quality assurance 3

[144x]

I want to visit a newly built cable company which makes
cables up to 132 KV .what are the most important things
that I should check in that factory in order to be sure that they make a good cable?

 

[busbar]

Dielectric purity and process temperature control seem like major factors in synthetic cable production. Look for evidence of that on your tour. You might also ask to see some in-house destructive testing of their products.

This seems corny, but look over their web site and technical publications and base some queries on elaboration of their printed comments.

Their expenditure on your lodging, meals and beverages can correlate to their desire for your future business.

 

[ausphil]

Check their quality system. Look specifically for instructions on what to do when a measurement or process is not correct (ie material thicknesses, conductor diameters, insulation grade [as mentioned by busbar]). All manufacturers have problems with processes at some stage (not just cables, but tranformers, switchgear etc), I judge them on how they rectify the problem at hand, and what steps they put in place to stop the same problem from happening again.

Have a walk through the factory and don't be afraid to ask questions of the machine operators, they usually are quite friendly, and you can gauge their knowledge of the instructions they are given to make the cable. Good operators don't answer questions with "oh, you know, about 3mm" or "what's that?", they will pull out the worksheet for that cable, and look it up for you. New machines may mean new operators who have been trained but have only limited experience on the machine they are using - unless they have been stolen at great cost from a competitor!

Have a look in their test area. Ask to see a drum being tested. Ask for their calibration certificates for the test equipment, even take PD calibrator and known resistance/capacitance standard if you are not sure of their calibrations. Also ensure you get to see a copy of a type test report for the cable you are specifying - don't just assume it has been done.

An example of a problem that the manufacturer identified and rectified was onion-skinning on the outer HDPE sheath of the cable. We ordered 18 drums of 33kV 3core cable, and this problem happened on 3 drums. The problem was found to be linked to the extruding temperature of the HDPE not being correct. The electrical tests verified the correct operation of the insulation, etc, and the spark test verified that the sheath was of the correct thickness and no holes were evident. But the company was not happy that the cables would leave the factory with some visual defect, and stripped the HDPE sheath and nylon barrier off all affected drums, re-laidup the conductors and re-covered the cable. That pride in workmanship and goods carrying the company name is good to see. They made sure of the extruding temperature by amending their operating instructions.

But, like any good engineer, don't base your decision on the salesman's pitch!

 

[144x]

thank you ausphil,
do you remember that I asked you a question about graphite coating ?can you please give a little bit more explanation
about the second paragraph of your answer?
thanks.

 

[144x]

oh,sorry ,you've already done it.
thanks for your help

 

[benlanz]

I know this comment comes late for the origin question, but perhaps it with help others.

Ask to witness the partial discharge test of your cable. Some factories are overlooking defects. How do I know? We are finding them in field PD tests. It is a low probability event, but it is happening enough for defects to show up in our sample of 10,000 km of cable since 1997.

Cable manufactures are not making much profit these days. Competition is stiff with the global economy. They are cutting back on qualified technicians and making due with antiquated PD test equipment.

In some cases we have witnessed factory tests where real PD was considered noise and they simply moved the 5pC base line and declared the cable clean!

One of our customers went to the factory and witnessed that the cable failed the PD test! A new cable was extruded and this one passed the test.

-Cheers