Overheating Power Cables

if the studds bolt connected to generator are loose of the particular winding the cable can be over heated or any imbalance current in particular phase can result in such problem

that's not due to the vertical or horizontal position of the cables. first of all whether all the thimbles are properly crimped and whether all the nuts and bolts fixing the thimbles to the breaker are tightened properly. then check whether the load of all the phases is equally distributed. on of the probable reason for the cable getting overheated can be exessive load on that particular phase.

There is one more thing to check besides the connections..

If the conductors (A-B-C) do not pass through the same opening, i.e. there is ferrous metal between any of the three phases this will cause eddy currents to build, which in turn will cause excessive heating. All three phases must pass through same hole, or if glands must be used the metal must be non-ferrous (non-magnetic).. We normally use aluminum to solve this problem..

hi

yes, you are right, the three power cables ''A-B-C'' are passing thru metal glands and thru ferrous metal plate. they are not passing thru the same opening.

also i have question maybe you can help me: why the middle cable 'B' getting overheat more than the others?

We have encountered this many times in transformer and generator applications. The way we resolved this problem in the past with cables already glanded was to take a jig saw very carefully and cut the plate around the glands and then have an aluminium plate manufactured in a split fashion to allow it be sandwiched back around the glands thus not requiring us to regland.. The ferrous glands will not be a problem, and the reason B phase is getting hotter is more than likely due to it`s physical location between A and C phase, which is normal in switchgear. When you put eddy currents on top of that then you are just adding fuel to the fire.

hi mr ekiechle

sorry for disturbing you, the other side ''generator side'' has no problem and it is also has cables going thru ferrous metal glands thru ferrous metal plate, but the different from the panel side that the thickness of generator plate is 2mm while the thickness of panel plate is 7mm.

could that makes any difference?

thanks for your help

Are you using a magnet to check the plate? If it is non-magnetic it is ok.. As far as eddy currents go yes the thickness of the metal could matter, but I`m not really sure.

In general it is not good practice to have cables running through metal plates individually, and the problems are heating. If it were me I would change out both plates and be done with it.. The more load you have on the machine the worst the problem will become..

EX: A situation I encountered once before was during load testing of a 6 megawatt diesel gen set we connected our load bank to a 480V 4000Amp main breaker in switchgear. The cables were routed A & B phase went through one side of the door, and C phase went through the door beside with a 3 inch metal piece for the door latches in between. When we started loading the machine the magnetic fields were so strong the switchgear started to rattle and the 3 inch metal started heating up rapidly. We rerouted the cables where they all went through the same opening thus resolving the problem. If the 3 inch metal was aluminum we would not have had this problem. This is obviously an extreme example of how ferrous plates will cause heating, but is a fact..

hi

i will do with your advice mr ekiechle and change the plates on both sides of both generators. maybe it takes two weeks to do this because i am not in location right now, so it will be grateful if you give me your email address so i can inform you with results after i finish. thank you very much for your help and thanks for every one helped me on this.

i realy appreciate it for you gentle men and i will do my best to help any one of you.

hi

sorry, i have another question: if i change the plate with non ferrous metal such aluminum and use the same glands ''ferrous metal glands'' will this solve the problem or i should also change the glands with non ferrous ones?

thanks

Hi to all, this is my first thread to this forum.

Actually this will also not solve the problem. What i think, one reason can be the laying of cable if there is so much stress to the cable like at bending whether it is sharp bend then heating will be there.

Another reason is that if the Lug is not properly crimped or Lug internal dia is much bigger than the cable dia, then there remains an air gap between Lug and Cable core, this could cause heating.

The third reason is that the bolt used is not properly tightened. make sure that grade of the bolt at both side Alternator & Breaker Fish Plates side should be of High Tensile strenth grade.

And in general practice you will never find the same current flowing through each phase. one phase will always be having higher current than others. this might be due to material construction of Alternator winding or cable material or again you can say while winding the machine at bends a stress can cause this.

hi

what i want to inform you that the middle power cable is over heating at both generators and they are tighten and grimped properly.

ok one more comment..

