Qualitrol 509ITM Series, Manual

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Oil Time
Constant
(4 fields) Allows you to set the time constant for the temperature rise of this
winding. The time constant is defined as the time it takes the winding
temperature to reach 63.2% of its final value for a given current input.
Note:
It takes approximately five time constants to elapse for the
temperature to reach full value for a given load. If the oil time
constant is not provided, the IEC 354 Loading Guide for Oil-
Immersed Power Transformers recommends:
For Distribution Transformers:
•
All cooling types: 180 minutes
For Medium and Large Transformers:
•
ON (natural convection): 150 minutes
•
OF (forced oil): 90 minutes
•
OD (directed forced oil): 90 minutes