Damper Cage Research Articles

The Shielding Effect of the Built in Damper Cage in a Synchronous Machine.

Because of the cost efficiency of modern machines, the design of a damper winding in a synchronous machine must be met the following both subjects. One criterion is a functional design, and a second one is an as cheap as possible design. Normally, the complete damper cage is substituted by the slot wedges of the rotor. But this replacement cage isn’t as effective as the original cage [1]. Furthermore the damping moments of the eddy currents in the massive rotor and in massive parts of a synchronous machine don’t changed. So in the case of an absent damper winding the sum of the damping moments decreases. In order to answer the question of the aims of a built in complete damper cage it must be differentiated between synchronous generators and motors. Generators have to produce sinusoidal voltages. As a result, the damping of higher harmonics in the generator is important. Furthermore, the damping of the negative sequence caused by an increased asymmetric load must be defined by the consumer. Normally, a five percent asymmetric load is acceptable. In the case of synchronous motors the damping of load impulses are important. One result is the difference between the damping moment of a complete built in damper cage and an incomplete built in damper cage. In addition this paper treats about the damping of higher harmonics and the damping of the negative sequence rotating field.

Design and Performance Evaluation of a Novel Axial-Flux Hybrid Motor With Permanent Magnet Rotor and Unpaired Damper Cage

In order to improve the performance of synchronous motors, especially in dynamic-transient conditions, induction damper cages are usually used in the rotor structure. In this paper, a new hybrid structure of an axial-flux motor is proposed, which uses a permanent magnet (PM) rotor and an unpaired induction damper cage with independent movement capability. The proposed motor design procedure is provided in some detail. The performance of the proposed motor is evaluated using the finite element method (FEM) simulation and the operational effects of the unpaired damper cage are evaluated. In addition, comparisons were made between three different motor structures including the structure without damper cage (WDC), the structure equipped with coupled damper cage (CDC), and the structure equipped with unpaired damper cage (UDC) (proposed structure). Dynamic-transient and steady-state characteristics of motors including current profile, torque, and speed are evaluated. In order to confirm the results of the FEM simulations, a prototype of the proposed motor is manufactured, and some functional tests were performed on it. The results show that the proposed new structure can have better dynamic performance than other structures in terms of the amplitude of fluctuations as well as the time to reach the steady-state.

Integrated Damper Cage for THD Improvements of Variable Speed Salient-Pole Synchronous Generators for the More Electric Aircraft

Wound field synchronous generators (WFSGs) have been implemented as aircraft main ac power generation for decades. The trend of moving toward more electric aircraft (MEA) made dc and variable-frequency ac buses favorable for the next-generation power systems in aircraft, as opposed to constant frequency ac grid systems. The minimization of the generators’ output voltage total harmonic distortion (THD) is an ever-more critical objective, especially for variable-frequency power systems where this target has to be met within the whole range of operating speeds. In conventional, constant speed, and WFSGs, a number of consolidated techniques are implemented to meet this requirement. In variable-speed SGs intended for the MEA, these techniques are no longer fully effective and new methodologies are thus necessary. This article replaces the conventional squirrel-type damper cage with a new integrated damper cage (IDC) located at the interpole regions. The proposed IDC, while acting as a mechanical structure to retain the field windings at high operating speeds, also achieves very low-voltage THD values at different speeds, thus complying with the power quality requirement. A 250-kVA prototype is designed, analyzed, built, and tested to prove the proposed concepts and methodologies.

Evaluation of the Damper Condition in Synchronous Motors Through the Analysis of the Transient Stray Fluxes and Currents Considering the Effect of the Remanent Magnetism

This article proposes the qualitative and quantitative analysis of stray-flux and current data under starting to detect damper faults in cylindrical rotor synchronous machines. These machines are typically employed in high power applications and their possible outages may imply huge costs for the industries or plants where they operate. The damper cage is a critical part of these machines and a potential source of catastrophic failures. However, few research works have provided feasible alternatives to monitor the condition of such element. This article analyses the viability of analyzing the electromotive force signals induced by the stray-flux in external coil sensors as well as current signals under starting to diagnose damper faults. The results obtained with laboratory machines with different levels of damper damage show that the analyses of those signals can provide very useful information for determining how the damper degrades over time. Moreover, the article studies the effect of the remanent magnetism over the viability of the approaches and provides solutions to overcome this problem. The conclusions are valuable for field engineers since, nowadays, there are few available solutions that allow monitoring the condition of such element without motor disassembly.

