Sagging Line Mitigator (SLiM)

This unique device would replace or work with standard insulated hangers on power transmission towers, to counteract the effect of temperature on the sagging of overhead transmission lines. This allows increased line ampacity (load current capacity) of existing lines during curtailed summer months, reduced tower heights, and/or increased tower spacing. This device will significantly reduce the risk of forest fires and outages caused by sagging lines, increase the efficiency of energy transfer, delay the need for additional line capacity, and delay the construction of new lines.

The design philosophy is: “Because of the unpredictable nature of ambient temperature, elimination of the sag must be accomplished by a device which operates based on the same change in temperature.”

This automatic mechanical device would counteract axial expansion and hence sagging of suspended lines, such as those used in overhead electric transmission lines, due to ambient temperature increases. The device keeps the profile of the line and hence its sag constant and independent of ambient temperature changes. This device works on the same principal as the axial thermal expansion mechanism of the line but reverses its impact on the sag. That is, as ambient temperature increases (or decreases) so does the line length and its sag. The same ambient temperature change will increase (or decrease) the length of an actuator. The change in actuator length is amplified and transferred through a series of mechanical linkages comprising of lever-type devices, cogs, gears, or alike to contract (or extend) the line connections to the device such that the increase (or decrease) in line length is compensated for.

Several concepts are considered for the actuator. One uses a material with a high thermal expansion coefficient and a high compressive modulus of elasticity. Another uses a series of shape memory alloys for response to temperature changes. Yet, another uses an incompressible fluid with a high bulk modulus. Either device can also be “heated” for higher performance by wrapping it in a “heater coil” powered by the magnetic flux of the power line.

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