By Bill Rose and Albert Leirbukt, ABB Inc.
August marks two dates of historical interest in the power industry: the fifth anniversary of the massive 2003 blackout that spread across the northeastern United States and Canada, and the three-year anniversary of the U.S. Energy Policy Act of 2005 (EPAct).
One prominent area of focus in EPAct is wide area monitoring systems (WAMS), which represent the next step in systemic reliability enhancement. Wide area monitoring systems now offer a supplement to existing SCADA/EMS systems.
WAMS use a combination of technologies to provide a highly accurate and dynamic view of the grid. The capabilities of these systems are also being extended to include control operations and soon will likely incorporate automated wide area protection schemes as well. The collective term for these distinct functional areas (monitoring, control and protection) has become known as wide area applications.
The EPA and WAMS
One section of the Energy Policy Act of 2005, section 1839, called specifically for the U.S. Department of Energy and FERC to produce a report on “Steps to Establish a Real-time Transmission Monitoring System for Transmission Owners and Operators within the Eastern and Western Interconnections.” That report paints an optimistic picture of the ability of WAMS to both mitigate and prevent major disturbances on the transmission system. It also points out a number of challenges that must be addressed if the full potential of WAMS is to be realized.
The DOE/FERC report draws heavily from the final report of the US-Canadian Blackout Task Force–in particular that report’s assessment of failures in monitoring of line loss, voltage stability and real-time diagnostics. A “lack of situational awareness” comes up again and again as a primary reason for why events in one region eventually precipitated outages in another.
The DOE/FERC report sets out what we need a real-time transmission monitoring system to do and then goes on to lay out the steps needed to establish such a system in practice. It notes that today’s SCADA systems have a few important limitations–proprietary data structures, low-bandwidth of existing communication protocols, a lack of connectivity between control centers–but it also makes clear that any meaningful improvement in monitoring capability will necessarily begin with existing systems.
One example of a near-term step would be to address the closed data structures of today’s SCADA systems. The common information model (CIM) could offer a ready alternative, and with an open data model much of the other work becomes that much easier.
However, as the DOE/FERC report acknowledges, improving SCADA systems will only be an interim step on the way to widespread deployment of WAMS. So, where are we in the development of this much-anticipated technology? As is the case in many other fields, the underlying component technologies are already here; it’s the implementation and the business case that need work.
At the heart of wide area monitoring systems are phasor measurement units (PMUs), which deliver a level of data granularity that is many times finer than that provided by current measurement devices like remote terminal units (RTUs). When combined with time stamps from GPS satellites and connected to a WAMS, the result is a picture of grid conditions that is truly real-time in nature.
For more than a decade, there has been a substantial R&D effort under way in WAMS, and, today, there is a substantial body of output from these initiatives. There are many pilot projects going on as well, but the number of operational applications of WAMS remains small, again largely due to remaining questions about implementation and economics.
Examples from Abroad
Perhaps the most newsworthy example to date of the benefits of wide area monitoring occurred in 2004 when the two separated regions of UCTE were re-synchronized with the help of PMUs deployed in the two previously asynchronous regions. Etrans, the independent grid coordinator in Switzerland, had already installed PMUs on its critical north-south transmission corridor in 2003 to assess actual loads, the impact on system security after a sudden loss of segments of the sometimes heavily loaded corridor, and the effect of wide area oscillations on the European grid generally.
Croatia’s HEP had also installed PMUs, which would help monitor the resynchronization process as well. In the lead-up to the reunification of the grid, a PMU in Greece was connected to the Etrans control center. With the support of real-time data provided by these systems, grid operators could observe grid conditions more precisely than ever before, and the reunification process was completed without incident in less than 90 minutes on Oct. 10, 2004.
The UCTE project was an important demonstration of WAMS capabilities, and both ETRANS and HEP continue to use their systems to monitor grid conditions across Europe.
APG, Austria’s largest producer and distributor of electric power, operates in a highly meshed system with interties to all of the surrounding countries. Congestion is a problem, with three 220 kV lines moving power southward from generators in the northeast of the country. The reliability issue came into sharp focus in 2003 when the trip of a neighboring 380 kV line nearly caused the complete shutdown of the 220 kV system. APG decided to deploy WAMS as an immediate measure to monitor system conditions while three phase-shifting transformers were installed to help prevent further problems. APG intends to deploy even more PMUs to assess the effectiveness of the phase-shifting transformers and then optimize their use into the future.
