132 kV OVERHEAD LINE TO MAESGWYN WIND FARMdocshare01.docshare.tips/files/21448/214487867.pdf3.6 BS...

LSTC is a trading name of LS Transmission Consultancy Limited, Yorkshire House, York Road, Little Driffield, Driffield, East Yorkshire, YO25 5XA. Registered in England No: 04191630. VAT No: 772401446

132 kV OVERHEAD LINE TO MAESGWYN WIND FARM

REPORT ON PLS ANALYSIS OF TOWER D32 AND TRIDENT WOOD POLE CONNECTION STRUCTURES

FOR

Western Power Distribution

Review History APFP 2009 Reg 5(2) Ref: Reg 5 (2) (q)

Author: Adrian Livesey BEng (hons)

Reviewed:

Eur Ing Peter Papanastasiou B Sc (Hons) C Eng MICE

Approved:

Graham Young B Sc (Hons) C Eng MICE

Document Number: 20‐10060‐01

Issue: Issue Date:

Description

A 20/04/2010 Issue to WPD B 17/06/2010 Stays removed

structures D32B & D32J C 16/07/2010 Revised for IPC

submission D 23/07/2010 Amended to reflect IPC

and WPD requirements E 26/07/2010 Minor corrections

Maesgwyn Wind Farm Connection

20/10060/01

Copyright: LSTC This report has been prepared by LS Transmission Consultancy Limited (“LSTC”) on behalf of Western Power Distribution (“the Client”) in connection with the detailed assessment of the Maesgwyn proposed wind farm connection and takes into account their particular instructions and requirements. LSTC will not be liable to the Client for any use of this report for any purposes other than those for which this report was produced. This report is for the private and confidential use of the Client and should not be reproduced in whole or in part without the express written consent of LSTC. If LSTC consents to the reproduction of this report then it may only be reproduced once in whole and not part. This report is not intended for and should not be relied upon by any third party and no duty of responsibility (including in negligence) is accepted by LSTC in relation to any third party. LSTC disclaims all liability of any nature whatsoever to any such third party in respect of this report. This report is not intended to confer any rights on any third party pursuant to the Contracts (Rights of Third Parties) Act 1999. This report may not be assigned to any third party without the express written consent of LSTC LS Transmission Consultancy Limited makes no warranties, express or implied, that compliance with this document would in itself be sufficient to ensure safe systems of work or operation. Users are reminded of their own duties under health and safety legislation.


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Table of Contents

1. Summary 4

2. Introduction 5

3. Maesgwyn 132 kV loading criteria 6

3.1 Line Location and configuration .................................................................. 6

3.2 Loading checks carried out ......................................................................... 6

3.3 Tower analysis methodology ...................................................................... 6

3.4 Conductor tensioning basis options ............................................................. 6

3.5 Maintenance Loads & Failure containment Loads ......................................... 7

3.6 BS EN 50341 Probabilistic Loading Criteria ................................................. 7

4. Conclusions 11

5. Glossary 12

Appendices Appendix A – PLS Pole Analysis summary Appendix B – PLS Tower Analysis summary Appendix C – PLS CADD screen prints Appendix D – Pole information


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1. Summary 1.1 This document describes the design assessment carried out on the proposed single

circuit overhead line connection between the planned wind farm at Maesgwyn and existing tower D32. The proposed structures to be used for this connection are based on the Electricity Networks Association (ENA) 43-50 trident wood pole design using 175 ACSR Lynx as the conductor.

1.2 Section 3 of this document details the approach taken to validate the suitability of the structures, outlining the climatic and geographical conditions considered. Loading criteria have been derived from British Standard EN50341-3-9:2001 UK NNA and applied in the analysis, which has been carried out using industry standard PLS CADD software.

1.3 Our initial investigation showed that standard thickness poles of the 43-50 structure design would not be suitable for this location. Strengthened designs using various combinations of stays, stay positions and pole thicknesses where analysed until a final design for each structure was determined. The proposed 43-50 steel terminal structure also required slight modification from the original design to achieve satisfactory design capacity under the applied loading. Our assessment also indicated that crossarm ties on the existing tower D32 would need to be strengthened to accommodate the new downlead loads. Further details are included in section 4.


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2. Introduction 2.1 Western Power Distribution is proposing to install a connection between a new

substation at the new wind farm at Maesgwyn and the existing 132kV route at tower D32

2.2 The proposed structure types are based on ENA TS 43-50 trident wood pole design

with a lattice steel terminal structure. 2.3 The proposed conductor system will be single circuit 175 ACSR LYNX conductor.

The ENA TS 43 50 line design is unearthed construction. 2.4 This document defines the design criteria that has been applied, the type of

structure used, the PLS analysis and the recommendations resulting from the outcome of analysis together with necessary strengthening.

