PEI (Peak Efficiency Index) Calculation

Transformer Losses

The Peak Efficiency Index (PEI) is used to evaluate the energy performance of power transformers under optimal loading conditions. The calculation is based on transformer losses and auxiliary power consumption of the cooling system.

The formula used for PEI calculation:


(%) PEI=1-[(2/Sr)*√((P0+Pc0+Pck(kPEI))*Pk)]
Symbol Description
P₀ No-load losses measured at rated voltage and rated frequency on the rated tap.
Pc0 Electrical power required by the cooling system for no-load operation, derived from the type-test measurements of the power taken by fan and liquid pump motors. For ONAN and ONAN/ONAF cooling systems, Pc0 is always zero.
Pck(kPEI) Electrical power required by the cooling system in addition to Pc0 to operate at kPEI times the rated load. Pck is a function of load and is derived from type-test measurements of fan and liquid pump motor power consumption. For ONAN cooling systems Pck is always zero.
Pk Measured load loss at rated current and rated frequency on the rated tap, corrected to the reference temperature.
Sr Rated power of the transformer or autotransformer on which Pk is based.
kPEI Load factor at which the Peak Efficiency Index occurs.
Note: The PEI concept is commonly used in transformer efficiency regulations such as Ecodesign requirements to ensure optimized transformer performance at the most frequently occurring load level rather than at full load.

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Transformer Manufacturer

DATSAN Transformer manufactures oil-immersed distribution and power transformers for industrial, utility, and infrastructure projects worldwide.

Established in 1992, DATSAN combines over 30 years of engineering experience with modern manufacturing and testing capabilities. Our products are designed in accordance with IEC 60076, ANSI C57 and relevant international standards, with Ecodesign-compliant options available upon request.

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Datsan Elk. İnş. San. ve Tic. Ltd. Şti.

Address: Kızıltepe Mardin Karayolu 6.km
Kızıltepe, 47400 Mardin / TÜRKİYE

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