I | | LNT | NI — 1 Iwn M—=N ~~ LIBR ARY Michigan State University MSU LIBRARIES A RETURNING MATERIALS: Place in book drop to remove this checkout from your record. FINES will be charged if book is returned after the date Stamped below. — - ome eo (tO Prate THESIS A COMPARISON OF THREE TYPES OF SMULTI-SPEED DIRECT CURRENT MOTORS. BY OPICK CARTER POST. ALVIN CROSMAN MICHIGAN AGRICULTURAL COLLEGE 1907. PRA fry i THESIS THESIS, A COMPARISON OF THREE TYPHS OF MILTI-SPRED DIRECT CURRENT FOTOKS. | Prime movers miv be divided into the three following classes: 1. Those which are capable of deliverins a constzint or warying pover at a stiven number of R.P.2. 2e Those which deliver:a varying nower with a varving number of R.P.M. 3e Those which are canahle of delivering 2 constant or varying power throucth a piven range of speeise To the first class belong motors for driving shops, pumps, etce To the second class belons motors for driving street- cars, cranes, hoists, etce These two classes were the first to come into seneral use and at the present have reacned a hieh state of efficiency. The third is comnarativel:: little developed. With in the last few vears machine tools and high speed steels have made immense strides. Engineers now recognize that it is the best practice to have these powerful machine tools driven by individual motors. however, these motors must have peculiar characteristics: le It is required that the motor be able to run at several speeds, backward and forward, and that for any set- tins of the controller its speed remain as constant as pos-~ sible from no load to full load. 2e That the means of control be simple, easily operated, and not too bulky. 35» That at any speed it be able to develope its full rated HP. This has lead to the third class, MULTI-SPEHED or VARIABLE SPEED MOTORS, asthey are called. The direct gurrent shunt motor is the only motor which up to date, has been adapted to these conditions. There are three ways in which the speed of a shunt motor may be varied: le By placing resistance in series with the armature; but this for large currents causes a large I*R loss and a consequent large drop in speed as the load is applied. 2e By the Multiple Voltage System, which is expensive and impractical. 3e By varying the strengtn of the shunt field. The last method is in most general use todayand will give wide ranges of speeds with not excessive drop as the load is put one To reverse the motor it is necessary to re verse either the field or the armature current. It is cuatomary to reverse the armature current; but in either case the result is the same. It is a familiar fact that the brushes of a shunt motor are given a backvard lead to prevent sparking. Now, if an ordinary motor be reversed, the brushes must be shifted. 103376 To do this as often as a motor driving a machine tool is reversed, would be impractical. Therefore the motor must be so designed that the brushes may be left in one position at all times. The reason for shifting the brushes is that when a cur- rent flows through the armature it is surrounded by lines of force which unite with those of the field, and cause a distortion of the field; consequently a shifting of the .- -: neutral planee- This is called crossmagnetization and is most noticable when the field is weak. The various types of multi-speed motors differ chiefly in the means they employ to minimize the effect of crossmagnetization.