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Sustainable Cities and Society 35 (2017) 350–364
Contents lists available at ScienceDirect
Sustainable Cities and Society
journal homepage: www.elsevier.com/locate/scs
A framework for holistic designs of power line systems based on lessons
learned from Super Typhoon Haiyan
MARK
⁎
Kaoshan Daia,b, Shen-En Chena,c, , Mingyan Luoa, Gregory Loflin Jr.c
a
b
c
State Key Laboratory of Disaster Reduction in Civil Engineering and College of Civil Engineering, Tongji University, Shanghai 200092, China
State Key Laboratory for Geomechanics & Deep Underground Engineering, China University of Mining and Technology, Xuzhou 221116, China
Department of Civil and Environmental Engineering, University of North Carolina at Charlotte, Charlotte, NC 28223, United States
A R T I C L E I N F O
A B S T R A C T
Keywords:
Climate change
Holistic design
Power delivery systems
Super Typhoon Haiyan
Resilience
Climate Change results in possible less frequent but more intensified storm events that include so called “super
typhoons”. To ensure the resilience of the energy power delivery systems, this paper offers lessons learned from
forensic investigations of the damaged power delivery systems from the Philippines after the 2013 Super
Typhoon Haiyan. The objective is to investigate new strategies to design the power delivery systems, especially
in the coastal regions, to defend against the intensified storm events brought on by climate change. A critical
review of current power line system design approach, especially load design based on ASCE 7–10, is conducted.
The review along with extreme loading calculations revealed limitations in current design philosophies. A design
framework using a holistic approach that includes a strong backbone line system is suggested. The strong
backbone line system is to be designed for extreme loading scenario with additional considerations including
debris loading, wind-storm surge interactions and local geospatial condition with multiple wind directions.
Preliminary design of a strong backbone system for McClellanville, South Carolina, power supply scenario is
presented as a case study and is shown to be economically viable.
1. Introduction
In December of 2015, the United Nations (UN) has come to another
agreement to address the climate change issue – The Paris Agreement
(COP-21) is the latest of several global efforts to limit greenhouse gas
(GHG) emissions with the desire to deter the paths of extreme climate
changes (UNFCCC, 2015), which have been identified to include
warmer winters, draught, floods, erratic weather patterns, etc. Physical
evidence of climate changes has already been identified at different
parts of the world. Extreme climate change-associated events have occurred in recent years which resulted in significant impacts on local
economics and a drastic increase in global disaster expenditures (IPCC,
2007). Many of these climate events are directly challenging the resilience of the regional populations.
A great interest to the engineering community is what role super
typhoons (wind forces in the Saffir-Simpson category of 4 or 5) play in
the extreme weather projection of climate change (Krishna, 2009;
McDonald, 2011; Nigam and Guan, 2011; Walsh, McInnes, & McBride,
2012). Research suggests that in terms of frequency, the increase in
surface wind temperature would actually result in fewer tropical storms
with likely increased intensities and wind speeds (Lin, Pun, & Lien,
⁎
Corresponding author at: University of North Carolina, Charlotte, United States.
E-mail address: schen12@uncc.edu (S.-E. Chen).
http://dx.doi.org/10.1016/j.scs.2017.08.006
Received 31 October 2016; Received in revised form 3 July 2017; Accepted 6 August 2017
Available online 12 August 2017
2210-6707/ © 2017 Elsevier Ltd. All rights reserved.
2014). For conditions that can create such events, several theories have
been proposed. For example, Takagi and Esteban (2016) used statistics
of the region to demonstrate a strong correlation between super typhoon frequencies and intensities and the regional sea surface temperature.
The focus of this paper is on the power and energy delivery systems
(power grid), which are essential to our daily lives, and can result in
significant losses in local economics and even human deaths when
subjected to extreme storm impacts. Vulnerability of the power systems
in association with climate change is a critical area that desperately
needs attention (Liu and Pang, 2012; Vickery and Lavelle, 2012). Recent extreme storm events including the hurricanes Katrina and Sandy
in the US have already demonstrated the fierce impacts of these storms
(Ewing, Liang, & Cui, 2014). Due to the complexity of the power delivery systems, which includes power generation, power transmission,
power distribution and substations, etc., it is difficult to devise an effective method to enhance the performance of the power system for the
impending climate changes.
Super Typhoon Haiyan, formed on November 3, 2013 and dissipated on November 11, 2013, was one of the deadliest tropical cyclones along the West Pacific coastal regions. An estimated 6300 lives
Sustainable Cities and Society 35 (2017) 350–364
K. Dai et al.
Fig. 1. Haiyan Path and Townships encountered disasters.
