ABB RELION REX640 - Page 393

Figure 230: Effect of the Weighting factor p factor and the difference between the
two time constants and one time constant models
The actual temperature of the transformer is calculated by adding the ambient
temperature to the calculated temperature.
Θ Θ Θ= ∆ +
amb
(Equation 37)
Θ temperature in transformer (°C)
ΔΘ calculated temperature rise (°C) in transformer
Θ
amb
set value of the Env temperature Set setting or measured ambient tempera-
ture
The ambient temperature can be measured with RTD measurement. The measured
temperature value is connected, for example, from the AI_VAL3 output of the X130
RTD function to the AMB_TEMP input of T2PTTR.
The Env temperature Set setting is used to define the ambient temperature if
the ambient temperature measurement value is not connected to the AMB_TEMP
input. The
Env temperature Set setting is also used when the ambient temperature
measurement connected to T2PTTR is set to “Not in use” in the X130 RTD function.
The temperature calculation is initiated from the value defined with the Initial
temperature and Max temperature setting parameters. The initial value is a
percentage of Max temperature defined by Initial temperature . This is done when
the protection relay is powered up or the function is turned off and back on or reset
through the Clear menu. The temperature is stored in a nonvolatile memory and
restored if the protection relay is restarted.
The Max temperature setting defines the maximum temperature of the transformer
in degrees Celsius (°C). The value of the Max temperature setting is usually given by
1MRS759142 F
Protection functions
REX640
Technical Manual
393