Prague, 8-11 June 2009

WATER TREES IN MEDIUM VOLTAGE CABLES:

VERY SHORT TIME ACCELERATED AGEING TESTS

HENNUY-Belgium-Session1-Paper1060

Prague, 8-11 June 2009

A WATER TREE IN A FEW WORDS

HENNUY-Belgium-Session1-Paper1060

Time

Alternating voltage

Impurities Water

A Cable

Prague, 8-11 June 2009

Consequences

• Higher dielectric losses• Insulation breakdown

HENNUY-Belgium-Session1-Paper1060

Prague, 8-11 June 2009

SOLUTIONS

• Water barriers• Better compound quality• Improvement of the manufacturing

process

• Blend of copolymer and homopolymer • Homopolymer and water tree retardant

additives

HENNUY-Belgium-Session1-Paper1060

Prague, 8-11 June 2009

Existing tests• Polyethylene blocks and needles

• Tests on full-size medium voltage cables

HENNUY-Belgium-Session1-Paper1060

Prague, 8-11 June 2009

ACCELERATED TESTS DEVELOPED BY LABORELEC

• 3,8 kV/mm

• 3 kHz

• Salted water solution

• 12 days

HENNUY-Belgium-Session1-Paper1060

Prague, 8-11 June 2009

Test set-up

HENNUY-Belgium-Session1-Paper1060

• High voltage, high frequency power supply• 20 °C • No preconditioning

Prague, 8-11 June 2009

Examination of the water trees

• 5 slices• Dyed with methylene blue• Optical microscope• Length and shape

HENNUY-Belgium-Session1-Paper1060

Prague, 8-11 June 2009

Homopolymer vs Copolymer

Author Name-Country Session X Paper IDx

Prague, 8-11 June 2009

Examples of investigations

Sample 0Homo

without TR7 days

3,86 kV/mm800 µm

Sample 1EAXeCWB

Copo11 days3 kV/mm

[100…300 µm]

Sample 2EAXeCWB

Copo7 days

3,84 kV/mmNo WT

Sample 3EAXeCWB

Copo12 days

3,84 kV/mm[240…512 µm]

Prague, 8-11 June 2009

Examples of results

Sample 4Homo+WTR

12 days3,84 kV/mm

215 µm

Sample 5Homo+WTR

12 days3,84 kV/mm

117 µm

Sample 6Homo

12 days3,84 kV/mm

440 µm

Sample 7Homo EAXCWB

Test stopped3,84 kV/mm

No WT

Prague, 8-11 June 2009

Conclusions

• Significant results and repeatable tests • Real cable samples• Test duration: 12 days• Information on intrinsic life time estimation• Assessment of new materials

HENNUY-Belgium-Session1-Paper1060

Prague, 8-11 June 2009

Future work• Study of the influence of parameters

– Impurities– Temperature

• Electrical measurements

HENNUY-Belgium-Session1-Paper1060

Prague, 8-11 June 2009

Thank you for your attention

HENNUY-Belgium-Session1-Paper1060