No full-text available
To read the full-text of this research,
you can request a copy directly from the authors.
Partioning of synchronous machine windings for internal fault analysis
Abstract
This paper discusses a technique for partitioning the stator
windings of large synchronous machines, for application to internal
fault analysis, and determining corresponding winding inductances. The
method employs a direct phase representation, which is shown to reduce
to the classical phase representation when the partitioned windings are
collapsed
... The fourth category is based on a suitable and simplified approach which is the partitioning one proposed first in [18] and [19]. This approach consists of subdividing or partitioning the machine windings into two parts. ...
... e s is the rms value of the total phase voltage and r s the total resistance per phase Eqn (18) ia shown at the bottom of the next page. e sa = sin(ω · t): EMF of the total winding of the phase "a," e sb = sin(ω · t − 2π/3): EMF of the total winding of the phase "b," e sc = sin(ω · t + 2π/3): EMF of the total winding of the phase "c" ...
... ft: the percentage of the leakage flux between two coils in different phases under the same pole-pair; ft/10: leakage flux between two subcoils in the same phase. Note that, in the matrix inductance (18), only the mutual inductances between the coils under the same pole-pair are considered. All the other mutual are set to zero because, for a PMSG with surface-mounted permanent magnets, the equivalent air gap is large, and, consequently, the linkage fluxes between the same pole-pair are almost independent. ...
... For modeling the internal fault in these two approaches, a technique for partitioning the windings of each phase should be used. The mentioned technique is provided in [18]. After implementing the winding partitioning, both VBR and direct-phase methods could be used. ...
... In order to apply an internal stator winding fault to the synchronous generator, the windings of each phase are assumed to be partitioned into two windings that are connected in series, and the connection node is considered as the fault location [18]. A fundamental assumption that is made in the partitioning is that all of the machine windings are sinusoidally distributed in space, and the system is magnetically linear, which means that only the unsaturated section of the saturation characteristic of the machine is taken into consideration, and also, magnetic hysteresis effects are negligible. ...
... Because of the assumption that the machine windings are sinusoidally distributed, winding of a single-phase machine is distributed as depicted in Figure 2. Angle α defines the angular location in which the winding is partitioned. Angles γ 1 and γ 2 are the magnetic axis locations of each partitions of the winding [18]. ...
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.
... Muthumuni et al. [4] used the physical arrangement of the conductors, but only the fundamental component of the MMF of the faulted section was considered. Peter et al. [5][6][7] used a straightforward method for partitioning the sinusoidally distributed stator windings. However, the actual stator windings were never perfectly sinusoidally distributed in space. ...
... Coefficients K 0 and K 2 are the machine geometrical constants and can be represented by the machine electrical parameters L md and L mq , as expressed Eqs. (5) and (6) [16] ...
... To calculate the mutual inductances between two arbitrary windings x and y, substitute Eqs. (5) to (8) into Eq. (4). ...
When an internal fault occurs in the lap-connected windings of turbogenerators, the symmetry between the parallel windings is broken, and different currents then flow because unsymmetrical magnetic linkage exists between the stator windings. The aim of this article is to present a real-time simulation model to investigate the internal fault currents in large turbogenerators with lap windings. This model is based on a modified winding function approach, where the machine inductances are calculated directly from the machine winding distribution. The calculation of the machine inductances are made easier by the use of machine electrical parameters instead of geometrical parameters. The simulation results have been obtained for different cases of internal faults. By using simulated internal fault data, a suitable numerical protection scheme for turbogenerators can be developed.
... Because of lack of data on winding distributions, the following example considers the case for initially sinusoidally distributed windings. This sinusoidal winding distribution has been considered earlier by others [5,7,8] and thus the results of the un-faulted case can be cross-checked against these papers. Note that even with this assumption, the faulted windings are no longer sinusoidally distributed, and so the example serves to demonstrate the validity of the proposed approach. ...
... This section compares the approach of this paper with that of others [5,7,8] and then shows real-time simulation results for winding faults. For comparison, the calculated inductances obtained with the proposed method are compared with those from [5,7,8]. ...
... This section compares the approach of this paper with that of others [5,7,8] and then shows real-time simulation results for winding faults. For comparison, the calculated inductances obtained with the proposed method are compared with those from [5,7,8]. To simulate the machine in real time, an embedded approach [1], is used. ...
This paper presents the development of a real-time digital simulator model for the simulation of arbitrary internal faults in synchronous machines. The model is an extension of the embedded phase-domain model of the synchronous machine (1). To represent a fault, the winding or windings involved in the fault are considered as a set of split windings(2,3,4,5) with their terminal nodes connected by a suitable fault impedance (or short circuit), which is switched in when the fault is applied. From the machine and winding geometry, values are calculated for the resulting set of mutually coupled inductances for this new winding arrangement. The proposed method takes into account the actual geometry of the slots and the number of turns in each coil and uses an off- line procedure to obtain the magneto-motive force (MMF) distribution due to each winding for a unit injection of current. This MMF along with the air-gap geometry information is used to calculate the flux linkages, and hence the self and mutual inductances of the windings. Thus in contrast with earlier approaches, it is able to calculate the inductances of the machine when the windings are arbitrary distributed. Since this model is developed for real-time digital simulator, it has the unique feature of being a tool to test the relays designed to protect the synchronous machines from internal faults.
... The fourth category is based on a suitable and simplified approach which is the partitioning one proposed first in [18], [19]. This approach consists of subdividing or partitioning the machine windings into two parts. ...
