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CONFIDENTIAL REPORT

Prepared for: CTC Cable Corporation

Vibration Analysis of ACCC (R) (Oslo) Conductor

Authors: David Horsman, Br ian Wareing and Alan Ward

P ro j ec t No : 75100

March 2010

CONFIDENTIAL - This document may not be disclosed to any person other than the addressee or any duly authorised person within the addressee's company or organisation and may only be disclosed so far as is strictly necessary for the proper purposes of the addressee which may be limited by contract. Any person to whom the document or any part of it is disclosed must comply with this notice. A failure to comply with it may result in loss or damage to EATL or to others with whom it may have contracted and the addressee will be held fully liable therefore. Care has been taken in the preparation of this Report, but all advice, analysis, calculations, information, forecasts and recommendations are supplied for the assistance of the relevant client and are not to be relied on as authoritative or as in substitution for the exercise of judgement by that client or any other reader. EA Technology Ltd. nor any of its personnel engaged in the preparation of this Report shall have any liability whatsoever for any direct or consequential loss arising from use of this Report or its contents and give no warranty or representation (express or implied) as to the quality or fitness for the purpose of any process, material, product or system referred to in the report. All rights reserved. No part of this publication may be reproduced or transmitted in any form or by any means electronic, mechanical, photocopied, recorded or otherwise, or stored in any retrieval system of any nature without the written permission of the copyright holder. © EA Technology Ltd March 2010

EA Technology Limited, Capenhurst Technology Park, Capenhurst, Chester, CH1 6ES; Tel: 0151 339 4181 Fax: 0151 347 2404 http://www.eatechnology.com

Registered in England number 2566313

Project No: 75100

Vibration Analysis of ACCC (R) (Oslo) Conductor

EA Technology Vibration Analysis of ACCC (R) (Oslo) Conductor

Project No. 75100

Vibration Analysis of ACCC (R) (Oslo) Conductor by David Horsman, Brian Wareing and Alan Ward

Summary

1. CTC Cable Corporation’s Oslo ACCC (R) conductor has been tested at the UK EA Technology Deadwater Fell test site for snow/ice loads (winter 2008/09) and vibration (summer – autumn, 2009 and winter 2009/10). Safag VR400 vibration monitors were used to monitor the conductor.

2. This report looks at the vibration data over 7 runs between May, 2009 and February,

2010, at different tensions and weather conditions and also with and without PLP Vortx dampers. These had been installed on one end of the span only at distances recommended by Babcock Networks.

3. Oslo conductor is equivalent to the standard AAAC Sycamore. Initially it was strung

at around 17% of its UTS and had a sag 1m better than Sycamore. It should be noted however that it is a stronger conductor than Sycamore. It was then reduced to around 12% of its UTS to match the Sycamore sag at 2.6m on the 190m span.

4. During the 2008/09 winter Oslo suffered wind/ice loads up to 29kN and hence had a

load shift so that 83% of the load was carried on the core. During the 2009/10 winter (and the final vibration test run) wind/ice loads up to 38kN (~26%UTS) were experienced.

5. Full vibration data and analysis graphs are provided in the Appendices of this report

6. In two undamped runs at ~23kN, vibration peaks at 10, 25, 50 and 143Hz were

recorded with the dominant amplitudes being at 50Hz. The vibrations noted in the 143/200Hz region have not been noted in standard ACSR or AAAC conductors and are presumably due to the characteristics of the composite core. The Sefag monitor indicated lifetimes of 9 and 17 years.

7. In two undamped runs at ~17kN, the peaks at 25 and 50Hz were significantly

reduced with the main vibration occurring at 10Hz. The vibration at 143/200Hz was still present. The Sefag monitor indicated lifetimes of >100 years for both runs.


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8. In the run at 17.6kN with PLP Vortx dampers fitted, the peaks at 25 and 50Hz were

virtually eliminated and the 10Hz peak was reduced. The 143/200Hz vibration was still present. The Sefag monitor indicated lifetime of > 100 years.

9. In the undamped winter period run at an average tension of 19kN, all the major

peaks at 10, 25, 50 and 143/200Hz returned with amplitudes up to 510µm – the highest of the series of runs. Despite this the Sefag monitor predicted a lifetime in excess of 100 years.

10. It was noted in all the Oslo runs that most vibration occurred at wind speeds ≥6m/s.

This is contrary to standard AAAC and ACSR conductors which exhibit vibration mainly at wind speeds <6m/s.

