Power modulation of Sidney HVDC scheme. I. RAS control concept, realization and field tests

The 200 MW back-to-back Sidney (Nebraska) Converter Station (SCS) provides an asynchronous tie between the east and west AC power networks. In order to maintain electromechanical stability of the east network under worst-case line outage conditions, a remedial action scheme (RAS) was integrated in the HVDC (high-voltage direct-current) control. Basic components of the SCS RAS are frequency-dependent power modulation combined with an effective voltage control in the western network. The authors present the conceptual development of the RAS, as well as details on the RAS control hardware and software. Studies and live system tests have demonstrated the ability of the relatively fast HVDC controls to change the power infeed from the DC station quickly. These rapid changes in power transfer properly coordinated with speed deviation of a nearby generation unit, help maintain, and in some cases improve, the electromechanical stability of the AC system