Collaborative Fault Handling and Area Identification of Grounding Faults in Distribution Networks With Directly-coupled Renewable Energy Sources

After the integration of direct-connected renewable energy power plants into the distribution network, compatibility issues and internal overvoltage protection challenges arise between the grounding methods of the source and the network neutral points. This presents new challenges for the safe operation of the distribution system and the identification of fault areas. To tackle these challenges, a model of the direct-connected renewable energy inverter unit is established for grid connection. The impact factors of harmonics on the neutral point grounding device are analyzed, revealing the development mechanism of harmonic overvoltage on the neutral point equipment. By constructing a model of the neutral point zero-sequence loop in the source and network sides, compatibility issues during ground fault handling are analyzed, and the reasons for fault arc reignition are elucidated. A method for coordinated processing of single-phase ground faults in distribution networks is proposed. The empirical wavelet transform is used to decompose the neutral point displacement voltage, feeder, and node zero-sequence current to obtain the attenuation direction characteristics of the free components during fault handling. This method enables the perception of ground faults, exclusion of asymmetric interference, and accurate identification of fault feeders and areas under high-resistance grounding faults. A series of simulations show that the method can accurately locate the occurrence of ground faults in feeders and areas when the fault transition resistance is less than or equal to 5 kΩ. In the context of widespread application of smart circuit breakers, this provides a new approach for diagnosing and identifying single-phase ground faults.