TRANSACTIONS O F THE AMERICAN INSTITUTE OF MINING ENGINEERS? ISWJECT TO REVIBIONI

DISCUSSION O F THIS PAPER IS INVITED. It shoulrl ~referpbly be presented in person a t the New .York meeting, February, 1916, when an abstract of the paper a.111 be read. If thie is ~mposaible. then discussion in writing may be sent to the Editor. American Institute of Mining Engineers. 29 West 39th Street. New York. N. Y-., for presentation by the.Secretary,or other regresentntive of its author. Unless a~ecia l arranzement is made, the discuas~on of thls oaDer m1I close Apr. 1. 1916. Any 'dscusaion oKered thereafter srould preferably be in the form of a n e w paper.

.Tests on Various Electric. Motor-Driven Equipment Used in the Preparation, of Anthracite Coal

BY H . hl. WARREN, A. 6. BIESECKER, AND E. J. PCIWELL, SCRANTON, PA.

(New York Meeting, February. 1916)

IN the past, stenin engines were used in practically all cases for clriving the ~nachi~lery in and about an a~lthracite breaker, and hence little or no accurate data were avail:tble as to the power require~ne~lts for starting and operating the individual machines, which make up the co~nplete ecluipment. It was impossible to segregate t,he power neces- sary to drive each incliviclual ~;lnchine, first, because the equipment was driven in groups, and second, because i t was impracticable to obtain graphic, integratecl, or instantaneous records of the horsepower used.

As a result of these conditions, i t was found, when individual electric nlotors were applied to the various machines, that more accurate ancl complete data were neeclecl in orcler to provide nlotors of the proper power ancl clesign for the particu1:tr services to be rendered.

In orcler to obtain the desired information, the writers made ancl col- lected a number of tests, from time to time, on the incliviclual nlotor cll.ives i n electrically oper:tted breakers, nlld as these tests have been of great value, iot occurred to them that a paper giviug the results might be of service to other engineers intere~t~ecl in si~nilar inst,zllations. Table I shows the results of these tests.

All the motors tested were of the three-phase, 60-cycle, 440-volt, induction, squir~el-cage type, escept a few, which, on account of size and starting conditions, were of the ~vound-rotor type.,

The instrmnG1ts used in ~naking these tests were: An integrating watt-hour meter, a graphic ammeter, ancl a graphic voltmeter. These instru~nents were connected in each motor circuit, and n record of n day's run of 9 hours was obtainecl from each machine.

From these tests, the running light load, the average all-clay load, ancl the instantaneous peak readings in amperes, volts, and kilowatt input, were obtained. By nleans of the characteristic curves obtained frorn these nlotors a t the factory, the power factor, the efficiency, ancl the horsepower output were calculated for each particular test. Starting tests were lnade hy the brake-arm method, in which the torclue in pou~lcls was messurecl directly on a spring balance.

. . w TABLE I.-Tests ofElect~ic ildotors, Etc., Enzl~loyecl in Anthracite Breaker 00

- -

These figures apply only when haulage chain is free from ice. The results are based on trip tests, not all-day tests. NOTE.--Revolution:l per minute of driven units figured a t synchronous speed of motor. Voltace a t motors. 415. Horsepower ratings ~nclosed with 0 are for back-geared motorr~. Iiey: F.L.T. = Full-load torque: P.F. = power factor; Eff. = e5ciency; F. load = full lo ad.

Unusual care was taken in making these tests and in calculating the results; therefore, the writers feel that they are reliable for all practical purposes.

As the characteristic curves on the various machines differ, graphic dharts taken under actual operating conditions, the results of the tests, arlcl the mechanical data pertaining to the machine driven, -follow in proper orcler.

Shakers

From Table I, i t will. he noted that tests were made on shakers of various sizes of the two-, three-, and four-deck types. The eccentric

clisplacement is diviclecl evenly in orcler to balance up the load, nncl the shakers have a 6-in. stroke. Tllere is a slight difference in the speeds a t which these various shakers are operated, the speed of the eccentric

' shafts ranging froin 134 to 163 r.p.111. From the graphic axmeter chart, Fig. 1, i t mill be noted that the

characteristic load on the average shaker screen is a fluctuating one, the fluctuation varying in direct proportion to the clegree of unbalancing in the various clecks. This unbalancing may he caused by several factors, which are practically inlpossihle to control, viz., unequal quantities of coal on the various clecks, uneclual weights of the clecks, uneclual friction in bearings of the suspension'~oc1s which support the decks, etc.; also,

'

a fluctu:ttion in the load may be causecl by improper spacing of the

i eccentrics. Theoretically, the load on each deck during a cycle of operation con-

forins very closely to a crank-effort curve as obtninecl on a steam engine; so, when the loacl curves of t,he cycle of operation of a compiete silaker are superimposed, the result,ant load curve is undulating. This variation in loacl mould tend to sho\; a considerable fluctuation on a gml>hic ammeter chart where the eccentric spacing is from 180 to 120°, clecreas- ing ns the spacing is decreased and the number of decks increased.

