When HVDC Started?
Components of HVDC Transmission System
- Converter unit
- Converter transformer
- AC filters & Capacitor banks
- DC filters
- Reactive Power source
- Smoothing Reactor
- DC Switchgear
HVDC Converter Station
HVDC Converter Transformer
- Supply of AC voltages in two separate circuits with a relative phase shift of 30 electrical degrees for reduction of low order harmonics, especially the 5th and 7th harmonics.
- Act as a galvanic barrier between the AC and DC systems to prevent the DC potential to enter the AC system.
- Reactive impedance in the AC supply to reduce short circuit currents and to control the rate of rise in valve current during commutation.
- Voltage transformation between the AC supply and the HVDC system.
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.
The least costly way to generate reactive power is in shunt connected capacitor banks. Some of these capacitor banks can then be combined with reactors and resistors to form filters providing low impedance paths for the harmonics in order to limit them from entering into the AC network.
Active DC filters
HVDC smoothing reactor
- To smooth the ripple current in DC
- To reduce the risk of commutation failures by limiting the rate of rise of the DC line current at transient disturbances in the AC or DC systems.
- Prevention of resonance in the DC circuit.
- Reducing harmonic currents including limitation of telephone interference
- Air-insulated smoothing reactor
- Oil-insulated (filled) smoothing reactor