August, 2013

Oncor and its partners are conducting pilot demonstrations to illustrate how utilities can successfully use Dyanamic Line Rating (DLR) technology on congested and overloaded transmission lines.  DLR is a rating that is based on actual line loading as well as ambient conditions of temperature, solar levels, and the wind speed and direcction, all of which affect how much load the line can handle. Oncor will install and commission DLR technology at 26 locations distributed along eight transmission circuits located in Bell, Bosque, Falls, Hill, McLennan, and Williamson counties in central Texas. These circuits have been identified as significantly constrained by the Electric Reliability Council of Texas. At each location sensors will be attached to transmission towers. Radio receivers will be installed inside ten substations. The remaining dynamic line rating components will be housed at a transmission management system control center in Dallas.

  • DOE: What are the top lessons learned (technical, regulatory, project management or customer engagement)?
    Oncor:

    Congestion constraints and their impacts on a transmission line can be effectively mitigated with Dynamic Line Rating (DLR). It is hard for a transmission provider to determine which lines are good candidates for mitigation since congestion is highly variable and dependent on many operating and market parameters that are not part of the transmission providers’ responsibilities. Most lines are not consistently congested. They might be congested for a period of couple of weeks, then things will change and the flows will be different.

  • DOE: How did DLR help you identify and mitigate line congestion?
    Oncor:

    We integrated fully developed Dynamic Line Rating (DLR), a rating that is based on actual line loading and ambient conditions of temperature, solar levels and the wind speed and direction, into the real-time telemetry on which grid operations are modeled and managed. This increased the line capacity, the reliability of the grid, and system awareness while helping to mitigate congestion on the target  lines. If the lines with congestion can be determined and DLR technology is applied in the streaming protocol as described above, Oncor found that congestion can be significantly mitigated with as little as 5 to 10% additional capacity provided by DLR ratings.

  • DOE: What does your team consider the biggest success (or successes) with the project?
    Oncor:

    The biggest success of the project has been the breakthrough of streaming real-time dynamic line rating from remote monitoring devices into the transmission grid’s state-estimator and load dispatch system, Security Constrained Economic Dispatch (SCED). SCED optimizes the interdependency of generation, load-demand, and grid operation for reliable and economical operation of the electric grid. Prior to this project’s transparent integration of the full dynamic rating, the ratings were displayed on a control-room operator’s console, which required direct interaction by an operator. By streaming the data directly to the grid management system, no changes are required to the operating regimen, fewer decisions are required of the operators, and increased Wide Area System Awareness (WASA) and reliability are achieved.

  • DOE: What has been the biggest challenge?
    Oncor:

    The biggest challenge has been verifying the actual real-time financial benefits of dynamic line rating to the grid. The capacity gained by DLR can be quantified and the availability and reliability of the technology and instrumentation measured, but the economic benefit in real-time is more difficult to assess. During day-of operations, the streamed DLR capacity is automatically integrated into the ISO’s state-estimator and load dispatch program where there is presently no capability to perform real-time, what-if scenarios of economic benefit “with” and “without” DLR. We have been able to approximate the "with" and "without" DLR scenarios by running comparative models in the day-ahead market (DAM) analysis with the assistance of ERCOT, our ISO.

  • DOE: Is there something that surprised the project team or something unexpected (challenge, opportunity, success or benefit)?
    Oncor:

    The project assessment of the congestion on the transmission grid revealed several unexpected findings:

    • Congestion is widely variable, sporadic and always changing. The results are that many more lines contribute significantly to congestion than expected. The congestion moves dependent on the grid topology and market influences.
    • Annual, seasonal, and market influences change the congestion patterns.
    • Outages drive only 25% of the congestion events/costs while the market drives the remaining 75%. The expectation was that outages were the drivers, especially when the variability was observed.
    • Minimum changes in capacity available through the technology of DLR can have dramatic impacts on congestion if the DLR monitoring is installed on the appropriate lines.  In our analysis of 2011 congestion, 5% additional capacity could relieve congestion by up to 60% on the target lines with DLR installed; while 10% additional capacity would practically eliminate all congestion on the target line. The studies found that most congested lines were a result of unexpected “events”, and were not consistently congested. Different lines become congested at different times due to changing power flows and it was difficult to find usually congested lines. Most lines are not consistently congested and instead are congested for a couple of weeks. Once the power flows in the system change, new lines will become congested and other lines drop off, which is why a only a 5% or 10% increase in capacity can have such a significant impact.

     

  • DOE: What advice would you give to someone starting a similar project?
    Oncor:

    One suggestion is to include system operations from both the transmission grid provider and the independent system operator early on as stakeholders in the project development. The real-time integration into the telemetry stream of a fully-defined DLR (including ambient temperature, solar level, and the effect of wind speed/direction continuously along the transmission line) rating upon which the state-estimator models and manages the system is critical to fully recognizing the benefits of DLR. These two stakeholders must endorse and support that integration into their operating environment.

  • DOE: Was there an “ah-ha!” moment during the project?
    Oncor:

    There were several. First, N-1 contingency resolution governs system operations and planning project development. In many cases, transmission lines are not that heavily loaded with current in real-time, yet they are considered congested because they must be able to carry the load for one or more anticipated contingencies. Second, congestion is variable; it changes due to many operating and market parameters. A specific mitigation plan may be successful or thwarted by those parameter changes, and may even become entirely un-needed in a short time frame.