Impact Factor Identification for Switching Overvoltage in an Offshore Wind Farm by Analyzing Multiple Ignition Transients

This paper investigates the impact factors of switching transient overvoltage (SOV) in an offshore wind farm (OWF) by analyzing multiple ignitions of a vacuum circuit breaker. The statistical features of transient overvoltages, which occur under real switching operation scenarios, are analyzed based on the measurements in a laboratory platform that is built according to the configuration of an actual OWF. Next, an OWF simulation transient model is established considering high-frequency characteristics of circuit breakers, which is verified to be able to calculate the SOV accurately. Based on the developed OWF simulation model, the occurrence mechanism of SOV is discussed in detail by studying characteristics of transient voltage and current during multiple ignitions within a vacuum circuit breaker when it is switched OFF. Then, the key impact factors of switching- OFF induced overvoltage are identified, which include the inter-phase capacitance of cable in a windmill tower, the actual operating capacity of a wind turbine generator, and the single-phase inlet capacitance in terminals of a wind turbine transformer. Finally, the recommended configurations are given for the transient mitigation in an OWF.