IEC 60076-2:2011 pdf Power transformers – Part 2: Temperature rise for liquid-immersed transformers
1 Scope
This part of IEC 60076 applies to liquid-immersed transformers, identifies power
transformers according to their cooling methods, defines temperature rise limits and gives
the methods for temperature rise tests.
2 Normative references
The following referenced documents are indispensable for the application of this document.
For dated references, only the edition cited applies. For undated references, the latest edition
of the referenced document (including any amendments) applies.
IEC 60076-1 , Power transformers – Part 1: General
IEC 60076-8:1 997, Power transformers – Part 8: Application guide
IEC 60085:2007, Electrical insulation – Thermal evaluation and designation
IEC 61 1 81 :2007, Mineral oil-filled electrical equipment – Application of dissolved gas analysis
(DGA) to factory tests on electrical equipment
IEC Guide 1 1 5:2007, Application of uncertainty of measurement to conformity assessment
activities in the electrotechnical sector
3 Terms and definitions
For the purposes of this document, the terms and definitions given in IEC 60076-1 and the
following apply.
3.1 external cooling medium
the medium external to the transformer cooling system (air or water) into which the heat
produced by the transformer losses is transferred
3.2 internal cooling medium
the liquid in contact with the windings and other transformer parts by means of which the heat
produced by the losses is transferred to the external cooling medium
NOTE The liquid can be mineral oil or other natural and synthetic liquid.
3.3 temperature rise
the difference between the temperature of the part under consideration (for example, the
average winding temperature) and the temperature of the external cooling medium
NOTE 1 In this standard, the use of insulating liquids K and L is considered only for safety and environmental reasons.
NOTE 2 In a transformer designated as having forced directed insulating liquid circulation (second code letter D),the rate of liquid flow through the main windings is determined by the pumps and is not, in principle, determined by the loading. A minor fraction of the flow of liquid through the cooling equipment may be directed as a controlled bypass to provide cooling for core and other parts outside the main windings. Regulating windings and/or other windings having relatively low power may also have non-directed circulation of bypass liquid.
In a transformer with forced, non-directed cooling (second code letter F), the rates of flow of liquid through all the windings are variable with the loading, and not directly related to the pumped flow through the cooling equipment.
4.2 Transformers with alternative cooling methods
A transformer may be specified with alternative cooling methods. In this case, the
specification and the rating plate shall then carry information about the power values at
which the transformer fulfils the temperature rise limits when these alternatives apply, see
IEC 60076-1 .
The power value for the alternative cooling methods with the highest cooling capacity is the
rated power of the transformer (or of an individual winding of a multi-winding transformer,
see IEC 60076-1 ). The alternatives cooling methods are conventionally listed in rising order
of cooling capacity.
Examples:
ONAN/ONAF. The transformer has a set of fans which may be put into service as desired
at high loading. The insulating liquid circulation is by thermosiphon effect only, in both
cases.
ONAN/OFAF. The transformer has cooling equipment with pumps and fans but is also
specified with a reduced rated power under natural cooling (for example, in case of failure
or reduction of auxiliary power).
5 Normal cooling conditions
5.1 Air-cooled transformers
Normal ambient temperature limits for power transformers are given in IEC 60076-1 .
IEC 60076-2:2011 pdf Power transformers – Part 2: Temperature rise for liquid-immersed transformers
