What is the difference betweem a transmission system and a distribution system?
What is the difference betweem a transmission system and a distribution system?
(OP)
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?
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?






RE: What is the difference betweem a transmission system and a distribution system?
http://books.google.com/books?id=Lo3b0OQsy0MC&pg=PA5&lpg=PA5&dq=ansi+transmission+voltage&source=bl&ots=ruGhHqj7MZ&sig=4fKSfBURPhGd55V03HmEUCwC3Cg&hl=en&sa=X&ei=k6bQT833Osj10gHcy5zYDQ&ved=0CGgQ6AEwAw#v=onepage&q=ansi%20transmission%20voltage&f=false
Distribution voltages would generally be no higher than 34.5 kV and often more likely to be around 15kV. The definitions could change based on what types of loads are in the area as well (industrial vs. residential).
There are many "it depends" to your question. The local (or regional) regulatory board may ultimately define this, as well as how the utility is structured (regulated or de regulated). Many utility companies, for example, are no longer vertically integrated, and have split up into separate transmission or distribution companies.
As far as the pole mounted equipment analogy, I would not necessarily consider that a useful one. There are many installations that utilize pad mounted transformers and associated switchgear at distribution voltages up to 34.5 kV.
RE: What is the difference betweem a transmission system and a distribution system?
In general, a distribution system is radialy fed, and has many distributive taps. The lower voltage idea, is a dividing line that has no clear level. But generally in the US, 15 kV class and lower is not transmission, and 69 kV and above is not distribution. What is inbetween is anybody's guess.
RE: What is the difference betweem a transmission system and a distribution system?
Two of the big utilities I worked for called 69kV and 45kV "Subtransmission".
old field guy
RE: What is the difference betweem a transmission system and a distribution system?
RE: What is the difference betweem a transmission system and a distribution system?
Distribution Systems: "Broadly speaking, 'distribution' includes all parts of an electric utility system between bulk power sources and the consumers service-entrance equipments... In general, a typical distribution system consists of (1) subtransmission circuits with voltage ratings usually between 12.47 and 245kV which deliver energy to the distribution substations; (2) distribution substations which convert the energy to a lower 'primary system' voltage for local distribution and usually include facilities for voltage regulation of the primary voltage; (3) primary circuits or 'feeders,' usually operating in the range of 4.16 to 34.5kV and supplying the load in a well-defined geographical area; (4) distribution transformers in ratings from 10 to 2500kVA which may be installed on poles, grade-level pads, or in underground vaults near the consumers and transform the primary voltages to utilization voltages; (5) secondary circuits at utilization voltage which carry the energy from the distribution transformer along the street or rear-lot lines; and (6) service drops which deliver the energy from the secondary to the user's service-entrance equipment."
Transmission Systems: "The function of the transmission system is the transmission of bulk power to load centers and large industrial users beyond the economical service range of the regular primary distribution lines."
RE: What is the difference betweem a transmission system and a distribution system?
Distribution system - step-down transformers convert the voltage to end user's level, 120V, 240V, 208, or 600V. Like local roads or county roads
RE: What is the difference betweem a transmission system and a distribution system?
RE: What is the difference betweem a transmission system and a distribution system?
Not always true. Some weak transmission is radial feed and some strong distribution is dual feed.
RE: What is the difference betweem a transmission system and a distribution system?
RE: What is the difference betweem a transmission system and a distribution system?
So what do you call a 7 kV delta circuit connected with one source, and has two generation sources, and three energy consumers?
RE: What is the difference betweem a transmission system and a distribution system?
RE: What is the difference betweem a transmission system and a distribution system?
Why is a gas distribution system called distribution? Or gas transmission called transmission? It's the same concept, except we use voltage level, not pressure in a pipe.
In the gas world they have a collector system, which we don't normally have (except renewables) because we have large generators connected directly to the transmission.
RE: What is the difference betweem a transmission system and a distribution system?
As never again or over my dead body?
RE: What is the difference betweem a transmission system and a distribution system?
Mainly small hydros, care takers houses, and a 911 relay tower. Very sparce.
RE: What is the difference betweem a transmission system and a distribution system?
In the US there are approximately 3,273 traditional electric utilities and around 1,738 nonutility power producers ranging from investor-owned, publicly-owned, cooperatives, and Federal/ Authorities (TVA, ACOE, Bureau of Reclamation, NYPA, BPA, etc). In few decades ago NERC grouped all utility in 8 regional organizations (PJM, WECC, NPCC, FRCC, MRO, etc).
It is not a surprise in the US there is not agreement to classifying distribution and transmission voltages since each utility is an independent entity many of then in operation long history before regulating agencies.
Even at the distribution level today there is several system voltages variation that survives after many years in operation such as 7.2/12.47-kV, 7.6/13.2kV, 7.9/13.8-kV, etc. In the pass, not only voltage levels were the issue but also different operating frequencies including DC. (NOTE: DC distribution services in NY City was suspended a few years ago)
RE: What is the difference betweem a transmission system and a distribution system?
RE: What is the difference betweem a transmission system and a distribution system?
RE: What is the difference betweem a transmission system and a distribution system?
As preposterous as it may sound, it is never-the-less very true as the utility retired the DC service for more than 4,500 customers in NY City 5 years ago. See the press Release below.
http://www.coned.com/newsroom/news/pr20071115.asp
RE: What is the difference betweem a transmission system and a distribution system?
Some small towns still use 4160, or 2400 V for distribution.
RE: What is the difference betweem a transmission system and a distribution system?
studies transmission system guidelines have totally different from studies on the distribution system.
The exceptions are handled separately.
RE: What is the difference betweem a transmission system and a distribution system?
See the enclosed reference:
www.eaton.com/Electrical/Consultants/.../idcplg?........
RE: What is the difference betweem a transmission system and a distribution system?
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
RE: What is the difference betweem a transmission system and a distribution system?
RE: What is the difference betweem a transmission system and a distribution system?
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.
RE: What is the difference betweem a transmission system and a distribution system?
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;
RE: What is the difference betweem a transmission system and a distribution system?
Oh, but they can. And will.
RE: What is the difference betweem a transmission system and a distribution system?
100 KV and above.
RE: What is the difference betweem a transmission system and a distribution system?
RE: What is the difference betweem a transmission system and a distribution system?
So 92 kV is also transmission?
RE: What is the difference betweem a transmission system and a distribution system?
RE: What is the difference betweem a transmission system and a distribution system?