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As a research organization we not only implement state-of-the art knowledge but also publish the results in international journals such as IEEE, IREE, etc.
In that respect we participate in all important conferences around the world presenting theoretical and practical results of our work. Below is a list of articles that we published during the last years. In case you are interested in a specific topic, submit the request form to get more information. |
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A NEW METHOD FOR INTER-COIL SHORT CIRCUIT DETECTION IN SYNCHRONOUS MACHINE ARMATURE WINDING
International Review of Electrical Engineering (IREE) (1827-6660) 7 (2012), 6; 6062-6069
Abstract
This paper deals with detection of inter-coil short circuits in the synchronous machine armature winding, for the machines having the armature winding with coils, based on the analysis of the machines magnetic field.
Applying FEM (finite element method) to the generator model, magnetic field wave forms in the machine have been calculated for every point of interest, under correct and faulty conditions. Selection of the stated points has been planned with the intention to reach a correspondence of the points of interest for flux density among the calculated points and points accessible for measuring with Hall sensors in the actual machine. Comparison of results shows changes in magnetic fields in the machine caused by analyzed faults. The results of calculations are confirmed by measurements on a real machine that is altered in a way that it is possible to simulate inter-coil short circuits of one or more coil turns of the armature winding.
The aim of this study is creation of a contribution to the knowledge portfolio pertaining to detection of rotation machines failures and faults, or, in other words development and improvement of monitoring systems in charge of monitoring and fault detections of rotation machines.
This paper deals with detection of inter-coil short circuits in the synchronous machine armature winding, for the machines having the armature winding with coils, based on the analysis of the machines magnetic field.
Applying FEM (finite element method) to the generator model, magnetic field wave forms in the machine have been calculated for every point of interest, under correct and faulty conditions. Selection of the stated points has been planned with the intention to reach a correspondence of the points of interest for flux density among the calculated points and points accessible for measuring with Hall sensors in the actual machine. Comparison of results shows changes in magnetic fields in the machine caused by analyzed faults. The results of calculations are confirmed by measurements on a real machine that is altered in a way that it is possible to simulate inter-coil short circuits of one or more coil turns of the armature winding.
The aim of this study is creation of a contribution to the knowledge portfolio pertaining to detection of rotation machines failures and faults, or, in other words development and improvement of monitoring systems in charge of monitoring and fault detections of rotation machines.
Air gap magnetic field – key parameter for synchronous and asynchronous machine fault detection
International Review of Electrical Engineering (IREE) (1827-6660) 8 (2013), 3; 1-8
Abstract
Calculations and measurements of a magnetic field at specific places in a machine air gap have been performed in order to determine magnetic field sensitivity to machine geometry and fault occurrence. Installation of measuring coils and a Hall sensor on and around the stator tooth, around stator yoke and the pole shoe has been considered.
Firstly, a series of numerical simulations based on the FEM model were conducted for various positions of the embedded sensors. In order to confirm results of the FEM calculation, measurements on a real machine were performed. There was a good agreement between the results obtained by the measurement and the results obtained by the FEM. Calculations and measurements were conducted for various operating states: idling and rated load, as well as for the normal and faulty state. In this paper it is shown that the machine air gap is a key place for monitoring the magnetic field and a main source of reliable information about a machine condition. It is also demonstrated that the measurement sensitivity to the machine construction effects becomes lower as a distance from the air gap increases. The best measurement sensitivity has been obtained by monitoring a flux density distribution from the stator tooth. On the other hand, the lowest sensitivity has been obtained with the measuring coil embedded around the stator yoke.
In the case of inter-turn short circuit of the armature winding, results obtained by measuring magnetic field in the air gap from the rotor side were more sensitive to the fault occurrence than those obtained from the stator side.
Calculations and measurements of a magnetic field at specific places in a machine air gap have been performed in order to determine magnetic field sensitivity to machine geometry and fault occurrence. Installation of measuring coils and a Hall sensor on and around the stator tooth, around stator yoke and the pole shoe has been considered.
Firstly, a series of numerical simulations based on the FEM model were conducted for various positions of the embedded sensors. In order to confirm results of the FEM calculation, measurements on a real machine were performed. There was a good agreement between the results obtained by the measurement and the results obtained by the FEM. Calculations and measurements were conducted for various operating states: idling and rated load, as well as for the normal and faulty state. In this paper it is shown that the machine air gap is a key place for monitoring the magnetic field and a main source of reliable information about a machine condition. It is also demonstrated that the measurement sensitivity to the machine construction effects becomes lower as a distance from the air gap increases. The best measurement sensitivity has been obtained by monitoring a flux density distribution from the stator tooth. On the other hand, the lowest sensitivity has been obtained with the measuring coil embedded around the stator yoke.
