Connecting cables for VLF test

[SecondGen]

Does anyone have specific literature that says whether you can tie together cables for VLF testing? All I see in IEEE are references to "cable systems" which could be interpreted as either a single cable feeding multiple buildings and splices or 3-phase feeder.

[Kalbi_Rob]

Does anyone have specific literature that says whether you can tie together cables for VLF testing? All I see in IEEE are references to "cable systems" which could be interpreted as either a single cable feeding multiple buildings and splices or 3-phase feeder.

IEEE 400.2 does not state how to separate the cable system, but does give example of unique testing situations, as annotated in the below excerpt:

In addition, some utilities may have components connected to the cable circuit being measured, e.g., oil-filled switches, that cannot be removed but can influence the test results. Most users of dielectric response techniques choose to measure the entire cable system response that would include the responses from all terminations, cable, and joints within the circuit.


Multiple companies I have been apart of, have always pushed that VLF testing is essentially a go/no go test that if failed, would require the removal of each component to determine the failed portion. So, testing all phases together would not effect the overall test if they all pass. If it fails, then further testing would be required. Obviously, the overall intention is profit driven vs results driven. It has been accepted by the customer as understandable and never had to retest due to tying the phases together, even after some very heated debates.
The issue comes up with VLF-TD, where we believe Phases must be separated to produce trending results. Where we have issues is whether to test multiple cables tied together in a circuit (such as A-phase on either side of a transformer with the switch off and testing through the terminations). This is discussed in the excerpt I provided above, and would be best left to the decision of the end-user.

[SecondGen]

IEEE 400.2 does not state how to separate the cable system, but does give example of unique testing situations, as annotated in the below excerpt:

In addition, some utilities may have components connected to the cable circuit being measured, e.g., oil-filled switches, that cannot be removed but can influence the test results. Most users of dielectric response techniques choose to measure the entire cable system response that would include the responses from all terminations, cable, and joints within the circuit.


Multiple companies I have been apart of, have always pushed that VLF testing is essentially a go/no go test that if failed, would require the removal of each component to determine the failed portion. So, testing all phases together would not effect the overall test if they all pass. If it fails, then further testing would be required. Obviously, the overall intention is profit driven vs results driven. It has been accepted by the customer as understandable and never had to retest due to tying the phases together, even after some very heated debates.
The issue comes up with VLF-TD, where we believe Phases must be separated to produce trending results. Where we have issues is whether to test multiple cables tied together in a circuit (such as A-phase on either side of a transformer with the switch off and testing through the terminations). This is discussed in the excerpt I provided above, and would be best left to the decision of the end-user.

Thanks for confirming my suspicions, Rob. I don't see any problem with connecting them together. My ultimate conclusion is that any dispute between the ITA and customer would ultimately be resolved by the end user. If the owner wanted the cables separated it would probably be a separate charge. This is one of those times where testing specifications are absolutely critical.

[changeabilities]

Does anyone have specific literature that says whether you can tie together cables for VLF testing? All I see in IEEE are references to "cable systems" which could be interpreted as either a single cable feeding multiple buildings and splices or 3-phase feeder.

You can connect them together but it is really important to check the capacitance of the cable. Because long cables might damage your device.