11. In all the runs, the vibration at 143/200Hz was not indicated by the Sefag software as

being responsible for any conductor damage. Conclusions It is standard practice to erect AAAC and ACSR conductors at 18-20%UTS as a vibration limit. It is difficult to justify applying these basic limits to the new conductor types which exhibit load shifting between the aluminium and the core. The software supplied with the Sefag vibration monitors treats the new conductor types on the old basis as no other experimental data is available to date to base revised lifetimes on. This is a major problem and should be dealt with as soon as practicable in order to evaluate field vibration data correctly. On the ‘old’ basis evaluated by the Sefag monitors, the predicted lifetimes of Oslo at 23-25kN (16-17%UTS) was 9 and 17 years. Operation at 17-19kN (11-13%UTS) gave values in excess of 100 years. The results of the present vibration tests imply that operation of Oslo at the same %UTS figures as standard conductors may be incorrect. It should be noted that Oslo is a stronger conductor than Sycamore. However, operation at similar sags to existing conductors (which is at much lower %UTS values) appears to generate much lower vibration lives and so high life expectancies. This was particularly demonstrated in the test during the 2009/10 winter when severe wind/ice loads were suffered. The use of dampers did reduce the ‘normal’ vibration peaks significantly but did not materially affect the 143/200Hz peaks. This was not unexpected as the dampers were never intended to deal with these high frequencies. It appears unlikely that these high frequencies are causing any damage (most damage is likely to come from vibrations in the 50Hz region which is damped out by the PLP Vortx dampers) but to be certain, this should be investigated in the laboratory. This report deals exclusively with vibration matters. A previous report dealt with the changes that occur in Lisbon ACCC (R) conductors accordingly to whether or not they had been subject to load shifting due to wind/ice loads. A previous EA Technology report had covered wind/ice loads on ACCC (R) conductors in comparison with AAAC Sycamore and a further report looked in vibration data for these same conductors. It would be useful to compile data on all this experimental work (including the severe wind/ice loads of the 2009/10 winter which has not been published to date) to gain an overall insight into mechanical aspects of ACCC (R) use. A further EA Technology report has looked into line design with new conductor types including sag and ampacity calculations. It would be useful to include such data to give an overall picture of ACCC (R) capabilities.


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Recommendations

1. That in network operation, Oslo conductor be restricted to tensions that allow equal sags with conventional conductors at below the knee point (above the knee point the sag changes very little).

2. The use of PLP Vortx dampers can be recommended for use as they noticeably

reduce vibration levels at all frequencies except for those at 143/200Hz which are not likely to be damaging.

3. That tests on the self damping properties of new and field tested Oslo or Lisbon

conductors be carried out to determine how load shifting has affected the situation. In this aspect, the use of the Lisbon and Oslo conductors at Deadwater Fell is strongly recommended. As these conductors are due to be removed in May, 2010, an early decision of their use/storage is necessary.

4. A significant of experimental work has been performed on ACCC (R) conductors by

EA Technology. It is recommended that this could be combined into one basic report covering the characteristics of ACCC (R) in network use.


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Contents Page

1 Introduction ................................................................................................................... 1 1.1 Background ......................................................................................................... 1 1.2 Line design with ACCC (R) ................................................................................. 1 1.3 Deadwater Fell test Site ...................................................................................... 2 1.4 Vibration monitor data ......................................................................................... 4

2 Conductors under Test................................................................................................. 4 2.1 General................................................................................................................ 4 2.2 Tension Details.................................................................................................... 5 2.3 Load History of Oslo............................................................................................ 5

3 Analysis of Oslo vibration Data ................................................................................... 5 3.1 General................................................................................................................ 5 3.2 Tension................................................................................................................ 6 3.3 Damping .............................................................................................................. 8 3.4 Effect of Severe Weather .................................................................................. 10 3.5 Vibration Related to Wind Speed ...................................................................... 12

4 Summary...................................................................................................................... 14

5 Conclusions................................................................................................................. 15

6 Recommendations ...................................................................................................... 16

7 References................................................................................................................... 16

Appendix 1 Conductor tensions .................................................................................... 17

Appendix 2 Frequency/Amplitude Matrices .................................................................. 25

Appendix 3 Data for damped Oslo ................................................................................. 29

Appendix 4 Undamped Oslo data................................................................................... 33

