ABB RELION REX640 Technical Manual page 376

Section 4
Protection functions
370
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Figure 205: 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
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Θ temperature in transformer (°C)
ΔΘ calculated temperature rise (°C) in transformer
Env temperature Set setting or measured ambient temperature
Θ set value of the
amb
The ambient temperature can be measured with RTD measurement. The measured
temperature value is connected, for example, from the AI_VAL3 output of the 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 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
1MRS759142 C
(Equation 36)
REX640
Technical Manual