THESIS Se Rae ae ee eS eS US H.L, BUNTING E.L. KARKAU 1920 sStoeloau. Stehlert & Gates Rook Bierclers Lonsine, Mich. Copy | ; 1 WESIS OC {-: es ———— Blaudeau, Siebert & Gores Bowk Binders Joorasttyar, Mich. Copy l. THESIS CCL, \ : I. : udean, Su & Gate: Paeuvig lore ener, N Cy. Se meme udeau, Ste & Gates Moyaix ir onaing. MM Cue 1 ‘ i « \ A STUDY OF VENTILATION OF ENCLOSED MOTORS.,, A Thesis Submitted to The Faculty of MICHIGAN AGRICULTURAL COLLEGE _ By €.~ , = “ \ . . ae tied a rn ~e. a “2 ie . * ry a u . cf pr , wat \ t- Te , f Y C Ls Bunting tv E. Le Karkau . Hy any Candidates for the Degree of Bachelor of Science. June, 1920. fucle i. Mae Xv Cites. conynttiat, MM ——— ed Cc TMESIS A . Ls _ fit PREFACE. Installations of totally enclosed motors as well as box enclosed motors are 80 built fundamentally for fire pro- tection. A typical example of dust laden atmosphere harmful to motors, is a flour mill. Flour dust in these mills collects on the motors forming a caking on the windings. This in turn hinders the radiating power of the stator, causes the motor to overheat, and has been the cause of many disastrous fires, Fire-protection broaczly speaking, means the abolishing of the causes that originate fire, and secondly, the providing means which confine fire to the space in which it originates. In motors, the first is fulfilled by enclosing the motor so thst nothing but clean air comes in contact with it. The second protection, if the motor should burn out from an Overload, is gotten by building the enclosure of asbestus lumber, thus confining the fire. _ These small enclosures as advocated by mill insurance inspectors, require ventilation to keep from running hot, and in this thesis, we have chosen the study of ventilation obtained by natural pipe draft. Procedure: The ventilation tests were carried on with a 5 H.P. 60 cycke 220 volt induction motor, and a 10 H.P. 60 cycle 110 volt induction motor. The first test was made by running the motor at full load belted toa D. C. generator. The K. W. input was held ‘constant by two wattmeters in the three phase circuit, and was kept at 4.8 #.W. on the 5 H.P., and &.3 K.W. on the 10 H.P. machine. 5 x_ 746 = 4s KW. (8 10 x 746. -90 - &.3 K.W. This test was run unenclosed, and gave us the ultimate temperature rise as 25 on the 5 H.P. and-30.¢ on the 10 H.P. motore Enclosing the motor in a wall board box with no tnlet or outlet, a curve of very rapid temperature rise was obtained. In less than two hours the temperature passed the safe limit at which a motor should be run. To ventilate such an enclosure, an inlet pipe anda variable height outlet pipe were put on the box (See Fig. 1), and tests run till the air drawn thru the enclosure by the exhaust head was sufficient to let the motor run at a constant safe temperature. I uw. Sieb Gates Bapicted car, Mic Problems met in Thesis. To get the temperature of the stator coils, a study was made of electrical temperature recording devices. As none were at hand in the department and the building of a fairly accurate electrical thermometer is a thesis in itself, we decided to use a two foot 100 ¢ mercury thermometer. A putty pad was placed on the outside stator coils under which the thermometer was placed for registering the coll tempera- ture. The length of the thermometer enabled us to read the scale outside of the enclosure. The 10 H.P. machine as received by us was connected for a 2 phase 220 volt circuit. The motor had 48 slots, 6 coils in series and was conpected series delta, Having 4Z glots we recut the stator, putting 4 coils in series and reconnected it into a parallel star. This gave a three phase four pole 110 volt machine. To have a steady load on the D. C. generator, we built a water barrel reostat