Line to neuteral floating

[ASHEED]

I HAVE Dyn11 650KVA, 4160/415V ,60 HZ . Y STAR POINT EARTHED.

SMALL D.B FEED A CAMP ( LIGTHS, A/C'S, WATER HEATER ....ect)
DISTANCE FROM D.B TO CAMP 1500 MTR.
CABLES :

3 ( 3C X 2 AWG), 5KV CABLE ,3 CABLES EACH CABLE USED FOR (R S T), 5 KV CABLE BUT USED FOR 415V
1C X 95 MM2, USED FOR NEUTERAL

LOAD: 40 - 60 KW

PROBLEM
WHEN CABLES LOAD :

CURRENTS UNBALANCE , NUTERAL CURRENT VARIED 9 -27 A, ACCORDING TO LOAD

BEFORE CONNECTED (N TO G ) AT LOAD & D.B SIDE N-G VOLT 9 -12 V.

L- L VOLTAGE CONSTANT AT LOAD SIDE 415V
L - N VOLTAGE VARIES 208 - 285 V (NOT CONSTANT 240V), CHANGE ACCORDING TO LOAD.
L - N VLOTAGE MOST TIME CONSTANT IN TWO PHASE BUT THE THIRD PHASE L - N CHANGE AND REACH TO 280V AND DOWN TO 240, 250, .... VOLT. AND SOME TIME VOLTAGE TO NEUTERAL FLOATING IN TWO PHASES.

WHY V(L-N) FLOATING WHILE V(L-L) CONSTANT?
HOW TO SOLVE IT?

NOTE: WHEN I CONNECT( G - N )IN D.B & LOAD SIDE NOTHING CHANG BUT THE FLOATING DECREASE.

REGARDS;

ASHEED

 

[Deleted member 9648]

High resistance connection on the neutral somewhere?

 

[johnboy6083]

Is the star point grounded correctly? Are the connections clean and tight?

 

[Engineer54]

So what was the installation method used for this cable run, direct buried, in duct(s) or surface?? What was the Ra value of the TX neutral earth connection?? What's the earthing method at the load end of this cable run?? Do these 5KV cables have SWA protection and do they have a semi conductive layer around the cores?? Were they terminated as 5KV cables ie, ....with correct cable termination kit, or as standard low voltage band cables??

 

[ASHEED]

johnboy6083

Is the star point grounded correctly? Are the connections clean and tight? neuteral point earthed properly and connection good but inside caravans the inernal wiring i don't check it.

Engineer 54 :
So what was the installation method used for this cable run, direct buried, in duct(s) or surface?? What was the Ra value of the TX neutral earth connection?? What's the earthing method at the load end of this cable run?? Do these 5KV cables have SWA protection and do they have a semi conductive layer around the cores?? Were they terminated as 5KV cables ie, ....with correct cable termination kit, or as standard low voltage band cables??

lay down dircet on ground surface
, R (G-E)1= 10 OHM ,
using normal earth pit with three electrod,
ATA (tube Corrugated AL Armour) without semiconductor layer,
used normal termination as L.V 415V becouse the voltage 415V but the cable 5KV
​

 

[ASHEED]

what do you mean.

 

[ASHEED]

neuteral point earthed properly and connection good but i don't check iinternal wiring inside caravans .

 

[ASHEED]

lay down dircet on ground surface
R (G-E)1= 10 OHM ,
using normal earth pit with three electrod + salt + charcoal
ATA (tube Corrugated AL Armour, UL standerd cable) without semiconductor layer, ESP cable
used normal termination as L.V 415V with out any kit, just lugs and glands, becouse the voltage 415V but the cable 5KV

 

[Engineer54]

Never used 5KV cable Asheed, i'm more used to 12-35KV cable and it's terminations. Now most MV cable i know, have semi conductor material coating each core, along with a foil shielding that acts like a drain. No matter what voltage is being used, ie your 415 volt, the semi conductive material (all cables have a semi conductive material over 1500 volts)needs to be cleaned off the cores and any shielding needs to be tied down to earth at the termination points. The termination kits should therefore have been used, even if using for 415 volts, that's how the cable type has been designed to be terminated and jointed!!! So what about the joints in this 1.5KM run of cable, how many are there and what was the method of jointing??? Was the AL armour used as your CPC?? What is your total voltage drop at the load end before and load is applied and after load applied

