Thermal Replica
The protection function calculates the overtemperature from the phase currents on the basis of a thermal
single-body model according to the thermal differential equation with
[fo_TOLP_diffgl, 1, en_US]
With the following standardization:
[fo_TOLP_normie, 1, en_US]
Θ Current overtemperature, in relation to the final temperature at a maximum permis-
sible phase current k I
rated, obj
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. The value is
calculated internally.
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
) and is calculated
internally.
I
rated, obj
Rated current of the protected object
[dw_TOLP_Temperature, 1, en_US]
Figure 6-170 Temperature History for Different Overload Currents ( K-factor = 1.1)
The overtemperature is calculated separately for each phase. The current overtemperature can be obtained
from the operational measured values. It is shown in percent. An indication of 100 % means that the thermal
threshold has been reached. The maximum overtemperature of the phases is regarded as the tripping temper-
ature. This means that the highest of the 3 phase currents is always assumed.
Protection and Automation Functions
6.20 Thermal Overload Protection, User-Defined Characteristic Curve
668 SIPROTEC 5, Overcurrent Protection, Manual
C53000-G5040-C017-8, Edition 07.2017
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