© Experimental and Numerical Analysis of Shorted Interlaminations in Transformer Cores Ivan A. Hernandez-Robles Departamento de Electronica y Control Centro de Tecnología Avanzada, CONACYT-CIATEQ A.C. San Luis Potosi, Mexico ivan.hernandez@ciateq.mx Juan C. Olivares-Galvan, Irvin Lopez-Garcia, J. Luis Hernandez- Avila, R. Escarela-Perez, Departamento de Energia Universidad Autonoma Metropolitana, Mexico D.F. jolivares@correo.azc.uam.mx Salvador Magdaleno-Adame Magnetic Engineering Department Correlated Magnetics Research Huntsville, AL, USA transformer.consultant@gmail.com Abstract— This paper presents an experimental and numerical analysis regarding shorted electrical steel laminations of core of a small transformer core (120 VA single-phase shell- type transformer). Experimental tests were performed to measure the core losses of the transformer with and without shorted electrical steel laminations. Soft solder was utilized to produce the shorted region in the transformer core. Furthermore, 3-D Finite Element (FE) simulations were carried out to compute the eddy current losses in the core of transformer with shorted electrical steel laminations. The laminations of the core and their insulation were taken into account in the transformer model. Finally, several FE simulations were performed to calculate the eddy current losses for several cases, where the location and size of the shorted lamination region was varied in the core of transformer. Keywords—core loss; eddy current loss; electrical steel; finite element; interlamination; insulation; no load test; steady state I. INTRODUCTION The importance to quantify the effects of shorted interlaminations have increased since transformer manufactures want to reduce core fault losses, avoid scrap and thereby economic losses; the analysis and results obtained in this paper intended be a support tool for the engineers in charge in solving this issue. Shorted laminations are a critic problem in power transformers that can eventually escalate into catastrophic faults and probably result in an overall network failure. The name "electrical steel" refers to special steel grade, it has good magnetic properties such as magnetization curve, permeability, coercive field, and core losses (W/kg). These materials are typically used to manufacture inductors, reactors, electric motors, and transformers. Basically, these steels are alloys of Fe-Si and they are laminated materials having a thickness of less than 0.5 mm. For transformers usually the thickness is in the range of 0.18 to 0.27 mm [1]. There are many factors that are considered as possible causes of increase of core losses: i) Improper handling of the core steel during transformer manufacturing (see Fig. 1(a)); ii) Poor insulation coating of lamination layers (see Fig. 1(b)); iii) Improper arrangements of air gap regions (see Fig. 2); iv) Burrs forming at slit edges or at the cut joints; v) Geometry of core pile during annealing for a batch-type furnace [2]; vi) Thermal cycle of core annealing not fulfilled, for example annealing time is incomplete [3]; vii) Atmosphere inside of the furnace during the annealing process; viii) Length of the air gaps [4]; ix) Dimensions of the core, especially the thickness; x) Number of electrical laminations per layer [5]; xi) When the carbon steel clamping frames make contact with the edges of the steel laminations of transformer core (see Fig. 3). Factors i), ii), iv), vi) and xi) can often produce shorted laminations. a) b) Fig. 1. Factors that increase core losses in the transformer. a) Mechanical stress is produced in laminations in the process involving a radius that is too small and sharp corners; b) The insulation coating of the laminations is damaged when there is an incorrect handling of the core steel during manufacturing. Burrs on individual steel laminations caused by poor cutting processes can create electrical connections between adjacent 2016 IEEE PES Transmission & Distribution Conference and Exposition - Latin America (PES T&D-LA). Morelia, Mexico 978-1-5090-2875-7/16/$31.00 ©2016 IEEE