Jacobs Recent changes to transmission line design standards and the impact on new construction and ageing assets in the Pilbara

Recent changes to transmission line design
standards and the impact on new construction and
ageing assets in the Pilbara
ENGINEERS
AUSTRALIA
ASIF BHANGOR, PRINCIPAL ENGINEER
AARON HAMILTON, SENIOR ELECTRICAL ENGINEER

What will we cover in this presentation?
1. Introduction
2. The Pilbara, where are we?
3. AS/NZS 7000:2010 key differences amongst others
4. Tower testing
5. Aged transmission lines, what do we do in case of failures?
6. Helicopter stringing
7. Current industry practice in tower installation
8. New method of tower installation
9. Recognitions/Awards

The Pilbara, where are we?
• Region D with cyclonic wind speeds
• Return periods for transmission lines generally 200+ years
whilst distribution lines typically 50/100 years
• Regional wind speed for say 200 years return is 72m/s
• Indigenous heritage sites, priority ecological areas & rivers
• Access constraints
• Crossing 3rd party infrastructure sensitive to shutdowns
– Mining company railways
– Mining or Industry distribution and transmission lines
– Highways

AS/NZS 7000:2010 key differences amongst others
Wind load
• No need to apply 10% amplification to the wind speeds in
AS/NZS 7000:2010
• No need to apply downdraft (high intensity winds) for regions C
and D

Wind load

Insulator swing
• High wind in insulator swing calculations has been typically
mentioned as 500 Pa for power frequency clearance of 500mm

AS/ NZS 7000:2010 key differences amongst others
Insulator swing
• Low wind and moderate wind is 100 Pa and 300 Pa
• Some utilities have used 240 Pa as moderate wind

Insulator swing
• Blowout calculation is linked to the serviceability wind but
insulator swing talks about high wind (limiting to 500 Pa only)
• If we apply maximum wind of the Pilbara, we get large swing
angles which lead to bracket extensions for clearances

Insulator swing

Insulator swing … suggested approach…
• The wind speed derived should be adjusted for the
terrain, height multipliers from AS1170.2 and considering
a drag factor of 1.2
• In addition, the wind speed is reduced for the effect of
span reduction factors which takes into account the
spatial characteristics of wind gusts and inertia offered by
the conductors. See figure B5 in AS1170.2 Page 129
• For easement calculations, refer to item R4 in AS7000
and Cb1 2006 table 10.3 for the 5 – 10 minutes averaging
period conversion which converts it to a serviceability
wind for checking the easement

Conductor assessment (strength and serviceability limits)
• The below table highlights the factored approach in
conductor assessment

Comparison of Cb1 and AS7000 (for conductors in the Pilbara region)
Wind Speeds up to 90m/sec for conductor selection (including height multipliers)
Conductor type UTS (kN) Ft, MWT (kN) Ruling span (m)
Special Diving ACSR (30/6/3.5+1/3.65) 146.0 119.4 470.0
AAAC Sapphire (37/3.75) 115.0 81.1 341.0
AACSR/AC/1120 (42/19/3.25) 264.5 145.0 360.0
Criteria/ Cb1
Conductor type 0.7UTS 1.5Ft
Special Diving ACSR (30/6/3.5+1/3.65) 102.2 179.0 Conductor fails
AAAC Sapphire (37/3.75) 80.5 121.6 Conductor fails
AACSR/AC/1120 (42/19/3.25) 185.2 217.5 Conductor fails
Criteria/(Failure/ Strength) AS7000
AAAC Sapphire (37/3.75) 103.5 101.3 OK
AACSR/AC/1120 (42/19/3.25) 238.1 181.3 OK
Criteria/(Damage/ Serviceability) Non Linear AS7000
AACSR/AC/1120 (42/19/3.25) 185.2 145.0 OK
Criteria/ (Damage/ Serviceability) Linear AS7000
AACSR/AC/1120 (42/19/3.25) 132.3 145.0 Conductor fails
Conductor
assessment

