Voorkomen van schade door derden aan land- en zeekabels. Dik van Houwelingen Risico Management Stedin Cigre B1-NL

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1 Voorkomen van schade door derden aan land- en zeekabels Dik van Houwelingen Risico Management Stedin Cigre B1-NL 1

2 Third-Party Damage to Underground and Submarine Cables Technical Brochure 398 Cigré Working Group B1.21 December

3 Contents Working group B1.21 Background Underground cables Submarine cables Risk based approach Summary and conclusion 3

4 Working Group B1.21 members Christian Jensen - Denmark (Convenor) Bart Mampaey - Belgium Josip Antic - Croatia Peggy Chevalier - France Sergio Tricoli - Italy Georg Balog - Norway Fer van Stekelenburg - The Netherlands Cristian Sorin Pispiris - Romania Maria Dolores Lopez Menchero Cordoba - Spain Allen MacPhail Canada (corresponding) 4

5 Background Frequently damage to power cables by external agencies, or third-parties Greatest threats Excavating for underground cables Anchors or fishing for submarine cables Much has already been done to minimize 'internal' failures Protection from third-party damage usually treated somewhat arbitrarily industry guidelines to reduce such risks are minimal Damage results in high repair costs and loss of reliability 5

6 Third party threats: Underground Cables Main threats to underground cables: Excavators Horizontal drilling, pipe jacking, etc. Vertical drilling (e.g. geotechnical boreholes) Incorrect information on cable location (X,Y, Z) Incorrect use of information: The information about cable route and cable depth is used incorrectly (i.e. map upside down). 6

7 Third party threats: Underground Cables Other threats: Traffic and heavy-duty vehicles (e.g. vibration) Vegetation (e.g. depleting soil moisture and root damage) Vandalism Influence from other installations (e.g. adjacent building foundations) Change in the thermal conditions of the surroundings Farmers draining fields (lowering water table) High depth ploughing 7

8 Average annual failure rate by installation type: Underground Cables Indication of which type of installation is most exposed to thirdparty damage (based on international survey by Cigre) Voltage level 60 to 219 kv Average Yearly Fault rate per 100 km circuit beginning 2001 to end 2005 km installed (Info B1.10 and B1.21) External - Other Physical External Parameters Direct Burial Ducts + pipes Tunnels Others (Bridges, troughs, Air) External - Third Party Mechanical External - Total Internal (cable only) to 500 kv km installed (Info B1.10 and B1.21) External - Other Physical External Parameters External - Third Party Mechanical External - Total Internal (cable only)

9 Survey conclusions: Underground Cables Failure caused by external agents is the most frequent About 70% of the failures are caused by mechanical works About 40% of third-party damage is related to insufficient information exchange Concrete encased ducts, pipes and tunnels gives a very good reduction in external damage by third-parties Cables in ducts or pipes can result in a reduction in transmission capacity Decide whether extra costs are justified, considering other possible benefits, e.g. lower construction impact, reduced repair costs, reliability improvements, etc. 9

10 How to reduce the risk of third-party damage: Underground Cables Improve mechanical protection by installing cables in ducts or pipes and encasing with concrete or equal Improve warning marker systems near cables Dialogue with third parties - excavation and construction companies Keep accurate and up-to-date cable location records Provide accurate and timely information to third-parties 10

11 How to reduce the risk of third-party damage: Underground Cables Establish processes for third-parties to get permission to do their construction work. Assist the third-party to understand the cable location information and consequences of damage. Monitor third party activities at the work site. Implement a Dial-before-you-dig program. 11

12 GBKN How to reduce the risk of third-party damage: Dutch approach Dial-before-you-dig program: Wet Informatie Uitwisseling Ondergrondse Netten Kadaster KOL Netbeheerders Grondroerder Predecessor of KOL was KLIC (kabel- en leidingen informatie centrum) Diggers must contact KOL >= 3 days before work starts Grid operators must supply grid information within 24 hours after request of digger Works with internet-portal 12

13 How to discover and detect third party damage to underground cables It may be possible to detect the damaged state before the final destroying effect is reached The following methods are possible for detecting shortterm effects, that may not immediately result in failure Regular DC-voltage testing of cable sheath insulation On-line monitoring of the sheath current in crossbonded systems On-line monitoring of corrosion potentials or cathodic protection current 13

14 How to discover and detect third party damage to underground cables Apply Distributed Temperature Sensing systems to monitor abnormal changes in temperature profiles along cable route Install simple pilot wires or fibres in the vicinity of the cables; if continuity is broken, an alarm could be raised Apply sensitive on-line monitoring of fluid pressures, volumes, flow rates, etc., for fluid-filled cable systems Regular patrols of cable routes 14