In the case of inter-turn short circuit of the armature winding, results obtained by measuring magnetic field in the air gap from the rotor side were more sensitive to the fault occurrence than those obtained from the stator side.
An Improved Model of Synchronous Generator Based on Finite Element Method Analysis
Proceedings of the XXth International Conference on Electrical Machines, ICEM 2012, Marseille, France, September 2-5, 2012.
Abstract
Machine, which results in an improved equivalent circuit of such a machine, is presented. Mutual couplings and dependencies of inductance with respect to rotor position are included in the circuit. A method for calculation of reactants of the equivalent circuit, which takes into account the actual form of air gap and MMF, saturation of iron, and their mutual connections, is described. The applicability of the proposed model for computation of static and dynamic states of synchronous machine is proven on an example of a generator.
It is shown that the improved model can be reduced to the standard form by neglecting higher harmonics. The model enables calculation of electrical and mechanical parameters that affect the waveform of output voltage, noise and vibrations, which is especially important in operation of a frequency converter.
Machine, which results in an improved equivalent circuit of such a machine, is presented. Mutual couplings and dependencies of inductance with respect to rotor position are included in the circuit. A method for calculation of reactants of the equivalent circuit, which takes into account the actual form of air gap and MMF, saturation of iron, and their mutual connections, is described. The applicability of the proposed model for computation of static and dynamic states of synchronous machine is proven on an example of a generator.
It is shown that the improved model can be reduced to the standard form by neglecting higher harmonics. The model enables calculation of electrical and mechanical parameters that affect the waveform of output voltage, noise and vibrations, which is especially important in operation of a frequency converter.
APPLICATION OF MAGNETIC WEDGES FOR STATOR SLOTS OF HYDRO GENERATORS
CIGRE Session 2010, Paris, France, 22 - 27 August 2010.
Abstract
The use of slot wedges made of magnetic material in a synchronous and induction motor or generator makes possibility to increase the efficiency of the machine. This paper presents the experiences acquired in design, installation, testing and exploitation of the magnetic slot wedges on two relatively large hydrogenerators of rated output 34 MVA, 10.5 kV, 50 Hz, 187.5 min-1, cos ϕ = 0, 8, vertical form.
The magnetic slot wedges with high mechanical strength and low average permeability of μr = 2.8 are embedded into open stator slots of the hydro generators. The fixation of magnetic wedges in the stator winding slots is described in detail. The data referring to magnetic and mechanical properties of the installed magnetic wedges are presented. With magnetic slot wedges the magnetizing current in excitation winding required to generate the air-gap flux is lower than with non-magnetic slot wedges.
The results obtained in the design stage and the compared to on-site testing results of the generator with non-magnetic wedges and the same generator with magnetic wedges show an increase of efficiency. The surface losses in the generator rotor pole shoe iron were reduced by app. 20% by installing the described magnetic wadges ; whereas the losses in the excitation winding were reduced by app. 8% due to the reduced air gap magnetizing current. In addition, the results obtained by analytical calculation and by measurement of the magnetic wedge influence on generator’s reactances are provided. Due to reduction of excitation current in no-load operation, synchronous reactances in direct and quadrature axis increase by app. 5% in the case of magnetic wedges. If an increase of reactances due to leakage reactance is taken into consideration, the total increase of synchronous reactances is app. 8%.
The use of slot wedges made of magnetic material in a synchronous and induction motor or generator makes possibility to increase the efficiency of the machine. This paper presents the experiences acquired in design, installation, testing and exploitation of the magnetic slot wedges on two relatively large hydrogenerators of rated output 34 MVA, 10.5 kV, 50 Hz, 187.5 min-1, cos ϕ = 0, 8, vertical form.
The magnetic slot wedges with high mechanical strength and low average permeability of μr = 2.8 are embedded into open stator slots of the hydro generators. The fixation of magnetic wedges in the stator winding slots is described in detail. The data referring to magnetic and mechanical properties of the installed magnetic wedges are presented. With magnetic slot wedges the magnetizing current in excitation winding required to generate the air-gap flux is lower than with non-magnetic slot wedges.
The results obtained in the design stage and the compared to on-site testing results of the generator with non-magnetic wedges and the same generator with magnetic wedges show an increase of efficiency. The surface losses in the generator rotor pole shoe iron were reduced by app. 20% by installing the described magnetic wadges ; whereas the losses in the excitation winding were reduced by app. 8% due to the reduced air gap magnetizing current. In addition, the results obtained by analytical calculation and by measurement of the magnetic wedge influence on generator’s reactances are provided. Due to reduction of excitation current in no-load operation, synchronous reactances in direct and quadrature axis increase by app. 5% in the case of magnetic wedges. If an increase of reactances due to leakage reactance is taken into consideration, the total increase of synchronous reactances is app. 8%.
