The response time of the control device is 2.3ms, the breaking time of the fast mechanical switch is 1ms, and the overall effective time is 9.2ms. The artificial grounding short-circuit test of the fast switch based fault current limiter (FCL) was successfully accomplished.
On December 20, 2021, the test results were announced at 750kV Helanshan substation of Ningxia Power Grid. As the first application in the EHV core hub substation in China, the performance indexes of PCS-8351 fast switch based FCL developed by NR were tested and verified by the short-circuit test of the actual system, and the short-circuit current limiting depth reached 31.5%, which was in full accord with the solution design.
With the formation of 750kV double loops in Ningxia power grid, the three-phase short-circuit current of the AC bus in 750kV Helanshan substation has exceeded the breaking capacity of the existing conventional circuit breaker, which will affect the safe and stable operation of the power grid, thus corresponding treatments need to be taken.
However, limiting the short-circuit current through operating some lines in hot standby will lower the operation reliability of the power grid and increase the loss of multiple no-load lines.
NR has accumulated rich experience in the fields of power system analysis, protection & control for many years, and achieved key breakthroughs in emerging technologies of high-voltage AC and DC fast switching. To solve the problem mentioned above, NR has carried out joint research with Northwest Branch of State Grid and State Grid Ningxia, and a scheme of installing FCLs at 750kV Helanshan substation was determined. The scheme shows that the short-circuit current limiting effect is significant, and there are no steady-state losses and voltage fluctuation problems.
At the same time, NR provided a series of system solutions including the action characteristics analysis of the transformer protection, the line protection and the bus protection after FCLs were put into operation. Besides, a third-party RTDS test was passed. In the test, a closed-loop simulation environment based on Helanshan substation and surrounding systems was built to comprehensively evaluate the protection characteristics after the FCL was set.
The basic principle of PCS-8351 FCL is a parallel connection of a fast mechanical switch and a current-limiting reactor. The PCS-8351 FCL also comes with a high-speed control device which applies highly integrated software and hardware design. The control device leads to the fastest detection and operation time of short-circuit current less than 3ms. When it goes to the fast mechanical switch, the breaking time is less than 1 ms, and the redundancy design of double breakers connected in series ensures the current can be reliably limited even if one breaker fails.
The deep integration of the fast mechanical switch and the control device realizes that the current limiting takes effect within one cycle after the fault occurs, which strictly limits the short-circuit current before the open of the conventional circuit breaker when the arc is generated. The application of the FCL can reduce the breaking stress of the conventional circuit breaker and ensure the reliable clearance of the fault.
PCS-8351 FCL cannot only be applied on the transformer side, but also be installed on the bus section/bus coupler or outgoing line, which can also achieve fast and flexible current limiting.
PCS-8351 FCL successfully passed the artificial grounding short-circuit test at 750kV Helanshan substation in Ningxia, which fully verified the effectiveness of NR protection solution and various performance indexes of the product. It also created favourable conditions to improve the power supply reliability of regional power grids and the power flow dispersion capacity of the subsection of Helanshan power grid.
At present, PCS-8351 FCL has been applied in many power grids such as Xinjiang and Ningxia. It provides a flexible and innovative solution that can be widely popularized and applied for the deteriorating problem of overlimit short-circuit current of high-voltage power grid. The success of PCS-8351 FCL also strengthens the leading position of NR fast switch products in the field of high-voltage power grid.