Appendix 5 Damage Against Wind Speed..................................................................... 37


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1 Introduction

1.1 Background

Wind/ice load and vibration tests have been carried out over the 2007/10 period on Gap (Hawk), Sycamore and the ACCC (R) conductors, Oslo and Lisbon, at the EA Technology Deadwater Fell severe weather test site on the English/Scottish border in the UK. Data from this period is reported elsewhere [1, 2]. CTC Cable Corporation’s composite core ‘Oslo’ (ACCC (R)) conductor was installed at the site in November, 2008. The Oslo conductor was chosen by CTC to have a close match in diameter to Sycamore as this conductor could be a possible replacement for this conductor on 132kV lines in the UK. This report describes tests over the summer and autumn of 2009 and the 2009/10 winter on the vibration performance of the Oslo conductor with and without dampers. The conductor had suffered severe ice loads during the 2008/09 winter and so had experienced load shifting from the aluminium to the composite core. The 2009/10 winter was more severe than the previous winter and hence the final vibration data was recorded over a period of heavy wind/ice loads and low temperatures with an average temperature (at the conductor level) of -4°C over the 3 month test period. The Oslo conductor had suffered 27 wind/ice incidents in the 2008/09 winter, with the worst case causing tension increases of up to 64% in the conductors. These incidents were mainly due to rime ice with some due to wet snow. Due to these wind/ice loads, the Oslo load bearing capability will have switched from an almost equally shared loading with the aluminium strands/composite core to most loading on the composite core, with only a small percentage of the load being borne by the aluminium. As a result of the first sets of vibration data from the Oslo conductor, it was decided to see what effect damping would have. The aim of this report, therefore, is to compare the vibration levels of the ‘undamped’ and ‘damped’ Oslo conductor during 2009 and 2010. This would aid future line design when using this type of conductor.

1.2 Line design with ACCC (R)

Two important basic parameters in line design are the wind/ice load and vibration limit. Currently, ACSR conductors are strung to 18%UTS and AAAC to 20%UTS as vibration limits. The totally different designs of ACCC (R) conductors – which have annealed aluminium strands which are commonly in compression in network operation and so not under the tensile stress experienced by conventional conductors - means that the allowable vibration limits may be higher as the supporting core materials are composite and not metallic materials. The lower sags that these conductors exhibit can allow a totally new concept of choice of conductor tension, pole and tower loadings and current carrying capacity. There are several high temperature, low sag conductors on the market and these can have core and stranding structures which differ significantly from conventional AAAC and ACSR conductors currently widely used in the UK. In that respect, it is therefore necessary for UK Utilities to have knowledge of the performance of these new conductor types in terms of ice loads and vibration limits under UK conditions.


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1.3 Deadwater Fell test Site

The vibration tests were carried out at the EA Technology Severe Weather Test Site at Deadwater Fell. The site is situated at a height of 580m on an isolated, exposed hill top near the Scottish/English border, equidistant between the East and West coasts of the UK. It consists of a 190m test span with terminal H-poles, each supported by 14 stay wires (Figure 1.1). It is equipped with meteorological measuring instruments and time lapse video cameras. All conductors are fitted with load cells, turnbuckles and Sefag VR400 vibration monitors (Figures 1.2 and 1.3). All data is logged at 10 minute intervals. Full details of the site are given in previous reports [1-3].

Figure 1.1 The Deadwater Fell Test Span showing the South Terminal Pole. The Oslo conductor is on the far left with the Sefag monitor head just visible.


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Figure 1.2 The Sefag VR400 Vibration Monitor On the Oslo Conductor at Deadwater

Fell. Time lapse video cameras are used to view the snow/ice accretion on the conductors

Figure 1.3 The Sefag VR400 Vibration Monitor head unit with the load cell and turnbuckle (wrapped in protective sheets) at Deadwater Fell


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1.4 Vibration monitor data

Sefag VR400 monitors were used. These provide a full set of data plus an estimate of conductor lifetime. This latter value is not relevant to new conductor types as no other tests have been done to determine their fatigue limits. Until such tests have been carried out, it is not justifiable to rely on this lifetime figure, but instead, this report concentrates on the actual measured data.