The co~~clitioi~ which arises in collnectioil with the load obtained on a two-deck shaker when the eccentrics are spaced 180°, deserves special nlent,ion. The cycle of operation of the decks when they are driven from the eccentrics spaced lSOO, gives the best condition for minimum vibra- tion of the sllnkers ant1 the nlasinlliln variation of load on the motor. If the eccentrics are sl~acecl 90" to obtain the llliniillulll variatio~l of load on tlle motor, then the lnasirnunl vibration is obtainecl on the shakers. If they were operated in this manner for any length of time, they would set up n very clestructive vibration in the surrouncling tiinhers of the breaker. I t llns been suggested to operate these shakers with lSOO spacing 011 the eccentrics, ancl install a flywheel on the inotor shaft t o conlpensate the load fluctuations.

The writers have had occssion froin tinle to time to investigate troubles occurring in connection with the operation of shaliers, and have found in almost all cases that they were clue to uneclud spacing of the eccentrics a t the time of installation; to the attendant's tightening the I~enrings on the clecks or the eccentric straps; to the inlproper lubrication of the bearings ancl eccelitrics, etc. a

Tests and esperiments were also nlacle in an enclcavor to rcduce this fl~ctunt~ion in loacl by making use of a flywheel, ancl also by attaching springs t,o the various decks; but the results obtained sho~ecl that, esccpt possibly in the case of flywheels on two-deck shakers, conditions were not bettered sufficiently to warrant the espense of installing the additional apparatus.

Rolls

Tlle rolls used in the tcsts ancl describecl in Table I were of the mangn- nese-segment type with cast-iron spiders, excepting No. 4 wllich was of '

the chilled-tooth type. The following are the sizes of coal treated by the several pairs of rolls:

M : L ~ I ~ rolls, Lt~nlp to grate co:~l; No. ? rolls, Grtlte to cgg co:tl; No. 3 rolls, Grate to egg co:ll; No. 4 rolls, In the washery-breaking coal from refuse dump dowll to egg s11cl

below;

WARREN, BIESECKER, AND POWELL 185

No. 5 rolls, In tlie n~cisliery-breaking coal fro111 refuse clump down to chestnut; No. 6 rolls, In the washery-breaking coal from the refuse dump fro111 chestnut

to hucknlheat.

The sizes and speeds of these various rolls are found in Table I under 11 ~nechanical data.!'

Since much more trouble has been esperienced with tlie individual motor drive used in connection with main rolls than with- any of the other incliviclual drives, the writers have made exhaustive tests and in- vestigations on this particular ecluipment. Trouble developed with these machines soon after the motors were installed, on account of enorlllous peakssuddenly thrown on the motor through the crowding of the rolls due to irregularity of feecl. This developed into a serious matter, Bs this

, . . - . 8 0 . r: r 0 - o' .:.. . ,. L-- L - -- , , -&lu ROLLS- . -

6-qhc Ammeter' Cv-e . ..

.

. - - . - -. ,z_-b%r>~+h. speed f l ~ ~ l - . - . . . .. . . -.-.-- --.rn_ineto~k~~.-- ,, -- .--.- - .. - - - -. -.-C--_L -. . .

. . -.- . . . . . . . _ ; . . . . -.-_BmpL' -- -- -. . .

feed reached sufficient proportions to stop the motor, and in time roasted the insulation so badly as to necessitate rewinding. Pet this, in itself, mas really a minor matter when compared to the annoyance and the num- her of delays in the operation of the breaker. In orcler to locate this trouble, graphic ammeter charts were taken with a special fast-reading instl.umentr, samples of which are sllowll in Fig. 2.

At this time a 2000-lb. solid cast-iron flywheel was lnounted on the roll shaft, and run a t about 96 r.p.m. Upon checking up the inertia of this wheel, i t was foun,cl to be practically valueless a t this speed.

