ABB RELION REX640 Technical Manual page 1393

1MRS759142 F
Figure 791: Location of top oil sensor
WARNING and ALARM signals are provided for the operator to take corrective
actions to reduce the temperature inside the transformer. Corrective actions include
switching on coolers, reducing the load on the transformers and so on.
The function only calculates hot-spot temperature based on the load factor of the
winding. This function does not calculate the rise in actual hot-spot temperature,
which occurs due to oil flow blockage or malfunction of cooler groups. That said,
the set oil and winding properties can be updated manually to indicate this change.
Based on the calculated hot-spot temperature, the function calculates the relative
ageing, that is, the accelerated or decelerated ageing of the insulation at current
load compared to its ageing at rated load. The variation of ageing acceleration
factor with respect to the hot-spot temperature for a sample transformer is plotted
Figure 792
in
an ageing acceleration factor of 1.0 is achieved.
REX640
Technical Manual
Normally, warning level is set to indicate if the temperature is nearing
the limiting value and alarm is generated when the limiting condition has
reached. Hence, alarm level is set at a higher value than the warning level.
. Here, 110 °C is taken as the rated hot-spot temperature at which point
Condition monitoring functions
1393