sub sea cable technology - sintef · sub‐sea cable technology ... test methods (subsea cables)...
TRANSCRIPT
EERA DeepWind’2014
Sub‐sea Cable Technology
Hallvard FaremohSINTEF Energy Research
Brief presentation of:
Wind Farm Cable R&D project
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High Voltage Subsea Cables Networking the North SeaApplication for a KMB project within the Research Council of Norway
• Project content• Education (PhD / MSc)• Scientific equipment• Financing• Financing• Research Partners
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High Voltage Subsea Cables Networking the North Sea Key words: Long operation times, Flexible designs, Qualification and test methods, HVDC/AC
AC Cable Systems
DC Cable Systems
Dynamic / Electric Test Methods
(Subsea Cables)Testing
DC systems in wet
( )
AC systems in wet environment
Treeing (water‐/
DC systems in wet environment
Terminations and joints
Dynamic load ‐materials
‐ DC / DC +AC ripple
QualificationLaboratory for electric/dynamic testing
Candidate materials
Long term
environmentCondition assessment
/electrical)‐pressure‐RH Cables‐ AC / RH
‐ AC / LF (0.1/1 Hz)
and joints
T P
tUFrequency
‐ DC currentinterruption‐ DC / RH
properties (stability)
Thermal
PublicationsEducation:1 Ph D
Frequency(0.1, 1, 50 Hz)
Education:1 Ph D2 MScEducation:
2 MSc
Establish facility for manufacturing of model cables
Full scale testing ?
Mechanical
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2 MSc cables
Project ContentProject Content
1. AC cable systems
2. DC cable systems. C cab e syste s
3. Test methods
4. Dynamic / electrical testing (prototypes)
5 Education (NTNU)5. Education (NTNU)
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AC Cable Systems
• Polymeric AC cables have been in use• Polymeric AC cables have been in use for decades in subsea environment
I l th i i i• In general the service experience is good
U d i di i• Under some service conditions water treeing has caused premature failures
• Dynamic high voltage cables have now been in service for some years
• A PhD student (NTNU) is working with partial discharge questions
Water treeing in a 24 kV XLPE cable
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DC Cable Systems• Polymeric HVDC cables have been
installed for more than a decade in ( h ll bl )Norway (The Troll Cables)
• The subsea HVDC cables are all water tight constructions (lead sheathed)
• Water treeing at DC stresses are not commonly expected to be a problem
• However, voltage ripple do exist in HVDC systems
• A PhD student (NTNU) is working with questions related to moisture ingress in XLPE insulation
Polymer HVDC cables
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Combined AC and DC Stresses
• As HVDC systems have some percent ripple – an AC voltage stress will occur in HVDC cables
• This will not cause any damage under y gdry conditions
• Combined AC and DC stress may ycause rapid water tree initiation and growth if the water barrier has been compromised
Electrical treeing due to rapid water tree growth under combined AC and DC stresses
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Combined AC and DC Stressing ‐Water tree analysisCombined AC and C Stressing Water tree analysis
2 weeks 4 weeks 8 weeks
25 kV/mm DC + 2.5 kV/mm AC 5 kHzpeak
2 weeks 4 weeks 8 weeks
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Dynamic / Electrical Testing
• Dynamic testing of high voltage cables have been performed for many years
• No electric stressing is usually g yapplied under the dynamic tests
Marintek – Dynamic test rigs
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Dynamic / Electric Testing y g
T diff t t t* Two different test rigs for combined dynamic and electrical testing have been developed
• Bending rig
• Axial strain rig
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Dynamic / Electrical Testing
‐ Tests have been performed in both test rigsTests have been performed in both test rigs
‐ More than 3 million dynamic cycles have been applied to XLPE cables
‐ AC stressing according to CENELEC standard have been used (both 50 and 500 Hz)
Th lt h i d b f t t h th XLPE bl i l ti‐ The results show an increased number of water trees when the XLPE cable insulation is exposed to combined dynamic and electrical stress
h l h h d i‐ The water tree lengths; however, do not increase
‐ Hence, as long as the dynamic stresses are kept at reasonable levels, no severe increased degradation is observed when the XLPE cable is aged under combined dynamic and electrical stresses
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SummarySummary
• The project was established in 2009
• Two test rigs for combined dynamic and electrical stressing of cable insulation avebeen built
• Long term tests have been performed in both test rigs
• Dynamic stressing at reasonable values (around 1 % elongation) do not result inDynamic stressing at reasonable values (around 1 % elongation) do not result in detrimental ageing phenomena
• Combined HVDC and AC ripple has shown to result in enhanced ageing if moisture pp g ghas penetrated the moisture barrier
• Two PhD students have been working in this project
• Several MSc students have also participated in the project
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Pressure Testing – not part of this presentation g p p
This presentation do not present results when testing in SINTEF’s high pressure vessels. All tests presented is performed at ambient pressure
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Thank you for your attention
Questions?
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