Optimalization Design Rules

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International conference on

New trends in design and

Technical Documentation

2009

Peter Arras---------------------------------------------------------------------

Optimization of design rules

for power transformers

through FEA

Ing. Peter Arras

De Nayer, Belgium


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2009

Peter Arras---------------------------------------------------------------------

Introduction

Transformer design 2D

Optimalisation of the design process

Evaluation of existing design rules

FEA analaysis and conclusions

750MVA transformer

Conclusions.


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Power transformers: tailor made.

Pauwels Trafo: 60 years of tradition in transformers

2000 employees Represented in 135 countries


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Design of housing: 2D CAD

Example of 375 MVA transformer.Overall dimensions of housing:

approximatif 5x2.5x3 mm


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Design through 2D CAD:

Design based on experience

Design rules lead to a library of components

which is not changed.

Design rules are static: no changes because theimpact on the CAD-design would be to great.

Errors common to 2D design:

Missing/different dimensionsin different views

Missing components: toosmall details onthe big overall

drawingwere left out for the sake of the drawing, but

forgottenfor the extractionof workingdrawings.


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Optimalisation of the design process.

Evaluate existing design rules

Calculate through FEA strengths of

housings: calculations demanded by

the customers. Restructure design to 3D CAD.

Minimize dimensional errors


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Scheme of approach:

Evaluation of existing design rules: Calculation of 1 existing design

Calculation of 5 new designs with existing

design rules

Conclusions

Calculation of new 750MVAtransformer


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Evaluation of existing design rules

FEA calculation scheme: Stripping of the 2D design drawing for 3D

modelling of the housing.

3D- Modelling of the housing

Construction of the FEA-model over the 3D CAD-

model

Constraining/loading

Calculation

Conclusions.


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Stripping of the 2D design drawing

2D CAD model contains all components forcalculation of prices

Contains no dimensioning scheme

No full projection relation between views


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Stripped model.

Simplification of: Welds (left out)

Profiles (no fillets)

Components: only housing


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3D model: detail of inside

Corner reinforcements


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Technical Documentation2009

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FEA calculations

Calculations done with Pro Engineer

MechWildfire 3.0.

Test as a design tool Quick

Evaluate design rules:

Plate thickness Distance between strengthenings

Shape of strengthenings

Evaluate possible 3D design Recuperation of 3D CAD effort?


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FEA model

Analysis type: 3D shell model

Loadcases:

Vacuum load: zero pressure on inside, bottomof transformer constrained to ground

Lifting of transformer: weight of active part,

weight and hydrostatic pressure of oil fi ll ing,

own weight, constrained on 3 out 4 lifting

hooks.

Jacking of transformer: weight of active part,

weight and hydrostatic pressure of oil fi ll ing,own weight, constrained on 3 out 4 standing

feets/weel bases


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FEA model


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Conclusions

Design rules: Major design rules can be kept

Allowable material strength has to be reduced

from 240 MPa to 215 MPa

3D CAD solution: Complete 3D (detailed) design demands:

Training of personel Reworkof CAD-libraries

Only minor gain for FEA model: Needsa lot of stripping, feature removal

Solves: dimensional errors.

Missing components.


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750 MVA transformer.


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750 MVA transformer

Biggest transformer ever build at

Pauwels Trafo

Some facts: total weight 306.5 tons

active part: 131 tons

housing 10x4x4m high voltage isolators 1800 kg/each

Oil fill ing: 90000 l

Needs calculation of housing, coverand beams for active part


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Peter Arras---------------------------------------------------------------------

750 MVA transformer: calculation of housing

Applied rules: Distances between strengthenings according to

old rules

Material allowable strength: 215 MPa

Inner reinforcement triangles substituted with

long plate

Calculation: Load: vacuum, lifting and jacking.

Special care taken on excentric loading due to

heavy weight of high voltage isolators and

fitting.


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750 MVA transformer: 3D stripped model


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750 MVA transformer: FEA model

6000 shell elements, 7 beams and 3

mass-elements


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Results after adding extra reinforcements

Vacuumload.


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Stress while jacking the housing.


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Conclusions.

After 3D modelling the housing: Dimensional mistakes in 2D CAD drawing corrected

After calculation: Extra strengthening needed around high voltage fittings

Excessive bending in r ight end wall.

On design rules: New rules result in fair design Decreased allowable stress together with simple

increasing of wall thickness leads to easy changes in the

design. In earlier cases design were worked over with

more profiles, repositioning etc, which were time- andmoney consuming.

Optimalization Design Rules

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