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C ontingency Ranking by Time Domain Simulations

C ontingency Ranking by Time Domain Simulations. ECE 422/522 Russell Patterson Micah Till Terry Jones. Project Goals. Identify top five critical contingencies in Zones 2-A and 2-B. Project Goals. Rank the top five contingencies by the stability criterion.

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C ontingency Ranking by Time Domain Simulations

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  1. Contingency Ranking byTime Domain Simulations ECE 422/522 Russell Patterson Micah Till Terry Jones

  2. Project Goals • Identify top five critical contingencies in Zones 2-A and 2-B

  3. Project Goals • Rank the top five contingencies by the stability criterion. • Rank the top five contingencies by their Critical Clearing Time and compare the ranking with that based on values of  • Determine the effect of varying load models

  4. Task 1: Rank N-1 Contingencies • A study was created in TSAT using the Case Wizard • Contingencies were ranked by the stability criterion: (1) • The results of this analysis are presented below

  5. Task 1: Rank N-1 Contingencies almost 4GW • Bus 83 is the major bottleneck for power flow between Zones 1-A and 2-A • As seen, all of the buses in Table 2 are electrically close to bus 83 • Many of these branches are negative reactance, which means they represent series capacitors • In reality, some of the series capacitors would be bypassed during faults

  6. Briefly - Series Capacitors • Used to increase the MW transfer capability of the path (XL – XC) • 60% series compensation means XC = 60% of XL • Too much compensation can lead to problems like overvoltage and subsynchronous resonance (SSR)

  7. Briefly - Series Capacitors • subsynchronous resonance (SSR) can result if too much series compensation is applied • More XC means higher fR • SSR usually in the range of 10 to 50Hz rad/s Hz IEEE definition: “Subsynchronous resonance (SSR) is an electric power condition where the electric network exchanges energy with a turbine/generator at one or more of the natural frequencies of the combined system below the synchronous frequency of the system.” Reference: EPRI Power Systems Dynamics Tutorial

  8. Briefly - Series Capacitors • Series capacitors are bypassed when current through produces voltage across of 150-300% • Initially bypassed by arrester (non-linear) • Hard bypassed prior to exceeding MOV energy capability V I

  9. Briefly - Series Capacitors • Series capacitors directly in faulted line will be hard bypassed • Series capacitors farther away will likely just be partially bypassed as their voltage peaks • Those not hard bypassed will be quickly re-inserted after fault is cleared • Hard bypassed will take as long as 5-cycles to reinsert (if at all)

  10. Briefly - Series Capacitors Series compensation at Dafang, China Ref: “Series Capacitor By-pass Switch – ABB”

  11. Briefly - Series Capacitors • TSAT – create user defined model which can be accessed in dynamic editor as SERUDM (TSAT has a test case of a thyristor-controlled series compensator (TCSC) model) • PSS/E has model called SCGAP2 • PSLF has model called SCGAP How can series capacitor bypassing be handled in transient stability analysis?

  12. Task 1: Rank N-1 Contingencies • To test the assumption that properly modeled series capacitor bypassing would change the results, a 3-phase fault was place close-in to bus 83 and the rotor angle of generator 112 was recorded. • This was repeated with the capacitive branches shorted out (bypassed). • Note that while the results will eliminate the effects of series capacitors, they still will not accurately reflect system response

  13. Task 1: Rank N-1 Contingencies • Initial run in black, run with series capacitors bypassed in red • Note that initial case loses stability shortly after fault inception

  14. Task 2: Critical Clearing Time • TSAT was able to identify the CCT by gradually increasing the clearing time until the stability criterion became negative. • The closer the faulted line is to generator 112, the smaller the CCT

  15. Task 2: Critical Clearing Time • Cannot transmit power through zero voltage bus

  16. Task 3: Load Model Comparison • The load models were varied as shown: • Note that conversion to a constant impedance load was required below a certain threshold for TSAT to calculate solutions for all contingencies • Results for LM2, LM3, and LM4 were compared to the CCT values from LM1

  17. Task 3: Load Model Comparison • Constant impedance (LM2) performs better than the mixed model (LM1) • Constant current (LM3) and power (LM4) cannot solve unless certain buses are converted back to constant impedance (LM2) • Even after this, LM3 and LM4 underperform LM1

  18. Task 3: Load Model Comparison Thank You!

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