of large enough capacity. It consisted of a cast iron plete at the bottom of the barrel and another plate suspended at a variable height above it, both being immersed in a weak salt solution. weecacoml ders 2 ay The anemometer used in measuring the velocity of air going thru the enclosure was calibrated by running around a toy track for a definite time. This actual velocity was then plotted against the dial reading and gave a straight line function from which to read correct velocities. (See Curve l.). rebert ets Mirch. oPy | ~~ WIR OUTLET q oid 4NLET DIAGRAM SHOWING PIPING FOR VENTILATION YSED IN TESTS. lal a A sy an Ny “ee FPOLE CGPHASE SERIES DELTA 4-POLE ZPHASE PARALLEL STAR wanes a 2 Calibration of Anemometer Data. Dial Reading Times around Distance Time in Actual Dial track. in feet. Seconds.Velocity Velocity. 110 6 1 La 168. 137. 119 g 132 32 Best a8" 140 7 157-5 5 ere 240 203 10 2B5 5 300 271 202 10 225 43 314 2&2 194 10 225 65 208 179 190 10 225 70 193 163 180 10 225 90 150 120 164 10 226 1120 :120.5 Ss il MICHIGAN AGRICULTURAL COLLEGE DEPARTMENT MATHEMATICS Time of Test. Number of Min. Temp. of Motor 1:20 1:2 ~ a) we e868 ©8 08 © ee ee ee OWL OO MH OOUIFWUUWNHHOOW Se FY NGI ON EE EE FE PUI GIGI GIGLI 90 10 10:19 10 100 NN BB BR ee ee 0 ee ee 0©68 06 @F8 00 eo e ee 60 680 ® HH 19110 OV FORTE AS FAO OUIW H Or O Test run on 10 H.B. Motor to get its temerature rise, Motor running at full load and unenclosed. 220 Final room temperature 23 C. ak oe @8_e @¢ @ Vn @ SVMN UWIAA MUTUIVI WTI “JU Wi Ww WIAD ATIVAN EE AE EO WN Fe UI Eo~v MM MUON NH ee OO OW Cr er ee er ee ee ee en en ee ee ee ee 0 0 C. Temperature rise 0 C. MICHIGAN AGRICULTURAL COLLEGE es A ay eB ie rt | MATHPMaTICS Test on 10 H.P. Motor to get a curve of temperature rise when motor is enclosed in wall board box with no ventilation. oO ° Time of Test. No. of Minutes. Temp. of Motor C. Temp. rise C, 2:08 0 24.6 0 2:18 10 2s 3.4 2:28 20 30 54 2358 26 34 9o4 2:40 32 es 13.4 2:58 50 S 23.4 3:07 2 51 26.4 3312 22 28,4 3:18 70 § 43,4 3:25 17 73 484 Box of wall board, 30 x 26 x 24 (high). MICHIGAN AGRICULTURAL COLLEGE + ") Oh #4 09 FuNOJ edctd ysneyxe Ut ATS FO esTI canjzeredmay oceraay O #°TS C22 O6T 2°ts 8°c2 td olT 00: 4°TS C22 O6T *TS 8°22 g°cl O9T OSih 4°TS ¢22 O6T Z°0S 9°22) gtal OST Ont 38 $¢2 OTe ToS) =e heee?) 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Copy | a _ MICHIGAN AGRICULTURAL COLLEGE sre ] =e | SS UURSENS RES FOOSE S weary su anep: DEPARTMENT OF MATHEMATICS | Sonteaup, Bicbert aX Cyiters Hoek Boders Loanestna. Mich. Copy id rs + ri COLLEGE HIGAN AGRICULTURAL - Mic Test run on 5 H. B. Motor to get its temperature rise, Motor funning at full load and unenclosed. Time of Test. No. of Temp. of Room Temperature Minutes. Motor %, Temperature rise %%, 6:25 0 20.6 20.6 0 RE 10 31.9 20,4 11.5 §: 5 20 333 20.4 15.2 355 QO $e 20.5 18.1 71305 0 1.2 20. 20.3 7215 50 42.7 2l. 21.5 7325 60 41 21.7 22. 1235 70 36 22. 23.6 1345 &0 46.8 2245 2 2 7255 90 46.4 22.8 23, ar12 at bere 25.5 250 225 120 49.3 25.7 52:2 B:35 150 50.3 oh 26.4 #52 150 20.7 ui ere 9305 120 2363 — 246 26.9 9:15 170 5l. 2k, 26.5 9:25 180 51.2 2u, 26.3 MICHIGAN AGRICULTURAL COLLEGE +++ 1? soc'ess! [Ba > ee, +} aes! 