Switching operation simulations in a large offshore wind farm with use of parametric variation and Frequency Domain Severity Factor

Transient voltages resulting from switching operations depend on an interaction between the breaker, the transformer, cables and a neighbourhood grid and imply a risk for the transformer and other components. In this paper the Frequency Domain Severity Factor (FDSF) is used to assess the severity of electrical stress imposed on wind turbine transformers by voltage waveforms produced during switching operations. The method is implemented in Matlab together with automatic and systematic variation of parameters. Simulations of a radial energization are performed on a 90MVA offshore wind farm model implemented in ATP-EMTP using standard component models and further validated against measurements. The results show the range of overvoltages on the transformer terminals as well as the corresponding FSDF for all turbines under a number of varying parameters. The maximum FDSF of 1.235 and frequency of 445 kHz has been found on the low voltage side of the transformer at the last wind turbine in the neighbouring radial to the one being energized.