type tests of cables 3

[144x]

if you are buying a single core power cable and manufacturer provides you the type test of a three core power cable with another cross section and same voltage level would it be acceptable?
thanx

 

[gabi49]

144x:
Can I take the chance of your question and ask what are the type tests of cables?

Gabi

 

[alehman]

I would not accept type testing alone for power cables. I think nearly all reputable manufacturers factory test all cable before shipment.

 

[advidana]

If your specification require testing, then don't accept the cables. Make them perform the test specified.
advidana

 

[ausphil]

2 different cables, I wouldn't let the manufacturer off that easy. Different stresses, different construction process, need to verify the cable properties with seperate type tests. Yes, electrically the cores may be off the same manufacturing line, but once they get bedded together in a single or triple core serving, it is a different cable.

How do they propose that the bending radius test with PD before and after would be the same? Surely the 3 core cable has a different bending radius, and hence different mechanical forces when bent (just to name one test).

If your spec asked for type test reports on the cable, get them to verify it.

 

[sdlloyd]

144x,

As ausphil points out, once the cable cores are laid up into a three core construction you have a different cable. The points he makes on cable bending are also valid. Another area that will be different will be radial and longitudinal water blocking on XLPE cables over the core.

If the cable conductor sizes are different then the stress on the insulation and connected joints/terminations will be different.

It is common to accept that if a manufacturer has tested a single core cable of identical construction with conductor sizes above AND below those you require then a test at the identical size is unnecessary. It is worth mentioning that some utilities in the Middle East and South America still require individual cable size type tests along with the accessory.

In the replies given by others above there seems to be some confusion over type testing and routine testing. Type testing is a more onerous set of mechanical and electrical tests on cables and accessories which tests the cable design and construction. Type testing in some countries will require that these tests are ultimately destructive and perform withstand tests to failure.

Routine tests however are tests of manufacturing quality either during manufacturing or prior to dispatch. These tests will generally only find gross defects, small latent defects are likely to escape detection. It is necessary therefore that you do not buy cables from manufacturers who take little care over their manufacturing quality procedures or choice of materials used in their products.

Hope this helps.

http://www.cableconsulting.net

 

[144x]

thanx for your response.as you mentioned some defects will escape the routine tests but these are sometimes big defects.I remember a case that we bought several kilometers of power cable from a reputable company.all the routine test reports were ok and cables were dispatched to the site .but after starting of insatallation it appeared that most of the cables on different drums have deep scratches on the outer sheath .it caused stopping of the work and traffic of the city and a total loss to the buyer and manufacturer.I always wonder could these problems be discovered befor even ordering of the cables and what factors in the manufacturing process should be inspected both on paper and on the factory to make sure that some new manufacturer is eligible for your big order.I'm sure that refernce list alone is not enough for this purpose .I would appriciate it if you share your experience with us.

 

[aali2208]

Hi 144X,

Yes I also know some brands in my country which clears all tests after manufacturing and after few year the insulation depriciate very rapidly, What I believe is that the type test of the Manufactured good was conducted only on sample Lenght or Equipments, and most of the manufacturer use the best Raw material for prepration of that sample where as in their production line they use the cheapest or the modest quality raw material and ultimatly customer has to face. The best way is to monitor the production if the order is too big like control of raw material can be checked and compare with the type test documentation. I have been part of the team who carry their product for type test & I can tell u lot of design document to be submitted with the product sample for certification and all those documents are the part of certification. The second way is to conduct the routine test at works in your presance and inspect the drums before Despatching, After arrival of material at site, & During Laying of cable as well, Repeat few test after the laying as well, I recommend you to review IEC 60502 for cable testing that will help u a lot.

 

[sdlloyd]

144x,

Cable defects that could "pass" routine test...

Conductor water blocking missing or inadequate
Conductor screening tapes incorrect size or type
Conductors screening material fall-in into conductor
Screening material too thin or missing
Conductor screen not bonded or marginal
Conductor screen hang ups due to precuring
Conductor screen material not smooth
Incorrect antioxident levels
Insulation, Poor cross linking
Insulation microvoids
High levels of cross linking by-products
Flow line defects
Contaminants in insulations, solvents, greases, metalic particles
Extrusion surge causing pulse thickness
Wrong insulation screen material
Insulation screen too thin
Insulation repairs attempted in factory
Poor cleanliness when handling materials
Semiconducting pellets fall into insulating pellet boxes
Semiconducting cushioning tapes not used
Extrusion runs too fast causing internal defects
Return conductors not equalised
Foils not sealed
Metallic sheaths to thin or wrong alloy
Corrugations incorrect
Water under metallic sheath caused during oversheathing
Bedding tapes rucked, not overlapped, not compounded
Wrong oversheath type used
Wrong oversheath thickness
Impurities in the oversheath causing localised thinning
Fork lift/crane/mechanical handling damage.
Leaking factory roof or open door during rain onto unprotected insulation.
Lack of adequate semiconducting layer on oversheath
Dispatch reel belly undersize
Dispatch reel with nails into cable
Wooden dispatch reel dries out and is unable to support
cable
No reel or sheath termite protection
Pulling eyes insecure, wrong type used
Inadequate reel protection (wooden battons)

This is a list off the top of my head for XLPE which I am sure others could add to, you would have additional sets for paper lapped, oil/fluid filled, gas, MIND, ppl and epr cables. I can't possibly list every defect that could pass routine test, there are too many. Routine test is a blunt instrument.

Specifications are fine but there is no substitute for inspection with eyes wide open. If you walk round a factory before you buy, inspect during manufacture, inspect after manufacture, witness testing and keep your own records and measurements then you are in a better position to get what you want and to identify what you don't.

The trouble is that few engineers have the time or staff to perform these inspections properly and even fewer have engineers that know what to look for. Being given paperwork is not the sole answer, it requires rigorous checks to be performed.

http://www.cableconsulting.net