Although phasor measurement units (PMUs) were developed years ago, many utilities are adding more of them to the grid today. Yet the meaningful use of this technology has not progressed much beyond the collection of massive amounts of data for display or forensics.

What is preventing this worthy technology from making that last-mile journey from a data-collection device to enabling proactive applications? What can the industry do to realize the full potential of this technology to improve grid reliability and performance?

The Promise

The conventional technology used by grid operators for monitoring the grid is supervisory control and data acquisition (SCADA). These data are then used by the state estimation (SE) application to determine and display the state of the power system. Synchrophasors are precise grid measurements taken by PMUs at high speed, typically 30 times per second, compared to one every 4 seconds using conventional technology. Each measurement is time-stamped according to a common time reference. Time-stamping allows synchrophasors from different utilities to be synchronized and combined, providing a precise and comprehensive view of a regional interconnection. Synchrophasor data enable the determination of grid stress and can be used to trigger corrective actions to maintain reliability.

Some applications use synchrophasor data to create the situational awareness for operators to detect sub-second phenomena across the power system. System stress across a wide area or an instantaneous measure of power system dynamics, such as swings, can be recognized nearly instantaneously using such highly accurate data.

Metaphorically, synchrophasor technology is like an MRI of the power system, as compared to an X-ray image provided by traditional SCADA technology. Because of instantaneous, high-resolution and more-detailed measurements, PMU data are well suited as input to activate local or centralized automated controls. Such use of synchrophasor technology for wide-area monitoring and control will facilitate the evolution of the existing grid into a smarter transmission grid.

Defining, designing and demonstrating a set of applications that use phasor measurements either to create decision support information for operators or to execute closed-loop control, thus replacing many of the existing SCADA-based tools, represents the last mile in the journey to enabling proactive applications.

The Evolving Transmission Grid

With the U.S. Department of Energy's (DOE's) vision for 20% of total electric generation from wind renewable energy by 2030, the nation has started to tap into variable renewable energy resources. The penetration of wind and solar generation is expected to increase over the next few decades. The Midwest and Southwest are seeing unprecedented levels of variable generation being added to the power generation mix. Adding higher levels of variable renewable generation creates system operation challenges.

In addition to introducing more variability and uncertainty, wind and solar photovoltaic generation can have an impact on the dynamic performance of the power system in response to disturbances. Many wind and solar photovoltaic generators do not have inherent inertial response because of the present controls associated with the power electronic interfaces to the grid. As a result, when these new technologies replace conventional generation, the frequency response and modal behavior of the power system will change. The industry needs to understand and quantify these challenges, and develop solutions to address them to enable effective and reliable integration of renewable resources for the energy future.

The Technology

The DOE is providing grants to install more than 850 PMUs. Per the DOE, these PMUs “will cover 100% of the U.S. electric grid and make it possible for grid operators to better monitor grid conditions and prevent minor disturbances in the electrical system from cascading into local or regional power outages or blackouts. This monitoring ability also will help to maintain grid reliability as the grid evolves in ways such as incorporating large blocks of variable renewable energy, like wind and solar power, to take advantage of clean energy resources when they are available and make adjustments when they are not.”

As the United States prepares to integrate larger amounts of renewable generation resources, synchrophasor technology can help in multiple ways:

• Situational awareness

  This is a real-time understanding of the state of the system and how potential actions may affect it. Having complete and up-to-date information is essential for managing complex systems such as the grid. When monitored at critical locations, the information may help detect system stress and foretell an impending system emergency. The operator may reach a high level of awareness much quicker using this information rather than using traditional SCADA data.

• Dynamic performance

  Synchrophasors can assess how the dynamic performance of the system changes with various levels of renewable generation penetration. Many of the new generation sources are more remote from load centers than conventional generation and will result in the need to move power across longer distances. Synchrophasors will provide the ability to monitor phase-angle differences and potential oscillatory modes that need to be managed to maintain system stability.

• System model validation

  As wind, solar photovoltaic and other emerging resources become more prevalent across the grid, accurate models will be needed to ensure reliable system planning and operation. Synchrophasors will provide a key data resource for developing and validating system and component models.