IVA o— co — af oie MW— aoa . ” a a7E8 FRI oe Mor ° % « Co eRe at tet “ ee b es at ad wy ‘ ae « tow 3 University w ‘ mm 3 1293 01072 5962 yore Ade xs! re ee ny wR Let The Design and Construction of a Constant Current Transformer. & Thesis Submitted to The Faculty of MICHIGAN AGRICULTURAL COLLEGE By He J. Horan Candidate for the Degree of Bachelor of Science June, 1916. THESIS 4OLT Ors PREFACE. The object of designing and building a constant ocur- rent transformer of the floating coil type was not only to further the designer's knowledge of transformer construction, but to leave a piece of arparatus to be used in experimental work in the Department of Electrical Engineering at the Michigan Agricultural College. Toe caldulations found herein were worked out from standard formulae. The design being the ideas and know ledge of the writer on capability of working, strength of apparatus, economical oonstruotion, and appearance. Any of the points are susceptible of demonstration, thus doing away with all methods leading to complexity... While the working qualities of any apparatus ap- proaches a standard that is desirable only after muoh e6x- perimenting and designing, and this being only the second one of its kind ever built, probably ocould be made more efficient after the final test has been performed. The idea in mind of designing and constructing of such apparatus, however, was to form a starting point whereby others may profit by tnat which has been done and, thus assisted, be able to construct one more efficient in its performances. He Je He le This thesis, a design of an exrerimental constant current transformer of the floating coil type, was select— ed with an object in view to construct and test the trans- former and note how the test results agreed with the theo retical results. The latter being derived from the theo retical formulae on transformers.. A constant current transformer is in some respects like an ordinary constant potential transformer of the Shell type. The latter haying a constant voltage impressed on the primary and a constant voltage taken from the second ary... This is not so with the former, while it is lixe the latter in regard to the primary, it uiffers in the secondary having a varying voltage and constant current. This result may be obtained in various ways, but in this design it is acoouplished by varying the distance ostween the primary and seoconuary coils as tne load changes. TNis slement of design maxes it inpossible to have the coils interleaved, as it is in many of the constant potential transformers, put that they must be separate and distinct. Another dif- ference is that there must be a low nmagnetiocal reluctance or more leakage in the oore and that it must be of greater length to allow for the separation of the ooils.. in general, there are two types of constant current transformers, first with floating coils, which has both coils movable, second with semi-floating coils, which has but one coil movable (usually the secondary). The latter Be type is the one seleczed for designed due to its simpler mechanical construction, and also because smaller sizes of this transformer are more often of tnis type. The movable secondary ovoil is suspended fyogran arm whioh is pivoted near its midale point. From tue outer end of the other arm is suspended a weight wnich countsrbalances the secondary ooil.. The theory of the operation of this transformer is as follows. First considering the primary ooil, witha constant E. M. F. impressed upon this coil the total mag netism within the coil will be practioally soonstant at all times.. The strength of the field surrounding the sedond ary ooil will govern the E. M. F. generated by that coil. In all types of stationary transformers the secondary cur- rent is nearly opposite in time-phase relation to the pri- mary current, so that there is not only a repulsive thrust between the two ooils but there exists a tendenoy for the magnetic lines from tne primary ooil to be foroed out into Space without penetrating the secondary ooil. In ths or- dinary potential transformer this repelling action is pre- vented from producing motion between the two coils by the rigid mechanical construction, while the proximity of the two coils linits the magnetio leakage. In the constant current transformer, however, the repelling aotion is utiliz ed to adjust the secondary