WTI Trip setting for power transformers

[polo78]

Transformer life is determined by the condition of the solid insulation (the paper). Normal Kraft paper will begin to accelerate thermal ageing at 95 degrees Celsius and thermally upgraded paper will begin accelerated ageing at 110 degrees Celsius. The IEC 76-2 standard commonly accepts WTI relay tripping set point to be set at 140 degrees for a medium type power transformers.

What is the general view of the group members as to setting the WTI at 140 degree set point for a new transformer?

 

[prc]

Normally WTI is programmed for indicating the hot spot temperature in the winding.

Trip setting of the WTI can be a maximum of 120C ( maximum permissible hot spot winding temperature during normal cyclic loading as per IEC 60076-7 Loading Guide for Power Transformers)Alarm setting will be 10-15 C lower than trip setting.

But utilities usually set the trip contacts lower than 120C.