... ft/10: leakage flux between two sub-coils in the same phase. Note that, in the matrix inductance (18), only the mutual inductances between the coils under the same pole-pair are considered. All the other mutual are set to zero because, for a PMSG with surface mounted permanent magnets, the equivalent air gap is large, and, consequently, the linkage fluxes between the same pole-pair are almost independent. ...
This paper proposes an original, simple and fast permanent magnet synchronous generator model, implemented with a new conception on the graphic interface of Matlab/Simulink environment. The obtained physical model suggests a new way to easily carry out different types of stator faults such as inter-turns short circuit faults, phase to phase faults and phase to ground faults as well as simultaneous multi-faults. This is handled by connecting the two desired points in the stator, on the graphic interface of Simulink, exactly as they can be carried out in the experimental tests. This model has the originality to take into account the arrangement of the stator windings of a multi-pole machine by differentiating between the windings under the same pole-pair and those under different pole-pairs. A comparison between the simulated and the experimental results is done to verify the behavior of the proposed model in both healthy and faulty modes under different operating speeds. The good comparison results lead to validate the correct behavior of the proposed model with a satisfactory accuracy.
... To overcome this shortcoming, the synchronous machine fault representation is carried out in the Phase Domain (PD) [4]. For instance, in5678, partitioning of machine windings is used to calculate the faulty machine inductance matrix in phase domain where a faulted winding is considered to be made up of two sub-windings with the effective displacement of the magnetic axis. Alternatively in91011, the synchronous machine is assumed to be formed from several electric loops and the inductances are calculated on a coil-by-coil basis. ...
... In order to simulate an internal fault, it is necessary to divide the faulty windings. The details of this partitioning can be found in678. An example of partitioning is shown inFig. ...
This paper presents a new approach for simulating the internal faults of synchronous machines using distributed computing and Large Change Sensitivity (LCS) analysis. LCS analysis caters for a parallel solution of 3-phase model of a faulted machine within the symmetrical component-based model of interconnected network. The proposed method considers dynamic behavior of the faulty machine and connected system and tries to accurately solve the synchronous machine’s internal fault conditions in the system. The proposed method is implemented in stand-alone FORTRAN-based phasor software and the results have been compared with available recordings from real networks and precisely simulated faults by use of the ATP/EMTP as a time domain software package. An encouraging correlation between the simulation results using proposed method, ATP simulation and measurements was observed and reported. The simplified approach also enables engineers to quickly investigate their particular cases with a reasonable precision.
... The physical arrangement of the conductors and only the fundamental component of the MMF of the faulted section were considered in [4]. A straight-forward method for partitioning the sinusoidally distributed stator windings was used in [5][6][7]. However, the actual stator windings are never perfectly sinusoidally distributed in space. ...
... The coefficients K 0 and K 2 are the machine geometrical constants and can be represented by the machine electrical parameters L md and L mq , as expressed in Eqs. (5) and (6) [18]: ...
When an internal fault occurs in the wave-connected windings of salient-pole synchronous generators, the symmetry between the parallel windings is broken, and different currents flow in them since unsymmetrical magnetic linkage exists between the stator windings. The aim of this article is to present a model to investigate the internal fault currents in large hydrogenerators with wave windings. This model is based on a modified winding function approach, where the machine inductances are calculated directly from the machine winding distribution, and the space harmonics produced by them are also taken into account. The calculation of the machine inductances are made easier by the use of machine electrical parameters instead of geometrical parameters. The fast Fourier transform analysis of the simulated results has been tabulated for different cases of internal faults. By using the simulated internal fault data, suitable numerical protection schemes for hydrogenerators can be developed.
... In this situation, these highly significant amplitude changes result in insulation degradation and demagnetisation. The matrix of inductance, resistance, and magnetic flux varies according to (18)(19)(20)(21)(22)(23)(24)(25)(26)(27)(28)(29)(30). ...
One of the most common faults in electric machines is a turn‐to‐turn short circuit (TTSC), which may destroy coil insulation and demagnetise the magnet. In addition, the phase‐to‐phase short circuit (PPSC) fault, which can have even more destructive effects than the TTSC fault, is introduced and analysed. The equivalent magnetic network (EMN) method, with high modelling accuracy and a short computation time, is employed for healthy and faulty machines. The current signal under fault conditions is analysed in the dqo frame, showing the presence of the second harmonic component in its waveform. This fault detection index is processed using the signal processing technique of discrete(wavelet transform (DWT). Besides, energy analysis is used to distinguish TTSC and PPSC faults. Finally, finite element and EMN modelling results are compared with the experimental data of the prototyped permanent magnet generator. The results show that the combination of the proposed EMN method and DWT has very good accuracy and speed. Furthermore, the proposed fault detection method remains unaffected by various linear loads with different power factors.
... As a result, the faulty winding is assumed to be made up of two displaced windings. Therefore, it is assumed that the faulty winding is made up of two offset windings, the combined effect being equivalent to that of the original winding under nominal conditions [21] ...
The development of offshore wind farmsaround the world is increasing significantly due to the needto decarbonize electrical energy systems. The implementationof wind turbines with permanent magnet synchronousgenerator (PMSG) in these wind farms is remarkable. Sincewind turbines become more powerful every year, it isimportant to improve maintenance plans and to preventfailures in order to keep reduce downtime. In the case ofoffshore wind turbines, the logistics required to carry outrepairs considerably increase the operating costs. This way,it is important to develop strategies that reduce operation andmaintenance costs and increase the lifetime of the equipment.This work was developed to analyze the main failures thatoccur in PMSG-based offshore wind turbines, and the stateof the art regarding failure modeling and simulation. Themost common and critical faults of the PMSG-based windturbines have been considered, which are usually in thepower converter and in the electric generator. The objectiveis to integrate the analysis into a model of an offshore windturbine and to develop a working digital twin.
