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,
or 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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