Power Line Carrier 5kV Tuner lead 2

[cbradley75]

I saw something yesterday that struck me a little weird. Maybe I just don't remember this from when I was a test engineer or maybe the company I'm with now is doing something different. For those of you familiar with Power Line Carrier applications, you know that besides the radio; we use a CCVT, Line Tuner, and Line trap to couple carrier. From the HV terminal in the CCVT there is a 5kv lead-in that connects to the tuning unit.

This single conductor 5kV cable is where my question lies. Does anyone know of the preferred way to install this cable. Should it be dangling freely between the tuner and the CCVT (that's the way its done here), or should it be run in a one inch conduit between the CCVT and tuner. In my mind, that's the way it was done when I was out in the field about 8yrs ago; but that was in another state and my memory could be hazy.

Has anyone done it either way, and could weigh in on this? It's bugging the heck out of me that I don't remember seeing the HV lead ever installed 'dangling' like that.

Thanks

 

[cranky108]

In the past I insisted that the 5kv cable be connected to standoff insulators.
The issue here is that the 5kv cable is sucipable to the capacitive effects of earth ground. This capactince shows up in the carrier circuit as signel loss.

Therefore standing it off the substation steel works to reduce the signel loss.

 

[scottf]

I concur with cranky's comments. I've seen it both in pvc conduit and on insulators.

In my opinion, from yrs of supplying and supporting CVTs, traps, and tuners, running on 5 kV insulators is the preferred method.

From what I've seen, the common configuration is to drop down from the HF bushing of the CVT to 1 or 2 insulators (depending on structure height, and then into the tuner via top bushing, side "u" bushing, or bottom bushing/hub.

Certainly running in pvc conduit can work, but it's more increased leakage current, which is what contributed to increased insertion loss of the carrier signal.

 

[cranky108]

I would suggest the 5kv lead enter the cabnents on the side, using a drip loop. A 90 degree piece of plastic condiut works as an method of exiting the cabnet, and should put the 5kv lead a sufficent distance from the structure.

 

[cranky108]

Another comment, we never used 5kv insulators. We always used 15kv insulators, because that is what we had in our store room.

 

[scottf]

cranky-

On the entrance configuration....it really depends on the tuner design. Side entrance on the GE type CL02 and CL03 type tuners works well. However, on other types, internal clearance can be an issue with side entrance. On some models bottom and top entrance is better. Bottom would always be preferred over top due to moisture entrance/sealing issues on top.

 

[cbradley75]

Thanks guys! I feel slightly better knowing that my memory probably serves me correct. I can only assume that the previous company I worked for years ago, was more comfortable with the level of losses associated with PVC install than they were with the 'HV dangle' method. Researching a little, it seems the mfr literature prefers the 'dangle' as well. I'm ok with it, I guess.

 

[cranky108]

I haven't worked with very many newer tuners. Just the old stuff. Every manufacturer usually has a different suggested method. They just can't make things easer for the users.

There is another exit point if it is not obstructed. The back, however it isen't a common kockout.