... It has a high level of accuracy and is able to consider spatial harmonics and other physical dimensions. However, its long computational time makes it difficult to use it in real-time applications [12,13]. ...
Abstract Operation of Vernier machines is based on flux modulation. They have some advantages including maintaining the rated torque in motor applications and the rated output power in generator applications at low speeds, high torque density and relatively low torque ripple due to their magnetic gear property and fault‐tolerance. In recent years, the motor with various topologies has been developed for different applications. Therefore, analysing and monitoring different faults is essential in the design and implementation stages. This study has two main purposes. First, to introduce an accurate frequency index independent of load variations for detecting the turn‐to‐turn short circuit (TTSC) faults in the stator windings of a permanent magnet Vernier machine. Second, modelling the machine in a healthy condition and in the presence of TTSC faults to investigate its effect on machine performance and output characteristics. An analytical model is presented using the modified winding function theory under the TTSC fault by taking into account the effect of stator slots which enhances the accuracy of the air‐gap permeance function estimation. In the process of calculating the fault index, frequency components of the output characteristics of the machine are obtained from the mathematical equations of the magnetic field. It is shown that the proposed indicators are robust against load variations.
... The modelling and solving of FEM are time-consuming, and the physical meaning of FEM is unclear [6][7][8][9]. In [10][11][12], the LPM is modified to establish a fault model of PMSM. In these models, the phase winding is divided into healthy and fault parts and the influence of each part on performance can be analysed. ...
Owing to its many benefits, including convenient and short computing time, the analytical model (AM) is widely used in the performance analyse of the permanent magnet synchronous motor (PMSM). The existing analytical models based on phase winding cannot sufficiently speculate about the contribution of the coil to the performances of direct‐drive PMSM (DDPMSM) with series coils and multiple branches. Hence, in this work, a novel AM for the DDPMSM is proposed. This model, which is based on the winding sub‐element, can analyse the influence of coil on motor performance. First, the structure and key parameters of the DDPMSM are reported. Second, an inductance matrix, which considers the spatial disposition of coils and the characteristics of large self‐inductance and small mutual inductance, is constructed. Then, the influence of the coil on motor performance is analysed based on the proposed AM. Finally, the results of AM, finite‐element model and experiment are compared. The results validate the correctness of the proposed AM. Furthermore, the proposed AM can speculate about the contribution of a coil in the DDPMSM performances with satisfactory accuracy.
... On the other hand, most of the works that deals with the diagnosis of SG remained restricted to few case's studies of typical failures such as rotating rectifier faults [5], [6], stator windings short-circuit [7], [8], and air-gap's irregularities [9]. Jointly, further research have been interested to the speed control of SG as fundamental subsystem involved in processes of power generation from renewable sources [10]- [13]. ...
In this study, we address the topic of monitoring the drive speed of synchronous generators by time-frequency analysis of electromagnetic quantities available at the machine's outputs. In this regard, after recalling the commonly used techniques to deal with signals of scalable spectral content, we present and discuss the detection of an abrupt variation of the drive speed by suitable processing of load currents. Afterward, we propose an alternative technique based on the instantaneous frequency estimation of the stray flux. Through experimental trials conducted on a laboratory test-rig, the effectiveness of the suggested approach has been assessed under various load conditions, and its performance has been judged against those stemming from load currents processing. Promising results have been concluded in terms of generator speed monitoring by the use of a low-cost noninvasive sensor.
... Two of the most important representations are the Direct-Phase representation and the Voltage Behind Reactance (VBR) representation [4], [5]. A technique, used to implement the internal fault for modeling the synchronous generator, is provided in [6]. A partitioned winding direct-phase model, which is given in [7] and [8], is used for the protection scheme proposed in this paper instead of the partitioned winding (VBR) model, which is given in [9]. ...
A new voltage controlled overcurrent protection scheme is proposed which is a backup protection method for differential protection. This scheme which is realized by fuzzy controllers is considered to be mounted beside a differential protection system, which operates in the cases that differential protection is unable to detect the fault. This novel protection scheme operates by adjusting the plug setting of the overcurrent relay that sends the trip signal to three-phase breaker. In the proposed method fault occurrences can be determined regardless of variations of voltage and current of terminal in different working states of synchronous generator. This is done by measuring other variables than those used in conventional protection methods. To demonstrate the proposed method, a synchronous generator with internal fault model is used. Numerical simulations validate the functionality of this novel scheme under different conditions.
... The physical arrangement of the conductors have been considered (Muthumuni et al., 2001), but only the fundamental component of MMF of faulty section has been used. A straight forward method for partitioning of the sinusoidally distributed stator windings has been used (Reichmeider et al., 2000a(Reichmeider et al., , 2000b(Reichmeider et al., , 2000c. However, the actual stator windings are never perfectly sinusoidally distributed in space. ...
When an internal fault occurs in a synchronous generator, the symmetry between the parallel paths of the winding is broken and different currents flow in them, due to unsymmetrical magnetic linkage between the stator windings. The aim of this paper is to present a simulation model to investigate the effect of internal fault on the parallel path currents of a large synchronous generator using direct phase quantities. This model is based on a modified winding function approach where the machine inductances are calculated directly from the machine winding distribution using machine electrical parameters instead of the geometrical ones. The simulation results for different cases of internal faults in salient-pole and non-salient-pole synchronous machines have been obtained. Salient-pole synchronous generator has wave winding distribution while the non-salient-pole generator has lap winding arrangement. Due to different stator winding arrangements, the two machines have been simulated individually. By using the simulated fault data, a suitable numerical protection scheme for synchronous generators can be developed.