Another reason B phase would be getting hotter is as the eddy currents circulate off of A and C phases, B phase is getting more due to it`s location. Change the plate and let me know if this fixes the problem of which I`m pretty sure it will...

A quick test you can do if you have access to the ferrous plate is to take a heat gun or IR camera and take a heat measurement of the plate and cables. This will require you to load the generator with as much load as you have available and take snapshots in ten to twenty minute intervals.. If there are heating problems due to the ferrous plate you will see them with whatever temp measuring device you have available..

CHECK THE STUD BOLT IS TIGHTLY FIXED OR NOT.

cable sizing to be done properly to take care of overloading factor also.the phase to phase distance to be maintained at the termination,cable sizing to take care of derating fators mentioned by IEC/b.S

jana MOTTMAC

Have you measured the current in each phase? If you have the same current, and that the electrical connections are correctly tighten, you have the same power dissipation in the cables. Eddy currents are possible but you would see an increase in the gland plate temperature if it were the case.

You didn't give us any parameters to work with. What are the temperatures of the conductors? What are the currents and the cable cross section?

It is also possible that the middle conductor becomes warmer because it is not cooled as well as the two exterior conductors. The losses in a cable are usually very small. The temperature rises simply because the insulation layer is also a thermal insulator. So is the air. This might not be a problem after all. Just take some real measurements and we will be able to really help you.

Are the cables armoured? If so, is the armour metallic? If so, here is another thing for you to look for.

When the metal armour on a single conductor cable, that carries a large current (usually anything over 200 amps is high enough to be an issue) is grounded at BOTH ENDS of the run, a circulating sheath current can and often is generated in the sheath. The current will flow in the sheath, through the ground to the other end and then through the sheath again.

If your B phase has its armour grounded at more then one point, this could be your trouble. The Canadian electrical code has a rule just for this issue, that rule is 4-008.

The circulating current can be rid of by ensuring that your metallic armour is bonded to ground at only the supply end.

This effect can and will happen with all types of metallic armour. Though is worse with steel versus aluminum.

Rick...

1. Check for the conductor size of the cable with reference to the current handled.
2. Deaerating facotor based on heat decipation possiblities.
3. Three phase cables are to be arraged in triangular (instead laying the conductors paralell to each other) fashion (trofoil) to avoid heating of cable due to capacitance effect which will incidently increase loading capacity of the cable.

R.Thiyagarajan.

Hello Guest,

I hope you will register and enjoy full benefits of the forum.

Can you provide additional info,

a) What is the cable size and how many runs per phase?

b) What is the total peak current on each phase?

c) Is your panel where the Breaker is mounted completely sealed, if yes, is the panel (body) temperature above ambient temperature?

d) Can you attach a photo of the breaker and breaker panel showing the cable terminations?

In case you have a Temp gun check temperature at the lug (thimble) on the breaker and continue recording it along the length of the cable at 100 mm intervals.

You have enough info already to work on, including the eddy current issue with ferrous gland plates.

A photo will be of great help.

Cheers.

To all the generous contributors.

This guest does not even bother answering our questions. He is not worth our time. Forget about his problem. It is probably just a mistake on his part because he doesn't know what he is looking at.

I don't mind helping people when they help themself. If he doesn't supply proper info on his problem, he is sending us on a wild goose chase.

He probably forgot that he even posted this question. He went fishing for a quick answer and we all bit...

Perhaps true... but may I offer that just the discussion that has transpired has helped raise the knowledge level of all who either commented or read the discourse. A win win for us and if the OP never saw any of it, so what.

The various skill sets found on CR4 are what make it such a wonderful resource. Sometimes, I look at the "guest" who drops a question and leaves as nothing more then a source for a good discussion.

hi

sorry i was away,

i had mention that the cables are sized for the loads and properly crimped and the lugs are tighten, it is drilling rig so most of the loads are induction 3phase motors so forget about unballance currents. the load current is about 450amps per phase which i just received about 30minutes ago. and i had mention that i am not in location right now,i am away from the rig about 1200KM.

Hello

I have answered your Post/comments,

Generally best to use the Cable Maker of your particular cable, but try:

http://relemaccables.com/

If you are still needing help, reply with

Kind Regards....