2 Conductors under Test

2.1 General

The basic characteristics of the Oslo ACCC (R) conductor under test during 2008-10 at Deadwater Fell are shown below together with the details of the standard AAAC Sycamore conductor that Oslo is equivalent to: ACCC (R) (Oslo)

- 22.4mm diameter - 147.5kN UTS - 307.0mm² aluminium area* - 992kg/km weight

Sycamore (AAAC)

- 22.61mm diameter - 84.97kN UTS - 303.2mm² aluminium area - 835kg/km weight

* Note: There are several versions of Oslo around. The current version which is being supplied to the industry has aluminium cross-section of 317.7mm² rather than 307.0mm2 version which was tested at Deadwater Fell.

The Oslo conductor was erected in w/c 3 November, 2008 and had one winter’s ice and snow load before the first vibration tests started. The Oslo conductor is the same size as Sycamore but is significantly stronger (81% stronger than Sycamore). Full details of the conductors are given in a previous report [3].

Figure 2.1 ACCC (R) Conductor Erected at Deadwater Fell


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2.2 Tension Details

The Oslo conductor was set at two basic tension levels during the tests. The tensions and air temperature (measured at the control cabin on the site) are given in Appendix 1. It can be seen that after the 2008/09 winter, Oslo was re-tensioned to 25kN at the then ambient temperature of around 15°C. On 10 July the conductor tension was reduced to around 18kN at the then ambient temperature of around 20°C. The tension figures given in Appendix 2 for the various runs are the average tensions measured over each test period. The reason for these two tension regimes was to:

1. Establish the vibration performance in conditions of very low sag useful when ground clearance is critical in any re-conductoring scenario (at these tension levels the Oslo sag was around 1m less than Sycamore);

2. Look at the vibration performance when tensioned to a level that gives the same sag

as Sycamore (this is useful when re-conductoring requires same sag as a previous standard conductor).

2.3 Load History of Oslo

As ACCC (R) conductors tend to shed load from the aluminium to the composite core according to the mechanical loads, it is relevant to consider this process of load shedding as it might affect the vibration performance. ACCC (R) has a composite core surrounded by annealed aluminium strands. On erection the load in the conductor is shared between the core and the aluminium (core load ~49% aluminium 51% at 5ºC for Oslo [5]). In situations of either high temperature or high load, a percentage of the aluminium load will shift permanently to the core. It has been estimated [5] that after the maximum winter weather load of 20 January, 2009, the load ratios would be approximately 83% on the core and 17% for the aluminium for Oslo. A more detailed discussion of the process of load transfer is given in a previous report [3]. The maximum tension reached by Oslo in the 2008/09 winter was 28.8kN at a temperature of -1°C. The highest wind/ice loads reached in the 2009/10 winter were 38.3kN at a temperature of -1°C as well as 30.3kN at -4°C, 37.1kN at 0°C and 37.2kN at -2°C. All these occurred during run 7 of the vibration monitoring.

3 Analysis of Oslo vibration Data

3.1 General

Appendix 2 gives the S/N matrix data for the seven vibration tests on Oslo conductor under varying weather conditions and tensions. The data for 7 May is not relevant as it was a single 24 hour test of the monitoring equipment. The other tests were:


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Table 3.1 Vibration tests on Oslo conductor at Deadwater Fell Test end Date Run Tension (kN) Average Temperature (ºC) Condition 9 June 2009 2 23.1 10 Undamped 29 June 2009 3 22.5 11 Undamped 27 July 2009 4 17.0 11 Undamped 14 September 2009 5 16.8 11 Undamped 5 November 2009 6 17.6 8 Damped 24 February 2010 7 19.1 0 Undamped As mentioned earlier, the tensions and temperatures quoted here are those monitored by the EA Technology equipment at the site. The air temperature is measured 2m above ground level near the control hut. The temperature array data in Appendix 2 is from the Sefag monitors mounted at conductor height and in winter this is likely to give a lower reading than that at the hut. It would be logical to compare the effects of conductor tension on the Runs numbered 2 and 3 (high tension) with the low tension runs 4 and 5. Run 7 is undamped but was taken through a severe winter with several major ice loads. Run 6 was damped and at approximately the same tension as runs 4 and 5. It would be beneficial, therefore to look at three sets of data to see the effects of:

1. Tension 2. Damping 3. Severe weather

3.2 Tension

The tensions and temperatures quoted are the average value over the period of each test taken from the EA Technology logging data. The undamped runs 2 and 3 (9 and 29 June in Appendix 2) were at Oslo tensions of around 23kN at temperatures around 10°C. Both runs exhibited peaks at 10, 25 and 45/50Hz with amplitudes up to 251, 251 and 439µm respectively. Both also exhibit a minor peak at around 143Hz but at a very low amplitude of 125µm. Figures 3.1 and 3.2 give the damage against frequency data from the Sefag monitors.

