I would like to know the likely megger (IR) value for 132 KV Copper Power cable, XLPE and Aluminum sheath type, approximately 10 years in service both 630 sq mm and 800 sq mm, single core and of approximate length 300 metres

 

If you are sure of its age, then please answer the following:

o What is the installation? In metallic or non-metallic conduit; in air or buried, nitrogen-cooled or oil-immersed?

Regards, Phil Corso

 

Thanks for the response Phil,

It is buried under ground from a cable sealing out door gantry (with oil) to the Gas Insulated Substation- line isolator as feeder input.

Regards,
Parthipan

 

PARTHIPAN... Unfortunately, high-IR values are not an indication of high-dielectric strength, but, low-IR probably indicates low dielectric strength.

If you are unable to obtain help from the cable manufacturer, then I suggest contacting other manufacturers.

Finally, if all you require is a "Figure of Merit", I suggest that readings be taken, first with a 500V Megger, then with a 3kV Megger.

The insulation-resistance value indicating adequacy is about 0.30 to 0.35 MegOhm-km normal ambient temperature!

Regards, Phil Corso

 

Parthipan... the IR range, corrected for 300 mt length, is 40-46 Meg Ohms.

Phil Corso

 

It is very kind of you. Today the cable was meggered and the readings in 5kv megger was:

for 1 minute 90 M. OHMS
for 10 minutes 120 M.OHMS.

The cable is yet to charged and awaiting the periodical tests on other equipment.

Parthipan

 

Parthipan... thank you for keeping me informed of your findings... a common courtesy lacking in so many of the Forum's posters!

I have a favor to ask: the difference between your measurement and my calculation is probably due to an error in my assumption regarding the cable's D/d ratio, where "D" equals diameter over insulation, and "d" equals diameter over conductor, excluding sheath thickness. Can you send me the actual value provided in the spec?

Phil