- The first type with which we have to deal is a simple shunt motor which varies its speed by varying the resistance of the field circuit. At low speeds, when the field poles are saturated, the crassmagnetization has very little effect and the motor runs satisfactorily; but at high speeds, when the field is weak, a large distortion takes place, and some special device is necessary to obviate it. This is done by placing a deep slot across each pole to increase the reluctance of the cross magnetic circuit, and by widen- ing the face of the pole so that the lines of force will very few of them be foreed from under the pole tips to where they will influence the cammutation. The motor of this type which we had was made by the Crocker Wheeler Coe, Ampere, N.J. Volts 230 Ampse 6¢2 Noe 2936 Size 3-I-F Type CM HeP. 1.5 at 525-1600 R.P.M. aa The second type is a motor of special construction which varies its speed by varying the reluctance of the : eS > ae ; fields magnetic circuit. This,accomplished by placing a movable core in the pole piecese Of course when this core is down into the pole piece the pole is satur- ated and the crossmagnetization has little effect, and when the core is removed it is claimed the lines of force will follow the shell of the pole piece and leave a very stiff field at the pole tips- This stiff field will not be distorted by the crossmagnetizing action of the armature current, which, because of the hollow pole piece, has a high reluctance in its path. The motor of this type which we had was the Stow Multi- Speed Motor, made by the Stow Manufacturing Coe, Binghamton, N.Y. Volts 110 H.P. 1 R-P.l!. 1250-2020 The third type is a shunt wound motor which varies its speed by varying the resistance in the field circuit. But in addition to the shunt winding it has a series winding placed on auxilliary pole pieces midway between the shunt field poles. The office of these pole pieces is to neutral- ize the crossmagnetization by opposing ite As the crossmagnetization increases with the current, so does the strength of the inter-pole and in the same ratio; therefore the inter-poles are always of the necessary strength, This is the latent method brought forward and has occas- sioned much commente The motor is known as the Inter~pole Motor and is made by the Electro-Dynamic Coe, Bayonne, Ned. This company has such demands for its product that it could not spare us one for test purposes; therefore we built over a common shunt motor (not designed for variable speed) into one of this type. The motor was made by the Three: Rivers Electric Coe, Three Rivers, Mich. H.P.5 Volts 110 - Amperes 40 Speed 1450 We bolted on to the frame, mid-vay between the poles of the shunt field, poles 7/&" wide and of the same length as the other poles and upon each of these ve wound 15 turns of wire in series with the arm:turee The motor was rated at 110 wolts; but we found that with 110 volts on the zermat- ure and a slight weakening of the field the motor weuld run beyond safe limits. Therefore we decided to run it as @ 2-5 HeP. motor with 50 volts on the Armature and with 110 volts on the field. This gave us a no ioad range of speeds from 870 to 2700. We testetthese motors with regard to the following qualities: l. Ease of control. 2e Range of speeds and comparative drop under load. Se Commutation. 4. Efficiency at (a) High speed. (b) Medium speed. (c) Low speed. Test for range and constancy of speed and commutation. We first made a testing platform, or stand, out of two yellow pine planks 3"x12"x9'0", nailed side by side to four cleats of 4"x4". Upon this we lagged the motor to be tested and connected it by means of a universal joint, or flex- ible coupling, to the generator by means of which we loaded ite In the case of the Crocker Wheeler motor and the Stowmotor we used a Westinghouse 125 volt generator rated at 1800 R.P.M. For the Three Rivers motor we used an 8 KW "Wood" cenerator (rotary converter) rated at 1500 R.P.lM. The coupling consised of two cast iron disks, one keyed to each shaft and having projecting from its face four pins about 1/2" long x 5/8" diam. These four pins from each disk fitted into each alternate hole (about 7/8" diam.) in a leather disk. (see drawing) This was adjusted to sive each shaft about 1/4" end play and worked very nicely. We called this combination otf the motor and the senerator "the unit". We had at our disposal, 1 Weston Dynamometer Voltmeter 0-75, O-150 volts. 