IEEE Electrification - March 2021 - 22

Currently, there are
synchrophasor
measurement
systems in every
developed country
worldwide.

60.2
60.1
60
59.9

Active Power (MW)

4:00

8:00 12:00 16:00 20:00 24:00 28:00
Time (s)
(a)

-0
-5
-10
-15
-20
-25
-30
-35
-40
0:00

4:00

8:00 12:00 16:00 20:00 24:00 28:00
Time (s)
(b)

50
0
4,

00
0
4,

50
0

00
0

50
0

00
0
2,

50
0

00
0

50
0

59.7

155
150
145
140
135
130
125
120
0:00

Old Model Simulation
PMU Data
New Model Simulation

59.8

Time in Seconds After 22:00:00.000
Figure 12. Oscillation at about 4.3 Hz caused by unstable inverter
control. The frequency is too high to be detected or analyzed by SCADA.

wide-area observability and detail
with accurate time stamps to resolve
system interactions.
System model accuracy has been a
long-standing problem. After the 1965
blackout in New York, utilities began
using models extensively to plan systems operation. The models were
somewhat incomplete but provided a
better tool to assure reliability than
simple scheduling. As grids have
grown and power transfers have
become more regional, reliance on models has increased.
However, limitations with accurate and detailed measurements to validate the model created some spectacular
failures, such as the 1996 blackout in the WECC. Since
then, increasing effort has been put into model validation. Phasor measurements have proven to be essential
for this task. Models are built with the same frequency
domain representation that phasors provide. Techniques
have evolved where we can take operational phasor data
and compare them to the model data for the same event
and demonstrate that the model is correct or not. Using
several events, we can apply techniques to update and
correct the model (Figure 13).

Reactive Power (MVAR)

the entity area. Each of these systems
covers a key area of a grid that enables
visibility of the grid for operation and
analysis. All of these systems include
real-time data reporting to an operation center to support monitoring and
control as well as system analysis. The
benefits of phasor measurement systems like these include:
xx
operation analysis
xx
model validation
xx
situational awareness for operators
xx
alerts for problems
xx
regulatory standards compliance
xx
RAS and other advanced controls
xx
tools to support phasor measurement systems.
The most common and important uses are operation
analysis and model validation. Since phasors capture system dynamic response so well, they provide essential
details of the system events and system characterization.
They provide detailed measurements of the system
response to a wide range of phenomena. This has become
increasingly important as power systems incorporate
power electronics. Unlike more traditional rotor and iron
core transformer-dominated electrical phenomena, newer
system generation resources and controls use electronic
controls. Grids are incorporating increasing numbers of
renewables. Most renewables either produce dc power or
convert their output to dc for inversion onto the ac power
system. System ac is generated by an inverter with electronic controls.
Other system controllers, such as SVCs and TCSCs,
use electronic controls. If the control is not properly
matched to the system, it can become unstable and
oscillate, potentially exciting an existing natural mode.
These controls can create very high frequency reactions
that are hard to detect with traditional measurements
(Figure 12). They can also create very unusual interactions that are hard to resolve without comprehensive,
long-term recordings taken over a wide area of the grid.
Phasor measurement systems can provide that

I E E E E l e c t r i f i cati o n M agaz ine / MARCH 2021

Figure 13. The model calibration showing generator (a) real and (b)
reactive power reacting to an event. First, the recorded PMU data
(blue) is compared with the simulation using the original model (red)
and then compared with the updated model (green) after calibration.
(Courtesy of Electric Power Group.)

IEEE Electrification - March 2021

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