Synchronous Generator Stator Research Articles

Influence of Temperature on Brushless Synchronous Machine Field Winding Interturn Fault Severity Estimation

There are numerous methods for detecting interturn faults (ITFs) in the field winding of synchronous machines (SMs). One effective approach is based on comparing theoretical and measured excitation currents. This method is unaffected by rotor temperature in static excitation SMs. However, this paper investigates the influence of rotor temperature in brushless synchronous machines (BSMs), where rotor temperature significantly impacts the exciter excitation current. Extensive experimental tests were conducted on a special BSM with measurable rotor temperature. Given the challenges of measuring rotor temperature in industrial machines, this paper explores the feasibility of using stator temperature in the exciter field current estimation model. The theoretical exciter field current is calculated using a deep neural network (DNN), which incorporates electrical brushless synchronous generator output values and stator temperature, and it is subsequently compared with the measured exciter field current. This method achieves an error rate below 0.5% under healthy conditions, demonstrating its potential for simple implementation in industrial BSMs for ITF detection.

Research on the Vibration Characteristics of Pumped Storage Unit Stator Core Based on Fiber Optic Sensing

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.

Experimental results and technique evaluation based on correlation function for a backup protection of synchronous generator stator windings

Unbalanced loads and faults cause power quality problems in power grids, which may lead to system elements failure, particularly to synchronous generators. Faults detection and identification of the disturbance severity level are essential in the grids. Important equipment are often protected with dual protection systems. A backup protection operates and trips appropriate circuit breaker(s) only if the main protection fails to detect the disturbance presence or miss opening the breakers. This paper proposes a backup protection scheme for detecting and evaluating the disruption severity of voltage and current signals for protecting the synchronous generators. This scheme is based on a numerical technique of correlation applied for the electrical signals to detect and assess the fault situation. Different fault types are experimentally conducted on a motor-generator set to test the proposed algorithm effectiveness using Data Acquisition Card (DAC) and LABVIEW software. The scheme has proven to be successful for fault detection and assessment. The algorithm has shown high reliability at various faults and operating conditions. Moreover, the practical results reveal that the scheme is able to evaluate the severity degree of disturbances/unbalances, and it is effective and secure considering the acceptable overloading, harmonics and temporary faults in power grids.

Determination of the Leakage Reactance of End Windings of a High-Power Synchronous Generator Stator Winding Using the Finite Element Method

The paper presents a description of the method and the results of calculating the leakage reactance of high-power synchronous generator end windings using the finite element method. This reactance is one of the components of the stator leakage reactance of synchronous generators. The calculations were carried out under the assumption of a three-dimensional field distribution in a synchronous generator. The thus calculated value of the leakage reactance of the end windings was compared with the calculation results obtained using traditional, analytical formulas known from the literature. The analysis of the influence of the reactance value of the end windings on the transient waveforms at a three-phase short-circuit of the stator windings was performed based on a two-dimensional field-circuit model.

Multiobjective Design Optimization of Stator for Synchronous Generator Using Bat Algorithm and Analysis of Magnetic Flux Density Distribution

— In this study, we aimed to optimize 3000 kVA synchronous generator (SG) stator design to obtain the desired magnetic flux density distribution and efficiency. We used Maxwell simulations for experiments on some design parameters of stator (slot height and teeth width). Then second-order regression models are calculated that represent the relations between the factors (design parameters) and the measured performance criteria (called as the responses: stator-teeth flux density, stator-yoke flux density, and efficiency). These regression models are used at the multiobjective optimization phase. Bat algorithm (BA) is used for performing the multiobjective optimization. By combining Maxwell with regression modeling and BA, the efficiency of the SG is increased to 96.84% from 96.5% with a more acceptable magnetic flux density (between 1.65 and 1.70 T ranges). The stator-teeth flux density and stator-yoke flux density are calculated as 1.9 T and 2.07 T for the current SG, whereas these values are reduced to 1.647 and 1,634 T, respectively, for the optimized SG. Results of this study show how the numerical simulation can be successfully combined with the BA to improve the efficiency of the SG by providing the desired magnetic flux density distribution.