15 Submarine Cables: Conclusions from the service experience survey (not including internal failures) Questionnaire did not provide reliable conclusions about the relation between installation method and failure probability. The average annual failure rate seems to be significantly lower for submarine cables than for underground cables. External damage is the most common cause of submarine cable failures. Fishing trawler and beam-trawl shoe Penetration of smaller anchors and fishing gear versus soil hardness 15

16 Submarine cables: Results from the service experience survey (not including internal failures) Voltage level 60 to 219 kv 220 to 500 kv km circuit installed (cumulative up to 2005) AC SCFF/SCOF AC HPFF/HPOF AC XLPE DC MI Internal (Cable only) External - Total External - Anchor External - Trawling External - Excavation Other + Unknown Total km circuit installed (cumulative up to 2005) DC SCFF/SCOF Internal (Cable only) External - Total External - Anchor External - Trawling External - Excavation Other + Unknown Total

17 Third party threats to submarine (onder rivier) cables Main threats to submarine cables are: Anchor contact Dragging of anchor chain Abrasion by tugboat tow lines Fishing (trawlers) Vessels running aground 17

18 Third party threats to submarine cables Ocean dredging and dumping of dredged material or garbage Military activity and unexploded ordnance Other installations including pipes, telecommunication cables, etc. The influence of other existing cables 18

19 Reducing the risk of third-party damage to submarine cables Bury submarine cables to reduce risk from fishing gear and very small anchors. Inform fishing authorities, marine pilots and owners/captains of vessels of cable corridor locations and areas where fishing/anchoring is restricted. 19

20 Reducing the risk of third-party damage to submarine cables The information shared between fishermen, mariners and utilities can be divided into two types: Information that fishermen and mariners must have on board Submarine cable routes Restrictions of activities in areas where submarine cables are positioned Protection corridors near submarine cables Information that utilities are required to provide to relevant organisations New cables installed Re-laid cable after maintenance or repair operations 20

21 Reducing the risk of third-party damage to submarine cables Maintain a good relationship with local fishermen and commercial vessel operators so that everyone is aware of the cables. Maintain accurate as-laid records of cable locations. Provide accurate records to appropriate marine charting authorities. 21

22 How to discover and detect third party damage to submarine cables Cable inspection using a ROV Optical or acoustic when unburied cable A survey showing the cable burial depth using an electronic cable tracker on an ROV 22

23 How to discover and detect third party damage to submarine cables Monitor cables with integrated optical fibres using DTS systems. DTS used for temperature sensing and ampacity determination. Place optical fibre above main cable: Highest temperature First to be hit by anchors 23

24 How to discover and detect third party damage to submarine cables (naar achteren) Other events identified using periodic geophysical surveys A side scan sonar survey to show the trawling activity in the area any objects (anchors, fishing net and trawl, anchor chains etc.) fastened to the cable whether the cable is visible and therefore unprotected. A high resolution multi-beam echo-sounder survey shortly after the cables are installed periodically repeated and changed conditions noted, such as new trawler scars, anchor drag marks, sand wave migration, sea bed mobility exposing buried cables, etc. 24

25 Risk assessment of cable systems Third-party damage can be a complex process which sometimes consists of several interdependent events. To minimise the overall risk of the cable system look at possible events followed by damaged states damage effects for the damaged states how severe is the damage effect for the cable system? Mitigation efforts must be prioritised correctly Focus must be on the damage events and damaged states with the most severe effects and the highest probability 25

26 Criticality (Risk) Matrix Criticality = Probability x Severity To help analyse, each are shown in a criticality matrix (risk matrix). Red: Action and studies needed to reduce the criticality. Yellow: Action and studies needed to check criticality and possibly improve. Green: Area with low risk, where no further studies or action are required. Probability of damaged state V IV III II I Severity of effect I II II I I V V There are two possible ways of reducing the criticality or risk: Reduce probability Reduce severity 26

27 Probability classes (example) Level Probability Description V > 0.5 /(100 km x year) Very high probability IV 0.5/(100 km x year) High probability III 0.25/(100 km x year) Average probability for cable systems II 0.1/(100 km x year) Low probability I 0.05/(100 km x year) Very low probability 27

28 Consequences classes (example) Level Consequence Description V Catastrophic Breakdown of all or part of the network Very high costs for the market IV Critical Breakdown of part of network High costs for the market III Major Breakdown of more than one line High costs for the market II Minor Breakdown of one line Moderate costs for the market I Negligible Planned disconnection of line for repair Low costs for the market 28

29 Summary and Conclusions The risk of internal damage has already been reduced The risk of underground cable damage by a third party is about 2.5 times higher than an internal failure for XLPE cable systems. Risk of external damage is approximately ten times greater for direct buried cables compared to in ducts or pipes. 29

30 Summary and Conclusions The number of third-party damage events can be reduced Good cable location records with geographical coordinates Improvement of information provided to parties on how to obtain permission for planned excavation or drilling activities Improved education and exchange of information between the enterprises regarding the problem Improved mechanical protection of cables Applying structured risk assessment methods 30