Cable Fault Location Test Devices

[HD ELEKTRONİK]

We have ancient CMC (Cable Meas.Car).
We share practicals here.

(Sorry , My English is very very bad).

 

[blueroomelectronics]

Is it a question? A statement?

 

[HD ELEKTRONİK]

Is it a question? A statement?

No , question not.
All methods.

 

[dknguyen]

I think he wants to share practical methods of finding faults in cables since he has a bunch of really old ones.

 

[JimB]

(Sorry , My English is very very bad).

We are also sorry, but this is the only part of your post which we understand.

Your original post does not make any sense in English.

JimB

 

[HD ELEKTRONİK]

1)_ Three Phase check Insulation Test with MEGGER (Min.500V).

**broken link removed**

Edit:X Width.

 

[RODALCO]

Need to know if HV ( 11kV or more )or LV cables. ( 230 / 400 V ).

From your schema it looks that the cables have a screen.

Firstly isolate and check that cable is safe to work on.
Disconnect both ends of cable including screens.

Megger between core and screen ( should be infinite or > 20 M ohms for LV cable ) Internal cable fault.

Megger between screen and earth to determine if screens are damaged ( external digging ) Should normally read infinite or > 20 M ohms . External cable fault.

In brief:

For internal cable faults a thumper is used. discharging high voltage capacitors repetetively and listen for noise where the cable arcs over.
It is good practise to mark the route of the cable prior to listening for the fault.
For externla faults a Pool of Potential is used and trace the fault to earth and locate with a µA meter.

Merry Christmas, Rodalco



I

 

[HD ELEKTRONİK]

Need to know if HV ( 11kV or more )or LV cables. ( 230 / 400 V ).
...
...
I

Yes...
But this examle HV Cable.
Not LV Cable.

**broken link removed**

 

[RODALCO]

For HV cable megger readings should be high Mega ohms e.g. 300 M.ohms +.

Screens should give clear readings. e.g 33 kV cable screen should be able to hold 5 kV DC from megger. 100 M.ohms or more.

For locate: use dart for pre location of approx distance, then thumper for fault locate.

 

[HD ELEKTRONİK]

For HV cable megger readings should be high Mega ohms e.g. 300 M.ohms +.

Screens should give clear readings. e.g 33 kV cable screen should be able to hold 5 kV DC from megger. 100 M.ohms or more.

For locate: use dart for pre location of approx distance, then thumper for fault locate.

Yes , Thanks.
This CTV in original Megger is 500V DC (use Min.500V) and Max.200M Ohm Scale.(It is present External Input).
Some Cable faults , this Megger correct show.But Cable is fault.
...
This is first procedure.
Also , other procedures than later.
...
...
(My work is Electrical Distribition Co.This is my job.And I post this jobs photos here).
Edit:Same-->Some

 

[RODALCO]

I need to know what voltage your HT cable is ? 10 kV 11 kV 33 kV ?

A mimimum of a 5 kV megger is required. a 500 Volts megger hasn't got enough voltage to perhaps jump a gap in the insulation where a void is or a tree has formed in the cable insulation.

An AVO BM 25 is a great Megger for HV cables.

If you have access to VLF set it will let you know if an intermittand fault is present.

A VLF ( Very Low Frequency ) test is good practise to do on a suspect cable or after a repair.

For an 11 kV cable ( 6.3 kV to screen ) the test voltage is peaked to 17 kV at 0.1 Hz test frequency, for a period of 15 minutes, no breakdown shall occur.

 

[Hero999]

I'm a bit confused, I thought the test voltage needs to be higher than the working voltage. At work we use 500V for phase to eath and neutral for 230V systems and 1kV phase to phase for 400V systems. I haven't done any HV work but if I was asked to megger a 11kV installation I would use 20kV phase to phase and 10kV phase to earth.

 

[HD ELEKTRONİK]

I need to know what voltage your HT cable is ? 10 kV 11 kV 33 kV ?

A mimimum of a 5 kV megger is required. a 500 Volts megger hasn't got enough voltage to perhaps jump a gap in the insulation where a void is or a tree has formed in the cable insulation.

An AVO BM 25 is a great Megger for HV cables.

If you have access to VLF set it will let you know if an intermittand fault is present.

A VLF ( Very Low Frequency ) test is good practise to do on a suspect cable or after a repair.

For an 11 kV cable ( 6.3 kV to screen ) the test voltage is peaked to 17 kV at 0.1 Hz test frequency, for a period of 15 minutes, no breakdown shall occur.

HV is 1KV and more (my be not International).

We use my City Electric Distribition 31,5KV and 15,8KV , not much 6,3KV.(Phase to Phase).

500V Megger is in CTV orginal.
CTV is 3KV to 110KV breed.
This CTV is on non existent VLF unit.
...
We use sometimes 5KV Megger.
...
We read often fault resistance is 1Khm: to 50Mhm: in HV Cable.
Megger Test is prefixing.(L1 or L2 or L3 Phase fault-->Which for show).

 

[HD ELEKTRONİK]

I'm a bit confused, I thought the test voltage needs to be higher than the working voltage. At work we use 500V for phase to eath and neutral for 230V systems and 1kV phase to phase for 400V systems. I haven't done any HV work but if I was asked to megger a 11kV installation I would use 20kV phase to phase and 10kV phase to earth.

Yes.
Megger Test is not Cable Test.
Megger Test is fault cable Insulation Test.
Cable Test make VLF Unit.

 

[RODALCO]

Hero999

5 kV Meggers are the industry standard. bigger than 5 kV meggers are hardly portable anymore.

A reading in high Ghm: or Thm: will give enough of an idea if there is an insulation problem in the cable.
Also out of balance readings between different phases indicate a potential problem.

We used prior to a VLF test, a couple of years ago, the old BICC DC test set which is a mains powered oversized megger and put 10 kV DC phase to screen, on single core or 20 kV DC between phases on 3 core PILC cables.
No breakdown should occur and the mA meter to remain on zero, exept when starting the test and charging the cable with DC.

A reason that we have gone over to VLF testing is that the XLPE cables don't like high voltage DC, which ages the insulation properties of the cable.