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What is the cost of a new 34.5 kV Transmission line today in Midwest US?

Rao Konidena's picture
Independent Consultant, Rakon Energy LLC

Rao Konidena found Rakon Energy LLC because Rao is passionate about connecting clients to cost-effective solutions in energy consulting, storage, distributed energy resources, and electricity...

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  • Feb 12, 2021

I want to know the cost of a new 34.5 kV Transmission line (T line) in the Midwest US because, I am trying to estimate the high end of network upgrade costs for interconnecting a new 5 MW solar at 34.5 kV substation. If the Transmission Owner asks for network upgrades at the 34.5 kV (which is sub-transmission), one option would be to increase the substation capacity at this substation by adding a new 34.5 kV line.

Midcontinent ISO (MISO) only provides cost estimates of projects starting with 69 kV.

NERC Electricity Supply & Demand (ES&D) database provides new T lines and transformers, but does not provide cost estimates only line length. Even then, 34.5 is not in that database because most T systems - this level is sub-transmission.


Your access to Member Features is limited.

This is almost exclusively considered the upper end of the distribution system and never subject to RTO oversight unless there is a source on that line which is bidding into the PJM market (this is my last recollection on this).  As a result, they will not have those costs. 

I checked with some contacts I have and got the following numbers:

34kv. -  $480K / mile

12kv -  $375K / mile

These would be typical for Northern Illinois and surrounding areas.

Hi Rao,

I agree with Paul here that 34.5 kV is pretty much out of the distribution class of voltages and falling under sub-transmission class which 60 kV and 70 kV lines belong to. The cost that I have is for a 60/70 kV woodpole line and is 520,000 per mile (I believe it is a PG&E cost reference). You can apply Paul's reduction (10%) to get to 34.5 kV cost per mile. Afshin.

CAISO posted these today.  They are drafts.  They go down to 60/70 kV.

Rao Konidena's picture
Rao Konidena on Feb 23, 2021

Thanks Paul.

Brock  Ramey's picture
Brock Ramey on Jan 10, 2023



Is there somewhere I can get this document, the link leads me nowhere. 


Generally, 69kV is the lowest voltage that could be considered transmission (sub-transmission really).  

FERC Order No. 888 sets forth the Commission’s seven-factor test to identify distribution facilities, and include:  (1) local distribution facilities are normally in close proximity to retail customers; (2) local distribution facilities are primarily radial in character; (3) power flows into local distribution systems and it rarely, if ever, flows out; (4) when power enters a local distribution system, it is not re-consigned or transported on to some other market; (5) power entering a local distribution system is consumed in a comparatively restricted geographical area; (6) meters are based at the transmission/local distribution interface to measure flows into the local distribution system; and (7) local distribution systems are of reduced voltage.

The purpose for this is mainly to set forth the facilities that will be included as assets in the transmission tariffs for the region.  As such, you are not going to find information in ISO searches on this voltage.  

The cost to build OH and UG lines is dependent on terrain and urbanization.  Utilities typically have some rule-of-thumb cost/mile estimates for these facilities in their regions and are generally fine sharing them if you contact the distribution planning and interconnection group.  If you have specific locations and routes that will help them zero in on the specifics to give you more accurate information.  The information given to you below by all of these great folks is a fine for the planning estimates for the actual line.

However, there can be very large variability once you get to the substation.  If you are planning on building an express feed back to the existing substation, the utility will have to add a breaker position in their facility.  Depending on the existing system, this could be a 'relatively simple' process of adding another breaker position or could be a difficult endeavor that would require another transformer and completely new distribution breaker bus.  It is all completely dependent on the facility.  

Ultimately, this will be governed by the local utility, not the ISO.  Your interactions need to be with the utility to determine all of this information.

Rao Konidena's picture
Rao Konidena on Feb 23, 2021

Thanks for the detailed reply, Chris. I appreciate it.

A good ballpark to start in is $900k to $1.3mil per mile based on the geo tech. The number can rise substantially if unstable soils are encountered or if traversing rough terrain and heli support is needed.

Rao Konidena's picture
Rao Konidena on Feb 23, 2021

Thanks Craig.

"transmission" or "distribution" of electric power are made in two basic ways - by power cables, or by overhead lines. Since the author of the question does not specify, we assume he is talking about 'overhead lines". 

