The inter-turn short circuit is a common fault in the synchronous generator. This fault is not easily detected at early stage. However, with the development of the fault, it will pose a threat to the safe operation of the generator. To detect the inter-turn short circuit of rotor winding, the feasibility of identifying the stator branch characteristics of synchronous generator during inter-turn short circuit was analyzed. In this paper, an on-line fault identification method based on Volterra kernel identification is presented. This method uses the stator branch voltage and stator unbalance branch current collected from the generator as input and output signals of the series model. Recursive batch least squares method is applied to calculate the three kernels of Volterra series. When the generator is in normal state or fault state, the Volterra kernel will change accordingly. Through the identification of the time-domain kernel of the nonlinear transfer model, the inter-turn short circuit fault of the synchronous generator is diagnosed. The correctness and effectiveness of this method is verified by using the data of fault experimental synchronous generator.

In order to improve the phenomenon that a traditional phase-locked loop based on a double second-order generalized integrator (DSOGI-PLL) cannot track signal amplitude and phase accurately when the input signal contains DC components and high-order harmonics, the structure of a second-order generalized integrator-quadrature signals generator (SOGI-QSG) is modified. The paper establishes the impedance model considering the DSOGI-PLL structure of the inductor-capacitor-inductor-type (LCL-type) inverter grid-connected system adopting current control measured from the grid terminal in alternating current side, introducing voltage feedback control to enhance the stability of the system. Meanwhile, analyzing the influence of parameters on impedance according to the impedance model established preferable design parameters. The improvement in SOGI-QSG structure is good for PLL to lock the grid voltage phase more accurately and the retrofitting in control strategy based on the impedance is able to uplift the inverter output impedance phase which is conducive to system stability by increasing the phase margin of the system. The simulation in Matlab/Simulink is carried out to verify the effectiveness of the proposed control strategy.

The rotor winding inter‐turn short‐circuit in hydro‐generators has been plaguing power producers in terms of production safety and economy. At present, the fault detection methods for hydro‐generator rotors are offline or complex. To solve this problem, this paper presents the no‐load curve reverse calculation method. The method only requires electrical parameters such as the active power, reactive power, voltage, and current. This method calculates the normal excitation current using the hydro‐generator's electromagnetic relationship and the no‐load curve in the case of saturated operation. It can identify the inter‐turn short‐circuit fault by comparing the difference between the normal calculated excitation current and the measured excitation current. The correctness of this method is verified with an experiment using an actual hydro‐generator of a hydropower plant and a faulty synchronous generator. Based on the no‐load curve method, the rotor inter‐turn short‐circuit fault diagnosis system is developed by the research team. The diagnostic system does not need to increase the new monitoring point of the hydro‐generator by reading the original electrical parameters of the generator to diagnose the hydro‐generator rotor inter‐turn short‐circuit fault online. © 2018 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.

Rotor winding inter-turn short circuit a common fault in hydro-generators. This fault would change the temperature, stress, and other thermal fields of a rotor and threaten the safe operation of the generator. In this paper, the Three Gorges hydro-generator is taken as an example. Mathematical models of three-dimensional temperature field and thermal stress field of rotor magnetic poles are established based on heat transfer theory and solved by finite element method. The temperature field, thermal deformation, and thermal stress distribution of magnetic poles in rotor winding inter-turn short circuit are calculated. On the basis of the calculation, the effects of the different turn numbers and positions of short circuit on the temperature, thermal deformation, and thermal stress of rotor magnetic poles are further studied. It is concluded that the thermal stress of the winding adjacent to the shorted turn would decrease, the thermal stress of the winding farther away from the shorted winding would increase, and so on. The results of this paper can provide references for inter-turn short circuit fault diagnosis and lay a foundation for the further studies of related faults.

The distribution characteristics of fault electromagnetic field and temperature field and the unbalanced stresses on the rotor could be obtained through establishing a three-dimensional model of the rotor and two-dimensional models of the stator and rotor, and respectively solving the electromagnetic field and the temperature field of excitation winding inter-turn short circuit fault by using the finite element analysis method. Two kinds of unbalanced stresses can be respectively equivalent to the unbalanced masses on the rotor surface. The equivalent centrifugal forces as excitation are added into the rotor dynamic equation, and solving the dynamic equation of the rotor by means of Newmark can finally obtain the rotor vibration response. The results show that the fault will cause the changes of amplitude and phase of rotor fundamental frequency vibration. So the amplitude and phase difference of the rotor fundamental frequency vibration can be used as the fault criterion in order to make an accurate diagnosis of excitation winding inter-turn short circuit fault.