Feasibility Study of Connecting Nuclear Generation to the National Electricity Transmission System via HVDC Technology

Abstract

High Voltage Direct Current (HVDC) technology has never before been used to connect a Nuclear Power Plant (NPP) directly to the National Electricity Transmission System (NETS). There are both technical and economic factors which need to be considered and understood before such a technology is adopted for an NPP connection.

In this thesis, both technical and economic factors surrounding the suitability of Current Source Converter (CSC) and Voltage Source Converter (VSC) HVDC technology for NPP connections are investigated. Power system models of both HVDC technologies, connected to an NPP, are studied in Power System Computer Aided Design (PSCAD) software.

The studies highlight the susceptibility of CSC-HVDC technology to commutation failure during a three-phase fault condition at the inverter, and simulations demonstrate some key benefits of adopting VSC-HVDC technology for NPP connections: provision of independent reactive power support to both the NPP and AC system; black-start capability; fast current reversal for dynamic conditions; and the ability to connect to a weak High Voltage Alternating Current (HVAC) system. The simulations show the vulnerability of VSC-HVDC vector current control when the short circuit ratio of the AC system is very low (<1); in such cases, the Phase Locked Loop (PLL) is affected and power transfer through the VSC-HVDC link may drop to 50% of nominal rating.

An economic analysis of HVDC technology development, cost and converter station size is presented. The size of a CSC-HVDC converter station can be much larger than an equivalent-rated VSC due to the additional filters required for reactive power compensation and harmonic mitigation. With the fast evolution of VSC-HVDC technology, the ratings required for an NPP connection are now available. The cost difference between the two technologies can vary from project to project and hence neither one can be ruled out for an NPP connection based only on price.