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Transformer
Seasonal Loading Analysis Guidelines
This DSTAR project develops
guidelines for determining how to divide the year into loading analysis periods,
and how to represent the load and ambient temperature cycles in each of these
periods
Transformer kVA ratings do not
pose an absolute limit to loading but simply represent the load capacity at
which the transformer could be expected to have a nominal service life if loaded
continuously to this rating at a constant ambient temperature of 30 °C.
Distribution transformers are routinely applied so that the peak load is well
above the rated capacity. The consequence of the overloading is increased
winding temperatures, which lead to accelerated aging. Because the transformers
are typically loaded to well below rating most of the time, there are tradeoffs
between the slower-than-nominal aging during underloaded periods and accelerated
aging during overloads. The industry has developed transformer loading analysis
algorithms to model transformer thermal behavior and insulation aging, allowing
the inherent overloadability of distribution transformers to be exploited. There
are a number of software tools available to perform this analysis, including two
tools developed by DSTAR: Transformer Owning
Cost Software (TOCS), and
Transformer Loading
Analyzer (TLA). These tools, and others available in the industry, perform
transformer loading analysis on a seasonal basis, with a representative hourly
daily demand curve and ambient temperature curve representing the transformer
behavior for all days in each of four seasons.
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