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 the name applies, dead-ends are designed to take the full component of every wire's tension
  • Does not necessarily mean the end of transmission line

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.