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Frankfurt (Germany), 6-9 June 2011
Speaker Jean LAVALLÉE
Authors Janislaw TARNOWSKI, Jacques CÔTÉ,
André GAUDREAU, Pierre GINGRAS,
Mircea IORDANESCU
Hydro-Québec
Lavallée – Canada – Session 3 – Paper 0373
Verification of LV Underground Cable Insulation by Air Injection
Frankfurt (Germany), 6-9 June 2011
Problem assessment Risk of arc faults on low-voltage (LV) underground cables,
which can lead to explosions An insulation break in LV cables is the main reason for this
phenomenon on Hydro-Quebec’s system
Examples of explosions
Lavallée – Canada – Session 3 – Paper 0373
Frankfurt (Germany), 6-9 June 2011
Lavallée – Canada – Session 3 – Paper 0373
Existing solutions:
There is no solution that is simple and easy to apply in terms of electrical protection to prevent LV arc faults;
There is no applicable « test » to verify the insulation when the cable is placed in service: electrical withstand tests will not detect an insulation break when the local area is dry;
Different « prevention » solutions : vented covers, tethered covers, sealing of conduits, use of ruggedized cables.
New idea:
Through the injection of compressed air into the cable core, check the mechanical integrity of the insulation in low-voltage cables
Frankfurt (Germany), 6-9 June 2011
Lavallée – Canada – Session 3 – Paper 03734
Principle of the method
« VIC» insulation fault detector
Universal air tight end connector
Instrument
loop
Frankfurt (Germany), 6-9 June 2011
Lavallée – Canada – Session 3 – Paper 03735
Laboratory tests – type of validation Capacity of the method to identify small breaks in the insulation, in a
reliable and repetitive manner Effects of air and cable temperatures ( - 20 to + 40 deg C) Effects of injected air humidity, especially into a frozen cable Deformation of the insulation layer under the injected air pressure
Laboratory tests – calibrated faults
*Cables used at 750 V or less, with extruded insulation up to 1 kV, and an compact, compressed or normal conductor.
LV cables*
(3/0, 750 kcmil)
Fault
No fault
Peak 0.5 mm hole
1 mm hole
1.5 mm hole
2 mm hole
6-12 mm cut
Total - type of fault 57 51 21 68 15 20 37
Total - tests 269
Frankfurt (Germany), 6-9 June 2011
Lavallée – Canada – Session 3 – Paper 0373
Diagnostic criterion Diagnostic duration
Frankfurt (Germany), 6-9 June 2011
Lavallée – Canada – Session 3 – Paper 0373
Performance results Fault detection capacity: hole 1.0 mm and less on cables up to
200 m in length Duration of diagnosis: from one to a few minutes; mainly depends
on cable size and length Environmental factors: method virtually unaffected by the
temperature and by the humidity level of the injected air Dielectric properties of the insulation: not affected by the pressure
of the injected air (~75 psi =~517 kPa) Automation:
entirely automated tests, with only one displayed result: airtight or leak.
no data to input (ex. cable size or length). test duration optimized for each individual cable
Frankfurt (Germany), 6-9 June 2011
Lavallée – Canada – Session 3 – Paper 0373
LV Cable Field Testing at Hydro-Quebec Objectives
To validate the performance of a new technique in real conditions
To collect and analyze data on LV cable defects during installation
Instrument installation
Frankfurt (Germany), 6-9 June 2011
Lavallée – Canada – Session 3 – Paper 0373
Summary of field tests
Example of detected insulation puncture
0
10
20
30
40
50
60
70
80
0 10 20 30 40 50 60
Temps (s)
Pre
ssio
n (p
si)
cap1 (psi)
cap2 (psi)
Number of cables
tested
Average duration
(including preparation)
Number of
« leak » detected
Remarks
45 20 min 4(~9%)
3 leaks on new cables 1 leak on existing cable after civil works (connectors removed)
Frankfurt (Germany), 6-9 June 2011
Main conclusions of field tests The new instrument easily detect LV cable insulation defects
through the insulation Electrical tests (continuous current withstand test) of the
same cable did not reveal the defect To our knowledge, the new instrument is only technique
available to verify the insulation of LV cable in a dry duct after installation
There are more defects than faults… but we didn’t knew about the number before we tested with the new technique
Lavallée – Canada – Session 3 – Paper 0373
Frankfurt (Germany), 6-9 June 2011
Future development Industrial instrument is under development for implementation
on Hydro-Quebec’s underground distribution system
The new instrument will be use as a « Quality Assurance » tool for newly installed low-voltage cables
The main value of this technology for Hydro-Québec is: Economical : Less faults, no need for a ruggedized cable
Strategical : Thought the explosions caused by arcing fault are not frequent, the consequences can be important in terms of installation and public safety
Hydro-Quebec and DOW Chemical Company are associated to investigate the potential of this method for use in utilities and industries
Lavallée – Canada – Session 3 – Paper 0373
Frankfurt (Germany), 6-9 June 2011