The effects of Haiyan have been most felt on the east coast of Leyte
Island and southern tip of East Samar Island. Fig. 2 shows the track of
Super Typhoon Haiyan with its mean velocity and Table 1 with the
timed event of Super Typhoon Haiyan (reproduced from Kim, 2015). It
is important to point out in Fig. 2 that the storm arrived at its highest
speed and lowest pressure at landfall – the critical conditions for
maximized hurricane effect. Most hurricane events are already at their
down swing with reduced wind speeds upon landfalls. The flood flowed
through Tacloban city reaching 7.0 m/s (Takagi et al., 2017). After
Haiyan, the Island of Leyte experienced months of electricity and
communication losses due to the loss of transmission and distribution
structures and systems.
Continental Americas experience similar seasonal cyclone impacts
on both the Pacific and Atlantic sides – even though west Atlantics
experienced far less category five storms than the western Pacific.
in the Philippines were lost due to Haiyan (Del Rosario, 2014). Fig. 1
shows the townships that have experienced significant impacts from the
storm. Current storm measurement techniques indicate (with ongoing
debate) that Typhoon Haiyan may be the strongest storm ever recorded
at landfall. Unofficially, records indicate wind speeds of 87.0 m/s, for
one-minute sustained wind, which, if verified, are the strongest recorded wind speeds associated with a typhoon in history. The storm
began as a low pressure system initially formed on November 3, 2013
near Micronesia. The low pressure system then intensified rapidly to a
super storm on November, 6, 2013. At 23:00 UTC of November 7, the
storm arrived at Tolosa of the Leyte Island and caused wide spread
disasters, which included 722 deaths in the city of Tanauan, which is
the second most severely damaged area by Haiyan in the Leyte Province
(Yi et al., 2015). The significant storm brought precipitation reaching
615 mm between November 3 and 12 (Nguyen et al., 2014).
Fig. 2. Track of Super Typhoon Haiyan Indicated on Google EarthTM (numbers indicate peak wind speed in mph).
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Table 1
Computation of Power Pole Design Requirements for Extreme Wind Loading Scenario (Wind Speed at 89.4 m/s, Risk Category IV, Exposure Category D and Location off the Florida
Coast).
Height above ground
level (m)
0−4.6
6.1
7.6
9.1
12.2
15.2
18.3
21.3
24.4
27.4
30.5
36.6
42.7
kz
1.03
1.08
1.12
1.16
1.22
1.27
1.31
1.34
1.38
1.40
1.43
1.48
1.52
qz (kPa)
51.9
54.4
56.5
58.5
61.5
64.0
66.0
67.6
69.6
70.6
72.1
74.6
76.6
h (m)
4.57
1.52
1.52
1.52
3.05
3.05
3.05
3.05
3.05
3.05
3.05
6.10
6.10
Af (m2)
1.39
0.46
0.46
0.46
0.93
0.93
0.93
0.93
0.93
0.93
0.93
1.86
1.86
F (kN)
74
26
27
28
58
61
63
64
66
67
68
141
145
Not Including Wind Load on Conductors
Including Wind Load on Conductors
Pole Height
(m)
Base Shear
(kN)
Overturning Moment
(kN m)
Pole Height
(m)
Base Shear
(kN)
Overturning Moment
(kN m)
4.6
6.1
7.6
9.1
12.2
15.2
18.3
21.3
24.4
27.4
30.5
36.6
42.7
74
100
126
154
212
273
336
400
466
532
601
742
887
169
306
490
722
1344
2176
3225
4494
6001
7734
9712
14453
20208
4.6
6.1
7.6
9.1
12.2
15.2
18.3
21.3
24.4
27.4
30.5
36.6
42.7
275
310
345
380
450
521
591
661
735
806
880
1031
1184
1088
1591
2155
2792
4247
5953
7901
10073
12568
15229
18218
25018
32866
Fig. 3. Haiyan Path and Townships encountered disasters.
Liu and Pang (2012) simulated climate change influence on hurricane wind hazard scenarios using stochastic hurricane simulation and
HURDAT model and concluded that there may be an average increase
in wind speed of 14–19 m/s at the Northeastern US regions. Fig. 5
shows the increasing trend in the continuing average sea surface temperature (SST) in the Atlantic and the trend of continuing average of
hurricanes in the US indicating an increasing trend since early 1900s.
The intensifying hurricanes are defined based on averaging of core
pressure and wind speed.
Drawing from the lessons learned from Super Typhoon Haiyan in
the Philippines, we present in this paper a discussion about the responses of the power systems against climate change. The documentation of the damaged structures from this storm event should increase
our understanding of the damaging forces of the storm and it should
help enhance the resilient design of coastal structures. Many of the
observations and contributions from the forensic investigation groups
can help enhance the post-disaster performance of the infrastructure
and the built-environment.
Nonetheless, recent storm records also indicate an increase in higher
wind speed storms. Notably, Hurricane Patricia on October 2015
reached a sustained one minute wind speed of 96.0 m/s over western
Atlantic Ocean. However, the storm had downgraded before reaching
land and made landfall at 66.7 m/s. Fig. 3 shows the paths of Haiyan
and Patricia along with several regional cyclonic events for the past 60
years (1945–2006). Climatology recognizes the cyclic warming and
cooling cycles of the ocean. Currently, the Atlantics region is in the
warming cycle and using hurricane landfall data, Vickery and Lavelle
(2012) has found that the projection of warming Atlantic oscillations
would result in higher hurricane activities and is consistent with historical data (110 year long term data) indicating that there is a high
probability of Category 3 and above hurricanes for the near future.
