Show electrical installations at the alaska juneau BY F SEWARD RICE the first unit of the ton concentrator of the alaska juneau gold mining company was put into operation in june 1917 this plant was built to treat the gold bearing ore from the alaska juneau mine one mile northeast of juneau alaska the concentrator site adjoins the city of juneau on the southeast and is built on a steep rocky cliff fronting gastineau channel and nearly opposite the famous mine and milling plant of the alaska treadwell gold mining company on douglas island electric power is generated in a kw steam turbo generator plant which was built in 1916 by the company this power is used throughout for all mining and mill with baldwin westinghouse storage battery locomotives of approximately 5 ton weight equipped with edison A 10 batteries from the mine the ore is hauled to the mill a distance of two miles in trains handled by baldwin westinghouse trolley locomotives the railway is also used for handling supplies between the mill and the mine the track way has a maximum grade of one half of one per cent in favor of the load descending from the mine to the mill it is double tracked throughout and passes through a total of three tunnels between tunnels the road is protected by snow sheds wherever it is exposed to slides which were formerly not an infrequent source of trouble A J twelve westinghouse ih p motors driving ball mills ing operations the steam station is tied in through a bank of volt transformers with the distribution system of the alaska treadwell gold mining company this distribution system is fed by both hydroelectric hydro electric and steam plants and through the arrangement in force all plants of both mining companies are able to interchange power and serve as auxiliary sources of electric energy halt half of the ultimate capacity of the juneau steam station was initially installed this consists of a kw horizontal steam generator with corresponding boiler plant and auxiliaries ore from mine to mill the broken ore in the mine is gathered the ore trains are made up of cars of 10 tons capacity each the average train weighs tons loaded and ninety six tons empty the locomotives are articulated tandem units particularly designed for the service each locomotive consists of two 9 ton bar steel units each unit has two motors the control for all of which is assembled in a cab on the rear end of the loading unit these 18 ton locomotives were built to special dimensions men in order to conform to the gauge which is 30 inch and in order to permit the locomotive passing entirely through the tipple at the mill the motors are the westinghouse in no type which are provided with forced ventilation the compressors 21 are mounted on the loading unit of the tandem while the air storage cylinders are divided so that the cylinder for straight air is on the leading unit while the auxiliary storage cylinder for automatic air is on the trailing unit through this arrangement the leading unit may he be disconnected from the trailing unit and used by itself as a switching locomotive with strength air brake equipment the locomotives are somewhat unique in that considerably more apparatus has been mounted upon them than is usually found in units of this size still it has been so wall well located and grouped so compactly that the whole appearance of the locomotive is good and accessibility of all parts is ex A jim ic owl so ipg mpg alaska juneau mill showing haulage railroad cellena cel lent the locomotives have been found to be easily handled under the exacting service conditions and have shown that they are fully capable of hauling in two 8 hour shifts the full tonnage of ore required to keep the mill running at maximum capacity three shifts per day direct current power supply the direct current power supply for the railroad is derived from two kw rotary converters one located in the power and one in the gold creek substation the latter feeds into the trolley near the portal of sheep creek tunnel two thirds of the distance from the mill to the loading bins in the mine each rotary converter has its in kw to six phase transformer the one in the power house has a primary voltage of 2300 corresponding to the generated voltage and the other has a primary voltage of which is the voltage of the alaska treadwell companas Comp anys transmission system dumped by revolving tipples the ore from the trains coming from the mine is dumped into the crude ore receiving bins at the mill by either one of two revolving tipples these tipples have a capacity of four cars each they are each trib ution system the slow speed which could be efficiently obtained with synchronous motors has permitted the elimination of counter shafting and extra belting thus permitting a most excellent arrangement of the crushing department from the mill operators era tors point of 0 view the crushing department is in two halves each half containing two no 9 gyratory set to crush to 3 inch size and a inch jaw crusher each half of the department is driven from a single shaft to which 7 RMA baldwin westinghouse 18 ton tandem locomotive driven by a 25 horsepower volt D C motor it is possible to readily dump an entire train of thirty two cars in a period of ten minutes the tipple motors are hand operated by reversing drum controllers which serve to align the wheels with the track rails readily whenever the tipple is turned over it has been found that there is considerable force tending to accelerate the motion of the tipple during the last quarter revolution due to the fact that the center of gravity of an empty car is below the axis of the tipple consequently in order to bring the tipple rails quickly into alignment with the track rails without overrunning the center it is frequently feces sary to plug the motor and to have a means such as is provided in the drum controller of easily reversing it in event that the tipple turns past its track center coarse crushing department the coarse crushing department at the mill is somewhat unusual in that the crushing machinery is all driven by synchronous motors this type of motor has not generally been considered for this duty but there is no reason why a proper design synchronous chr onous motors should not be applied to crusher drive the success of the juneau insulation has definitely proven that properly constructed synchronous motors are entirely suitable for such service the motors have given entirely satisfactory mechanical ch performance and at the same time provide the additional advantage of improving the power factor of the electrical dis the crushers are connected by friction clutch pulleys each shaft is direct coupled to a horsepower ava rpm 2200 volt westinghouse synchronous motor with direct connected exciter the motors are designed with heavy starting torque and good synchronizing characteristics so that even in case of the clutches becoming tures and the exciter builds