Siemens SINAMICS G130 Engineering Manual page 62

Fundamental Principles and System Description
Engineering Information
In the event of an internal short circuit in the power unit caused by spontaneous component failure, the line-side
short-circuit current is interrupted by tripping of the line-side fuses. The recommended fuse types can be found in
catalogs D 11 and D 21.3. The effects on the main contactor differ according to the fuse type used. These are
defined by the degree of damage which is specified for coordination types 1 and 2 according to IEC 60947-4-1.
When the only fuses installed on the line side of the converter are line fuses of type 3NA, it can be assumed that the
degree of damage to the main contactor from utilization category AC-1 (switching of resistive loads) will comply with
the requirements for coordination type 1:
The contactor is defective following a short circuit and thus unsuitable for further use. It must be repaired, if
possible, or replaced.
When dual-function fuses of type 3NE1 are installed on the line side of the converter, it can be assumed that the
degree of damage to the main contactor from utilization category AC-1 (switching of resistive loads) will comply with
the requirements for coordination type 2:
The contactor is still operative following a short circuit. However, the risk that the contacts have become
welded cannot be completely eliminated. Slight welding of the contactor contacts is permissible provided that
they can be separated easily again without any noticeable deformation. For this reason, the contactors
should if possible be examined for signs of welding after a short circuit event.
For further information about line-side fuse protection of the converters, please refer to section "Connection of
converters to the supply system and protection of converters".
Circuit breakers
Circuit breakers are switchgear which perform additional safety functions in the event of overloads, when making on
a short circuit or breaking a short circuit which has developed during operation.
The key selection criteria for a circuit breaker are the rated current, the response values of the delayed and the
instantaneous short-circuit releases as well as the short-circuit breaking capacity. As a general rule, the rated current
of the circuit breaker should be higher than or equal to the rated input current of the converter.
If the making current is higher than the response value of the delayed or instantaneous short-circuit release, the unit
might be immediately tripped by the circuit breaker during startup.
The making currents of the line-side circuit breakers 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. These circuit breakers can therefore be selected according to the
rated input currents of the converters.
The input currents of SINAMICS converters contain harmonic components, the amplitudes of which are determined
by the type of rectifier circuit and the impedance of the supply system. These cause increased loading of the
thermally delayed overload releases. For this reason, the circuit breakers should be designed according to the rated
input currents in which the harmonic components of the input currents are already included.
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 line-side circuit breaker. 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 circuit breaker, thus forcing the breaker to open. Owing to the
mechanical inertia of the circuit breaker, the contacts open under practically no load in this case as well.
In the event of an internal short circuit in the power unit caused by spontaneous component failure, the line-side
short-circuit current is interrupted (depending on its magnitude) either by the response of the short-time delayed
short-circuit release or by the response of the instantaneous short-circuit release of the circuit breaker.
SINAMICS Engineering Manual – November 2015
62/528
Ó Siemens AG