to kL ey tf (3 AAMOTIAT OOD NN LAN Va VATA Oa 0s be en Oe ia Yee eee ee ote. ee oe, ee P| Lae - a ee ee AG! VAI EUR ESE eee SRF ee eae Copy [, ERS A CONSTANT SPEED GOVERNOR For MOTOR GENERATOR NO.2 A THESIS Submitted to the Paculty of the MICHIGAN AGRICULTURAL COLLEGE BY ri HARRY W. COON — Candidate for the Degree of Bachelor of Science. June, 1922. JHESIS < 9192"9 DY INTRODUCTION For accuracy in laboratory work it is frequently necessary to have machinery driven at constant speed. There is a demand also in the commercial world for con- stant speed on current motors. A Shunt wound motor is said to be a constant speed motor but, in reality it is not, for in the oase of a variable load and a variable voltage, a regulator of some kind is neceasary to maintain a constant speed. There are a number of devices in the commercial field for the purpose of controlling the speed of a motor, but only a digcussion of the type designed and built in this thesia will be given here. vi 2 HEORY The object of this work is to produce a peice of apparatas that will accurately regulate the speed of a compound motor when subjected to variable loads and variable voltages. This is accomplished by varying the field current as the speed requires. The field flux is directly proportional to the field current within small limits. The field current is varied by inserting and ocut- ting out resistance in the field. Two resistances are used. One is cut in and out of the field cirouit by contacts controlled by a coil that is connected across the main line and is operated by slight variations in voltage. This resistance regulates the speed of the motor with respect to the voltage on the source of sup- ply. The other resistance is out in and out of the oir- cuit by contacts that are operated by a D.C. generator relay coil. This D.0. generator is a small separately excited machine, directly connected to the regulated motore As the speed of the motor tends to vary, the re- lays either insert or out out registunce and thereby bring the motor back to normal speed beosuse of the dependency of the speed upon the field, as shown in the speed ourve graphs. A motor whose field is shunt wound is practically considered to be a constant speed motor, that is, it tends to maintain a constant speed as the load varies. A series wound motor is a variable speed motor. Its speed varies inversely as the load. A compound wound motor speed ourve may go up or down, depending on whether it is oumalatively or differentially compounded. If it is cumulatively compounded the flux of the series winding will work in conjunction with the flux of the shunt winding, thereby making a stronger flux and lessening the speed as the load Lnoreases. [If it is dif- ferentially compounded the flux of the series winding will act against the shunt winding flux and produce a weaker total field, thereby inoreasing the speed as the load inoreases. The motor to be regulated in this thesis is a cum- ulative compound motor. The regulator must therefore maxe correction for 4 drop in the speed us the load increases. The purpose of this regulator is to make straight lines of the speed load and the speed voltage curves (shown On speed curve graph) at 1800 R,PeM. aN ~ Sy S La T iss bs 3 LU 600 F Ae od 2400 AL05 Zgoer | Pr Ce a SPEED itt PLAST : nv SPEED CURVES § 1a00 {RPM Sue we FULL LOAD | | | | he, Ps 5 0 eal Py 2 ara el any AEE IN AMPERES ia 3 Py "se " iT 150% OVA 4 at eT) ai m7) Prz) aT Pyar xT: 7 yy YT) LINE PRESSURE IN VOLTS A GRAPH SE The Principles of Speed Contrd a) ME a change of speed to be mace by Tr /s +5 — caro Pet d’) ascorgL SPEED CURVES ar /600 ~ N ~ (F060 Ne : a /2Z00F } ~ | 2 Se} or S| | | q oe G) sco} Ni KY Pe: : a : ‘5 U l 75 Zz 400 b apa CURRENT es AMPERES Far) i a 7a Pv ITA Ry LOAD 'IN\| PERCENT 4] Tt aT) a2} 7¥0 Prez] oT PP) 230 ar” ears 7 0 L/NE PRESSURE IN VOLTS A GRAPH ae The Principtes of Speed Contrd The tneximum change of speed to be mace by Tr /s r+s Tis DESIGN Of A COUSTAUT S24ED REGULATOR Por MOTOR GENERATOR SET NOe 2 A small 110 volt D.C. motor was secured and tested as a generator. It was a series wound motor and would run at about 1200 kh.P.M. 01. 110 volts but when driven at 1200 R.P.M. it would not build up voltage. It was necessary to rewind tne field and separately exoite it from storage batteries. It was excited with .3 amperes and at 1800 k.P.M. it generated 250 milliamps at a pressure of 6 volts. Yrom this data the Generator lhelay Coil was designed. GENERATOR RELAY COIL DESIGN (le) Re Data Given 6 volts 25 amperes 2 ohms Assume Coil 2.5 incnes long 2-2‘) inches diameter °/5 incnes thickness of coil. 4p L(De = a%) All formula from "Pne Electro iiagnet" by Wolcott Kenelly Vorley sz Constant for given size wire se j.esistance of coil = Length of coil Outside diameter of ooil A Oo Fr we w inside diameter of ooil ain -—~iie Substituting these values pe» 24 Ls 2.5 De 2025 da ef) R= 4 =x 24 = 8.4 205 ((2025)*=(475)*) For Rw» 8.4 - # 24 Bé& Sgage wire is necessary (from table in "The klectro Magnet") * “~ Assume io. 22 B & S gage wire. Then to compute the number of Ampere turns (NI) NIe 2E “K(D@) NI ws Ampere turns Impressed voltage K = Constent for given size wire Substituting