electronics and activates a monitoring and interlocking logic circuit. The thyristor electronics
then determine the operating status of the thyristor and relays it to the Power Stack Adapter via
the checkback fiber-optic cable. The control commands and checkback signals correlate with
each other. Any disruption to this relationship, for example an open circuit in an FO conductor
or a failed thyristor, is relayed to the open-loop/closed-loop control system as an error message.
3.3.1.3
Current transformer
Current transformers are used to measure current. The analog output signals from the current
transformer are post-processed by the AVT combination module and sent via the fiber-optic
cable to the power stack adapter. The primary circuit is separate from the secondary circuit.
3.3.1.4
Surge arresters
Overvoltages can occur when inductive loads are switched, for example, in the case of
transformer disconnections at no load. These overvoltages can pose a danger to the converter.
For indoor systems, surge arresters without spark gap are connected in a star configuration
between the phases to limit the overvoltages.
3.3.1.5
Isolating cylinder
The isolating cylinder prevents dangerous high voltages from developing around the current
transformer. For this purpose, the outer cable must be connected to ground and the inner cable
to potential.
Figure 3-3
Isolating cylinder
Description
3.3 Power unit
3rd Party LCI Control Upgrade
Operating Instructions, 02/2022, A5E31872818
27
