Influence of Power System on Operation of an HVDC Link. A Case Study

Abstract

An HVDC link enables power and energy exchange between unsynchronised power grids. Large possibilities of controlling active power flows through such systems enable commercial transfers, as well as emergency power balancing operations. During operation of an HVDC SwePol Link disturbances related to thyristor commutation triggered by the grid (commutation failures) are observed; these occur during power import (inverting operation) to Poland. A commutation failure may lead to an outage of the HVDC link and therefore restrict power exchange with Sweden. An outage may additionally cause some technical defects (e.g. damage of return cable insulation). This damage may lead to long outages of the link, and repairing it may be quite expensive. The paper presents results of the cause-effect analyses of the closed grid operation in the northern area of the National Power System, in the context of disturbances in operation of the HVDC SwePol Link. Events related to commutation failures have been analysed; the influence of operating conditions in the grid near an HVDC link on such occurrences has been evaluated. So far, during the operation of the link such a phenomenon has occurred more than 200 times, and some of the events led to the system shut-down. In a few cases some link components were damaged in the process.