Voltage Security Assessment

1
Voltage Security Assessment

• SEEKS----SEcurity Evaluation Knowledge-based
  System

2
The Knowledge Base of SEEKS

• Knowledge base contains several rule modules,
  each
• handling different task
• Operating Point Evaluation
• Branch Weighting
• Single Contingency Selection
• Double Contingency Selection
• Remedial Action

3
Operating Point Evaluation

• Evaluate the security of base case operating
  point
• Search and identify bus branch structures
  (1). Radial (2). Loop (3). Cluster
• Emulate the operational planners grouping of
  buses into subsets
• This network structural information along with
  the current operating point will be used to
  select worst case outages

4
Structure Examples

• Radial a collection of single branches in series
  such that any radial branch outage islands some
  buses in the structure
• Loop a path of single branches which begins and
  ends at buses connected to the remaining system
• Cluster a collection of several buses
  interconnected by low impedance lines

Loop
Radial
30
26
29
25
27
Cluster
28
22
21
10
Partial IEEE 30 Bus System
5
Branch Weighting

• The impact of each branch outage is ranked by
  assigning weights to branches
• The branch weight adjustment rules are dependent
  on the operating point, local topology and
  heuristics derived from experience solving power
  flow
• Outages are grouped into consistent sets, which
  impact the same local areas and result in
  violations because of the same deficiencies in
  the operating point.
• Only the impact of the worst case contingency in
  each set need be investigated.

6
Double Contingency Selection

• SEEKS incorporates possible failure of
  coordination, relays and breakers with single
  branch outages to produce double branch outages
• Each candidate outage is comprised of two
  branches sharing a common bus, and has weight
  equal to the sum of the two branch weights
• The selection of double contingency scenarios for
  power flow evaluation proceeds much like the
  selection of single contingency

7
Conclusion

• An expert system called SEEKS was presented which
  uses operational planning knowledge to provide
  insight into power system voltage behavior
• Structure identification and branch weighting
  together filter away many branches outages from
  power flow analysis.

8
Reference

• Voltage security assessment using
• generalized operational planning knowledge
• Cote, J.W. Liu, C.-C. Power Systems, IEEE
• Transactions on , Volume 8 Issue 1 , Feb. 1993
• Page(s) 28 -34