Voorkomen van schade
door derden aan land- en
zeekabels
Dik van Houwelingen
Risico Management
Stedin
Cigre B1-NL
1
Third-Party Damage to
Underground
and Submarine Cables
Technical Brochure 398
Cigré Working Group B1.21
December 2009
2
Contents
•
•
•
•
•
•
Working group B1.21
Background
Underground cables
Submarine cables
Risk based approach
Summary and conclusion
3
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
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
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
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
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
220 to 500 kV
Average Yearly Fault rate per
100 km circuit beginning
2001 to end 2005
Others
(Bridges,
troughs,
Air)
Direct
Burial
Ducts
+
pipes
Tunnels
km installed (Info B1.10 and
B1.21)
11579
12758
1236
1357
External - Other Physical External
Parameters
0.054
0.003
0.000
0.015
External - Third Party Mechanical
0.154
0.014
0.000
0.118
External - Total
0.207
0.017
0.000
0.133
Internal (cable only)
0.081
0.011
0.049
0.000
km installed (Info B1.10 and
B1.21)
1303
2725
1319
110
External - Other Physical External
Parameters
0.153
0.015
0.030
0.029
External - Third Party Mechanical
0.292
0.022
0.000
0.044
External - Total
0.445
0.037
0.030
0.000
Internal (cable only)
0.292
0.000
0.030
0.000
8
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
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
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
How to reduce the risk of third-party
damage: Dutch approach
• ‘Dial-before-you-dig’ program:
• Wet Informatie Uitwisseling Ondergrondse Netten
Kadaster
KOL
Netbeheerders
GBKN
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
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
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
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
Submarine cables: Results from the service
experience survey (not including internal
failures)
AC
SCFF/SCOF
AC
HPFF/HPOF
AC
XLPE
DC
MI
km circuit installed
(cumulative up to 2005)
10179
104
5675
5239
Internal (Cable only)
0
0
0
0
0.049
1.918
0.035
0.114
0.039
1.918
0.035
0.019
0
0
0
0.076
0.010
0
0
0.019
Other + Unknown
0.079
0
0.035
0.019
Total
0.128
1.918
0.070
0.133
km circuit installed
(cumulative up to 2005)
6779
147
10021
2894
Internal (Cable only)
0
0
0
0.035
0.030
0
0.050
0
0.015
0
0.0200
0
0
0
0.030
0
0.015
0
0
0
Other + Unknown
0.044
0
0.050
0
Total
0.074
0
0.100
0.035
Voltage
level
External - Total
60 to 219
kV
External - Anchor
External - Trawling
External - Excavation
External - Total
220 to 500
kV
External - Anchor
External - Trawling
External - Excavation
DC
SCFF/SCOF
16
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
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
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
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
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
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
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
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
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
Criticality (Risk) Matrix
• Criticality = Probability x Severity
Probability of
damaged state
• 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.
• There are two possible ways of
reducing the criticality or risk:
– Reduce probability
– Reduce severity
V
IV
III
II
I
Severity
of effect
I
II
II
I
I
V
V
26
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
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
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
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