DIS-TRAN Steel Blog

3 Transmission Structures Broken Down

Posted by Wendy Gintz on Jul 7, 2015 9:45:00 AM

When designing transmission structures...

it’s not as simple as saying “ok, I want self-supporting tangent mono poles with delta configuration for my entire 80 mile stretch.”  While that idea might be more economical than having h-frame or 3-pole structures, it’s just not practical.

Ultimately, the wire configurations determine which type of structure will be used, and typically there will be a mix of these structures in order to follow the right-of-way through small or tight turns. Right-of-ways go alongside or through interstates, highways, fields, woods and even water, so an engineer must keep all these situations in mind when designing.

Three common transmission structures:

  •  Tangent
    • Used when transmission route is straight
    • Generally, no longitudinal loads on the structure
  • Angle
    • Used when transmission route changes direction
    • Used from anywhere less than a 5 degree angle to a 90 degree angle
  • Dead-End
    • As name applies, dead-ends are designed to take the full component of every wire's tension
    • Does not necessarily mean end of transmission line 

                              

tangent_info_graoh_ANGLE_INFORGROAH

 

 

 

 

 

dead-end_infogrpah_pic

 

Whether the structures are tangent, angle or dead-end, wire phases can run in multiple configurations.  Horizontal Configurations provide the lowest profile. Vertical Configurations require the minimum width right-of-way. And Delta Configurations is an attempt to use the value of both horizontal and vertical configurations to maintain phase clearances.

Transmission structures can be classified as either self-supporting or guyed.

Self-Supporting Structures do not use guys: meaning they are not tied to the ground or any other structure in a way that offers additional support. They are better for restrictions to right-of-ways and tend to have loads small enough to not warrant guys.

Guying of structures is used to support the structure and allow for a more economical design in both the steel structure and foundation. Guying reduces bending and deflection. However, the downside is that it requires more right-of-way. 

*Here are some main contributing factors to keep in mind when deciding on whether or not to guy a structure:

  • Structural loading
  • Right-of-way requirements
  • Aesthetic design criteria

**Here are some other contributing factors you may want to consider:

  • Line voltage
  • Electric air gap clearance requirements
  • Ground clearance requirequirements
  • Insulation requirements
  • Number of circuits to be supported
  • Electric and magnetic field limits

There is so much to learn about Transmission Structures.  What questions do you have?  We would love to hear from you so please leave a comment below.

Check out our newest resource for Anchored Transmission Structures.  Click below.
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Tags: transmission structures, guyed structures, tangent, dead-end h-frame structures, configurations

DIS-TRAN Take2: How to Calculate the Anchor Bolt Embedment of Transmission Poles

Posted by Wendy Gintz on May 7, 2015 12:30:00 PM

It's been awhile, but we are still at it...  Thats, hopefully createing ueseful tips that make your job easier.

AnchorBolt

We have had a sort of series of Take2s referencing Anchor Bolts.  For this edition we will look at calculating the embedment of steel transmission structures.  Please feel free to go back and view the two previous Take2 Blog posts.

     Anchor Bolt Loads
     Anchor Bolt Design

What you will hear about...

  1. What to consider when calculating the embedment.
  2. What resources to use.
  3. A working example
  4. Additional information to consider

   

Thank you for viewing the DIS-TRAN Take2. We look forward to your feed back.  Please leave any comments or questions you may have about transmission pole or anchor bolt design below.

Until next time...

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Tags: transmission structures, transmission poles, design of steel transmission pole structures, anchor bolts

10 Tips: How to Save Money When Submitting a Bid to a Steel Fabricator

Posted by Brooke Barone on Jun 19, 2014 11:25:00 AM

Every structural steel fabricator is different when it comes down to pricing substation and transmission steel structures. But, there are some commonalities that could help save you money when submitting a Request for Quote (RFQ). How do you do that you might ask?

Well, generally, there’s a rule of thumb to consider: the more information you give the Estimating Department, the better price you’ll receive. If very little information is given, it’s harder for the estimating department/engineers to easily go through and pick out requirements, design the structure and then send the RFQ back in adequate time. And sometimes the price might reflect the assumptions that had to be made. 

Different terms used:

  • Request for Quote (RFQ)
  • Request for Proposal (RFP)
  • Purchase Requisition
  • Inquiry
  • Bid Event / BidQuote / Proposal

DTS_Employee

So, if you’ve asked yourself, “what can I do to save money when submitting a bid,” here are five good starting points.