up voltage as the synchronous motor comes up to speed the grinding department the grinding department of the concentrator has twelve ft ball mills each driven from a h b p r p in 2200 volt type CS motor fine grinding is carea for in twelve ft tube mills each driven by a h p r p m 2200 volt type CS westinghouse motor although it was anticipated that the starting duty of these motors would be rather severe squirrel cage motors were chosen instead of slip ring motors slip ring motors have been more often u used sed for this class of service in order to obtain adequate starting torque and to relieve the generating station of the high peak down during starting in the P resent present instance the peak drawn drawsby by any of these squirrel cage motors was small in comparison with the capacity of the power system and adequate torque was insured by designing the motors for as high a starting torque as could be secured without sacrifice of efficiency the slight resultant sacrifice in power factor was offset by the synchronous installation in the crushing department squirrel cage motors seemed advisable owing to the simplicity of their starting equipment and the elimination of any possibility of trouble from dust which was anticipated owing to the dry quality of the ore in order to simplify starting both the ball mill and the tube mill motors are thrown directly on full line voltage by means of specially selected circuit breakers no starting com pensa tors whatever being used each ball mill and tube mill has a friction clutch pulley on its pinion shaft so that the motor can be started ahead of its load but in actual practice these clutches are seldom used A twelve westinghouse h p motors driving tube mills clogged with dust they will permit starting without undue strain the starting control for the motors has been simplified to such an extent that the operation of putting them into service is entirely analogous to the starting of an induction motor the use of direct exciters excite rs permits the mhd motor fields to be short circuited through the exciter arma and the motors have proved fully capable of starting satisfactorily with the mills clutched in As the torque of an induction motor is very nearly proportional to the square of the voltage impressed on its terminals the maximum i possible starting torque is secured by connecting the motors directly to athe the 2200 volt circuit as described above of course this high starting torque is secured at the expense of drawing a large line current from the power feeder at the moment of starting ordinarily this large current flow might produce poor voltage regulation on the feeder and might impose a heavy momentary drag on the prime mover at the generating station the birst source of difficulty is obviated by the use of amply heavy feeder cables and in this particular installation the second creates no trouble owing to the comparatively large capacity of the power supply the large available power supply was taken advantage of in this case to secure the maximum simplicity of electrical operation special forms of belt drive special forms ot of belt drive from the motors to the mills was selected owing to the steep gradient of the ground on which the mill is located these belt drives are shown in an accompanying illustration vertical is pumped from gastineau ch channel annei the pumping plant is located in a sub base ment of the power house the pumps are set eighteen feet below maximum high tide level in order to equalize the head due to tide variation which at its greatest rise amounts to twenty six feet the mill pumps of which there are two have a combined capacity of gallons per minute and ana are driven by h p dire direct ct connected squirrel cage type induction motors these pumps deliver water to the storage tanks above the concentrator circulating water is pumped by two centrifugal pumps each of gallons per minute capacity two ava r p in 2200 volt synchronous motors drive these pumps these motors are designed to carry from to rn mechanical ch horsepower with maximum power factor correction they are coupled to the pump shafts through jaw clutches which when disconnected permit the use of either ri M baldwin westinghouse 52 ton storage battery locomotive short center drives with count counterweighted counter er weighted idler pulleys are used and are so arranged that they occupy a minimum amount of horizontal space this was a very desirable feature owing to the economy in limiting the width of the mill section the pulley of each ball mill motor is vertically beneath the driven pulley on the pinion shaft of the mill which it drives the drive on the tube mills is similar except that they are so arranged that the motor pulley is above the driven pully on the mill pinion shaft it will be seen that in the case of the ball mill motors the shaft reaction action re due to the belt pull is vertically upwards against the bearing caps A careful check of the design of the bearings prior to installation showed that they were amply capable or of taking care of this vertical reaction re action and no trouble due to this feature has been experienced water supply for the mill the water supply for the mill and the circulating cooling water for the plant con motor as a synchronous condenser lor power factor correction the rheostats li 51 the field circuits of these motors are controlled either from the motor starting panels near the pumps in the basement or from the main switchboard in the power house on the floor above instruments and remote control field rheostat at the latter position give the switchboard attendants control of the amount of power factor correction which it is desired to effect the design of these synchronous motors differ considerably from those used in the crushing plant for the motors in the crushing plant as explained above high starting torque was desirable in starting centrifugal pumps the starting torque is low but the required running torque increases as the speed approaches synchronism therefore the synchronous pump motors were designed with particular regard for obtaining high synchronizing torque the design employed giving a synchronizing torque of 33 per cent of full load torque has proven entirely successful these motors are not provided with direct connected ex citers aiters but obtain their excitation fro from inthe the exciter circuit in the powerhouse the designers the complete crushing and concentrating plant as well as the powerhouse of the alaska juneau gold mining co were designed by bradley bruff labarthe engineers of san francisco the electrical equipment described above including all motors rotary converters transformers and switchboard were supplied by the westinghouse electric mfg mag co who designed the locomotives the synchronous motors and the motors for the grinding department departs ent along special lines to meet the requirements specified by the plant designers |