Nexus - 0218 - New Times Magazine-pages

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NEWSCIENCENEWSCIENCEN layer of thickness less than the 100 micron resulting from the bimetallic lamination eddy-current effect. makes the loop cllipti- dimension, the size of a magnetic domain feature. Having done Ph.D. research study- cal and the width of the loop, in tending to formed within the larger crystals of the ing anomalous eddy-current losses experi- fill more and more of a bounding geometri- y c i 8 8 material. mentally, I was particularly curious as I cal parallelogram form, is a measure of the | In the subject experiment, there was no had never heard of anyone ever before test- loss portion of the reactive volt-amp input. transverse deflection but the other condi- ing @ transformer built using bimetallic Remember that magnetic energy is stored tion was met. Commercially available steel Fe:Ni laminations. Moreover, I knew that I as inductance energy and, in oscillating, foil (known in the trade as ‘shim steel’) of 2. Was — pei ors — —— thin- this fern 4 — the loss which is repre- thousandths of an inch in thickness was ef, ough more conductive, than 1s cus- sen! ly that loop. obtained, and an electroplating firm was ‘mary in transformers. Added to this, = Now, what happened was astounding asked to coat one face with nickel using an knew from my Ph.D. research days during because, upon bringing the current input up electroless plating process. The nickel Which I measured the loss factors in differ- to near mid-range, the B-H loop became P & PI ~ : Sr coating was 0.7 thousandths of an inch in ¢Mt elemental sectors of the B-H loop, that very wide and quite clliptical. thickness. It was found that this could be - was a oe 2 ee, Furthermore, as expected, it shifted lateral- cut into small rectangles for assembly in a © © '0SS IM a part of the loop where It was ly by a small but very apparent amount 100 VA met may supplied fi kit least to be expected. (about 15%). However, the ultimate sur- form (e.g., by a Radio Shack dealer—RS in. In the event, what I found was astound- prise was that, as the current input UK). Thin card placed between the lami- ing in the light of my experience. I did not increased, the loop began to topple and tum natiqng War Lael ib fulete Gem feck = to do any ep such thin clockwise until, with a greater current, it cach other. The arrangement was as shown laminations magnetised wel low satura- actually went over so far as to lie in the in Fig, 1, with legs A and B being formed tion at + ~ power oem, the B-H ‘top-left to bottom-right’ sector of the oscil- oe ae ; Picture on the screen at low current was a_loscope screen, whereas it began at low bye beers pie. Panay ee straight line angled to represent the mag- current in the conventional ‘bottom-left to ondary windings, respectively series-con- ‘ sae A . A r Pipes netic permeability. The fact that it was a top-right’ orientation. nected in pairs, were formed oneach of the). rod line meant that there was negligible loss, i legs A and B. tog: . : This means that the transformer core ; P ._ Which is what I expected until a certain having the bimetallic laminations has either The tast involved cbetrving om mescil- dngshold was:reacherd nee a capacitor, which it is not, or the pret 2 nba tae I ati oe My reasoning was that the transformer phase governing the power and magneto- placa Pas pranery pul action would introduce heat into the core motive force reaction has inverted through 4 ; and that heat would be conducted away. I 180°. This is an obvious indication that the To present the B-H loop on an oscillo- had planned to arrange for the heat to flow core wants to act as a generator by which scope screen, the secondary winding was one way so as to set up a temperature dif- heat sustains a current producing its mag- comm ; iP per: pro 8 is connected across a 100 K resistor in series ference across the laminations, and then my _netisation and, instead of demanding input 7 : C y , insti g inp with a 2 WF capacitor and the y input to the presumption was that a DC current would current to set up the reaction to the chang- oscilloscope was taken across the capacitor circulate thermoelectrically and affect the ing magnetic flux, it produces current in a terminals. The H input was provided by form of the loop. Indeed, a DC bias would —_ forward direction augmenting that magnet- incorporating a series resistor in the prima- displace the position of the loop on the jc condition. In the experiment ting rt q e ‘he 100p periment, of course, ry feed circuit and taking the x input from screen both in the x and y directions. all that extra current drawn from heat goes the potential drop across that resistor. Note that a B-H loop with little eddy- into enhancing the eddy-current losses ‘ . Pp y 8 y What I was intending by this experiment current has a rather special shape represent- enormously. This is why the loop gets so was to estimate the eddy-current loss ing hysteresis effects. An over-dominant wide. Fig. 2 Fig. 1 NEXUS®55 ee LAYERS OF CARD INSULATION IN POLE GAPS BIMETALLIC Ni:Fe LAMINATIONS FEBRUARY - MARCH 1994