The online monitoring of inter‐turn short‐circuit (ITSC) faults in excitation windings of pumped storage units is easily affected by static air‐gap eccentricity (SAGE) and armature response, and the ...early fault characteristics cannot be easily identified effectively. To address these problems, this study proposes a frequency‐resolved circulation spectrum (FRCS) fault diagnosis method for ITSC faults in excitation windings. Firstly, the equation for the same phase multi‐branch circulation under SAGE compound ITSC conditions is derived based on the structural characteristics of pumped storage units and electromagnetic induction relations, and obtains the characteristic harmonics of the loop current caused by ITSC faults. Secondly, this study introduces the implementation method of FRCS, considering a pumped storage unit with a generation capacity of 334 MVA as the research object. This study develops a two‐dimensional finite element simulation model, calculates the magnitude of the in‐phase branch circulation at different fault levels, extracts the corresponding time and frequency domain spectrum and FRCS, and verifies the effectiveness of the proposed method based on comparative experiments. Finally, based on the MJF‐30‐6 Synchronous Generator Experimental Platform in the Power System Dynamic Simulation Laboratory, ITSC operation at different fault levels is simulated, and the corresponding in‐phase branch current data are collected for FRCS analysis. The experimental results demonstrate that the method can effectively eliminate SAGE and armature reaction interference, identify early weak ITSC faults and visualise the severity of faults in the form of pixel dots.
Stator core vibration (SCV) response of pumped storage units (PSU) can effectively reflect its operation status and provide reference for excitation winding inter-turn short circuit (ITSC) fault ...diagnosis. Considering that traditional piezoelectric acceleration sensors (PAS) are difficult to be installed on the stator core surface, this study proposes an online monitoring method based on fiber optic vibration sensing (FOVS). Firstly, this study derives the SCV response equations for the normal and ITSC states of the excitation winding, and obtains the vibration characteristic harmonics corresponding to each state. Secondly, a three-dimensional finite element simulation model of PSU with a generating capacity of 278 MVA is built, and the acceleration amplitude and characteristic frequency harmonics of the stator core are calculated to provide a reference for fiber optic vibration detection. Thirdly, this study focuses on the principle of modulation and demodulation of optical phase, builds an optical frequency-domain reflectometer (OFDR) - based FOVS system, and calibrates its sensitivity, amplitude and frequency characteristics as well as the lower detection limit. Finally, FOVS probes are installed on the surface of synchronous generator stator core to capture the vibration signals under different degrees of ITSC, and compared with the collected signals of PAS. The experimental results prove that the proposed method has obvious advantages in vibration monitoring in the low frequency band below 100 Hz.
Because excitation winding short-circuit faults that occur in steam-turbine generator will lead to heavy financial losses, accurately detecting excitation winding short-circuits (EWS) can help power ...generation operations. It can allow them to take timely actions and shorten downtime as well as cut the costs of troubleshooting. This paper introduces a method for detecting EWS faults online using a new detection coil. Here, a large-dimension detection coil is installed inside the generator to span over an iron-core segment in the stator. The even or fractional harmonics induced by the detection coil are used to determine whether an EWS fault has happened, and the short circuit position can also be determined. This method can reveal short-circuit faults that occur in one turn of the excitation winding, and with obviously higher sensitivity.
Different from the induced electromotive force (EMF) in armature winding, the induced EMF in excitation winding is detrimental to the performance of wound field synchronous machines by causing ...unstable excitation field and thus extra torque pulsation and losses. Moreover, it also imposes challenges to machine control, particularly for high-speed operation. This article investigates the induced EMF in the excitation winding of 3-phase non-overlapped stator wound field synchronous machines (SWFSMs). It has revealed that the amplitude of the excitation winding induced EMF is largely dependent on the slot-pole combination. Therefore, with suitable slot-pole combinations, the induced EMF issue will be significantly alleviated by eliminating low-order induced EMF harmonics. Although the excitation winding induced EMF can also be reduced by passive techniques, e.g., optimization and shaping of rotor pole arc, the average torque will be greatly degraded as well. Finally, the finite element predictions are validated by measurements on two prototyped non-overlapped SWFSMs.
