Investigating the use of peak efficiency index as an alternative efficiency metric for distribution transformers

Transformer technical specification is the first step in establishing the long-term effectiveness of transformers in reducing greenhouse gas (GHG) emissions.

byDr. Bhaba P. Das


Transformer technical specification is the first step in establishing the long-term effectiveness of transformers in reducing greenhouse gas (GHG) emissions by considering efficiency metrics. It has been reported by the UN that almost 730 million tons/year are contributed by distribution transformers [1]. There are international policies that support the energy efficiency of distribution transformers, such as the Minimum Energy Performance Standards (MEPS) in many countries such as the United States of America [2], Australia [3], Vietnam [4] and Star Ratings [5] in India. Transformers complying with these standards have reduced losses, so they reduce energy consumption and consequently reduce the need for the generation of electrical energy and consequently GHG emissions. These broadly fall into two main categories:

  1. Specifying maximum no-load and load loss.
  2. Specifying minimum efficiency values at 50 % load.

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When no load loss and load loss are specified, this means that a minimum level of performance is assured, whatever the level of loading applied to the transformer. Similarly, when efficiency is specified, it allows transformer design engineers to trade off no-load and load losses while trying to produce an optimized transformer for a specific load. Apart from these two categories, IEC 60076-20 [6] also introduces another method of evaluating the energy performance of a transformer: the peak efficiency index (PEI), both for 50 Hz and 60 Hz transformers. IEC 60076-20 provides two levels of recommended PEI:

  1. Level 1 is for basic energy performance.
  2. Level 2 is for a high-energy performance.
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