DC breaker testing in the Nan'ao Multi-terminal station

Testing of the DC circuit breaker that was recently installed in the Nan'ao multiterminal HVDC grid in China. The video shows the single pole manual short circuit test that was completed successfully, with the dc circuit breaker opening during the applied dc fault with both terminals maintaining  steady operation.

Brief Updates for 2017

Two brief updates on HVDC projects and related programs:

1.  Firstly, the construction of the Hubei-Chongqin back-to-back HVDC system based on VSC technology started earlier this year, more specifically on the 25th of May 2017. The project that is expected to be completed in late 2018 has a transmission rated power transfer of 50000MW, and a rated voltage of ±420KV, rated current at 1500A. Each station includes two sets of 1250 MW HVDC light  converters.
2. Secondly, the Jiangsu Zhongtian Technologies Co. Ltd announced the successful testing and production of a  ±525KV cross-linked polyethylene (XLPE) insulated cable for HVDC light applications.

The First ±800KV UHVDC project in Northeast of China come into service

On the 15^th of October, the Zhalute-Qingzhou ±800KV UHVDC project completed its pre-operation trial tests, with the three converter unit HVDC  (3*2500MW) came into service successfully, it is the fist UHVDC project connecting Northeast China to central China.

The project rated dc voltage is ±800KV, and its rated capacity at 10000 MW (a configuration that is becoming quite standard in the current generation of LCC-HVDC projects in China). The inverter station side of the UHVDC system is connected to two AC lines, a 500kV and an 1000kV AC system. The project is a link between the renewable energy generation centers in northeast of China and the main load centers, preventing wind curtainlment, an issue that has plagued quite a few of the wind plants, especially in the west of China. 

The project starts from the Zhalute converter station in Tongliao, Inner Mongolia Autonomous Region, crossing the provinces of Hebei, Tianjin, and Shandong. The total transmission distance is 1234km and the total cost of the project is 21.1 Billion RMB(~AU$4B).

The path of the Zhalute - Qingzhou UHVDC line 

Aerial photo of the converter station and the reactive compensators

Test of Synchronous Condenser for HVDC systems

On the 24^th November 2017, testing for the first 300MVAr large synchronous condenser for UHVDC projects, manufactured by the Harbin Electric Group, was completed. The testing report (see figures below) shows that the dynamic performance of the synchronous condenser meets the operational requirements of the State Grid Corporation of China (SGCC).

As investment in HVDC technologies continues and more and UHVDC projects are connected to the system, the need for reactive power support of the networks also becomes important. Cascading faults within the AC and the DC systems increase the threats of voltage instability and synchronism with the grid. Once an UHVDC station with large power capacity suffers an outage, the converter will receive a large amount of reactive power from AC system, which leads to major voltage drops and further cascading faults in the ac network. The large synchronous condenser will provide greater amounts of reactive power in the transient period to prevent voltage drop and help with the fast voltage recovery requirements in post-fault conditions.

The following picture show the HVDC performance after voltage drop with condenser and without condenser, the red one show the converter station with condenser.

At the time of writing, the synchronous condenser has been sent to both the Zhatelu and the Jiuquan 800kV UHVDC converter stations where it is being installed and commissioned for full testing. The installation of larger synchronous condensers with allow for new stabilization strategies in the grid when it comes into service.