In the application of the Superconducting AC homopolar machines(SAHM), HTS exciting windings carry DC currents under external AC magnetic fields, and generally cause dynamic loss and magnetization ...loss, which will deteriorate the stable operation of SAHM. The conductor on round core (CORC) cables is a promising choice for HTS exciting windings because of its high current-carrying capacity with low AC losses and excellent mechanical stability. In this study, the dynamic resistance and magnetization losses of CORC cables carrying a DC current under an AC magnetic field were studied using numerical and experimental methods at 77 K. The numerical methods(3D H homogenization model, 3D T-A full model, 3D T-A homogenization model) were compared with experimental datas to validate them. Subsequently, the current distribution of CORC cables was studied under different working conditions. The effect of weak anisotropy and the shielding effect of CORC cables on dynamic resistance was researched. In addition, the dependence of CORC structure parameters on dynamic resistance and magnetization losses were analyzed, which is very helpful for the engineering applications of CORC cables as the exciting windings in homopolar machine. Besides, The results provide a reference for dynamic loss behaviors in CORC superconductor.
Due to increasing single unit capacity and large-capacity of each pole, the unit volume loss of excitation winding of the pumped storage power generation/motor elevates accordingly, which may give ...rise to the damage of turn-to-turn insulation. When the damage developed to some degree, the turn-to-turn short-circuit and the burned excitation winding can occur, impacting security and stability considerably. To address this problem, the reasonable arrangement of heat dissipation turns in excitation winding is investigated, aiming to improve the cooling capacity. Taking a pumped storage power generator/motor with large capacity of 277.8 MVA (generator condition)/286.4 MVA (motor condition) and rotating speed of 250 rpm as an example, the fluid–solid coupled heat transfer equations are established, and the solution domain, boundary conditions and assumptions are given. Through the comparison and analysis of the calculated results of the temperature parameters of the excitation winding with different cooling structure types, the reasonable structure type is thoroughly investigated. Based on the genetic optimization algorithm, the value scope of
W
parameter related to temperature non-uniformity coefficient, temperature rise of the excitation winding and copper cost is determined, which is taken as the basis for comprehensive judgment. Additionally, the simulation results show good agreement with the measured data validating the theoretical calculation method.
Synchronous generators are important components of power systems and are necessary to maintain its normal and stable operation. To perform the fault diagnosis of mild inter-turn short circuit in the ...excitation winding of a synchronous generator, a gate recurrent unit-convolutional neural network (GRU-CNN) model whose structural parameters were determined by improved particle swarm optimization (IPSO) is proposed. The outputs of the model are the excitation current and reactive power. The total offset distance, which is the fusion of the offset distance of the excitation current and offset distance of the reactive power, was selected as the fault judgment criterion. The fusion weights of the excitation current and reactive power were determined using the anti-entropy weighting method. The fault-warning threshold and fault- warning ratio were set according to the normal total offset distance, and the fault warning time was set according to the actual situation. The fault-warning time and fault-warning ratio were used to avoid misdiagnosis. The proposed method was verified experimentally.
In this paper, the electromagnetic processes in a coreless synchronous machine with a superconducting excitation winding and a stator winding connected by a zero-flow scheme at a skewed rotor axis ...are considered. It is shown that, in conditions of “pure” nutation, the zero flow contours do not function, and this machine operates as an ordinary synchronous machine. In this regard, the moment of nutation is formed due to the interaction of the unperturbed stator current with the perturbed excitation field and is, therefore, dependent on the load angle. When the longitudinal (in the sense of Gorev) current of the stator changes sign, the moment of nutation also changes its sign and can become either stabilizing (reduce the angle of nutation) or destabilizing. The destabilizing nature of the moment of nutation can appear at small load angles. The basics of this machine theory are described.
Purpose
The purpose of this paper is to study the pipe-type electromagnetic induction heating device under power frequency condition.
Design/methodology/approach
To reduce eddy current loss and ...improve heating efficiency, the structure of a pipe-type power-frequency electromagnetic heating device was optimized. Based on the maximum load flow formula, a parallel excitation winding structure is designed, and the distribution of electromagnetic field under four different powers is analyzed by simulation. Four heating modes were proposed according to the structure of diversion ring, inner wall and outer wall. Two heating modes with better heating effect were obtained by comprehensively considering the factors such as magnetic field distribution, thermal power and energy consumption.
Findings
The double-wall structure of the pipe-type electromagnetic heating device can make the heat source distribution more uniform, and the use of power-frequency power supply can increase security, the installation of diversion ring can make the heating more sufficient and the heating efficiency of the two heating methods selected according to the structural performance is more than 90%.
Originality/value
In view of the medium or high frequency of pipe-type electromagnetic heating device, it is necessary to configure high power electronic frequency conversion drive system, and eddy current can only be produced on the tube wall, resulting in uneven distribution of heat sources. A pipe-type power-frequency electromagnetic heating device with double-wall structure was proposed.