Fro111 Fig. 2 i t will be noted that the load on these rolls varied greatly so that the peaks a t times reached the breakdown point on the motor.

In order to rectify this trouble, i t was found advisable in some cases 4

186 TESTS ON VlRIOTTB FT,EC!TRTC h1OTOR-DRlVEN EQUIPMENT

to design a special feedkr to deliver the coal to the rolls more uniformly. A type that was found to work well was shaped like a paddle-wheel, and

' was installed in the chute leading to the rolls. The feecler was revolved by iiieafis 6f n belt c!ri:ren from a> pulley on the motor shaft or from one of the countershnfts. Where picking tables or conveyors are usecl, the feed is sufficiently regular for good operation without the paddle-wheel feeder. After the coal passes through the main rolls, the flow is sufficiently regu-

- lar on the other rolls for all practical purposes. In designing special flywheels to tnke care of the 1krge peak loads.

thrown on the main rolls, a careful study was made of the graphic am- meter charts obt,ainecl from the tests on this equipment. From these peaks i t was found that certain conditions had to be ta,k&n care of in order to smooth out the.curve, and with this informntion a t hand, a special high-speed flywheel was designed and built up from boiler-plate iron.

After this new wheel was installed, other charts were taken with the same high-speed graphic ammeter. One of .them is shown in the lower half of Fig. 2. The con~parison of the charts shows conclusively that the peak conditions were nicely taken care of by the flywheel. These rolls have not been blocked since i t was installed.

The size and capacity of this special wheel were calculatecl as follows: By measuring and calculating several peak loads, i t was founcl that

the horsepower-seconds of these peaks were about 100. Since the t o t d horsepower-seconds in the old flywheel a t 160 r.p.m. was onlG.95, 'and for a 10 per cent. slip in the motor there were only 18 hp.-sec. nvailkble, and since n watt-hour meter showed that the average load was less than half load on the motor, the inadequacy of the flywheel wasevident. I t was therefore decided that i t would be necessary to replace the old fly- wheel with A new one so designecl that i t would carry these peaks without slowing clow~i to such an 'extent that the lnotor would be,seriously overloaded.

Thenew flywheel was'calculatecl from the following formula:

Where W = the nreigllt of the wheel in pounds. V = the velocity a t the radius of gyration in feet per second.

By substituting 2rHS for V we have 6 0

Where R = raclius of gyration in feet. S = speed in revolutions per minute.

WARREN, BIESECKER, AND POWELL 187

In tlie first place i t was decided to design the wheel so that i t would give out approximhtely 160 hp.-sec. for a 10 per .cent. slip or reduction in the speed of the motor.

As the horsepower-seconds in a wheel are proportibnal to the square of the speed, the total horsepower-seconcls necessary in ol1der to give out 160 hp.-sec. in slowing down 10 per cent. (or to 90 per cent.) speed would be

Since i t ,was desirable t o keep the weight of the wheel as small as possible, i t was found tha t the wheel would have to run a t the speed of the motor or 900 instead of 160 r.p.m., the speed of the rolls. It was also, thought that in order to make the wheel perfectly safe, i t would he better to build i t up from boiler iron and limit the rim speed to 10,000 ft. per minute. ' Substituting these values in the above formula, we have

As the wheel was to be built up, the radius of gyration would be 0.7 of the total raclius. For 900-r.11.m. and 10,000 ft. per minute rinl speed, the radius of the wheel is 1.88 ft. or a radius of gyration of 1.31 ft. All of the dimensions of the wheel were thus determined with the exception of the face or thickness. Since a cubic foot of iron weighs about 480 lb., it was found that the thickness of the wheel woulcl have to be 5 in. It is interesting to note that the new wheel weighs only 2,190 lb. or only 190 lb. more than the old wheel, but on account of its speed i t delivers nine times the horsepower-seconds in dropping 10 per cent. of its speed.

Another important item for attention is the starting torques of these rolls. Table I shows under the heading of percentage starting torque, tha t in almost every case over full-load torque is required. The writers suggest for consideration the possibility of using roller or ball bearings in order to decrease the high starting torque.

The conveyor lines are of the ordinary single, chain-flight type, with the exception of the nlai~l and the refuse conveyors, which are of the mono-bar and doul~le-chain types, respectively. The length, height, and speed of the line, also the number, area, and the distance between scrapers are shown under "mechanical data" in Table I.

