Glossary
SIRIUS Innovations
System Manual, 01/2011, A8E56203870002-03
769
Protective technology
A basic distinction can be made between two current-based protective technologies: thermal
and electronic protection. Motor starter protectors and thermal overload relays provide
protection by means of bimetal releases, while solid-state overload relays, 3RW40 soft
starters, and 3RA6 compact starters offer protection via electronic means. Electronic
protective devices not only offer a significantly lower level of power loss, they also provide a
wide setting range of 1:4 and, as a result, much less variance than thermal releases. The
SIRIUS modular system offers the right solution for every type of switching technology.
Ramp time
With SIRIUS soft starters, the length of the set ramp time determines the time taken to
increase the motor voltage from the parameterized starting voltage to the line voltage. This
influences the motor's acceleration torque, which drives the load during the startup process.
A longer ramp time results in a lower acceleration torque as the motor is started up. The
startup is slower and smoother as a result. The ramp time should be long enough for the
motor to reach its nominal speed. If the time selected is too short, in other words if the ramp
time ends before the motor has started up successfully, a very high starting current that can
even equal the direct starting current at the same speed occurs at this instant.
Ramp-down time
The "Ramp-down time" potentiometer on the SIRIUS 3RW40 soft starter allows you to
specify how long power should still be supplied to the motor after the ON command has
been removed. The torque generated in the motor is reduced by means of a voltage ramp
function within this ramp-down time and the application stops smoothly.
Ramp-up detection for soft starters
The SIRIUS 3RW40 soft starter is equipped with an integrated ramp-up detection function. If
it detects a motor startup, the motor voltage is immediately increased to 100% of the line
voltage. The internal bypass contacts close and the thyristors are bridged.
Rated conditional short-circuit current I
q
The guaranteed short-circuit breaking capacity of switchgear assemblies and load feeders,
also called "rated conditional short-circuit current".
Rated data for the control circuit
The most important rated data for the control circuit in terms of selecting a contactor are the
rated control supply voltage U
s
(voltage of the coil terminal) with the associated frequency
(e.g. 50 Hz), as well as the power input of the coil (closing power and holding power).
Rated data for the main circuit
The most important rated data for the main circuit in terms of selecting a contactor are the
rated operational current I
e
(current specified by the conditions of use) or the rated power
(motor power), as well as the corresponding rated voltage U
e
.
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