Zhoushan five-terminal VSC-HVDC Project

Zhoushan islands include Dinhai, Daishan, Qushan, Yangshan and Sijiao five main islands. The islands are highly critical and aggressively developing archipelago, which are situated at the south-east coast of China. There were frequent power instability and power failure problems due to high load demand and weak power integration system.

In order to improve the system stability, State Grid Company of China(SGCC) keeps to find the solution to improve the reliability of Zhoushan Grid. Considering advantages of VSC-HVDC, five-terminal VSC-HVDC was chosen as final solution. It was put into service in July, 2014 and is the first and only five-terminal HVDC project worldwide up to date.

Case Study

The total installed generating capacity and peak load demand of Zhoushan island was 765.3 MW and 818 MW. The forecasted power demand will rise up to 2649 MW by 2020 and 4775 MW by 2030. Moreover, prior to installation of VSC-HVDC, there were only one 220kV double-circuit line and three 110kV transmission lines connected Zhoushan islands to the mainland. Between Dinghai and Daishan, there was only one 220 kV & one 110kV AC line, whereas only one 110 KV AC line was used for all remaining islands. Weak interconnection and unavailability of big power sources within the islands makes the Zhoushan grid a highly unavailable and unstable grid, which always relied on small generation.

VSC-HVDC possesses several unique features, fast control to grid, enhance system stability, black start function, wind energy integration, reactive power compensation. Consequently, five-terminal VSC-HVDC is optimal solution in terms of both technical and economic.

Besides benefits above, VSC-HVDC also a good solution to integrate renewable power to each and every island.

Technical Data
AC Voltage Level 220kV,220kV,110kV, 110kV,110kV
AC Frequency 50Hz
DC Voltage Level 200kV
Power Rating

400MW/Dinghai station

100MW/Qushan station

100MW/Yangshan station

100MW/Sijiao station

Cable Length 129km submarine cable in total
Converter 5-terminal with MMC

 

Single Line Diagram of Zhoushan grid

Base on strong technical background and vast experience, NR Electric provides its state of the art service and manufacture to Zhoushan five-terminal VSC-HVDC project.

System Design

1. Research on Zhoushan five-terminal VSC-HVDC main wiring/main circuit scheme
2. Operation mode research
3. Control and protection strategy research
4. Overvoltage and insulation coordination research
5. Transient current calculation and research
6. Converter station layout plan
7. Interface of NR equipment with other equipment.

Manufacturing

1. Design, manufacture and testing of IGBT valves and controllers for the Dinhai, Daishan and Qushan converter station;
2. Design, manufacture and testing of control and protection for five terminal stations
3. Design, manufacture and testing of electronic measurement instrument for all five terminal stations
4. Develop and implement the overall five terminal control scheme

Factory Acceptance Test

1.Control and Protection system RTDS test;
2.Control and Protection system function performance test;
3.Control and Protection system static performance test;
4.Control and Protection system dynamic performance test;
5.IGBT valve support DC voltage test and partial discharge measuring;
6.Valve support AC voltage test and partial discharge measuring;
7.IGBT valve Hydrostatic test;
8.Communication test between VBC and modules
9.Water cooling system pre-commissioning and load test;
10.System start-up operation test;
11.Protection tripping test;
12.Duplicated Equipment switching test;
13.System island mode test;

Installation

1. Supervise installation of NR equipment including valve tower, control& protection cabinets, DC measurement equipment, etc.
2. Drawings and assistances of subsystem interfaces.

Commissioning and Site Acceptance Test

1.Check if the performance of system are in accordance with requirements;
2.Coordinate and optimize system coordination;
3.Test to ensure economic and stable operation of the system;

Since its operation, Zhoushan five-terminal VSC-HVDC project takes advantages to Zhoushan grid.

  • It increases the amount of power supply and enhanced reliability of power grid, especially for the grid systems on the northern islands.
  • It improves power quality by reactive power compensation. This is especially important on Yangshan and Sijiao inlands where the grid suffers impact loads attributable to cargo handling at the ports.
  • It provides voltage support to existing ± 50 kV 60 MW LCC-HVDC system on Sijiao island to prevent commutation failure.
  • It prevented black out in squally weather, it operated normally and adequately when typhoon “Nakri” and “Canhong” swept Zhoushan island in July, 2014 and July, 2015 respectively.