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LV 400V AC armoured cable glands are geeting overheat(Temp. measured more than 60 deg C)

Rohit Sharma
Hello Electrical Team.

I would like to discuss an issue being facing in our Power plant(90MW). Our plant generation voltage is 11KV & Plant auxiliary & MCC voltage is 400V AC 50Hz. We have two sections of Power plant PP1 & PP2. In PP2 we are facing issue in LV MCC Panels. 

In LV system we have two BUS A & B. Both BUS's are getting power from their individual T/F(11KV/400V AC) & from here power is distributed to various MCC panels in plant. 

Booster no. 1 MCC have two LV breakers(Q1 & Q2) which are getting power from BUS A & B.

During last week we were found that Q1 breaker incoming cable insulation was melted around the cable gland area & checked the other glands also & they are also found overheated with abnormal temperature. then we took changeover to Q2 breaker but this is also now getting overheat. In main LV distribution panel side also cable glands are getting overheat which are connected to Q1 & Q2 breakers in MCC.

In one phase two cable are laid & connected, size is 400 sq.mm Armoured cable. R phase(L1 & L2), Y Phase(L1 &L2) & B Phase(L1 & L2). The current also not equal in two length of each phase.Pl see the below readings.
Line

Without Armoured

With Armoured

R Phase

L11

195 A

328A

115A

174A

L12

137 A

72A

Y Phase

L21

103A

332A

145A

306A

L22

167A

175A

B Phase

L31

150A

328A

120A

317A

L32

183A

199A


without armoured = Cable outside of MCC before entry in panel.

with armoured = After gland inside the panel. 

Team kindly go through the above said issue & your kind comments will be highly appreciated.
  • 0
    Extra additional loads connected over time perhaps?


    Z.
  • 0
    Hello Team, 

    Extra load does'nt put on the system, same load are running since long back.
  • 0
    Have you confirmed the material of the gland plates and the glands?  The gland plates look like aluminium - are they aluminium or are they steel?  The glands don't look like brass - are they aluminium or are they steel?

    Have you checked with a contact thermometer whether it is the gland getting hot or the cable getting hot?
  • 0
    Well the photo shows a design doing both things wrong, in that there are single phase currents going through a hole each, and there is no attempt to insulate all but one gland from the termination plate. 

    Is the white thing on the left a fan ? If this is part of the original installation it may always have been running a bit too hot. 

    Also how close is the rest of the design - how hot is the cable at a place further from the gland ?
  • 0
    Hello Team,

    The gland plate material is aluminum but gland itself not a brass material, this is sure, gland looks like steel. 

    LV Cables only get hot in length of 3--4 inches from glands after that the cable temperatures are normal. Complete gland plate area also hot. 

    That White color is cooling fan which was recently installed near overheated glands area to keep temperature in normal range. This was not a part of original design. 

    Both the glands plates are very near to each other. 

  • 0
    So the culprits are the steel glands then.


    Z.
  • 0
    Sounds like high losses in a bad choice of magnetic material - you could try with a small test magnet, but if they really are steel, then think about making arrangements to change those glands for something that is not.

    Brass is the normal favourite round here. Steel is only a good idea if the cores are such that the currents in any one gland are more or less cancelling out.


    Also note if you have to take it all apart anyway, that on single phase cores it is better to connect armour at one end only, or at least not to put multiple armours of single core cables each  with different induced voltages accross the ends in parallel with each other, so to add insulating bushes may also be worth considering - but that problem would give cable hot all along, so your first problem looks like the choice of gland metal, and the glands themselves are the hottest thing.


    Mean while, adding the fan is not a bad idea, and it certainly will help things last a bit longer.
  • 0
    Hello. 
    Renewal of the glands is big task as the plant application is very critical & can't be stopped for the gland modification. Really the choice of gland material was not good. 

    For the time being we are thinking about proper gland earthling & also i made one drawing for that. Hope it will resolve the heating impact after proper grounding of glands. 

    Pl have a look on attached file & kindly share your comments. 




  • 0
    I suspect from the photos you posted that the gland plate is ferrous. If this is the case, then changing your earthing arrangements will make no difference. Replacing your gland plate with a brass one may make a significant difference, especially if the old one was steel. 


    Regards,


    Alan.
  • Former Community Member
    0 Former Community Member
    the plant application is very critical & can't be stopped for the gland modification


    No power cuts or outages in your area then?!!!!!


    Regards


    BOD

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