Fig. 4 shows how simulated warm and cold Atlantic oscillation activities compared with historical data (long term). The data are presented
in ratio of warm or cold period versus long term data. It is shown that in
most cases the warming period would result in significant increase in
very intense hurricanes such as categories 4 and 5 storms for the entire
coastal USA. Except Florida and northeastern regions, the category 3
hurricanes would increase for most coastal USA. On the other hand, for
the cold period, there is generally a reduction of intense hurricanes with
the exceptions of Florida and northeastern regions.
2. Effects of Super Typhoon Haiyan on electric utilities
Because of the lack of storm data, the projected intensity of Haiyan
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K. Dai et al.
Fig. 4. US Hurricane Event Projection during AMO.
Fig. 5. Continuing Average Annual Sea Surface Temperature and Hurricane Events.
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K. Dai et al.
Eastern Samar Island (Bricker et al., 2014; Kennedy et al., 2016). Based
on post-disaster field observations, Yi et al. (2015) reconstructed a
storm surge map for Tanauan, which does not match the storm surge
hazard map provided by the local municipal office to the local residents. Kim (2015) used global climate modeling tools and simulated
significant wave heights during Haiyan at 30 m in outer West Pacific.
Finally, Nakamura et al. (2015) compared numerical modeling and
actual field observations of storm surge and suggested that the storm
surge height had reached 5 m at Tacloban on November 8. Other storm
surge related studies involved the investigation of the coral reefs both
as an indicator of the damaging effect of the storm waves (Engel, May,
Brill, & Brueckner, 2015) and as a modifier of wave energy (Shimozono
et al., 2015). Shimozono et al. (2015) suggested that the combined
wave height from infragravity waves and sea swell can reach as high as
16–20 m (near Matarinao Bay).
Based on our own field observations, the storm surge with wave
setup effects can be much higher than 5 m at locations. This is especially true for the Port of Tacloban where coaster ships that did not
evacuate from the shallow strait (with a spacing less than 2 km between
Leyte and East Samar Islands) during the typhoon were forced to shore
on the coastline of Balangay 70 in Tacloban. Some of the ships docked
at shore sites are at least 2 m above average sea level – indicating that
the wave height must be much higher to create the buoyancy that
moved the ships. The Tomi Elegance (IMO: 8351508), for example with
self-weight of 249 tons has a 600 dwt (deadweight tonnage) capacity,
would have a draft of at least 5 m. Hence, the inundation height at the
Port of Tacloban should be higher than 5 m.
As part of the Cancabato Bay of the San Juanico Strait, Tacloban is
uniquely located within a siting where the northeast traveling wind
driven waves from the Pacific East can streamline into the Port of
Tacloban and increase the water volume within the strait without encountering much obstruction. The San Juanico Strait is about 38 km
long and limits the flow of the waves until reaching Babatñgon
(Janbatas Channel), which opens into the Samar Sea. San Pedro Bay
also has a particularly shallow sea floor with an average depth of about
20 m and a maximum depth of 36.6 m (Campos, 2003). As shown in
Fig. 6, the direct waves and the reflected waves from East Samar were
based on satellite observations was weaker than the actual ground observed
intensity. Hence, the observations of structural damages collected on the
ground are important data that can help establish the effects of Haiyan on
built structures and supplement other disaster observations (Shimozono
et al., 2015; Tajima et al., 2014). Disasters associated with Haiyan included
heavy rain, storm surge, flooding, strong wind forcing, heavy debris accumulations and landslides, etc. As a result, many structures have experienced
multiple damage scenarios (Chen et al., 2015). Other than wind loading,
there is also evidence of high storm surges associated with inundations as
well as high wave actions.
Extreme water surface elevations during a storm surge can be amplified locally by regional bathymetries (Kennedy et al., 2011; Mori
et al., 2014). However, extremely high resolution topography, bathymetry and atmospheric data are needed to accurately hind cast the
actual surge heights. The near shore wave phenomenon associated with
a tropical storm wind is complicated by time-varying incident forcing
and wave-induced motions. As a result, the storm surge is a complex
compilation of infragravity motion (short wave forcing), static sea
swells, and long waves driven by winds (Contardo and Symonds, 2013;
Holman and Bowen, 1979). Despite several satellites monitoring data,
there are no actual measurements of the storm surge heights during
Haiyan (Nguyen et al., 2014). The storm surges were estimated at 5 m
in most climate models; however, considering local conditions, the
wave height can be as high as 20 m at some locations, especially off
Eastern Samar Island (Bricker et al., 2014; Kennedy et al., 2016).