Pole foundation assessment
• In the past utilities have used C(b)1 suggested empirical
assessment of L/10+0.6 for foundation depths – having
no interaction with soil data
• Historically, utilities have deemed this acceptable for
wood poles in region A where wind speeds are around 39
– 43m/s
• However, in the Pilbara where cyclonic wind speeds are
present due care has to be considered for poles carrying
mine load thus requiring higher reliability (basically no
foundation failures acceptable)

• Mindset exists that “We have done this in the past using
L/10+0.6m so why increase the embedment depth now?”
• More recently, utilities have moved away from L/10+0.6m
embedment with proper soil interaction methods such as
Broms, Brinch & Hansen etc.
• Essential Energy, Electranet, Powerlink, Energy Australia
design standards all refer to Brinch & Hansen now
• Please refer to Table 9.7 of handbook HB331 which
states disadvantages of the L/10+0.6(0.8) formula

Tower Testing
Tower Testing
• Failures exhibit load sharing
issues in lattice steel
• Important to understand tower
failures are catastrophic in
nature
• Hence the need to test towers
and eliminate any issues in load
sharing between members,
plates, bolts etc.
• Leg loads for cyclonic wind
regions reach to around 2000kN
per leg

Aged transmission lines
What do we do in case of failures?
• Gradual ageing of steel structures exposed to extreme
weather events exposes owners to high cost of
refurbishment, let alone lost time of production if local
generation does not exist
• Generally utilities have dealt with this problem using
emergency response structures (i.e. Lindsey Guyed
Masts)
• The network in the Pilbara is at risk…failures mean
complete shutdown…

• There is a need to consider design of transmission lines
with higher reliability (i.e. 500 years return wind speeds)
and a high degree of accuracy when it comes to detailing
and fabrication of steel for new projects
• For ageing projects, there is a need to frequently check
and maintain/ replace the ageing towers, conductors, and
insulators using effective maintenance plans

• Wednesday 28th September TransGrid had a failure on
the 220kV line from Darlington Point to Buronga
• The failure was at tower 557 and 558, approximately 30
kms east of Balranald (“in the middle of nowhere” was
the first description). The cause was a high wind event
• 3 towers have been damaged. Initially, towers 557 and
558 failed on the Wednesday night
• On the morning of Friday 30th September, leg buckling
on Tower 556 was observed
• The line has been restored using timber pole
emergency structures – 4 structures have been used

• Tower 558 has failed in the “classical” manner of
compression failure in the legs and has fallen at 90 deg
to the line direction
• The foundation shows obvious signs of severe corrosion
of the reinforcement and necking of the remaining reo at
failure
• Some analysis needed to check the reo and concrete to
determine the cause and age of the corrosion (an old
construction joint? locally aggressive soil?)

TransGrid Failure Event
28/09/2011 220kV Line
from Darlington Point to
Buronga, NSW
• Region A7 Downdraft
winds (high intensity
winds)
• Zone II, Span reduction
factor = 1.0 (0-200m
spans)
• Wind speeds up to
43m/s (1.1kPA)

TransGrid Failure Event
28/09/2011 220kV Line
from Darlington Point to
Buronga

Leigh Creek to Davenport 132kV line experienced a cyclone
in SA

Helicopter stringing in the Pilbara
Some recent challenges experienced
• Access constraints
• Cultural heritage sites
• River crossings
• Priority ecological areas
• Crossing 3rd party infrastructure sensitive to shutdowns
• Mining company railways
• Mining or Industry distribution and transmission lines
• Highways

YM-CL 220kV Stringing Detail
• Helicopter fitted with side
pull rather than belly hook
• Side pull is a customised
piece of equipment designed
specifically for stringing
transmission lines
• Side pull increases the
helicopter fuel efficiency
over a belly hook
• Pilots prefer side pull as
complete assembly is visible

• Helicopter pulls the cable
out sideways, to ensure
vision can be maintained in
the direction of travel and
the direction of load

