POWER February 2021 - 25

OPERATING BEST PRACTICES
According to Intertek's Asset Integrity
Management division, the effects of cycling
have a " large spread " in terms of
costs, as well as reliability impacts, with
special significance for older conventional
units, including coal and older CCGT
units, which is why the firm urges that
transmission expansion studies include
power plant cycling as an input.
" Every time a power plant is turned off
and on, the boiler, steam lines, turbine,
and auxiliary components go through
unavoidably large thermal and pressure
stresses, which cause damage. This
damage is made worse by the phenomenon
we call creep-fatigue interaction, "
Intertek said in a report compiled for the
Western Electricity Coordinating Council
in May 2020. " Relating this discussion
to power plants, if an older, base loaded
plant (that used to have three to six
starts per year and is at 40 to 80% design
life from creep damage) is now suddenly
dispatched to operate at 50 starts
per year, it may take only 2 to 6 years to
cause component failure, " it explained.
" Thus, while cycling-related increases
in failure rates may not be noted in the first
months, critical components will eventually
start to fail. Shorter component life expectancies
will result in higher plant equivalent
forced outage rates (EFOR) and/or higher
capital and maintenance costs to replace
components at or near the end of their
service lives. In addition, cycling increases
may result in reduced overall plant life.
How soon these detrimental effects will
occur will depend on the amount of creep
damage present and the specific types
and frequency of the cycling, " it said.
Weather-Related Lapses
Extreme events related to weather and
fires have typically figured prominently
as key causes of forced outages in
NERC's GADS data, but NERC continues
to monitor them for their severe implications
on reliability. In 2019, it recorded
five days that qualified as " extreme. "
" On these days, the generation portion
of the BES [Bulk Electric System]
experienced outages that were two to
three times as severe as the average
day, " NERC explained. " These outages
were initiated by a variety of causes with
fuel, ignition, and combustion systems
being the main contributor, primarily
within the Eastern Interconnection. Additionally,
lack of fuel continues to appear
as an issue for natural gas and oil units
within the Eastern Interconnection during
cold weather events. "
In 2020, extreme events continued,
February 2021 | POWER
2. Generation forced outage events per unit caused by human error since 2015. Source: NERC
most prominently in August 2020, when
the California Independent System Operator
(CAISO) suffered two load-shedding
events. In a final root cause analysis released
on Jan. 13, CAISO, the California
Public Utilities Commission (CPUC), and
the California Energy Commission (CEC)
pinned the events on a climate change-
induced heat wave that drove power demand
beyond existing electricity resource
planning targets. The final root cause analysis
suggests that the supply gap was exacerbated
by an underperformance of its
natural gas fleet. While it notes the rotating
outages were not caused by any single
generator or resource type, at least one
gas unit, the 494-MW Blythe Energy Center
in Riverside County, went out of service
because of " plant trouble " on Aug. 14.
(On Aug. 15, the Panoche Energy Center
in Fresno County ramped down unexpectedly
from 394 MW to about 146 MW, exacerbating
that day's crisis, but CAISO has
since determined the ramp down was due
to an " erroneous dispatch " from CAISO.)
However, acknowledging that " Under
very high temperatures, ambient derates
are not uncommon for the natural
gas fleet, and high temperatures reduce
the efficiency of these resources, " the
CEC in December held workshops to
explore potential technology options to
increase the efficiency and flexibility of
the existing gas fleet to meet near-term
system reliability as the state transitions
to zero-carbon resources. Improvements
suggested at one workshop included
installing advanced gas path (AGP) technology;
inlet air cooling; and other cooling
system improvements in combined
cycle and simple cycle gas turbines, as
well as considering onsite battery storage
and software upgrades.
During the session, GE Gas Power and
Siemens Energy separately presented a
suite of solutions that could be implemented
in phases before the summer
of 2021 and 2022. AGP would require replacing
mechanical components such as
www.powermag.com
blades, buckets, noodles, and shrouds
within turbines to enable operational
flexibility and efficiency. Inlet air cooling
involves cooling the air through evaporative
coolers or mechanical chillers before
it enters the gas turbine to increase air
density. A number of power companies
at the session also discussed advantages
and disadvantages of some of the
suggested solutions, including their results
with APG installation, combustion
turbine enhancements, and hybrid gasbattery
plant operation.
The Bane of Human Error
NERC's GADS data shows that forced
outages attributed to human error averaged
1% of all forced outage events over
the past five years-which is small, but
still substantial. NERC groups these errors
into three categories: general human error,
procedural human error, and staff shortage.
Only nuclear generation showed a
" notable increase " in human-error-caused
events in 2019 (Figure 2), NERC noted.
" The sub-causes of staff shortage and
procedure human error were present for
nuclear generators in 2018 and 2019. "
Over 2020, the pandemic and its ensuing
workforce challenges prompted a number
of regulatory changes across the industry,
but how human error played out amid
these challenges remains to be seen.
According to NERC, many of the
top root causes recorded over the past
five years suggest a lapse in company
management
and
organization. Root
causes include job scoping that did not
identify special circumstances or conditions;
system interactions that were not
considered or identified; work packages
that were inadequately prepared; risks or
consequences associated with changes
that were not adequately reviewed or assessed;
and finally, management policy
guidance or expectations that were not
well-defined, understood, or enforced. ■
-Sonal Patel is a POWER senior
associate editor.
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POWER February 2021

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