Siemens 6MD85, Manual

Page: 897 / 1256

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
rated, obj
of the protected object (for example, resistance) is the basic current for overload
sensing.
You can determine
K-factor
on the basis of the thermally permissible continuous current I
max, perm.
:
[fotolpkf-100810-01.tif, 2, en_US]
i i
NOTE
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
rated
= 100 A
Values for the overload capability:
•
1.1 I
rated
permanent (k-Factor = 1.1; k = 1.1)
•
1.5 I
rated
for 20 s for charge by cold
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
rated
,
the tripping occurs in 20 s.
Protection and Automation Functions
7.27 Thermal Overload Protection, 1-Phase
SIPROTEC 5, High-Voltage Bay Controller, Manual 897
C53000-G5040-C015-9, Edition 11.2017