Thermal Overload (49); Thermal Overload - Siemens Reyrolle 7SR45 Argus Device Manual

5.6

Thermal Overload (49)

Continuous overload current can cause the electrical equipment (cables/transformers) to heat above the rated
temperature or thermal equilibrium. This would result in damage to the protected equipment. In order to
overcome this issue, the electrical equipment must be protected from Thermal Overload.
The thermal overload function monitors thermal levels (θ) of the electrical equipment thus tripping them in
case of thermal overload. The function prevents re-energizing of electrical equipment until the equipment is
cooled.
The element uses maximum RMS value of phase currents to estimate the real-time thermal level (θ) of cables
or transformers. The thermal level is based on both past and present current levels, thermal level θ = 100 % for
maximum thermal withstand of equipment or the trip threshold.
[dw_7SR45_thermaloverloadheat&coolchar, 1, en_US]
Figure 5-7
Behavior in Case of Power Supply Failure (Aux/CT Power)
In case of power supply failure, depending on the selection of the setting, the thermal level stored in the
non‑volatile memory will either be the initial level or the previous level. In the latter case, the thermal replica
uses the stored value for calculation and matches it to the operating conditions.
Thermal trip followed by power restored
Case 1: Initial level θ = 30 %
[dw_7SR45_thermallevel_initiallevel, 1, en_US]
Reyrolle, 7SR45, Device Manual
C53000-G7040-C101-2, Edition 09.2020
Thermal Overload Heating and Cooling Characteristic
Applications

5.6 Thermal Overload (49)

99