With the following standardization:
[fonormie-310510-01.tif, 2, en_US]
Θ Current overtemperature, in relation to the final temperature at a maximum
permissible current k I
rated, obj
Θ
V
Standardized ambient temperature, where ϑ
Amb
describes the coupled ambient
temperature. The coupled ambient temperature ϑ
Amb
can be the measured
ambient temperature or the ambient temperature preset using the Default
temperature parameter.
Δ ϑ
rated obj
Overtemperature of the protected object set at rated current
τ
th
Thermal time constant (temperature rise/cooling) of the protected object
k This factor indicates the maximum continuous permissible phase current. The
factor refers to the rated current of the protected object (k = I
max
/I
rated, obj
)
I
rated., obj
Rated current of the protected object
At the same time, I
rated, obj
is the rated current of the protected object.
In a steady state, the solution to the thermal differential equation is an e-function whose asymptote repre-
sents the final overtemperature Θ
end
. The time constant τ
th
determines the rise. After reaching an initial adjust-
able overtemperature threshold Θ
warn
(Threshold thermal warn.), a warning indication is given.
If the overtemperature limit Θ
Off
(tripping overtemperature) is exceeded, an operate indication is immediately
issued and the equipment disconnected from the power supply. This threshold is specified at 100 % and corre-
sponds to the final temperature set at a flowing permissible continuous current (I
max
).
Figure 6-174 shows the temperature rise at different overload currents and the supervision thresholds.
[dwtempve-030211-01.tif, 1, en_US]
Figure 6-174 Temperature History for Different Overload Currents (K-factor = 1.1)
Protection and Automation Functions
6.21 Thermal Overload Protection, 1-Phase
678 SIPROTEC 5, Overcurrent Protection, Manual
C53000-G5040-C017-8, Edition 07.2017
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