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Internal faults in synchronous machines. II. Model performance
Abstract
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 presents hurdles in the widespread use of such models. The authors in [17] and [18] proposed a method in which the need for information about the distribution of the windings is eliminated. In this approach, it is assumed not only that the healthy windings create a perfect, sinusoidally distributed MMF, but also that the MMF due to the subwindings is sinusoidal. ...
... Based on the above description, the method of [17] and [18] with certain enhancements is used in this paper to calculate the inductances of subwindings. ...
... Experimental validation of the model is not the focus of this paper; instead, the paper uses the flexibility of this model to validate several protection elements in a new generator relay and provide associated application guidance. (Note that the above techniques and assumptions have been previously validated [10]- [18].) ...
Correct operation of generator protection is critical to avoid forced outages and to minimize damage during internal faults and other abnormal events. Testing security for external faults and system disturbances has been carried out in the past using real-time systems or transient simulation software. Scaled physical models have been employed to simulate internal faults. However, these machines are restricted in the types of faults that can be applied and the variety of systems that can be modeled.
This paper describes a new synchronous generator model that has been developed in a real-time digital simulator. The model can be configured with a wide range of electrical and mechanical parameters and can simulate various types of faults both on the rotor and on the stator.
The paper also describes how the new model was used to validate a new multifunction generator protection relay. The relay incorporates several novel protection elements, so comprehensive validation of these elements was very important. A wide range of faults were applied, including external faults, power swings, stator winding faults, field short-circuits, and faults during static starting.
This paper focuses on stator winding protection for ground faults, phase faults, turn-to-turn faults, and series faults. The performance of the protection was measured for these events. Application guidance for stator ground, split-phase, and negative-sequence directional protection for generators is provided.
... After implementing the winding partitioning, both VBR and direct-phase methods could be used. A partitioned winding direct-phase model, which is given in [19] and [20], is more appropriate for the protection scheme proposed in this paper than the partitioned winding VBR model, which is given in [21]. The reason is that in [19] and [20], the applicable faults are not limited to symmetrical faults. ...
... A partitioned winding direct-phase model, which is given in [19] and [20], is more appropriate for the protection scheme proposed in this paper than the partitioned winding VBR model, which is given in [21]. The reason is that in [19] and [20], the applicable faults are not limited to symmetrical faults. Therefore, in this paper, the machine model is obtained from [19] and [20], and a backup overcurrent protection scheme for the stator winding of a synchronous generator is proposed to operate in conditions that the main protection scheme, which is the high-speed differential protection, fails to operate. ...
... The reason is that in [19] and [20], the applicable faults are not limited to symmetrical faults. Therefore, in this paper, the machine model is obtained from [19] and [20], and a backup overcurrent protection scheme for the stator winding of a synchronous generator is proposed to operate in conditions that the main protection scheme, which is the high-speed differential protection, fails to operate. In this protection scheme, a fuzzy controller is used as the final decision maker and sets the plug setting of the overcurrent relay. ...
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.
... 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.
... To illustrate the process involved in the model development and avoid the use of the machine geometric parameters, which are usually not fully available, the phase domain model developed in [7] is used as a starting point, however, if machine geometric data is available the models in [5], [6] may be used instead. In this model sinusoidally distributed windings are assumed and the system is considered lineal it should be noted that [7]- [8] use only the fundamental component of the magneto motive force (MMF) of the resulting sub-windigs even though spatial harmonics exist as shown in the waveforms of Fig. 2. However, the good agreement with the finite element simulation in [8] gives a strong indication that space harmonics may not impact significantly in the fault current level, as will be shown in comprehensive simulation in section D of this paper. ...
... In this model sinusoidally distributed windings are assumed and the system is considered lineal it should be noted that [7]- [8] use only the fundamental component of the magneto motive force (MMF) of the resulting sub-windigs even though spatial harmonics exist as shown in the waveforms of Fig. 2. However, the good agreement with the finite element simulation in [8] gives a strong indication that space harmonics may not impact significantly in the fault current level, as will be shown in comprehensive simulation in section D of this paper. Voltage equations in the phase frame of reference for a synchronous generator with a two part per phase partitioned stator windings may be expressed as: p abcs abcs s abcs ...
... A single machine connected to an infinite bus through an RL tie-line is used to analyze and compare results between the PD model and the proposed VBR implementation. The machine and tie-line parameters are obtained from [8] and summarized in Appendix V. In order to validate the response of the proposed VBR model, the case used in [8] is reproduced and the results compared. ...