Figure 3.1 Run 2 Damage against frequency


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Figure 3.2 Run 3 damage against frequency. In both the above figures it can be seen that almost all the damage is caused by the 45/50Hz peak with no contribution at all from the higher frequencies (143 and 200Hz). The main frequencies mentioned – 10Hz, 25Hz and 45-50Hz are typical of most OHL conductors. The energy from the 50Hz peak is typically dealt with by standard Stockbridge type dampers. The vibration at higher frequencies (up to 200Hz) is not typical of standard OHL conductors and is presumably due to the composite core. Undamped runs 4 and 5 (27 July and 14 September in Appendix 2) were at tensions of 17kN and temperatures of 11°C. These lower tensions showed a significant reduction in vibration levels. The dominant peak is now the 10Hz frequency which peaked at amplitudes of 314 and 413µm on the two runs. The 25Hz peak is virtually indistinguishable from the background vibration level whilst the 45/50Hz peak is now greatly reduced and only reaches amplitudes of 125 and 188µm in the two runs. The third peak at 143Hz is again lower with amplitude levels of 63 and 125µm. Figures 3.3 and 3.4 give the damage against frequency data from the Sefag monitors. At these tensions the Oslo conductor matched the sag (2.6m over the 190m span) of the Sycamore conductor. It would appear that at these tensions the vibration levels are quite low and in fact vibration dampers may not be required.

Figure 3.3 Run 4 Damage against frequency


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Figure 3.4 Run 5 damage against frequency.

3.3 Damping

Run 6 (5 November in Appendix 2) was made with PLP Vortx dampers installed (Figure 3.5) at the South end of the span. Figure 3.6 shows the location of the dampers relative to the dead end clamp. The dampers were installed at the distances recommended by PLP and Babcock Networks after consultation with CTC and were D=660mm and B=810mm. No dampers were installed at the North end. The average tension (17.6kN) was slightly higher than runs 4 and 5 (17kN) with a lower temperature (8°C). The S/N matrix data is given in Appendix 2 but is also reproduced here as Figure 3.7. The 10Hz peak is still present but at a lower amplitude of 188µm but the 45/50Hz peak has been eliminated. A very minor peak at 60Hz and 125µm amplitude is visible but another minor peak at 200µm has appeared. This latter peak is at a very low amplitude (63µm mainly with only ~1% of the vibration occurrences at 125µm) and should not be significant. Figure 3.8 gives the damage against frequency data from the Sefag monitor. This is similar to runs 4 and 5 but with the vibration around 45/50Hz reduced even more. This is to be expected as the Vortx damper, although exhibiting a multi-frequency response, is most efficient at these frequencies (see Figure 3.9). The lower temperatures may mean that the aluminium comes out of compression and takes more of the conductor load. The Sefag monitor predicted a lifetime in excess of 100 years.

Figure 3.5 Vortx damper (courtesy PLP)


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Figure 3.6 Damper positions at the South end of the Oslo span. Values

recommended by Babcock Networks D=660mm, B=810mm

Figure 3.7 Oslo vibration data for the test period with dampers installed


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Figure 3.9 The energy dissipation response of the Vortx damper (courtesy PLP)

3.4 Effect of Severe Weather

The dampers were removed on 5 November, 2009, and the conductor vibration monitored for a further 3½ months during the winter (run 7 on 24 February, 2010, in Appendix 2, reproduced here as Figure 3.10). Although still classed as having a lifetime in excess of 100 years by the Sefag software, the levels of vibration were the highest recorded throughout these series of tests, although this test had run for the longest period. The average tension was 19kN, due mainly to the low temperature average of 0°C recorded at the EA Technology hut and -4°C by the Sefag monitors at the conductors. The 10Hz peak is dominant with amplitudes up to 502µm and this level is also just reached by the 25Hz peak. The 45/50Hz peak reaches an amplitude of 376µm and there are significant vibration occurrences at


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143/200µm at up to 251µm. Figure 3.11 shows the damage against frequency data for this run. The Sefag monitor again predicted a lifetime in excess of 100 years. It is likely that if the dampers had been left on then the minor damage susceptibility at 25 and 50Hz would have been eliminated.

