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Temperature measurement:

When considering the overhead line safety margins, one of the key information is the conductor temperature. With such information, the operator can monitor when a specific line is approaching its temperature limit. But we must also consider that the same conductor temperature in winter or in summer period reflects the completely different current situation. The current conductor temperature alerts the operator if it is approaching a temperature limit because it considers momentary influences (current, wind, solar radiation, precipitation etc.) that reflect on the line temperature.

OTLM Sag measurement:

OTLM system measures sag based on real-time inclination and conductor temperature measurements combined within a mathematical model. Information gathered only with the mathematical model can be misleading. The mathematical model uses 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. By implementing inclination measurements in the OTLM sensors and using the developed mathematical field-tested model, we have an accurate sag measurement. 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. A mathematical model for the calculation of the geometry of the catenary curve and tensile strength has been developed as a basis for the continuous monitoring of the temperature and conductor inclination.

Required data to define sag:

For accurate sag measurement, OTLM company require site measurements with geodetic instrument (span with OTLM sensors) and conductor technical data. In case, the TSO is conduction site measurements, OTLM will send all instructions on how to perform the measurements.




The relationship between the conductor’s tensile force and sag is crucial for the calculation of the conductor’s expansion (tension) and final length over a constant span distance. The principal is the same as for sag measurement. The only difference is that we require site measurements for the object (highest point) below the overhead line. User can add up to 5 critical points for clearance.

Conductor creep:

Development of sag and clearance opened new possibilities for measuring extension (conductor creep) of the conductor using the OTLM sensor. The OTLM system sensor and the software continuously measure the temperature and angle of the conductor at the place of the attachment and sends the results to the OTLM software – LiMa. Based on the continues measured of inclination and conductor temperature, the software can detect changes in the geometry of the catenary. The OTLM system with computer support continuously records the measured parameters (maximum sending interval is 1 minute) and statistically processes, analyses and compares the current values with statistical data in the past at the same temperature and approximately at the same time with approximately the same current transmission loads. If the newly calculated geometry, and thus the length of the conductor is detected, then the system sends warning to the operator. In this case, it is necessary to perform an on-site check.

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