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OZ T°SS 08 Ons1 °96 2G2 Ze S°T? Og g°2g ol oee1 2° Sh S3T Gt 9°62 2°02 9S 0 O2s1 ° 5 3lT Ght 9°12 = #°6T *Lh 0 OT: G*e2 +hT Ott T°¢2 "Od T°¢ Of 00:2 G°2¢ T OTT L°lt = €*tz °6 0 05:9 4°92 eT 06 G*ot = 2°Tt2 Le og 04:9 0 BHT STT 6°S T'T2 Of OT 0239 0 0 0 0 T'TZ tte 0 02:9 *Tenqoy “Tet ‘ngey oTQnofoxequt ‘aqnuym zed y90y = tastz 6 6*duey duet *soanutpy NId4 ITS JO SuNTOA 8ASYUT UT ate Jo AZTOOTIA ‘dus, wooy IOVOK JO “ON °9894 fO GUT] (su prrng JO OpTsgno ey uo “93 OT) edtd yd JO *4F ST SUM SaInsoTOUS UO TeEey Jo yUPTay ‘DEqZUeTT USA 4nq ‘fTesoTOUS ST TOJOM USM SAINO OFFI 9anjyerecmeq, yos 09 ZOOM *g°H G uO Ysa] = oh, Mee a + fim — weSH, 7 Tyr - Sie MICHIGAN AGRICULTURAL COLLEGE Seeeesus 28a ; é - ne e= 2 = se aa ss ® = Bisconasns BaseReaee Motors, both alternating ani direct current typ:2, are built with the windings open in a much greater number than those with the windings enclosed, This is due largely to the fact that they operate in places in which dust is not prevalent. But in some intustries, such as flour mills, grain elevators, cement factories, etc., the motors must Operate in very dusty places. If these motors are not piaced in rooms especially designei for them, as in the case Of the steam engine, they must be housed in smaller and expensive enclosures, to be kept clean, Such an enclosure serves a dual purpose when viewed from the insur2nce company's standpoint. It keeps the dust from the motor and confines the fire in ease such a misfortune happens, to the seat of its source. The first point is an advantage because dust when mixed with an olly vapor given off from the bearings, settles on the windings and forms a very good barrier to heat radiation, due to its poor ability to conduct heat. The dust also works in between the rotor and stator requiring the motor to carry an added load dus to the friction set up by the rubbing Oily surfaces. The second point is an advantuge because a fire started by a motor is very likely to start any inflammable material in the vicinity, thereby causing a much greater loss than the motor itself. Hence, if the enclosure be built of a fire- resistive materisl, the motor would be the only loss in case of a burn-out. —- When such an enclosure is built, it mpst be venti- lated in order that it may run as cool as when located in the open. The ventilation pipes must be run to the outside of the building, and whenever possible, to the same side, so that the wind-pressure would have no effect on the draft. In case it is not possible to carry both intake and outlet to the same side of the building, some means must be devised whereby the wind will aid rather than retard the draft. When very large motors or generators are used, and must be enclosed,a forced draft may be used very efficiently, but in the case of smaller motors, natural draft must be used in order that the system may be built and operated on an economi- cal basis. Hence, the problem of the engineer is to find the cor- rect amount of air necessary to keep the motor at the desired tem- perature rise with only the use of natural draft. In order to do this, the correct head ani the correct diameter of the pipe must be known, or possibly predetermined with some degree of accuracy. But since very little data has been published in regard to this phase of engineering, we have attempted to make a study of enclosed motors, ventilated by natural draft in order to find a means whereby the correct amount of air necessary can be Calculated, and also the proper ventilation head and pipe diameter necessary to economically carry the air. In order to first find the natural temperature rise of the motor, it was run open, allowing the free passage of air thru the windings as was intended by the desizgnets. Bhis test was made mainly for the purpose of finding what margin of safety is allowed for conditions which arise, that tend to reduce its ability to operate in the manner for which it could be designed in case such conditicns would not be introduced, Then in order to find the oprosite or poorest con- dition under which the motor may be made to operate, it was entirely enclosei, so that no air could get to it at all. This latter test shows very clearly that when operating under such conditions, it