1 " Voltmeter 0-600 n 1 " Millivoltmeter (with shunt) O-1.5, O-15 amps. 1 " Ammeter 0-50 " 1 Jewel Milammeter (with shunt) O-1.5 " The above were all test instruments; we standardized the 150 volt Weston Voltmeter and the 50 amp. Weston Ammeter and compared the others with them and by means of curves reduced the readings of the other instruments to these standardse Only corrected readings are given. In addition we had several Weston "Station Instruments" which we used where we desired only approximate readings which would not enter into our results. All speeds were taken with a Starrett speed indicator. For electrical connections see diagram. Without excitinz the field of the fenerator we first drove the unit by means of the motor and noted the applied voltage, amperes, speed and the commutatione Next we excited the field of the senerator and increased the load on the generator so as to sive five approximately equally separat- ed points on the characteristic curve of the motore We noted the applied voltage, amperes, speed, commutation and the load on the cenerator. Then the test was repeated for another speed. In this way we obtained a series of curves showing ranse of speed of the motor, the drop in speed-_as the load is applied and data concerning the commutation. Efficiency teste The efficiency of each motor was determined Ly the stray power method. We loosened the fastenings of the generator and moved it away from the motor. We then ran the motor at the desired speeds vith no load and noted the speed, voltage, amperes armature and amperes field. We also measured the armature resistance, including brush and brush contact resistance, for the various currents by the fall of potential method. The armature current was plotted as abscissae and the resistance as ordinatese The stray - rower for any speed was found bv subtracting from the power delivered to the armature the I*R loss in the arm- ature e These values of strav power and their corresponding speeds were nlotted. | To find the efficiency: The power delivered to the motor equals, EI+F = WtStl* R+F The efficiency equalsyy 0g Where E is the applieé voltaze I is the armature current F is the watts lost in the field W is the out put in watts S is the stray power at speed corresponding to load, taken from characteristic and stray power curves R is the armature resistance for current I We plotted three efficiency curves for each motor. One curve for the highest speed which the motor developes, one for the lowest, and one for a medium speed. We plotted load on the motor as abscissae and efficiency as ordinates. Conclusions. As to ease of control the Stow motor is the least desir- able, as it requires either a reversin; switch and starting box, or a controller for starting, and thento change the speed one must go to the motor and change the position of the core. The other motors may be placed in anv out of the way place and controlled by one handle of a controller. Range and constancy of speede Both the Stow and the Crocker Wheeler motors gave their ratedrange of speeds. The Crocker Wheeler giving the widest range of all four (including the Tnree Rivers without inter-poles). The Crocker Wheeler gave the least drop in speed from no load to full load; the minimum drop being at medium speeds. The average drop being 11.2° of no load speed The Stow motor ranks next wit an average drop of 12.7%, m minimum