Transient Stability Assessment

Real-time Transient Stability Assessment & Enhancement (TSA&E)

Transient or Dynamic Stability Analysis looks at the system response to disturbances, seeking to determine whether machines will return to a synchronous frequency following a disturbance. Disturbances can include loss of generation, faults, and sudden load changes, among others. Historically, time-domain simulation is used to assess Transient Stability. However, this is not as practical for real time.

TEPCO-BCU Direct Method for Transient or Dynamic Stability Assessment

BSI Transient Stability Assessment and Enhancement (TSA&E) performs real-time assessment of transient stability by employing patented Direct Methods for the fast screening and ranking of dynamic contingencies. The Direct Method package called TEPCO-BCU was developed in partnership with the Tokyo Electric Power Company (TEPCO) in 1997 and identifies critical contingencies (based on the energy margin and critical clearing time (CCT)).

TEPCO-BCU fast screening and ranking integrates with Time-Domain Simulation for fast and accurate transient stability assessment. Once instabilities are found, the online control engine provides suggestions for mitigation via control switching.


Field Validation of Direct Methods

In 2005, PJM Interconnection put the Direct Method (TEPCO-BCU) for Transient Stability Assessment to the ultimate test. PJM ran the BSI TSA&E tool over the span of one year on 5.29 million contingencies on their enormous system (14,500 buses and 3,000 generators at the time). They validated the results with conventional time-domain simulation software.

The results of this engineering study are shown below:

Contingencies Reliability Speed Screening Operation
Total number of contingencies Percentage of captured unstable contingencies Time to compute each contingency Percentage of stable contingencies screened out Computation Mode
5,293,691 100% 0.135 seconds 92% to 99.5% Online

For 5.29 million contingencies, the direct method was able to screen out all “definitely stable” contingencies and capture 100% of the potentially unstable contingencies. This engineering study was performed on a desktop computer, yet still achieved 0.135 seconds per contingency processed. The percentage of stable contingencies screened out per batch ranged from 92% up to 99.5% and the entire study was performed with on-line data. This shows the amazing capabilities of the direct method when applied to this application of real-time transient stability assessment.

Key Functions

  • Fast dynamic contingency analysis via screening and ranking (<1 second per contingency) allows for real-time operation.
  • Differentiates between critical and non-critical contingencies with a computed energy margin and critical clearing time (CCT)
  • Determines necessary control actions to mitigate critical contingencies in real time
  • Integrates with the current Time-Domain simulation tool or provides its own time-domain simulation tool
  • Study mode to bring real-time and archived cases into an environment for further analysis under different network conditions set by the user.

Key Features

  • Accepts any input format (PSS/e, CIM, PSLF, etc.) allowing for EMS integration capability
  • Parallel design for real time application with the implementation of a distributed parallel computing platform
  • Works for both operations and planning groups; for planning groups, it can help run studies on 100,000+ bus systems
  • Modern and intuitive user interface designed in collaboration with long-term control center operators and engineers

Key Benefits

  • Improve situational awareness
  • Save manpower in stability analysis
  • Reduce the operating margin by a factor of 10 or more
  • Enable accurate utilization of the transmission capability
  • Load the system to accurate / maximum throughput
  • Support the dispatch of remote cheap generators
  • Allow more energy trading

For more information on the theoretical foundation, see the following textbooks: "Direct Methods for Stability Analysis of Electric Power Systems" and Stability Regions of Nonlinear Dynamical Systems by Dr. Hsiao-Dong Chiang.

Learn more about how electric utilities use BSI Transient Stability tools in the book "Use of Voltage Stability Assessment and Transient Stability Assessment Tools in Grid Operations" by Sarma Nuthalapati.

Also, visit the IEEE profile of professor Chiang to see published IEEE papers on Transient Stability Assessment and Control.

Small Signal Stability Assessment

Bigwood Systems’ commercial tool for Small Signal Stability Analysis and Mitigation is called “EigenStructure Calculations for Large Interconnected Power Systems”, also known as ECLIPS

ECLIPS performs small signal stability analysis of large power systems. ECLIPS is designed to be able to initiate computation based on a simulation file using the interactive parameter setting interface and perform small signal stability analysis through analyzing the eigenstructure of the system state matrix. Outputs of the computation engine include simulation result files and message files. The tool will report dominant eigenvalues and eigenvectors as well as the entire set, the load margin to small signal stability limit for the base case, the steady state frequency response report, the sensitivity of critical eigenvalues to system parameters, and unstable modes.