... The steady-state and transient behaviour of large generators have been studied under a variety of representative fault conditions in references [1,2,[7][8][9][10]. Based on the different mathematical models, simulation results have indicated that when an internal fault occurs on a stator winding, not only the airgap field harmonics are very strong, but also fractional harmonics are yielded, except for both odd and even harmonics. ...
This paper proposes a digital computer technique based on wavelet transform for generator incomplete differential protection scheme. Exploitation of the fault-generated high frequency currents, the new scheme can provide fault detection with high sensitivity and is also capable of discriminating between internal and external faults. The effectiveness of the proposed scheme was verified both in the experiment and in the field. The results show that the scheme can detect the generator fault with high sensitivity and selectivity during all operation conditions.
... The study on the dynamics of electric motors began long time ago. But the chaos phenomenon exhibited in induction motors was not introduced until 1989 by Kuroe and Hayashi [88]. After that, the chaotic behavior of PMSM was also investigated based on its dq-model. ...
Faults in engineering systems are difficult to avoid and may result in serious consequences. Effective fault detection and diagnosis (FDD) can improve system reliability and avoid expensive maintenance. FDD is especially important for some special applications, such as Navy ships operating in hostile environments. So far, FDD for nonlinear systems has not been fully explored. There is still a big gap between FDD theories and applications. This dissertation makes an effort to fill the gap by developing an integrated FDD system structure and a series of algorithms for FDD of Permanent Magnet Synchronous Motors (PMSM).
A fault model is proposed for the stator winding turn-to-turn fault of PMSM. The model provides a good compromise between computational complexity and model accuracy and is versatile for both the healthy and the fault condition. Simulation studies demonstrate a good correspondence with both the theoretical analysis and the experimental observations in the existing literature. The model is especially important for the design of model based FDD algorithms.
Based on the fault model, a series of algorithms are proposed for the fault detection and diagnosis of PMSM. Since the reliability of sensors is the basis of FDD and control systems, a nonlinear parity relation based algorithm is proposed for sensor fault detection. The algorithm can successfully detect single faults in the currents and speed sensors. To track the parameter variations, which are symptoms of system internal changes and faults, an adaptive synchronization based parameter estimation algorithm is proposed. Simulation and experimental studies demonstrate that the algorithm can estimate not only constant parameters but also slowly time varying and abruptly changing parameters in a fast manner. Besides the detection of PMSM internal faults, the algorithm can also provide accurate parameters for the sensor fault detection algorithm. Based on the fault data, a Particle Swarm Optimization based fault diagnosis approach is proposed to find the fault location and severity information of a stator winding turn-to-turn fault. Finally, the proposed algorithms are integrated into a general FDD system structure. The integration provides a FDD system with enhanced robustness to system parametric uncertainties, as shown by extensive simulation studies.
... Parameters N 1 , N 2 , γ 1 , γ 2 depend on the location where the short circuit has happened. In [2][3][4][5][6][7][8], the formulations of these parameters have been derived. ...
In this paper, we have modelled a synchronous generator with internal one phase to ground fault and then the performance of this machine with internal one phase to ground fault have been analyzed. The results show that if the faults occur in vicinity of machine's terminal, then we would have serious damages. To protect the machine from this kind of faults we have suggested integrating a SFCL (superconducting fault current limiter) into the machine's model. The results show that the fault currents in this case will reduce considerably without influencing the normal operation of the machine.
... In (5), U is the identity matrix and γ 1 and γ 2 represent the magnetic axis displacement of the equivalent winding with respect to the original axis localization [9], as illustrated in Fig. 1(a). In Fig. 1(b) α represents the angular localization of the fictitious internal node f in the stator winding, with 0<α<π. ...
An internal fault in a synchronous generator produces an effect similar to increasing the number of grouped coils in the stator winding, making it necessary to use additional time-variant inductances to represent the condition, with the ensuing increase in modeling complexity and computation time required for its solution. In this paper, a new model for the simulation of internal faults in synchronous generators is presented. The model is based on the so-called voltage-behind-reactance (VBR) representation, a contemporary reference frame, which has proved to be numerically more efficient than the classical phase-domain model used to study internal faults in synchronous generators; making it a better fit for large-scale, multimachine power systems applications, the long-term objective of this research work. An implementation for electromagnetic transients program (EMTP) type solutions is presented together with a test case where internal faults are applied, producing results that are in close agreement with results available in the open literature. Furthermore, an external perturbation is also carried out and results match exactly those produced by an equivalent VBR implementation.
... N 1 , N 2 , γ 1 and γ 2 are dependent to location of coil short circuit point. In figure 2, if the first component of local distribution for each of independent fictional coil is calculated, the local condition of coils N 1 , N 2 , γ 1 and γ 2 are computed as follow [6]: [ Therefore, the projection of these two components of magnetic axis in equations (10) and (11) along coil c equals: ...
In this paper, the modeling and analyzing of synchronous machines, when the single and double phase internal fault happens is explained. Results show recognition of faults that happen near the center of star connection of winding by means of ordinary traditional protections is very hard. Disability to detect those faults will reduce the usual life and performance of machine. Here, a new method for analysis and evaluating insensible short circuit is shown.
