V&R Energy: Fast Fault Screening (FFS) - Identify and Rank Most Severe Faults
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Fast Fault Screening (FFS) feature of POM-TS quickly scans thousands of the potential transmission fault locations and identifies the most severe of them for transient stability studies. These are the weakest points in the transmission network.
FFS analysis is performed in two steps:
- Selection of the most severe fault locations
- Ranking of the most severe faults using Ranking Index (RI)
FFS performs these two steps consecutively within the same run.
During the first step of analysis, the most severe faults are identified using the heuristic approach. These faults are ranked using the Ranking Index (RI). The index is an analytical tool with the coefficients derived using regression analysis.
The RI provides a very fast approximation of the fault severity but does not require running time-domain simulation. The larger value of the RI corresponds to a more severe fault.
Fault severity is classified as follows (starting with the most severe situation):
- Post-fault regime does not exist (i.e., steady-state instability)
- Loss of generation
- Situations corresponding to faults with small critical clearing time
It takes under one minute to determine the most severe fault locations and rank these faults. Thus, FFS reduces run time for planning studies and allows for bringing transient stability analysis into real-time environment.
FFS has the capability to rank three-phase as well as unbalanced faults.
The transient stability analysis process involving FFS is described below.
FFS capability is a part of the POM-TS. FFS computations are executed from the FFS Tab.
There are three-pre-built activities in the FFS:
1. Determine Critical Buses
This action scans the network and identifies the most severe fault locations.
2. Determine and Rank Critical Buses
The action identifies the most severe fault locations and ranks them based on the RI .
3. Compute CCT for Critical Buses
The action automatically computes the critical clearing time (CCT) for the most severe fault locations.
FFS may be also used to compare various scenarios, for example transfer scenarios (or various EMS cases). This capability was recently utilized during a project with NYISO “Fast Fault Screening for Real-Time Transient Stability Assessment”. The comparison is performed to identify the most severe scenario in terms of transient stability limitation. FFS is performed for each case, and then comparison of cases is being made based on the RI value for the case. The case with the highest RI is the most severe case. The figure shows that case 3 is the most severe case in terms of transient stability limitation.
FFS may be also used to rank unbalanced faults. There are two options to rank unbalanced faults:
- Based on the RI (from transient stability perspective)
- Based on the short circuit current magnitude (from short circuit perspective)
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