Siemens SIRIUS 3RT Series System Manual page 770

Glossary
Rated impulse withstand voltage (U
Peak value of a surge voltage with a defined waveform and polarity, which can be applied to
the device under specified test conditions without the device failing and to which the
clearances refer. The rated impulse withstand voltage of a device must be equal to or
greater than the transient overvoltages which occur in the network on which the device is
being used.
Rated insulation voltage U
Voltage value which specifies the insulation strength of the switching device or accessory
and to which the insulation tests and the creepages and clearances refer. The maximum
rated operational voltage must not be greater than the rated insulation voltage under any
circumstances.
Rated service short-circuit breaking capacity I
Compared to the rated ultimate short-circuit breaking capacity I
are stricter and the short-circuit current is usually lower. Determined using test sequence II,
operating sequence O-t-CO-t-CO (O = open, t = time, CO = close-open). The function of the
motor starter protector/circuit breaker must remain unrestricted following this test.
Rated short-circuit breaking capacity I
According to IEC 60947-2 and DIN EN 60947-2, the rated short-circuit breaking capacity of a
motor starter protector/circuit breaker is the value of the short-circuit current, which it can
switch off at the rated operational voltage, rated frequency, and specified power factor (or
specified time constant). The value of the prospective current (for alternating current, the rms
value of the AC component) specified by the manufacturer applies. For AC motor starter
protectors/circuit breakers, the rated short-circuit breaking capacity must be independent of
the magnitude of the DC (direct-current) component. The rated short-circuit breaking
capacity also ensures that the motor starter protector/circuit breaker can switch off every
current up to the rated short-circuit breaking capacity in the event of a line-frequency
recovery voltage with 110% of the rated operational voltage.
This applies
● For alternating current, at every value of the power factor, but not lower than the value
defined in the relevant test specification
● For direct current, if no other specifications have been made to the contrary by the
manufacturer, with every time constant, but not greater than the value defined in the
relevant test specification.
The short-circuit breaking capacity does not apply in the event of a line-frequency recovery
voltage above 110% of the rated operational voltage.
Rated ultimate short-circuit breaking capacity I
Maximum short-circuit current I
which can switch the motor starter protector/circuit breaker off under specific conditions.
Determined using test sequence III, operating sequence O-t-CO (O = open, t = time,
CO = close-open). The function of the motor starter protector/circuit breaker may be
restricted following this test.
770
)
imp
i
cs
cn
cu
(limit value of the rated short-circuit breaking capacity),
k
, the test conditions here
cu
SIRIUS Innovations
System Manual, 01/2011, A8E56203870002-03