DIS-TRAN Steel Blog

3 Transmission Structures Broken Down

Posted by Wendy Gintz on Jul 7, 2015 10:45:00 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

SUBSTATIONS: 3 Common Steel Structures Found Inside

Posted by Wendy Gintz on Feb 26, 2015 8:54:00 AM

Before 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.

For this particular Blog, lets just identify the Main Substation Structures.

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.

HFrame Substation Structure   t&d_1-resized-600

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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 andstatic pole situations when compared to AISC standard shape structures.

 

 

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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. 

 

Examples of some equipment stands include:t 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.

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

 

When it comes to which type of steel is used, galvanized or weathering, inside a substation, I won’t say that you will never see weathering steel, but it is very rare. Weathering steel is used more in transmission structures than substation. One of the main reasons is because aesthetically, galvanized steel “looks” better inside a substation. Typically a substation is surrounded by a fence, has a metal building inside as well as white rock on the ground surrounding it. So the look of weathering steel, which is usually a dark brown color, aesthetically, goes better with a transmission line running through the woods to blend in versus in a substation.

Let us know if this information was helpful.  Comment below with and questions you may have, we would love to hear from you.

 

 Ultimate Utility Guide

 

Tags: steel structures, DIS-TRAN Steel, standard shape steel structures, switch stands, substation, dead-end structures, H-Frame structures, dead-end h-frame structures

Direct Embedded versus Drilled Pier Foundation for Transmission Poles

Posted by Brooke Barone on Apr 17, 2014 3:00:00 PM

Before I started writing and learning about the utility industry, I honestly never really noticed the difference, nor did I actually know the difference, in transmission poles or how they were installed. Now, a year and eight months later, I catch myself scurrying to get my iPhone out while driving down the highway to take pictures of tapered tubular davit arms or dead-end h-frame structures.

Have you ever paid attention to the way a transmission pole was installed? I’m sure if you’re not an engineer or someone in the utility industry your answer would be no, but for those of you who are, have you noticed the foundation method? Do you know the different methods?

Well, in the ASCE 48-11, Design of Steel Transmission Pole Structures, three specific methods used to place a steel transmission pole into the ground are pointed out:

1. Drilled Shaft Foundation with Anchor Bolts

2. Direct-Embedded Foundation

3. Embedded Casing Foundation

There are also other methods such as spread, pile, rock anchor foundations, etc. that can be used for more specific applications. But the two that I want to focus on are drilled shaft foundation (also known as drilled pier foundation), and direct-embedded.

When deciding on which method is best suited, there are some considerations that should be addressed in initial design as well as restrictions to pay attention to. Things like type of structure, importance of structure, allowable foundation movement or rotation and geological conditions are important and shouldn’t be overlooked.

Direct Embedded Poles:

  • Tends to be more economical over concrete foundation because it essentially just requires digging a hole, dropping the pole into the ground and then backfilling it with rock, concrete or other specified backfill.  
  • Typically used for tangent and light angle structures where the overturning moments are smaller.
  • As loads get larger, embedding a pole becomes less favorable because they are solely using the pressure of the specified backfill to resist the pole from coming out of the ground.
direct embedded transmission pole

Drilled Pier Foundation:

  • After the hole is dug into the ground, a combination of reinforcing steel and anchor bolts are lowered in place followed by concrete.  
  • Typically used in medium to heavy angle structures as well as dead-end steel structures.
  • The massive weight of the concrete that is in the ground is larger in diameter than the pole, so it can engage more soil, as well as have a greater bending force at the base.
drilled pier foundation

 Other things to consider when selecting foundation types include:

  • Soil properties
  • Foundation loads
  • Design limitations
  • Equipment availability and accessibility
  • Environmental restrictions
  • Cost/budget

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Tags: direct embedded versus drilled pier foundation, tapered tubular davit arms, dead-end h-frame structures, ASCE 48-11, design of steel transmission pole structures, drilled pier foundation, drilled shaft foundation, direc embedded foundation, embedded casing foundation, combination of reinforcing steel and anchor bolts

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