IEEE Electrification - March 2021 - 23

Situational awareness became an important consideration after the 2003 blackout in the northeastern United
States. In that incident, the utilities involved did not have
the visibility to evaluate the overall situation that was
evolving. It involved several utilities spread over a large
area; customary procedures focused the operators' attention on the area that they control with little visibility outside of that area. Situational awareness should present
information about the entire grid in which they operate to
prevent surprises from outside of their control area. Phasor
systems have evolved as wide-area systems since they
look at the key grid parameters of voltage magnitude,
angle, and frequency. Both utilities and commercial companies have developed displays and alarms for operators.
These products started off with more traditional observations like voltage profiles and system phase angles and
have evolved to include oscillation detection with source
location, one line diagrams, and voltage stability sensitivity.
Most use various color schemes and alarm limits to alert
operators to potentially unstable situations (Figure 14).
Features have been added to take advantage of phasor
capability. Phasors have proven the best way to detect
oscillations. New techniques can locate the source of oscillations in real time and provide notification to operators so
that they can resolve the problem. Phasors can provide
input to real-time contingency analysis that can be used as
validation or backup for a similar application supported by
the energy management system (EMS). Phasors can also
supply system phase angles that can be used to check that
the angle across an area is within the allowable limits. This
can provide a backup to the traditional monitoring of

individual line power flows. These new applications complement the traditional EMS operation, give a wider area
view, and provide independent backup.
Traditional power systems up to the 1980s were mostly vertically integrated with each utility, supplying their
own generation and transmission to serve their own load.
With deregulation and the growth of renewables, systems
have become more diverse, interconnected over large
areas, and dependent on a variety of resources for energy,
some quite intermittent. Governmental regulation [under
the North American Electric Reliability Corporation
(NERC) in North America] has increased to manage this
growth and tried to assure the reliability of supply. NERC
regulations are focused on planning, operation, design,
maintenance, and so on without citing a particular technology in most cases. However, there are 23 standards or
regulations that can be addressed using phasor data since
it has proven to be so accurate and comprehensive. In
addition, another seven regulations call for measurements that phasor measurements can and do supply. In
this way, NERC has recognized the important contribution
that these measurements bring to the industry.
One of the earliest targets for phasor measurement systems was control systems, both medium speed, such as
voltage control, and high speed, like RAS systems. So far,
phasors have been used only in a few controls, and those
have been operated intermittently. One of the first, though
intended only as a demonstration project, was the EPRIsponsored wide-area control for WECC in 1993. This project
produced some valuable PMU deployments but no definitive control results. The North American blackouts in 1996

Figure 14. An operator display using phasor measurements showing phase angles on a geographic map, an alarm dashboard with a trend
chart, and the system frequency, with both a current value and a historical chart. (Courtesy of Electric Power Group)

IEEE Electrific ation Magazine / MARCH 2 0 2 1

IEEE Electrification - March 2021

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