Frankfurt (Germany), 6-9 June 2011 Speaker Jean LAVALLÉE Authors Janislaw TARNOWSKI, Jacques CÔTÉ, André GAUDREAU, Pierre GINGRAS, Mircea IORDANESCU

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


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




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



Principle of the method

« VIC» insulation fault detector

Universal air tight end connector

Instrument

loop



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



Diagnostic criterion Diagnostic duration



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



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



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)


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



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



Documents

Frankfurt (Germany), 6-9 June 2011 Speaker Jean LAVALLÉE Authors Janislaw TARNOWSKI, Jacques CÔTÉ, André GAUDREAU, Pierre GINGRAS, Mircea IORDANESCU