ABB RELION REX640, Technical Manual, Page: 1386 / 1960

Distribution
Transformers Medium and Large power transformers
Cooling mode ONAN ONAN ONAF OFAF ODAF
Constant K21 (k
21
) 1.00 1.00 1.00 1.00 1.00
Constant K22 (k
22
) 1.00 1.00 1.00 1.00 1.00
Oil Time Constant
(
Շ
0
) [minutes]
180 210 150 90 90
Winding Tm Constant
(
Շ
w
) [minutes]
4 10 7 7 7
A transformer is a distribution transformer if the
Transformer rating setting < 2.5
MVA and
Transformer type is set to "Three phase" or if the Transformer rating
setting < 0.833 MVA and
Transformer type is set to "Single phase".
Transformer parameters vary with the material used for winding and insulating
oil. The
Parameter Sel method setting can be set to "Manual" and the constants
can be set individually through the
Oil exponent, Winding exponent, Constant K11,
Constant K21, Constant K22, Oil time constant and Winding Tm constant settings.
If
Parameter Sel method is set to "Manual", the Cooling mode setting has
no effect on the transformer parameters.
Since there is no direct
Cooling mode based time constants' selection
mentioned in the IEEE Std C57.91
™
- 2011 standard, the oil time constant
(
Շ
0
) and winding time constant (
Շ
w
) in
Table 1324
are kept same as in
Table 1323
.
For more accuracy, the values of the constants can be entered manually
by setting
Parameter Sel method to "Manual".
7.3.5.2 Top oil temp calculation
The function receives two sensor inputs for measuring top oil temperature and
ambient temperature.
The top oil temperature of the tank is obtained through a sensor placed at
the upper inner turn of the winding. If the top oil temperature sensor status
TOIL_SNSFLT
is FALSE, the top oil temperature is directly obtained from the
TOIL_TEMP
input.
If the status of
TOIL_SNSFLT
is TRUE, indicating that the sensor is faulty, the top oil
temperature is calculated with the help of measured ambient temperature.
The status of the ambient temperature sensor is obtained through the
AMB_SNSFLT
binary input. If
AMB_SNSFLT
is FALSE, indicating the healthy status of the sensor,
the ambient temperature is directly measured through the
AMB_TEMP
input. Else, if
AMB_SNSFLT
is TRUE, the ambient temperature is taken from the Average ambient
Tmp setting.
The formula for calculating the top oil temperature from the measured or set
ambient temperature is shown in
Equation 322
.
Condition monitoring functions 1MRS759142 F
1386 REX640
Technical Manual