2.5 LSTC carried out a detailed survey of the line route which included positions of

existing towers D31, D32 and D33. 2.6 LSTC carried out a topographical survey of the proposed 132kV connection and a

profile was produced, ref LSTC 01-10060-05. This profile along with the survey data and wire clearance diagram LSTC 17-10060-01 were used as the basis of the PLS CADD model.

2.7 The profiles identified structures (see Appendix C for PLS CADD screen prints) that

were outside the generic design parameters for the ENA TS 43 50 technical specification and as a result further site specific analyses were proposed.

2.8 This investigation details the site specific analysis of the wood pole structures and

the connection arrangements at tower D32. The site specific loading analysis is carried out using PLS-CADD, PLS-Pole and PLS-TOWER programs.

2.9 BS50341-3-9:2001 was used for the basic wind speed and ice thickness. 2.10 Records have been requested and no information was found on the existing tower

D32. It was therefore considered prudent to adopt a conservative value of 247 N/mm2 yield stress for the mild steel grade on the PL16 D2s (D32)

2.11 For the new ENA TS 43-50 steel terminal structure values of 275 N/mm2 for mild

steel and 355 N/mm2 for high yield steel were used in the analysis.


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3. Maesgwyn 132 kV loading criteria This section outlines the loading criteria used for the proposed Maesgwyn wind farm connection.

3.1 Line Location and configuration

3.1.1 The proposed line is located in South Wales. Detailed works and access plans are

referenced 03-10060-04 & 03-10060-13 respectively. 3.1.2 The proposed conductor is 175 ACSR LYNX.

3.2 Loading checks carried out

3.2.1 Loading checks were carried to verify the strength for all the wood poles and lattice steel structures for the proposed wind farm connection.

3.2.2 Structure overloads were identified using PLS-CADD, PLS POLE and PLS-

TOWER. 3.3 Tower analysis methodology

3.3.1 Power line Systems’ software PLS CADD, Tower and Pole are industry standard packages for transmission line analysis. The software runs a Non-Linear Elastic analysis of the tower steelwork using BS EN 50341 part 3-9 UK NNA section 7 methodologies (based on ECCS 39). Angle member properties are calculated in accordance with BS EN 10056-1.

3.3.2 Structures were modelled in PLS Pole for wood pole structures and PLS Tower for

lattice steel towers. 3.3.3 The OPTIMAL profiles were converted into PLS CADD model and each wood pole

and steel tower structure models were then added to the PLS CADD line. 3.3.4 Site specific climatic criteria together with, where appropriate, Construction and

Maintenance loading conditions were input into the PLS CADD Model. The line was then analysed in PLS to determine the site specific applied loadings on all the structures. These loadings were then transferred to the structural analysis packages PLS Tower and PLS Pole for checking the integrity of each structure.

3.4 Conductor tensioning basis options

3.4.1 The sagging basis adopted in the PLS CADD analysis is as set out below: 3.4.1.1 Lynx sagging basis used for conductors on wood poles

• 20 % of UTS at an Everyday Tension of 5 Degrees Celsius • 23.3kN at a temperature of Minus 20 Degrees Celsius

3.4.1.2 Lynx sagging basis used for conductors on towers


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• 20 % of the UTS at an Everyday Tension for 5 Degrees Celsius • 25 % of the UTS at an Maximum Erection Tension for Minus 20 Degrees Celsius

3.5 Maintenance Loads & Failure containment Loads

3.5.1 Tower D32 is the only structure for this project where these conditions will apply. 3.5.2 The Maintenance case considers a load of 4905 N on each crossarm, with downleads attached. This represents the weight of equipment necessary to install semi tension insulator strings including a 132kV platform and linesmen. 3.5.3 Tower D32 also has applied load cases to simulate broken wires (failure containment). These 12 load cases each consider 1 broken wire either ahead or behind the cross arm. These do not include (a conservative approach) any reduction in conductor tension (alleviation) caused by the swing of the suspension link connecting the tension sets to the crossarm. 3.6 BS EN 50341 Probabilistic Loading Criteria

3.6.1 The following sets out the relevant site specific design criteria/inputs for determining the ultimate applied loadings. These are based on BS EN 50341 ‘general approach’ requirements as set out in part 3, section 9, UK NNA: 3.6.2 Input Loading Conditions: Item BS EN 50341 UK

NNA ref Wind Speed High wind 22 m/s 4.2.2 GB.1 Wind+Ice 18.7 m/s 3yr RP with Ice 14.21 m/s 3yr RP no Ice 16.72 m/s Kd – direction factor 1.0 for High Wind 0.85 for Wind + Ice 4.2.2 GB.2 Terrain Category II 4.2.2 GB.3 Gc – conductor gust

response factor Calculated by PLS‐CADD

For all wind load cases

Basic Ice thickness (conductors and towers)

ro Without wind 55 mm 4.2.3 GB.1rw With wind 5 mm 4.2.4 GB.1r3yr 3 year return Ice with

wind 5 x 0.76 = 3.8 mm NGTS 2.4/ENATS 43‐

125 table 3.1 Ice Density Towers/Conductors Without wind 5000 N/m3

Towers/Conductors With wind 9000 N/m3 Whichever more onerous for tower loading only. Conductor ice in presence of wind is always 9000 N/m3

Towers only With wind 5000 N/m3

Ice thickness ‐ conductors

rb Calculated by PLS CADD


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rr Calculated by PLS CADD

Conductor Ice capping

For initial investigation, no ice cap proposed.

