voltage regu- G X ,lator. Pilot exciter voltages are adjustedby manual control of the pilot exciterfield rheostat. An overvoltage relay in-serts additional resistance in the pilot ex-citer field during periods of overspeed to 3

prevent excessive overvoltages. The twogenerating units which furnish station- (service power are provided with directvoltage regulators on the pilot exciters inorder to obtain closer regulation of thestation voltage.The regulators are of the indirect-acting

type with a low-speed element controllingthe motor-operated field rheostat and ahigh-speed element controlling an auxil-iary relay which cuts out exciter field re-sistance or inserts additional field resist-

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ance. The low-speed element responds tosmall changes in voltage while the highspeed element will respond to the largechanges caused by sudden pronouncedchanges in load. Sudden system changessignificantly affecting system voltage willcause high-speed voltage regulating equip-ment to overshoot, so that this regulatingmechanism tends to operate briefly forshort intervals until the low-speed volt-age regulating mechanism is able to re-store the voltage to normal.

POWER TRANSFORMERS

Each generator is connected throughbus and cable to a 3-phase power trans-

former rated at 45,000 kva, self-cooled,56,250/60,000 kva forced-air cooled, 13,600 volts to 132,800/230,000 Y volts. Onaccount of the high ambient temperaturesprevailing at Davis, the transformerswere designed to carry their self-cooledoutput with a 45-degree-centigrade riseby resistance and a 55-degree centigradehot spot. These values are 10 degreeslower than standard and resulted in sig-nificant increases in transformer weights.

Each transformer contains 21,000 gallonsof oil and when completely assembled,weighs slightly over 200 tons. The extrakilovolt-amperes available in the forced-air rating permit carrying continuousoverload on the generators without thetransformets overheating.The transformers, being located on a

step on the face of the intake structure,are separated some distance from the gen-erators. This considerable distance,partly within the power plant and partlyin the open area between the power plantand intake structure, led to the considera-tion of both cable and bus. Several tapsin these conductors were required in theruns. These included connections withinthe power plant to the generator surgeprotective equipment, instrument trans-formers, and disconnecting switches.Since physical limitations prevented theinstallation of this equipment in one metalclad line-up, it was decided to install buswithin the power plant to avoid thenumerous cable terminations which other-wise would have been required. Thisbus extends from the generator terminalsthrough the outside upstream wall of thepower plant. The taps are incorporatedin the bus structure.The generator voltage bus structures

are of the metal-enclosed, air-insulatedtype, with an air space between each ofthe metal enclosures. The bus structurehas a continuous rating of 2,000 amperesand is designed to withstand line-to-linefault currents of 21,000 amperes rms, and

Figure 10 (left).View of turbinepit with mainshaft and cou-pling of a45,000-kva gen-

erating unit

Figure 11 (right).Lowering turbinerunner throughgenerator stator

Denton, Britt-The Davis Dam Power Development924 OCTOBER 1952

Figure 12 (above). Erectionof turbine scroilcase

Figure 13 (left). Loweringgenerating unit shaft into posi-

tion

Figure 14 (below). As-sembled generator rotor beingmoved into position by 325-

ton gantry crane

3-phase fault currents of 26,000 initialrms value. These bus runs terminate onthe outside wall of the power plant in ter-minal boxes. The run is continued by theuse of cables from the terminal boxes tothe transformer terminals. The cablesare 15,000 volt, shielded, varmished-cam-bric insulated and are provided with alead sheath. Three single-conductor1,500,000 circular mil cables per phaseare used for the generator main leads. Theexceptionally high ambient temperaturesin this area necessitated the liberal useof copper for these connections. Thecables are mounted on a special cablestructure spanning the V between thepowerhouse and intake structure. Alouvered housing on the cable structureprotects the cables from the direct raysof the sun.The generator neutral equipment is

located in the same general area as the busstructures. Each generator neutral isconnected to the station ground throughthe high-voltage winding of a 100-kva13,200- to 120/240-volt single-phase 60-cycle Askarel-filled distribution trans-fortner with a resistor rated 85 kw, 145volts, and 0.25 ohm connected across thesecondary terminals of the distributiontransformer.

SWITCHYARDS

The 230-kv switchyard has a doublebus arrangement with two circuit breakersin each line and in two of the transformerpositions. The installation consists ofthree bays for outgoing lines, one bay foreach of the five transformer circuits, anda bay to provide for a future 230-kv line.As mentioned previously, the generatorsare synchronized with the 230-kv systemthrough the oil circuit breakers in the 230-kv switchyard.A 69-kv switchyard is also being con-

structed which ultimately will accom-modate four incoming line positions andtwo transformer positions. The 69-kvcircuits will be fed from transformersconnected to generators number 4 and 5.The connections will be arranged so thatpower may be interchanged between the230- and 69-kv switchyards during shut-down periods of generators number 4 and5. The 69-kv switchyard has a main andtransfer bus with one transfer circuitbreaker and one circuit breaker for eachline and transformer.