can be operated at only very low loads, or for only a short space of time. The enclosure was then equippei with an inlet and Outlet consisting of 7" galvanized iron pire. The inlet was about two feet long and was necessary only to give the same condition as when used in actual practice, as the laws governing the flow of air through an orifice ani through a pipe, are very different. The outlet was of varying lengths. Each length was decided upon with respect to the first, so that each head would give a definite ultimate temperature riss, with respect to the first. The first length was chosen merely for its cone venience. -—— oo ee perenne Pe The volume of air usei was measured by means of an anemometer placed in the intake. Readings were taken at intervals of ten minutes as in the case of the temer:itures. Because of the fact that the anemometer did not give accurate results, it was calibrated as stated previously under the head, problems met in the thesis. The reaults obtained by the use of this calibration, were those used in the computations for findingg the amount of air necessary to absorb the heat given off by the motor. From the results obtained, computations show the following: Taken from the test on 10 H.P. Motor, with 20 ft. hea, for which test an ultimate temperz2ture rise of 48 Cc. was obtained. But to allow for any small discrepancies which may arise, the 0 temperature rise may be considered as being 50 C, 10 x ee x 10 = g29 watts given off in the form of heat. The motor was taken as being ninety per cent efficient which mezns that 10% of the enerzy supplied is lost in the form of 1 B.T.Ue equals 778 foot pounds of mechanical energy. 1 H.P. equals 33,000 foot pounds of mechanical enercy, . during the time of one minute. Ager = eguals 42.5 B.T.U. per H.P. per minute. 1 H.P. equals 746 watts. gee re ge » e e a ° * e an a ‘ ~ » e es s e a s » * s —_— _— - 7 - 2 - rr 47. Uv. Hence re = .0569 per matt per minute. Then .0569 x 829 equals 47.2 B.T.U.ziven off per minute by the motore According to the flow of air in pipes, the entire area of the pipe cannot be considered as carrying equal amounts over the entire area. Hence according to the direct proocortion, 24" actual dizmeter = 7.1" actual diameter or, 22" effective diameter X | X equils fh we 6.5", or effective diameter of pipe. Actual velocity in pipe as found, equals 286 feet per minute. _ e 285 x " x 5.5 = 66.0 cudic ft. per minute,being supplied to the + x 144 motor. 00569 x 1000 equels 55.9 B.T.U. per K.W. minute. Then to find the volume of air necessary to absorb the heat equivalent of one K.W.: 660 x 56.9 . 79-5 cubic ft. which may be considerei as 80 cubic ft. 47.2 avr alemperalere rise of 5 0°@.- per minute necessary to absorbd one K.W. of equivalent heat energy, According to Harding and Willard, the specific hest of air remains practically constant between the temperature O and 150 °c, Since the specific heat merely shows the ability of one substance to absorb heat as compared to some other substance, and since the specific heat of sir is practically constant, the ratio at which it would absorb heat at varying temrsratures, would be an inverse ratio. — Rem ee me eee Hence: Oo SO cu, ft. 4C C.,temp. rise 5 - .temp. or X = 50 x 80 sz 100 cu. ft. x 50 °c, 8 n +0 0 necessary to absorb one K.W. of equivalent heat energy at a 40 C. temperature rise which compares favorably with results given by the Standard Handbook for Electrical Engineers. From Harding and Willard: Vs V2 e A-B , where A ecuals weight of air at outsids pire A+B temperature and B. Bquals weicht of air at inside pipe temperature. Temperature, Dee. C. Weight per cubic ft. in lbs. 1.67 0810 733 08025 023 . 079 10,00 * 0 5B6e 5055 ©0771 18.35 05 bie 21.15 © 07567 23.90 00749 25-70 0742 29240 « 07356 32.20 ~07289 35.00 . 