vr Hy ea aed a = = a ) mn s EPSTEIN APPARATUS FOR DEYERRINING CORE LOSSES H, J. KNOWLTON eek BS BS XX [26 KL ee THESIS #** Construction and Testing of an Epstein Apparatus for the Determination of Magnetic Losses. A Thesis Submitted to The Faculty of MICHIGAN AGRICULTURAL COLLEGE H. J. Knowlton W. B. Brown ‘Candidates for the Degree of Bachelor of Science. June 1916. xe DEDICATION ee * 70 * The Electrical Engineering Department of the Michigan Agricultural College for Increasing and Bettering the Laboratory Equipment and the Benefit to the Course therefrom this Work is heartily Dedicated by the Authors ** PREFACE *2 This book is a collection of notes and details for the construction and use of an Epstein apparatus for the deter- mination of magnetic losses, especially in sheet iron and steel such as is used in transformer and armature lamina- tions; We selected the construction of this apparatus in view of the fact that it is a standard instrument and mich needed to better the equipment of the department. Also, we consid- ered the benefit to ourselwes derived from the working out of the details of construction, the pleasure of seeing it materialize and work out under test after completion. The general specifications were taken from the 1915 year book of the American Society for Testing Materials, as per their requirements for the Standard Magnetio Tests for Iron and Steel, with such changes as were recommended by the com mittee AB on that subject. } In the course of our work we received much help from various departments and persons connected thereto and we Wish to express our deep indebtedness to; Prof. W. L. Lodge and Prof. A. R. Sawyer for advice on construction, general information and supervision. The Phisics Department for the use of laboratory and apparatus. A. P. Krentel and C. N. Rix for material, uee of tools and benches and also personal help. C. A. Evans for the use of the machine: shop in the winding of the coils and the machining of the metal parts. F. Mitchel, college electrician, for the contribution of various articles of brass which entered into the apparatus. A. B. Howard for finish used on the base and other wooden parts. Barker Cole Electric Co. for extension of credit on our wire bill. Everybody with whom we came in contact for general good will, readiness to help, and interest in the work. We feel that we are well repaid for our efforts to make this work a success, and hope that the instrument which we have constructed will be of use and value to the Department. We will be glad if these notes, as the benefit of our exper- lence, may be of use to any one considering the same or a Similar project. HJ KXnowlton. W.B.Brown. M.A.C. May, 1916. ** TABLE OF CONTENTS *#* Page Introduction - -----+--+-+-+--:- 1 Chapter 1 Core Loss = |\----|-- ------- 3 Chapter 3 Conditions of test - ------ mw = 3 Chapter 3 Specifications ----------°- 4 Chapter 4 Procedure --------"-rerr°- 6 Chapter 5 Details of constructions - - - - - - Chapter 6 Wiring compution --------- 11 Chapter 7 The test ------------- 13 Voltage Wave ----------- 16 Pictures of apparatus - ----- - 19 Appendix - ------------ 18 ¢ Blue Prints - eo ew Pe eel elle bet) * « INTRODUCTION. * » The manufacturers of electrical apparatus using sheet steel laminations require from the Steel Companies, material of guar- enteed quality as regards the magnetic losses. Some means had to be provided for the determination of these losses and the apparatus formerly used required the use of the balistic gal- vanometer. The sample were put up in ring form and the mag- netizing coils had to be wound on by hand. The samples being in the ring form required the expenditure of money for special machinery to punch them accurately from the sheets as they had to be either punched accurately to size, or turned to size after being punched. The winding of the magnetizing coils had to be very carefully done in order to obtain the correct number of turns. Before making the test the sample had to be carefully demagnetized, as a slight amount of magnetism would cause much error in the deflection of the galvanometer. A very careful test was then run, taking readings of the galwanometer deflection and current through the coil. From this data the hysteris loop was plotted and from the area of this curve the less in joules could be calculated. This loss in joules had then to be transformed into loss in watts, either per lb. or per Kg. This made a slow and expensive process of the test and for this reason it was not suited for commercial work. In an effort to better these conditions, Epstein brought out his apparatus for the determination of magnetic losses, whioh, with some modifications was adopted by the American Society for Testing Materials. The following notes pertain to an apparatus of this type. we STANDARD MAGNETIC TESTS OF IRON AND STEEL. . Chapter l. Core Loss. The power consumption in electtical sheet steel when subjected to an alternating magnetization is known as the core loss. The standard core loss is the total power in watts consumed in each kilogram of the material at a temperature of 385°9C., when subjected to a harmonical- ly varying induction having a maximum of 10,000 gausees 10,000 Maxwells per sq. C. M.) and a frequency of 60 Cycles per second, when measured as specified below. It is represented by the symbol W)0/60. The ageing coefficient is the percentage change in the standard core loss after continued heating at 100°C for 600 hours. Fad Chapter 3. Conditions of Test. The Standard core loss shall be measured under the following conditions: The magnetic circuit shall consist of 10 kg. (23 lbs) of the test material, cut with a sharp shear into strips 50 om, (19 11/16 ins.) long and 3 om. (1 3/16 ins) wide, half parallel and half at right angles to the direction of rolling, made up into four equal bundles, two containing material parallel and two containing material at right angles to the direction of rolling, and finally built into the four sides of a square with butt joints and opposite sides consisting of material out in the same manner. No insulation other than the natural soale of the material (except in the case of scale-free material) shall be used between the lamina- tions, but the corner joints shall be separated by a tough paper 0.01 om. (0.004 in) thick. Chapter 3. Specifications. The magnetizing winding shall consist