BLACK BOX FOR ELECTRICAL MACHINES
CIGRE Session 45, 2014, Paris, France, 24th to the 29th August 2014
Abstract
This article describes a specific monitoring system for electrical machines, called black box for electrical machines (Electrical Machines Black Box, EMBB).
Detailed analysis about problems of harmful working conditions that can occur on all electrical machines has been made. Based on these data and on measurement and control of various parameters such as voltage, current, temperature, vibration, black box detects and records the following harmful working conditions: asynchronous operation, incorrect synchronisation, significant asymmetry, two-phase operation, run-out (over-sped), overloading, excessive heating of stator iron and/or stator winding, excessive vibrations of the generator housing. In addition to these harmful working conditions, EMBB system records the number of machine starts, which also represents vital information that significantly affects the machine lifetime.
EMBB system is realised as a combination of measurement sensors, programmable processing unit associated with measuring modules and application program that manages the process unit. EMBB modular type design enables additional system extensions.
Calculation of Asynchronous Traction Motor Start Up Characteristics by FEM Method
International Symposium on Power Electronics, Electrical Drives, Automation and Motion
Abstract
2D and 3D calculation of squirrel-cage traction motor start-up characteristics at rated voltage and frequency have been performed by using a numerical FEM based program. From the equivalent circuit parameters, which are obtained by analytical calculation, a simulation of a start-up using an analytical dynamic model was performed. The calculated start-up characteristics of the induction motor have been compared with the measurement results. On the basis of the obtained results, an analysis of rotor skew effect, skin effect and the saturation on the accuracy of the presented calculations have been undertaken.
2D and 3D calculation of squirrel-cage traction motor start-up characteristics at rated voltage and frequency have been performed by using a numerical FEM based program. From the equivalent circuit parameters, which are obtained by analytical calculation, a simulation of a start-up using an analytical dynamic model was performed. The calculated start-up characteristics of the induction motor have been compared with the measurement results. On the basis of the obtained results, an analysis of rotor skew effect, skin effect and the saturation on the accuracy of the presented calculations have been undertaken.
CALCULATION OF SYNCHRONOUS GENERATOR SHORT CIRCUIT CURRENTS BY MEANS OF 3D NUMERICAL SIMULATION
ISEF 2015 - XVII International Symposium on Electromagnetic Fields in Mechatronics, Electrical and Electronic Engineering
Abstract
Salient pole synchronous generator short circuit currents waveform has been determined by means of finite element method calculation. Paper describes the 3D simulation method suitable for analyses of large synchronous machine. The applied method allows fast computations by modeling only one stator stack of the machine. Description of the generator model used for simulations and comparison of calculation and measurement data is presented.
Characteristic features of stator winding bars of the new hydro-generator of power 160 MVA installed in Zakučac HP
CIGRE A1 Colloquium, Sydney 20th - 25th September, 2009
Abstract
A new insulation system made in VPI technology comprising inside protection (screens), up to the nominal voltage of 16 kV (developed on the base of the existing system having the nominal voltage of 13.8 kV), has been applied to new generators of the power of 160 MVA, in Zakučac HPP (foreseen by the refurbishment programme).
This paper gives a brief description of construction of the bar insulation system in the function of a basic element of the stator winding and results of its type testing and main insulation voltage endurance tests achieved by application accelerated aging method. Other tests and inspections of the main insulation are presented as well (geometry of the longitudinal bar cross section and characteristics of the shell removed from bars after application of accelerated aging method). Achieved results of all testing and inspections of VPI insulation system 16 kV as well as operation experiences of application of the system VPI 13.8 kV by the time being show that the recently developed system is going to enable reliable operation with a long life time of the equipment.
A new insulation system made in VPI technology comprising inside protection (screens), up to the nominal voltage of 16 kV (developed on the base of the existing system having the nominal voltage of 13.8 kV), has been applied to new generators of the power of 160 MVA, in Zakučac HPP (foreseen by the refurbishment programme).
This paper gives a brief description of construction of the bar insulation system in the function of a basic element of the stator winding and results of its type testing and main insulation voltage endurance tests achieved by application accelerated aging method. Other tests and inspections of the main insulation are presented as well (geometry of the longitudinal bar cross section and characteristics of the shell removed from bars after application of accelerated aging method). Achieved results of all testing and inspections of VPI insulation system 16 kV as well as operation experiences of application of the system VPI 13.8 kV by the time being show that the recently developed system is going to enable reliable operation with a long life time of the equipment.
