Electrical RP Solutions

The electrical transmission market in North America is experiencing an ever-increasing need for the replacement and/or upgrading of transmission lines.  Most major utilities in Canada and in the United States still use wooden H-frame structures that were installed in the 1950s. These lines have passed their life expectancy and require replacement within the next 10 years.  

Cross arms are used throughout the world as structural elements to support aboveground electrical power transmission lines. These transmission cross arms, normally between 6 and 14 meters in length, can be made of a variety of materials, the most common of which is timber. Timber cross arms have a limited and unpredictable life expectancy. Furthermore, timber cross arms are combustible and propagate fire rapidly in forest fires; they are attractive to woodpeckers; and under certain weather conditions, they can initiate a pole top fire. Timber cross arms also creep (e.g. deflect) under heavy loads over long periods of time.

In collaboration with British Columbia (BC) hydro professionals, Lafarge recognized such challenges and developed a precast cementitious composite cross-arm solution that specifically meets the customer's requirements: a balance of mechanical and electrical characteristics with enhanced durability and reliability properties. RP cross arms are an example of how Lafarge's precast business has actively and effectively undertaken its differentiation strategy through value-added proposition.

Advantages of RP cross arms

• Engineered, stable and durable
• Greater reliability
• Predictable and consistent performance
• 75-plus years life expectancy
• Better insulating value than wood
• No UV degradation
• No partial discharge
• Safer live-line maintenance
• Freeze/thaw and corrosion resistant
• High resistance to tracking damage
• Mechanical strength: elasticity and ductility
• High resistance to damage from flashovers

Structural Test 

• Flexural capacity (four-point bending test on strong and weak axis)
• Flexural capacity of cross arms subjected to lightning impulses
• Full-scale testing under combined loads (vertical, longitudinal, transverse)
• Fatigue testing
• Durability performance of cross arm under severe environmental and loading conditions
• Combined accelerated durability and mechanical tests

Material Durability

• Freeze/thaw test
• Rapid chloride test
• Salt-scaling test
• Impermeability test

Electrical Tests 

1. Dielectric strength test
2. AC voltage partial discharge test
3. AC voltage flashover test
4. Lightning impulses voltage flashover test
5. Tracking wheel test
6. Lightning impulse withstand test

Testimonials 

Commentary on Lafarge RP Cross Arms

"Powertech Labs Inc. carried electrical tests on fiber-reinforced cementitious composite cross arms and materials manufactured by Lafarge Canada Inc. The measured electrical properties are comparable to conventional wood cross arms. There was damage to the material during the lightning impulse tests. Subsequent evaluation of the damage by the University of Calgary concluded that it did not affect the structural and mechanical properties of the cross arm. The fiber-reinforced cementitious material had a slight conductivity, which is not normally seen on insulating materials but a desirable property for cross arms on transmission lines.

"It means that under normal operating conditions there will be good voltage grading between the insulators and the transmission line structure."

A. John Vandermaar, P. Eng.

Manager, High Voltage Laboratory

Powertech Labs Inc.

Commentary on Lafarge RP Cross Arms for Transmission Use

"As a utility engineer with more than 35 years of transmission line design and maintenance experience, I have watched the development of Lafarge's RP cross arms and cross braces with great interest. In recent years there has been growing concern about the performance and reliability of traditional sawn-wood timbers and wood spars. This has caused utility engineers to look for viable alternative materials that could deliver the same or better performance, but with higher reliability and longer life.  As an engineered material, I believe Lafarge's new RP cross arm provides the right attributes: a balance of electrical and mechanical characteristics that make it a very attractive replacement alternative to traditional wood members. Lafarge has completed a comprehensive array of electrical and mechanical tests on this material that verifies its suitability for use on both transmission and distribution line structures.  In my opinion, these test results will allow utility engineers to specify this new product with confidence."

Jim H. Duxbury, P. Eng.

Transmission Engineering Consulting