Figure 3.10 S N matrix data for Oslo during the 2009/10 severe winter



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3.5 Vibration Related to Wind Speed

It is normally assumed that aeolian damage to conductors occurs at low wind speeds (<6m/s) but recent data [3] has shown that conductors with a defined knee point that have most of their load carried on the core seem to suffer damage at higher wind speeds rather than low values. This does not mean that they suffer more damage – just that the range of wind speeds that damage occurs at is higher. This has implications for vibration levels in lowland areas where average wind speeds are lower i.e. ACCC (R) should have lower vibration levels than standard conductors in these areas. The data of actual wind speeds and damage against wind speed for each run is given in Appendix 5. The final winter (run 7) data shows a high frequency of winds ≤1m/s. This is because the monitor anemometer (which uses mechanical rotation) would have been frozen for much of the winter (the average temperature as recorded at the conductor was -4°C). The EA Technology ultrasonic anemometer does not suffer from this problem and Figure 3.12 shows the wind and temperature data for January, 2010. There are virtually no wind speeds below 1m/s. The maximum (10 minute average) wind speed recorded was 37.4m/s (~82 mph). The winter wind speed data from the Sefag monitor in Run7 in Appendix 5 must therefore be disregarded for this evaluation.

‐10.0

‐5.0

0.0

5.0

10.0

15.0

20.0

25.0

30.0

35.0

40.0

28/12/2009 00:00 02/01/2010 00:00 07/01/2010 00:00 12/01/2010 00:00 17/01/2010 00:00 22/01/2010 00:00 27/01/2010 00:00 01/02/2010 00:00 06/02/2010 00:00

Wind spee

d (m

/s) and

Tem

perature ( C )

Weather data for January, 2010 at Deadwater Fell

Wind speed

Temperature

Figure 3.12 Deadwater wind speed and temperatures for January, 2010. Data for Run 5 in Appendix 5 (shown here as Figures 3.13 and 3.14) show the actual wind speed normal to the span and the damage against wind speed for Oslo. Figure 3.15 shows data for the same period from the ‘New’ Lisbon conductor which had been erected in 2009 and so had not suffered any wind/ice loads and so no load shift onto the composite core. It can be seen that whilst for all the Oslo data the damage occurs at 6-10m/s wind speed, the previously unloaded Lisbon showed instead the typical pattern of damage occurring mainly around 3m/s. Historically, aeolian damage has been found to occur at wind speeds ≤6m/s.


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However, this data – for the same weather conditions at the same period in time at the same position – shows definitively that for conductors which carry tensile load on their cores vibration occurs at higher wind speeds and that damage at low wind speeds is distinctly less.

Figure 3.13 Run 5 Wind speed array normal to span, 14 September, 2009.

Figure 3.14 Run 5 Damage against wind speed, Oslo conductor, 14 September, 2009.


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Figure 3.15 Damage against wind speed for previously unloaded ‘New’ Lisbon

ACCC (R) conductor, 14 September, 2009.

4 Summary 1. CTC Cable Corporation’s Oslo ACCC (R) conductor has been tested at the UK EA

Technology Deadwater Fell test site for snow/ice loads (winter 2008/09) and vibration (summer – autumn, 2009 and winter 2009/10). Safag VR400 vibration monitors were used to monitor the conductor.

2. This report looks at the vibration data over 7 runs between May, 2009 and February, 2010, at different tensions and weather conditions and also with and without PLP Vortx dampers. These had been installed on one end of the span only at distances recommended by Babcock Networks.

3. Oslo conductor is equivalent to the standard AAAC Sycamore. Initially it was strung at around 17% of its UTS and had a sag 1m better than Sycamore. It should be noted however that it is a stronger conductor than Sycamore. It was then reduced to around 12% of its UTS to match the Sycamore sag at 2.6m on the 190m span.

4. During the 2008/09 winter Oslo suffered wind/ice loads up to 29kN and hence had a load shift so that 83% of the load was carried on the core. During the 2009/10 winter (and the final vibration test run) wind/ice loads up to 38kN (~26%UTS) were experienced.

5. Full vibration data and analysis graphs are provided in the Appendices of this report

6. In two undamped runs at ~23kN, vibration peaks at 10, 25, 50 and 143Hz were recorded with the dominant amplitudes being at 50Hz. The vibrations noted in the 143/200Hz region have not been noted in standard ACSR or AAAC conductors and are presumably due to the characteristics of the composite core. The Sefag monitor indicated lifetimes of 9 and 17 years.