1. Well-Defined Scope of Work- this could include everything from what the fabricator’s responsibility is, to needing the structures galvanized or weathering, delivery process, how hardware should be shipped, etc.  

2. Technical Specifications- this tells the fabricator how you want the structures built, like what kind of steel to use, etc.

3. Commercial Terms- this is more on the legal side, meaning what type of payment or who to invoice, insurance requirements, warranties, damages, etc.

4. Structure/Electrical Layout- this gives the overall dimensions of a structure such as height and width or phase spacing.

5. Enough Time to Bid- it’s important to keep in mind that fabricators typically have a quote backlog already scheduled out. 

Often, in order to send a bid to a fabricator, customers require the fabricator to be on an approved vendor list in order to quote the project.  The approval process usually involves quality assurance / quality control (QA/QC) audit, industry experience, project references, customer references, commercial term agreement, credit approvals, etc. 

Facts That Could Affect Pricing:

6. Weathering steel generally costs less because unlike galvanized steel, it doesn’t get the galvanized coating. (Typically see weathering steel more with transmission structures.)

7. Usually, the more steel ordered at one time could help give you a better price. In this instance, if you had different structures for one substation, instead of ordering separately, try to coordinate to order all the structures together, which could save money on freight and other expenses.

8. Loads with over-length and over-width sections could get costly because you have to get freight permitting depending on the states along the delivery route. Typically, the price for wider structures is greater than longer structures.

9. Expedited lead times can increase price. Since a production backlog is already in place, fabricators would need to expedite engineering, detailing, rearrange product schedule or may have to include some overtime.

10. Special weld inspection requirements and tests that are beyond typical industry standards could raise the price. If the fabricator needs to pull in a third party to inspect, send material off for testing or bring in an expert, it could increase the price.

These are just a few suggestions, and are not meant to be taken as the rule in every situation when dealing with every fabricator. But it is good to know how your project was priced and what affected it so that there are no hidden surprises or confusion.   

So remember: supply ample information, receive accurate price. 

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Tags: transmission structures, substation structures, structural steel fabricators, structural steel price, rfq request for quote, engineering estimating software, structural steel

10 Ways Knowing About Structural Steel Pricing Will Save You Money

Posted by Brooke Barone on Oct 29, 2013 2:52:00 PM

Every structural steel fabricator is different when it comes down to pricing substation and transmission steel structures. But, there are some commonalities that could help save you money when submitting a Request for Quote (RFQ). How do you do that you might ask?

Well, generally, there’s a rule of thumb to consider: the more information you give the Estimating Department, the better price you’ll receive. If very little information is given, it’s harder for the estimating department/engineers to easily go through and pick out requirements, design the structure and then send the RFQ back in adequate time. And sometimes the price might reflect the assumptions that had to be made. 

Different terms used:

  • Request for Quote (RFQ)
  • Request for Proposal (RFP)
  • Purchase Requisition
  • Inquiry
  • Bid Event / BidQuote / Proposal

So, if you’re asking yourself-“well, what exactly do I need to include when submitting a bid,” here are five good starting points.

1. Well-Defined Scope of Work- this could include everything from what the fabricator’s responsibility is, to needing the structures galvanized or weathering, delivery process, how hardware should be shipped, etc.  

2. Technical Specifications- this tells the fabricator how you want the structures built, like what kind of steel to use, etc.

3. Commercial Terms- this is more on the legal side, meaning what type of payment or who to invoice, insurance requirements, warranties, damages, etc.

4. Structure/Electrical Layout- this gives the overall dimensions of a structure such as height and width or phase spacing.

5. Enough Time to Bid- it’s important to keep in mind that fabricators typically have a quote backlog already scheduled out. 

Often, in order to send a bid to a fabricator, customers require the fabricator to be on an approved vendor list in order to quote the project.  The approval process usually involves quality assurance / quality control (QA/QC) audit, industry experience, project references, customer references, commercial term agreement, credit approvals, etc. 

5 Facts That Could Affect Pricing:

1. Weathering steel generally costs less because unlike galvanized steel, it doesn’t get the galvanized coating. (Typically see weathering steel more with transmission structures.)

2. Usually, the more steel ordered at one time could help give you a better price. In this instance, if you had different structures for one substation, instead of ordering separately, try to coordinate to order all the structures together, which could save money on freight and other expenses.

3. Loads with over-length and over-width sections could get costly because you have to get freight permitting depending on the states along the delivery route. Typically, the price for wider structures is greater than longer structures.

4. Expedited lead times can increase price. Since a production backlog is already in place, fabricators would need to expedite engineering, detailing, rearrange product schedule or may have to include some overtime.

