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...​