To determine the actual storm surge level during Haiyan, several
studies have been conducted: Takayabu et al. (2015) used high resolution regional wave model to estimate the worst climate change
effect in Tacloban and resulted in 5.15 m of surge; Lee and Kim (2015)
used a comprehensive hydrodynamic model that included meteorological conditions and wave induced dissipations stress from wave
breaks, whitecapping and wave breaks from variable ocean floor
depths, to simulate storm surges; using historical data, Lapidez et al.
(2015) determined vulnerable areas in Philippines using simulated
Typhoon Haiyan-level storm surges. The storm surges were estimated at
5 m in most climate models; however, considering local conditions, the
wave height can be as high as 20 m at some locations, especially off
Fig. 6. Theorizing Landshoring of Cargo Ships at Tacloban as a Result of Wave Actions during Haiyan.
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Fig. 7. Communication Tower Collapse at Dulag.
(Ormoc-Babatngon) owned by the National Grid Corporation of
Philippines and step down to distribution lines. In Tabloban, most
distribution line pole structures are either wood or concrete poles.
Significant number of distribution/transmission pole structures has
been damaged by wind and wave impacts, especially close to the
coastal areas. Some mountain top transmission towers also sustained
structural damages, but no complete destructions. Because coconut
trees are the predominant regional hard wood tree types and many of
the trees were brought down by the storm, there was a huge amount of
debris, which also impacted the distribution lines. The combined effects
from the storm on the power delivery systems resulted in an overhaul of
the entire system at the disaster area.
Forensic investigation of the failed power structures in Leyte and
East Samar indicates that the failure profiles of pole structures can include tilting (leaning), buckling, uprooting of foundation, etc. Fig. 10
shows examples of failed distribution lines pole structures. Also shown
in Fig. 10, the conductor cables can play critical roles to the loading and
stability performance of the poles. There were buckled pole structures
such as shown in Fig. 10c, which is a pole structure close to the Tacloban airport. However, due to the massive debris accumulation, it is
not certain if the pole breakage was due to debris impacts or actually by
flood water. Post disasters images from several internet sources showed
many power pole structure failures (regardless of material type).
forced together at the Port of Tacloban and resulted in strong waves
that brought ships on land. Such convergence of waves unfortunately
cannot appear in climate models which typically have a resolution of
1 km or higher.
To study the effects of Haiyan on the power delivery systems, observations were made on both distribution and transmission structures
at various locations on both Leyte and East Samar. Current reported
study on Haiyan is based on data collected during a trip made in 2014
and only considered failed power and communication structures with
forensic investigation of failed structure damages based on wind and
flood water effects (Chen et al., 2016). A notable observation is the
water damaged structures can reach as far as 1000 m from the coast.
This is because many of the storm surges ran up the riverine system that
connects to the Leyte Gulf. More detailed studies on storm damage effects on electric power systems for other storm events have been studied
such as by Kwasinski, Weaver, Krein, and Chapman (2006).
First of all, the strong wind forces are evident from the destruction
of several communication structures near Tacloban and in East Samar:
Fig. 7 shows a communication truss tower near the coast of Dulag that
was damaged by the strong hurricane. The location is about 200 m from
the coast and did not experienced storm impact. Protected by surrounding housing, the structure failure is all due to the strong wind.
Also shown in figure is the coastal destruction near the tower.
Fig. 8 shows examples of damaged communication towers including
poles, truss poles and truss structures from both Leyte and East Samar.
It is especially interesting regarding the structure shown in Fig. 8b,
which experienced both severe wind load and water damages. Close ups
shown in Fig. 9 revealed that the structure experienced separation of
the base plate from the foundation indicating the strong insufficient
base plate thickness to resist against structure pull out. There is also
evidence that shows that the structure was immersed in inundating
water for some time.
The regional power supply is through a 138 kV transmission line
3. Conventional wind and flooding design considerations
Most US power transmission and distribution structure designs are
based on ASCE 7 (2013) wind and flood load provisions. The basic wind
and flood requirements for structural design of transmission systems are
derived from statistical and historical analyses of severe weather
events. The current design method for wind uses a 50-year return
period on “extreme radial ice thickness combined with 3-s wind velocities” shown by a base wind speed map for different design values to
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K. Dai et al.
Fig. 8. Examples of Collapsed Communication (a) Pole, (b) (c) Truss Poles and (d) Truss Structure.
represent the loading situation in different locations. The statistical
analysis performed helps to determine how severe the weather loading
should be based on how it has played out in the past as well as factoring
in the potential increases due to anomalous weather events. The basis of
design suggests a reliability-based design (RBD), which helps simplify
the process of turning severe weather conditions into loading scenarios
Fig. 9. Communication Truss Pole Structure Collapse at Tacloban near Picas- San Jose DZR Airport Road (Structure Experienced both Wind and Water Damages).
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K. Dai et al.