07222 205° ©07157 0.60 « 079093 46.00 06908 49,00 06848 51.70 ~ 06790 54.50 - 06332 7220 © 06675 0.10 «06620 (Above table bassd on barometric pressure of 29.921"). From the Law of Charles,-P.T. = P' T', this enabling one to find the weicht at any barometric pr:ssure. a“ a MD a) > re “4 cs ‘2 } ‘ Cas ~ = a C be di This introfuces such a slight variation in checking the head required for tentilation,th:t it is unnecessary and impractics:l. In order to find the effective heai with the velocity and average temperature given:- V «2 gh _A-B ~ AeB O For an average temperature rise of 40 C which corresponds to the average temperature rise in the 6 ft. head, as actually found: 64.4 h x (.07495 - .06565) wm 64.4 x .0666 bh —-(.07495 + 06565) Ve 64.4 x .0666 h oF £830) = 64.4 x .0666 h he 14.71 = 3.45 feet height of head. 025 ° ° For an average temperature rise of 30 C. as assumed in the case of an eleven foot hea: V yew x (07567 - .06 0) orhs= bf 3h 5.0 ft., (607507 # 00790 at. of head. For an average temperature rise of ig. C. as assume in the cease of 20 ft. headia 2 oh x (29 gps! - .07093) or hs= 22,8 ll ft. vey 007567 # 207093) 2.08 ht. of head. For heais greater than 10 feet, the temperature difference becomes so low that its effectiveness drops below a practical point. Bb find the correct diameter of the pipe, the following direct formula applies:- Yol. = pels 5+ Ds Vel. x 4 Vol. x 7 all of Wt In tests of the 10 H.P. Motor with 6 andll ft. head, draft where no constant temperature was arrived at in a three or four hour run, extrapolation of the heating curve gave us the ultimate temperature. The method is taken from Karape2toff, and briefly is as follows: Let the abscissa of the final point of the durvse be T T_, and x and the ordinate Ff ani their ordinates, T a? T 4" 1’ Ty; Measure the ordinates and solve the equation: 4733 [t,- 7, To get the ultimate temperature rise, calculate any or all of the following four expressions: T Aa 1 l1- Z T As e _ 1- 2° T As 3 1 - g? _ 4 A= ——y le- Z The average of the above four equations was taken for tke ultimate temperature rise. - & (10 H.P. Motor, 6 ft. head) g 2/51 - 47.5 41.6 - 27 As a = 2] = 1-.49 251 a= 41.6 = 41,6 - 1-.239 »7 62 = 47.5. s 4793 = , 1 -.117 855 As _ 51 = _ 51. | 1=.0572 9428 = V.239 = OMY 53 5h 6 52.7 53.2° Average temperature, 53.62. ay/¥¥- 3 = /2 os e221 = 472 2 *Y 35.2 - 23 ii. Ae _ 23 =: 23) og 435 1 - .471 529 A= _ 35.2 . 35.2 - 45.3 1 - .221 -779 A= _ 41.3 = 4, = 46.1 1-.104 089 _ = aa = 46.3 Average temperature, 4s 3°, As 1-049 51 J (20 H.P. Motor, 20 ft. head) Z= 47 « 46.6 = 4 ~H2.6 - 30.6 } 12 0.6 . 0.6 As 12,183 e- W2.6 lk 42.6 A= 12,0535" 3665 46.6 =. 426 A= T-.0061 9939 > _ 4 - y 1-.00111 99889 37.4 Te 183 47 47 O Average temperature, 43.65 . eee ILLEGE TURAL Ct sRICUL A rane) Li A a ne a ee prow TOY Mn dat dat ae ety ts ge Ode ee (AH OCL) f Se ne eee TeeReaSaae se. | Fale. 2 Er OSH Bae ar 2 ad A . Te Ff 2. Curve twelve in which height head is plotted against the ultimate temperature rise, shows plainly that bare metal piping is not dependable above a certain height for drawing air thru the enclosure. The draft created is due to the hot air enclosed in the pipe rising, but where a height of head is used above 10 feet, the radiating power of the piping is so great that further additions of length are not effeotive in appreciably lowering the temperature rise of the motor. CONCLUSIONS. In the past, very little has been done in rezard to ventilation of motors, and consequently very little or no data is obtainable on this subject. Hence, in making the test, many problems xere met, which were not anticipated, and many conditions which, before the thesis, were not con- sidered