33kV Cable Jointing
33kV Cable Jointing
(OP)
Our plant will be connecting to the local electrical utility via two feeders of 33kV. Each feeder will be rated at 700Amps. The distance between the utility and our plant is 5500 metres. These cables will be installed in a common power corridor. We have selected to use 2*630sqmm single cores per phase. We have estimated that we will need approximately 96 joints. We believe that these joints should be installed in a concrete chamber to allow for the possible failure, testing and quick repair.
Is there a IEEE or IEC specification or good engineering practise that would advise what to do for such a high number of joints?
Is there a IEEE or IEC specification or good engineering practise that would advise what to do for such a high number of joints?






RE: 33kV Cable Jointing
Regards,
William
RE: 33kV Cable Jointing
Regards
Ralph
RE: 33kV Cable Jointing
RE: 33kV Cable Jointing
RE: 33kV Cable Jointing
RE: 33kV Cable Jointing
Is there any specific reason why you are doing this underground? You could just as easily do this run in overhead wiring using single core ACSR cable. Just make sure to fan out the wire strands and clean them with #220 silicon carbide abrasive paper. Also make sure that you use an overhead antilightning wire as well.
You can also get twinned ACSR cable that consists of a twisted pair of say two 4/0 or 266 KCM conductors. This allows you to use conductors that have a single layer of aluminum strands over the steel core which simplifies full current taps as only the outside of the cable needs to be cleaned of aluminum oxide.
RE: 33kV Cable Jointing
-Cheers!
RE: 33kV Cable Jointing
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If we learn from our mistakes,
I'm getting a great education!
RE: 33kV Cable Jointing
From the standpoint that welding is the best way to make an electrical connection aluminum is the superior material over copper. It takes something like 6 times as much heat to weld copper. For what copper costs you can usually put in twice as much aluminum cross section and have the circuit run cooler.
In fact, for a high current circuit in a factory such as DC for electroplating, I would very seriously consider using aluminum wire with welded lugs. An alternative would be tin plated aluminum busway. I have had 100% success with every instance of supplying power to an industrial machine using aluminum SER cable using box lugs.
If it is a reallycorrosive environment, such as salt mines, automotive wiring, and so forth, then using unplated copper lugs and wire does work as long as you clean out the copper oxides.
RE: 33kV Cable Jointing
I am also the vice chair of IEEE 400 which is the field guide to cable testing. This puts me a good position to view the different types of tests available, assess their benefits and limitations and recommend technology for different applications. If I happen to know the most effective way of thoroughly testing shielded power cable for workmanship defects, isn't that information worth sharing? I welcome anyone to critique the technical merit of my statements.
For clarity I have added my signature to the bottom of each post.
-cheers
Benjamin Lanz
Sr. Application Engineer
IMCORP
RE: 33kV Cable Jointing
If you loose a circuit you can operate at half power while the other is being repaired.
RE: 33kV Cable Jointing
RE: 33kV Cable Jointing
In many locatoions wiremen won't work in such a situation. You could rebuild a splice but if you have to put in sheaves etc. to set up for pulling a new cable segiment in that too much. Splices can set around with potential faults for a long time before they fail. A movement of the cabel can be the trigger. IF inspectiong an energized splice means touching and moving it around, update your insurance.
If you need a good reason to seperate systems read up on the Fire at Belliagos in Las Vegas. http://w
There has been lots written in trade magazines on this particular fire. The root cause is supposedly "A design flaw" . They only lost a million a day, maby jimScott can afford a few days loss.
RE: 33kV Cable Jointing
Think through thermal expansion and contraction. Direct burial in thermal sand is a good design to help achieve the best ampacity. 5500m of cable will expand a lot, how will you accommodate the expansion?
Concrete vaults will aid in maintenance and repair if you assume that the splices are the weak point. This may not be the case. Also, consider the ampacity effects of cable in air in a sealed or ventilated vault versus burial in thermal sand. Splices are designed for direct burial.
If you bond the neutrals, watch out for circulating current on the concentrics. Run the calculations and use cross bonding, especially at 35kV and high currents! I was involved in 100 miles of 35kV underground and we had to go back and cross bond the cables to eliminate the circulating currents to get the thermal rating we needed.
RE: 33kV Cable Jointing
I have not made the decision on whether to use concrete chambers which may have phase segregration and each chamber would only cover one circuit.
Testing of the joints and fault finding is clearly an issue irrespective of the choice.
If you can help me here with reference to specifications i would be most appreciated.
RE: 33kV Cable Jointing
Thanks for your reply. Not all members fully explore Eng-Tips to find the additional profile information, so putting your details in your signature is a nice touch. I enjoy reading your posts - they are informative and helpful, and obviously backed up by a deep understanding. The intent wasn't to imply you were doing anything underhand.
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If we learn from our mistakes,
I'm getting a great education!
RE: 33kV Cable Jointing
However, using 69 KV cable on 34.5 KV does not help any since nobody makes a 34.5x69 KV primary substation transformer.
At 1 time they tried doing 34.5 KV overhead lines without an overhead antilightning wire and used lightning arrestors on the top hot wire once every 2 poles. These have had quite a few lightning arrestor just simply explode on these lines that do not have an overhead ground wire. They are now back to using overhead antilightning wires on replacement and new 34.5 KV lines.