OTLM sag measurement

OTLM system measures the OHL sag based on real-time inclination and conductor temperature measurements that are combined within a mathematical model. For additional sag accuracy, we are conducting span measurement with a terrestrial laser scanner or total station. For old OHL we also conduct conductor laboratory tests to include accurate conductor technical data (fracture force, elasticity, etc.).

Why do we use inclination, conductor temperature and conductor technical data?

Information gathered only with the mathematical model can be misleading. The mathematical model uses only the ideal elastic flexibility without inner friction. This assumption simplifies the calculation and the OHL span is presented as a free moving conductor, whose length changes in accordance with ambient conditions like gravity, wind, ice, and sun, etc..

By implementing inclination measurements in the OTLM devices, carrying out laboratory tests and using a newly developed mathematical field-tested model, we can produce accurate sag  measurements.

Our new mechanical model takes into account the measured span with all project boundaries. For its calculation, the software uses geometrical parameters between two handles and mechanical characteristics of the conductor. Geometric data, such as span and sag, are then bound to the temperature of the conductor.

Due to the combined inclination and OHL temperature measurements, the OTLM Center can alert the grid operator when freezing rain occurs.

Sag and tension accuracy 

Sag accuracy – conductor diameter/2






Tension – accuracy is less than 1%