Application Features of Thyristor Regulators to Control the Light Flux in Industrial Fishing

To control the intensity of the light flux when fishing saury it is necessary to widely change the voltage of the lighting fishing equipment. It is reasonable to carry out this by controlling additionally installed thyristor regulators supplying individual symmetric three-phase groups of light sources that will ensure balanced loading of the synchronous generator stator windings. In this research the features of using a thyristor voltage regulator in a four-wire system of ship power supply are studied based on mathematical analysis, conclusions are made using computer modeling and the use of current limiting reactors is justified.

Neural Network Based Fault Detector and Classifier for Synchronous Generator Stator Windings (Dept.E)

This paper presents an application of multilayer feedforward neural network (MFNN) as a differential protection for synchronous generators. Two MFNN are designed, trained, and tested in this paper. The first one has two outputs which detect the internal and external fault state. The other neural network has four outputs to classify the faulty phases. The proposed neural fault detector and classifier were trained using various sets of data available from a selected synchronous model and simulating different fault scenarios (fault type, fault location, fault resistance and fault inception angle). The results show very good behavior of the MFNN and it was more reliable and accurate than conventional methods. It shows that MFNN offer the possibility to be used for on line synchronous generator protection and give satisfactory results.

Permanent magnet synchronous generator stator current AM-FM model and joint signature analysis for planetary gearbox fault diagnosis

Wind energy is renewable and wind power generation facilities have been growing rapidly around the world. Permanent magnet synchronous generators (PMSGs) and planetary gearboxes are commonly used in wind turbines (WTs). For planetary gearbox fault diagnosis, PMSG stator current signal analysis provides a potential alternative approach because stator current signals contain fault signatures with easier accessibility comparing to conventional vibration signals. Planetary gearbox faults result in PMSG input torque oscillations, leading to both amplitude modulation and frequency modulation (AM-FM) effects on stator current signals. To better reveal gear fault features in PMSG stator current signals, this paper proposes to diagnose planetary gearbox faults from three complementary analysis results of the PMSG stator current, i.e., Fourier spectrum, amplitude demodulated spectrum and frequency demodulated spectrum. For this purpose, an AM-FM current signal model is derived through mechanical-magnetic-electric interaction analysis. Explicit equation of Fourier spectrum is derived with its sideband characteristics investigated. Both amplitude and frequency demodulation analyses are proposed to compensate for or mitigate the difficulty in the intricate sideband analysis of Fourier spectrum. Due to its capability in signal mono-component decomposition for accurate estimation of instantaneous frequency, adaptive local iterative filtering is utilized in frequency demodulation analysis. Explicit equations of corresponding demodulated spectra are derived, and gear fault signatures in PMSG stator current signals are revealed. The theoretical derivations and proposed methods are validated through lab experiments by diagnosing localized faults on the sun, planet and ring gears.

Recurrent Neural Networks Based Fault Detection for Synchronous Generator Stator Windings Protection. (Dept. E.)

This paper presents a proposed approach for fault detection and faulty phase(s) identification for synchronous generator protection-based om artificial neural networks. In order to perform this approach: the protection system is subdivided into different neural network modules for fault detection and classification. The proposed approach uses Recurrent Neural Network (RNN) to detect and classify the synchronous generator internal faults. The RNN uses the three-phase current measurements from both sides of the synchronous generator stator winding as its input data. RNN was trained using various sets of data available from the simulation results of the selected synchronous model under different fault scenarios (fault type, fault location, fault resistance and fault inception angle). Simulation results of the proposed RNN based synchronous generator stator winding protection provide a great performance; in terms of accuracy, speed and reliability.