tnese values Loe 6 K ws 000071 (from tablc) D s Ze 25 de 075 NI = 12 - 1056 ampere 200071 (2625 x 675) turns Is e2) amperes NI = 1050 1056 = 4224 tarns of wire ec) ps at Length of wire Le DEXENX/ | Lo Ds average dianeter L= 1.5 x 4224 x 3.1416 + « 1662 or 1700 feet id of +22 wire required. DESIGN OF LINE heLaY COIL Data Given 220 volts Assume Coil 2.5 inches long 2.25 incheg diameter e75 inches thickness Formula Re 4 Ee Constant for given size wire eo hw =x Impressed voltage Outside diameter of coil 2 Inside diameter of soil cH ff & s Length of ooil Substituting these values E = 220 B° = 48400 De 2.25 Dp? = 5 00° Le 2.5 L° e 6.25 d «= 75 a2 = 05625 Ks 4 x 48400 = 960 501416 x 2.25 E O02) x 4656 When R # 960 the size of the wire corresponding is #35 Assume #32 B& S gage wire. To compute ampere turns (NI) NI 2E KID dj) (from Z.ectro Magnet ) Substituting these values E 2 220 K = .086 for #32 wire Ds 2025 ds «75 NI = ex 220 == 1703 ampere turns e086 x 5 Area of coil » .75 x 2.5 = 1.6885 square inches area Ho. 32 wire will wind 9,610 turns per square Linon. 1.6885 x 9,610 » 16000 turns of No. 32 B &S gage wlre on Line relay coil. 10 CONSTRUCT ION The Frame, lever arms and springs were made after the coils were wound. aA flat piece of oold rolled steel 24 x ¢ was used as a base. The cores also of cold rolled steel were fastened to the base in an upright position by cap sorews through the base. Large brass washers were fastened on top of the coils, by a ledge on the end of the oores, to hold the coils in place and protect them. Two brass standards were fastened to the sides of tne base midway between the coils to hold the pivot rod of the lever arms in place. The lever arms were first made from twisted pieces of cold rolled steel but they were found to be tuv heavy. Then they were out from thin pleces of cold rolled steel. Some difficulty was found in finding suitable contacts, hut silver points were finally tried and found to be satisfactory. Then a support wag made from the smbll D.C.generator at the end of the motor by the use of strap irons fastened to the motor freme and bent into place. The generator Was mounted on a flat pieoe of steel that was held in place by the strap irons. The generator was then coupled to the motor by an ordinary tuchometer coupling. The greatest difficulty was encountered in getting a satisfactory spring action. Flat steel springs were used at first and made adjustable by a set screw. The apparatus was get up and these were tried out but it was found that the li magnetism would hold the springs from acting as they should. Then the design of the spring control was changed to use a tension brass coil spring. This required a change in the frame design. A flat piece of brass was fastened to the frame and bent over the lever arms on both sides. The spring adjustment, and lever arm stops were fastened to this piece of brass. It Was designed so that the spring and stop adjustments could be made by turning small brass nuts on the top of the apparatus. lay at} FIELO DIAGRA/T of CONSTANT SPEEU CONTROLLER L2 TESTS AND RESULTS The first teats were made using flat steel springs. The action of the levers was so slow that no data was taken of the test. This sluggish action wag due apparent- ly to the magnetic pull of the core on the spring. The design was changed and brasa ooil springs were used in place of the flat steel springs. This teat showed that 40 volts change in the line voltage was required to operate the line relay coil and that a change of 300 R.P.M. was required to furnish enough current to operate the generator relay coil. Nee 14 CONCLUSION This Test proved three things. le. That the theory was correct. 2. That the method of applying the theory was not oorrect. 3- That the correct method of applying the theory in the design could not be worked out mathematically, but mast be experimented with until the desired results are obtained. This leads to the conclusion that this design is not correct and that it ig not correot because it has not great enough sensitiveness. This may be due to a number of faults. The friction and weight of the lever arm, the lack of sufficient winding in the coils to provide oper- ating flux from slight changes of current in the ooils, and the saturation of the lever arma above the knee of the saturation ourve. In the origional design of the coils, a change of 5 volts or of 10 R.P.M. should supply enough flux to operate the contacts regardless of the total amount of flux. This means that the scope of operating ability of the apparatus as built must be narroweé down to these limits, Altho this design is not oorreot it provides valuable data from whioh a guccessful device may be designed and built. 14 Any future design should make use of this data; That there should be no oversaturated parts in the mag- netic circuit; that the flux should be large enough so that a slight variation in the ourrent will produoe enough flux to operate: the contacts; That the lever arms should be so designed that the friction and waight would be a minimum and would not materially affect the action of the arms. qd NLY y 4 ¥ SE G MICHIGAN STATE UNIVERSITY LIBRARIES Wii ii P= oT ie 3 1293 03046 I