IEC 60076-12:2008

FOREWORD
INTRODUCTION
1 Scope
2 Normative references
3 Terms and definitions
4 Effect of loading beyond nameplate rating
  4.1 General
  4.2 General consequences
  4.3 Effects and hazards of short-time emergency loading
  4.4 Effects of long-time emergency loading
5 Ageing and transformer insulation lifetime
  5.1 General
  5.2 Lifetime
  5.3 Relation between constant continuous load and
       temperature
  5.4 Ageing rate
  5.5 Lifetime consumption
  5.6 Hot-spot temperature in steady state
  5.7 Assumed hot-spot factor
  5.8 Hot-spot temperature rises at varying ambient
       temperature and load conditions
  5.9 Loading equations
       5.9.1 Continuous loading
       5.9.2 Transient loading
  5.10 Determination of winding time constant
       5.10.1 General
       5.10.2 Time constant calculation method
       5.10.3 Time constant test method
  5.11 Determination of winding time constant according
       to empirical constant
  5.12 Calculation of loading capability
6 Limitations
  6.1 Current and temperature limitations
  6.2 Other limitations
       6.2.1 Magnetic leakage field in structural metallic
              parts
       6.2.2 Accessories and other considerations
       6.2.3 Transformers in an enclosure
       6.2.4 Outdoor ambient conditions
Annex A (informative) Ageing rate
Annex B (informative) Examples of lifetime consumptions
        for 3 load regimes
Annex C (informative) List of symbols
Bibliography

IEC 60076-12:2008 is applicable to dry-type transformers according to the scope of IEC 60076-11. It provides the means to estimate ageing rate and consumption of lifetime of the transformer insulation as a function of the operating temperature, time and the loading of the transformer.