7. In two undamped runs at ~17kN, the peaks at 25 and 50Hz were significantly reduced with the main vibration occurring at 10Hz. The vibration at 143/200Hz was still present. The Sefag monitor indicated lifetimes of >100 years for both runs.


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8. In the run at 17.6kN with PLP Vortx dampers fitted, the peaks at 25 and 50Hz were virtually eliminated and the 10Hz peak was reduced. The 143/200Hz vibration was still present. The Sefag monitor indicated lifetime of > 100 years.

9. In the undamped winter period run at an average tension of 19kN, all the major peaks at 10, 25, 50 and 143/200Hz returned with amplitudes up to 510µm – the highest of the series of runs. Despite this the Sefag monitor predicted a lifetime in excess of 100 years.

10. It was noted in all the Oslo runs that most vibration occurred at wind speeds ≥6m/s. This is contrary to standard AAAC and ACSR conductors which exhibit vibration mainly at wind speeds <6m/s.

11. In all the runs, the vibration at 143/200Hz was not indicated by the Sefag software as being responsible for any conductor damage.

5 Conclusions It is standard practice to erect AAAC and ACSR conductors at 18-20%UTS as a vibration limit. It is difficult to justify applying these basic limits to the new conductor types which exhibit load shifting between the aluminium and the core. The software supplied with the Sefag vibration monitors treats the new conductor types on the old basis as no other experimental data is available to date to base revised lifetimes on. This is a major problem and should be dealt with as soon as practicable in order to evaluate field vibration data correctly. On the ‘old’ basis evaluated by the Sefag monitors, the predicted lifetimes of Oslo at 23-25kN (16-17%UTS) was 9 and 17 years. Operation at 17-19kN (11-13%UTS) gave values in excess of 100 years. The results of the present vibration tests imply that operation of Oslo at the same %UTS figures as standard conductors may be incorrect. It should be noted that Oslo is a stronger conductor than Sycamore. However, operation at similar sags to existing conductors (which is at much lower %UTS values) appears to generate much lower vibration lives and so high life expectancies. This was particularly demonstrated in the test during the 2009/10 winter when severe wind/ice loads were suffered. The use of dampers did reduce the ‘normal’ vibration peaks significantly but did not materially affect the 143/200Hz peaks. This was not unexpected as the dampers were never intended to deal with these high frequencies. It appears unlikely that these high frequencies are causing any damage (most damage is likely to come from vibrations in the 50Hz region which is damped out by the PLP Vortx dampers) but to be certain, this should be investigated in the laboratory. This report deals exclusively with vibration matters. A previous report dealt with the changes that occur in Lisbon ACCC (R) conductors accordingly to whether or not they had been subject to load shifting due to wind/ice loads. A previous EA Technology report had covered wind/ice loads on ACCC (R) conductors in comparison with AAAC Sycamore and a further report looked in vibration data for these same conductors. It would be useful to compile data on all this experimental work (including the severe wind/ice loads of the 2009/10 winter which has not been published to date) to gain an overall insight into mechanical aspects of ACCC (R) use. A further EA Technology report has looked into line design with new conductor types including sag and ampacity calculations. It would be useful to include such data to give an overall picture of ACCC (R) capabilities.


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6 Recommendations 1. That in network operation, Oslo conductor be restricted to tensions that allow equal

sags with conventional conductors at below the knee point (above the knee point the sag changes very little).

2. The use of PLP Vortx dampers can be recommended for use as they noticeably

reduce vibration levels at all frequencies except for those at 143/200Hz which are not likely to be damaging.

3. That tests on the self damping properties of new and field tested Oslo or Lisbon

conductors be carried out to determine how load shifting has affected the situation. In this aspect, the use of the Lisbon and Oslo conductors at Deadwater Fell is strongly recommended. As these conductors are due to be removed in May, 2010, an early decision of their use/storage is necessary.

4. A significant of experimental work has been performed on ACCC (R) conductors by

EA Technology. It is recommended that this could be combined into one basic report covering the characteristics of ACCC (R) in network use.

7 References

1. Wareing J B & Horsman D P, ‘Experimental investigation of icing of novel conductors’, EATL Report 6143, October, 2008.