Last year, EGAT, the state-owned grid operator in Thailand, installed a WAMS on the country’s long north-south transmission corridor. Operations on this line were limited due to power oscillations. This presented concerns not only about reliability but also about the transmission system’s ability to support the push toward privatization of the generation sector. Now the Thai operators can monitor damping, frequency and amplitude of oscillations and take corrective action before minor fluctuations become major disturbances. In this way, the WAMS serves as an early warning system.
Meanwhile, Back in the USA
The Consortium for Electric Reliability Transmission Systems (CERTS), a consortium of national laboratories, universities and industry entities formed after the western U.S. blackout in 1997, has been researching WAMS technologies for 10 years. BPA, along with California ISO, Southern California Edison, Pacific Gas and Electric and other major WECC utilities, have also been working in the WAMS area since 1997 when EPRI sponsored WAMS projects at BPA. There are currently more than 50 PMUs installed in the WECC.
More than 35 PMUs were installed at various utilities across the eastern U.S., as part of the former Eastern Interconnect Phasor Project (EIPP)
In 2007, (DOE) and the North American Electric Reliability Corporation (NERC), along with involved electric utility companies and other organizations, formed the North American SynchroPhasor Initiative (NASPI). This effort combines the previous Eastern Interconnection Phasor Project (EIPP) and various activities associated with WAMS research, development and deployment activities that have been under way in the North American electric power system for a number of years as the primary focal point for continued DOE and NERC support and facilitation.
Most of the “early adopters” in the NASPI family are larger utilities and RTOs–AEP, TVA, Entergy, Ameren, NYPA, FirstEnergy, Florida Power & Light, Manitoba Hydro and Southern Company. TVA has committed to providing data collection services for the system through its super-PDC (phasor data collector) until 2008. Data streaming in from the WAMS network is already available to participating utilities, and a benchmarking process has been initiated for phase angles and other information that will help to calibrate the system. The project is also looking at how to best integrate phasor data in state estimation.
The vast amount of data coming from PMUs presents a variety of challenges, not the least of which is security. Managing who can see that information and how much of it they can see are two of many questions that EIPP is working to answer. For now, NASPI participants must sign non-disclosure agreements to gain access to the data stream, but clearly this is only a first step in a robust security regimen.
The aforementioned need for a common data structure is another hurdle. CIM could provide a model here, but the utilities must first agree on what data to gather. There are also disparities in terms of data collection process (filtering practices, sampling rates, data compression techniques), data analysis (differences in algorithms used by PMU vendors), and data archiving (what to save, how and where to store it). The DoE/FERC report under Section 1839 of EPAct goes on to identify additional issues such as the need for a common visualization package so that all users will be able to view the real-time information in a similar fashion.
Finally, there is the question of ownership: Who will hold the keys to the WAMS infrastructure, especially the communications systems that link the PMUs with the PDCs and the utility control rooms with one another?
This brings us to the business case for WAMS, and here the water gets murkier. Everyone seems to agree on the potential of the technology; what’s not so clear is who is willing to pay for it.
Beyond the Business Case
The much-heralded reliability standards being established under the U.S. Energy Policy Act of 2005 (EPAct) could act as a motivating force, but it still isn’t clear if that will translate into investment in WAMS. The fact remains that even when all of the technical challenges are overcome, the work of educating the industry will still remain.
Transmission owners, RTOs and others responsible for managing the grid will need to be convinced of the value of WAMS in relation to the cost, and they will need to have a clear integration/upgrade path drawn out for them.
NERC, in its role as the Electric Reliability Organization (ERO), plays a pivotal role in this process after the establishment of the NASPI project in 2007. NERC could impose standards for real-time monitoring, or at the very least for “situational awareness,” that would drive the adoption of WAMS across the industry.
Taking the long view, it seems inevitable that phasor-based wide area monitoring is destined to become an integral part of everyday grid operations. The benefits are compelling, and with the amount of work being done in the field, WAMS advocates are confident we will eventually get there. NASPI is only one of several initiatives. There are research projects being conducted by the California Energy Commission’s PIER project, and ERCOT is reportedly looking into launching a phasor research initiative of its own.
In his presentation at the May 2006 EIPP Workshop in Chicago, program executive steering committee chair Terry Boston included a slide showing the development of MRI technology as an analogy for WAMS. Beginning with a Nobel Prize in 1952, the R&D process went on for 25 years before the first scan of a human subject was done, and it would be many more years still before the technology became commonly available.
Similarly, in our own industry, SCADA/EMS systems underwent their own cycle of development, adoption and widespread implementation. WAMS will likely follow a similar path.
At this point, WAMS technology has been proven and the development step is more or less complete. We’re now in the adoption phase. If we can overcome technical challenges, build a business case and establish a workable system of reliability standards that include requirements for real-time monitoring, the stage will be set for WAMS to realize its full potential.