Transformer Modelling

This section covers the modelling of the 3 phase 100kVA Dry type energy

efficient switchable transformer designed, by using the finite element

modelling technique. The purpose of the modelling was to find out how the

magnetic flux density distribution, magnetic field intensity distribution, thermal

distribution on the industrial distribution transformer. In addition, the

transformer modelling with finite element method also allowed for the eddy

current present, impedance, and also power losses to be seen. This will allow

for the purposes of optimizing and increasing the performance of the power

transformer for the future design.

Before start modelling the transformer, first thing is to research the industrial

conventional transformer on its core size, window size as well as the volts per

turn, for this project, proj2007z team members have visited ETSA to obtain all

relevant 100kVA transformer information. After that, the transformer core is

designed by according to the AEM core manufacturer standard. For the dry

type transformer, the current density has to be maintained between 2.4A/mm2,

and all the design parameter is depending on this factor.

The purposes of developing the switchable transformer is to reducing the

copper losses produced during high load, and core losses produced during

low load period by switching the transformer to the parallel and series

configuration respectively. Modelling a transformer’s characteristic by applying

ANSYS finite element analysis, analysed the flux present in the transformer’

core material. This will model the effect of the core flux that has on the

transformer.

This modelling can be used to explore the effect has on the transformer core

once the changed applied to the coil configurations. Beside that, the effect on

the transformer performances and also the efficiency has on the transformer

can also be shown under the modelling of the finite element method. This

modelling provided a better way to investigate and hence more accurately

provided information of the transformer before the actual design of the

transformer.

Register Trademark of ANSYS Software

Finite Element Modelling (FEM)

The finite element modelling software used for modelled this 3 dimensional

100kVA distribution transformer is the ANSYS Multiphysics ver.10 software

elaborated with the PRO Engineering Wildfire 3.0 CAD software. The ANSYS

software is a powerful tool for the 2D and 3D finite element simulation

software with the ability to animate the results. Pro E CAD software is a

powerful tool to design in 3 Dimensional prospective hence it is user friendly

and it had in house experts that able to recommend the most suitable

software for the 3 Dimensional design.

Figure 1: 3 phases Dry type Transformer

[http://www.emeraldinsight.com/fig/1740200226017.png]

Construction of the 3 Dimensional Models

The first step of the finite element modelling is to construct a 3 dimensional

model with using the ProEngineering CAD software. From the reference of the

AEM core manufacturer data, the core selected is one size bigger than the

conventional 100kVA transformer. The core chosen was E600/110/120/190

where it indicated the high, depth, leg width and also the window width

respectively in millimetres. The figure below depicted the geometry model of a

100kVA power drawn by the ProEngineering CAD software.

Figure 2: Geometry model of 100kVA Transformer in ProE

Secondly, this geometry model was imported into ANSYS Multiphysics work

space and the figure below indicated the 100kVA geometry models in ANSYS

work space. The difference in colour indicated the phase A, B and C primary

and secondary winding and also the core material for the 100kVA energy

efficient transformer.

Figure 3: 100kVA transformer in ANSYS Environment

Step in the ANSYS Multiphysics Finite Element Analysis

Establishing Model

In defining the physics environment for an analysis, you establish a

mathematical simulation model for the physical problem. In the ANSYS

electromagnetic analysis, the electromagnetic fields are governed by

Maxwell’s Equations such as ,

, and also where

= magnetic field intensity vector

= total current density vector

= applied source current density vector

= induced eddy current density vector

= velocity current density vector

= electric flux density vector

= magnetic flux density vector

= electric charge density

Mesh Generation and Parameter Setting

In order to perform the finite element analysis of the 100kVA dry type

distribution transformer, the next thing is to perform transformer model

meshing. The ANSYS Multiphysics software provides with the ability to mesh

the model with triangle elements. The size of these triangle elements

determined how fine or how coarse the finite element modelling of the model

will be in the mesh calculation of the software. The triangles spacing can be

set as desired value depending on the setting during the meshing process of

the model. In the 3 dimensional analyses, the meshing is normally started with

the coarser so that to ensure that the computer used to perform the analysis

can cope with the memory taken during the operation. The area required

greatest or frequent change required finer triangle mesh size. For the case of

the transformer, the transformer core required much finer mesh size

compared to other element in order to verify the regions of the transformer

core with rapid changed that occur.

Figure 4: Build and Mesh of the100kVA Geometry model of transformer

For the model created, materials properties need to be assigned to each

component. Below showed the B-H table and material properties of the M3

high efficiency silicon steel for the electromagnetic material of the transformer

core. These values are inserted via the material library from the ANSYS

software.

Figure 5: B-H properties of M3 High Efficiency Silicon Steel

Applied Boundary Condition and Load

This modelling for the 100kVA transformer model in three phases 3

dimensional, the primary coil has the width of 60.0559mm whereas the

secondary coil has the width of 19mm with in between the both winding, it has

a insulator of about 3mm thickness. The core has dimension of 600mm

window height, 190mm for the window width, 110mm for the leg width and

with depth of 120mm as shown on the geometry model shown on figure 1.

The primary coil has total 2097turns numbers of winding, and secondary has

the total winding of 115turns. This transformer is modelled by stranded coil

with SOURC36 and a solid conductor using solenoid (F,,amps) loading. This

demonstration was intended the main flux of the coil in three phases

transformer.

Figure 6: Applied load and energy distribution model

The green colour indicated the applied voltage; the purple colour indicated the

current distribution on the coil of the transformer.

Conclusion

The development of the model was not an easy and beside that it is very time

consuming to produce a model. The model was required to duplicate the

physical transformer itself to be as accurate as possible to the actual condition

itself. In order to achieve or modelled an actual transformer, it required a

brilliant idea and intricate knowledge regarding the quality of the core and also

how does it effects the performance of the model as the difference DOF was

selected.

ANSYS Multiphysics is a software that required a lot of practices and also it is

very powerful on the three dimensional analysis of the finite element model.

But due to the time constraint, the overall transformer modelling is unable to

complete on the time given. Therefore this project might be carried on by the

new project students to accomplish for next year.

Generally, in actual transformer the flux leakage into the surrounding air

would be substantially higher for the central leg thus it can reduced the flux

density on the other two of the outer core legs.

This finite element modelling is worth learning for further use for work, but

again the finite element modelling on three dimensional performance of the

transformer required great deal on knowledge and also required a lot

practicing on the software use.