http://www.legislation.gov.uk/eur/2014/548/article/2/2014-05-21Commission Regulation (EU) No 548/2014 of 21 May 2014 on implementing Directive 2009/125/EC of the European Parliament and of the Council with regard to small, medium and large power transformersCommission Regulation (EU) No 548/2014Commission Regulation (EU) No 548/2014 of 21 May 2014 on implementing Directive 2009/125/EC of the European Parliament and of the Council with regard to small, medium and large power transformersKing's Printer of Acts of Parliamenthttps://webarchive.nationalarchives.gov.uk/eu-exit/https://eur-lex.europa.eu/legal-content/EN/TXT/?uri=CELEX:32014R0548texttext/xmlen2025-01-242014-05-21 Definitions Article 2 For the purpose of this Regulation and its annexes the following definitions shall apply. ‘Power transformer’ means a static piece of apparatus with two or more windings which, by electromagnetic induction, transforms a system of alternating voltage and current into another system of alternating voltage and current usually of different values and at the same frequency for the purpose of transmitting electrical power. ‘Small power transformer’ means a power transformer with a highest voltage for equipment not exceeding 1,1 kV. ‘Medium power transformer’ means a power transformer with a highest voltage for equipment higher than 1,1 kV, but not exceeding 36 kV and a rated power equal to or higher than 5 kVA but lower than 40 MVA. ‘Large power transformer’ means a power transformer with a highest voltage for equipment exceeding 36 kV and a rated power equal or higher than 5 kVA, or a rated power equal to or higher than 40 MVA regardless of the highest voltage for equipment. ‘Liquid-immersed transformer’ means a power transformer in which the magnetic circuit and windings are immersed in liquid. ‘Dry-type transformer’ means a power transformer in which the magnetic circuit and windings are not immersed in an insulating liquid. ‘Medium power pole mounted transformer’ means a power transformer with a rated power of up to 315 kVA suitable for outdoor service and designed to be mounted on the support structures of overhead power lines. ‘Voltage Regulation Distribution Transformer’ means a medium power transformer equipped with additional components, inside or outside of the transformer tank, to automatically control the input or output voltage of the transformer for on-load voltage regulation purposes. ‘Winding’ refers to the assembly of turns forming an electrical circuit associated with one of the voltages assigned to the transformer. ‘Rated voltage of a winding’ (Ur) is the voltage assigned to be applied, or developed at no-load, between the terminals of an untapped winding, or of a tapped winding connected on the principal tapping. ‘High-voltage winding’ refers to the winding having the highest rated voltage. ‘Highest voltage for equipment’ (Um) applicable to a transformer winding is the highest r.m.s phase-to-phase voltage in a three-phase system for which a transformer winding is designed in respect of its insulation. ‘Rated power’ (Sr) is a conventional value of apparent power assigned to a winding which, together with the rated voltage of the winding, determines its rated current. ‘Load loss’ (Pk) means the absorbed active power at rated frequency and reference temperature associated with a pair of windings when the rated current (tapping current) is flowing through the line terminal(s) of one of the windings and the terminals of the other windings are in short-circuit with any winding fitted with tappings connected to its principal tapping, while further windings, if existing, are open-circuited. ‘No load loss’ (Po) means the active power absorbed at rated frequency when the transformer is energised and the secondary circuit is open. The applied voltage is the rated voltage, and if the energized winding is fitted with a tapping, it is connected to its principal tapping. ‘Peak Efficiency Index’ (PEI) means the maximum value of the ratio of the transmitted apparent power of a transformer minus the electrical losses to the transmitted apparent power of the transformer.