Siemens SIPROTEC 7ST6, Руководство пользователя, Страница: 99 / 356

2.7 Thermal Overload Protection
99
7ST6 Manual
E50417-G1176-C251-A3
2.7.4 Setting Notes
General A prerequisite for the application of the thermal overload function is that during the
configuration of the functional scope in address
142 Therm.Overload
=
Enabled
was set. The function can be turned
ON
or
OFF
in address
4201 Ther. OVER LOAD
.
When overload protection is disabled, the thermal replica will also be reset.
Time Constant
τ
The thermal time constant
τ
is set at address
4203 TAU
. This is also provided by the
manufacturer. Please note that the time constant must be set in minutes. Quite often
other values for determining the time constant are stated which can be converted into
the time constant as follows:
permissible current for an application time of 1s (1-s-Strom)
Example:
Regular overhead contact line Re250 with
Perm. 1-s-current 10.5 kA
Perm. continuous catenary current 750 A
Set value
TAU
= 3.3 min
Permissible current for application time other than 1 s, e.g. for 0.5 s
Limit Current
Factor k ITRise The limit current factor is set in address
4204 k ITRise
. It is determined by the re-
lation 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-func-
tion of the overtemperature has its asymptote. Manufacturers of electrical machines
usually state the permissible continuous current. If no data are available, k ITRise is
set to 1.2 times the rated current of the protected object. For conducting lines, the per-
missible continuous current depends on the cross section, the insulation material, the
design and the way they are laid, 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.
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