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

3.9

Thermal Overload Protection (49)

Overview of the Function (49)
The thermal overload potection is used to:
•
Monitor the real-time thermal levels (θ) of the electrical equipment
•
Provide protection from thermal overload by tripping the electrical equipment
NOTE
i i
The thermal overload protection function (49) is not available for 7SR450[1/3]-xGA10-1AA0 MLFB variants.
Structure of the Function (49)
One thermal element is provided in the 7SR45 Argus Relay.
The temperature of the protected equipment is not measured directly. The function measures the thermal
level of the equipment based on hot curve & cold curve characteristics (as described in IEC 60255-149) and by
calculating the maximum RMS values of phase currents. If the RMS current rises above the 49 Overload
setting for a defined time, then an output signal to trip is given.
As per IEC 60255-149, the operating time is a function of the thermal heating time constant 49 TauH and
previous current levels.
[fo_thermal level operate time_deviceManual, 1, en_US]
where t = Time in minutes
τ = 49 TauH setting (in minutes)
ln = Natural logarithm
I = Measured RMS current
I = Previous steady-state current level
P
I = 49 Overload setting (same as the k ⋅ I
θ
k = Constant (1.05 predefined)
I = Basic current (same as I
B
Cold Operating Characteristics
The cold operating characteristic comes into effect when the relay has no prefault current and the previous
thermal level is 0. Thus, I
[fo_cold_operatetime_devicemanual, 1, en_US]
Hot Operating Characteristics
The hot operating characteristic comes into effect when the relay has a steady-state prefault current. This
current increases the previous thermal level above 0. The time to trip is given as:
[fo_thermal level operate time_deviceManual, 1, en_US]
Reyrolle, 7SR45, Device Manual
C53000-G7040-C101-2, Edition 09.2020
setting mentioned in IEC 60255-149)
B
)
rated
= 0 and the time to trip is given as:
P
Functions
3.9 Thermal Overload Protection (49)
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