Experts explain UHVDC transmission technology

Ultra-high voltage direct current transmission (UHVDC) refers to direct current transmission and related technologies
± voltage levels of 800kV (±750kV) and above.
The main characteristics of UHVDC transmission are large transmission capacity, long transmission distance, high voltage, and can be used for non-synchronous networking
of power systems.

In the construction of China's UHV power grid, 1000kV AC UHV transmission will be the main to form the backbone network frame of UHV power grid to realize the synchronous interconnection of power grids in major regions; ± 800kV UHVDC transmission is mainly used for long-distance, middle-of-the-middle high-power transmission projects
without voltage support.

1.
UHVDC transmission equipment
.
Mainly including: converter valve, converter transformer, flat wave reactor, AC filter, DC filter, DC arrester, AC arrester, reactive power compensation equipment, control protection device and telecommunication equipment
.
Compared to traditional HVDC transmission, UHVDC transmission has a higher
voltage on the DC side.
The capacity is larger, so higher requirements
are placed on equipment such as converter valves, converter transformers, flat wave reactors, DC filters and lightning arresters.

2.
Wiring method
of UHVDC transmission.
UHVDC generally adopts a high-reliability bipolar two-terminal neutral point wiring method
.

3.
The main technical characteristics
of UHVDC transmission.
Compared with UHV AC transmission technology, the main technical features of UHVDC are:

(1) The UHVDC system has no drop point in the middle, and can directly transmit power to the load center from point to point, high power and long distance;

(2) The UHVDC control mode is flexible and fast, which can reduce or avoid a large number of over-grid currents, and change the flow according to the changes in the operation mode of sending and receiving at both ends;

(3) UHVDC has high voltage, large transmission capacity and narrow line corridor, which is suitable for high-power and long-distance transmission;

(4) In the case of AC/DC hybrid transmission, DC active power modulation can effectively suppress the power oscillation of the parallel AC line, including regional low-frequency oscillation, and improve the dynamic stability of the AC system;

(5) When DC system blockage occurs, the AC system at both ends of UHVDC will withstand a large power impact
.