CONTEMPORARY APPROACH TO DETERMINATION OF MAGNETIC INDUCTION IN WIND GENERATOR AIR GAP
International conference on renewable energies and power quality, Santander 12-14 March, 2008
Abstract
The paper describes a system for measuring of magnetic induction on the wind generating unit. The manner of operation and the application of the Hall effect probe are detailed. Dynamic electromagnetic field computing results are shown through application of MKE on the synchronous generator model installed in a windmill unit and compared to the actual metering results. Two subsequent magnetic field calculations on the modified model were made to be used for analyses of the obtained results. Influences of air gap forms and saturation to time dependence of magnetic induction at a point within the machine are explained.
The paper describes a system for measuring of magnetic induction on the wind generating unit. The manner of operation and the application of the Hall effect probe are detailed. Dynamic electromagnetic field computing results are shown through application of MKE on the synchronous generator model installed in a windmill unit and compared to the actual metering results. Two subsequent magnetic field calculations on the modified model were made to be used for analyses of the obtained results. Influences of air gap forms and saturation to time dependence of magnetic induction at a point within the machine are explained.
Detection of inter-coil short circuits in coils of salient pole synchronous generator field winding on the basis of analysis of magnetic field in the machine
International Conference on Renewable Energies and Power Quality (ICREPQ'10), 23th to 25th March, 2010
Abstract
This paper deals with detection of inter-coil short circuits in coils of the salient poles synchronous generator excitement winding on the basis of the analysis of the magnetic field in the machine. Applying FEM to the generator model, magnetic field wave forms in the machine, on the points of interests, under both, faultless and faulty conditions were calculated.
When results were compared, changes in wave forms caused by the analyzed fault were identified. On the model, magnetic inductions and magnetic fields were calculated on the points accessible for measuring with Hall’ s sensors and measuring coils in the actual machine. The gold of this paper is a contribution in the field of identification of faults and failures in rotating machines, or, in other words, improvement of monitoring systems in charge of rotating machine condition monitoring.
This paper deals with detection of inter-coil short circuits in coils of the salient poles synchronous generator excitement winding on the basis of the analysis of the magnetic field in the machine. Applying FEM to the generator model, magnetic field wave forms in the machine, on the points of interests, under both, faultless and faulty conditions were calculated.
When results were compared, changes in wave forms caused by the analyzed fault were identified. On the model, magnetic inductions and magnetic fields were calculated on the points accessible for measuring with Hall’ s sensors and measuring coils in the actual machine. The gold of this paper is a contribution in the field of identification of faults and failures in rotating machines, or, in other words, improvement of monitoring systems in charge of rotating machine condition monitoring.
Detection of inter-coil short circuits in synchronous machine armature winding on the basis of analysis of machine magnetic field
XIX International Conference on Electrical Machines (ICEM'10), Roma (Italy), 6th to 8th September, 2010.
Abstract
This paper deals with detection of inter-coil short circuits in the synchronous machine armature winding, for the machines having the armature winding with coils, based on the analysis of the magnetic field present in the machine.
Applying FEM (finite element method) to the generator model, magnetic field wave forms in the machine have been calculated for every point of interest, under correct and faulty conditions. Selection of the stated points has been planned with the intention to reach a correspondence of the points of interest for flux density among the calculated points and points accessible for measuring with Hall sensors in the actual machine. Comparison of results shows changes in magnetic fields in the machine caused by analyzed faults.
The aim of this study is creation of a contribution to the knowledge portfolio pertaining to detection of rotation machines failures and faults, or, in other words development and improvement of monitoring systems in charge of surveillance of rotation machine condition.
This paper deals with detection of inter-coil short circuits in the synchronous machine armature winding, for the machines having the armature winding with coils, based on the analysis of the magnetic field present in the machine.
Applying FEM (finite element method) to the generator model, magnetic field wave forms in the machine have been calculated for every point of interest, under correct and faulty conditions. Selection of the stated points has been planned with the intention to reach a correspondence of the points of interest for flux density among the calculated points and points accessible for measuring with Hall sensors in the actual machine. Comparison of results shows changes in magnetic fields in the machine caused by analyzed faults.
The aim of this study is creation of a contribution to the knowledge portfolio pertaining to detection of rotation machines failures and faults, or, in other words development and improvement of monitoring systems in charge of surveillance of rotation machine condition.
