120 likes | 255 Views
Verification of LV Underground Cable Insulation by Air Injection. Speaker Jean LAVALLÉE Authors Janislaw TARNOWSKI, Jacques CÔTÉ, André GAUDREAU, Pierre GINGRAS, Mircea IORDANESCU Hydro-Québec. Lavallée – Canada – Session 3 – Paper 0373. Problem assessment
E N D
Verification of LV Underground Cable Insulation by Air Injection • Speaker Jean LAVALLÉE • Authors Janislaw TARNOWSKI, Jacques CÔTÉ, André GAUDREAU, Pierre GINGRAS, Mircea IORDANESCU Hydro-Québec Lavallée – Canada – Session 3 – Paper 0373
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
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 Lavallée – Canada – Session 3 – Paper 0373
Principle of the method • Instrument loop « VIC» insulation fault detector Universal air tight end connector Lavallée – Canada – Session 3 – Paper 0373 4
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. Lavallée – Canada – Session 3 – Paper 0373 5
Diagnostic criterion • Diagnostic duration 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: airtightor leak. • no data to input (ex. cable size or length). • test duration optimized for each individual cable 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 Lavallée – Canada – Session 3 – Paper 0373
Summary of field tests • Example of detected insulation puncture Lavallée – Canada – Session 3 – Paper 0373
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
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