Figure 792: Variation of insulation ageing factor with hot-spot temperature (Graph
produced using values from Table 11 of IEEE Std. C57.91-1995)
The variation of insulation life with respect to the hot-spot temperature depends
upon the type of insulation paper used. Thermally upgraded insulation paper
neutralizes the production of acids caused by the hydrolysis of the material over
the lifetime of the transformer and slows down insulation ageing when compared to
the normal insulation paper (IEC 60076-7). The proper selection of insulation paper
type is needed for better accuracy of loss of life calculation.
In certain cases, it is necessary to monitor the loading of the transformer over a
defined time period. For example, during a planned overloading of a transformer for
a period of one month. In such cases it is important to know the ageing rate during
that period of overload rather than the overall loss of life transformer. Hence, an
additional output on average ageing rate over a settable average ageing period is
provided in the function.
The function can be applied for new transformers and also for transformers already
in service using the
Initial loss of life
setting.
7.3.7 Signals
7.3.7.1 HSARSPTR Input signals
Table 1325: HSARSPTR Input signals
Name
Type Default Description
I3P SIGNAL - Three-phase currents
TOIL_TEMP FLOAT32 0 Measured top oil tem-
perature
AMB_TEMP FLOAT32 0 Measured ambient
temperature
Table continues on the next page
Condition monitoring functions 1MRS759142 F
1394 REX640
Technical Manual
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