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.
... From the works has been done so far on the subject, experimental tests and extensive time-domain simulation has been of interest [1,2]. Most popular synchronous machine analysis has been established based on a so called two-reaction theory [3]. ...
... Similar cases were investigated considering different time steps and different internal fault locations to compare the proposed method with ATP solution. The fault location has been adjusted to be within the recommended limits in [2] to avoid numerical instability due to small number of turns in one of the sub-windings. Fig. 14 depicts the relative error for varying internal fault locations between ATP and proposed method. ...
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 difficulties and inaccuracies involved in the calculations of loop inductances make this method impractical. Reichmeider et al. [7], [8] considers a two pole, sinusoidally distributed winding. Such windings are hardly ever found in power systems and, hence, it is also limited in application. ...
... In this paper, α has been chosen as π/2. The phase voltages e a , e b , and e c in the pre-fault period are defined as (8) where E is the amplitude of the infinite bus voltage. ...
An accurate determination of internal fault currents is needed for the design of adequate protection schemes for cable-wound high-voltage generators. A model of a synchronous machine in direct phase quantities for an internal single phase-to-ground fault is presented. A single phase-to-ground fault at the first turn near the generator neutral is simulated when the generator is either isolated or connected to a power system network. Simulations are also performed for when a single phase-to-ground fault occurs at different locations along the winding. The simulations are applied on the world's first high-voltage cable-wound generator installed at Porjus, Sweden which is rated at 45 kV and 11 MVA.
... Hence, a comprehensive simulation model is required to analyze the characteristics of such faults and to accurately predict the associated voltage and current waveforms. Several methods for analyzing the effect of internal faults in synchronous generators have been proposed [1]- [7]. Strong space harmonics exist in the air-gap magnetic field and significant time harmonics exist in the phase currents due to the resulting asymmetry in the stator windings. ...
... However, this is correct only when the air-gap field has a fundamental component or if the windings are concentrated. A direct phase representation was also used in [5]- [7], and a unique winding partition technique was employed to analyze internal faults. A winding with an internal fault was divided into two sub-windings, each being treated as an equivalent sinusoidally distributed winding. ...
An improved model for simulating the transient behavior of salient-pole synchronous generators with internal and ground faults in the stator winding is established using the multi-loop circuit method. The model caters for faults under different ground conditions for the neutral, and accounts for the distributed capacitances of the windings to ground. Predictions from the model are validated by experiments, and it is shown that the model accurately predicts the voltage and current waveforms under fault conditions. Hence, it can be used to analyze important features of faults and to design appropriate protection schemes.
... 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.
... Therefore, ignoring higher harmonics will affect the accuracy of the simulation analysis. In [5][6][7][8], the direct domain approach is used for modelling and analysing the internal fault of synchronous machines. The short-circuit winding is divided into two parts: one adjacent to the neutral point and the second adjacent to the load, and assuming that the inductances of fault windings are proportional to the effective turns of windings. ...
Fractional pole‐ratio winding is a new type of AC winding, consisting of coils with different pitches. The application of fractional pole‐path ratio windings in synchronous generators will bring new problems to the modelling and simulation of internal faults. It is important to establish a mathematical model for the fractional pole‐path ratio synchronous generators with internal faults and accurately calculate the fault currents. In this study, the multi‐loop model of fractional pole‐path ratio synchronous generators is first proposed. The method for calculating mutual inductances between stator coils with arbitrary pitch is given, and all the space harmonics, including the fractional ones, are considered in the inductance calculation. In order to improve the simulation accuracy of turn‐to‐turn faults, the effect of core localised saturation is modelled by modifying the air gap function of fault coils. A 300 MW fractional pole‐path ratio synchronous generator is set as an example, and three types of internal faults are simulated. The comparisons of simulation results are made between the multi‐loop model and the finite element model to verify the validity of the multi‐loop model proposed in this study.
... In this case, the differential relay may not operate. The windings subjected to an internal fault are split into two parts with a connection point available for the insertion of fault branches [12][13][14]. To simulate an internal fault, it is necessary to use split-phase winding in the affected stator winding(s). ...
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.
... There have been a lot of researches, including automatic control of voltage and speed of energy transformation in synchronous generators [4][5][6]. The behavior of the alternators feeding the electrical system has a serious effect on the stability of power system in a fault situation [7,8]. Steady state operation of alternators so most important subject to provide the power system stabilization, especially sudden load changes and faults [9,10]. ...