5. Special weld inspection requirements and tests that are beyond typical industry standards could raise the price. If the fabricator needs to pull in a third party to inspect, send material off for testing or bring in an expert, it could increase the price.

These are just a few suggestions, and are not meant to be taken as the rule in every situation when dealing with every fabricator. But it is good to know how your project was priced and what affected it so that there are no hidden surprises or confusion.   

So remember: supply ample information, receive accurate price. 

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Tags: transmission structures, substation structures, structural steel fabricators, structural steel price, rfq request for quote, engineering estimating software, structural steel

How Do Electrical Transmission and Distribution Systems Work? Find Out.

Posted by Brooke Barone on Aug 9, 2013 8:52:00 AM

A Transmission and Distribution (T&D) System, has a notorious job of delivering electricity to consumers 24/7, 365 days a year.

But before the electricity can travel into your home, it must pass through a substation first. A substation is an assemblage of equipment where electrical energy is passed in order to be stepped up or stepped down.

Transformers inside a substation change the voltage levels between high transmission voltages and lower distribution voltages. The high transmission voltages are used to carry electricity longer distances, like across the country, whereas lower distribution voltages travel to industrial, commercial or residential consumers.

In a T&D system, the major components typically consist of transmission lines, distribution lines, substations and switchyards.

Inside a substation is like its own unique “power world” where every pole, bolt, stand, surge arrestor or structure plays its own individual role.

The three main types of structures found inside a substation include:

1.)    Dead-End Structures

2.)    Static Poles

3.)    Bus Supports/ Equipment Stands

Dead-end Structures are where the line ends or angles off. They are typically constructed with heavier steel in case they are needed to carry heavier tension. The two most common dead-end structures are H-Frame and A-Frame structures.

H-Frame Structure

A-Frame Structure

The second structure, a Static Pole, is a single, free-standing pole that creates a shield to protect all of the equipment inside a substation from lightning. Static poles may or may not have overhead shield wires attached to enhance protection. It depends on the size of the substation as to how many static poles are needed.             

NOTE: Tapered tubular design is typically efficient and economical in dead-end and static pole situations when compared to AISC standard shape structures.

Bus Supports are the most basic structure found inside a substation. Its main purpose is to provide support for rigid bus as it travels though the substation. Rigid bus is stiff and will not move around during weather events. Unlike rigid, flexible bus is typically used in high seismic areas in order to be able to move and dampen the seismic forces that occur. 

Electrical equipment can be of significant weight and must meet specific guidelines for structural loads, deflection limits or clearance requirements.Equipment Stands are the structures that the actual equipment sit on.

Examples of some equipment stands include:

  • Potential Transformers (PT) Stands
  • Current Transformers (CT) Stands
  • Coupling Capacitor Voltage Transformer (CCVT ) Stands
  • Lightning Arresters (LA)
  • Switch Stands

 So, although the concept seems quick and simple like flipping a light switch, much more is going on behind the scenes.  

Transmission lines act as the utility interstate system where electricity is transmitted at high voltages in order to reduce the energy lost in long-distance transmission.

Although it’s hard to quantify structure types since there are always exceptions to the rules and never-ending configurations, transmission structures can be considered dead-end, strain or suspension.

dead-end structure is where conductors and ground wires are pulled only on one side, unless it is a double dead-end structure, and are used where:

•    Line ends
•    Line turns at a large angle
•    At major crossings like highways or rivers
•    Divide line into segments


For strain structures, the conductors are directly attached through in-line insulators through or around the tower. In suspension transmission structures, the conductor phases pass through the structure, and are suspended from the insulator.

Each structure type can either be classified as tangentwith no line angle, or anglewhen there is a line angle.

Steel transmission structures can be designed with tapered tubular poles, which are hollow, can be multi-sided and have a large base that tapers down, typically in the range of .18 to .45” per foot.

And to dig a little deeper, all of these structures can either be guyed or unguyed. A guyed structure provides extra support by fastening a wire from the structure to the ground or another structure, whereas an unguyed structure is self-supporting.

Transmission Structures

When deciding which type of structure is most economical, as well as best suited for varying conditions, there are many considerations that can influence which to select, such as:


•    Terrain type 
•    Erection techniques
•    Electrical constraints
•    Access & transport situation
•    Procurement & easements
•    Structural loading

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Tags: steel structures, tapered tubular steel poles, transmission structures, substation structures, tangent, switchyards, dead-end structures, electrical transmission and distribution

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