High-voltage power electronic
substations are special because of the valve rooms and buildings
required for converters and controls, respectively. Insulation
clearance requirements can lead to very large valve rooms (halls).
The valves are connected to the yard
through wall bushings. Converter transformers are often placed
adjacent to the valve building, with the valve-side bushings
penetrating through the walls in order to save space.
The valves require controlled air
temperature, humidity, and cleanness inside the valve room. Although
the major part of the valve losses is handled by the valve cooling
system, a fraction of the same is dissipated into the valve room and
adds to its air-conditioning or ventilation load.
The periodic fast switching of
electronic converter and controller valves causes a wide spectrum of
harmonic currents and electromagnetic fields, as well as significant
audible noise. Therefore, valve rooms are usually shielded
electrically with wire mesh in walls and windows.
Electric interference with radio, TV,
and communication systems can usually be controlled with power line
carrier filters and harmonic filters. Sources of audible noise in a
converter station include the transformers, capacitors, reactors, and
coolers.
To comply with the contractually
specified audible noise limits within the building (e.g., in the
control room) and outdoors (in the yard, at the substation fence),
low-noise equipment, noise-damping walls, barriers, and special
arrangement of equipment in the yard may be necessary. The theory of
audible
noise propagation is well understood,
and analytical tools for audible noise design are available.
Specified noise limits can thus be met,
but doing so may have an impact on total station layout and cost. Of
course, national and local building codes also apply.
In addition to the actual valve room
and control building, power electronic substations typically include
rooms for coolant pumps and water treatment, for auxiliary power
distribution systems, air conditioning systems, battery rooms, and
communication rooms.
Extreme electric power flow densities
in the valves create a certain risk of fire. Valve fires with more or
less severe consequences have occurred in the past.
Improved designs as well as the
exclusive use of flame-retardant materials in the valve, coordinated
with special fire detection and protection devices, reduce this risk
to a minimum. The converter transformers have fire walls in between
and dedicated sprinkler systems around them as effective fire
fighting equipment.
Many high-voltage power electronic
stations have spare transformers to minimize interruption times
following a transformer failure. This leads to specific arrangements
and bus configurations or extended concrete foundations and rail
systems in some HVDC converter stations.
Some HVDC schemes use outdoor valves
with individual housings. They avoid the cost of large valve
buildings at the expense of a more complicated valve maintenance.
TCSC stations also have similar valve housings on insulated platforms
together with the capacitor banks and other equipment.
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