at lowest speeds. The Three Rivers without inter- noles comes third with an averare of 29.9%, the minimum being at medium speeds. Last the same with inter-poles at 37.27, minimum at low speedse Comparison of commutation. In respect to commutation the inter-pole motor far sur- passed the others; it beins able to run both forvard and backward from no load to full load and from very high to very low speeds with practically no sparking and without changing the position of the brusheseThis same motor with- out inter-poles sparks badly unless the brushes are set off the central position and as this prevents its running backward it is out of the question for machine tool drive. Second comes the Crocker Wheeler which will run very nicely at no load through its entire range; but at high speeds and under toad it sparks considerably. It was noted that a bad feature of this motor was a noise and chattering of its brushese The Stow comes last. It runs nicely at no load; but it will not carry full load at any speed without sparking Comparison of efficieccifs. In this regard the Stow motor stands first. It gives practically the same efficiencies at low and medium speeds, its maximum of 85.2% being at full load. The efficiency is slightly lower at high speeds. The Crocker Wheeler Motor «> comes second withits maximum efficiency occuring at full load and reaching 190, for medium speeds; being slightly less for low and high speedse The Three Rivers motor sives very much lower efficiencies; but this is partly due to its being designed to give 5 H.-P. at 110 volts instead of 205 HP. at 50 voltse GENERAL SUMMARY. All of the motors tested gave their rated or required range of speeds. The Crocker Wheeler Ranked high in all regardse It was easy to control, of high efficiency, fair commutation and little drop in speed with increased load. The Stow motor ranked high in efficiency and drop in speed; but was noticably inconvenient as to control and its commutation was not up to requirements. The inter-pole motor excelled in commutation, was eaual- ly as easy to control as the Crocker Wheeler; but ranked low in efficiency and constancy of speed. Of all the motors tested the Crocker Wheeler was the most satisfactory. The Stow motor does not accomplish sparkless commutation and its expensive construction is not warranted. The inter-pole motor gave fine results as to commutation and it seems reasonable to suppose that with proper design it could be made a success in other regards. None of the motors gave excessive temperatures. ye Si Range and Constancy of Speed. : Stow Motor coupled to Westinghouse Generator ae ; March 26. Input | Output es iy E i Ee ; ae Ach Tachomereh 2S te te eae ES BE | SEES esse AAS ane ak a) | Se ec re OY) 1210 (2) waists 443.2 3.8 95.5 | 6 | 4466 | “50 | (nt 2 ae aoe) ee 940 3.7 AE} 4/00 fe) Slight Spark. 143.5 3.0 85.5 | €68 iia) (O0FO ° Ewe ae | 79.0 | 40.4 | sorT 4000 o| 7 té 29 geire aaddy. Tamar 75.7 | 4.7 290 370 of tb TAC a 13.0] 2.2 ca ; Tree ‘3.7 #o a. ae) “( } ! : ” ee ee) Ad , eet ig4t Spark. | Tm i ne ee Ae at Sylhet ee — = = March ae 13.4) 22 | 6.0 | —~—| 4650 ‘| “to| Axcellene TE a a) Ae ee ee | sa eee /2.8| 8&4 | (08.8! 425 | 4435 111.0 41.75 | /00.0| 7.16 /330 1SF | Considerable Spark | 488| Bad Sparking | March = Se maa > ‘= ON ee BS ae Vat Titre 13.0| §2 | /36.0| 6 ot te " _113.0| 2.4 | [ae EF) 3.0 : SAR4S3 3.8 FLY Wf Ce Spark. ae se Th 41.4 : a Gy Ft aS . oy Sa oS] Flange and Constancy of Speed Crocker Wheeler Motor Tread to Westinghouse Generator Fi cae Pla tae at dm eck P29 7 i ade ray ee Pe aan FZO ns 8:49 PETITE ie 2210| 3/0 | 370| 79 | 496 | ~- | 8:52 : 220.0] 5/5 | 330 | 7686| 480 | - | B65!) 