2. Horsman D P & Wareing J B ‘Experimental investigation of novel conductors at

Deadwater Fell – vibration tests’ EA Technology STP report S2154_3, January, 2010.

3. Horsman D P, Wareing J B & Ward A S, ‘Testing of Oslo Conductor at Deadwater Fell’ EA Technology Report 6385 Project 74230. April, 2009.

4. Horsman D P, Wareing J B & Ward A S, ‘Vibration field testing of Lisbon ACCC (R)

conductor’ EA Technology Project 75200, December, 2009.

5. Bosze E, CTC Cable Corporation. Private Communication

6. Cigré SC22-WG04, "Recommendations for the Evaluation of the Lifetime of Transmission Line Conductors", Electra, No 63, March 1979, pp. 103-145.

7. Cigré Technical Brochure 332 ‘Fatigue Endurance Capability of Conductor/Clamp

Systems – Update of Present Knowledge’, 2004


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Appendix 1 Conductor tensions Conductor Tensions Conductor tensions are shown below for the period of the Oslo vibration tests from 1 May, 2009, to 23 February, 2010. ‘Lisbon 1’ is the Old Lisbon and ‘Lisbon 2’ is the New Lisbon. 1-18 May, 2009.

18 May – 3 June, 2009.


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3-10 June, 2009.

10-30 June, 2009.


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30 June -10 July, 2009.

10-29 July, 2009.


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29 July – 21 August, 2009.

21 August – 23 September, 2009.


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23 September – 22 October, 2009.

23 October – 3 November, 2009.


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3 – 24 November, 2009.

25 November – 22 December, 2009.


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1 December, 2009, – 4 January, 2010.

1 -20 January, 2010.


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17 January – 2 February, 2010.

2 – 23 February, 2010.


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Appendix 2 Frequency/Amplitude Matrices Oslo: 715 Measurement 1, 7 May, 2009. Undamped. Tension 27kN Temp 2°C. One day test

Oslo: 715 Measurement 2, 9 June, 2009. Undamped. Tension 23kN Temp 10°C


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Oslo: 627 Measurement 18, 29 June, 2009. Undamped. Tension 22.5kN Temp 11°C

Oslo: 627 Measurement 19, 27 July, 2009. Undamped. Tension 17kN Temp 11°C


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Oslo: 627 Measurement 20, 14 September, 2009. Undamped. Tension 17kN Temp 11°C

Oslo: 676 Measurement 4, 5 November, 2009. Damped. Tension 17.6kN Temp 8°C


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Oslo: 676 Measurement 6, 24 February, 2010. Undamped. Tension 19kN Temp 0°C


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Appendix 3 Data for damped Oslo The following data is for the period 30 September to 5 November, 2009, when the Oslo conductor was fitted with dampers. S/N curve

Wind array


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Temperature Array

Damage against wind speed


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Amplitude class

Damage against amplitude class


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Frequency classes

Damage against Frequency


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Appendix 4 Undamped Oslo data The following data is for the winter period 5 November, 2009, to 24 February, 2010, when the Oslo conductor was not damped. S/N curve

Wind array (note: anemometer on monitor will have been frozen for long periods)

Temperature Array


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Amplitude

Frequency


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Damage v Amplitude


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Damage v Frequency

Damage v Wind speed (note monitor anemometer will have registered zero wind speeds when frozen)


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Appendix 5 Damage Against Wind Speed It is normally assumed that aeolian damage to conductors occurs at low wind speeds (<6m/s) but recent data [Rep 72100] has shown that conductors with a defined knee point that have most of their load carried on the core seem to suffer damage at higher wind speeds rather than low values. This does not mean that they suffer more damage – just that the range of wind speeds that damage occurs at is higher. This has implications for vibration levels in lowland areas where average wind speeds are lower i.e. ACCC (R) should have lower vibration levels than standard conductors in these areas. Data is provided below for each test run on Oslo conductor with the range of wind speeds normal to the span and the damage v wind speed data from the Sefag monitor software. Run 2 Monitor 715/2, 9 June, 2009.

Run 3 Monitor 627/18, 29 June, 2009.


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Run 4 Monitor 627/19, 27 July, 2009.


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Run 5 Monitor 627/20, 14 September, 2009.


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Run 6 Monitor 676/4, 5 November, 2009.


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Run 7 Monitor 676/6, 24 February, 2010. Note – Monitor anemometer will have been frozen for extended periods

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