 Since he knows the cost of 69 kV overhead transmission lines, the short answer for the construction cost of 35 kV distribution lines would be about 60% of 69 kV line.  As an example:   69 kV per mile $70k x 0.6 = 42K USD per mile for 35 kV..  This is estimated maximum cost of construction, does not include engineering / design efforts and overheads. 

 To estimate an actual cost of transmission or distribution overhead line one would need  to figure out many parameters such as: 

 Type of terrain, types, and numbers of support poles and structures to be used (Wooden, steel...); types of foundations required for the support structures; the profile and length of the line; type of wire used, number of circuit (single or double, 3-phase or  single phase); the cost of acre of land needed for right-of-way; types and numbers of line insulators, plus engineering and design efforts. 

Rao Konidena's picture
Rao Konidena on Feb 23, 2021

Gerald - Thank you! for your detailed reply.


Most transmission owners do not have standards for 34.5kV transmission lines as 34.5kV is now utilized as distribution. Typically, when engineering and estimating the per/mile cost of 34.5kV transmission lines a TO will utilize their 69kV line standard. That said, I recommend the developer reference the MISO cost estimating guidelines shown below, and scope the 34.5kV line as a 69kV line for the purpose of developing a cost estimate.

Rao Konidena's picture
Rao Konidena on Feb 23, 2021

Thanks, Ryan.

This is a difficult question to answer as there are a lot of variables.

Will this be an overhead or underground 34.5 KV distribution line?

Will the line be built in a wooded area, an open area, or a populated area?

Can this be an extension of an existing line that is rebuilt as needed?

Who will own the line?  Utility or Solar Farm Owner?

Will this be a 600 amp line (Standard utility line) or a 5 MVA line (dedicated to the solar farm)?

Will other solar farms be connected to this line?

As a starting point, I think $1,000,000 per mile is a high end cost.  If you use Google Maps to survey the area between the substation and the solar farm, you can justify reducing the cost estimate based on your findings.

If you add a new line in an existing 34.5 KV substation, the circuit breaker with protective relays, etc. will add another $250,000 to the project.

If the solar farm is connected to an existing radial, 34.5 KV, three phase line, the solar farm will reduce distribution line amps during the day and have no impact on distribution line amps during nighttime.  If this is the case, 34.5 KV line costs can be minimal.

It's important to note that although transmission systems need to be upgraded when energy sources are added, distribution systems require minimal changes when energy sources are added. 

Rao Konidena's picture
Rao Konidena on Feb 23, 2021

Thanks Tony. I really like reading your last sentence.


Transmission network has been developed for evacuating power generated and to distribute the same to customers. Most transmission lines are high voltage three phase AC although single AC is sometimes used in railway electrification systems.  However, High Voltage Direct Current (HVDC) technology is deployed over very long distances for greater efficiency. 

Normal Extra High Voltage lines in place today are – 800 kV(Plus or minus) HVDC.  Transmission access charges of a zone is generally determined by computing weighted averages (generation/Load) of nodal charges at each node in the Zone which facilitates PoC charges for the zone.  We do come across 765 kV; 400 kV; 230/220 kV; 110 kV and 66 kV AC lines.

Many details need be worked out before laying the desired lines and choosing the right material for transmission is very crucial.  Materials used for transmission lines are indeed different starting with Copper, Aluminium, Cadmium (copper alloys), Phosphor bronze, Galvanized steel, Steel core copper, steel core aluminium.  Planning, scoping, mapping, environmental review, public comment, project approval, permitting, land acquisition, and construction are just a few of them to be considered, in addition.

Aluminium, due to its super conductivity-to weight ratio scores over copper and is also now used in wiring in residences, buildings, aircraft

Lattice towers (framework construction of steel or aluminium sections) are used for power lines of all voltages and are the most common and are generally made of galvanized steel. Tower design takes into consideration several aspects – ground clearance of the lowest conductor point, length of the insulator string, minimum distance between conductors and between conductor and tower. Most common conductor materials are copper, copper covered steel, high strength copper alloys and aluminium. Dead-end towers are where the transmission line ends.

Type of towers include Waist-type tower (most common); Double circuit tower for voltages ranging from 110 to 315 kV, in India;Guyed-V tower for voltages ranging between 230 and 735 kV; Tubular steel pole and Guyed cross-rope suspension tower.