7 218.5 7.20 288 | 29.0 460 eS 7 i ee 2 re ore ee ee lee ee 218.5| 283|55.0| 60 | 726 | » | o:0/ z 218.0 | $90 | $9.3 | s6.0 r+ Fe) y rer} Good 2/7.0| 8.00 | 46.0| 245| 672 “ | 9:04 | Facrly Good 220.5| /.3/ | 3.0 | — | (042 |/243| 9:07| Aycellent. B/9.0| 3.07 | 76.5 4 Ak die f 9:/0 Br 218.0! 6.32 | 70.0! #/.8 Pr ” ee ~~ | 21/8.0| 9.19 | 63.5 | /9.0 9/0 ” ed PPTs Ms i Ti eR RSIS ers Ee eee 940 22 | 4240 | ~ 9:20 ar sea a Pgs. te 87.0 8.7 | //890 i te eae A 78.5 | 16.6 | (//0 z Cad eT ae Es 5.0 ameceelh NaF 2 PB 20% | 9-28| Excedlent. mu i 7 ee ee eT _ 99.6 | §.22 | /36/ » | 9:36 | Slight Spark _ -e85|/3.10 | a39 | . |9:37| Sore : =s 6.0 | —— | /74#6_ oe cre mae Se er fo} V4 S687 « | O53 * - i 4/40 $.0 /570 9:57 | _ . *] VAS) 11.0 fg66._| . 9:59 Cia oe oF 2 99.0 | /4/ 4394 | « | sO'0/ a oe he , ey 100.0| J/./ | (4.06 Pr 10:08 With SJneer-poles er MCRL T- and Constancy of Speed. iTS ate Motor coupled to eee LEE Generator. aaa tek Commutation Tese for ere 3 Me ee Aa 570 ere Tr VA — — —— — —e Witsout Jneer-poles rd acter Es and ACES Sy Cy ey L VE ie TACT OTT ae Weseiaghouse Generator WMT EEO Trey aah 6 eS a 706 | 7 | 2:40 | Aycedlens. | 9/8 | 2° | 2i¢5 een aed V/A X- Yael , eye. #% | Z:50 2/79 | 5% 2:55, |) Daca DUET ro MCY Tar & Prone wo load to fuld load. C7276 eT tate of rated to actual speed range, Crocker Wheeler Motor Hiated Prange --- F355 - (600 APM. Tested Flange ---530 ~/790 AAPM TOTS er aes | Fe | APM \2Drep | Average High Speed _/790 | /5€O | 250 | 428 wr ee ade RIX //80 sBO ce ee a RET) cid (ha 12.3 Te a Stow Motor ital A Alange ~-- /230-2020 eS ee eee! {OS 22. es Se ee High Speed ROTH | 7765 | Flo | wo | 2 Jledium »« Zier Lee 200 | /2./ Low o 1230 {090 aoe Ad 12.7 he Three Rivers Motor Tested Afange 87/- 2695 __ Hegh Speed | R693 | /4Z0 ee 2.2 aes Medium _ | 469 | 960 | 809 | 546 | ow ees wee ok ee ee ee Ae ‘thout Inter poles tas Tested Aan e 706- 2/79 eee = si a Le mT 17 A ‘ee | 25d Medium « PEL 850 R80 2 eee | oT 706 #80 | 226 | 52.0| 29.9% _ STANDARD CROSS SECTION ere) aoe TBR IBN UE fight fs epee oe heal | | WAt ke Lcr hod | eel bd lela tv a00/ r/o ky ae e; a ™ oT ; gf oo EET y of Armature Fesistance. _TAr-ee Ri Crocker Wheeler me ae oe _s— Motor. Apr. Bre ess es a eo 2. rae ey EE SY Tr — Za eee 484|/8-2 | zee | 49 Om ee ee $421 267 4 260 wrime raat a Ei 2 ar) Freee wie Oe ete Prev are is ———_ eee Fc 34.7 | 8.70 | 3.99. 42.0 | 10.20 | 407 Generator Data of Stray Powerin watts. Vere Perermination of Armature Fesistance. ees a Crocker Wheeler VEZ a nn a a 2 7ter- __ Metor Apr. eee Ee 7S | .72_ | 3.84 | &.7/ | 40.4 -268 |2.75 9 hee ee ee ee ee! | GFL | LET Mk a et -R69 -ues| 420 | les | 1085 ie ok Generator Data of Stray Power in watts. eee Sete ie = ; iiss: = . 7 ye = ss ; aS: , = rs f SS Soe ae esd Sass eS ee eet aes SSS . . Poe, Gab es PUR as RAGE ES ASE T =: ; er ee ee ee ee he re ase ' ae ; 3 : Necks f 7s 77 ere sis pa ers ee ce ee =e = =: 7 A™peres of Current. 4 wt a i i ’ . : Wa URES 30 © eubrcshede st < , - ee | : my =: Sst hie iz ta py assed Se ppp e CROSS SECTION Bere nt 30} & MMLIMETER Stow Motor Fo Be Fe} Westinghouse Generator. wt WACRAM OF CONTPOLLER USED WITH CROCKER-W) OD L/L lati — etek ii} _ eam C=, i Vy wa) Boa. x =i TC 3 ors) Fie 200 Ort 170 ores 130 O25 Aaa 0 See 16éO Bs 150 O28 1440 Ort) 13O O30 ae) O3/ He) We a Sai nied Counsesione Stow and Creekey Wheeler Motors. a lade 1 Osi F Or o-- le eee at 3 be (ees - RS aes Three Fo Feas Moor: BU ULL (5 eS } | i} : H i AT aT ART | [ Trt a 1 ; | ; ; i 1 : } | | Has a / | | | Ti feappfiteeiehali til hatiteeent ' } ! . } SESS WE ! aerate / | pephi beach es ; } / PM HAART ; : ‘| : aa Rag ba BEES Gs { : : | / / | | ! nie } | / ’ : | | / | | } i + Ss sect MILLIMETER | pe ban ae ind eS r ery i } 4 I ; et eee tenes Drm AC et : ee oe : in feet per minute l | yo) ae s tanaake cacss Peo a 4990 ese N’30) @ MNLIMETER dha Oo Thiet