Stator-Interturn-Fault Detection of Doubly Fed Induction Generators Using Rotor-Current and Search-Coil-Voltage Signature Analysis

A novel technique for detecting stator interturn faults in a doubly fed induction generator (DFIG) is proposed by analyzing its rotor current and search-coil voltage. So far, fault-diagnostic techniques proposed for stator-interturn-fault detection in DFIGs are based on analysis of stator current or vibration of generator. Results from these methods are ambiguous because they either fail to account for condition when the DFIG is operating under imbalanced load or these methods are based on experimental results alone without any theoretical basis. Our recent observations suggested that harmonics induced in the rotor circuit are very promising in detecting stator interturn faults in DFIGs. Hence, in this paper, an in-depth investigation is conducted to determine the origin of various harmonic components in rotor currents and their feasibility to detect stator interturn faults unambiguously. Detailed analysis is presented, which explains the mechanism by which the stator-interturn-fault-related harmonics are induced in the rotor circuit. The theory is verified with simulation and extensive experimental results. To confirm the feasibility of the proposed technique for detecting stator interturn faults and obtain results on speed sensitivity of fault detection, a prototype of digital-signal-processor-based fault-diagnostic system has been developed, which is capable of producing very fast trip signal in about 2 s.

I. Introduction

Research in the area of fault diagnosis and condition monitoring of wind generators has generated keen interest as the clamor for renewable energy [1]–[5] becomes louder and clearer due to burgeoning oil prices. Wind generators used for high-power range (660 kW to 2 MW) are mainly wound-rotor synchronous generators and doubly fed induction generators (DFIGs) [5]. Normally, 690-V DFIGs are used in this power range and relate to major market share [5]. The need for an accurate condition-monitoring and fault-detection method is high to reduce the operating and maintenance costs of wind energy systems. In particular, with plan of offshore installations, which makes it more inaccessible, it is vital to simultaneously increase reliability and service interval [1].