Siemens Sivacon S8, Планировочная информация

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104
SIVACON S8 Planning Principles – Glossary and rated parameters
Time values > 1 s can be converted with
I ² x t = constant.
For example, from I
cw
= 50 kA, 1 s,
I
cw
= 28.9 kA can be calculated for 3 s:
I
cw
( t
2
) =
t
1
t
2
I
cw
( t
1
) x
I
cw
(3 s) =
1 s
3 s
50 kA x = 28.9 kA
11.2 Rated parameters
The manufacturers of low-voltage switchgear and control-
gear assemblies specify rated values in accordance with
IEC 61439-1 and -2. For the low-voltage switching devices
applied, rated values must be stated which are in accord-
ance with the relevant product-specific standards from the
IEC 60947 series. These rated values apply to defined
operating conditions and characterise the usability of a
switchgear and controlgear assembly.
The following ratings in accordance with IEC 61439-1 and
-2 shall be the basis for assembly configurations:
Rated voltage U
n
The highest nominal value of alternating (root mean square
value) or direct voltage specified by the assembly manu-
facturer for which the main circuits of the switchgear and
controlgear assembly are designed.
Rated operational voltage U
e
(of a circuit in an assembly)
Value of voltage, declared by the assembly manufacturer,
which combined with the rated current determines its
application.
Rated insulation voltage U
i
Root mean square withstand voltage value, assigned by the
assembly manufacturer to the equipment or to a part of it,
characterising the specified (long-term) withstand capa-
bility of its insulation.
Rated impulse withstand voltage U
imp
Impulse withstand voltage value, declared by the assembly
manufacturer, characterising the specified withstand
capability of the insulation against transient overvoltages.
Rated current I
n
Value of current declared by the assembly manufacturer
which considers the equipment ratings and their
arrangement and use. It can be carried without the tem-
perature rise of various parts of the assembly exceeding
specified limits under specified conditions.
Rated peak withstand current I
pk
Value of peak short-circuit current, declared by the
assembly manufacturer, that can be withstood under
specified conditions.
Rated short-time withstand current I
cw
The root mean square value of short-time current, declared
by the assembly manufacturer, that can be withstood under
specified conditions, defined in terms of a current and
time.
Tab. 11/1: Factor n as a function of cos
j
and I
cw
n cos
j
Rated short-time withstand current
I
cw
1.5 0.7
I
cw
≤ 5 kA
1.7 0.7
5 kA <
I
cw
≤ 10 kA
2 0.3
10 kA <
I
cw
≤ 20 kA
2.1 0.25
20 kA <
I
cw
≤ 50 kA
2.2 0.2
5 kA <
I
cw
Rated conditional short-circuit current I
cc
Value of prospective short-circuit current, declared by the
assembly manufacturer, that can be withstood for the total
operating time (clearing time, duration of current flow) of
the short-circuit protective device (SCPD) under specified
conditions.
Rated current of the assembly I
nA
The rated current of the assembly is the smaller of:
• the sum of the rated currents of the incoming circuits
within the assembly operated in parallel;
• the total current which the main busbar is capable of
distributing in the particular assembly configuration.
Rated current of a circuit I
nc
The rated current of a circuit which is specified by the
assembly manufacturer depends on the rated values of the
individual items of electrical equipment in the circuit within
the assembly, their arrangement and their type of appli-
cation. The circuit must be capable of carrying this current
when operated alone without that overtemperatures in
individual components will exceed the limit values
specified.
Factor n = I
pk
/ I
cw
To determine the surge current, the root mean square.
value of the short-circuit current must be multiplied with
factor n. Tab. 11/1 lists values for n from IEC 61439-1.