TREFINASA low sag conductors

GAP type conductor (GTACSR & GZTACSR)

The aluminium inner layer is constructed with trapezoid wires that contain the high strength Al-clad steel core, creating a gap filled with high temperature resistant grease. Outer Al layers could be round shaped or trapezoid in case of alternative compact designs.

The low sag conductor operation is based on the lower coefficient of thermal expansion of the steel core as regards the aluminium layers. Conductor sagging is made tensioning the steel core only, keeping the aluminium layers without mechanical stress.

INVAR type conductor (ZTACIR)

The construction of ZTACIR conductor is similar to standard ACSR, but the main difference is the material used for the core that is Invar alloy. Invar alloy contents 36% of Nickel and provides to the material a very low coefficient of thermal expansion.

Typical sag-temperature curves for GAP and INVAR conductors

GAP conductor installation (SAPREM METHOD©)

The method developed by SAPREM facilitates the difficulties associated to the installation of gap type conductors from several points of view:

  • Technical problems related to the unwrapping and wrapping of the aluminium layers are avoided.
  • Clamping working time is reduced, leading to cost saving.
  • Safety aspects:
    • The use of special machines and tools allow linemen to work closer to the tower body without the use of special platforms.
    • The tensioning method avoids steel core tensioning without unwrapped conductor wires in the working area, that it’s a disadvantage for the conductor handling, and hazardous especially in live line works.
    • The system provides double safety prevention for the steel core slipping during the tensioning stage, improving the performance of the conventional come-along clamps for steel.


TREFINASA-SAPREM have developed special fittings for the right installation and operation of the low sag conductors. Specially designed complete sets of tension and suspension sets can be supplied as well as damping systems according to the vibration characteristics of the line.


TREFINASA-SAPREM have a Technical Department specialized in low sag conductor, which principal function is to help in the line engineering. Our Technical Department, after the analysis of the line parameters and the objectives raised by the customer, designs the right conductor and provides a feasibility study on the use of low sag conductor in the line. Similarly, there are complementary additional services like the inspection of conductor installation in the line and the remote monitoring of conductor’s performance.

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