开云体育

ctrl + shift + ? for shortcuts
© 2025 开云体育
  1. Repeater-Builder
  2. Topics

TDR for power line

 

Anyone have experience using a TDR to locate an underground fault for high voltage ?
There's a PUD in central Washing that can't appear to fix an outage for the past three weeks or so.
It's affecting several comm sites and one ski area. It's high up around 7,000 ASL with 20-foot drifts. ?The road is derivable around the first or second week of July each season.?
?
I'm not sure if it's incompetence or lack of training but the concept seems simple enough to me; send a pulse down the line and watch for the return indicating something is wrong.?
There are several of these units on the market, on line.?
?
I also suspect it's not an exact science and requires lots of experience to be effective.?
If I were in the area I suppose I could hook up the (dead) line to a spark plug circuit (from an engine or whatever) and walk the mile line listening for anomalies with an AM radio.?
For now, one leasee is dragging large amounts of propane to keep one site alive.?
--
-
Regards, Karl Shoemaker
To contact me, please visit SRG's web site at?
for the current email address.
 

Not for high voltage, but for fire alarm cabling on utility poles.

I had a Riser Bond TDR that I used for fault location.? A long time ago I was asked to find a fault in a municipal cable that was once used for fire alarm call boxes.? The fault was an open circuit.? One of the things that you have to take into consideration is the velocity factor of the cable that you are troubleshooting.? This is usually impossible to know.? So I used another method.? I measured the fault from either end.? Just for a theoretical example, the TDR measurements were 1000 feet and 500 feet.? The actual physical length of the cable was 1000 feet. Interpolating that, the fault was 666 feet from one end and 333 feet from the other.? Sure enough, we found the cable had visible physical damage at this distance and fixed the problem.

I've never done underground TDR testing, but the same method should apply.? If it is a single hard fault (open, short) you should be able to find it.? Multiple faults could be very hard to find.? Be careful of any stray voltage on the cable, as it can damage the test equipment.? We had an Hewlett-Packard TDR test set that was damaged by voltage on the cable.

Joe, K1ike

On 4/7/2025 11:38 PM, Karl Shoemaker via groups.io wrote:
Anyone have experience using a TDR to locate an underground fault for high voltage ?
 

I've used TDR to find fault on small JKT(telephone wire) to underground tech cable (10-3)?

The velocity can be anywhere between 50 to 90 % Make sure there is no remaining power connected to any of the wire and I would suggest that you put a known terminating load at the?cable end and make the same test without. This helped me find a lot of strange breaks in the security system cable. And in a oil refinery regulation system.?

Pierre
VE2PF

On Mon, Apr 7, 2025 at 11:38?PM Karl Shoemaker via <srg734=[email protected]> wrote:
Anyone have experience using a TDR to locate an underground fault for high voltage ?
There's a PUD in central Washing that can't appear to fix an outage for the past three weeks or so.
It's affecting several comm sites and one ski area. It's high up around 7,000 ASL with 20-foot drifts.? The road is derivable around the first or second week of July each season.?
?
I'm not sure if it's incompetence or lack of training but the concept seems simple enough to me; send a pulse down the line and watch for the return indicating something is wrong.?
There are several of these units on the market, on line.?
?
I also suspect it's not an exact science and requires lots of experience to be effective.?
If I were in the area I suppose I could hook up the (dead) line to a spark plug circuit (from an engine or whatever) and walk the mile line listening for anomalies with an AM radio.?
For now, one leasee is dragging large amounts of propane to keep one site alive.?
--
-
Regards, Karl Shoemaker
To contact me, please visit SRG's web site at?
for the current email address.
 

Such a device exists.? Its commonly referred to as a Thumper. Basically
it is a high voltage pulse that causes the fault to break down.? I
rented one on 2 occasions to locate a underground fault in a underground
feeder to a microwave site.? The package also included an ultrasonic
detector that was used to pinpoint the exact location of the fault.?
Once we got close you could actually hear and feel the arc generated by
the thumper.? In both instances we contracted with a HV splicing company
to do the actual repair. There is also a mode called a burn down that
uses a high voltage DC to cause the fault to get bad enough to locate.?
The book that comes with the Thumper lists the various dielectric
constants for the various forms of cables, very similar to the velocity
factor of coax cables.

The actual splice kits have the shrink tubing to splice the power
conductor, the dielectric insulator and the outside jacket called the
semiconductor to prevent a point failure due to corona point discharge.?
Generally you have to use 2 splice kits and a short section of
compatible feeder to make up for the damaged section.

Jack K6YC

1 - 4 of 4