Development of Economical Analysis and Technical Solutions for Efficient Distribution Transformers

Development of Economical Analysis and Technical Solutions for Efficient

Distribution Transformers

Federal University of Itajubá and AES Sul Utility Company

Brazil

Federal University of Itajuba High Voltage Laboratory

Introduction

Operational Losses: No-load and load losses;

The losses are an important parameter in the evaluation of the total transformer costs: investment and operation costs;

Distribution systems: transformers are responsible for roughly one third of the total power losses;


Introduction

The proposal is to design an efficient distribution transformer:

The model the supplied load for a specific region load, peak and factor, and the load increase rate;

The analysis a set of transformer designs presenting reduced losses;

The steps: recognition of the problem, construction of a set of problem solutions and search for the optimal design.


Manufacturing and Total Costs Surfaces

The set of design possibilities considering manufacturing cost and total cost versus no-load and load losses.

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Manufacturing and Total Costs Surfaces

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Manufacturing Cost Surfaces

Variations in design parameters: magnetic induction density – no-load losses, LV winding current density and HV winding current density.

Each point on the surfaces represents a transformer design.

45 kVA mineral oilthree-phase Distributiontransformer


Total Costs Surfaces

The total cost depends on the impact of the energy costs on the no-load and load losses.

Period of the day (in hours) that the transformer

operates in full load condition with the same area (energy)

below the load cycle profile.

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Total Costs Surfaces

Total cost surfaces considering variations in LV winding current density, HV winding current density and magnetic induction density.


Design Surfaces: Establishing a set of solutions

The second step of this method : searching tool will try to find an optimal design;

Three-dimensional matrixes are built considering the variations in the design parameters;

• Thickness of the conductor of the LV winding;• Width of the conductor of the LV winding;

• Diameter of the conductor of the HV winding;• Magnetic induction;• Insulation thickness;• Clamp dimensions;

• Design of the end insulation;• Gap between LV and HV windings.


Design Surfaces: Establishing a set of solutions

The design surfaces are based on solution sets considering variations and relation on several transformer parameters.

The design has a current density of the

HV winding, an insulation thickness and a

magnetic induction


Optimal Design Based on the Surfaces

The optimal transformer design must present reduced loss costs: the points on the total cost surfaces represent an element of the three-dimensional design matrixes.



a) The first minimum cost is a random value;

b) For the iteration k, in the column j, each element c(i,j,k) is compared with the minimum cost value;

c) The search must satisfy the level of the no-load losses, load losses and short circuit impedance according the national or utility standards in the set of solutions;

d) The payback is defined by the customer.



The local minimum point results in a design in which the

purchase price is not attractive to the customer. Because

of this, global minimum points located between the local minimum

and the costs presented by a standard transformer

can be attractive economical solutions.


Optimal Design Related to the Time Supplying the Maximum Rated Power

It is possible to express the concept that for each TSMP

there are several efficient transformers to supply the

load. Some of them have the “best” manufacturing

characteristic and therefore are a logical choice. In theory this is

the “optimal technical and economical solution”

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Energy cost of 59.87 US$/MWh,Interest rate of 8% per year

and 10 years analysis period.

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kReduction of Total

Cost [%]Reduction of No-Load

Losses [%]Reduction of Load

Losses [%]

0 5.66 4.44 33.60

1 5.60 3.15 30.36

2 5.40 2.70 30.11

3 5.35 3.03 29.84

4 4.91 1.46 29.88

5 4.84 2.01 33.42

6 4.78 0.64 28.10

7 4.67 1.93 24.87

8 4.66 0.90 25.50

9 4.34 2.17 32.52

10 4.04 1.66 23.68



kReduction of

the Total Cost [%]

Pay-back, [Years]

Operational Cost Reduction per unit,

[US$/Year]

Energy Saved [MWh/Year]

0 5.66 2.50 75.09 1.3248

1 5.60 2.06 67.02 1.1195

2 5.40 2.20 66.07 1.1036

3 5.35 2.22 65.82 1.0995

4 4.91 2.49 64.40 1.0757

5 4.84 3.00 72.39 1.2092

6 4.78 3.26 59.84 0.9996

7 4.67 1.98 54.29 0.9068

8 4.66 2.02 54.36 0.9125

9 4.34 3.31 70.64 1.1801

10 4.04 2.38 51.51 0.8604



This analysis considers point (k=0) as being the “best” solution: maximum total cost reduction;

A payback perspective, this is not the “best” solution: assuming that all design options are feasible for manufacturing, the final solution will be related to the utility policy. For instance, from a payback standpoint, the answer is design 7;



However, design 9, presents the second operational cost reduction, would also be a possible choice;

Set of solutions variations on the current density of the HV winding, on the gap between the coils and on the design of the end insulation.



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Energy cost of 59.87 US$/MWh,Interest rate of 8% per year

and 10 years analysis period.



k Pay-back, [years]Reduction of No-Load

Losses [%]Energy Saved

[MWh/Year]

0 1.18 8.84 0.041

1 1.94 8.84 0.035

2 2.68 8.28 0.030

3 4.45 7.73 0.016

Magnetic Induction of Silicon Steel(E004)

1.68 Watts/kg



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kReduction of No-Load

Losses [%]

0 17.12

1 16.57

2 16.57

3 15.46

Magnetic Induction of Silicon Steel1.52 Watts/kg

The strong Goss orientation of grain oriented Silicon Steel is developedby secondary recrystallization.



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Study Case

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100 kVA Single-phase oil-immersed distribution

Transformer:Pay-back = 1.4 year

Saved money = 220.9 US$/year


Study Case


Conclusion

The time supplying maximum rated power (TSMP) is the first parameter to be considered in the design of an efficient distribution transformer;

This is related to the influence that this parameter bears on the cost of the transformer designs, mainly because it directly controls the load losses and plays an important indirect role in controlling the no-load losses;


Conclusion

The final choice must consider financial

restrictions, manufacturing process restrictions

and recommendations, the price of the main

transformer commodities, the utility internal

policy and governmental energy saving

regulations, all of which are normally conflicting

issues and therefore must be properly balanced.


Thank You for Your Attention

MSc. Alessandra Freitas Picanço

[email protected]

Prof. PhD. Manuel L. B. Martinez

[email protected]

+55 35 3622 3546

Minas Gerais, Brazil

mailto:[email protected]

mailto:[email protected]

Development of Economical Analysis and Technical Solutions for Efficient Distribution Transformers

Technology

design surfaces

optimal transformer

design options

atransformer design

total cost surfaces

total costs

set of design possibilities

reduction of total cost