Recent Experience Restoring Damaged Transmission

Lines by National Power Corporation of the Philippines

by
R. Rex F. Corpuz
National Power Corp.
Philippines
1.0

Paul Erickson, PE
Lindsey Mfg. Co.
USA

Dr. Keith E Lindsey

Lindsey Mfg. Co.
USA

Introduction

The National Power Corporation (NPC) of the Philippines was established as a non-stock
corporation of the Republic of the Philippines in 1936 and was converted into a stock
corporation in 1960. NPC has its head office in Quezon City, Metro Manila, Philippines.
NPC is responsible for the strategic and rational development of the Philippine power
grids and the construction of generating facilities, the latter in cooperation with the
private sector, and its success is therefore a key factor in assisting the countrys economic
growth. NPCs Power Development Plan sets out the proposals to meet future power
demand through the coordinated addition of generation and transmission facilities, and
sets out detailed proposals for the development of new plants in conjunction with the
private sector.
Keeping pace with the countrys continuing economic growth and the rising demand for
power has resulted in several power plants being put on line in the last few years. With
this addition, NPCs total generating capacity now stands at over 11,000 MW.
The addition of new power plants has required expansion of the transmission facilities
and strengthening of existing transmission lines to ensure effective and reliable
distribution of power to customers (retailers and distributors). A total of 637 circuitkilometers (ckt-km) was constructed throughout the country in 1996 alone. There are
currently over 17,000 ckt-km of transmission lines owned and operated by NPC.
These overhead transmission lines play an important role in the operation of a reliable
delivery system. At the same time, because of their length and exposure to the elements,
these transmission lines are vulnerable to catastrophic failure from a variety of initiating
events, such as extreme weather, floods, vandalism and even volcanoes.
2.0

The Challenge

The Philippines lies between about 5o and 20o N. latitude, entirely within the humid
tropics. Monsoon climates (large wind systems that reverse directions seasonally)
predominate, so most of the islands experience distinctive wet and dry seasons. Most
rain arrives in short, heavy showers, often causing severe flooding. The northern and
eastern
Reprint from Power Delivery Asia, 1 October 1998, New Delhi, India
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sections of the Philippines are exposed to violent tropical storms called bagyos, or
typhoons. These storms originate in the western Pacific Ocean, normally during the
summer and early fall months. There are, on average, twenty-two typhoons each year.
These typhoons are characterized by extremely powerful winds, typically in excess of
100 miles (160 kilometers) per hour, and very heavy rains. One such typhoon in 1911
deposited 46 inches (117 centimeters) of rain on the upland resort city of Baguio, on
Luzon, within a 24-hour period--a world record. The winds, heavy rains, and their
associated high seas and flooding can be very destructive.
The southern part of the Philippines, the area south of 8o N. latitude, is nearly free of
typhoons; however, prior to the 1996 agreement between the Philippine government and
rebels who had waged a 24-year rebellion in the southern island of Mindanao, many
transmission towers were vandalized.
3.0

The Solution

These and many other types of problems present a significant challenge to NPC to adhere
at all times to its vision statement of providing quality and reliable electricity. In order
to increase the reliability of NPCs transmission system and reduce the risk of
catastrophic and costly outages, NPC has utilized a new technology for rapidly restoring
damaged transmission lines since 1995. This new technology involves the use of a
standardized, interchangeable design of universal modular emergency restoration
structures, specified by ANSI/IEEE Standard 1070 (Reference 1). With the addition of
insulators, hardware, anchors, crew training and application software, this universal
modular emergency restoration structure, has become known in the Philippines as the
Emergency Restoration System (ERS).
4.0

Examples of Utilizing the ERS

The remainder of this paper will present several unique examples of how NPC is utilizing
this new technology.
4.1

Northern Luzon: Lahar flow from Mount Pinatubo destroys five circuits

In 1991 Mount Pinatubo, a 5,842-foot (1,781-meter) peak in central Luzon, erupted

explosively after lying dormant for more than 600 years. Along with associated
earthquakes, heavy accumulations of ash, and heavy rains, this volcanic eruption took
330 lives and destroyed much property.
In October 1995 after a heavy tropical storm, a large flow of lahar (a mixture of ash and
water from Mount Pinatubo) destroyed five circuits of 230kV transmission lines that
supplied the city of Manila (Reference 2). At that time these five circuits carried an
average 1200Mw of power to Manila. Figure 1 shows a plan view of the five circuits
affected by the lahar flow.

