Qualitrol 509ITM Series, Manual

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Winding Time
Constant 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 time
constant is unknown, the IEEE Std C57.91-1995 Annex G
recommends a value between 3 and 7 minutes. Qualitrol uses a
default value of 6 minutes.
Oil Rise Parameters
This section of the Simple CT Temperature Scaling Setup window includes the parameters
that are required if you want to use the Critical Forecast feature of the TransLife
TM
Setup. If
you are not using the Critical Forecast feature, leave these parameters at the default values.
The fields in this section are described below.
Oil rise
temperature Allows you to set the temperature rise value of the transformer oil at
nominal load. This is derived from the Transformer Heat Run Report by
taking the value of the
Oil Rise Temperature field over ambient at
nominal load, and subtracting the ambient test temperature.
Oil Rise Temp = (Oil Rise Temp over Ambient - Ambient Temp)
Oil time
constant 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 (oil forced): 90 minutes
•
OD (oil directed): 90 minutes