Line-Side Contactors And Circuit Breakers - Siemens SINAMICS G130 Engineering Manual

Fundamental Principles and System Description
Engineering Information
1.2.12

Line-side contactors and circuit breakers

General
Line-side, electromagnetically actuated switchgear is required in many applications in order to automatically
connect/disconnect the SINAMICS converters to/from the supply system. In some instances, electromagnetically
actuated switchgear is an essential requirement, for example, if it is needed to precharge the DC link or to implement
the safety functions EMERGENCY OFF or EMERGENCY STOP which require automatic electrical isolation of the
converter from the supply system.
Contactors or circuit breakers can be used as electromagnetically actuated switchgear on the line side. These are
available as system components for SINAMICS G130 Chassis units and for the modular SINAMICS S120 Chassis
units (catalogs D 11 and D 21.3). Contactors or circuit breakers are either available as an option or installed as
standard (depending on the unit type) in SINAMICS G150 and S150 cabinet units and SINAMICS S120 converter
cabinet units in Cabinet Modules format.
For the SINAMICS devices described in this engineering manual, contactors are recommended as system
components for Chassis units with rated currents of ≤ 800 A and circuit breakers for Chassis units with rated currents
of > 800 A. Contactors are also available as options or fitted as standard switchgear for cabinet units with rated
currents of ≤ 800 A and circuit breakers for cabinet units with rated currents of > 800 A.
Exception: With parallel connections of SINAMICS G150 converters, contactors are used as standard for rated
currents of < 1500 A and circuit breakers for rated currents of ≥ 1500 A.
Contactors from the SIRIUS 3RT14 range Circuit breakers from the SENTRON 3WL range
Contactors
Contactors are switchgear only and do not perform any protective function when making on a short circuit or breaking
a short circuit which has developed during operation. For this reason, the line-side short-circuit protection for the
converter must always be provided by use of the fuses recommended in the catalogs. For further information about
line-side protection of the converters, please refer to section "Connection of converters to the supply system and
protection of converters".
The rated current and the making, breaking and short-circuit capacity are the key selection criteria for contactors. As
a general rule, the rated current of the contactor should be higher than or equal to the rated input current of the
converter.
If the making current is higher than the making capacity or the breaking current is higher than the breaking capacity,
the contactor contacts can lift or bounce. The arcs produced when the contacts bounce cause the contact material to
liquefy, resulting finally in contact adhesion or welding.
The making currents of the line-side contactors always remain lower than the rated input currents of the SINAMICS
G130, G150, S120 (Chassis and Cabinet Modules) and S150 converters described in this engineering manual owing
to the precharging circuit design. As a result, it is possible to use contactors from utilization category AC-1 (switching
of resistive loads) which have a maximum making and breaking capacity which equals around 1.5 times their rated
current. These contactors must be selected according to the rated input currents of the converters. They are used for
SINAMICS G150 cabinet units, S120 cabinet units in Cabinet Modules format and S150 cabinet units up to currents
of 800 A. These contactors are part of the SIRIUS 3RT14 range for resistive loads.
With regular converter shutdown operations and automatic fault trips of the kind caused by overcurrents at the output
or excess temperatures, the internal sequence control of the converter first issues a pulse disable command for the
power components (thyristors, IGBTs) before sending an OPEN command to the contactor. As a result, the contacts
open under practically no load. When the safety functions EMERGENCY OFF, Category 0 (uncontrolled shutdown of
the drive with instantaneous isolation from the supply system) and EMERGENCY STOP, Category 1 (controlled
shutdown of the drive with subsequent isolation from the supply system) are triggered, the contactor safety
combination bypasses the internal sequence control to issue the pulse disable command for the power elements as
well as the OPEN command for the main contactor, thus forcing the main contactor to open. Owing to the mechanical
inertia of the main contactor, the contactors open under practically no load in this case as well.
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Ó Siemens AG