IEEE Power & Energy Magazine - September/October 2015 - 37

The Deployment of Phasor Measurement
Technology in the ERCOT Region

T

THE ELECTRIC R ELIABILITY COUNCIL OF TEXAS (ERCOT) SERVES AS THE
independent system operator for most of the state of Texas. There is more than 74,000-MW capacity
for peak demand and over 11,000 MW of operating wind generation capacity in ERCOT. In February
2015, wind generation reached a record output of 11,154 MW, which was 34% of the load at the time.
Recognizing the benefits of synchronized phasor measurements, ERCOT began a project in 2008
to implement this technology in its operations and planning processes. The project, coordinated by the
Center for the Commercialization of Electric Technologies (CCET) under a grant from the U.S. Department of Energy, engaged various entities, including ERCOT transmission owners (TOs) and the Electric
Power Group (EPG). EPG contributed several real-time and offline data processing and analysis tools to
the project, which were used by ERCOT engineers to monitor and study the synchrophasor data. These
analyses have indicated that synchrophasor data can greatly improve operations procedures and planning
studies at ERCOT.

The ERCOT Phasor Measurement Unit Network
Presently, synchrophasor data is available only from phasor measurement units (PMUs) installed on
the networks of transmission service providers participating in the CCET-related collaborative effort.
Figure 1 shows the geographical locations of the existing networked PMUs in the ERCOT system. The
data transmitted by the PMUs, at a resolution of 30 samples/s, is very valuable in postevent dynamic
analysis, real-time small signal stability monitoring, and generator model validation. PMUs installed
in the west and north-central areas allow ERCOT to monitor the stability conditions on the interface
between these two regions. In addition, as most of wind generation is installed in West Texas, the data
from PMUs located close to wind power plants has also helped ERCOT to validate dynamic wind generation models. The communications network is shown in Figure 2. The ERCOT phasor data concentrator (PDC) synchronizes the data and provides the data stream to real-time visualization applications in
the ERCOT control center and also archives the data for offline studies.

Detection of Oscillations in Real Time
During a real-time event in January 2014, ERCOT operations engineers observed oscillations from a single PMU located near a wind plant (Figure 3). The wind plant, due to controller settings, had been susceptible to oscillations in the past under weak system conditions (the outage of a nearby line). However,
with the plant generating around 56 MW and no outages in the area, the oscillations were unexpected.
Removing the wind farm automatic voltage regulator (AVR) from service did not help mitigate
the oscillations; to address the situation, ERCOT advised the wind farm to curtail output to 45 MW.
This reduced the oscillation magnitude but did not remove it completely. The unit was further constrained to 40 MW, and the oscillations ceased thereafter (Figure 4).
The oscillation frequency was 3.3 Hz with damping below 1% (Figure 5). This was in agreement
with earlier studies, indicating a relation to controller settings at the plant. The plant operator confirmed
that a system update had been installed (to improve performance) around the time the oscillations
began. The updates were uninstalled, and this eliminated the oscillations for all levels of plant output.

ERCOT Phasor Measurement Task Force
During the latter half of 2013, the ERCOT board of directors adopted a 2014-2018 strategic plan,
which acknowledged "the greater use of synchrophasor measurement of real-time grid status" as a
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Table of Contents for the Digital Edition of IEEE Power & Energy Magazine - September/October 2015

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