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T69 DEAD END

LINE 2 ON TOP

Figure 1

HERMOSA
ROAD

HERMOSA

138

The drawing to the left shows

the lahar flow from right to left.
Tower T26A on the HermosaMexico and tower 143 on the
Hermosa Balintawak lines
were washed away. Tower T69
on the San Jose-Hermosa line
collapsed. All other towers
were buried in 6-8m of lahar
mud.

LAHAR

200 M (TYP)
139

T28
SAN JOSE
-HERMOSA
T70

T27

140

T68
T69
COLLAPSED

141
T26A
WASHED
OUT

NEW
RIVER

142 DE
OK
143 WASHED
OUT

LAHAR
FLOW
T26

145

LAHAR AFFECTED AREA

ROAD

FIGURE No.1

146

144 DE

T25

MEXICO

BALINTAWA

Figure 2

Figure 3

The double circuit ERS suspension

tower above and the two ERS tension
towers were user to replace tower
T26A on the Mexico-Hermosa line.

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The two ERS tension tower and

two ERS chainette tower were
used to bypass one circuit of the
San Jose-Hermosa line. Tower
T69 can be seen to the left. Another
ERS bypass was eventually used to
remove the energized circuit still
attached to tower T69.

The Northern Luzon power transmission group manager, Mr. Roque Rex Corpuz, area
6 manager, Mr. Wilfredo Mangulabnan and area 5 manager, Mr. Danilo P. Mercado,
were given the responsibility of restoring the circuits. In order to stabilize the system and
prevent low voltage problems in the city of Manila, NPC purchased an ERS in order to
restore four of the five circuits in the lahar affected area. Figure 2 shows a double circuit
herringbone emergency restoration structure used for an in-line restoration of the double
circuit 230 kV
Mexico-Hermosa line. Figure 3 shows a by-pass restoration using a deadend structure
and two tangent chainette and deadend structures used to restore one circuit of the San
Jose-Hermosa 230kV transmission line. Installation of the ERS required adding wood
cross arms beneath the ERS foundation in order to increase the bearing area of the
foundation in the soft lahar. Swamp type screw anchors were installed to guy the ERS
structure. The foundations were tied to these anchors using steel guy wire, to prevent
them from moving during additional new lahar flows.
While an ERS system is typically meant to stay in service for only a short period of time,
the unusual circumstances in the lahar affected area has required that these systems stay
in place for the last three years. Utilizing this technology, NPC has minimized the risk of
line outages at their major load centers in Manila and provided a flexible restoration
system capable of being moved as the lahar flow dictates.
4.2

Mindanao: Mud slide destroys double circuit 138kV tower

In October of 1996, heavy rains caused a massive mud slide that completely destroyed a
full tension tower No. 24 and damaged a cross arm on suspension tower No. 23 on the
Abaga-Tagoloan double circuit 138kV transmission line. A plan and elevation of the
failure site is shown in figure 4.
Mr. Roberto Marzo, transmission line manager, and Mr. Simeon Clerigo, Lanao area
manager, were responsible for the restoration of this critical transmission line. It was
decided to restore both circuits with four horizontal-vee ERS structures. Due to the
remote location, all ERS material had to be hand carried the last 2km to the site of the
land slide. The four horizontal-vee ERS structures were built in five days using an
aluminum gin pole and a small portable capstan hoist. The foundation of the ERS was
placed on the sloping and unstable soil of the mud slide. It took an additional two days to
transfer the conductor, figure 5 shows one of the circuits transferred and the ERS for the
second circuit under construction. Both circuits were re-energized in seven days.
4.3

Mindanao: River flooding threatens previous wood pole restoration

In September 1997, swollen and flooding rivers threatened a wood pole bypass on the
Aurora-Sta. Clara single circuit 138kV, a radial feeder in western Mindanao. A year
earlier the flooding river had destroyed a river crossing tower No. 190. At that time a

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ERS
TOWER
ERS
TOWER

ts.
300 M

DAMAGED
TOWER No.23
300
Mts.