of appreciable consequence, were found to be of great importance. Hencs,due to our lack of knowledge in regard to the subject, ani to the lack of time to make a second complete test, some of our results depend upon assumptions which we find to be more or less in error, The particular cass to which this refers, is to the calculation on the head necessary to give the correct flow of air. We are inclined to believe that the rate of cooling in the outlet ventilation pipe, is very similar to the cooling curve of the motor itself, but have no data to prove this. When making the calculations, we considered the cooling in the outlet pipe as being in accordance to a straight line function which would necessarily give a higher average temperature rise in the pipe than if the other type cooling curve was used, This may be readily seen by placing Curve 2 against a light, turning the sheet top for bottom (no end for end), and looking at the curve from the back. Consider the actual ultimate Temperature of the curve, as 7¢ro Temperature rsse rise,or room temperature, and the actual zero temperature of the curve as the maximum temperature of the pipe at a point just outside the enclosure. Consider the new abscissa as the length of pipe used, and the ordinate, as the temperature taken at equal intervals long the pipe. Then, if a straight line is drawn from the maximum pipe temperature rise at zero ventilation head, to zero temperature rise at maximum ventilation head, and an average of the ordinates taken at equal intervals, the average orcinate which corresponds to the average temerature rise is greater than the average when taken from the cooling curve as we believe it actually exists. We are fairly confident thet the calculations with regard to the amount of air necessary to absorb the heat given off at various tempersture rises, are correct, due to the fact that they check with results given by the Standard Handnook for Electrical Enzinserse As a sugzestion to any others who might wish to carry the thesis further, we submit the following outline: I, Find the efficiency and power factor for motors from 5 HP. to /5 H.P. at the normal full-rated load. (a) Calculate the heat lost from this data. II. Bulld resistance coils to generate the same amount of heat at the same temperature rise as the motors. (a) One coil with taps at the proper points, is sufficient for the entire test. IIt. Build the coils in the enclosure so that the temperature may be regulated by means of a thermometer. (a) Vary the ventilation so that the temperature may be made to drop. (1) From this data, the quantity of air necessary is found experimentally from different temperature rises, IV. Place thermometers at intervals of one or two feet ig outlet ventilation pipe. (a) This will give the radiation along the pipe from which the average temperature rise of air in pipe may be found. (ob) By using different pipe diameters, fini the radiation. (1) By mathematics, the raijiiation is inversely pro- portional to the square of the diameter. Ve. The velocity of air in the pipe should be messured with some degree of accuracy. (A) This may be done by means of an anomometer or pitot tube. (1) Ths effective diameter of each pipe should be calculated or found by experiment. This may be done as explained in the treatise on Hydraulics by Hughes and Saffori, Pages lll and lle. If desirei, insulated pipes could be used in procedure as explained under IV to find their effectiveness. This outline, we believe, will give an efficient means of going about the test in the future, aniis the outline which we would follow if we were to repeat the test. —- = RCO "USE Gia ATE U MICHIGAN ST NIVERSITY LIBRARIES NN 4 3 1293 03082 2922 ul i ; P| i ! , ? P f is n°