Simplified Damper Cage Circuital Model and Fast Analytical–Numerical Approach for the Analysis of Synchronous Generators

The long and enduring history of utilization of the wound-field synchronous generator in a large number of applications makes it one of the most known and consolidated electrical machine technologies. Thus, its design, modeling, and analysis processes have been widely exploited and implemented through various and different methods, including the equivalent circuit approach. When a damper cage is embedded within the rotor of the synchronous generator, its theoretical analysis becomes quite complicated. Thus, today numerical tools are being used. In this paper, an alternative way of modeling symmetric damper cages of salient-pole synchronous generators is presented. The proposed approach is embedded in the circuital model of the generator. A hybrid analytical–numerical model is implemented, permitting to accurately predict the voltage waveforms of the generator with excellent accuracy, however, at a lower cost of computational resources than the pure numerical method. A case study of an off-the-shelf 400 kVA machine is considered to develop and validate the proposed technique. The results are compared with the corresponding finite-element and experimental evaluations for validation purposes.

A Methodology to Remove Stator Skew in Small–Medium Size Synchronous Generators via Innovative Damper Cage Designs

This paper proposes and investigates an innovative methodology that can have a significant impact on the market potential of wound field, small–medium size synchronous generators (SGs). The technique proposed here is aimed at removing the need for the traditional stator skewing that is so commonly used in SGs to achieve acceptable values of voltage total harmonic distortion. To do this, a nonstandard damper cage configuration is proposed that comprises modulation of the damper bars’ positioning. An off-the-shelf, 400-kVA generator is used as a benchmark machine. Its rotor is optimized and modified according to the proposed technique. The results of the final machine are then compared to the benchmark machine highlighting the excellent advantages that can be achieved through this technique. A full-scale prototype of the modified generator is then built to experimentally validate the concept. Finally, a detailed analysis on all the performance aspects of the prototype is carried out, to guarantee that the proposed technique has no negative impact whatsoever on the generator's performance.

Flux Observer Model for Sensorless Control of PM BLDC Motor With a Damper Cage

Sensorless control methods are commonly employed to derive the rotor position and speed information indirectly in permanent magnet (PM) brushless motor drives. Thereinto, the simple yet effective flux observer method is extensively applied in a wide range of applications. However, damper cage is sometimes employed in the rotor of certain PM brushless motor. Normally, high-order current harmonic components occur in such damper cage during operations. The introduction of these extra current contents can significantly hinder the performance of the conventional flux observer. By applying Park transformation, the fundamental harmonic components of stator phase currents, flux linkages, and voltages during steady-state operation, become constants under rotor synchronous reference frame, while the currents in the rotor damper cage are still alternating. In this paper, an improved flux observer method is proposed to filter the harmonic contents under the rotor synchronous reference frame for PM brushless motor with rotor damper cage. The validity and performance of the proposed flux observer are verified by both numerical analysis and experimental results.

Finite Element Computation of Transient Parameters of a Salient-Pole Synchronous Machine

This paper presents a novel method for calculating the transient parameters of a saturated salient-pole synchronous machine (SPSM) with damper cage using finite element analysis. All detailed leakage inductances in a modified d-q model are discussed and separately extracted. In addition; the frozen permeability method is used in a 2-D finite element analysis to consider saturation and skin effects for determining the inductances. The terminal reactance parameters are obtained from all elements of the d- and q-axis equivalent circuits in all the chosen time constants during the transient process. The variation of leakage inductances of the SPSM in transient processes is also investigated and discussed. To determine transient time constant parameters; the Prony algorithm is applied in the presented method. A program developed to automatically solve the simulation and computation with the proposed method is described. This method is applied to a prototype and validated by experimental results. Some discussion about the relationship between rotor geometric design and the transient parameters of SPSMs is provided. The variation of leakage magnetic field of SPSMs in transient processes is also investigated. This method can be applied in transient parameter estimation and optimization of SPSMs in the design stage.

Improved Damper Cage Design for Salient-Pole Synchronous Generators

The benefits of implementing a damper winding in salient-pole synchronous generators are widely known and well consolidated. It is also well known that such a winding incurs extra losses in the machine due to a number of reasons. In order to improve the overall efficiency and performance of classical salient-pole, wound field synchronous generators that employ the traditional damper cage, an improved amortisseur winding topology that reduces the inherent loss is proposed and investigated in this paper. This is essential in order to meet modern power quality requirements and to improve the overall performance of such “classical” machines. The new topology addresses the requirements for lower loss components without compromising the acceptable values of the output voltage total harmonic distortion and achieves this by having a modulated damper bar pitch. As vessel for studying the proposed concept, a 4-MVA salient-pole synchronous generator is considered. A finite element model of this machine is first built and then validated against experimental results. The validated model is then used to investigate the proposed concept with an optimal solution being achieved via the implementation of a genetic algorithm optimization tool. Finally, the performance of the optimized machine is compared to the original design both at a steady state and transient operating conditions.

