Project: Sub-synchronous Interaction Study in Europe

Service: SSR

Client: (Confidential)

Country: Europe

Year: 2014


TGS carried out a detailed sub-synchronous interaction study for a power system with three large wind plants, one nuclear unit with torsional oscillations, one large LCC HVDC system, one VSC HVDC system and a large number of STATCOMs and SVCs using their in-house small signal stability assessment tool (TGSSR).

TGS Study services:

  • Modeling existing and proposed dynamic devices in the study area for SS analysis, including large nuclear units, wind power plans, STATCOMs, SVCs, VSC HVDC link and LCC HVDC link - TGSSR
  • Impact of various dynamic devices on torsional oscillations of  a large nuclear unit —TGSSR
    • Identify the impact of dynamic devices and their controls such as HVDC, VSC, STATCOMs, SVCs and wind power plants on torsional oscillations of a large nuclear unit in the study area (in terms of electrical damping) for various system conditions
  • Possibility of Sub-Synchronous Torsional Interactions (SSTI) — Screening studies (UIF)
  • Detailed SSTI Studies - TGSSR SSTI is a special condition and if the ac system devices (LCC HVDC, VSC, FACTS or combination of them) can produce an oscillation close to one of the torsional modes, these oscillations can interact with each other causing SSTI. 
    • Determine the sub-synchronous torsional interactions between the generator-turbine units and the HVDC/VSC systems for a range of controller gains of those devices.
    • Identify the worst conditions and worst contingencies in terms of SSTI
    • Make recommendations for SSR studies to be performed by the client and device manufacturers for proposed devices in the study area
  • Identify possible control interactions —TGSSR


This was challenging in the sense of the number of devices involved and the number of SSR related issues to be identified. The project involved conventional generators with torsional interactions, LCC and VSC HVDC systems, STACOMs, SVCs and Type-3 wind power plants.