Functions
2.7 Thermal Overload Protection 49
SIPROTEC, 7SD80, Manual
E50417-G1140-C474-A1, Release date 09.2011
113
Figure 2-45
Logic diagram of the thermal overload protection
2.7.2
Setting Notes
General
A prerequisite for the application of the thermal overload function is that during the configuration of the func-
tional scope in address
142
49
=
Enabled
was set. At address
4201
FCT 49
the function can be turned
ON
or
OFF
. Furthermore
Alarm Only
can be set. With the latter setting the protection function is active but only
outputs the indication
„49 Winding O/L“
(address 1517) when the tripping temperature is reached. The in-
dication
„49 Th O/L TRIP“
(address 1521) is not generated.
K-Factor
The nominal device current is used as a basis for overload detection. The setting factor k is set under address
4202
49 K-FACTOR
. It is determined by the relation between the permissible thermal continuous current and
this rated current:
The permissible continuous current is at the same time the current at which the e-function of the overtemper-
ature has its asymptote. It is not necessary to determine the tripping temperature since it results automatically
from the final rise temperature at k ·
I
N
. Manufacturers of electrical machines usually state the permissible con-
tinuous current. If no data are available, k is set to 1.1 times the nominal current of the protected object. For
cables, the permissible continuous current depends on the cross-section, the insulation material, the design
and the method of installation, and can be derived from the relevant tables.
Please note that the overload capability of electrical equipment relates to its primary current. This has to be
considered if the primary current differs from the rated current of the current transformers.
