ABB Relion 620 Series - Page 346

constant settings. The Short time constant setting describes the warming of the
transformer with respect to windings. The Long time constant setting describes
the warming of the transformer with respect to the oil. Using the two time-constant
model, the protection relay is able to follow both fast and slow changes in the
temperature of the protected object.
The Weighting factor p setting is the weighting factor between Short time constant
τ
1
and Long time constant τ
2
. The higher the value of the Weighting factor
p setting, the larger is the share of the steep part of the heating curve. When
Weighting factor p =1, only Short-time constant is used. When Weighting factor p =
0, only Long time constant is used.
Figure 172: 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 17)
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
Protection functions
1MRS757644 H
346 620 series
Technical Manual