Ice thickness ‐ structures

rb Calculated by PLS CADD

rr Calculated by PLS CADD

Line altitude Site specific (ice and wind adjusted by PLS‐CADD for each structure)

(max altitude 312 m)

Conductor Temperature

High Wind Cases – 0°C Ice, Wind + Ice Cases ‐ ‐10°C Still air no ice Broken Wire Cases ‐ 0°C Wind + Ice Broken Wire Cases ‐ ‐10°CMax operating – 75°C –

Reliability Level – Angle/Tension

2 – 150 year return period

γv = 1.1 132 kV line –peripheral

4.2.11 GB1 –

Reliability Level – Suspension

1 – 50 year return period

γv = 1.0

Conductor Drag Coefficient

Calculated by PLS‐CADD

Table 4.2.2(b)/GB

Tower Drag Coefficient

Calculated by PLS‐CADD

4.2.2 GB9

Span lengths Site specific Conductor heights Automatically determined by PLS‐CADD Vertical loadings + or ‐ 10% γDL = 1.1 γDL = 0.9

3.6.3 BS EN 50341 Partial Strength Factors for determining material/equipment capacity Item Foundations γM = 1.35 (under high

wind and wind/ice cases)

γM = 1.60 (under high ice cases)

Tower Steel γM = 1.10 Conductors γM = 1.25 Tower steel work design

ECCS#39


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3.6.4 PLS CADD UK NNA Criteria inputs – blue selected text is inserted below.

Note that separate runs for each terrain category and reliability level and subsequent partial factor need to be carried out.


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3.6.5 PLS Criteria notes for UK NNA 3.6.5.1 Notes on inputs to Criteria/Weather Cases for ‘EN50341-3-9:2001 UK NNA’: 3.6.5.2 Input wind speed should be Kd*Vb where Kd is the wind direction factor from section 4.2.2 GB.2 and Vb is the basic wind speed from 4.2.2 GB.1 (maximum mean hourly wind speed 10m above level ground in basic open terrain category III at sea level) (4.2.2 GB.1). 3.6.5.3 Kcom (combination factor to take account of the improbability of maximum gust loading on both conductors and towers simultaneously) should be entered in the structure wind area factor column in the load case table. 3.6.5.4 Wire wind height adjust model set to 'EN50341-3-9:2001 UK NNA' applies the following:

• Wind speed will be increased 10% for each 100m above sea level as per 4.2.2 GB.1

• Wind speed adjusted for terrain roughness factor Kr for selected terrain category as per 4.2.2 GB.4

• Wind speed multiplied by 'partial factor for desired reliability level' above including an adjustment of .8 in the presence of ice (Table 4.2.8(a)/GB.1)

• Wind speed adjusted for average attach height above ground as per 4.2.2 GB.5.1 • Ice thickness adjusted for wire diameter and avg. attachment elevation as per 4.2.3

GB.1.1 • Ice thickness multiplied by 'partial factor for desired reliability level' above and for

shape factor (4.2.3 GB.2 and Table 4.2.8(a)/GB.1) 3.6.5.5 Wire gust response factor set to 'EN50341-3-9:2001 UK NNA' applies the following:

• Wire GRF adjusted for span length, average attach height and terrain roughness using formulas from 4.2.2 GB.7

• GRF further adjusted for drag coefficient as function of Reynolds number and ice thickness as per Table 4.2.2(b)/GB values for conductor locked coil ropes, spiral steel strand with more than seven wires

3.6.5.6 Structure wind load model set to 'EN50341-3-9:2001 UK NNA' applies the following:

• Wind speed passed to TOWER is adjusted for ground elevation, terrain category and 'partial factor for desired reliability level'.

• Structure ice thickness passed to TOWER is adjusted for structure top elevation as per 4.2.3 GB.1.1

• Structure ice thickness multiplied by 'partial factor for desired reliability level' above (4.2.3 GB.2 and Table 4.2.8(a)/GB.1)

• TOWER will increase wind with height logarithmically. • TOWER will apply gust response factor calculated as (1+Kcom*Gb).


