FEATURE TEST & MEASUREMENT
PREDICTING ICE formation on power lines
deposits on high voltage overhead power line masts may no longer be able to bear the rising weight of the wires and therefore collapse. So, as early as the 1920s, BKW installed sensors to measure the ice load on the transmission lines. This information, along with local weather data, was communicated several times per day back to BKW for action. Over time, the measurement system was gradually improved as new tools became available. The ice load is measured at critical
points using strain gauge sensors attached to the masts.
THE SOLUTION BKW Energie needed a solution that would enable it to not only estimate the potential for ice formation, but also minimise grid disruptions and report them at shorter notice. The basis for this is the measurement of the humidity in the air. To achieve this, a meteorological
When ice forms, the lines are disconnected from the grid and heated to melt the ice. However, not only does disconnecting the lines mean financial loss, but the interruption has to be reported in advance to the grid operator
In the Alps, ice can quickly build up on the high
voltage power lines that transport electricity across Europe. With the reliability of these of the utmost importance, the ability to predict ice formation
allows for preventative steps to be taken prior to a power line failure. To help, a meteorological probe from Rotronic has been selected
W
eather conditions change rapidly in the Alps, and low temperatures
combined with high humidity means ice can quickly build up on the high voltage power lines which transport electricity across Europe. The formation of ice on the power
transmission lines can result in their weight increasing to ten times what it is normally. Although the lines are installed to minimise danger to people, it is possible that a falling chunk of ice could injure or
even kill a person or animal. In addition, the added weight could damage the line. BKW Energie operates transalpine
high voltage lines. When ice forms, the lines are disconnected from the grid and heated with a power of around 50MW to melt the ice. However, not only does disconnecting the lines mean financial loss, but the interruption has to be reported in advance to the grid operator – Swissgrid in Switzerland. In critical weather conditions the ice
probe from the Rotronic HM4 series was installed on two masts, including one on the Grimsel Pass in Switzerland, both with a weather protection shield. The probe is heated constantly which helps to prevent condensation on the sensor in mist. The heated sensor, which is able to reliably measure humidity even during periods of condensation, can be heated to 0.1...10˚C above ambient temperature depending on the setting. Apart from the tensile forces acting
on the wires, weather data at exposed masts is measured and transmitted in real time via the company’s optical fibre cables to its control centre in Mühleberg. BWK decides, together with Swissgrid, when a transmission line is removed from the grid and heated to remove the ice formations, based on current trends and defined limit values for weight, humidity and temperature. The reliability and accuracy of the
measurement data for tensile force, humidity and temperature are therefore of decisive importance. Working closely with BKW, Rotronic facilitated a comprehensive evaluation of the HM4 meteorological probe and shield. The HygroMet4 is suitable for use
The HM4 meteorological probe is heated constantly to help prevent condensation on the sensor
wherever high humidity prevails for a short or long time. In such environments conventional probes can become covered in condensation and may deliver false measured values.
Rotronic T: 01293 571000
www.rotronic.co.uk
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OCTOBER 2015 | INSTRUMENTATION
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