RISK CRITERIA TO APPLY AND MANAGE DISTRIBUTION TRANSFORMERS

1
RISK CRITERIA TO APPLY AND MANAGE DISTRIBUTION
TRANSFORMERS

• M. A. Hernandez M. R. Gouvea
• ENERQ University of São Paulo

2
Objectives

• Solutions to minimize energy interruptions caused
  by failures in distribution transformers
• Reintroducing (from maintenance) distribution
  transformers in the system
• Evaluating the risk of failures of distribution
  transformers in operation

3
Sources of Transformer Failures

• Failures due to problems arising from
• severe system requirements (grounding, lightning
  protection, etc.)
• network installation procedures
• project design
• maintenance procedures

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Basic Methodology

• Evaluation of

Transformer Supportability (TS)
System Requirements (SR)
Compromise solution
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Transformer Supportability (TS)

• design characteristics
• operating characteristics
• The above characteristics lead to the evaluation
  of the TS indices

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System Requirements (SR)

• Physical characteristics
• location
• average expected rate of failures caused by
  trees, pollution, shielding from the buildings,
  grounding, etc.
• - supplied load with predictable behavior
• network design
• insulated cables to avoid short circuits
• underground network,
• etc.

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SR indices

• obtained by direct measuring of
• loading, voltage levels and statistical records
  of transformer failures, etc.
• obtained by network simulations
• loading from typical customer daily curves
• lightning performance

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Clustering network locations

• classifying the network locations where
  transformers may be installed,
• according to their physical, design and
  operational characteristics,
• grouping these locations according to similar
  characteristics
• representing each group through an element
  whose features equal
• the average characteristics of the group

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Transformer Clustering

• classify the transformers, according to their
  statistical indices
• - supportability under specific
  requirement levels,
• - expected economic life (calculated with
  Arrenius equation)
• - expected supportability in overvoltage
  situations according to
• technical standards
• - group these transformers according to similar
  characteristics
• represent each group through an element whose
  features equal
• the average characteristics of the group

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Two-dimensional Example
TS
Loading
SR
Minimise Associated Cost
(
)
-

D
TS
SR
f
C
TS
Over-voltage
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Optimization Model

• Propose a set of possible solutions for the
  allocation of transformers in the system
• Represent TS and SR, for each possible solution,
  in a n-dimensional space
• Determine the overall associated cost for each
  solution
• The Risk of each solution is represented by the
  convolution between the SR and TS statistical
  distributions
• The optimum solution is the best compromise
  solution comprising cost and risk associated to
  the set of distances between SR and TS

12
Conclusions

• The suggested methodology is an efficient tool to
  manage distribution transformers, in that it
• considers the technical characteristics of the
  transformers and the network locations in which
  they are applied
• optimizes associated costs
• avoids failures as it identifies risk areas
• Improves the presently used transformer
  management methodology by introducing new control
  parameters.