NEW TOWER
LOCATION

DESTROYED
TOWER No.24

ERS
TOWER

MUD SLIDE

FIGURE No.4
ABAGA - TAGOLOAN
TRANSMISSION LINE

Figure 4

Figure 5

The drawing above shows the placement

of the four ERS horizontal-vee structures.
The mud slide destroyed tower No. 24 and
damaged a suspension arm on tower No.23.

The photograph above shows

the first circuit to be repaired.
The conductor is transferred
from Tower No.23 to one
ERS while the ERS in the
In the forground bypasses
Tower No. 24.

OLD TEMPORARY
WOOD POLE BY PASS

Figure 6

TOWER No.190
DESTROYED
BY RIVER
NEW TOWER LOCATION

NEW TOWER LOCATION

750 Mts.

42 Mts. ERS
3 phase DEAD END

30 Mts. ERS
3 phase DEAD END
0N 10 Mts. HILL

RIVER

FIGURE No.6
AURORA-STA. CLARA
RIVER CROSSING

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A 750m river crossing

was constructed using
two ERS tension
structures. One was
built 42m tall and the
other, which was on a
hill, only needed to be
30m tall.

Figure 7 `

Figure 8

All material had to be hand carried

into the site, the aluminum ERS was
carried through 3km of rice paddies.

The river was crossed by using the

steel guy wire as a suspension cable
and pulling the ERS across.

Figure 9
The photograph to the left shows
the erected 43m tall ERS tension
structure prior to string the
conductor.

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bypass was built utilizing six wood pole H-frame type structures. One year later the
wood pole structures were failing for the same reason, the flooding and meandering river
was washing out their foundations.
Mr. Ruben Conti, transmission line manager, and Mr. Lorrymir S. Adasa, North Western
Mindanao area manager, were given the responsibility of building a new bypass that
would allow construction of new permanent river crossing towers. It was decided to
install two full tension ERS structures to span the approximately 750m river crossing.
Due to the span a 43m tall ERS tension tower was required in order to maintain
clearance. A plan view of the ERS bypass is shown in figure 6.
Access to site was through 3km of rice paddies. and the ERS equipment had to be
transported across the river using temporary suspension cables and pulleys, as shown in
figures 7and 8. An aluminum gin pole and a small portable capstan hoist were used to
construct each ERS tension structure. Figure 9 shows final construction of the 43m tall
ERS tension structure prior to stringing of conductors. Because of the critical nature of
this radial feed transmission line, conductors were strung between ERS tension structures
before taking a short outage to connect the slack spans to the permanent towers.
4.4

Mindanao: Vandals cut legs on a double circuit 138kV tension tower

Vandals cut two legs on a double circuit 138kV tension tower, No. 44, on the radial feed
Kibawe-Davao transmission line. The tower listed at a 45 angle but did not topple.
NPC braced the tower with several guy wires in order to maintain the energized line.
This line is a radial feed into a major city and could not be de-energized. When one
circuit was de-energized, a 50 megawatt diesel had to be started up in order to maintain
voltage at the load center. To complicate matters, the tower was located on the top of a
narrow ridge, and the only access to the site was by helicopter. The plan and elevation of
tower No. 44 is shown in Figure 10.
Mr. Ernesto Guinares, transmission line manager, and Mr. Emy Abellanosa, North
Central Mindanao area manager, were given the responsibility of repairing this tower
while always keeping one circuit energized. Their solution was to use two ERS
horizontal vee temporary towers to bypass both circuits around the damaged tower. With
these in place, the damaged tower could be replaced, as the foundation was not damaged.
Access to this site was difficult. All line crews and equipment had to be flown in by
helicopter. It took one day and 18 trips (of 20km each) to get all personnel and
equipment to the site. Helicopters were required to fly in supplies everyday and the line
crew camped at the site. Approximately 25 linemen were involved. A gin pole and small
portable capstan hoist were used to construct each ERS horizontal vee tower. The
horizontal vee towers were offset longitudinally from the damaged tower approximately
5 to 10ft on either side. Since the site was on top of a ridge, the back and side guys on
the ERS horizontal-vees were two to three times longer than normal, as can be seen in
figure 11. In order to minimize outage time of transferring conductor from the lattice
tower to the ERS

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Figure 10

APPROXIMATE 10 Mts.
ERS
TOWER

RIDGE

Vandals cut the legs of

tension tower No. 44. This
tower is located on the top of
a narrow ridge. In order to
keep the line energized, the
conductor from one circuit
was transferred to the ERS
horizontal-vee structures
while the other circuit was
energized.

