Distribution lines passing below overhead power lines 8

[M. R. Habibi]

Hello everyone
It has been observed that a fault in an overhead power line can make problems for the distribution network passing below.
What can make such an influence?
Are there recommendations to prevent this interaction?

Thanks everyone in advance.

 

[LittleInch]

It's called ac induced voltage.

You can get high voltages, especially for fault currents.

Basically you need to earth the pipe, but consult an experienced CP engineer.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[M. R. Habibi]

Thanks dear LittleInch
As you mentioned, The induced currents can make corrosion in pipelines and so on.

But how about the electrical distribution lines? Which standards or technical guidelines to prevent it?
Thank you

 

[LittleInch]

Sorry - I have a one track mind and "distribution" to me means gas pipelines....

Do you mean O/H electric cables?.

If so then you need an electrical transmission person to answer.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[M. R. Habibi]

Thank you so much. In fact you helped me find a clue to search for articles on this topic.
This article seems to be relevant and I will share my future conclusions:

https://ieeexplore.ieee.org/document/4144488

 

[waross]

Saturation and loading of the distribution transformers will tend to isolate the induced voltages from the consumers.
On the other hand I once lived in an area where a 12 kV distribution circuit feeding east was underbuilt on the same poles as a 60 kV transmission line feeding west.
We were never aware of any issues until the night that a car hit a pole several miles away.
A 60 kV line kissed a 12 kV line.
Our TV went brilliant white and the lights went out.
When the lights came back on, our TV still worked.
About 1/2 mile closer, TVs were destroyed.
About 1 mile closer to the fault, both TVs and refrigerators were lost.


Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[LittleInch]

What are your relevant voltages of the two lines?

Separation distance?

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[M. R. Habibi]

Thanks Waross for sharing this helpful experience.

Dear LittleInch, I havn't investigate it very well, but it's about a 63vK power line over a distribution network.

 

[bacon4life]

As Bill mentioned, occasionally a transmission line mechanically fails and falls into the distribution line below. I have definitely wondered as to the range of customer damage when it occurs. From the utility perspective it can be hard tell the difference between zero customer damage, and having zero damage reported because customers who do not realize they can file an insurance claim against the utility. In a couple of example fallen transmission lines I am familiar with, there were no blown distribution surge arrestors in the vicinity, indicated the overvoltage on the distribution was not as extreme as Bill's experience. Using high speed, communications assisted relaying should result in less collateral damage than slower overcurrent relaying.

Any time there is a metallic conductor in parallel with a transmission line, workers need to take precautions. This is true for conductors including distribution circuits, communication circuits, metal pipelines, fences, train tracks, etc. Is there some particular issue you are worried about? As far as the physical construction standards, I do not know of any special construction practices for distribution underbuilt versus stand alone distribution circuits intended to address induced voltage. There may be minor differences in cross-arm length to allow for a line worker to climb the pole past the underbuilt distribution. The NESC also requires additional clearance if the distribution and transmission are owned by different companies.

 

[FacEngrPE]

This might be an interesting read "Application of Station Class Arresters on Underbuilt Distribution Lines"

https://www.inmr.com/application-station-class-arresters-underbuilt-distribution-lines-3/

Fred

 

[crshears]

This

https://www.google.com/maps/@44.694...4!1s-piPg1RoFx1LcDJbhIr3tA!2e0!7i13312!8i6656

is a Google Maps link to one of thousands of locations in my province that clearly illustrates my utility's approach to how to mitigate AC induction issues where LV distribution feeders must cross under a HV [in this instance, double 230 kV in the middle and twinned 500 kV on the outside] corridor; just "travel" down the road a ways to see where the buried cables for both MV and LV distribution feeders transition back to overhead conductor.

 

[RRaghunath]

I have seen a metallic mesh hung under the transmission line all along the length, separating the two lines.
This ensures the distribution line is protected against fall of conductor on it from transmission line above. I think it is a good practice and a must from safety of consumers as well as lineman who may have to approach the distribution line for repair etc.

 

[LittleInch]

"Are there recommendations to prevent this interaction?"

Like CR shears says - burial of the lower and lower voltage system when crossing under other power lines is quite common and removes / mitigates a number of interference issues.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[crshears]

An additional benefit of buried Tx ROW crossings is that line sags due to high loadings in hot weather are less likely to cause circuit trips.

Something similar happened in North Toronto once when over the winter a tall light standard was installed in a Toronto Transit Commission parking lot directly below a 230 kV ckt without consultation with the utility or any notification thereto...with the predictable result that during high loadings the following summer the 230 kV line conductor sagged into the light standard, severely damaging it and tripping the circuit out of service. The log of the incident made for interesting reading, as did the subsequent finger-pointing, blame-dodging and liability-evading documents...

CR

"As iron sharpens iron, so one person sharpens another." [Proverbs 27:17, NIV]

 

[bacon4life]

crshears- I am familiar with induction on parallel lines but I am confused how induction applies to perpendicular lines. About 3 spans northeast of the link you posted there is an overhead distribution line crossing the same transmission lines at

https://www.google.com/maps/@44.7232415,-79.7022533,196m/data=!3m1!1e3.

The main difference I see between the two locations is that along Vasey Rd the distribution is near the low point of the span, whereas along Gratrix Rd the overhead line is positioned much closer to the towers where there is plenty of vertical clearance. My utility has certainly added lots of underground dips like the one pictured as part of line uprates and LiDAR studies, but we also have many overhead crossing. As far as I know all our dips have been based on obtaining the NESC (US utility regulatory code) required clearance between conductors to prevent flashover. Adding an underground dip can cost more than $100k, while also adding many new failure mechanism to the system.

RRaghunath- Where have you seen metallic mesh between voltage classes used?