FINITE ELEMENT ANALYSIS OF TURBINE GENERATOR ROTOR WINDING SHORTED TURNS
IEEE transactions on energy conversion (0885-8969) 27 (2012), 4; 930-937
Abstract
Online magnetic flux monitoring via permanently installed air-gap flux probes is a well- established technology to determine the presence of shorted turns in a turbine generator rotor winding. Flux measurements are normally performed using flux probes installed in the machine air gap (on a stator wedge) and connected to portable or permanently installed instruments. In this “flux probe” test, to achieve a reliable diagnostic results, the signal from the flux probe has to be measured under different load conditions ranging from no load to full load. This requirement presents a serious obstacle when applying this method on base load units.
Recently, a new design of magnetic flux probe installed on the stator tooth was implemented. In addition, new algorithms used to analyze measurements using different types of flux probes were developed to minimize the need for tests at different load conditions. A finite element model (FEM) has been created to verify these new algorithms in different loading conditions. Based on this model, and real-world measurements, it has been demonstrated that accurate detection of shorted turns can be obtained without the need to vary the load on the machine if suitable sensors and algorithms are applied. This paper describes the new method and its advantages, comparing results obtained from online measurements on working generators and the FEM created to simulate different rotor conditions.
Online magnetic flux monitoring via permanently installed air-gap flux probes is a well- established technology to determine the presence of shorted turns in a turbine generator rotor winding. Flux measurements are normally performed using flux probes installed in the machine air gap (on a stator wedge) and connected to portable or permanently installed instruments. In this “flux probe” test, to achieve a reliable diagnostic results, the signal from the flux probe has to be measured under different load conditions ranging from no load to full load. This requirement presents a serious obstacle when applying this method on base load units.
Recently, a new design of magnetic flux probe installed on the stator tooth was implemented. In addition, new algorithms used to analyze measurements using different types of flux probes were developed to minimize the need for tests at different load conditions. A finite element model (FEM) has been created to verify these new algorithms in different loading conditions. Based on this model, and real-world measurements, it has been demonstrated that accurate detection of shorted turns can be obtained without the need to vary the load on the machine if suitable sensors and algorithms are applied. This paper describes the new method and its advantages, comparing results obtained from online measurements on working generators and the FEM created to simulate different rotor conditions.
Iterative Procedure for Determination of Synchronous Generator Load Point Using Finite Element Method
XXth International Conference on Electrical Machines, ICEM 2012, Marseille, France, September 2-5, 2012.
Abstract
Periodical changes in the magnetic field of a synchronous generator, and its mechanical or electrical unbalances, have effect on the armature voltage, current and electromagnetic forces. Determination of these values during the design stage of a machine gives insight in its possible operation problems, and enables their easier prevention. Quantities of interest can be determined by using the finite element method calculations. However, in order to obtain data that correspond to real working conditions of a machine, simulations of different operation points have to be done.
The procedure described here provides algorithm for determination of synchronous generator load condition parameters. It relates to symmetrical 3-phase load, it is based on physically measurable values, and can be universally used on any synchronous generator with field winding. This method was applied on a 34 MVA generator and the obtained results show good agreement with the measured data.
Periodical changes in the magnetic field of a synchronous generator, and its mechanical or electrical unbalances, have effect on the armature voltage, current and electromagnetic forces. Determination of these values during the design stage of a machine gives insight in its possible operation problems, and enables their easier prevention. Quantities of interest can be determined by using the finite element method calculations. However, in order to obtain data that correspond to real working conditions of a machine, simulations of different operation points have to be done.
The procedure described here provides algorithm for determination of synchronous generator load condition parameters. It relates to symmetrical 3-phase load, it is based on physically measurable values, and can be universally used on any synchronous generator with field winding. This method was applied on a 34 MVA generator and the obtained results show good agreement with the measured data.
Methods for inter coil short circuit detection in excitation winding coils of turbo generator in operation and in standstill condition
CIGRE Colloquium on new development of rotating electrical machines, SC A1, Beijing, China, 11-13 September 2011
Abstract
Detection of inter-coil short circuits has a significant importance in nowadays diagnostics of rotating electrical machines. In this paper two modern, reliable and economically viable methods for such detection in excitation windings of turbo generator have been described. One can be applied in operation and the other in standstill condition.
First method for detection of excitation winding insulation state at standstill condition is based on impulse voltage test. Test impulse passes through the winding turns and in the case of weak or faulty point in insulation, directly continues through this weak point to the next winding coil turn, coil, group, phase, or if possible to the ground. Inter-coil short circuit between turns reduces inductance of the faulty winding coil, which results with higher oscillating frequency. In that case voltage stress response curves have oscillations that are not identical i.e. fault is present in winding. By combining winding connections and analysis of response characteristics, inter-coil short circuit extent and its approximate location (± 0, 5 m) can be determined.