DAMAGED
TOWER
No. 44

ERS
TOWER

550 Mts.

550 Mts.

FIGURE No.10
KIBAWE-DAVAO
TRANSMISSION-LINE

Figure 11
The photograph to the left shows
the placement of the two ERS
horizontal-vee structures directly
on top of the ridge. Note that the
dead-end insulators and hardware
are in the span and to the left of
the ERS in the forground.

WOOD POLE
BYPASS

NEW TOWER
LOCATION

TOWER No.11
DESTROYED
BY MUD SLIDE

Figure 12
Mud slides destroyed
tower No. 11 on the
Palimpinon II-Amlan
transmission line in the
Visayas area. An ERS
tension structure was
erected to restore the
second circuit.

MUD
SLIDE

ERS
TOWER
300 Mts.

FIGURE No.12
PALIMPINON II-AMLAN
TRANSMISSION LINE

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500 Mts.

Figure 13
Visayas area field crews erected the ERS tension
structure using only manpower and an aluminum
gin pole. The erection of this structure was used
as a training exercise by the field crews.

structure, the deadend insulators were tied together and the conductor with insulators
were simply pulled to the side and attached to the ERS horizontal vee towers. The
normal jumpers on the deadend hardware were tied to the insulator strings with small
aluminum wires.
It took a total of four days to fly all the equipment in and erect the two ERS horizontalvee towers. In addition, one day planned outage was given for each circuit to be
transferred. The circuits were transferred one at a time over two days, therefore, one
circuit was always energized during this restoration process.
4.5

Visayas: Floods destroy a double circuit 138kV suspension tower

Rain and heavy mudslides destroyed a 138kV double circuit suspension tower, Tower
No. 11 on the Palimpinon II-Amlan transmission line, on the island of Negros, in the
Visayas area of the Philippines. A temporary wood pole bypass had been constructed;
however, this single circuit bypass was heavily loaded and was being threatened again by
the mudslide.
Mr. Alfredo Arzaga, transmission line manager, and Mr. Manuel Terez, Central Visayas
area manager, were given the responsibility of increasing the reliability of this line. As
shown in plan and elevation view of tower No.11, figure 12, it was decided to erect an
ERS full tension tower longitudinal, and outside of the mudslide area to carry one circuit
of the 138kV line. The site was difficult to erect the ERS since it was located on a
sloping hill. A gin pole was used to construct the ERS tension structure, as shown in
figure 13. The line crews from the Visayas area used this for a training exercise and
erected the ERS structure in only 2 days.

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5.0

Conclusion

The Philippines is a chain of 7000 islands. The use of the Emergency Restoration
System, ERS, has proven itself on both the large islands of Luzon and Mindanao as well
as in the Visayas area. This is in large part due to the extensive field training conducted
by NPC and the ERS supplier. From NPCs many applications of the ERS system, we
have concluded that the ERS provides the most positive and cost effective means of
limiting the risks of economic loss due to damaged transmission lines. By using a
standard structure (ANSI/IEEE Standard 1070), which insures interchangeability, mutual
assistance between the major transmission grids in the Philippines is possible. Structures
from one area can be utilized in other areas, depending upon requirements.
NPC will continue to use the ERS, not only to restore damaged transmission lines, but is
currently looking at using the ERS to help the construction of new lines in areas where
right-of-way is difficult to obtain. The use of temporary bypass lines may be the only
means to complete construction of vital transmission links on a timely basis.

References
1. IEEE Guide for the Design and Testing of Transmission Modular Restoration
Structure Components, IEEE Std 1070-1995, ISBN 1-55937-592-2.
2. Joe. C. Pohlman, Dr. Keith E. Lindsey, R. Rex F. Corpuz, Controlling the
Economic Risk From Catastrophic Failure of Overhead Transmission Lines, ESMO
98 - 1998 IEEE 8th International Conference on Transmission & Distribution
Construction, Operation & Live-Line Maintenance, April 26-30, 1998, IEEE Catalog
No 98CH36230, paper 984-C-TPC-2.

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