Tests indicate the load to be fairly constant and the friction load very high. A grnphic a~nmeter chart showing the characteristic load on one of these lines is shown in Fig. 3. This chart was taken on the main con- veyor line which carries all the coal from the hoisting shafts to the breaker.

188 T E W s ON VARICIUS, ELECTRIC B:ZTOC-3Cn'kN EQLTIP\#JENT

T11el.e has been no- trouble of any impol~tance in connection with the illotor driving this line. The sizc of t,he motor t o b e used clcpencls on the elevation and length of the line, 8he :tillount of coal to be moved, and. possibiy on tile type of cunueyor. ,.

Elevators

The elevator lines are of the "perfect" and gravity discharge types, ecluipped with double chains, with the exception of the buckwheat eleva- tor, which has a single clpin. The length ancl speed of the lines, also the number, cubic contents, and spacing of buckets, are given in Table I under " mechnnical data."

The load developetl on these lines, like that obtained on s corlveyor line, is pl-acticplly constant. A characteristic chart of the load on one of these lines is shown in Fig. 4. This chart was taken on the top elevator which hnnclles the coal fro111 the refuse conveyor and carries i t to the top of the mashery.

No serious trouble has been esperienced with the no tors installecl on these lines. The deternliilation of the proper size of inotor is clepenclent practically on the amount of coal ant1 the height to which i t is lifted.

Jigs

Jigs of the Hazleton standard, single type are operated in groups fro111 a line shaft. Each jig is operated froin this line shaft through s counter-

WARREN, BIESECKER, AND PORTELL

shaft,- i n which are mountecl the eccentrics necessary for the reciprocating motion recluired.

From the graphic chjrt shown in Fig. 5, i t will be noted that the char- acteristic ioaci on ti~ese jigs resemb!es t h ~ t cf the shnkcrs in fluctuating greatly.

No serious trouble has developed with the operation of these jigs.

Dr~sl Fan

The dust fan is of the multivane type and its size, speed, etc., will be found in Table I. .

With this type of fan the load is practically constant, depending on the anlount of air passing and the speed; i t was thought therefore that a graphic recorcl of its performance woulcl be uninteresting.

Car H a t ~ l s

Car hauls consist of a single, enclless, reinforced chain with 9-in. pitch equipped with knockovers to catch the car. The loacl is dependent on the running-light friction of the chain, the friction of the cars, the grncle of the haul, tile weight of the loaded car, and the speed.

For loaded cars or trains there is practically no variation in the power required.

Washery Pump

This pump is of the centrifugal type, and the capacity and head under which i t operates are found in Table I. The load is constant, depending on the head and amount of water l~anclled.

' Rock ~.ulverizLr t

The rock pulverizer is of the bar-and-hammer type, and its capac- ity i s approsirnately 40 tons per hour. The load on this apparatus is somewhat sinlilar to ,that obtninecl on the rolls, viz., being made up of sharp instantaneo,~~ peaks, while the average all-day load is compara- tively low.

Table I1 is a collectio~~ of tests nlacle on a number of rock pulverizers now in service, from whicli i t kill be noted that under average operating

'

co~lclitions 17.8 tons of rkfuse per hour was handled, with an average consumption of power of1.488 kw.-hr. per ton, also that the ratio of the average instnntaneoiis to the avern'ge lost1 on the motor mas 1.92. Fig. 6, n graphic c2lal.t taken on one of these rock pulverizers, probably shows t<l~e characteristic load to better advantage. -

These peaks are due to irregularity in the flow of rock to the pulveri-

'WARREN, BIESECKER, AND POWELL 191

TABLE 11.-Tesbs 0.11. Rock Pt~lverdze~s

Colliery 1 1 2 1 3 1 4 1 5 1 6' 1 7 ( ~ v e r :

AIotor horsepower.. ........ 75.0 75.0 40.0 75.0 75.0 Afotor'speed,r.p.m . . . . . . . . 555.0 1110.0 855.0 1110.0 1110.0 Crusher speed, 1.p.m.. . . . . . 780.0 ...... : . . . . . . . . 800.0 550.0 Number of hammers.. . . . . . 104.0 44.0 44.0 . 44.0 44.0 Spacing of grates.. . . . :. . . . . 2-in. 0.875 0.875 0.S75 0.87:

rd. mesh Clearance between grates and hammers; inches.. . . . . $46 t o % t o 36 $5 to W H to W $4 t o % -----

Tests

Rock in tons per hour.. . . . . Input, average kilowatt.. . . . Output, average horsepou.er. Input, kilowatt-hour per ton ......................

