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  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  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 Peak0.5 mm hole 1 mm hole 1.5 mm hole 2 mm hole 6-12 mm cut Total - type of fault Total - tests269

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 Number of cables tested Average duration (including preparation) Number of « leak » detected Remarks 4520 min4 (~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