Fig. 10. Distribution Line Pole Structure Failures in Tacloban.
loadings. Tornados, microbursts, and downbursts are the qualified highintensity winds (HIWs). Tornado wind speed is based on published 30year return period map (Tescon, Fujita, & Abbey, 1979) where an F 5
tornado can reach wind speed as high as 142 m/s. While tornado wind
is not the focus in current study, but possible induced tornado wind
within a tropical storm has been recognized by researchers (Baker and
Parker, 2009; Novlan and Gray, 1974).
The design for flooding and storm surge varies from that of wind
design. When designing for flood loads one must ensure that “structures
shall be designed to resist flotation, collapse, and permanent lateral displacement due to action of flood loads” (ASCE 7). ASCE 7 (2013) also
mentions that the effects of erosion and scour must be factored in with
any flood loading of a structure. Flood hazard areas should be designed
based on the design flood. Hydrostatic and hydrodynamic loads will be
applied depending on the level of water in the area of the structure.
Wave loads may be analyzed in three ways for the structure: the analytical method outlined in the code, an advanced modeling method, or
based off of experimentation. The method described in the code first
has one classify the wave zone as either a ‘V-zone’ or an ‘A zone’ having
0.9 m high or higher waves or less than 0.9 m waves, respectively. It is
obvious that this wave height definition is not sufficient to address the
storm surge scenario of Super Typhoon Haiyan.
For a transmissions system structure the main wave load to focus on
is the load of breaking waves on vertical pilings and columns. To calculate the main wave load, one needs to determine the specifics of the
structure and its specific location and distinguish whether it is a salt
water or fresh water wave that will be acting on the structure. One more
thing to know is the wave height that will be acting on the structure,
which can be found in conjunction with the local still water depth. All
of these variables will give the values needed to find the force of the
wave and be able to design for any flood or storm surge event.
Fig. 11 shows summaries of the design approach for wind and flood
loading using ASCE 7. It should be noted that the load designs only
that can be used for design and analysis purposes. ASCE-7 is a generalized minimum design loading guide meaning it is suitable for any
type of structure.
Along with using the wind speed maps to find the base wind speed
for the area of a structure, the design procedure requires one to take
into account many other factors for the wind design requirements for a
power transmission structure. The first step in the analysis is to assign a
risk category to the structure. This is done based on how devastating the
failure of this structure would be and is described in ASCE 7. One must
also factor in the wind directionality, which is the effect of the shape of
a structure on how it is loaded by the wind forces. How the surrounding
area in which the structure will be exposed to wind force is also considered – This is done by selecting an exposure category for the location. These categories are described in ASCE 7 and are used to determine which maps and equations are used in the wind load design
process. Another effect that needs to be factored in is the effect of the
topography surrounding the area of the structure. ASCE 7 lays out
different scenarios that the site topography may affect the loads to the
structure and the specific sizes of said topographical effects. The localized gust factors that need to be factored in to account for the dynamic
fluctuations of the equivalent static wind force also considered (for
example, taken as 0.85 for rigid buildings). Another trait of the structure that needs to be used in the design is the enclosure classification of
the structure. For transmission systems most will be classified as open
and some will require protection for glazed openings depending on
their geographical location. All of this variability plays into the design
for wind of these structures and from all of these variations one can
follow through ASCE 7 to select the appropriate coefficients, factors,
and equations to correctly find the respective wind loads at the respective heights of a transmission system structure.
Wind design for power transmission structures is further described
in ASCE 74 (2010), where wind effects are further distinguished into
extreme wind, high-intensity winds and ice and wind combined
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K. Dai et al.
Fig. 11. ASCE 7 Load Design Approach for Wind and Flood.
under current climate change scenario.
considers the effects on a single structure and does not account for the
interactions from the surrounding structures. The RBD approach allows
ASCE 7 to account for the likelihood of a wind or water (flood) dominated design using factored load combinations. However, RBD is based
on historical events and uncertainty of an extreme environment is not
easily projected in its development. The ASCE 7–10 (2013) code has a
maximum sustained wind speed of less than 90 m/s with return periods
of 300 years, which may already be unrealistic for some coastal regions
4. Design considering climate change effects
To address the resiliency of the power transmission systems under
the effects of climate changes, most attentions are placed on the rapid
recovery mechanisms including ensuring survivability by mechanisms
to enhance the supply of power to the communities (Cooke, 2013).
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Table 2
Computation of Power Pole Design Requirements for Extreme Storm Surge Loading Scenario (Surge Height at 20 m, Risk Category IV, Salt Water).