Ideally, 34.5 kv to 69 kv power is sent to regional distribution stations and sometimes, sub-transmission voltage is tapped along the way for use in industrial or large commercial operations. Voltages of transmission line vary between 44,000 and 765,000 volts.  Higher the voltage, more electricity can be carried by the line.  However, su-transmission lines carry reduced voltages from the major transmission line system.

As mentioned above, it is not a single formula calculation as the details pertaining to above vary from country to country.  In India, one km. long transmission line costs around Rupees 5 lakhs (roughly, 6865 US$ at the current rate).  The current rate could be higher.

I therefore would suggest that calculations for 1 mile transmission line need be worked out independently considering the factors mentioned.

Rao Konidena's picture
Rao Konidena on Feb 18, 2021

Thank you for the detailed answer.

A. K. Shyam, PhD's picture
A. K. Shyam, PhD on Feb 23, 2021

My pleasure.  Regards,

The cost of any transmission / distribution line is dependent on several factors such as:

  1. Voltage
  2. No. of Circuits, conductor type
  3. Terrain
  4. Length
  5. Type of structure
  6. Pole/Structure material
  7. Soil profile

In the present case, the 34.5 kV is yes, a sub-transmission voltage. But costs can be closely approximated with a 46 kV/69 kV assumption.

Here is what I have in my files.

  1. Base is ACSR conductor at 1.00. If ACSS conductors are used, multiply costs by 1.08.
  2. Base is line length > 10 miles at 1.00. Shorter lines use a factor of 1.10 to 1.20.
  3. Base is flat terrain at 1.00. Hilly terrain and suburban areas use a multiplying factor of 1.20 to 1.30.
  4. Single Circuit tubular steel pole 69 kV base = $ 1,120,000 per mile (not including wire, length and terrain multipliers)
  5. Single Circuit wood poles = costlier than steel

Costs relative to 34.5 kV can be approximated as 80% of the 69 kV values. If line is brand new, then Right of Way costs need to be added.

Hope this information helps.

Dr. Amal Khashab's picture
Dr. Amal Khashab on Feb 17, 2021

Great . 

Rao Konidena's picture
Rao Konidena on Feb 18, 2021

Thank you for the detailed answer. I appreciate it.

Use the 6/10ths rule and do a comparison based on the differences between the other voltages.

Doug Houseman's picture
Doug Houseman on Feb 16, 2021

Best source available in the midwest (and mostly anywhere). Lots of things will factor into real numbers. If the EIA wanted to do the US a favor, this kind of information would be collected.

Rao Konidena's picture
Rao Konidena on Feb 18, 2021

I agree, we need an independent source for cost estimates of transmission equipment for sub-transmission voltage classes because with grid modernization and blurring of transmission and distribution voltages - the industry needs this data.

I worked on 27Kv and 44 Kv related works a few years ago in Canada and typical North America you can say and the cost depends upon many factors like New line, Recloser requirements, other requirements like switch etc.

The average cost could be around USD 200k to 250K but again depending upon many factors and I am not sure specifically about Midwest abut ballpark figure can be used

Terry Blalock's picture
Terry Blalock on Feb 22, 2021

I think this range is reasonable for a rough estimate.

In the midwest, I would use $100k per circuit mile for longer 138kV class lines over 20 miles.  Since a transmission line contractor has many fixed costs to amortize over the length of the project, and since this project is only 5 miles of smaller 35kV class conductor, I would be comfortable with $75,000 per circuit mile and know I had some contingency for terrain, soil, weather, commodity and labor price fluctuations and more.  

You'll find here the cost estimate amounts from MISO. They go down to 69 kV -- one notch above 34.5 kV. Begin looking at page 33. 

I also found several lists of 34.5 kV projects being done in New England, but they did not contain cost estimates. I recommend using the 69 kV line MISO estimates per mile and discounting them 10% (my rough estimate) to recognize the lower costs of 34.5 kV lines. 

Rao Konidena's picture
Rao Konidena on Feb 18, 2021

Thank you, I was aware of the MISO cost estimation guide. But, I didn't realize how extensive is the MISO guide. I also wish they go 1-2 voltage levels below the 69 kV because, I believe Alliant West (ITC Midwest now) in Iowa has 34.5 kV under MISO functional control.


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