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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.
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  • 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.
Reply
  • 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.
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