Second presented method for detection of inter-coil short circuits in excitation winding during generator operation is based on magnetic field measurement in the air gap of the machine. Magnetic field can be measured using Hall sensors or measuring coils fitted on the stator tooth. If an inter-coil short circuit appears in excitation winding, it will cause disturbance of magnetic field in the machine. This change will be seen as localized disturbance in measured magnetic field or flux density waveform. Signal from measuring sensors are collected via analog input modules of adequate monitoring system and process measuring data using algorithm specifically developed for this purpose, based on mathematical model using FEM (finite element method). Monitoring system can provide information weather inter-coil short circuit is present in excitation winding coils and number of shorted turns per coil.
Detection of inter-coil short circuits has a significant importance in nowadays diagnostics of rotating electrical machines. In this paper two modern, reliable and economically viable methods for such detection in excitation windings of turbo generator have been described. One can be applied in operation and the other in standstill condition.
First method for detection of excitation winding insulation state at standstill condition is based on impulse voltage test. Test impulse passes through the winding turns and in the case of weak or faulty point in insulation, directly continues through this weak point to the next winding coil turn, coil, group, phase, or if possible to the ground. Inter-coil short circuit between turns reduces inductance of the faulty winding coil, which results with higher oscillating frequency. In that case voltage stress response curves have oscillations that are not identical i.e. fault is present in winding. By combining winding connections and analysis of response characteristics, inter-coil short circuit extent and its approximate location (± 0, 5 m) can be determined.
Second presented method for detection of inter-coil short circuits in excitation winding during generator operation is based on magnetic field measurement in the air gap of the machine. Magnetic field can be measured using Hall sensors or measuring coils fitted on the stator tooth. If an inter-coil short circuit appears in excitation winding, it will cause disturbance of magnetic field in the machine. This change will be seen as localized disturbance in measured magnetic field or flux density waveform. Signal from measuring sensors are collected via analog input modules of adequate monitoring system and process measuring data using algorithm specifically developed for this purpose, based on mathematical model using FEM (finite element method). Monitoring system can provide information weather inter-coil short circuit is present in excitation winding coils and number of shorted turns per coil.
New Method for Rotor Cage and Winding Fault Detection Based on Machine Differential Magnetic Field Measurement (DMFM)
Abstract
A technical problem solved by this new method (patent-pending) is detection of rotor winding inter-coil short
circuits of synchronous machines and induction machines with slip rings, as well as rupture of one or more rotor bars and cage ring of induction machines. So far, various methods for detection of the above mentioned faults have been developed over the years. This new method enables rotor winding fault detection with much higher sensitivity, which enables more reliable fault detection. In comparison with the MCSA (motor current signature analysis) method, which is the most used method for rotor cage fault detection, according to the available literature, this new method gives 200 times higher sensitivity to fault occurrence.
Method for rotor winding fault detection is based on differential measurement of magnetic field by using two
measuring coils. By measurement of the voltage that is induced in the measuring coils, it is possible to unambiguously detect rotor winding faults. By connecting the measuring coils in series, magnetic field present in the machine without any winding faults is excluded from the measured signal, so that the measured signal depends only on the magnetic field caused by rotor winding fault. That means that measured voltage is approx. zero without a winding fault. If a winding fault appears, increase of measuring voltage is present. Analysis of the measuring signal enables fault detection and also location of the fault. The method is a result of numerous FEM simulations which have been tested in a Laboratory on a real synchronous and induction machine. This patent-pending method is already implemented in three innovative products placed on market, so this method is fully confirmed in practice.
The aim of this paper is to contribute to the knowledge portfolio pertaining to detection of rotating machines failures and faults, or in other words, development and improvement of systems in charge of monitoring and fault detection of rotating machines.
A technical problem solved by this new method (patent-pending) is detection of rotor winding inter-coil short
circuits of synchronous machines and induction machines with slip rings, as well as rupture of one or more rotor bars and cage ring of induction machines. So far, various methods for detection of the above mentioned faults have been developed over the years. This new method enables rotor winding fault detection with much higher sensitivity, which enables more reliable fault detection. In comparison with the MCSA (motor current signature analysis) method, which is the most used method for rotor cage fault detection, according to the available literature, this new method gives 200 times higher sensitivity to fault occurrence.
