PNNL

View Interactive Demo: Real-time path rating allows operators to complete simulations of transmission path ratings quickly and efficiently. (Hint: engage the three generation types and slide the dial from before to after.)

Imagine that transmission lines are like our roads or bridges, which can get congested during rush hour. But for the power grid, it isn’t a typical morning or evening commute—it’s the result of competing, and increasing, energy supply and demand.

Congestion on transmission lines worsens when atypical power demands patterns hit the grid. Abnormal spikes in demand or renewable energy coming online must squeeze into the existing transfer limits. But are these limits — called “path ratings” — unrealistically conservative?

PNNL and its partners are using high performance computing techniques to develop a “real-time path rating” software tool. The tool allows operators to complete all required simulations of the transmission path ratings within minutes, instead of hours, and at 5–10 minute intervals. With this drastic time reduction, the path ratings are basically in real-time, allowing grid operators to tap unused capacities and optimize use of transmission assets 30 percent more efficiently. The ultimate benefit is billions of dollars in savings each year by reducing congestion costs and deferring new transmission investments.

Software helps avoid adding infrastructure

Today’s system operators have only very conservative ratings of inter-area transmission lines based on worst-case scenarios projected weeks or months ahead. Thus, the inputs usually don’t reflect a real-time picture of what's happening on the grid. The result is calculated transfer limits that are overly-conservative, making the transmission lines look artificially congested. And because it takes so much computer processing time to calculate the rating using today’s commercial software tools, it’s nearly impossible for operators to receive accurate simulations of path ratings.

New transmission lines, thus adding more wires to an already packed grid, is not an easy solution. Power demands will likely continue to rise while lots of money and time are spent on building new infrastructure. And there are environmental impacts to consider.

Fortunately, the new software tool gives us the significantly enhanced speed we need to operate the power grids closer to their true limits and for grid operators to take actions in a timely manner.

There are three parts to the bones of the software:

Massive contingency analysis enabled by dynamic load balancing Parallel transient simulation to speed up single dynamic simulations Fast voltage stability simulation through a non-iterative approach

In the simplest of terms, we use multiple computer processors to run many analyses at the same time. This parallel processing technique allows operators to assess different types of power grid security issues under massive contingency conditions.

The next step in development is to identify and work with a software vendor to pursue commercialization and large scale testing with power utilities. For more information, check out Non-Wire Methods for Transmission Congestion Management Through Predictive Simulation and Optimization.

ARPA-E funded development of the tool.

PNNL Research Team: Henry Huang, Ruisheng Diao, Yuri Makarov, Shuangshuang Jin, Yousu Chen, Bruce Palmer, and Bharat Vyakaranam