Requirements For The Circuit Breaker Provided By The Customer - Siemens SINAMICS MV 9LD4110-7EX70-1AA0 Operating Instructions Manual

Transformers for start-up operation
For short-time operation, the converter as well as the associated step-down and step-up
transformer (if being used) are utilized to a higher degree. In the case of starting converters in
the LCI design version, usually only the DC link reactor is affected. If just one or two motors have
to start up consecutively, the transformers can be significantly overloaded. In this case the only
limits are thermal load capacity of the winding and the iron core. When specifying/ordering the
transformer, mention heavy-duty starting (>> 2 min).
When using a step-up transformer, the following applies: Starting at zero speed, the transformer
can transfer up to 100% converter output current for a specific time. However, in order to avoid
the risk of saturation when starting from standstill, at low speeds, the converter current is
initially reduced to approximately 50% (no heavy-duty starting).
A transformer only becomes saturated when a certain voltage-time area is exceeded. This is only
indirectly linked to the current to be transferred, because the current that is fed in causes a
certain voltage (at least i*r), which also leads to saturation after the relevant time.
Transformer specification
For the transformer, as minimum take into account the following specifics:
• Converter transformer for a B6C bridge
• Percentage of the current harmonics
• Voltage load
• Control angle for feedback (90° or 40° electrical)
• Transformation ratio during idling
• Short-circuit voltage u
4.1.3

Requirements for the circuit breaker provided by the customer

To ensure adequate protection for converters, the circuit breaker provided by the customer must
fulfill the following conditions:
• The tripping time of the circuit-breaker must not exceed 80 ms.
• The circuit-breaker must be equipped with an undervoltage release. The undervoltage
release (undervoltage release coil) is controlled via the release circuit, into which the
"undervoltage release" output of the converter must be integrated as well. The auxiliary
voltage from the switchgear (this is a reliable supply) is used as the supply.
Note
In power converters, the undervoltage release is not normally supplied from voltage
transformers that are connected to the main supply network. As a consequence, an
undervoltage condition in the main line supply does not result in shutdown/trip by the
switchgear or the voltage transformer.
• Avoid additional delay times when controlling the circuit breaker. All commands from the
converter to the circuit breaker must act directly without intervention of coupling relays.
3rd Party LCI Control Upgrade
Operating Instructions, 02/2022, A5E31872818
for the step-up transformer
K
Preparations for use
4.1 Notes for system integrators
61