long runs swa

[ban-all-sheds]

What if the fault itself contains a significant impedance?

 

[Jackrae]

What if the fault itself contains a significant impedance?

spoil-sport

 

[Adam_151]

What if the fault itself contains a significant impedance?

I am not sure if

a) You have skim read and haven't got the right end of the stick of what I was describing

or

b) You have, but you are proposing a reasonbly unlikely scenerio of a high resistance 'semi-break' in a conductor combined with a fault to earth there was well

 

[Lectrician]

Most cable faults of this nature will be a relatively high resistance failure (conductor to earth, conductor to conductor), typically caused by water ingress into a poorly made joint. The 400/230v AC being able to pass current, pop, arc, bang, operate the protection. A 12v battery would be oblivious to this typical fault.

Encapsulated resin joints often fail because the cable itself has been damaged somewhere else, allowing water to ingress the joint through hygroscopic action in the cable.

 

[Adam_151]

Most cable faults of this nature will be a relatively high resistance failure (conductor to earth, conductor to conductor), typically caused by water ingress into a poorly made joint. The 400/230v AC being able to pass current, pop, arc, bang, operate the protection. A 12v battery would be oblivious to this typical fault.

Unless the fault was a failure of the kind that needed sufficient voltage to flash across something to show up, then the method described should be able to detect it. Water ingress into a joint will normally leave a fault that will measure a few K ohms at ELV (worst case), as long as the DVM used has a relalatively high impedance input would be able to get a reading.

The load of the lamp is not being fed through the fault, but rather through a pair of conducters jointed at the far end, the fault is just allowing a volt meter to be connected at the point of the fault and the series resistance it adds to it should not substantially affect the reading, and any affect it does have can be somewhat compensated for by measuring from both ends

 

[333rocky333]

Firstly they did the equivalent of "meggering" the 11KV cable and found a short between phases. Then they got a "thumping box" which sent pulses of 11KV down the cables and monitored the cable route for vibrations. They also had a "pulsing" machine which sent an echo pulse and measured any reflections. The intensity and time of the reflection indicated the type and distance of fault. Both of these processes, and they excavated right onto the faulty section of cable.

I was pretty impressed.

Well thats what they came and done, it was a failed joint, .
Trench was 2 metres as they encountered a lot of "noise" due to nearby machinery.
used a Megger Thump 12 cost about £13000

20161111_125015

• 333rocky333
• 12 Nov 2016