Demonstration of Synchronous Motor Start by Rotor Polarity Inversion

Synchronous motors are reliable and efficient, but it is relatively difficult to start them. In some cases, a variable frequency drive is utilized. In some other, asynchronous start is achieved by virtue of induced currents in a solid rotor, or a rotor damper cage installed for this purpose. In this contribution, a method to start a synchronous machine without a damper cage is presented. The starting was achieved by inverting the polarity of the rotor field winding in a timely manner with respect to the rotating stator field. The technique was verified with experiments performed on a 200 kVA experimental test rig and also simulated on a 20 MVA machine.

Time-Stepping Finite-Element Analysis of a 14-MVA Salient-Pole Shipboard Alternator for Different Damper Winding Design Solutions

Salient-pole synchronous machines are conventional electric machines which have been widely used and studied over decades. Some aspects of their modeling and analysis, however, still constitute a challenge for designers and require state-of-the-art methodologies to be applied. As an example, this paper addresses a 14-MVA salient-pole shipboard alternator, of which full-scale prototypes are built and tested with different damper cage designs. A time-stepping finite-element (FE) analysis is assessed against test results as a method to predict generator performance for the various damper cage design alternatives. FE simulations are shown to give accurate results even without model tuning if continuous end rings are used to short circuit damper bars. For the design solution with partial end arcs, model tuning is required, instead. For this purpose, a calibration method is proposed and successfully validated, which only requires a set of impedance measurements to be taken on the machine at standstill.

Damper Cages in Genset Alternators: FE Simulation and Measurement

This paper describes an investigation of the function and effectiveness of the damper cage in small salient pole genset alternators. A time-stepping finite-element (FE) simulation is described and its application to the damper circuit is validated through the use of a specially manufactured rotor with wound damper coils. Further validation is provided by comparison of measured and predicted stator and main field quantities in a standard machine when subjected to sudden application of load. The simulation is then used to predict the performance of the alternator with and without the dampers for balanced and unbalanced load conditions. The effect of the damper circuit is also investigated when a nonlinear, rectifier load is applied to the machine with the modified rotor.

The behaviour of damper cages

European Transactions on Electrical PowerVolume 9, Issue 3 p. 203-204 Letter to the Editor The behaviour of damper cages W. Fritz, W. Fritz Univ.-Prof. Dr.-Ing. Werner Fritz, Gerhard-Mercator-Universität-GH Duisburg. Fachbereich 9 Elektrotechnik, Elektrische Maschinen und Antriebe, D-47048 Duisburg/Germany. Phone: +49 2 03/3 79-33 78, Fax: +49 2 03/3 79-60 04, E-mail: w.fritz@unidui.uni-duisburg.deSearch for more papers by this authorM. Hyrenbach, M. Hyrenbach Dr.-Ing. Maik Hyrenbach, ABB Calor Emag Schaltanlagen AG, Department EMA, Bahnstraße 39-47, D-40878 Ratingen/Germany, Phone: +49 2 1 02/12 17 85, Fax: +49 2 1 02/12 19 33, E-mail: maik.hyrenbach@deace.mail.abb.comSearch for more papers by this authorH. W. Schneckmann, H. W. Schneckmann Ing. (grad.) Heinz Willi Schneckmann, Gerhard-Mercator-Universität-GH Duisburg, Fachbereich 9 Elektrotechnik, Elektrische Maschinen und Antriebe, D-47048 Duisburg/Germany, Phone: + 49 2 03/3 79-23 76, Fax: + 49 2 03/3 79-60 04Search for more papers by this author W. Fritz, W. Fritz Univ.-Prof. Dr.-Ing. Werner Fritz, Gerhard-Mercator-Universität-GH Duisburg. Fachbereich 9 Elektrotechnik, Elektrische Maschinen und Antriebe, D-47048 Duisburg/Germany. Phone: +49 2 03/3 79-33 78, Fax: +49 2 03/3 79-60 04, E-mail: w.fritz@unidui.uni-duisburg.deSearch for more papers by this authorM. Hyrenbach, M. Hyrenbach Dr.-Ing. Maik Hyrenbach, ABB Calor Emag Schaltanlagen AG, Department EMA, Bahnstraße 39-47, D-40878 Ratingen/Germany, Phone: +49 2 1 02/12 17 85, Fax: +49 2 1 02/12 19 33, E-mail: maik.hyrenbach@deace.mail.abb.comSearch for more papers by this authorH. W. Schneckmann, H. W. Schneckmann Ing. (grad.) Heinz Willi Schneckmann, Gerhard-Mercator-Universität-GH Duisburg, Fachbereich 9 Elektrotechnik, Elektrische Maschinen und Antriebe, D-47048 Duisburg/Germany, Phone: + 49 2 03/3 79-23 76, Fax: + 49 2 03/3 79-60 04Search for more papers by this author First published: 09 July 2012 https://doi.org/10.1002/etep.4450090310 Read the full textAboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat No abstract is available for this article. Volume9, Issue3May/June 1999Pages 203-204 RelatedInformation

