Cable Pulling 2

[pithpal]

Hi Everybody,

I was working on pulling 600 MCM teck90 armoured cable from basement of a building to 10 th floor through electrical rooms on each floor. The current is 2000 Amp, that means 3 cables/ phase. As I wantd some specs, I spoke to NEXANS and ALCAN.
The ALCAN gus told me that you should go for a Alcan cable and that also three conductor cable, as this will lead to less voltage drop and you can run three cables each three conductor side by side as one has to be very care ful of the phase imbalance which arises due to different lengths of cable. Here is arrangement below:
All phase in one section: Three conductor cable:
O 0 O O
OO OO OO OO

Then I spoke to NEXANS guy, ofcourse both were application engineers not sales guys, he told me as I have three conductors per phase then I should go for single conductor cable and each in a traingular configuration to have less voltage and then he said if you have even no of conductors per phase then you should go for a rectilinear configuration. All factors are attributed due to voltage drop. A B C phase in one section adn neutral in middle.
N N N
O O O
O O O O O O O O O

Now when I explained this story to my big boss, he said we will go in a different way, and that will be like below but in outward direction horizontally.
A B C N
O O O O
O O O O
O O O O

so this is All phase in parallel outward way.

Now here is my question, which arrangement is good and why?

Please advise any free software available where I can test this configuration.

Why cable pulling is an issue and as an engineer how to figure out that I should not leave it to contractor and come out my self with the exact bending configurations.

I appreciate you time always.
Regards,

 

[waross]

Hi pithpal
The manufacturuer was correct. Any magnetic material encircling a conductor will be subject to heating from eddy currents and hysterisis. With the current levels that you are considering, you can expect serious overheating to the point of early failure if you ignore this rule. The heat will be generated in the magnetic material.

If yes then if we ground the armour of teck cable both at source as well load, will this problem disappear?

Now you will have added sheath current heating which will be present for the entire length of the cable. The code will require that you derate the cable.
Please take the time to reread my post. If I have not explained myself well, ask and I'll try to explain.
Be aware that if the floor penetrations are individual holes then it is important that the holes not be encircled by reinforcing bars.

Option one.
Single conductor cables. Aluminum plate at feed end, micarta or similar plate at load end. All non-ferrous connectors and locknuts.
Option two.
Terminate the cable in the steel switchgear at both ends. Use a Sawzall to make cuts in the steel from "A: to "B" to "C" to Neutral. Do this again for the second group of 4 cables, at both ends. At the load end, insulate the concentric neutral conductors and the armour with varnished cambric tape.
Option two is much cheaper in both material costs and labour.
We did an installation years ago in Western Canada involving a 500 KVA Standby generator at 208/120 Volts, up to 1388 Amps. The electrical inspector liked it so well that he added a short comment praising the neatness of the installation next to his signature on the permit.
The last similar installation I was involved with was feeding a 1000 KVA transformer bank at 480 volts. Phase current up to about 1200 amps. It has been working fine and staying cool for years.
On the other hand, down south here I saw a 400 amp switch destroyed by heat with a load that peaked at about 200 Amps.
The manager told me that this was the third time the switch had been destroyed. There were two steel conduits rising verically about 7 feet to weather-heads. One pipe held "A" phase and one half of "B" phase. The other pipe held the other half of "B" phase, "C" phase and a neutral. The pipes were to hot to hold (unless your pain threshold is higher than mine). The conduits were heating the cables which were conducting the heat to the switch terminals. The high temperature was causing the copper hardware to oxidize badly. This was probably adding to the heat. The fiber back plate that supports the switch hardware was charred by the heat of the mounting bolts. I have seen the paint burnt off of switchgear by improper cable entry.
The procedures are found in the notes in the back of the Canadian Electrical Code. The hacksaw cut is one of the remedies described.
You can derate the cable and live with the sheath currents and pay for the losses on the power bill every month.
You CANNOT get away with ignoring magnetic induction. Past about 250 or 300 amps per cable you will feel the switchgear getting uncomfortably warm. Probably by 50% load the paint will be smoking. In the ensuing investigation your code violations will be identified and you won't have a leg to stand on. Settle out of court.

 

[pithpal]

Thanks Waross, Could you please answer my second question also in regard to capactior bank switching, and thanks again for devoting your precious time for answers.

Regards,

 

[waross]

Hello pithpal
Re the capacitors;
I think you must look inside and fine out exactly what's in there. You may already know if there is a power factor controller and contactors inside.
Other than that, I was hoping that davidbeach would handle this question. His code books and his knowlege of current pratices and the availability of hardware is more current than mine. I've been on holiday for a long time, and there have been some changes to the codes since I left home.
yours

 

[mpparent]

pithpal,

I think you'll have some angry electricians when they find out they'll be running 1000MCM.


Mike

 

[Ares]

Proper solution is to use 2000A rated bus.
3 runs of 600MCM would produce voltage drop over 5% and I do not think any arrangment would provide the ampacity you need.
Check Underground Ampacity calculator @

http://www.mc-group.ca/download.htm

It is for U/G but shows cable configurations - there is no diference for horizontal/vertical runs as far as EM although the rating will be diferent.