Siemens 7SK80 Manual page 161

Ambient or Coolant Temperature
The specifications made up to now are sufficient to model the overtemperature. The ambient or coolant tem-
perature, however, can also be processed. This has to be communicated to the device as digitalized measured
value via the interface. During configuration, parameter 142 49 must be set to With amb. temp..
If the ambient temperature detection is used, the user must be aware that the 49 K-FACTOR to be set refers
to an ambient temperature of 104° F or 40° C, i.e. it corresponds to the maximum permissible current at a tem-
perature of 104° F or 40° C.
Since all calculations are performed with standardized quantities, the ambient temperature must also be stan-
dardized. The temperature at nominal current is used as standardized quantity. If the nominal current deviates
from the nominal CT current, the temperature must be adapted according to the formula following. In address
4209 or 4210 49 TEMP. RISE I the temperature adapted to the nominal transformer current is set. This
setting value is used as standardization quantity for the ambient temperature input.
with
Θ
Nomsec
Θ
Nom Mach
I
Nom CT prim
I
Nom Mach
If the temperature input is used, the tripping times change if the coolant temperature deviates from the internal
reference temperature of 104° F or 40° C. The following formula can be used to calculate the tripping time:
with
τ
k
I
Nom
I
I
Pre
Θ
Nom
Θ
k
SIPROTEC, 7SK80, Manual
E50417-G1140-C344-A5, Release date 11.2012
Machine temperatur at secondary nominal current = setting at the protection device (address
4209 or 4210)
Machine temperature at nominal machine current
Nominal primary CT current
Nominal current of the machine
TIME CONSTANT (address 4203)
49 K-FACTOR (address 4202)
Nominal device current in A
Fault current through phase in A
Prefault current
Temperature at nominal current I
Coolant temperature input (scaling with address 4209 or 4210)
(address 4209 49 TEMP. RISE I)
Nom
Functions
2.9 Thermal Overload Protection 49
161