This paper introduces and analyzes the turn-to-turn short-circuit (TTSC) fault and phase-to-phase short-circuit (PPSC) fault in a permanent magnet synchronous generator (PMSG). The analytical equivalent magnetic network (EMN) method is used to model the PMSG under healthy and faulty conditions. This method provides a high modeling accuracy and has a shorter processing time compared to the finite element method (FEM). The faulty current signal in the dqo frame is evaluated, and mathematical relations are employed to demonstrate that the short circuit fault changes the 2
<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">nd</sup>
harmonic amplitude of the current signal. The short-time analysis of the signal amplitude ripple intensity (ST-SARI) method is presented, and the fault index is obtained by extracting signal amplitude in real-time. In addition, this method separates TTSC and PPSC faults. Finally, the FEM and EMN modeling results are compared with the experimental test results of the prototyped PMSG. The results show that the combination of the proposed EMN and ST-SARI methods leads to high accuracy and speed in tracking and detecting faults at different stages of their occurrence.
This paper offers methods to analyze the performance of three-phase synchronous machines operating with an unsymmetrical stator winding caused by cutting out and bypassing coils. The resulting unsymmetrical current distribution in the stator winding tends to produce overheating in parts of the stator and damper windings at full load as well as torque pulsations. Thus, the main objective of this study is to determine the maximal load, under which the unsymmetrical machine may operate without exceeding the permissible temperature limit. Based on the multi-loop method, a mathematical model of a synchronous machine with missing coils in the stator winding is developed. In order to determine the current distribution, the machines' system of differential equations is solved by using a numerical integration method (Runge-Kutta method). As an alternative method, the system of differential equations in the steady state is reduced to a system of algebraic equations, which can be solved with the Gaussian elimination method. Both methods are validated by the measurement results of a 25-kW salient pole synchronous machine. Furthermore, both the circulating current within the parallel branches and the line currents of the different phases as a result of coil or coil group cut-outs are analyzed for a large 41-MW cylindrical-rotor synchronous motor.
A precise simulation of the internal faults of synchronous generators is crucial for the design of the main protection scheme; therefore, an accurate model is necessary. In this paper, based on the circuit-coupled finite element method (CCFEM), an improved model of a synchronous generator with internal faults is proposed, wherein, the localized model of each stator coil is built as per its actual structure. Using this model, the internal fault occurring inside the coil can be accurately simulated, better approximating the location of the actual fault point; thus, the fault currents can be calculated more accurately. The accuracy of the improved model is verified by a dynamic simulation experiment. Moreover, the electromagnetic magnitudes, such as the air gap flux density, fault currents, field current, and all the damper currents are investigated in detail, under fault conditions, thereby, revealing the fault characteristics more clearly and providing a basis for designing protection schemes.
Much attention has been continuously paid on the model development and stability analysis of the doubly fed induction generator (DFIG) widely applied in wind power generation. Similarly, this study develops the form-standardised state-space model in the dq reference frame of the DFIG with stator winding inter-turn fault (SWITF). Compared with those previously developed, it is definitely preferable for the simulation and stability analysis of the DFIG with SWITF due to its standard form. Moreover, for the DFIG with SWITF working in stator-voltage-oriented control frame, the small-signal stability analysis is conducted using MATLAB simulation, yielding the conclusion that SWITF will never eradicate the DFIG's small-signal stability but deteriorate it to some extent. This conclusion is further validated by means of the Lyapunov stability theory. As a kind of contribution of this study, the analytical expressions of the eigenvalues of the DFIG with SWITF are derived. Case study based on an MATLAB/Simulink demo routine is completed to demonstrate the validity of the model development and small-signal stability analysis of the DFIG with SWITF.
A lumped magnetic equivalent circuit model is proposed to predict the electromagnetic performance of an interior permanent magnetic machine under stator inter-turn winding short-circuit fault. The model design takes into account iron core magnetic saturation, magnetic cross-coupling due to rotor saliency, and airgap magnetic circuit optimization. By comparing with finite element method analysis, the model presents appealing accuracy but much less required computation time in predicting machine flux distribution, winding inductance, and electromagnetic torque. These features prove the usefulness to promote MEC model as a convenient tool for machine performance prediction and fault analysis.
In this paper mathematical models for simulating internal faults in powerformer, using direct phasor method, are described. Internal faults are simulated when the generator neutral point is either high resistance grounding or arc-suppression coil grounding. Simulations are also performed when a internal fault occurred at different locations along the winding. Simulation models during single phase-to-ground fault and two phase-to-ground fault are established by a powerformer prototype, and results about the fault currents are given. The fault current (p.u.) of powerformer is much smaller than the same capacity conventional generator.
In order to effectively detect the stator winding inter-turn short-circuit of synchronous generator, the frequency, amplitude and phase of inductive potential in the parallel branches of stator winding and the harmonic characteristics of inductive potential in rotor winding are analyzed based on AC machine winding theory for stator winding inter-turn short-circuit. The fault characteristics of stator winding inter-turn short-circuit and asymmetrical operation of generator are calculated for the fault simulation generator. It indicates that, the change trend of generator field current harmonics, 4 times and 6 times of fundamental frequency of armature current, during stator winding inter-turn short-circuit is different from that during asymmetrical operation. It is proposed to apply the even harmonics of generator field current to distinguish stator winding inter-turn short-circuit from asymmetrical operation. Dynamic simulation is carried out for five fault conditions, which verifies its effectiveness.