Is this a temporary installation overseas, like Afghanistan or somewhere similar?? If so, your earth rod enhancement method isn't a problem, using a salt and charcoal mix, it certainly would if it was a permanent installation ...lol!!! When you say 3 rods i take it you mean coupled together?? So what is the total depth of these combined rods??


Sorry about all the questions, but i'm trying to get an overall view of your problem installation...

 

[ASHEED]

Never used 5KV cable Asheed, it standerd cable for oil field ESP pump. i'm more used to 12-35KV cable and it's terminations. Now most MV cable i know, have semi conductor material coating each core,(no semiconductor layer) along with a foil shielding that acts like a drain. No matter what voltage is being used, ie your 415 volt, the semi conductive material (all cables have a semi conductive material over 1500 volts)needs to be cleaned off the cores and any shielding needs to be tied down to earth at the termination points. The termination kits should therefore have been used, even if using for 415 volts, (no need for termination kit while no semiconductor) that's how the cable type has been designed to be terminated and jointed!!! ( by using proper J.B)So what about the joints in this 1.5KM run of cable, how many are there and what was the method of jointing??? (one J.B in each run)Was the AL armour used as your CPC?? What is your total voltage drop at the load end before and load is applied and after load applied (load too small 50 A/phase max no voltage drop) 230 V at far end.

Is this a temporary installation overseas, like Afghanistan or somewhere similar?? (No permenant but to safe the cost of new cable old cable used but cable checked and itis ok )If so, your earth rod enhancement method isn't a problem, using a salt and charcoal mix, it certainly would if it was a permanent installation ...lol!!! When you say 3 rods i take it you mean coupled together?? So what is the total depth of these combined rods?? (1.5m x 1.5m x1.5m , 3 road coupled togther in triangle arrangment by 120 mm2 cable)


Sorry about all the questions, but i'm trying to get an overall view of your problem installation...​

 

[Engineer54]

Asheed,

I've been trying to find a UL listed 5KV 3 core AL armoured cable that hasn't a semi conductive component in it's construction, i haven't been able to find any that meets the description you have given!! Here's couple of the examples i have found, with and without shielding.... Are these anything like the cable you have used in your installation??

http://www.generalcable.com/NR/rdonlyres/DA1C1600-CA0A-4BB3-ACB5-13E66395E7CD/0/Spec_8250.pdf

http://www.generalcable.com/NR/rdonlyres/69A9827D-56AA-418F-8DFC-6EBFAE48951C/0/Spec_8325.pdf


Is this TX supplying any other loads?? Are they having similar problems to your own?? If not, then it's down to your cable installation.... Were they also wired with this same 5KV cable type?? If there is a similar problem then look at that neutral earth point, check that you DO have 10 ohms, ...but i very much doubt it, with just 3 x 1.5mt stakes. (What method did you use to test the Ra value, loop test or 3 point earth tester??) Not unless you have a very good ground soil type like a marshy loam... Oh and having rods surrounded in salt, isn't a good idea as a permanent installation, not if you want the rods to last any time at all.... You would have been much better off, deep driving 3 X rods in 2 locations At TXs usually at diagonal opposed corners and linked.

You need to go through and test what you have installed. Check the supply feed source for any high resistance connections, what is the source method, Switch fuse or Breaker?? Check the same at the load end, if there switch fuses and not new check the switch blade contacts.... Now what do you mean by ''JB box'' ?? Have these been terminated in the same way as at the TX and the DB at the load end?? Now if everything checks out, surprise surprise it must be those 5KV cables with no termination kits, at the MDB/DB's/joints....

Any chance of some photo's of the supply TX end, and load end of this cable run a shot of that ''JB' box would be nice too...