Relaying and Control

EQUIPMENT PROTECTION

Relay protection of the differentialtype is provided for the generators andtransformers. Faults within the genera-

Denton, Britt-The Davis Dam Power DevelopmentOCTOBER 1952 925

tor protective zone trip the high-voltagecircuit breakers connecting the unit to thesystem, trip the main exciter field circuitbreaker, shut the unit down, and initiatethe discharge of carbon dioxide gas intothe generator housing. A low pickup con-

tact making voltmeter functioning as a

generator ground relay operates from thesecondary of the generator neutralgrounding transformer. Operation of thegenerator ground relay performs the samefunctions as the operation of the genera-

tor differential relays with the exceptionthat the carbon dioxide is not discharged.A generating unit overspeed switch isprovided to initiate closure of the turbinegates and operate the annunciator in case

of overspeed in excess of that obtainedfrom normal full-load rejection.The transformer differential zone in-

cludes the generator voltage bus struc-tures and cables. Faults within this zonecause relays to perform the same functionsas the generator differential relays withthe exception of the release of carbondioxide gas in the generator housing. Theswitchyard bus zone of protection in-cludes the lines from the main power

transformers to the switchyard, the oilcircuit breakers, and the 230-kv switch-yard busses with all interconnections.Operation of one or more of the switch-yard bus protective relays will trip all ofthe 230-kv oil circuit breakers in theswitchyard, lock-out the line circuitbreaker reclosing relays, trip the genera-

tor main exciter field circuit breakers, andoperate an annunciator in the controlroom.

The three 230-kv transmission lines are

equipped with carrier-current relayingfacilities which operate to trip the linecircuit breakers within 1 to 3 cycles afteroccurrence of a fault. In addition to theprimary function of relaying, the carrier-current channels are available for emerg-

Figure 16. Looking

downstream from230-ky transformer

deck showing a

portion of the trans-

former installaitionand power plant

ency communication use and for certainsupervisory functions. High-speed direc-tional distance and directional ground re-lays act as backup protection for the car-rier relays. Operation of either of theserelays will initiate the tripping of theassociated line circuit breakers and oper-ate the annunciator. Provision is madefor automatic reclosing of the line circuitbreakers to include one reclosure.

SYNCHRONIZING

An automatic synchronizer has beenprovided and normally will be used whenclosing circuit breakers between genera-tors, busses, or transmission lines requir-ing synchronizing. A single automaticreclosure is also provided for the 230-kvline circuit breakers without the use of thesynchronizing equipment, with the opera-tion controlled by carrier relaying. Theautomatic synchronizing equipment willinitiate closure of a circuit breaker onlyafter frequency and voltage of the twosystems are closely matched. A syn-chroscope and synchronizing lamps withthe two voltmeters are also provided on

swinging panels for use with manual syn-chronizing.

LOAD AND FREQUENCY CONTROL

The output of one or any number ofgenerating units may be controlled auto-

Denton, Britt-The Davis Dam Power Development

Figure 15. Assembly of 230-kv transformer

OCTOBER 1952926

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matically by the load and frequency con-

trol system subject to the range of outputof the units. When the units under con-

trol are unable to maintain the pre-estab-lished load or frequency requirements, theautomatic controls are de-energized andthe units return to normal operation underthe control of their individual governors.The load and frequenc- control equip-

ment provides for either of the followingtypes of control:

1. A flat frequency control.

2. A frequency time error control whichordinarily maintains flat frequency butvaries just slightly as required to limit themaximum time error to a few seconds.

3. A flat tie-line control that maintains a

constant total load for all controlled trans-

mission lines.

4. A tie-line bias control that provides a

flat tie-line control but varies its controlpoint slightly as required to assist in thereduction of the frequency time error.

COMMUNICATION FACILITIES

Both dial and manual local telephoneservice is available at the power plant

Denton, Britt-The Davis Dam Power Development

2

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OCTOBE-R 1952 927

with provision fol two-way dialing be-tween any dial telephone and toll opera-tor at the public exchange telephone atKingman, or between the control opera-tor's cordless manual telephone and theKingman toll operator. Carrier-currenttelephone equipment also has been pro-vided to permit communication from theDavis Power Plant to our system dis-patcher or other points on the system asrequired.

For checking the operation of the chan-nel and for emergency use, push-to-talktelephone communication is availableover each of the carrier relay channels.A communication receiver has been pro-

vided for the reception of National Bureauof Standard Time Signals and covers afrequency range of from 550 kc to 30megacycles. Accurate time signals maybe obtained from the standard frequencytransmissions of the National Bureau ofStandards; these signals are made con-tinuously.