Height (m)
Aeff (m2)
Force (kN)
D at top of water (cm)
D at bottom (cm)
M1 (kN m)
M2 (kN m)
Moment (kN m)
9.1
12.2
15.2
18.3
21.3
24.4
27.4
30.5
36.6
3.8
5.4
7.2
9.2
10.8
11.9
13.0
14.1
16.3
3616
5137
6817
8654
10212
11249
12286
13324
15398
33.6
33.6
33.6
33.6
36.0
41.5
47.0
52.5
63.4
50.1
55.5
61.0
66.5
72.0
77.5
83.0
88.5
99.4
13279
23608
36887
53117
68087
78463
88839
99215
119967
2168
5139
10037
17344
22699
22699
22699
22699
22699
15447
28747
46924
70461
90786
101162
111538
121914
142666
Prevention of disastrous outcomes from super typhoon impacts would
require significant improvement of power delivery systems that includes hardening against potentially extremely high wind speed and
storm surges. Using high resolution cloud-resolving global climate
modeling, Tsuboki et al. (2015) suggests that the significant future
super typhoons could attain wind speeds of 85–90 m/s. Most studies
focused on the estimation of impacts of increased wind loads or flood
loads including Davidson, Liu, Sarpong, Sparks, and Rosowsky (2003),
Eidinger and Kempner (2012), Shafieezadeh, Onyewuchi, Begovic, and
DesRoches (2013), and Pang, Chen, Liu, and Holmes (2013), which
relies mostly on projection of historical storm data. A study on the effects of significant hurricanes of 2004, Cannon (2005) reported that
most wood distribution and transmission poles would not have survived
the wind forces driven by Category 4 and 5 hurricanes. The damaged
pole systems reported are consistent with what we have observed in the
Philippines, but the amount of pole structures damaged is more extensive.
To enhance the resiliency of power delivery systems under climate
change effects, EPRI (Electric Power Research Institute) described three
critical elements of resilience: prevention, recovery, and survivability.
EPRI (2013) further suggested the hardening of the power distribution
system to counter climate effects. Citing increasing Category 4 and 5
hurricane events from 1970 to 2004, Peters, DiGioia, Hendrickson, and
Apt (2007) recognized the challenges in upgrading and refurbishing
existing power lines and suggested a survivability design strategy by
developing a strong (hardened) backbone line system with improved
structural reliability to enhance the resilience of the power infrastructure. The strong backbone line system approach allows focused
investments from the energy industry to enhance the survivability of
the power grid under extreme loading. The implementation of such
design would require considerations at the system level – the grid
manager needs to define the extent of the backbone line within the
power grid. At the structure level, one would need to have the different
loading quantification for different reliability levels.
There is a general agreed difference in criticality between power
distribution and transmission: Since existing power transmission systems lack redundancy due to limited alternate paths for electricity flow
when compared to distribution systems, they are more critical to the
electric infrastructure reliability. Pang et al. (2013) simulated a 230 kV
transmission line system under simulated high wind hazard. The
modeling technique included realistic line and support structure system
modeling and was able to project critical failure locations within the
line system. The modeling approach would help realize the system level
vulnerability and resiliency and determine the critical geospatial information to establish the backbone system. However, the modeling
technique does not include windborne or waterborne debris hydrostatic
and dynamic loadings.
Table 3
Pole Moment Capacity and Extreme Loading Moments Comparison (Including 10 m
Storm Surge Scenario).
Height (m)
M (kN m)
from
Wind
Loads
M (kN m)
from 10 m
Storm
Surge
M (kN m)
from 20 m
Storm
Surge
Cracking
Moment
Capacity
(kN m)
Ultimate
Moment
Capacity
(kN m)
9.1
12.2
15.2
18.3
21.3
24.4
27.4
30.5
36.6
3042
4763
6889
9448
12464
16077
20170
24953
36629
7724
14607
25037
39765
52487
57675
62863
68051
78427
15447
28747
46924
70461
90786
101162
111538
121914
142666
159
205
268
325
370
419
470
526
651
378
498
643
785
919
1056
1192
1329
1600
accumulations that can cause damages to both distribution and transmission line structures. Hence, considering the uncertainties in climate
changes and the effects from extreme cyclone events such as Super
Typhoon Haiyan, a holistic approach is needed to determine how
conventional wind and flood loading scenarios can be modified to establish a framework for structure system design to deter the damaging
effects from such storm events.
To help understand the effect of extreme loading scenario for
transmission line systems, an analysis using a wood pole structure is
conducted. Table 1 shows the calculation of possible extreme loadings
on a single pole using worst scenario of a 89.4 m/s wind speed and for a
risk category IV and exposure category D. Both with and without
powerline wind loads are considered in the calculations for up to
36.5 m high poles, which show that the extreme loadings may exceed
the design capacities of most commonly used wood pole equivalent
materials (wood, concrete and steel) available. Table 2 reports results
for calculation of extreme storm surge height (20 m) effects on poles.
Again extreme risk category (IV) is assumed. The load scenarios are
considered separately; thus, are not representative of RBD design. Also
wind/waterborne debris loading is not considered. Table 3 compares
typical wood pole equivalent capacities where the extreme loading
moment capacities would disqualify many pole classes and demand
higher and stronger structures.
