Project 1 –Contingency Ranking byTime Domain Simulations

Problem and Approach:

Consider the 179-bus WECC system model. Powerflow and dynamic data in PSS/E format will be provided.

Its loads can be represented by one of the following load models:

  • Load Model #1: P load is represented as 100% Constant Current load; Q load is represented as 100% Constant Z; convert P load to 100% Constant Z when the bus voltage is lower than 0.7pu
  • Load Model #2: All loads P and Q represented as Constant Impedance
  • Load Model #3: All loads P and Q represented at Constant Current
  • Load Model #4: All loads P and Q represented at Constant Power

Task 1: Rank N-1 contingencies

Adopt Load Model #1 for all buses. Consider the following N-1 contingencies:

  • Add a three-phase short-circuit fault at each end (zero distance to one bus) of every transmission line rated at 500kV
  • After a fault duration time (clearing time), trip the line at both ends to isolate the fault

Note: if the line trip with a contingency splits the system into two segments, e.g. a contingency on line 73-75, it should not be counted in the N-1 list (since it is already addressed by grid design or planning).

Rank all contingencies by this stability criterion: Let the fault clearing time be 5 cycles. Simulate each contingency for 10 seconds and calculate stability margin index  by the largest angle distance max, as illustrated by the figure and table below.

Identify the number (denoted by N) of contingencies that cause angular instability (<0) and the top-5 critical contingencies from the ranking. Analyze why those 5 contingencies more easily cause instability than the others.

Task 2: Determine the Critical Clearing Time (CCT)

For each of the top-5 critical contingencies, determine its critical clearing time (CCT), i.e. the longest fault clearing time with ≥0. An approach could be to simulate the contingency for 10 seconds with a fault clearing timethat is gradually increased from 1 cycles to 20 cycles at a small stepuntilthe frist time <0. Rank the 5 critical contingencies by their CCTs and compare the ranking with that based on values of .

Task 3: Compare different load models

For the top-5critical contingencies identified, check theirCCTs and stability margin indices for simulations withLoad Models #2 ~ #4. Compare the results with those from Load Model #1.

Deliverable

  • Project presentation on 4/24
  • A no more than 6pages report by 4/30. Use the IEEE paper template at

Hints:

You may use either PSS/E or Powertech’s TSAT software to do simulations. TSAT software integrates that stability criterion and can do automatic CCT search.