ANNUNCIATOR AND ALARM SYSTEM

Annunciators are provided to indicateoverloads, trouble or failure of equip-ment, operation of relays, tripping of cir-cuit breakers, failure of station service orcontrol power supply cooling water orother essential station auxiliaries. An-nunciation is provided on the main con-trol board, unit control board, or station-service board as required. Single-strokechimes are provided in the control roomand an alarm horn in the governor gal-lery for operation with the annunciatorsin case of trouble.

Miscellaneous Facilities

STATION AUXILIARY POWER

The station power supply is obtainedfrom the generator voltage bus of each ofgenerators number 4 and 5. One 3,750-kva 3-phase 14.4/4.16-kv transformer isconnected to each of these generator leadswith the 4.16-kv service feeding one endof a unit substation switchgear. The4.16-kv switchgear is arranged with a bustie circuit breaker which normally will beopen with each half of the bus energizedfrom its respective transformer. In theevent of loss of voltage from one of thetransformers, its supply circuit breakerwill trip and the tie circuit breaker willclose, thereby maintaining essential sta-tion-service power supply. Nonessentialloads such as heating loads may be drop-ped if severe undervoltage conditions existduring heavy load periods.

UNIT AUXILIARIESThe power supply for operation of unit

auxiliaries is furnished at 460-volt 3-phase alternating current. Control powerfor unit auxiliaries is available at 115-volts alternating current and 125-voltsdirect current. The unit auxiliaries re-quiring power supply and control fromthe above voltages include the penstockgates, governor oil pumps, the generatorand turbine lubricating systems, and theunit cooling system. The control powersupply for opening and closing the pen-stock gate is provided by auxiliary trans-formers located in the local controlcabinets. The gates also may be remotely

controlled from either the unit controlboard or the main control board by meansof the 125-volt d-c control power so thatthe gates still may be closed in the eventof loss of a-c power. The water supplyfor the unit cooling system is taken fromits respective scrollcase and is controlledby motor-driven valves. The coolingwater supply is an independent systemfor each unit and provides water for thegenerator air coolers, turbine runner seals,turbine main shaft stuffing box, generatorthrust bearing, and cooler for air-condi-tioning unit.

Conclusion

The purpose of this paper is to bring a

description of the salient features of theDavis Dam power development into a

single paper. Much has been writtenabout this project, and the authors wishto acknowledge the work of previousauthors who have covered certain aspectsof the development. The papers listedbelow will add further information aboutcertain design features of the project.

References

1. PROPOSED PROJECTS DEVELOP POWER AND

IRRIGATION POTENTIALS OF COLORADO RIVERSYSTEM, H. F. McPhail. Civil Engineering, Ameri-can Society of Civil Engineers (New York, N. Y.),August 1947, page 31.

2. COLORADO RIVER DEVELOPMENT, E. A. Moritz.Civil Engineering, American Society of Civil En-gineers (New York, N. Y.), May 1950, page 20.

3. DAVIS DAM COMPLETES STORAGE REGULATIONOF COLORADO RIVER BELOW BOULDER, L. R.Douglass. Civil Engineering, American Society ofCivil Engineers (New York, N. Y.), January 1947,page 14.

No Discussion

THE Division of Design and Construc-tion of the Bureau of Reclamation in

Denver, Colo., has developed structurelimitation charts which take into accountsimultaneously all factors that must beconsidered when locating the structureson the plan-profile survey of a powertransmission line. Since January 1946,the Bureau of Reclamation has con-structed, or awarded contracts for the con-

struction of, approximately 3,600 miles of115-kv H-frame wood-pole lines, 1,450miles of steel tower 230-kv lines, and 700miles of 34.5- and 69-kv wood-pole lines.The charts presented here have been usedin the design of Bureau lines for the past 3years and have saved much time as well aspromoting more accurate selection of thestructure types required at each loca-tion.

In order to determine the type andheight of structure required for each loca-tion when locating transmission-linestructures on the plan-profile surveysheets, it is necessary to determine whe-ther the vertical and transverse loads andline deflection angle are within the limit-ing values for the type of structure to beused. On suspension-type structures, itis also necessary to determine whether theinsulator sideswing with wind will remainwithin the limits required to maintain thedesired clearance from the conductors to

Paper 52-252, recommended by the AIEE Trans-mission and Distribution Committee and approvedby the AIEE Technical Program Committee forpresentation at the AIEE Pacific General Meeting,Phoenix, Ariz., August 19-22, 1952. Manuscriptsubmitted October 9, 1951; made available forprinting July 7, 1952.

THOMAS M. AUSTIN is with the Bureau of Recla-mation, Denver, Colo.

A9ustin-Structure Limitation Charts for Transmission Lines

Structure Limitation Ckarts rorransmission LinesTHOMAS M. AUSTIN

MEMBER AIEE

OCTOBER 1952928