Practical Implementation and Testing of RNN Based Synchronous Generator Internal-Fault Protection

Background: Differential relay is normally used to detect faults in Synchronous Generator (SG) stator windings. Nevertheless, detection of ground fault depends on the generator grounding type. For high impedance grounding, the ground faults near the neutral terminal of the stator windings are not detectable by the differential relay. So, the ability to identify the internal fault of SG is a very important task for stable and safe operation of power systems. Methods: Accurate algorithms for fault detection and classification based on Recurrent Neural Network (RNN) are suggested in this paper. RNNs are trained using different data available from SG MATLAB/ SIMULINK model. Simulation of different fault scenarios based on LabVIEWTM program is discussed. The studied fault scenarios include; fault type, location, resistance and fault inception angle. The RNN based algorithm is experimentally tested using an actual SG. Practical design and implementation of the proposed fault detector and classifier are presented. The hardware system is designed and built to acquire the currents at both ends of SG terminals. Results: The presented results confirm the effectiveness of the proposed algorithm to detect minor ground faults near the neutral terminal (less than 5% of stator winding). Conclusion: The experimental analysis shows that the proposed RNN detects and classifies the internal faults correctly, fastly and remain stable after the faults occur.

An Artificial Neural Network Based Digital Differential Protection Scheme for Synchronous Generator Stator Winding Protection

This research depicts another artificial neural network (ANN) based digital differential protection scheme for generator stator winding protection. The scheme incorporates two feedforward neural networks (FNNs). One ANN is utilized for flaw recognition and the other is utilized for inward deficiency

Application of GEP to investigate the imbalance faults in direct‐drive wind turbine using generator current signals

This study proposes a novel wind turbine generator (WTG) imbalance fault classifier using gene expression programming (GEP). Proposed GEP fault classifier is able to achieve very high classification accuracy with relatively small number of samples. Ours is a first attempt at designing a WTG imbalance fault identifier using GEP for fault segregation. The identifier does not assume prior knowledge of WTG model. Raw current data of permanent magnet synchronous generator stator side are processed through empirical mode decomposition to generate 16 intrinsic mode functions or IMFs. Classifier employs the J48 algorithm to further prune these 16 IMFs to eight most relevant input variables which serve as inputs to the GEP imbalance fault classifier. The authors compare performance of the proposed GEP classifier with other contemporary artificial intelligence (AI) based classifiers such as neural networks and support vector machines. Simulation results and performance comparison against other AI approaches elucidate that the proposed GEP-based identifier could serve as an important tool for WTG fault diagnosis.

A novel protection scheme for synchronous generator stator windings based on SVM

This paper proposes a novel scheme for detecting and classifying faults in stator windings of a synchronous generator (SG). The proposed scheme employs a new method for fault detection and classification based on Support Vector Machine (SVM). Two SVM classifiers are proposed. SVM1 is used to identify the fault occurrence in the system and SVM2 is used to determine whether the fault, if any, is internal or external. In this method, the detection and classification of faults are not affected by the fault type and location, pre-fault power, fault resistance or fault inception time. The proposed method increases the ability of detecting the ground faults near the neutral terminal of the stator windings for generators with high impedance grounding neutral point. The proposed scheme is compared with ANN-based method and gives faster response and better reliability for fault classification.

Electromagnetic Vibrations of Hydropower Generator Stator Core and Transformer Core at 100 Hz Frequency

This paper aimed to compare obtained results and collected theory for 100 Hz frequency vibration of hydropower generator stator core and transformer core. Electromagnetic vibration with 100 Hz frequency occurred both at slow-speed salient poles synchronous generator stator core and oil-filled power transformers tank, but the nature of hydropower and transformer 100 Hz vibration was different. The vibration analysis procedure and acceptable limits for hydropower generator stator core were already covered in the standards, while the health grade system for vibration measurements of power transformer has not beet yet developed. This study discussed the experimental results aiming to extend the knowledge about reasoning for non-existing statistical health grade system, based on power transformers vibrations, measured on tank. The experimental results of hydropower generator stator and power transformer spectrum were reported. Two salient pole hydropower generator stators and four transformers with different construction (including shell-type) and different cooling system (including air forced cooling system) were chosen to present vibration spectrum results. It was demonstrated that increasing clamping pressure of the core does not always reduce 100 Hz harmonic component neither for hydrogenerator stator, nor for transformer. Bad clamping pressure and defects in core, in contrary, will not result into increase of 100 Hz component for some units. Results showed that air forced cooling equipment (fans) would not add higher harmonics to vibration spectrum of the power transformer tank. It was shown that the shell-type construction of transformer core would not necessarily result in high vibration values on tank.