Ratio instantaneous peaks ......... t o average load..

Ratio instantaneous peaks to rate load.. . . . . . . . . . . . .

Average power factor.. ...... Load factor. ...............

- Fly Wheels

Diameter in inches.. . . . . . . . Faceininches . . . . . . . . . . . . . . . . . . Rim depth. inches.. Total hor~epower 8econds..

None

. . . . . . . . . . . : . . . . . . . . . . . . . . . . . . . . .

32.0 4.0 3.6.:

32.0 4.0 3.62

213.0

32.0 4.0 3.62

176.0

32.0 32.0 4.01

. 3 . 6 2 3.62 200.0 213.0 . .

32.0 34.0 4 . 0 ' 4 . 0 I . . . . .

3.62 . . . . . . 176.0 1 . ...:

zer. The original pulverizers were driven by 50-hp. motors, which were . very often loadecl to their breakdown point when crowding occurred.

I11 an endeavor to elilni~late this difficulty gates were installed in the chutes leading to the ~;u!vcrizer, so t!nt the a t t , end~n t could regulate the feed. The writers would not care to recom~nencl this scheme, unless i t is in charge of an esperiencecl man, because disastrous results have fol- lowecl when this n~achine was operated by a green man. It has been pro- posed to use a pacldle-wheel feeder similar t o tha t mentioned under rolls.

Conveyor lines are solnetilnes used to carry the rock to these pulveri-

6 w . E r . oer Ton . -

3 1 2 ;:

d 1 P.F.

3 f '70

E PI 60

250 a

4: 200 6 "160

,. ",ooo m

2 5 I000 - a 8 o

7 7.30 6 8.30 9 9.30 10 10.30 11 11.30 1.2 1?.:30 1 1.30 2 2.30 3 3;30 to to to to to to to to t o to to to to to to to to to 7.30 8 8.30 9.00 9.30 10 10.30 11 11.30 I? 12.30 1 1.30 2 2.30 3 3.30 4 A.M. 11. F.BI.

Time

FIG. CHART OF TOTAL LOAD O N BREAKER, INCLUDING RIAIN CONVEYOR, ROCK PULVERIZER, RI IT^^^^^^ PUAIP, AND CAR HAUL.

zers, and they act as good feeders. No trouble has been espcrienced where they were used. .

Pickers

The slate pickers are of the standard Emery type, ancl its the loacl is comparatively constant ancl light, and also does not have any inherent characteristic of any interest, no chart is shown of them..

Curves giving the coal rate, loacl on the breaker, with and without the rnsin conveyor running, the total kilowatt input, the power factor, and the rate in kilowatt-hours per ton, are shown in Fig. 7.

. -

WARREN, BIESECKER, AND POWELL 193

These curves, as mill be noted, are all plottecl over timc on the basc ' line, and the readings were taken every half hour. It is therefore easy to see how these factors vary with the rate of coal flowing through the breaker.

In Fig. 8, curves are given showing the variations in the kilowatt input, the load and the power factors in the brealier, also the efficiency and the horsepower output of the maih conveyor line, with different rates of flow of the coal through the brealier.

Much coulcl be said ns t o the proper type and design of motors for this service, but as i t was thought t o be outside the scope of this paper, i t was deemed advisable not to discuss them a t this time, but simply to say that they should be of heavy and rugged design.

GOO

600 100

90

400 80

6 i70 0

p" 300 5 60 " d g50

c? !d

200&40

! 30 a EI

100 $20

E 10

0 0 600 1000 1500 2000 2500 3000

Rate of Feed In Tons per Day

I n conclusion, the writers wish to emphasize the importance of making a careful study of the characteristics of the nlachine to which the appli- cation of incliviclual motors is to be made, since, for constant loads, the determining point in selecting the size of the machines is dependent on the heating of the motor. 'Then, again, machines with either high start- ing torque or large insta~ltaneous peaks, or possibly both, require a motor to meet these conditions rather than for continuous capacity.

To a careful student, some of the inotor ratings in the tables here given may seem a little large when compared with the tests; but this is explained by the fact that the breaker on which these tests were made was handling a t the time only about 60 per cent. of its rated capacity.