Functions
2.23 Thermal Overload Protection
SIPROTEC, 7SD5, Manual
C53000-G1176-C169-5, Release date 02.2011
417
Calculating the overtemperature
The thermal replica is calculated individually for each phase. Address
4206
CALC. METHOD
decides whether
the highest of the three calculated temperatures (
Θ
max
) or their arithmetic average (
Average
Θ
) or the tem-
perature calculated from the phase with maximum current (
Θ
from Imax
) should be decisive for the thermal
alarm and tripping stage.
Since overload is usually a symmetrical process, this setting is of minor importance. If asymmetrical overloads
are to be expected, however, these options lead to different results.
Averaging should only be used if a rapid thermal equilibrium is possible in the protected object, e.g. with belted
cables. If the three phases are, however, more or less thermally isolated (e.g. single conductor cables or over-
head lines), one of the maximum settings should be chosen at any rate.
2.23.3
Settings
The table indicates region-specific presettings. Column C (configuration) indicates the corresponding second-
ary nominal current of the current transformer.
2.23.4
Information List
Addr.
Parameter
C
Setting Options
Default Setting
Comments
4201
Ther. OVERLOAD
OFF
ON
Alarm Only
OFF
Thermal overload protec-
tion
4202
K-FACTOR
0.10 .. 4.00
1.10
K-Factor
4203
TIME CONSTANT
1.0 .. 999.9 min
100.0 min
Time Constant
4204
Θ
ALARM
50 .. 100 %
90 %
Thermal Alarm Stage
4205
I ALARM
1A
0.10 .. 4.00 A
1.00 A
Current Overload Alarm
Setpoint
5A
0.50 .. 20.00 A
5.00 A
4206
CALC. METHOD
Θ
max
Average
Θ
Θ
from Imax
Θ
max
Method of Acquiring Tem-
perature
No.
Information
Type of In-
formation
Comments
1503
>BLK ThOverload
SP
>BLOCK Thermal Overload Protection
1511
Th.Overload OFF
OUT
Thermal Overload Protection OFF
1512
Th.Overload BLK
OUT
Thermal Overload Protection BLOCKED
1513
Th.O/L ACTIVE
OUT
Thermal Overload Protection ACTIVE
1515
Th.O/L I Alarm
OUT
Th. Overload: Current Alarm (I alarm)
1516
Th.O/L
Θ
Alarm
OUT
Th. Overload Alarm: Near Thermal Trip
1517
Th.O/L Pickup
OUT
Th. Overload Pickup before trip
1521
Th.O/L TRIP
OUT
Th. Overload TRIP command