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• TOWER: 'wind on face' with drag coefficients a function of solidity ratio and apply Kø wind incidence factor

4. Conclusions 4.1 For the wood pole section of the line, standard pole structures were selected in line with criteria set out in ENATS 43-50. The analysis results (see Appendix A) showed that due to the altitude of the line, the 4 intermediate single pole structures are heavily loaded or overloaded. It was therefore decided that these structures should be strengthened and pole diameters were increased. 4.2 Results of the subsequent analysis of the wood pole structures show a maximum usage of around 83% which is considered acceptable. However, it is noted that the wood pole structure with the non standard poles may require modifications to the steelwork and different fittings to attach the crossarm to the pole. This is due to the thickness of the poles at the attachment point. 4.3 The ENATS 43-50 steel terminal structure shows one horizontal member at the tower waist (see Appendix B) which is overloaded. 4.4 By replacing the original design member with a high yield steel 65x50x5, connected on the short flange and using high yield bolts, this structure no longer has any failing members under the applied probabilistic loads and a gamma V of 1.1 reliability level of 1. 4.5 At tower D32, on the side where the downleads are to be attached, the analysis indicated both the middle and bottom crossarm ties are overloaded and should be replaced (see Appendix B). 4.6 Top crossarm ties are also heavily loaded so it is recommended that ties are strengthened at all 3 crossarms prior to the downleads being attached. It will also be necessary to incorporate a means of attaching the downleads to the suspension tower crossarms which may require additional or modified plates to be installed. 4.7 There are various ways that tower D32 crossarm modification could be undertaken, however the approved method should be decided by the contractor in consultation with WPD and the CDMC which may be based on their preferred safe methods of work and subject to appropriate design checks. 4.8 The method considered in this analysis is for conductor loads to be temporarily removed from the crossarm whilst work is being undertaken. Temporary supports are then applied whilst each individual member is changed and members added and replaced, noting that only 1 crossarm can only be strengthened at any one time.


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5. Glossary Angle member: Steel members with perpendicular angles Cables: see Conductor. Conductor: That which has the property of transmitting electricity. The name given to the metallic wires strung from tower to tower to carry electric current Circuit: Consists of metal conductors, single or grouped in bundles for each of the three phases in which electricity is transmitted under an alternating current. Downleads: Downleads are conductors used to connect the overhead cables to a lower level structure. Earthwire: A wire commonly erected above the top most conductor at the tower peak for protection against lightning strikes and to earth any faults. It is connected directly to all supports. Insulators: Materials that are very poor conductors of electricity. Air exists as natural insulation around the bulk of the conductor, but at support structures, an insulator string or strings are required to provide a safe insulation gap between the live conductors and any point of earth. Lattice steel: A framework of steel angle sections with the form of their main components corresponding to a triangular lattice. PLS CADD, PLS Pole and PLS Tower are industry standard software packages produced by Power Line Systems for analysis of overhead lines, pole structures and steel lattice towers respectively. Span length: The distance from one structure to the next. Substation: Electricity generated at power stations is fed into the National Grid System through associated substations. They control the flow of power through the system by means of transformers and switchgear, with facilities for control, fault protection and communications. Topographical: The topography of an area is its surface shape and features. Towers: Overhead transmission line supports more commonly known as pylons. Wire clearance: Specified minimum clearances that must be maintained between overhead transmission line live conductors and the ground, obstacles, railway property and other power lines. Yield stress: The stress at which a material begins to permanently deform.


20/10060/01 Appendix A – PLS Pole Analysis summary

Preliminary assessment:

Final assessment allowing for thicker poles and stays where necessary, in line with final profile:


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Appendix B – PLS Tower Analysis summary

Tower D32 Blaw Knox PL16 D2S Tower summary

Criteria Detail Tower Type Blaw Knox PL16 D2S Extension STD Tower Number D32

Loading

Conditions

BS EN 50341-3-9 UK NNA

‘General Approach’

High Wind (HW)

Wind Ice (WI)

Heavy Ice (HI)

Maintenance and erection (ME)

Failure Containment (FC)

Reliability Level 2 (γv=1.1)

Outgoing angle N/A

Maximum member

utilisation

Middle crossarm ties are up to 144%

NET section capacity in tension under

(HI)

It is recommended that the crossarm ties are strengthened


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Tower 43-50 steel terminal structure summary

Criteria Detail Tower Type 43‐50 steel terminal structure Extension N/A Tower Number P12

Loading Conditions BS EN 50341‐3‐9 UK NNA

‘General Approach’

High Wind (HW)

Wind Ice (WI)

Heavy Ice (HI)

Reliability Level 2 (γv=1.1)

Outgoing angle N/A

Maximum member

utilisation

The member show below is 156% of L/R

capacity in compression under (HI)


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Appendix C – PLS CADD screen prints (not to scale) Profile view

3D view 1


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3D View 2


20/10060/01 Appendix D – Pole information


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