Method for rotor winding fault detection is based on differential measurement of magnetic field by using two
measuring coils. By measurement of the voltage that is induced in the measuring coils, it is possible to unambiguously detect rotor winding faults. By connecting the measuring coils in series, magnetic field present in the machine without any winding faults is excluded from the measured signal, so that the measured signal depends only on the magnetic field caused by rotor winding fault. That means that measured voltage is approx. zero without a winding fault. If a winding fault appears, increase of measuring voltage is present. Analysis of the measuring signal enables fault detection and also location of the fault. The method is a result of numerous FEM simulations which have been tested in a Laboratory on a real synchronous and induction machine. This patent-pending method is already implemented in three innovative products placed on market, so this method is fully confirmed in practice.
The aim of this paper is to contribute to the knowledge portfolio pertaining to detection of rotating machines failures and faults, or in other words, development and improvement of systems in charge of monitoring and fault detection of rotating machines.
NOVEL PREDICTION TECHNIQUE FOR DIRECT TORQUE CONTROL OF INDUCTION MOTOR
International Conference on Electrical Machines - ICEM 2014, Berlin, 2-5 Sept. 2014
Abstract
A novel prediction technique for the direct torque control (DTC) of an induction motor is presented in the paper. The conventional DTC method selects voltage vectors from switching table. The application of these vectors does not satisfy demands for torque increase or decrease at all operating conditions and is not optimal regarding torque ripple.
The novel prediction technique calculates in every sampling period the torque changes for different voltage vectors and selects discrete voltage vector which results in minimum torque deviation from the reference value. The voltage vector is selected from new switching table and applied for the whole sampling period. In comparison with the conventional DTC method, the novel technique considerable reduces torque ripple in medium and high speed region. Simulation and experimental results for 525kW motor are presented to validate the proposed technique.
A novel prediction technique for the direct torque control (DTC) of an induction motor is presented in the paper. The conventional DTC method selects voltage vectors from switching table. The application of these vectors does not satisfy demands for torque increase or decrease at all operating conditions and is not optimal regarding torque ripple.
The novel prediction technique calculates in every sampling period the torque changes for different voltage vectors and selects discrete voltage vector which results in minimum torque deviation from the reference value. The voltage vector is selected from new switching table and applied for the whole sampling period. In comparison with the conventional DTC method, the novel technique considerable reduces torque ripple in medium and high speed region. Simulation and experimental results for 525kW motor are presented to validate the proposed technique.
shaft current and voltage protection relay
HYDRO 2014 - Building on recent development progress, 13 to 15 October 2014., Cernobbio, Italy
Abstract
The paper deals with the specific protection relay for all types of generators. The instrument, called Shaft Current and Voltage Protection Relay (SCVP) was developed at KONCAR – Electric Engineering Institute Inc. This instrument is a part of Institute's product line used for monitoring and diagnosis of rotating electrical machines.
The most important parts of every electric power system are electrical rotating machines, especially those involved in the production of electrical energy. Nowadays, electrical rotating machines must fulfill more complex requirements of electrical power system which are constantly increasing and at the same time the production of electrical energy must be optimized. On the other hand, long lifetime and increased reliability of the machines is expected. Various monitoring and protection systems represent solutions for owners of expensive electrical machines and they can enable better asset management. This can prolong the lifetime of the machines and reduce costs caused by unplanned downtimes and unnecessary maintenance.
Problems that can occur in electrical machines are shaft currents and voltages. Due to the asymmetry of the magnetic field in the machine, a voltage in the shaft can be induced, which, depending on the type of machine, its size and load, varies in amplitude and frequency composition. Low impedance of the circuit consisting of shaft, bearing, oil film and other structural components, can cause shaft current flow which leads to bearing destruction.
Continuous measurement and analysis of shaft currents and voltages can prevent major faults. Through detailed processing of the measured data the causes of occurrence of shaft currents and voltages can be identified. The main purpose of SCVP system is to detect shaft currents and voltages that may damage the generator bearing, and thus prevent greater economic damages. The aim of this paper is to show how data obtained by SCVP system can extend the life-time of the machine and provide manufacturers and users of the machine insight to useful information during machine work period that can help in better asset management.
System for detection of excitation winding shorted turns in hydro generators
HYDRO 2013 . Promoting the Versatile Role of Hydro, Innsbruck, Austria, 7-9 October 2013
Abstract
This article describes a specific instrument for detection of excitation winding shorted turns in hydro generators, developed in Koncar - Electrical Engineering Institute Inc., called Hydro generator Winding Fault Detection (HO WFD). This instrument is a part of the Institute's product line used for monitoring and diagnosis of rotating electrical machines.
