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Technical Discussions
Patrick Huttenhuis
Patrick Huttenhuis
09:19 Jan-09-2003
NDT's for middle voltage cables

A client of us, a producer of middle voltage cables (up to 50 kV) has problems during the extrusion process. During the extrusion process once in a while there arise small bubbles (1-3 mm) in the isolating poly-ethylene layer. It is believed that this bubbles will result in undesirable voltage breakdown.
The cable consists of a 12-22 mm aluminium pipe. Around this pipe a three layer polymer is constructed during one extrusion step. The three layers are:

- a black (carbon) PE layer of appr. 0.5 mm
- a white PE layer of appr. 5 mm. In this layer the bubbles have been seen,
a black (carbon) PE layer of appr. 0.5 mm

After the extrusion the cable is vulcanised and cooled.

Do you know if there are non-destructieve methods (preferable online) which can indicate the bubbles in the polymer layer. If yes, what kind of methods are available, what are the conditions and advantage / disadvantages of the methods. The production speed of the cable is betwen 8 and 30 m/min.

Thank you in advance for your advice.

Kind Regards,

Patrick Huttenhuis
Procede Twente B.V.
patrick.huttenhuis@procede.nl


    
 
 
Godfrey Hands
Engineering,
PRI Nadcap, United Kingdom, Joined Nov 1998, 289

Godfrey Hands

Engineering,
PRI Nadcap,
United Kingdom,
Joined Nov 1998
289
09:45 Jan-09-2003
Re: NDT's for middle voltage cables
: A client of us, a producer of middle voltage cables (up to 50 kV) has problems during the extrusion process. During the extrusion process once in a while there arise small bubbles (1-3 mm) in the isolating poly-ethylene layer. It is believed that this bubbles will result in undesirable voltage breakdown.
: The cable consists of a 12-22 mm aluminium pipe. Around this pipe a three layer polymer is constructed during one extrusion step. The three layers are:
:
: - a black (carbon) PE layer of appr. 0.5 mm
: - a white PE layer of appr. 5 mm. In this layer the bubbles have been seen,
: a black (carbon) PE layer of appr. 0.5 mm
:
: After the extrusion the cable is vulcanised and cooled.
:
: Do you know if there are non-destructieve methods (preferable online) which can indicate the bubbles in the polymer layer. If yes, what kind of methods are available, what are the conditions and advantage / disadvantages of the methods. The production speed of the cable is betwen 8 and 30 m/min.
:
: Thank you in advance for your advice.
.
: Kind Regards,
.
: Patrick Huttenhuis
: Procede Twente B.V.
: patrick.huttenhuis@procede.nl
.

Dear Partick,
Sounds as if an Electronics solution rather than an NDT solution may be able to detect these bubbles.
I suggest that you speak with some electronics experts.
My thoughts are that the bubbles inside the 5 mm layer will affect the effective dielectric constant, and looking at the electrical capacity between the aluminium pipe and a separate electrode on the outside of the wrapped cable may provide a solution.
The thicknesses however may be fairly high to have a measurable effect.

Veel succes met de toepassing.
I wish you success with the application.

Godfrey Hands


    
 
 
Jörg Collrep
Jörg Collrep
00:02 Jan-09-2003
Re: NDT's for middle voltage cables
Dear Patrick,
this kind of defects could easily be detected by shearography but not within the production speed as we need some time ( 3 - 5 sec )to excite the cable with a very low thermal or vacuum excitation and acquire an image under loaded and unloaded condition. If you would like to know more about the technique pls reply to me directly.
Thanks
Jörg Collrep
Steinbichler Optotechnik GmbH
www.steinbichler.de


: A client of us, a producer of middle voltage cables (up to 50 kV) has problems during the extrusion process. During the extrusion process once in a while there arise small bubbles (1-3 mm) in the isolating poly-ethylene layer. It is believed that this bubbles will result in undesirable voltage breakdown.
: The cable consists of a 12-22 mm aluminium pipe. Around this pipe a three layer polymer is constructed during one extrusion step. The three layers are:
:
: - a black (carbon) PE layer of appr. 0.5 mm
: - a white PE layer of appr. 5 mm. In this layer the bubbles have been seen,
: a black (carbon) PE layer of appr. 0.5 mm
:
: After the extrusion the cable is vulcanised and cooled.
:
: Do you know if there are non-destructieve methods (preferable online) which can indicate the bubbles in the polymer layer. If yes, what kind of methods are available, what are the conditions and advantage / disadvantages of the methods. The production speed of the cable is betwen 8 and 30 m/min.
:
: Thank you in advance for your advice.
.
: Kind Regards,
.
: Patrick Huttenhuis
: Procede Twente B.V.
: patrick.huttenhuis@procede.nl
.



    
 
 

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