Project: Cahora Bassa AC Filter 3 Design Studies

Service: LCC HVDC, PQ

Client: EATON Capacitors

Country: Mozambique

Year: 2013-ongoing


The Cahora Bassa HVDC link is a 1920 MW two-terminal LCC HVDC link connecting Mozambique to South Africa.  At the rectifier station, an additional third AC filter is being installed.  TGS performed the design studies for this new AC filter.

TGS Study services:

  • Verification of HVDC Model — performed using PSCAD
  • AC System Model Development — performed using PSS/E
  • Harmonic Impedance Scans — performed using TGS’ in-house frequency scanning program
  • AC Filter Performance Study — performed using TGS’ in-house AC filter design program
  • AC Filter Steady State Rating Study — performed using TGS’ in-house AC filter design program
  • Electromagnetic Transient Studies — performed using PSCAD
    • Breaker study — determined the AC filter circuit breaker duties including TRV, RRRV, short-circuit current, and back to back switching
    • AC filter transient rating — determined the switching and lighting performance as well as the insulation coordination requirements
  • Self-Excitation Study — determined the various generator/filter combinations allowed to avoid self-excitation

TGS Power Quality services:

  • Harmonic measurements — on site
    • TGS performed background harmonic measurements at the converter station prior to installation of the third ac filter
    • Once the filters are installed, TGS will perform further background harmonic measurements to ensure performance requirements are met.


Most of the studies listed above deal with integrating new equipment with existing equipment, so all studies need to ensure that any retained equipment’s ratings are not exceeded and determine how to stage the integration of the new equipment in order to minimize outages.