A key issue in the operation of all machines is its proper and reliable work, which in economic terms means to achieve the maximum financial benefit and to stay within technical constraints. Therefore, the reduction of unplanned downtime and unnecessary maintenance is very important, and detection of machine failure conditions is of the utmost importance if we want to achieve better asset management. The main goal of each detection method is early and accurate failure detection, which allows the fault to be eliminated before it causes major damage.
One of the common failures that can occur in hydro generators is excitation winding shorted turn. Short circuits are the result of failure of the winding insulation between individual turns, and by aging of the isolation they become more likely and more frequent. Impact on the generator, if it works with short circuited tums, ranges from practically no influence on the operation of the machine, to the occurrence of expressed vibrations, load limits, high operating temperatures and forced outages. The magnitude of the effect to the machine working with short-circuited turns, depends on the location and number of turns that are shorted.
This article describes a specific instrument for detection of excitation winding shorted turns in hydro generators, developed in Koncar - Electrical Engineering Institute Inc., called Hydro generator Winding Fault Detection (HO WFD). This instrument is a part of the Institute's product line used for monitoring and diagnosis of rotating electrical machines.
A key issue in the operation of all machines is its proper and reliable work, which in economic terms means to achieve the maximum financial benefit and to stay within technical constraints. Therefore, the reduction of unplanned downtime and unnecessary maintenance is very important, and detection of machine failure conditions is of the utmost importance if we want to achieve better asset management. The main goal of each detection method is early and accurate failure detection, which allows the fault to be eliminated before it causes major damage.
One of the common failures that can occur in hydro generators is excitation winding shorted turn. Short circuits are the result of failure of the winding insulation between individual turns, and by aging of the isolation they become more likely and more frequent. Impact on the generator, if it works with short circuited tums, ranges from practically no influence on the operation of the machine, to the occurrence of expressed vibrations, load limits, high operating temperatures and forced outages. The magnitude of the effect to the machine working with short-circuited turns, depends on the location and number of turns that are shorted.
The Effects of Pole Number and Rotor Wedge Design on Unbalanced Magnetic Pull of the Synchronous Generator
International Conference on Electrical Machines - ICEM 2014, Berlin, 2-5 Sept. 2014.
Abstract
In the paper, the effects of magnetic saturation and damper winding currents on the unbalanced magnetic pull of synchronous generator were analyzed by using the Finite Element Method calculations. Analyses were conducted for no load and rated load conditions on two types of generators. Firstly on the 40-pole, 10, 5 MVA, salient pole synchronous generator and then on 2-pole, 40 MVA turbo generator.
From the results it can be seen that magnetic saturation and damper winding currents decrease the force of unbalanced magnetic pull. In no load condition, for voltage level lower than the rated value, the maximal value of this force is achieved. In case of 2- pole generator, magnetic saturation has smaller effect on the force of unbalanced magnetic pull, than on the damper winding currents. The use of magnetic wedges on rotor can cause superposition of alternating component to the static component of the unbalanced magnetic pull.
In the paper, the effects of magnetic saturation and damper winding currents on the unbalanced magnetic pull of synchronous generator were analyzed by using the Finite Element Method calculations. Analyses were conducted for no load and rated load conditions on two types of generators. Firstly on the 40-pole, 10, 5 MVA, salient pole synchronous generator and then on 2-pole, 40 MVA turbo generator.
From the results it can be seen that magnetic saturation and damper winding currents decrease the force of unbalanced magnetic pull. In no load condition, for voltage level lower than the rated value, the maximal value of this force is achieved. In case of 2- pole generator, magnetic saturation has smaller effect on the force of unbalanced magnetic pull, than on the damper winding currents. The use of magnetic wedges on rotor can cause superposition of alternating component to the static component of the unbalanced magnetic pull.
THE COMPARISON OF MAGNETIC VALUES OBTAINED FROM HALL PROBES AND MEASURING COILS IN SYNCHRONOUS GENERATORS
ICEM'08 - XVIII International Conference on Electrical Machines, Portugal - Vilamoura, 6th -9th September 2008
Abstract
This article gives a review of a part of measuring results obtained during factory tests and inspections of a wind mil power unit. Magnetic fields were measured by two different measuring methods and the results were compared consecutively. The article also gives the results of calculation of dynamic electromagnetic field by application of FEM to the model of a synchronous generator installed in the wind mill power unit. Those results were compared to the measuring results as well.
This article gives a review of a part of measuring results obtained during factory tests and inspections of a wind mil power unit. Magnetic fields were measured by two different measuring methods and the results were compared consecutively. The article also gives the results of calculation of dynamic electromagnetic field by application of FEM to the model of a synchronous generator installed in the wind mill power unit. Those results were compared to the measuring results as well.