of four solen- Oide surrounding the four sides of the magnetic circuit and joined in series. A secondary coil shall be used for ener- gizing the voltmeter and the potential coil of the watt- meter. These solenoids shall -be wound on a form of any non- magnetic non-conducting material of the following dimensions: Inside cross-section ......66 4 by 4 om. Winding length .......cclsss 48 ome The primary winding on each solenoid shall consist of 150 turns of copper wire wound uniformly over the 43 om. length. The total resistance of the magnetizing winding shall be between 0.3 and 0.5 ohm. The secondary winding of 150 turns on each solenoid shall be similarly wound beneath the primary winding. Ite resistance shall not exceed 1 ohm. The voltmeter and the voltage coil of the wattmeter shall be connected in parallel to the terminals of the secondary winding of the apparatus. The ourrent coil of the watt meter shall be connected in series with the primary winding. A sine wave electromotive force shall be applied to the primary winding and adjusted until the voltage of the + > secondary is given by the equation: p= SfNnBu » £HNn BM jo" - 4ID1loa, rot 42D in which f....form factor of primary E.M.F.... 1.11 for sine wave N.oeonumber of secondary turns .......600 N.oeenumber of cycles per second .... 60 BeeeeMaximum induction ......ceccesevee 10,000 H....total mass in grammB .....ccoese 10, 000 1....length of strips in om. ....... 50, = ota}, Leng Th D.-. specific gravity a cecceccececece 7.5 for high reeis- | . . tance steel. 7.7 for low-resis- tance steel. E... 106.6 volts for high resistance steel for sine voltage. Ek...-103.8 volts for low-resistance steel for sine volt- age. | A specific gravity of 7.5 is assumed for all steels having a resistance of over 2 ohms per meter-gram, and 7.7 for all steels having a resistance of less than 3 ohms per meter gram. These steels are designated as high and low resistance steels, respectively. The wattmeter gives the power consumed in the iron and in the secondary circuit. The loss in the secondary circuit is given in terms of the total resistance and the voltage. Subtracting this correction term from the total power gives the net power consumed in the steel as hysteresis and eddy current loss. Dividing this value by 10 gives the core loss per kilogram. id ° o . o * » . a . . ° oe « ‘ 9 ’ o Chapter 4, Procedure. The core loss material shall be cut from two or more sheets taken at random from the shipment. The strips should be distributed symetrically over the sheet, as nearly as may be practicable. For example,see plate No.l. Cut from the test material a number of strips 3 by 50 om. half at right angles and half parallel to the direction of rolling. Place on the balance a pile of strips weighing 25 kg, (5.5 lbs). Add a second pile of the same kind, bringing - the weight up 5 kg, (11 lbs). In each case the weight is taken to the nearest strip. Add in succession two piles of 3.5 kg, (5.5 lbs) each, of the other kind of strips, bringing the weight up to 7.5 kg (16.5 lbs} and 10 kg (22 lbs) respectively. Secure each bundle by string or tape (not wire) and insert in the apparatus as indicated. Apply the alternating voltage to the primary coil and tap the joints together until the current has a minimum value, as shown by the ammeter in series. Then clamp the corners firmly by some suitable device. pane Shunt the ammeter and adjust the primary curyent un= til the voltmeter indicates the proper value. This adjust- ment may be made by an auto-transformer, by varying the field of the alternator, or by both, but not by inserting resistance or inductance into the primary circuit. Simul- taneously the frequency must be adjusted to 60 cycles. Read the wattymeter. Calculations. Subtract from the wattmeter reading the instrument losses, which will be constant for any set of instruments and voltage, and divide by 10. The result is the standard core loss. Chapter 5. Details of Construction. The first detail considered was the construction of a form on which to shape the cores and wind the coils. This form was made of hardwood, according to the dimensions given on the detailed drawing, sheet #3. It was parted diagonally and held together by screws, one in each end. This construction allowed the form to be removed from the finished coil without binding, as after the screws were withdrawn the two parts could be taken out separately. The core was made of two layere of horn fiber, held together with glue, the joints being butted and on opposite sides of the core. This core was made about 1-1/2 in. longer than the winding length so that when the fiber ends were glued on none of the glue would work between the core and the wooden form, and thus cause difficulty in with- drawing the latter. The secondary winding was wound on first. The forn, with the core on it, was placed in a lathe set to cut nine threads per inch, and the wire was fed over a smooth groove in a tool set in the tool post. The ends of the wire were brought out through holes in the fiber next to the core. After wrapping one layer of thin fish paper on the second- ary coil, the primary wires were wound on in the same man- ner. Care was taken to have the winding smooth and in the same direction on each of the four coils. Each coil was > covered with a wrapping of heavy paper and shellaced. The inside surface of each core was also shellaced to provide protection against injury from the samples. The base was made from 5/8" redwood lumber, glued up in two layers of strips approximately five inches wide and twenty six inches long, the direction of the grain in the two layers being at right angles. Holes were drilled for wires, binding posts and screws. Blocks were made to sup- port the ends of the samples so that they would lie centrally in the colle, the bbocks being fastened to the base with brass screws. The next detail was the providing of suitable means for Clamping the ends of the samples during the test. The clamp- ing device selected consisted of two arms fastened at right angles to each other with a half lap joint in the center. Blocks were placed on the ends of the arms to bear on the ends of the samples. The clamping was effected by means of an eccentric lever which acted on the center of the cross arms. Adjustment of the pressure was obtained by means of thumb nuts, which raised or lowered the eccentric.