• Pulling order planned to
ensure that cables already
strung are in front of or
below the height of the
aircraft rotor system
• At no point should cables be
behind the aircraft at the
same height as the one
being pulled

• Stringing broken in to 13 pulls
• 7 of the 13 pulls involved 5 towers
or fewer
• Generally helicopter pulled draw
wire for phase conductors and
Earthwire and OPGW direct
• Direct pulls need to be done under
tension to keep off ground
• Phase conductors are generally not
pulled direct due to the weight,
distance from the ground
• Helicopter used to pull all
conductors direct for rail and line
crossings (due to outage limitations)

Advantages
• Schedule improvement
• 4.5km drawwire pull takes approximately 45 minutes
• 12km OHEW or OPGW pull under tension takes approximately 3
hours
• Critical path moves to linesmen sagging and terminating
• Low impact on heritage sites (line crosses directly over 18)
• Simplified stringing over heavily vegetated river crossing (620m)
• Simplified, faster stringing over existing 132kV transmission lines
• Simplified, faster stringing over rail

Current industry practice in tower installation

Changing the way we do things? Counter arguments by stakeholders
• Crane rated 10 times higher than load
• Load calculations done for all critical lifts
• Lift plans reviewed and signed off by engineer
• Crane inspected at regular intervals
• Crane operator is very experienced and has worked with rigging team for a
long time
• Rigging equipment rated 5 times higher than load
• Rigging equipment inspected daily by crew as well as monthly inspections by
accredited third party inspectors.
• Rigging crew is well trained and very experienced in tower construction
• Verification of competence of all riggers and crane operator
• PPE inspected daily including safety harnesses, ropes etc.
• Very quick installation reducing riggers time spent on the tower and risk of fall

• Incidents reported in failures

• Incidents reported in failures
• Close Call for Big Truck Mount
01/17/14
• Newcastle, Australia
• A 54 meter truck mounted lift lost
balance near Newcastle, Australia
when the ground gave way under one
of its outriggers.
• Fortunately the boom came to rest
against the pylons of the high tension
power line that it was helping to install
– no one was injured or hurt in the
incident

New method of tower installation
“Safety guide” design
This allows crane operators to lower the top section without manual
intervention
of crew
• Once the lower portion of the tower is installed on the ground and fitted with
the foundation base, it is fitted at the connection point to the top structure
with the safety bracket
• The top superstructure is suspended by the crane operator and lowered
into the safety bracket, landing the top superstructure inside the bracket.
The load of the top superstructure is relieved by the crane operator as the
weight of the top does not rest on the steel itself
• The rigging personnel can then go to the top section and connect the
relevant bolts to the holes of the relevant plates and release the safety
bracket. This enables them to work without being under suspended load

Site Construction Team developed option which included:
• Purpose-made temporary “docking brackets” to be installed at the fixing
positions to ease “landing” of the suspended structures onto their bases,
without the need for riggers to be under the suspended loads.
• Installation of temporary brackets to guide sections in to place isn’t new, but
their use has to date been limited to helicopter based tower construction.
• Spacing the splice plates of the suspended structure sections (mid sections), to
gape open, thus easing the landing of those structures through carefully
lowering, with control provided by tag lines with the riggers safely away from
danger.

Achievement of outcomes
• Eliminated the need for riggers to work under suspended loads or manually
move the sections into place risking injury.
• Riggers are no longer exposed to the swinging momentum of the tower
sections.
• Does not require additional brackets to be installed or design modifications
for the most part and the changes were mostly procedural. Existing splice
plates join the adjacent sections, which is easy to implement.
• Developed new, safer site construction methodology that involves sections
of the tower being landed onto the bottom sections with the combined use
of brackets, guide ropes and or other equipment and material already
available on site.

Longer splice plates significantly improves landing of the superstructure

Recognitions/Awards
Recognition in the Australian Industry to promote safety and innovation
in current practices for Tower Design and Installation

Jacobs Recent changes to transmission line design standards and the impact on new construction and ageing assets in the Pilbara

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