Voltage Collapse Contingency Selection

Overview
VCCS searches for single and double contingencies with a predisposition to either producing cascading voltage instability or local voltage instability by simulating a set of 500,000-1,000,000. It then determines those equipment outages that have no solution using snapsnots approximating a quasi dynamic simulation followed by a four step diagnostic for separating voltage instability and loadflow convergence for each simulated contingency.

Realistitic Modeling
  • Study region, diagnostics and mitigation measures each can include the higher voltage distribution, subtransmission and transmission system rather than just the transmission system
  • Contingencies are simulated via a set of snapshots that approximate a dynamic simulation in order to assure that the simulation reflects the response of the actual system as accurately as possible
Sound Simulation
  • VCCS can simulate bus branch or breaker to breaker (dependent) contingencies
  • Uses industry standard Siemens PSSE 30 and GE PSLF 15 loadflow to perform full Newton simulations rather than a proprietary loadflow algorithm that may use a decoupled loadflow algorithm. GE and Siemens recommend against using a decoupled solution for voltage stability studies
More Comprehensive
  • Study can focus on an entire utility or a reliability region instead of one or two major load centers
  • Manpower and computing resource costs would be prohibitive if a study with this level of comprehensiveness was attempted using traditional methods
  • Using a very large study region permits identification of contingencies across a large region exploiting the same structural weakness such as a unknown seams, unit commitment, voltage rescheduling, active rescheduling or inordinately strong transmission paths causing regional coupling and requiring sufficient reactive reserves
  • Finds the obvious heuristically determined contingencies for a given known loadpocket or area but also the hidden unknown contingencies that cause voltage instability in that loadpocket
  • VCCS simulates 500,000 1,000,000 contingencies while traditional P-V and V-Q methods can handle at most a few hundred contingencies
Issue Diagnosis
  • Voltage instability problems are separated from numerical convergence difficulties using a four step diagnostic procedure
  • Searches for and often finds single contingencies that do indeed cause voltage instability based on a four step diagnostic that separates loadflow non convergence from voltage instability
  • Finds single contingencies that are predisposed to producing voltage instability in some area and exhaustively simulates hundreds of thousands of such contingencies to find those that produce voltage instability via the diagnostic procedure
  • Uses a four step diagnostic to separate voltage instability from loadflow convergence and low voltage problems