Airport circuit

[Billyohms!]

Most airport runways here in Alaska have edge ,taxi, and threshold lights. These are powered by a regulator that maintains a stepped amperage for uniform brightness throughout the runway on a series circuit.
The lights are powered by a # 8 awg 5kv conductor buried 24" in a 2" PVC conduit.
The problem is these conduits inherently accumulate water, freeze and the expanding ice breaks the conductor.
The regulator shuts down when it can't supply enough voltage to maintain amperage.
How can I locate the break?

 

[hillbilly1]

They make a fault finder, but don’t know how well it would work on 5 kv cable, but should work though. It injects a high frequency pulse on the line. This one of them. Probably could rent one from a tool rental place too.

A-Frame Fault Locator | RIDGID Tools

The RIDGID® A-Frame Fault Locator is a purpose built system to simplify the location of ground faults in direct buried insulated wire. Shop now.

www.ridgid.com

 

[Billyohms!]

They make a fault finder, but don’t know how well it would work on 5 kv cable, but should work though. It injects a high frequency pulse on the line. This one of them. Probably could rent one from a tool rental place too.

A-Frame Fault Locator | RIDGID Tools

The RIDGID® A-Frame Fault Locator is a purpose built system to simplify the location of ground faults in direct buried insulated wire. Shop now.

www.ridgid.com

There's a good possibility that water will be in the vicinity of the break. Will the signal conduct across?

 

[ActionDave]

I haven't had much luck with a fault finder when the wire is in conduit.

There is an expensive meter called a Time Domain Reflectometer (sp?) that is supposed to be able to measure the length of wire. I've never used one.

 

[don_resqcapt19]

Maybe when you re-do the conduits, you could do something like this. This is from the utility service manual for my utility. Have never seen it done in the field.

I have seen the freeze damage in conduits around here, and at one point I submitted a proposal for a code change the require conduits to be buried below the normal frost line. However even around here that is about 4' and expect it would be much deeper in parts of Alaska.

 

[hillbilly1]

I haven't had much luck with a fault finder when the wire is in conduit.

There is an expensive meter called a Time Domain Reflectometer (sp?) that is supposed to be able to measure the length of wire. I've never used one.

I think those are for fiber, at least that’s what I have used on fiber.

 

[hillbilly1]

There's a good possibility that water will be in the vicinity of the break. Will the signal conduct across?

I think it’s actually better. I know with locating faults under pavement, they say to wet the pavement.

 

[Strathead]

I haven't had much luck with a fault finder when the wire is in conduit.

There is an expensive meter called a Time Domain Reflectometer (sp?) that is supposed to be able to measure the length of wire. I've never used one.

I have, we used them on Aircraft. I believe it would work at getting the distance, but then they would need to know the routing of the conduit.

 

[synchro]

What kind of lights are they? Incandescent or LED, and do they have a transformer?
It would be best to disconnect both ends of each wire between lights and test them separately, even though this might be daunting if there are a lot of lights. Since the lights are connected in series, this may impact the ability of a fault locator or TDR to find the break in the wire if the ends are not disconnect. More importantly, if there are LEDs and/or solid-state electronics like regulators or drivers they might potentially be damaged by such testing. A tone type locator would not likely do any damage, but it may not be effective over longer distances and could have a problem passing through any transformers if present.
If you can provide more detail about the lights used, that might help in determining the best approach.

 

[hillbilly1]

I haven't had much luck with a fault finder when the wire is in conduit.

There is an expensive meter called a Time Domain Reflectometer (sp?) that is supposed to be able to measure the length of wire. I've never used one.

I haven’t used a TDR either, an OTDR was what I used.

 

[zbang]

I have used a TDR on copper lines*, but with LED lamps (if they are) I doubt it'll help.
You're probably on to jumping out segments to find which is bad, then a TDR will help you find where. Doesn't sound like fun.

*LOTS of both thick and thin wire Ethernet and also on some 3000' twisted-pair audio lines (IIRC it was a Tektronix 1503b or c)

 

[Joethemechanic]

Sounds like an old time series street lighting circuit with a constant current transformer. I didn't read through this manual, but maybe there is a 1947 trick for finding a break in a conductor.

https://waterandpower.org/sitebuildercontent/sitebuilderfiles/DWP_Streetlight_Mnanual_1947.pdf

 

[LarryFine]

How about a non-contact tester?

 

[Joethemechanic]

Is the secondary of the constant current transformer bonded to ground?

There used to be one of these series runway lighting setups in Cape May NJ. You could turn on the lights and adjust the brightness by going to a frequency and keying your mic. I always wanted to get a look at it but never did

 

[AK_EE]

Most airport runways here in Alaska have edge ,taxi, and threshold lights. These are powered by a regulator that maintains a stepped amperage for uniform brightness throughout the runway on a series circuit.
The lights are powered by a # 8 awg 5kv conductor buried 24" in a 2" PVC conduit.
The problem is these conduits inherently accumulate water, freeze and the expanding ice breaks the conductor.
The regulator shuts down when it can't supply enough voltage to maintain amperage.
How can I locate the break?

Alaska DOT&PF has a YouTube video, "DOT&PF Troubleshooting of Airfield Lighting Systems" that walks you through the process of fault finding on a constant current lighting system.

 

[tom baker]

I haven't had much luck with a fault finder when the wire is in conduit.

There is an expensive meter called a Time Domain Reflectometer (sp?) that is supposed to be able to measure the length of wire. I've never used one.

I have used years ago and they work well. Newer ones probably better. They have to be calibrated to the wire type.

 

[Hv&Lv]

I haven't had much luck with a fault finder when the wire is in conduit.

There is an expensive meter called a Time Domain Reflectometer (sp?) that is supposed to be able to measure the length of wire. I've never used one.

Finding a fault in conduit is one of the hardest to find. I agree with you.

We have one at work to find faults in primary cable. It’s a VON thumper with TDR.
Plug in the VOP of the cable. You can see splices, transformers, breaks, sharp bends, etc..

I haven’t used a TDR either, an OTDR was what I used.

OTDR- optical time domain reflectometry.
Same principle, different methods

 

[electrofelon]

Finding a fault in conduit is one of the hardest to find. I agree with you.

We have one at work to find faults in primary cable. It’s a VON thumper with TDR.
Plug in the VOP of the cable. You can see splices, transformers, breaks, sharp bends, etc..

OTDR- optical time domain reflectometry.
Same principle, different methods

Even in PVC conduit? No experience with this but I wouldn't think nonmetallic conduit would make a difference.

 

[mtnelect]

This is very technical and requires advanced education in electrical engineering.

In my apprenticeship I worked with a journeyman electrician that did electrical work at golf courses. One of the most common problems was sprinklers that stopped working. His solution was to go to the controller of that circuit. Then he would disconnect that circuit, then remove a spark plug wire from his truck's engine and attached it to the problem circuit. Then take a am radio dial it into a quiet station. Then follow the popping sounds until a very loud popping sound is herd. Dig down at that point, you have found the break.

 

[Hv&Lv]

Even in PVC conduit? No experience with this but I wouldn't think nonmetallic conduit would make a difference.

You find it with sound(listen) in combination with TDR
Admittedly, it can be difficult, but who wants to dig a hole and hope the fault is there? At least this way we are close