The air-gap magnetic field characteristic of the synchronous generator, caused by stator winding inter-turn short circuit fault, was analyzed in this paper with a consideration of the air-gap eccentricity. Then the characteristics of electro-magnetic torque and vibration of generator were obtained, especially the magnitudes and frequency variation of the instantaneous pulse torque. And the characteristic of the 17th and 19th order component of terminal current under this condition was also analyzed by the coupled field-circuit method. Lastly, in the dynamic simulation experiment, the vibration acceleration data in the vertical direction of a 7.5 kVA generator with stator winding inter-turn short circuit fault were acquired, and then these data were analyzed by discrete fast Fourier technique. The results show that the change of the double frequency vibration acceleration is bigger when stator winding inter-turn short circuit faults occur and the 17th and 19th order component of terminal current can be used to detect the dynamic eccentricity of machines with or without internal faults.
This paper investigates the stator winding short circuit characteristics in synchronous generators under rated operating conditions by combing the single-winding analytical method and the finite element method (FEM), which is still the effective method to determine currents and torques under specific fault conditions. Some special measures have to be considered in case of the electromagnetic transient process under the condition of inner faults, e.g., the correct interconnection between sub-strands and the grid is of the particular importance for inner fault simulations. The previous results show that the traditional calculation method based on the equivalent networks fails in case of the inner asymmetry magnetic field. Based on the systematic investigation of a turbo generator with inter-turn short circuits, the results of this paper show the short circuit currents, phase currents, torques and the radial forces have strong correlations with the location and the turn number of faults. In some cases of inter-turn short circuits, the fault currents exceed that of the outer faults. Furthermore, strong radial forces acting on the magnet wheel might lead to the damages of the total shaft train.
A reliable and accurate diagnosis of inter-turn short circuit faults is a challenging issue in the area of fault diagnosis of electrical machines. The purpose of this study is to present a more efficient technique in fault detection and to provide a reliable method with low-cost sensors and simple numerical algorithms which not only detects the occurrence of the fault, but also locates its position in the winding. Hence, this paper presents a novel method for diagnosis of different kinds of inter-turn winding faults in a salient-pole synchronous generator based on changes in the magnetic flux linkage. It describes the influence of inter-turn winding faults on the magnetic flux distribution of the generator. The main feature of the proposed method is its capability to identify the faulty coils under two types of inter-turn winding faults. Also, the occurrence of two other types of faults can be detected by the proposed technique. Simple algorithm, low cost sensor and sensitivity are the other features of the proposed technique. Experimental results derived from a 4-pole, 380V, 1500 rpm, 50 Hz, 50 KVA, 3-phase salient-pole synchronous generator confirm the validity of the proposed method.
For the problem of hydro-generator stator winding internal faults transient current computational, the FEM coupled with electric circuit method, which effectively combined multi loop method and FEM analysis method, was adopted to analyze this problem detailed. SF600-42/1308 large hydro-generator was used as the object of study. In the no-load condition, sudden single-phase and two-phase and three-phase short circuit fault current were calculated, and the results was verified by classical analytic formula method;In the generator with three phase symmetric resistor load condition, turn to turn short-circuit and branch to branch short-circuit and branch to branch short-circuit with different phase transient process were analyzed, and the laws governing the internal faults of the hydro-generator were investigated. The result shows that the position of internal faults and the moment of internal faults occurring have great influence on the current after occurring internal faults. The different faults are also compared to find their influence on the internal faults of generator. It provides the theoretical support for good configuring main protection of hydro-generator.
When an internal fault occurs in a synchronous generator, the symmetry between the parallel paths of the winding is broken and different currents flow in them, due to unsymmetrical magnetic linkage between the stator windings. The aim of this paper is to present a simulation model to investigate the effect of internal fault on the parallel path currents of a large synchronous generator using direct phase quantities. This model is based on a modified winding function approach where the machine inductances are calculated directly from the machine winding distribution using machine electrical parameters instead of the geometrical ones. The simulation results for different cases of internal faults in salient-pole and non-salient-pole synchronous machines have been obtained. Salient-pole synchronous generator has wave winding distribution while the non-salient-pole generator has lap winding arrangement. Due to different stator winding arrangements, the two machines have been simulated individually. By using the simulated fault data, a suitable numerical protection scheme for synchronous generators can be developed.
This paper presents the generator's internal fault modeling and analysis based on the one-machine infinite-bus power system for the simulation of internal faults in a synchronous generator. The model applied is a low-order synchronous generator model, and is based on the so-called fourth-order representation with the mechanical mode from the second-order system and the electrical mode from the second-order system. The test cases for internal faults demonstrates the output waveforms for id, iq, vd, vq, ω, Efd, Vt, Te, ia, ib, ic, va, vb, and vc using the MATLAB tool. Furthermore, the fault perturbations for internal windings and for an exciter terminal are also carried out and are compared by the results of four cases of simulations.
This paper presents a general method based on a permeance network (PN) in order to study stator turn faults in permanent-magnet synchronous machines (PMSMs). This approach includes two main parts: first, static computations are performed to identify the various parameters of a faulty machine. Leakage inductances as well as self and cross saturations are taken into account to improve the results without increasing the CPU time compared to finite element analysis (FEA). Then, a faulty model of the PMSM is used rather than time-stepping finite element method (TSFEM) which requires large CPU time. The model gives dynamical results and it is suitable to studying PMSM's behavior under faults, testing, or investigating fault detection methods under parameter variations. The method can be applied for any type of winding arrangements and different fault configurations. Various comparisons validate the proposed approach to determine precisely the parameters of the PMSM model under turn faults including the saturation effect and leakage inductances.
When an internal fault occurs in the wave-connected windings of salient-pole synchronous generators, the symmetry between the parallel windings is broken, and different currents flow in them since unsymmetrical magnetic linkage exists between the stator windings. The aim of this article is to present a model to investigate the internal fault currents in large hydro generators with wave windings. This model is based on a modified winding function approach, where the machine inductances are calculated directly from the machine winding distribution, and the space harmonics produced by them are also taken into account. By using the simulated internal fault data, suitable numerical protection schemes for hydro generators can be developed.
