IEEE Power & Energy Magazine - January/February 2022 - 77

observe pre-event load flows and rapidly detect conductor
breaks, even on multiterminal lines. Charging currents into
broken conductor sections from each end helps to locate a
break for rapid field crew deployment. Along with the FCP
algorithms, the TFCP scheme includes high-sensitivity
ground fault detection to trip within a few power cycles for
nonbreak fire risk events, such as tree branches falling on
and blowing into lines from outside the vegetation management
right-of-way.
The TFCP system can detect and de-energize a line in fewer
than 400 ms for falling conductor events and arcing ground
faults of thousands of ohms whether accompanied by a break
or not. The design is based on automation controllers installed
in substations adjacent to protective relays. PMU data streams
from local relays and remote line terminals-the same data
streams supplied to the WASA system at the control center-
provide the controller with complete, real-time current and voltage
measurements. Programmed algorithms detect evidence of
a conductor break or low-current ground fault and issue trip
commands through local relay outputs to line circuit breakers.
Some relays are also programmed with an internal logic that
can detect conductor breaks in parallel with the scheme based
on PMUs and automation controllers.
TFCP equipment and programming have been extensively
tested on a model of a section of the SDG&E 69-kV transmission
system, programmed on real-time digital simulator
arrays in the company's integrated technology facility and at
developer sites. In laboratory hardware-in-the-loop tests, the
TFCP solution has demonstrated its tripping speed, dependability,
and avoidance of undesired behavior for a host of
break simulations, faults, and operating events on protected
line and adjacent power system elements. TFCP controllers
capture records of PMU data surrounding an apparent break
or ground fault for postmortem plotting of algorithm performance
and event replay using PC tools.
Figure 11(a) and (b) presents example plots of TFCP operation
for a simulated break of a 69-kV line carrying a load. Every
time increment (trace dot) is a synchronized measurement frame
time of 16.7 ms (60 PMU data frames/s). The real-time digital
simulator model of the break event includes a simulation of
the series arc that may occur as broken load-carrying conductor
ends separate. Automation controller logic checks for normal
line operation before the event as well as a variety of conditions
to distinguish a conductor break from other problems.
Break detection is confirmed within two to three data frames
or fewer than 50 ms. Separate current differential algorithms
detect ground faults, even with thousands of ohms of resistance,
and issue trip commands within a similar time frame.
Summary
SDG&E is among electric utilities in the western United
States and other regions around the world facing an alarming
increase in wildfire risks due to changing weather patterns
and drought. Fires can be triggered by faults, failures,
and dry vegetation contacting operating power apparatus.
january/february 2022
SDG&E has confronted this risk for more than a decade
with a combination of operating and situational awareness
innovations, organizational preparedness, hardening of system
infrastructure, and sustained technical innovation.
On the innovation front, the company's initiatives include
the following:
✔ advanced weather data gathering and processing
✔ operational monitoring, event preparedness, sectionalizing
ability, and safety shutdowns
✔ big data processing platforms and tools for fire riskrelated
analysis
✔ grid hardening programs based on asset data analysis
✔ advanced circuit apparatus to reduce fire risk
✔ new circuit monitoring equipment
✔ new fault protection methods and schemes
✔ WASA development, including a system for the transmission
grid
✔ new fault protection strategies that improve the sensitivity
and speed of existing relays to reduce the arcing
ignition risk from failures and faults
✔ pioneering transmission and distribution circuit FCP
schemes that can anticipate, minimize, and avoid arcing
ground faults from conductor and hardware failures.
Distribution FCP is being aggressively deployed across
the system, with priority for service areas with elevated fire
risks. TFCP has been proved in the laboratory and is being
installed for testing on the 69-kV transmission system at the
time of writing. With PMUs already installed across the
transmission system for WASA, TFCP can be expanded for
the protection of the transmission grid in high-fire-risk areas.
For Further Reading
W. O'Brien, E.A. Udren, K. Garg, D. Haes, and B. Sridharan,
" Catching falling conductors in midair - Detecting and tripping
broken distribution circuit conductors at protection speeds, " in
Proc. 69th Annu. Conf. Protective Relay Eng. (CPRE), Apr.
2016, pp. 1-11, doi: 10.1109/CPRE.2016.7914881.
P. Fairley, " When power lines break, a new control system
keeps the sparks from flying, " Interview of W. O'Brien
of SDG&E, IEEE Spectr., Sep. 2018.
E. A. Udren and T. Rahman, " WASA and the roadmap to
WAMPAC at SDG&E, " PACworld Magazine, vol. 49, Sep. 2019.
Biographies
Eric A. Udren is with Quanta Technology, Raleigh, North
Carolina, 27607, USA.
Chris Bolton is with San Diego Gas & Electric, San Diego,
California, 92123, USA.
Dan Dietmeyer is with San Diego Gas & Electric, San Diego,
California, 92123, USA.
Tariq Rahman is with San Diego Gas & Electric, San
Diego, California, 92123, USA.
Sergio Flores-Castro is with San Diego Gas & Electric,
San Diego, California, 92123, USA.
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