To address extreme storm event, we suggest a design framework
adopting the backbone system suggested by Peters et al. (2007). The
backbone system approach recommends a hardened and critical primary power transmission system (strong line) coupled with a flexible
design of secondary transmission and distribution power lines (flexible
line) that, though not as structurally strong as the backbone system,
would allow for rapid site access and effective line repair. The primary
power transmission system represents a relatively permanent power
delivery unit that would be strong enough to resist any speculated
weather effects due to climate change scenarios and is suggested to
design against a wind effect set at 89.5 m/s–111.8 m/s wind force and
20 m storm surge. With the hardened backbone system, there will be no
extensive power outage and would allow for rapid power recovery for
5. Framework of a holistic design consideration
From Super Typhoon Haiyan, we summarize that the category five
storm can result in significant storm surge, strong winds and debris
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Fig. 12. Tree Down Analysis in Tacloban: Estimated over 44 Million Coconut Trees were Destroyed due to Haiyan with over 300 Million Remaining (Durst 2015).
deforesting effect can result in significant loading on the structures.
For the non-backbone transmission and distribution systems, multihazard loading conditions for coastal power systems should consider as
load combination using the RBD approach. Hence, a detailed probabilistic analysis of different loading scenarios should be conducted to
establish the RBD factored loadings (Fenton and Sutherland, 2011;
Goodman, Vanderbilt, & Criswell, 1983; Goodwin, Mozer, & Digioia
(1983); Peyrot and Dagher 1984). Current design wind velocity considerations identify the terrestrial conditions and the cluttering
(buildings) of a site and divide into different exposure categories.
However, such consideration works for a uniform wind over a landscape. Using Google Earth™ roof damage images, the static wind force
projection can be determined which shows significant disturbance near
the most populated areas in Tacloban. Fig. 13 shows the wind direction
spatial display and the path of Haiyan.
Finally, Fig. 14 summarizes the holistic power delivery system design and includes a strong backbone power transmission system (strong
line) couples with flexible power transmission and distribution system
(flexible lines). The backbone system should be designed based on extreme loading where storm effects should include revised wind and
water (storm surge and flooding) loadings based on extreme wind speed
and storm surge height. The flexible line should be designed based on
factored loads that include wind and water loadings and wind and
waterborne debris impacts.
A detailed evaluation of design guidelines for power transmission
and distribution systems is ongoing to generate more specific data for
formulating the holistic design framework. More storm damaged
structural data are also being collected to provide critical information
that can help us understand the effects of super typhoons.
nearby distribution lines. The extent of the design for the backbone
system is an issue of economy and necessity.
Using the holistic approach, the design of strong line structures
should consider expanding the cleared right-of-ways from surrounding
tress or structure and that the structures be placed on high grounds to
minimize flood and debris loadings. Since power transmission structures are further away from urban areas, hence, have less distinct damage modes than distribution systems, i.e. less windborne or waterborne debris attack and less friction from surrounding ground cover,
but more direct wind impacts.
For windborne debris/projectile/missile impacts on structures,
Vickery, Lin, and Twisdale (2003) and Lin and Vanmarcke (2008) have
studied the extent of windborne debris/projectile impacts from hurricanes. However, both studies have not considered heavily wooded regions. Thus, those studies are still inadequate in providing a comprehensive view of damaging effects of an extraordinary hurricane.
Hatzikyriakou et al. (2016) has pointed out the significance of waterborne debris impact on residential structures. Lessons learned from
Super Typhoon Haiyan indicate that extreme wind speed, unprecedented storm surge heights, which run much further inland than
typical typhoon events in the area and extensive debris accumulations
are some of the critical factors that exceed current design requirements.
There needs to be a quantification of the effects of solid wastes, debris
and projectiles from trees down – this is especially critical for heavily
wooded areas.
One characterization of Super Typhoon Haiyan is the extensive
amount of trees down that at some locations may exceed 90% of the
original standing trees. Fig. 12 shows the extent of fallen coconut trees
in the Haiyan-affected areas. Super Typhoon Haiyan revealed that the
accumulation of solid wastes such as debris due to significant
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K. Dai et al.
Fig. 13. Final Damaging Wind Directions Based on Roof Damages from GoogleEarth™ (Tacloban City Characterization Including Cluttering of Multi-Story (Typically One to Three
Stories)) Structures with Occasional Higher Structures with No High Rise Structures.
Fig. 14. Holistic Approach for Resilient Power Delivery System that
Utilizes the Strong Backbone Transmission System Concept.
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Fig. 15. Strong Backbone Transmission Line Proposed for McClellanville, SC, Considering Loading at 89.4 m/s Wind Speed, Risk Category IV, Exposure Category D with no Storm Surge
nor Debris Loading.
6. Economic and feasibility analysis of power supply system for
McClellanville, SC
Comparing to Table 2, the 20 m storm surge effect only increases the
applied moment load by 25% to the 89.5 m/s wind force. For additional
reliability, US National Academy Council recommended the purchase of
the 365 kV:138 kV/200 MVA (RecX) transformer technology for rapid
recovery during natural disasters (Cooke 2013). With a price tag of $7.5
million, such recommendation would be a challenge for the people of
McClellanville.