PARALLEL UNIT-CONNECTED GENERATOR MODEL FOR THIRD HARMONIC STATOR GROUND FAULT PROTECTION

Conventional ground fault protection schemes can be applied for any generator terminal connection but it covers at most 95% of generator stator length. 100% protection for synchronous generator stator winding can be achieved by a combination of zero sequence and third harmonic protection schemes. The implementation of the third harmonic scheme on any generator is determined by magnitude of third harmonic voltage produced in the generator. The methods of connecting the generator terminal also influence the range of third harmonic voltage at the stator terminal and neutral. An investigation into the compatibility of particular generator configuration with the third harmonic scheme is important to prevent protection mal-operation since the scheme is hampered in performance by certain factors which include grounding method employed and generator terminal connection among others. In this paper, the modelling of parallel unit-connected generators of the second order is presented to study the influence of parallel unit-connected generators on third harmonic stator ground fault protection. Application of mesh analysis method to the circuit models produced ordinary non-linear algebraic equations. The equations were solved using Cramer’s rule. Simulations of the circuit models were performed for no-load, light load and full load conditions using MATLAB/SIMULINK to study the character of third harmonic voltage at stator neutral and terminal when a ground fault occurs to validate the results of the models. Introduction of a ground fault at the neutral point of the single generator showed that the third harmonic voltage decreased towards zero at the neutral but increased towards maximum at the terminal.

Synchronous generator stator protection using a fuzzy logic-based voltage-controlled overcurrent protection scheme

Summary The most common protection scheme for synchronous generators against stator windings fault is the differential protection scheme. In this paper, a new voltage-controlled overcurrent protection scheme is proposed as a backup protection method for the differential protection method. This scheme is designed to operate in conditions in which differential protection fails to do so and is implemented by fuzzy controllers. The fuzzy controllers set the plug setting of the overcurrent relay. In the proposed method, the fault conditions can be determined regardless of variations of voltage and the current of terminal in different operating states of the synchronous generator. This is realized by measuring not only the terminal voltages and currents of the generator, which are usually used in conventional voltage-controlled overcurrent protection schemes but also other variables that promote the accuracy of the proposed scheme. For presenting this protection method, a synchronous generator with internal fault model is used. The fault model is based on the direct-phase representation that uses the conventional and readily available machine data. Simulations for various types of stator faults of synchronous generator validate the proposed method. Copyright © 2013 John Wiley & Sons, Ltd.

Synchronous Generator Model with Nonlinear Magnetic Circuit

A synchronous generator with voltage controller is a system whose work describes the ordinary differential equation set for the equivalent circuits. For the nonlinear magnetic circuit of a synchronous generator (stator and rotor saturation) the differential set is nonlinear. The solution of such a problem needs to develop the appropriate model for numerical simulations of the generator. First of all, the gene rator model type e.g. (1,1), (2,2), (3,3) or other should be chosen. Furthermore, the equivalent parameters for the model of synchronous generator should be chosen. The nonlinearity of magnetic circuit leads to changes of some equivalent parameters and additional numerical computations. There is a numerical program developed in C++ for simulations of transients in order to investigate their sensitivity to generator nonlinearity (saturation effect) and equivalent parameters values. The described program (available at www.elektr.polsl.pl/dspalek/) enables to decide whether the nonlinearity for d/q axis should be taken into account and which equivalent parameter are of high importance. Subsequently, the presented model leads to conclusions on which parameters should influence significantly synchronous generator work in a power system. DOI: 10.12736/issn.2300-3022.2013412 D. Spalek | Acta Energetica 4/17 (2013) | 144–151 1. Synchronous generator model 1.

