EoW November 2007

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Figure 8 presents a partial view of the processing unit with four optical fibre cables on the left hand side, carrying the data from the FBG temperature and strain sensors and the outgoing RS232 data. The monitoring software runs on any PC and can be adopted to the actual situation or needs. With the data from the weather station sent to the computer, the power line operator gets a comprehensive set of information to manage his lines. 3. Field installation After a simulation of the temperature and strain monitoring system in 2005 which proved the feasibility of the idea, a field installation was performed in April, 2006. The long time between the feasibility study and the field installation was due to the fact of looking for a power line with an already installed OPPC where a Distributed Temperature System (DTS) based on Raman scattering could be implemented.

After finding an appropriate line and a co- operating power utility, the data of the line and the accompanying conditions were: • A 110 kV line equipped with a 243- AL1/39-ST1A phase conductor • Connecting optical underground cable to be blown into a duct between the installation tower and substation building; its length: 1,000m • Installation time for the connecting cable and system: 2 days, with a 4 hour outage time for the line In order to fulfill the electrical requirements for the separator, a 123 kV, pollution class IV, T-branch type with a total height of 1.83m and a weight of 33kg was selected. Normally, a separator used on an OPPC line is completely installed on site. But because of the tough time schedule and the sensible work of inserting the FBG sensors into the jumper cables, the jumpers including the separator fixing clamps were already assembled in the plant. The underground cable blowing was arranged for the first day; that left the second day for the rest of the installation: • final assembly of the separator including all splice works and its fixing on the tower

Figure 5 : FBG strain sensor attached to clevis strap

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Figure 6 : T-branch separator

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Figure 7 : Autonomous, wireless weather station

Figure 8 : Signal processing unit

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The electrical current flow is ensured by using appropriate clamps at the entries and a solid aluminium cup. Short-circuit tests as well as permanent current tests have proven the capability and reliability of the design. 2.3.4 Weather station In order to complete the monitoring system and to get the relevant environmental data, a small weather station was added. It is independent of a power supply, energised by a solar panel. Figure 7 shows the weather station mounted on the tower top. The data, air temperature, humidity, wind speed and direction is transferred to the control computer via a wireless connection. 2.3.5 Data processing and control unit In order to use the FBG sensors for a monitoring system controlled by an ordinary PC, their wavelength coded optical signals have to be converted into a data stream. Two steps are necessary: first an optical to electrical conversion and finally an A/D conversion. The outgoing data is transferred to a PC via a serial RS232 interface. The whole µ-processor controlled unit fits into a 19" rack for indoor use or can be delivered in a robust case for outdoor use.

Figure 9 : Completely assembled separator prior to lifting ▼

Figure 10 : Separator top – details of cable entries

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EuroWire – November 2007