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

ENGINEERSAUSTRALIA

ASIF BHANGOR, PRINCIPAL ENGINEERAARON 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

AS/NZS 7000:2010 key differences amongst othersComparison 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/ Cb1Conductor type 0.7UTS 1.5FtSpecial Diving ACSR (30/6/3.5+1/3.65) 102.2 179.0 Conductor failsAAAC Sapphire (37/3.75) 80.5 121.6 Conductor failsAACSR/AC/1120 (42/19/3.25) 185.2 217.5 Conductor failsCriteria/(Failure/ Strength) AS7000 Conductor type 0.9UTS 1.25FtSpecial Diving ACSR (30/6/3.5+1/3.65) 131.4 149.2 Conductor failsAAAC Sapphire (37/3.75) 103.5 101.3 OKAACSR/AC/1120 (42/19/3.25) 238.1 181.3 OKCriteria/(Damage/ Serviceability) Non Linear AS7000 Conductor type 0.7UTS 1.00FtSpecial Diving ACSR (30/6/3.5+1/3.65) 102.2 119.4 Conductor failsAAAC Sapphire (37/3.75) 80.5 81.1 Conductor failsAACSR/AC/1120 (42/19/3.25) 185.2 145.0 OKCriteria/ (Damage/ Serviceability) Linear AS7000 Conductor type 0.5UTS 1.00FtSpecial Diving ACSR (30/6/3.5+1/3.65) 73.0 119.4 Conductor failsAAAC Sapphire (37/3.75) 57.5 81.1 Conductor failsAACSR/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 TestingTower 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…

Aged transmission lines

What do we do in case of failures?

• 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

Aged transmission linesWhat do we do in case of failures?

• 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

Aged transmission linesWhat do we do in case of failures?

• Tower 558 has failed in the “classical” manner of compression failure in the legs and has fallen at 90 degto 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?)

Aged transmission linesTransGrid Failure Event28/09/2011 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)

Aged transmission linesTransGrid Failure Event28/09/2011 220kV Line from Darlington Point to Buronga

Aged transmission linesTransGrid Failure Event28/09/2011 220kV Line from Darlington Point to Buronga

Aged transmission linesLeigh 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)

Helicopter stringing in the PilbaraAdvantages

• 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 interventionof 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 innovationin current practices for Tower Design and Installation

Engineering

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