The parameter waveforms of synchronous generator are related closely to their operating conditions, which can reflect and foresee some certain states or faults to occur in generator. The chaos and fractal theory is used to synthetically analyze parameter waveforms in this paper. The steady and transient process of synchronous generator with internal fault has been investigated based on the rescaled range analysis. Through fractal dimension analysis of the simulative and experimental data respectively, two main useful laws are obtained. Firstly, transient waveform's fractal dimension is a quantitative representation of generator's internal fault type and have great relevancy with its spectrum distribution. Secondly, the steady and transient state fault pattern can be detected by using R/S analysis method to some extent, but it should combine with other method before it can be applied into practice. These results provide new criterions for the protection and fault detection of the generator with internal fault
A new adaptive unit transverse differential protection based on the fault contributed zero-sequence current for the generator is introduced in this paper. The performance of the conventional unit transverse differential protection is usually greatly affected by the unbalanced current. To overcome this disadvantage, the fault contributed zero-sequence current is applied to remove the influence of the pre-fault current. At the same time, analysis results show that the unbalanced current always present the linear relationship with the stator current. According to that, the proposed scheme can change the setting value adaptively, which improves the protection sensitivity for the generator light internal fault. For the external fault, the scheme can enhance the protection reliability because it ensures a high restraint current. The new scheme is developed and the practical implementation of the protection equipment is also demonstrated. The test results show that the proposed approach is successful in detecting the generator internal fault, and could have high sensitivity and selectivity. Copyright © 2007 John Wiley & Sons, Ltd.
Purpose
The purpose of this paper is to describe a systematic investigation of the currents, torques and other electromagnetic quantities in a machine after different short circuits by the means of coupled numerical field and network calculation. The behaviour of a synchronous machine after a stator‐winding fault still is a little known issue. Nevertheless, the occurrence of winding faults can damage the stator winding of the machine severely and may also destroy the whole stator core. Therefore, there exists a strong need for reliable calculation methods for the evaluation of these faults, e.g. the reconstruction of the details of an accident.
Design/methodology/approach
The paper discusses an analytical approach which calculates all possible winding connections when absence of nonlinear material behaviour is assumed and nonlinearity is only considered by adjusting the inductances after solving the differential equations. In the following, a more accurate method is given by the numerical field calculation, considering a two‐dimensional time variant permeability distribution on the cross‐section of an electrical machine.
Findings
First results of transient time‐stepping calculations of short circuits with special respect on winding currents and radial forces on the rotor are presented.
Practical implications
The approach presented in this paper can be applied in the field of R&D for the dimension of electrical machines and its protection system as well as for the investigation of possible sources of an occurred machine failure.
Originality/value
The bulk of publications that contribute to the topic of inner winding faults are comprised of derivations of analytical models with the assumption of linear material behaviour. The paper puts strong emphasis on the consideration of the nonlinearity.
This paper discusses the set-up of a mathematical model of powerformer, a new type of salient pole synchronous machine, for analyzing internal phase and ground faults in stator windings. The method employs a direct phase representation considering the cable capacitance. To effectively implement the internal fault simulation, the magnetic axis locations of fault parts are arranged appropriately. Besides, all machine windings supposed to be sinusoidally distributed in space and the system is magnetically linear. With above-mentioned assumptions, the current equivalent equations, voltage equivalent equations and the rotor motion equations are formed and combined to implement the fault simulations. Simulation results showing the fault currents, during a single phase to ground fault, a two phase to ground fault and a phase to phase fault, are presented. With the data generated by this internal fault simulation model, the protection scheme used for powerformer can be validated and improved accordingly.
This paper presents a novel differential protection of power former, a type of high-voltage graded insulated cable wound generator. The false differential current associated with the distributed capacitance of power former stator windings is analyzed. Based on the investigation results, the winding capacitance can be equivalently arranged on the terminal and neutral of the generator respectively in a reasonable partition. And the phase voltages at the terminals are utilized to estimate the capacitive currents, which can be compensated to improve the sensitivity of the differential protection. Extensive simulation results prove that this compensation scheme can improve the reliability of the current differential protection of power former.
This paper presents a novel differential protection of powerformer, a type of high-voltage graded insulated cable wound generator. The false differential current associated with the distributed capacitance of powerformer stator windings is analyzed. Based on the investigation results, the winding capacitance can be equivalently arranged on the terminal and neutral of the generator respectively in a reasonable partition. And the phase voltages at the terminals are utilized to estimate the capacitive currents, which can be compensated to improve the sensitivity of the differential protection. Extensive simulation results prove that this compensation scheme can improve the reliability of the current differential protection of powerformer
A fuzzy neural network (FNN) based inter-turn short circuit fault detection scheme for generator is proposed. The second harmonic magnitude of field current and the negative sequence components of voltages and currents are used as inputs for the FNN fault detector. The negative sequence voltage and current are obtained from the phase voltages and currents using the symmetrical component analysis method. And the second harmonic magnitude of field current is achieved by the FFT technique. The FNN fault detector with Gauss membership functions is trained off-line using the training data which comes from the Multi-Loop simulation program. The proposed fault detection scheme can perform the inter-turn short circuit fault detection, the fault type classification, and the fault location identification. Experimental results corroborate the effectiveness of the proposed scheme, which is implemented on a TI's DSP.
