Converter and converter stations

The four functional blocks of a converter station

The structure of a converter station is similar to that of a substation – with portals, conductor connectors, pipe connections and transformers. A total of four functional blocks go to make up a converter station:

1. AC terminal

The AC terminal connects the entire converter station to a substation to which the overhead AC line is connected.

2. Converter

The heart of the station is the converter unit housed in the hall. This is where the current is converted from AC to DC or vice versa. A converter is made up of transistors, diodes, capacitors and reactors. In order to convert the current, the transistors are switched on and off alternately in line with precisely calculated patterns.

The transistors and diodes used are electronic power semiconductor devices that heat up during operation. To cool them, they are mounted on aluminium plates around which cooling water circulates. The heated cooling water, which flows in a closed circuit, is itself cooled by externally mounted cooling units.

3. Transformer

The converter is connected to the AC terminal by means of a transformer that matches the grid voltage to the input voltage required by the converter.

4. DC terminal

The DC terminal connects the converter station to the DC power line (overhead line or cable) that runs to the other converter station in the system.