What is the difference betweem a transmission system and a distribution system? 3

[TransPlanner86]

Is there a good definition somewhere that determines what is the difference between a transmission system and a distribution system?

When I think a distribution system, I usually think of lines coming out of substation that have all of the equipment mounted on poles (transformers and circuit switchers). I am dealing with a 33kV system that has no pole mounted equipment, and customer load and generators are connected via substations. This sounds more like sub-transmission to me. Any thoughts?

 

[odlanor]

distribution system is a radial system.
studies transmission system guidelines have totally different from studies on the distribution system.
The exceptions are handled separately.

 

[cuky2000]

There are different types of distribution systems such as single ended, double ended or network configuration with network protector.

See the enclosed reference:

www.eaton.com/Electrical/Consultants/.../idcplg?...GET...Rendition...

 

[DTR2011]

Mr. odlanor

I see your point, but let us look at a hypothetical situation and test this.

Let's say that Utility XYZ was once vertically integrated, owning transmission, generation and distribution. The transmission system was fed by multiple sources and carried electrical energy over long distances. The distribution system was radial and distributed the electrical energy to the end customers. The transmission system (per the old Utility XYZ) was internally defined and segregated as >69kV. Anything less was internally defined as distribution.


After deregulation (or librilisation), the company is now split (or sold) and we have 2 Companies, (XYZ (Transmission) and ABC (Distribution)). Let's assume that the intent of the breakup of the vertically integrated Utility model was forced upon the utilities, with the goal of offering customers "choice", or to end "monopolistic" practices. There, once and for all, the powers that be have made the legal definition and division.


Along comes further regulation / deregulation as well as a push for green energy / distributed generation. We now have all kinds of independent power producers feeding into the Utility ABC system with wind farms, solar, bio mass, etc. What was once legally defined as a distribution Utility, having a radial system, now has multiple sources on it's network. Is it then, once again a transmission utility, subject to the rules and regulations of that definition?

My point is that the answer lies somewhere between the legal (or regulatory body) definition and the technical one.

To the OP, although I am generally skeptical of Wikipedia, it has a fairly good description of your original question.

Transmission

Distribution

 

[DTR2011]

How about this. I believe it was a US Supreme court ruling on the definition of pornography and one of the judges states "I know what it is when I see it." ...

 

[jghrist]

All right, I might as well put in my 2 cents worth. I go along with pwrtran and davidbeach. The relevant difference is that distribution systems either serve the end customer directly (secondary distribution) or through one transformer (primary distribution). If you have to go another step, it is either subtransmission or transmission, depending on the voltage. But then, there are industrial customers that have transmission service and own their own power transformers. This doesn't make the transmission line a distribution line.

You could also classify the system by whether or not it has voltage regulators. We have one municipal client that has both 25 kV distribution and 25 kV subtransmission. The subtransmission is used to serve regulator stations which have distribution feeders.

 

[odlanor]

what I know, when designing an independent power plant to be connected to a substation with local load , owned by a distribution system (radial system), the connection of our Transmission Line to the substation, has restrictions:
- if Substation lose connection with the distribution system , TL should be automatically disconnected ;
- TL can only be connected to the substation after system returned;
- TL may not reclose;

 

[dpc]

NERC can't even tell us what is a transmission system

Oh, but they can. And will.

 

[cranky108]

So exactly when will NERC tell us what a transmission system is? Only after FERC orders them to, and not before.
100 KV and above.

 

[davidbeach]

Read the FERC/NERC report on the Southwest outage. Somehow it won't surprise me if we find the 100kV threshold coming down to some lower value.

 

[cranky108]

I read it. They even presented it at the last syncrophasor conference in Denver.

So 92 kV is also transmission?

 

[davidbeach]

It might become transmission. Or we might just have to prove that everything we have below 100kV has no impact on the BES. What ever, more compliance documentation activities coming our way. Can you say "unfunded mandate?"

 

[dpc]

NERC seems pretty funded.....