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Parameter: Dropout threshold operate
•
Recommended setting value (_:105) Dropout threshold operate = 90 %
The Dropout threshold operate parameter is used to cancel pickup and tripping when the value drops
below this threshold. A setting on the order of magnitude of the warning threshold is recommended. You can
select a lower setting value for special applications, desired additional cooling, or longer blocking of switching
on.
The calculation of the operational measured value Time until close refers to this value.
Parameter: K-factor
•
Recommended setting value (_:106) K-factor = 1.1
The K-factor parameter is used to describe the limiting value for the maximum permissible continuous load.
The rated current I
sensing.
You can determine K-factor on the basis of the thermally permissible continuous current I
[fotolpkf-100810-01.tif, 2, en_US]
NOTE
i
i
The thermally permissible continuous current for the protected object is known from relevant tables or
from the specifications of the manufacturer!
Siemens recommends using the default value as it is a typical value for many applications.
Parameter: Thermal time constant
•
Default value (_:110) Thermal time constant = 900 s (15 min)
The Thermal time constant parameter is used to define the operate curve of the stage. If no time
constant is given, you can derive it from other values.
EXAMPLE
Protection of a current-limiting resistance
Rated current of the resistance: I
Values for the overload capability:
•
1.1 I
permanent (k-Factor = 1.1; k = 1.1)
rated
•
1.5 I
for 20 s for charge by cold
rated
The following time constant results from these assumed values:
[fo_time_constance_11082015, 1, en_US]
For Thermal time constant, set 26 s.
The following time-dependent characteristic results from the data. In case of a current increase to 1.5 I
the tripping occurs in 20 s.
SIPROTEC 5, High-Voltage Bay Controller, Manual
C53000-G5040-C015-9, Edition 11.2017
of the protected object (for example, resistance) is the basic current for overload
rated, obj
= 100 A
rated
Protection and Automation Functions
7.27 Thermal Overload Protection, 1-Phase
max, perm.
:
,
rated
897
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