This month’s Featured Technical Paper is from the Proceedings of the 2018 International Conference of Doble Clients. The paper is titled: Investigation of Cable Failures at Wind Farms.
Renewable Energy programs have resulted in a huge increase in the number of windfarm projects commissioned over the past decade. Underground cabling is typically chosen within windfarms since it is practical with regards to the dual use of the land and it is aesthetically preferred. The most common circuit configurations comprise of radial feeders from the windfarm substation and daisy chain from one turbine to the next via switches at each step up or kiosk transformer. A feeder (collector cable) may have any number of turbines connected, with the most heavily loaded cable being the section that runs from the substation to the first turbine. This section of the feeder may be several thousands of feet long depending on the substation location and may have one or more joints (splices) in it.
Wind farm collector circuits in the United States comprise mostly of medium voltage cables. They are typically 35 kV rated, XLPE insulated with stranded aluminum conductors, direct buried in the ground. Many of these cable systems have exhibited in service problems and failures which have adversely affected windfarm operating costs and reliability. This paper will review trenching, installation and backfilling along with cable system formation and screen bonding methods. Typical load patterns compared to that of normal T&D cables will also be reviewed. We will look at failure trends and describe the investigation of such failures at two windfarm and provide a summary of the root cause analysis findings. Finally; installation, acceptance and maintenance testing practices will be identified and discussed.
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