Siemens SIRIUS 3RT Series System Manual page 768

Glossary
Overload relay
Inverse-time delayed relay which responds to an overload in accordance with a time-current
characteristic, thus protecting the switching device and load from overloads.
Overload release
Overcurrent release that provides protection against overload.
Phase loss sensitivity
A product feature which enables the protective device to respond even when a three-phase
asynchronous motor is running in single-phase operation, before the motor sustains thermal
damage (DIN VDE 0660 Part 102).
Polarity balancing for soft starters
In 2-phase controlled SIRIUS 3RW30 and 3RW40 soft starters, the current that results from
the superimposition of the two controlled phases flows in the uncontrolled phase. The main
advantages of 2-phase control include the more compact size compared to a 3-phase
version and the lower hardware costs.
The occurrence of DC components, caused by the phase control and the overlapping of
phase currents, is a negative physical effect of 2-phase control during the startup process
that can mean a louder noise is produced by the motor. The "Polarity Balancing" control
principle was developed and patented by SIEMENS to prevent these DC components during
starting.
"Polarity Balancing" effectively eliminates these DC components during the startup phase. It
allows the motor to be started up with a constant speed, torque, and current rise. The
acoustic quality of the startup process comes very close to that of a 3-phase controlled
startup. This is made possible by the continuous dynamic alignment and balancing of current
half-waves with different polarities during motor startup.
Positively driven contacts for contactor relays
Positively driven contact elements are a combination of "n" NO contacts and "m" NC
contacts, which are designed such that they cannot be closed simultaneously (EN 60947-5-
1, Annex L).
Preferred wiring for star-delta (wye-delta) starters
According to the preferred wiring, the motor terminals of a motor running in the clockwise
direction are connected correctly if phase L1 is connected to motor terminals U1 and V2, L2
to V1 and W2, and L3 to W1 and U2. This order should be observed during installation in
order to keep the switchover current peaks in a motor running in the clockwise direction as
low as possible during switchover from star to delta operation.
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SIRIUS Innovations
System Manual, 01/2011, A8E56203870002-03