This paper aims at presenting a method for modeling and simulation of internal single phase-to-ground faults in d-q axis model in stator windings of large synchronous machines. The method of partitioning the stator windings is used in analyzing the internal faults. This Partitioning method, under internal faults determines inductances of the affected windings which, is extended. In this paper, we modeled the machine in d-q axis models under specific conditions by using the obtained inductances and park transformation. The application of this method is analyzing internal single phase-to-frame faults. Finally, this method is simulated to evaluate an internal fault in stator windings.
This paper describes a model of a 75 MVA and 150 kV synchronous machine (powerformer), which can be used to simulate internal fault waveforms for power system protection studies. The method employs a direct phase representation considering the cable capacitance. A method to calculate the inductance and its magnetic axis location of the faulty path is outlined. The machine equations are then solved using a suitable numerical technique. Comparisons are made between the simulated waveforms and recorded waveforms to verify the accuracy of the model
Winding insulation failures within a synchronous generator cause extensive damage and are expensive to repair. The understanding of the machine behavior during internal failures is very important for the full protection of the machine. Within the literature, little is written relating to modeling, analysis, and experimental testing of synchronous generators during internal fault conditions. This paper provides a summary of an experimental approach taken to capture this phenomenon. These results discuss real-time measurements taken during controlled internal faults on a laboratory scale generator. This data were also compared to data recorded by protective relays during an evolving internal insulation failure of a 145 MVA utility generator
This paper describes a mathematical model of a 25 MVA and 78 kV powerformer that can be used to simulate internal fault waveforms for power system protection studies. The machine equations are solved using a suitable numerical technique in MATLAB. Simulation results showing the fault currents, during a single phase to ground fault and a two phase to ground fault, are presented.
The paper describes a mathematical model for the simulation of a 3-phase synchronous machine using direct-phase quantities, thus obviating the need for any transformation. Numerical solution using a digital computer has also been described, and compared with digital simulation in transformed d-q-0- and ¿-Ã-0-axes models of a synchronous machine. The proposed model in direct-phase quantities enables a unified approach to be adopted in the study of both symmetrical and asymmetrical conditions. Since the constraints to be imposed are direct operating conditions, asymmetrical operating conditions can be studied very easily. Modifications required in the model to simulate various types of faults are described. Versatility of the proposed model is illustrated by the study of a single-line-earth fault with single-phase opening and automatic reclosure. It is shown that this type of fault can be studied as simply as, say, a 3-phase fault.
The main and leakage inductances are found from the flux linkages with the short-circuited part of the armature winding. The mutual inductances between the short-circuited part of the armature winding and the remaining part of the armature and rotor windings are proportional to the main inductance. A synchronous machine with a single phase-to-ground fault embracing a number of turns, Nf, can be regarded as an imaginary symmetrical machine having the armature winding with Nf turns in each phase and the same rotor construction as the actual machine. With such a provision, the synchronous and subtransient inductances of a part of the armature winding can be determined by the general theory of a synchronous machine. The damping of harmonic fluxes by currents in the short-circuited rotor winding is taken into consideration by the calculation of the subtransient inductances. The measurements of the subtransient reactances of portions of the armature winding have been performed on a synchronous machine. The calculated subtransient inductances deviate from the measured values; however, they can be used for the internal fault calculations within the permissible engineering accuracy.
An internal fault in the armature winding of a synchronous machine occurs at the breakdown of either the minor insulation (turn-to-turn fault) or the major insulation (phase-to-ground fault). The faulty synchronous machine is represented by an equivalent circuit in three symmetrical components which can be connected to the corresponding network. The fault currents can be calculated from the obtained equivalent network. The calculation of internal fault currents has been programmed for the IBM 7090 digital computer, and the calculated values have been compared with the experimental results.
First Page of the Article
Along with the development of the electric power industry, the
protection for internal faults of large hydrogenerators with
multi-branch and distributed neutral arrangements has become more and
more important. The internal short-circuit current may be several times
larger than the terminal short-circuit current inside the stator
windings, and such strong current could cause severe heat and mechanical
damage. The authors discuss various relay protection schemes for
internal hydrogenerator faults. They briefly describe the multi-loop
method for the analysis of such internal faults
A synchronous machine with a fault in its armature winding may be represented by an equivalent circuit in three symmetrical components. The line and neutral terminals of the equivalent circuit are connected to a system network in each sequence. The fault point of the positive sequence is connected to the neutral of the negative sequence, and so forth, representing a single phase- to-ground, or turn-to-turn, fault. Electromotive forces behind the corresponding reactance are introduced in every branch of the positive-sequence network of the faulty machine and an equivalent electromotive force of the system is considered. The resulting network consists of three loops with four electromotive forces. The calculation of the current flow in this network is programmed for solution on the IBM-7090 digital computer.
For pt.I see ibid., vol.15, no.4, p.376-9 (2000). This paper
applies techniques for analyzing internal phase and ground faults in the
stator windings of large synchronous machines. A variety of internal
fault conditions are considered, with results for a 75% ground fault
presented, along with comprehensive data for a test machine. The
methodology is validated by comparison with results obtained from
independent finite element analyses
This paper discusses the construction of a mathematical model of a
large synchronous machine suitable for analyzing internal phase and
ground faults in stator windings. The method employs a direct phase
representation, and uses conventional, and readily available, machine
data. The methodology was validated by comparison with results obtained
from independent finite element analyses
An internal fault in the armature winding of a synchronous
generator occurs due to the breakdown of the winding insulation. In this
paper, a method for simulating internal faults in synchronous
generators, using direct phase quantities, is described. Simulation
results showing the fault currents, during a single phase to ground
fault and a two phase to ground fault, are presented