McCamey Area Limits

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					Current Operational Challenges

          • Computing the West –
            North Limits
          • Potential IROLs
          • Local Voltage & Thermal
            issue (OOME)
          • High Voltage
          • Outages
                   Computing the W-N Limits

• Power Flow Analysis
  – Build base case
     • Determine next day’s peak hour using load forecast
     • Use peak hour load and generation plan
     • Include scheduled outages for peak hour
        – Must clear any base case violations where Normal Rating ≥
  – Save as STNET case:
                  Computing the W-N Limits

• West – North thermal SOL
  – Increase West – North transfer
     • Increasing generation at West and Far West zones
     • Scaling load up in the North Central zone and scaling
       load down in the West and Far West zones if more
       transfer is need
  – The sum of the flow on Graham-Parker and
    Graham-Benbrook 345 kV DBL Ckt is W-N
    thermal SOL
    West-North CSC

W           N
                         W-N Transient Stability Limit
• 6 lines
     –   345 kV Graham SES – Long Creek Switch
     –   345 kV Graham SES – Bowman Switch
     –   345 kV Graham SES – Tonkawa Switch
     –   345 kV Graham SES – Sweetwater Generation Plant
     –   345 kV Bowman Switch – Jacksboro Switch
     –   345 kV San Angelo Red Creek – Comanche Switch
•   Number of units on-line at each plant site
•   Status of Power System Stabilizers
•   West and Far West plants
•   Outages
•   Transient Limit
•   Several conditions that are controlled by ERCOT operators
W-N Stability Limit
             Objectives for SOLs and IROLs

• Know the definitions and the differences
  between an SOL and an IROL

• Understand the steps in determining an
                               What is an SOL?

• System Operating Limit (SOL) – The value (such as MW, MVAR,
  Amperes, Frequency, or Volts) that satisfies the most limiting of
  the prescribed operating criteria for a specified system
  configuration to ensure operation within acceptable reliability

• SOLs are based upon certain operating criteria. These include but
  are not limited to:
    – Facility Ratings (Applicable pre- and post- Contingency equipment on
      facility ratings)
    – Transient Stability Limits (Applicable pre- and post- Contingency
      Stability Limits)
    – Voltage Stability Limits (Applicable pre- and post- Contingency
      Voltage Stability)
    – System Voltage Limits (Applicable pre- and post- Contingency
      Voltage Limits)
                             What is an IROL?

• Interconnected Reliability Operating Limit (IROL) – System
  Operating Limit that, if violated, could lead to instability,
  uncontrolled separation, or Cascading Outages that adversely
  impact the reliability of the Bulk Electric System.

• IROLs are a subset of SOLs.

• If a limit is violated for more than 30 minutes then we are in
  violation of NERC Operating Criteria.
                 How do you Identify an IROL?

Use the following criteria to disqualify exceeded limits.
   – Magnitude and Time over Limit: SOLs which are not exceeded
     by 100% of the calculated value, using the emergency rating,
     for over 30 continuous minutes are considered controllable and
     not IROL violations.
   – Double Circuit Contingencies: Post Contingency Overloads as
     a result of the outages of multiple elements that are considered
     as feasible due to proximity of each other (i.e. shared structure
     or right-of-way) and not due to the absence of circuit breakers
     between elements.
   – System Impact: SOLs exceeded that would not expose a
     widespread portion of ERCOT even under worst-case
     scenarios. Some contingencies may cause overloads to
     equipment that if lost would not credibly result in cascading
     outages, instability, or uncontrolled separation.
                  How do you Identify an IROL?

If an IROL is identified, must report to NERC within 72 hrs of the
     – Determine which form(s) needs to be filled out.
          • Interconnected Reliability Limit violation non-compliance
          • NERC Operating Security Limit and Preliminary
            Disturbance Report
          • DOE Form EIA- 417 Emergency Incident and Disturbance
     – Email report to NERC within the appropriate time frame. (If
        report cannot be sent within the time frame, call NERC and/or
        DOE and report a brief summary. Then fill out report and send
        in As Soon As Possible).
                        Active Constraints vs.
                       Congestion Management

• Challenges with current Market Operator Interface
  (MOI) Congestion Management tools
   – Monitor Actual Zonal Flows vs. calculated CSC Limits
   – MOI Utilizes Calculated Flows
      • Operator must enter new projected constraint limit in MOI prior
        to the execution of the Real Time Balancing Market (RTB)
   – Entered into the MOI 30 – 40 minutes before the interval
     is completed
   – Monitor Real Time Contingency Analysis (RTCA)
   – Must not violate NERC Operating Criteria
MOI Constraint Management
Wind QSE Low & High
Frequency Excursions
High Voltage
High Voltage
    Zonal Transfers

W       N

                  Outages affecting Wind

• 345 kV Graham SES – Sweetwater Generation Plant
• 345 kV Graham SES – Long Creek Switch
• 345 kV Long Creek Switch– Abilene Mulberry Creek
• 138 kV Putnam – Leon Switch
• 138 kV Adamsville – Evant
• 60% due to maintenance to improve reliability during
  light load season
• 40% due to W-N transfer

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