Micro Hydro Power Plants (MHPPs) have become prominent in hydropower plants as a solution to provide the energy demands of the grid. In this study, a new hybrid renewable energy based DC excitation system for synchronous generator in the developed MHPP system is introduced. Proposed hybrid DC excitation system consists of solar&hydrogen energy based power generating systems. Hybrid renewable energy based system is used for the excitation of the synchronous generator in the MHPP test system. The renewables are used as a secondary energy source to provide the excitation current to a synchronous generator that generates energy in MHPP. A photovoltaic (PV) array is used as the main source of excitation, and a fuel cell (FC) stack is used for DC excitation in the lack of sunshine. In the experimental setup, an electrical control card is developed, and a microcontroller is used to perform the proposed excitation system. All experimental results obtained from 5 kW rated power MHHP test system. Experimental results show that the proposed method provides the continuous excitation current, and the operation of the synchronous generator is uninterrupted. The proposed method is also practical and easily implemented for MHPP systems.
... 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]. The reason is that in [7] and [9] the possible occurring faults are not limited to symmetrical faults. ...
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.
... 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. ...
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.
... 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. ...
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.
... 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 this case i n and i m are fictional currents in coil a and i b and i c are currents in normal coils of the machine. The voltage equations of this case are stated according to figure 4 as follow [7], [8]: [ ...
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.
A new internal fault detection and classification technique for synchronous generators is presented. First, the presence of an abnormal/fault condition is detected based on the Negative Sequence Component (NSC) of neutral end current. Thereafter, the internal fault and abnormal/external-fault conditions are discriminated by utilizing the instantaneous phase angle between the NSCs of the terminal voltage and current. Subsequently, the internal fault is classified based on phase angle between NSCs of terminal voltage and neutral end current along with the zero sequence component of the neutral end current. Efficacy of the proposed scheme has been verified on a Phase Domain Synchronous Machine model developed on the Real Time Digital Simulator (RTDS®). The results derived from various fault data sets show that the proposed technique is able to effectively distinguish between internal and external faults including special cases such as current transformer saturation, overloading and unbalance condition. Further, it provides added capability of detecting and identifying inter-turn faults irrespective of the winding configuration of the generator. Comparative assessment of the proposed scheme in terms of detection time and incorporation of different types of faults with the existing techniques proves its superiority.
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.
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.
In order to analyze the fault feature of the field winding inter-turn short circuits, this paper proposed multi-loop mathematical model of turbine generator with field winding inter-turn short circuits fault considering eddy effect of the solid rotor. The inductance related to the field windings was given, the normal and the short circuits fault operation conditions of generator under no load had been simulated based on the model, which was verified by the simulation and the experiment results. A summary of fault features were obtained, such as, the harmonics circumfluence of stator parallel branches emerges and the field current increases gradually to a new constant value under the constant field voltage after the field windings short fault. The model and results provide the theoretic basis for fault analysis and fault diagnosis of turbine generator with field winding inter-turn short circuits.
The power generator is important and precious apparatus in the power system. The protective relay must operate the circuit breaker instantaneously with high sensitivity when the fault occurs in the generator. According to previous research, the fault current of inter-fault in some situation is very large. But on the other faults, the fault current of inter-fault is so small that it is difficult to be identified by relay. The construction of large capacity generators, especially for hydroelectric power generator, is very complicated and differences each other. Besides that the difficulty and complicate exist in the calculation of the fault quantity and analysis of the sensitivity of the protection scheme, the difficulty exists in the verification the correctness of calculation algorithm too. In this paper, it was introduced the researching result about the inter-fault of the power generator both using the methods based on digital simulation and physical simulation. At the end of this paper, the comparison of these two methods was given. It shows the digital and physical simulation modes using in this paper can be used in the works of design, operation and research. (5 pages)
SUMMARY This paper presents a model for the analysis of internal faults of synchronous generators with multiple parallel connection paths for phase. Several kinds of faults between different portions of the stator windings (and ground, if the case) can be described in the subtransient time frame. Data necessary for the model derive from the electromagnetic design of the machine, as well as from details on equivalent parameters of the external grid and from the neutral connection characteristics. Such modeling procedure allows accurate insight of currents in windings and terminals, exploring each possible fault configuration. In the second part of this work, the developed model will be applied to assess the validity and to define possible improvements of conventional protection configurations against internal faults. Copyright © 2013 John Wiley & Sons, Ltd.
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.
