Monday, November 25, 2019

Viewing the Power Grid Over Time

Share this article:

How Open-Source EPRI Software Sparked Innovation in Distribution System Planning

Utility Innovation: Time and Distribution Planning

EPRI’s OpenDSS tool equips distribution planners to compute power flows over time and assess when and how distributed energy resources benefit or adversely impact the power system. “A big value [of OpenDSS] is that it has made multi-state iterative analysis possible, where conditions are always changing,” said Justin Price, FirstEnergy’s supervisor of distribution planning and protection. “Some commercially available tools have the ability to generate thousands of simulations, and OpenDSS was a driver in making that happen.”

When created in 1997, EPRI’s comprehensive distribution system simulation tool, OpenDSS, was ahead of its time. Although the number and impact of grid-connected distributed energy resources (DER) were limited then, some distribution planners already needed a tool that was more robust than the simple load projection spreadsheets then in use.

“Distribution planners project peak load a certain number of years in the future and design the system to deliver the needed power,” said EPRI Senior Technical Executive Roger Dugan. “With more distributed resources on the grid, we realized that you needed to examine the system over time rather than use a static peak load value.”

The OpenDSS tool introduced time-series power flow simulations to distribution system planning as an efficient way to capture the time-dependent impacts and benefits of DER. “A time-series power flow simulation involves computing a series of power flows that correspond to varying load and generation over time,” said Dugan. “Unlike historical planning based on a single snapshot of power flow on the distribution grid, time-series simulations equip planners to assess how and when new energy resources will benefit or adversely impact the power system.”

For example, planners need to know about weather-related changes in solar output to determine the regulation equipment necessary for distribution feeders to safely handle resulting voltage changes.

If load shapes change little from year to year, simple load projections can drive planning. Today, such projections are inadequate because the influx of solar generation and electric vehicles alters traditional load shapes.

“Using OpenDSS, we have been able to demonstrate how the power industry can move from time-consuming manual processes to more automated methods for planning, saving valuable engineering time,” said EPRI Senior Program Manager Jeff Smith. “The tool enables planners to quickly run thousands of feeder scenarios. As new DER are deployed, they can simulate the system repeatedly to determine the range of impacts and better assess the potential value of DER as an alternative to building new grid infrastructure. This can inform investment decisions.”

Con Edison finds high value in OpenDSS software,” said Simon Odie, a senior engineer at Con Edison, the utility that serves New York City and Westchester County, New York. “As DER penetration increases in our service territory, alternative methods to study system impacts are critical for understanding and processing new customer DER installation requests. The capabilities in OpenDSS to conduct time-series analyses and modify inverter functionality provide great insight for us as we endeavor to identify optimal smart inverter settings that comply with IEEE 1547-2018.

As open source software for more than a decade, OpenDSS provides many features that have found their way into commercial planning software used by utilities, consultants, universities, and national research laboratories. It has been downloaded by nearly 80,000 users in countries such as the United States, Brazil, China, India, Germany, Italy, and South Korea.

Justin Price, FirstEnergy’s supervisor of distribution planning and protection, cites OpenDSS’s positive effects on features offered in commercial tools. “A big value is that it has made multi-state iterative analysis possible, where conditions are always changing,” he said. “Some commercially available tools have the ability to generate thousands of simulations, and OpenDSS was a driver in making that happen.”

For FirstEnergy’s interconnection training in 2017, 169 engineers used OpenDSS to study DER impacts on the distribution system. OpenDSS made the course possible because FirstEnergy didn’t have enough licenses for its commercial planning tool for all the students to perform the study simultaneously.

Universities around the globe use OpenDSS as a teaching tool to give new distribution engineering students an opportunity to practice their craft in a simulated environment. IEEE (Institute of Electrical and Electronics Engineers) used the tool to develop distribution feeder models for testing the capabilities of distribution planning tools.

Over the past two decades, EPRI has added new capabilities to OpenDSS, such as:

  • Simulation of advanced inverter controls: This enables planners to characterize voltage changes as a result of variable generation—and can inform adjustments to the control equipment used to support system reliability.
  • Simulation of energy storage controls: This can equip planners to determine optimal storage control settings as load and generation vary.
  • Analysis of a feeder’s hosting capacity for solar: This enables planners to determine whether new solar capacity may cause grid problems.

In 2018, EPRI introduced an interface that makes OpenDSS easier to use. “The interface makes the tool more accessible with features such as click, point, and drag,” said Dr. Davis Montenegro, an EPRI engineer scientist. “It enables engineers to go straight to the problem they want to examine.”

The tool drives research within EPRI. “OpenDSS is a critical tool in a dozen EPRI programs related to the distribution system—from DER integration and energy storage to power quality and transportation,” said Smith.

Key EPRI Technical Experts:

Roger Dugan, Jeff Smith, Davis Montenegro, Lindsey Rogers
For more information, contact

Additional Resources:

Artwork by MCKIBILLO