To determine the cost scenario and feasibility of the holistic design
approach, the power transmission and distribution scenario at
McClellanville, South Carolina, is considered. McClellanville is a small
coastal town along the Atlantic west near Charleston, SC. The community has very small electrical distribution loads, as of 2016, it does
not have any major transmission infrastructure. In 2005, a power
supply alternative study was conducted by local power company and
indicated that the construction of a power transmission line is the
cheapest cost scenario to supply the township with sustained electricity.
The study included all possible scenario plays including the construction of a local power generation, upgrade of existing distribution lines
or substations. In all cases, the projected 30 years loss exceeds US $100
million (CEPC, 2005). Since the study, McClellanville was hit several
times by major hurricanes in the area – notably and more recently,
Matthews in October 2016. Hurricane Matthews resulted in more than a
million dollar loss associated with the power grid failure. If possible
future extreme climate events were to occur during next 30 years, the
projected loss may push beyond US $200 million.
A strong backbone, 115 kV transmission system for a 26 km stretch
connecting from Belle Isle substation to McClellanville is suggested.
Fig. 15 shows the proposed 26 km backbone transmission line extending from Belle Isle substation to McClellanville distribution point.
The average distance of the line to the coast is about 8 km and eliminated possible loading due to debris and water inundation (historical
flooding due to riverine and watershed rising did extend beyond
Georgetown and Berkeley counties). Using the holistic backbone line
design approach (Fig. 14), the strong backbone transmission line is
sited away from likelihood of both storm surge and debris loadings and
involved the construction of lattice self-supporting towers with additional guy lines that can withstand the extreme wind load moments
outlined in Table 1.
The total cost of the construction of the line is about $26 million
(Western Electricity Coordinating Council recommendation for capital
cost for per mile lattice transmission) and the projected 30 year total
cost with loss is about $133 million. This is substantially lower than the
30 years cost ($163 million) of only upgrading the local distribution
system without considering the effect of extreme climate effects.
7. Conclusions
Extreme climate effects can result in severe damages to critical infrastructures. But the design against extreme events has not been addressed in current design codes. This paper summarizes the overall
observations of power delivery systems investigated during recent
Hurricane Haiyan in the Philippines. Haiyan is the world’s most powerful typhoon to date and has been deemed as a likely scenario of climate change induced tropical storms of the very near future. At the
time of this study, two additional category 5 hurricanes have already
occurred: Patricia (maximum one minute sustained wind speed of
96 m/s) on October 20, 2015 and Matthew (maximum one minute
sustained wind speed of 72 m/s) on September 28, 2016. An understanding of the impacts of Haiyan can help in the improvement of the
design of power systems that can help ascertain the survivability of
coastal populations.
Current power delivery system is designed on the basis for physical
strength. Based on the Haiyan observations, a framework for designing
a resilient power delivery system is suggested. The framework recommends a strong backbone power transmission system (strong line)
coupled with flexible power transmission and distribution system
(flexible lines) and holistic considerations of different damaging mechanisms. The strong backbone system should be designed based on
extreme loading where storm effects should include revised wind and
water (storm surge and flooding) loadings based on extreme wind speed
and storm surge height. The flexible line should be designed based on
factored loads that include wind and water loadings and wind and
waterborne debris impacts.
A case study for the power supply scenario in McClellanville, SC, is
presented to demonstrate the feasibility of using the strong backbone
system which consists of a self-supporting 115 kV transmission line
supported on guyed trusses. Holistic considerations would require the
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K. Dai et al.
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line to be placed deeper inland (8 km) to eliminate possible effects of
debris and storm surge loading. A 30 year projected total cost of the
proposed line, including losses, is shown to be less than the scenario of
only upgrading the local power distribution system without considering
the losses due to power outage during possible extreme climate events.
This case study demonstrated that it is possible to establish a sustainable power transmission system that can help deter the effects of extreme weather disasters.
While scientists continue to investigate the causes of extreme
weather events such as supertyphoon Haiyan, designs against extreme
conditions should be included for coastal populations to prevent escalating financial losses and losses of human lives. Lessons learned from
Haiyan and similar storm events should continue to help improve the
performance of the power delivery systems.
Acknowledgements
The authors would like to acknowledge the support from ASCE
(American Society of Civil Engineers) on the Haiyan project. The authors would like to acknowledge National Science Foundation (NSF)
Program Director Dr. Kishor Mehta for supporting this project under
RAPID Response award 1433262. The authors are grateful to the local
support from the Philippines India including PICE President Ernesto S.
De Castro, and former ASCE Region 10 Director, Potenciano A. Leoncio,
Jr., Ms. Nannette C. Villanueva and Mr. Ferdie Briones. The authors
would also like to acknowledge the supports from State Key Laboratory
of Disaster Reduction in Civil Engineering (Grant No. SLDRCE14-B-02);
State Key Laboratory for Geomechanics & Deep Underground
Engineering (Grant No. SKLGDUEK1514), and International
Collaboration Program of Science and Technology Commission of
Shanghai Municipality (16510711300).
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