Upon occurrence of an internal fault on the permanent magnet synchronous machine (PMSM), the topology of the stator is amended causing structural imbalances due to the change of the connection within the windings. In this work, a state model of internal faults of the PMSM is developed. This model is in the (abc) reference frame. The modeling approach is based on the assumption that each stator phase is replaced by two major and minor sub-windings. This model is used subsequently in the residual generation for diagnosis. The fault indicators are obtained by the projection in parity space and estimated using the Luenberger observer. A scenario of fault inter-turn by the short-circuit occurring between phase (a and b) is validated by simulation.
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.
Inter-turn short circuit of field windings is a common electrical fault of generators. Simulation is an important method of investigating the fault and providing data support for fault monitoring. However, huge numbers of pole pairs and damper loops in large hydro-generators would lead to lengthy calculation time, hindering scientific research and engineering application. To deal with this problem, we analyze a theoretical basis for a damper winding simplified model and then propose an equivalent treatment method. Through the analysis of steady-state current harmonic characteristics of generators with different stator winding configurations during the fault, the simplified models suitable for steady-state calculation are derived from two aspects, namely, additional rotor harmonic current frequency characteristics and the relationship of the amplitude as well as the phase of each branch current of the stator. The calculation and experimental results of the two simplified models are then compared to verify the models’ correctness. A calculation example of the Three Gorges left bank VGS generator shows few deviations between the calculation results of the simplified model and the original model. Moreover, the calculation time using the simplified model is 1/1500 that using the original model, which provides a more effective tool for on-line fault monitoring. Finally, the sensitivity-verification application of the fault-monitoring scheme based on the stator steady-state unbalanced current RMS is depicted. The result shows that the scheme can monitor two-turn short circuits of field windings in the Three Gorges generator and provide high sensitivity.
The inter-turn short circuits fault of field windings is a common fault in generators. According to the multi-loop method of AC machines, this paper proposes multi-loop mathematical model of turbine generator with inter-turn short circuits fault of field windings. Based on the model, the normal operation and the short circuits fault operation of generator with no load have been simulated combining with the actual structure of a 300MW turbine generator. The time-varying mutual inductances between stator and rotor winding are calculated, from simulation results, the field current and stator voltages show the model reasonable under normal operation, After the field windings short faults, the field current increases gradually to a new constant value under the constant field voltage, the transient feature of stator voltage are obtained, which provides the basis for further fault analysis and fault diagnosis of turbine generator with field winding inter-turn short circuits.
The inter-turn short circuits fault of field windings is one common fault in generators. It will cause serious damages if such faults are not handled properly in time?For this reason, according to the multi-loop method of AC machines this paper proposes multi-loop mathematical model of turbine generators with inter-turn short circuits fault of field windings. The inductance parameters are calculated by air-gap permeance method and the calculated wave-form of inductance parameters shows reasonable. Combining with the actual structure of a 300MW turbine generator, the normal rated load operation and the short circuits fault operation of generator have been simulated based on the model. The normal stator winding currents and the fault currents difference in stator winding parallel branches of same phase were obtained. The currents of normal and fault field winding are calculated. The model considers the different structure and the harmonics in air gap magnetic field, which provides the basis for further fault analysis for turbine generator with inter-turn short circuits of field winding.
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
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.
Internal stator winding faults in salient-pole synchronous
machines can cause serious damage to a machine and the system to which
it is connected. Thus, it is highly desirable to be able to accurately
model their transient behaviour and to predict the resulting currents
and voltages in order to develop appropriate protection schemes,
particularly for high power machines. Based on the multi-loop circuit
method, a general mathematical model for a salient-pole synchronous
machine with internal faults is established, and subsequently employed
to simulate both the steady-state and transient behaviour for three
different types of internal fault. Predicted results are validated by
experimental measurements
This paper discusses the set up of a mathematical model of the 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. Moreover, all machine windings supposed to be sinusoidally distributed in space and the system are magnetically linear. With the 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 here. With the data generated by this internal fault simulation model, the protection scheme used for the powerformer can be validated and improved accordingly.
M.T. Holmberg et al. comment on the original paper by P.P. Reichmeider (see ibid., vol.15, no.4, p.380-3, 2000). They briefly mention the rotor d-axis alignment and fault location computation for partitioned windings. The original authors reply to the comments
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
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
This paper discusses application of MATLAB(R)-Simulink(R) to
transient analysis of large synchronous machines, with specific
reference to the analysis of internal faults, and integration with the
computer program GENSIM
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
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
Per-unit systems with special reference to electric machines
- J M Stephenson
Accurate generator modeling for power systems applications
- P P Reichmeider
- D Querrey