coil into a ppysition relative to the amount of electrical pressure used; when the secondary 3e coil is at a great distance from the primary the paths for the leakage lines are inoreased and the lines whioh inter- link the secondary are less than when the coils are nearly together. The counter weight mechanically attached to the movable ooil is so adjusted that, when the desired current exists in the seoondary coil (independent in its position along the core), the weight is just balenoed. An inorease in current increases the repulsion and causes the ooils to move further apart. With any current less than normal, the repelling force diminishes and the secondary coil falls nearer to the primary, thereby restoring the current to normal.. This type of transformer is used to produce constant current for series nitrogen filled lamp circuits which are being used very extensively in street illumination. This transformer, when completed, most likely will be used for laboratory experiments anda as the one wnich was in the laboratory was destroyed in the recent purning of the Engineering Building, it was necessary to use the frequency and voltege that would be surplied to the laboratory. There- fore soxe of the specifioations were fixed. First, the available primary voltage was 220. The frequency was 60 oycles.. The secondary load was to be a number of four amps series maZda lamps giving a secondary output of about 600 watts, when all the lanyns were burning. Knowing this, the most logical order of procedure was 4 as follows: 1. Calculations and design. 2. Construction of mechanical, eleotrioal and mag- etio parts.. 3. Assenbly. 4. Tdsting. De Recorts. ELECTRICAL AND MAGNETIC DESIGN. The design involved an investigation of what had pre- ‘viously peen done along this lines It was found that there were no ovooks which treatea of constant current transformer design... However, with some information of the theoretical results oy a Ceneral Electric designer and the results of the former tnesis by Messrs. Lester and Fox, it was decided to use some of their ideas. Their finished piece of anpara- tus showed that the leakage was far too small as was the limits of motion between coils. This was overcome by de creasing the size of cors and increasing the number of turns in the coiis. It was also decided to design the transformer as a constant potential transformer of lengtnened nagnetio chrouit, which it woula be if the two ooils were in contaot at all times. As it was impossible to get the required oon- Stants for the transformer iron it was necessary to use those and the metnod outiined in Sheldon, Mason, & Haus— De mann's, “Alternating Current idachinery," (page 155 to 160). g,2 tb a 3 A & ag 5 1 if iH | " i yf 1 HH if = i NIL= _~ 1 _ it an) i < Il HOt OS Ii i tt = i Notation Used in the Design.. Maximum flux. Primary Voltage. Number of crimary turns.. 2 Wf Frequency, cycles per seconde Secondary voltage. 3.1416 Number of sedondary turns.. Sectional area of core. Magnetic flux density.. hagnetic permeability. Aupere turns. Lengtn of magnetic chrouit. 1 = Ta - Wagnetio reluctance. Current in amyperes.. = Eddy current power. A constant depending uron the resistivity iron.. Volume of core in om? . Hysteresis power. The hysteresis constant of the iron. Thickness of one lamina in om. Resistance in ohms. liean length of turn. of the Ge Calculations. The size of core decided u»on was as shown in the blue crint No. le The delivered secondary voltage at full load = age = 150. 5 volts were approximated as the secondary voltage Grop.. Therefore Eg = 15045 = 155 volts induced in the seconuary. B was taken as 60,000 lines per Syuare inch. £= 60 cycles. A=1.75 «1.75 = 3.06 Bye in. 9=>Ax B= 3.06 x 80,000 = 245,000. 1 = 31 inches. — From Sheldbn, uason & Hausman dn = 108 V2 Ep DW 108 V2 Ep 10°V8 Ep = 10° & wx Pn arf x On \b 1 f9n from which Ny = i Therefore ng = 10° 4s We TT £9q, 100,000,000 x 155 - 237 Substituting above values ng = sk a7qig x G0 x 545,000 > _ 320 “Hg 156 or Np = 348 From "Dynamo Electric Machines," by Wiener, (page 336) u for annealed wrought iron (B= §0,000). Nioir = 0.3133 x 80,000 = 25,064. NIsron = 3108 Te NI | u= air . 25,064 — W.-C F 803503 NI yon oie R- 2 - $1 UA ** 60303 xX 3.06 x (2.54)* = 9-00196 Inagnetizing = 20 Ra _ 10 x 0.00196 x 245,000 ve 4VE TD, 4 xV/6 x 3.1416 x 348 - 0.775 amperes. Ps =_ Kv f°t"By? ~ 106 * = Toytt