Approaching the Processes in the Generator Circuit Breaker at Disconnection through Sustainability Concepts

Nowadays, the electric connection circuits of power plants (based on fossil fuels as well as renewable sources) entail generator circuit-breakers (GCBs) at the generator terminals, since the presence of that electric equipment offers many advantages related to the sustainability of a power plant. In an alternating current (a.c.) circuit the interruption of a short circuit is performed by the circuit-breaker at the natural passing through zero of the short-circuit current. During the current interruption, an electric arc is generated between the opened contacts of the circuit-breaker. This arc must be cooled and extinguished in a controlled way. Since the synchronous generator stator can flow via highly asymmetrical short-circuit currents, the phenomena which occur in the case of short-circuit currents interruption determine the main stresses of the generator circuit-breaker; the current interruption requirements of a GCB are significantly higher than for the distribution network circuit breakers. For shedding light on the proper moment when the generator circuit-breaker must operate, using the space phasor of the short-circuit currents, the time expression to the first zero passing of the short-circuit current is determined. Here, the manner is investigated in which various factors influence the delay of the zero passing of the short-circuit current. It is shown that the delay time is influenced by the synchronous machine parameters and by the load conditions which precede the short-circuit. Numerical simulations were conducted of the asymmetrical currents in the case of the sudden three-phase short circuit at the terminals of synchronous generators. Further in this study it is emphasized that although the phenomena produced in the electric arc at the terminals of the circuit-breaker are complicated and not completely explained, the concept of exergy is useful in understanding the physical phenomena. The article points out that just after the short-circuit current interruption by the generator the circuit-breaker (when the GCB has been subjected at the metal contact terminals to the high temperature of a plasma arc, up to 50,000 K) between its opened contacts, there arises the transient recovery voltage (TRV) which constitutes the most important dielectric stress after the electric arc extinction. Since the magnitude and shape of the TRV occurring across the generator circuit-breaker are critical parameters in the recovering gap after the current zero, in this paper, we model, for the case of the faults fed by the main step-up transformer, the equivalent configurations, with operational impedances, for the TRV calculation, taking into account the main transformer parameters, on the basis of the symmetrical components method.

Design of the robust synchronous generator stator voltage regulator based on the interval plant model

In this paper a novel method for the stator voltage regulator of a synchronous generator based on the interval plant mode, is presented. Namely, it is shown in the literature that, in order to design a controller for the first-order compensator, the limited number of interval plants needs to be examined. Consequently, the intervals of the plant model parameter variations used to calculate the four extreme interval plants required for the sequential PI controller design are determined. The controller is designed using frequency-domain-based techniques, while its robust performance is examined using simulation tests.

Laboratory and Field Investigations of Generator Stator Insulation

This Paper presents the condition assessment of synchronous generator stator insulation used in Sri Lankan power stations. The work has three parts i.e. theoretical, laboratory and field investigations. In the first part, theory behind dielectric insulations have been broadly discussed with the aid of different non – destructive test methods used to assess the conditions of the generator insulation. In the laboratory investigations, two naturally wetted asphalt mica, one dry polyester mica and one dry epoxy mica spare stator windings were tested under drying and wetting conditions. The used test methods were DC ramp, time variation resistance (IR), polarization and depolarization current (PDC), frequency dielectric spectroscopy (FDS) and partial discharge (PD) tests and the relationships have been est5ablished among them. In the field investigations, different generators belonging to Ceylon Electricity Board were tested by using DC ramp test. It was found that the DC ramp test, as an easy and simple field test, can be effectively used to investigate the moisture effect on generator insulation.