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HVDC Thyristor valves

Thyristor valves are the heart of the HVDC conversion process. Modern valves have an excellent performance record and very small losses.

Graetz bridge
6-pulse Graetz bridge



Three quadruple valves forming a 12-pulse converter.



Valve layer with four series connected thyristor and reactor modules.



ABB HVDC thyristor module with the corona screens removed.


Tyristor with control unit

.The thyristor valves do the actual conversion from AC to DC or vice versa. The basic circuit used is the Graetz bridge consisting of six valve functions, but in order to eliminate the largest harmonics, two such bridges are connected in series forming a 12-pulse converter.

The valves are normally located in a valve building and arranged as three structures (quadruple valves) suspended from the ceiling of the valve hall, but other arrangements do exist. (See for example the ABB
outdoor HVDC valve.)


Outdoor valve

Each valve consists of a number of series connected thyristor and reactor modules. The reactors are needed to limit the rate of rise of the current when the valve is triggered (= made to conduct current).

The HVDC valves are water cooled by a closed loop with de-ionised water. (Link to: SwedeWater )

The thyristors are triggered by electrical gate pulses generated in a small electronic thyristor control unit (TCU) located near each thyristor. These units receive triggering impulses 50 or 60 times per second from the HVDC control system by means of light guides, that can transmit the triggering order from ground potential to each thyristor position in a valve in spite of the fact that a thyristor may have a voltage of 500 kV to ground!

Read more about ABB's system in: The art of triggering an HVDC valve

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    ABB contact for United States of America

    Mike Bahrman
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