英文关键词：Generalized Two Scalar Potential Method, Stray field, Transfmer. I. INTRODUCTION In large transfmer design, it is very imptant that the distributions of winding 3D stray field are known other relating parameters like stray loss of structure parts, winding mechanical fce at sht circuit are analyzed. However, because of both many kinds of media complicated geometric structure of 3D stray field in large transfmer, it is very difficult that 3D stray field is solved me exactly by using dinary computing method like A-φ, A so on, specially, f solving 3D eddy current problem in metal parts of having big size of both length width, thin thick, f example, eddy current loss in transfmer tank. F solving above problem me nicely, therefe, the model of winding 3D stray field in large transfmers is set up by using generalized two scalar magnetic potential method in this paper, penetrating phenomenon of electromagnetic wave in metallic parts is simulated by using surface impedance boundary condition. Then, 3D numerical analysis result is validated using both measuring value 2D numerical computing result of stray fields in typical transfmers, A number of useful conclusions in transfmer design are given[1-2]. II. MODEL Assumption: A. Both up down segment of tank, winding, tie-plate Manuscript received September 18, 2000. J. Wang, S. Song are with Baoding Tianwei Baobian Electric Co., Baoding 071056, China （telephone: +86-0312-3227971-5872）. X. Cui is with Nth China Electric Power University, Baoding 071003, China （telephone:+86-0312-5024951-2553）. so on are symmetrical along winding middle plane ofgeometric height, both front back segment of those parts is also symmetrical along plane consisted of center lines of three phase windings. B. The current densities of each subregion in the windings are unifm, the eddy effects of winding conducts are igned. C. The material of tank, tie-plate, clamp are linear, unifm, isotropical, bushing case lead are igned. By the above assumptions, the 3D simplified model of winding stray field of large transfmer can be acquired, as shown in Fig.1. Although the solved variable numbers of dinary two scalar magnetic potential method are less than those of vect potential methods, computing 3D magnetic field created by source current is trouble. Therefe, using generalized two scalar magnetic potential method f overcoming deficiency of dinary two scalar potential method, the function G of similar to magnetic field Hs created by source current like transfmer circular winding conducts can be defined as follows:B. Example Using the given model generalized two scalar magnetic potential method, 3D stray field eddy current losses of structure parts in typical transfmer are computed, they are compared with measuring value 2D computing result respectively. The computed partial results of magnetic field are shown in Fig.2~Fig.5. The sign * in Fig.4 represents measuring values of magnetic flux density component By Bz. As may be seen from Figures, the computed results of magnetic flux density is in consistence with the measured values. Because tangential component Bx（ By）in section yoz（ xoz）is less than two other components in cresponding section，the results computed by 2D numerical method are very good as seen in Fig.5（a,b,c）. The influences of magnetic media around sections both xoz yoz to magnetic flux density of same coil radial location are shown in Fig.3~Fig.4, the computing errs of magnetic flux density resulted from the difference of coil ampere turns arrangement are shown in Fig.2~Fig.4. When the eddy current losses in transfmer metallic parts are computed, the computing value of 3D eddy current losses （in tank, ce clamp ,tie-plate so on） is 0.593 if both relative permeability conductivity of metal material are 200 （s/m）respectively eddy loss is relative value. The measured value of eddy loss in cresponding metallic parts is 0.618. Relative err between both computation measurement of eddy loss is 4.05 per cent. The eddy current loss density in ce clamp is larger than that in other metallic parts its value is 5.6kw/m . When transfmers are designed, therefe, It is very imptant to prevent ce clamp from local overheat. IV. CONCLUSION Using the measuring result of stray field additional loss in typical transfmer, the generalized two scalar magnetic potential method used in this paper is validated. Furtherme, through comparative analyzing of computing results of both 3D 2D stray field, each advantage applicability of both 3D 2D method are shown respectively, thus, useful tool in transfmer design is given.REFERENCES[1] C. Lu, “Power transfmer computation”, China: Heilongjiang science technology publishing house, 1985（in Chinese）. [2] K. Zhou et al, “Theetical methods applications of numerical computation in engineering electromagnetic field”, Higher education publishing house, 1994 （in Chinese）.
