Study on voltage stability of island grid supplied by large grid with long submarine cables considering different load patterns

The voltage response characteristics considered different load patterns are studied in the paper. The effects of on-load tap changer (OLTC), over-excitation limiter (OLE), and high voltage direct current (HVDC) link on voltage stability are also analyzed. In which, the converter terminals of HVDC link are considered as a constant real and reactive power load under steady state and the effects of HVDC control modes on voltage stability are also studied. A practical system of larger grid (Taiwan grid) connecting to a smaller island grid (Peng-Hu grid) via two circuits of long submarine cables is used to study. The strategies for improving voltage stability include reactive power support and under-voltage load shedding (UVLS) are proposed. Based on the simulation results, it shows that the voltage response characteristics are affected significantly by different load patterns. The OLTC plays an important role during the load voltage restoration. The reactive power support devices and UVLS can improve the short-term voltage stability, which makes the power system achieve voltage stability operation. However, the interactions between OLTC and OEL under HVDC link connected operation would lead the power system to voltage instability. The constant current control mode of HVDC link has better effect on voltage stability. All of these studies are performed by software package, namely power system simulation for engineering (PSS/E) in this paper.