This European Standard covers medium power transformers. ‘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.
National practices may require the use of highest voltages for equipment up to (but not including) 52 kV, when the rated voltage is less than 36 kV (such as Um = 38,5 kV or Um = 40,5 kV). This is considered to be an unusual case of a large power transformer, where the requirements are those for
a medium power transformer with Um = 36 kV.
NOTE 1 ‘Large power transformer’ means a power transformer with a highest voltage for equipment
exceeding 36 kV and a rated power equal to or higher than 5 kVA, or a rated power equal to or higher than
40 MVA regardless of the highest voltage for equipment. Large power transformers are in the scope of EN 50629.
NOTE 2 Transformers with tap changer (DETC or OLTC) are included in this European Standard even if they
have separate tapping winding.
The object of this European Standard is to set up requirements related to electrical characteristics and design of medium power transformers.
The following transformers are excluded from this European Standard:
a) instrument transformers, specifically designed to supply measuring instruments, meters, relays
and other similar apparatus;
b) transformers with low-voltage windings specifically designed for use with rectifiers to provide a
c) transformers specifically designed to be directly connected to a furnace;
d) transformers specifically designed for offshore applications and floating offshore applications;
e) transformers specially designed for emergency installations;
f) transformers and auto-transformers specifically designed for railway feeding systems;
g) earthing or grounding transformers, this is, three-phase transformers intended to provide a
neutral point for system grounding purposes;
h) traction transformers mounted on rolling stock, this is, transformers connected to an AC or DC
contact line, directly or through a converter, used in fixed installations of railway applications;
i) starting transformers, specifically designed for starting three-phase induction motors so as to
eliminate supply voltage dips;
j) testing transformers, specifically designed to be used in a circuit to produce a specific voltage or
current for the purpose of testing electrical equipment;
k) welding transformers, specifically designed for use in arc welding equipment or resistance
l) transformers specifically designed for explosion-proof and underground mining applications;
m) transformers specifically designed for deep water (submerged) applications;
n) medium Voltage (MV) to Medium Voltage (MV) interface transformers up to 5 MVA;
o) large power transformers where it is demonstrated that for a particular application, technically feasible alternatives are not available to meet the minimum efficiency requirements set out by the commission regulation (EU) No 548/2014;
p) large power transformers which are like for like replacements in the same physical location/installation for existing large power transformers, where this replacement cannot be achieved without entailing disproportionate costs associated to their transportation and/or
In case one of the last two exclusions is claimed, this should be documented at the signature of the contract with a declaration made by the customer.
NOTE 3 This standard covers the transformers under the Commission Regulation (EU) No. 548/2014 and
gives additional specific guidance for single phase transformers, multi winding transformers and for transformers with OF or OD cooling systems, necessary for the correct application of energy efficiency requirements to these categories of transformers.