Multiscale Park's Vector Approach for Identifying Early Stator Fault Severity Using MCSA in DFIGs

Early fault detection of Doubly-fed Induction Generators (DFIG) is a key problem for reliable operation of wind power generation. Motor current signature analysis (MCSA) is the most reliable and widely used technique, gaining favor because it is non-invasive. In the initial stage of wind generator fault, the fault characteristic information is weak and easy to be covered by noise and interference signals, which makes early fault detection difficult. In this manuscript, a Multi-scale Park's Vector Approach for early fault severity identification of DFIGs stator based on MCSA is proposed, and features of early weak faults are extracted and enhanced by multi-scale method. In this method, the three-phase current of the generator stator is converted into orthogonal two-phase current by Park's Vector Transform, and then the two-phase current is computed in multi-scale layers to obtain park's current vector trajectories of different scales. Curve fitting is performed for the current vector trajectories of different levels and scales. The stator faults are identified and the severity of the faults is quantitatively evaluated according to the spatial trajectory change of the fitted curve. The proposed method is verified by the experimental data of healthy, 2, 7 and 15-turn stator short-circuit faults of a doubly-fed induction generator. The results show that the Multi-scale Park's Vector Method can not only detect the stator inter-turn fault, but also estimate the severity of the fault, and realize the enhancement of the early weak fault characteristics.

I. Introduction

The operating environment of wind turbines is harsh, and the failure rate is high. Among these components, wind generators are one of the parts with a higher failure rate in wind power plants [1], [2]. According to statistics, the probability of generator failure in wind turbines is about 22.8% [1], while 38% of generator failures are stator winding faults [2]. Interturn short-circuit faults of the stator windings are the main form of wind turbine generator winding faults. They may cause less damage in the early stages for low-turn number winding insulation faults, but if not dealt with in a timely manner, they may evolve into more turns of interturn short-circuit faults, even some irreversible serious faults such as interphase and ground faults, within a very short period of time [2]–[5].