Carrier Pilot Protection. 1

[beyond86]

Hello,
I would like to discuss carrier pilot protection.
Do you apply this type of protection for high voltage lines in your country? For which voltage level?
Which is the principle of operation using?
How is pilot channels organized?
And the last question. Do you think, this protection is better than differential protection with optical channels?

 

[cranky108]

I did take classes years ago on carrier pilot protection, but my present company does not use carrier.
Carrier schemes I believe have been used in the US from about 35kV to 500kV.
Simple really, impress a RF signal on the power line, and take it off at the remote end.
The channels are organized by band with, and through a coordination between companies.
Better can be a question of the values you have.

Power line carrier can be cheaper than installing a long fiber, and the protection can be as fast as fiber based differential. It also has the advantages of being more than two terminal, with little added cost.
That said, a communication scheme that is external to the power system has it's own advantages.
It is also possible to use microwave and not fiber.

You need to verify for yourself, what you need.

 

[sushilksk]

Carrier protection is in use for EHV lines above 66kV. In most cases Digital tele-protection has replaced carrier based protection. Compared to line differntial, it does not require optical fiber connectivity and there is no limitation of line length. Differential protection have certain range for optical power (say 90km).

 

[cranky108]

Let me be clear, any protection scheme, other than the new traveling wave, requires the relays to be able to read the wave forms to determine a fault.
A line differential is no different, and if you find you need extra layer of filtering, it can be cycles slower that a DCB or POTT scheme.
DCB schemes have been used with line carrier for decades, and can work well if maintained properly.

That said, telling a tech to check spark gaps, is like telling them to empty the trash. If they do it, it may not be done well.

 

[scottf]

Cranky-

Do you mean the spark gaps on the line tuner and CVT drain coil? Curious why that is a maintenance challenge. Unless you're speaking to the smaller gas-filled gaps that some manufacturers use.

We tend to only use open air-gaps which are very simple to inspect visually and only maintenance required is to confirm the nuts are tight.

 

[cranky108]

My old company had problems with 'carrier holes', which can be caused by flash overs of the spark gaps.
The tech's refused to inspect them, as to there thinking they are maintenance free devices.
I am sure all of the gaps were spaced as from the factory, and never touched again.
Who knows if the gap was correct.
In one installation it was known that we had some bad cable between the last hybrid, and the tuner in the yard. But the tech's never seemed to have the time to replace it.
That said, it did work when needed.
Another problem is keeping the bird guards on the line traps, to keep the birds from nesting.
Never seemed important to maintain those for the line crews.
Another issue was the substation designs, never seemed to include an outlet near the line tuner for testing.
After seeing 200 ft of cord across a substation yard, I would insist on having a heated included in the tuner, not for heat, but so we had testing equipment power.

Don't get me wrong, Power line carrier works, but has some interesting issues, because so many people don't understand the needs it has.
Stand that with the needs of fiber terminal equipment, and life of equipment, and carrier costs less. But it requires a different working group, that has a different thinking.

 

[scottf]

Yeah, on the line traps, especially older "cement" models, the bird guards didn't last forever.

I'm always amazed at the money and maint some utilities spend trying to keep a 40 year old line trap operational, when new ones are relatively cheap and they're normally really simple to change out.

And your comment on a heater in the line tuner is something I've seen a lot. I've questioned many engineers about why they require a heater in their line tuners and I've never heard one make a good case for condensation prevention (because enough heat is generated from the other components), but it forcing station control power to the run to the line tuner makes sense. We supplied some before with actual outlets attached to the heater circuit for use by testing.

 

[cranky108]

Last line tuner heater I saw I recall as being 12 watts.

 

[scottf]

Yeah, we would typically supply a 10W 120/240V heater, unless someone asked for something different.

 

[cranky108]

Let me answer a question with a question. Why is maintenance of spark gaps a problem? Why don't the substation crews empty the trash cans from the control buildings?
It is more of a matter people don't understand it is part of their jobs.
If I would go out and do it, first I would be written up, and be told I was doing someone else's job.

 

[jwatty]

I may be wrong here, but I assumed the issue with adjusting spark gaps was this may require a line outage - since the spark gap is a protective device, does cleaning and adjusting require removing the line to allow you to adjust and clean it safely? It's going to spark over as a result of transients being impressed onto the high voltage line.

 

[Mbrooke]

Question. Is there any country or system on earth which doesn't use some type of pilot protection on its BPS power system? I've long thought about the "what if" scenario of not having pilot protection.

 

[scottf]

The carrier circuit has a ground switch in the CCVT and there is normally one in the line tuner as well. The carrier protection obviously has to be taken out but the line doesn't have to be taken out...assuming the utility allows work in CVT terminal box when line is energized. There are normally spark gaps across the CVT drain coil and on the input of the line tuner.

 

[sushilksk]

I have not heard about any spark gap issues in pilot carrier schemes. Are you taking about this:

Instead of carrier pilot protection, we can use fiber based protection.

 

[cranky108]

We now use fiber for all telaprotection. Maybe some digital microwave.

If you are asking me about new stuff or made outside the US, I likely can't help you, except with the theory.

I worked with power line carrier for a previous employer. I don't work with it now.