Rules and Guidelines
Want to participate in the discussions? Please read our Community Rules and Guidelines. Need some help? Visit Support and Answers.

  • State Not Answered
  • Locked Locked
  • Replies 28 replies
  • Subscribers 32 subscribers
  • Views 4371 views
  • Users 0 members are here
Options
You may also be interested in
This discussion is locked.
You cannot post a reply to this discussion. If you have a question start a new discussion

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.
Parents
  • Former Community Member
    0 Former Community Member
    How are the cables laid up on the containment ?


    Looking at the currents measured, there appears to gross variations in current share - suggest that all the cores of one phase run together, and so on - add to that badly fitted glands and inadequate earthing of those glands to a common gland plate and you could reasonably expect some pretty big circulating armour currents and those currents being particularly problematic at points of high resistance (such as between the gland and the armour)


    I may have missed it but the cable runs appear to be reasonably long  - so I suspect you are now at the point of deciding to accept the circulating currents (maybe not feasible considering the damage you are experiencing) or accepting that you need to change to insulating glands (or gland plate) at the load end, and accepting the potential risk of a standing voltage on the system with the attendant shock risk


    I suspect it was potentially badly designed, probably badly installed and has taken a few years for the heating effect to cause real problems - earthing the glands may help, but I would also check the gland is correct for the cable and is making sound contact with the armour. It's also possible that the gland plates are also getting pretty hot due to the circulating current flow and that is conducting heat into the gland, then into the armour and that local heating effect is rapidly deteriorating the cable bedding and insulation.


    You could also consider exposing the armour along the runs and adding a connection to the armour to effectively cross bond to adjacent armours (Raychem and similar sell heat shrink kits for this activity) - typically this would be done twice along the length of run


    Good luck


    OMS
Reply
  • Former Community Member
    0 Former Community Member
    How are the cables laid up on the containment ?


    Looking at the currents measured, there appears to gross variations in current share - suggest that all the cores of one phase run together, and so on - add to that badly fitted glands and inadequate earthing of those glands to a common gland plate and you could reasonably expect some pretty big circulating armour currents and those currents being particularly problematic at points of high resistance (such as between the gland and the armour)


    I may have missed it but the cable runs appear to be reasonably long  - so I suspect you are now at the point of deciding to accept the circulating currents (maybe not feasible considering the damage you are experiencing) or accepting that you need to change to insulating glands (or gland plate) at the load end, and accepting the potential risk of a standing voltage on the system with the attendant shock risk


    I suspect it was potentially badly designed, probably badly installed and has taken a few years for the heating effect to cause real problems - earthing the glands may help, but I would also check the gland is correct for the cable and is making sound contact with the armour. It's also possible that the gland plates are also getting pretty hot due to the circulating current flow and that is conducting heat into the gland, then into the armour and that local heating effect is rapidly deteriorating the cable bedding and insulation.


    You could also consider exposing the armour along the runs and adding a connection to the armour to effectively cross bond to adjacent armours (Raychem and similar sell heat shrink kits for this activity) - typically this would be done twice along the length of run


    Good luck


    OMS
Children
No Data

Join us to get the best from IET EngX.

Joining EngX lets you personalise your experience so you stay up to date on the topics that interest you, plus you’ll be able to make connections who are looking to collaborate, exchange ideas and more.

Join us Not now

Community Rules & Guidelines