Rated voltage (Un)
Highest nominal value of the a.c. (r.m.s) or d.c. voltage,
declared by the assembly manufacturer, to which the
main circuit(s) of the assembly is (are) designed to be
connected. In three-phase circuits, it is the voltage
between phases.
Rated operational voltage (Ue)
it is the rated voltage of a circuit of an assembly which
combined with the rated current of this circuit determines
its application. For three-phase circuits such voltage corresponds
to the voltage between phases.
In an assembly there are usually a main circuit with its
own rated voltage and one or more auxiliary circuits with
their own rated voltages.
The manufacturer of the assembly shall state the limits of
voltage necessary for correct functioning of the circuits
inside the assembly.
Rated insulation voltage (Ui)
it is the voltage value of a circuit of an assembly to which test voltages
(power frequency withstand voltage) andthe creepage distances are referred.
The rated voltage of each circuit shall not exceed its
rated insulation voltage.
Rated impulse withstand voltage (Uimp)
it is the peak value of an impulse voltage which the circuit
of an assembly is capable of withstanding under specified
conditions and to which the values of clearances
are referred. It shall be equal to or higher than the values
of the transient overvoltages occurring in the system in
which the assembly is inserted.
Rated current of the assembly (InA)
It is a new characteristic introduced by the Std. IEC
61439 and normally indicates the maximum incoming
permanent and allowable load current or the maximum
current which an assembly is capable of withstanding.
The rated current shall be withstood in any case, provided
that the temperature-rise limits stated by the Standard
are complied with.
Rated current of a circuit (InC)
It is the current value to be carried out by a circuit without
the temperature-rise of the various parts of the assembly
exceeding the limits specified according to the testing
conditions of Clause 7.
Rated short-time current (Icw)
it is the r.m.s. value of the current for the short-circuit test
for 1 s time; such value, declared by the manufacturer
does not imply the opening of the protective device
and is the value which the assembly can carry without
damage under specified conditions, defined in terms of
current and time. Different Icw values can be assigned to
an assembly for different times (e.g. 0.2 s; 3 s). Manufacturer,
can withstand satisfactorily for the operating
time of the device under the specified test conditions.
Rated diversity factor (RDF)
it is the per unit value of the rated current, assigned by
the assembly manufacturer, to which outgoing circuits
of an assembly can be continuously and simultaneously
loaded taking into account the mutual thermal influences.
The rated diversity factor can be stated:
- for groups of circuits;
- for the whole assembly.
The rated diversity factor is:
The rated diversity factor multiplied by the rated current
of the circuits (In) shall be equal to or higher than the
assumed loading of the outgoing circuits (Ib).
The rated diversity factor is applicable to the outgoing
circuits of the assembly and demonstrates that multiple
functional units can be partially loaded.
When the manufacturer states a rated diversity factor,
this factor shall be used for the temperature-rise test,
otherwise reference shall be made to the values recommended
by the Standard 61439-1 in Annex E.
Rated frequency
value of frequency to which the operating conditions are
referred. If the circuits of an assembly are designed for
different values of frequency, the rated frequency of each
circuit shall be given.
-ABB technical application papers
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