The behaviour of damper cages

AbstractThe central point of the following treatise is the investigation of the reaction mechanism of the single bars and rings of a damper cage when it is hit by the normal component of an alternating field. The reacting field of the cage is calculated by Ampere's law. The bars and rings generate positive and negative field components which are superimposed to the total reacting field. The resulting flux in a mesh is an indicator for the damping effect. The validity of the theory will be proved by measurements at a damper model in a room with constant permeability.

Determination of damper winding and rotor iron currents in convertor- and line-fed synchronous machines

The damper winding currents of a synchronous machine with a solid iron rotor are analyzed. Based on the self and mutual inductance modelling technique, the damper currents are described by a detailed damper model taking the damper cage and the rotor iron into account. The model's component elements are determined by the finite element method. Theoretical results are verified by measuring damper bar currents of a six-phase synchronous machine fed by two six-pulse converters. For a number of different operating modes the model is used to calculate the damper current distribution of a six-phase machine. >

Measurement of eddy-current damping of small synchronous generator with two types of cylindrical solid rotor

An experimental model is used to represent a generator the solid rotor of which is hunting about synchronous speed. The eddy-current damping factor, and hence the losses in the rotor, are measured at different stages in the construction of two different forms of rotor to assess the effect of the various components such as wedges, end rings and copper damper cage. It is found that a well-connected damper cage is particularly important in improving the damping.

Transient Behaviour of a Current-Source Inverter-Fed Synchronous Motor with a Solid Rotor

This publication presents a solution which enables one to investigate the transient behaviour of a 2 × three-phase current-source inverter-fed synchronous motor with a solid rotor. Based on the block structure of the whole system it was split into components for which mathematical models in state-space were derived. A focal problem was describing the synchronous machine: With inverter-fed operation increased rotating waves of the magnetic air-gap field arise which do not rotate with synchronous speed and thus induce eddy currents in the rotor. As these eddy currents not only flow in the intended paths provided by the damper cage but also in the solid iron it is not possible to formulate coupling inductances in accordance with the classical theory of machines. The set of equations describing the machine is therefore incomplete. Numerical calculation of the magnetic field and system-theoretical expressions yield further sets of equations which can be presented in a complete form. It is also shown how the mutual interactions between the subsystems interconnected in the circuit can be determined mathematically and by programming. Based on the coupling conditions the coupling voltages can be calculated for each time-step in the digital simulation as fictitious control quantities enabling the respective phase-state differential equations to be integrated independently of each other. The presented theory was converted into a simulation program taking the regulation into account. A concluding comparison between test and calculation results shows good correlation.

Frequency domain-based methods to predict turbogenerator transients with particular emphasis on the field current

Transients occurring in synchronous machines are calculated using Fourier transform methods. Particular attention is paid to the field current oscillograms following sudden short circuits. The field current in the short-circuit test is shown to be a sensitive indicator of the state of the damping circuits present in the rotors of turbogenerators. The paper goes some way to clarifying the degree of effectiveness of the damper cage in three example machines, using a combination of results from testing and from calculations using frequency-response data calculated by finite elements and measured in standstill tests. The Fourier transform methods used are discussed and the exponential Fourier transform shown to be advantageous for transients of long duration. The method is extended to cover the response of the machine to step changes in the field voltage and used to examine the effect of damper-cage design.

LAMINATED SALIENT-POLE MACHINES: NUMERICAL CALCULATION OF THE ROTOR IMPEDANCES, STARTING CHARACTERISTICS, AND DAMPER-BAR CURRENT DISTRIBUTION

ABSTRACT This paper describes a numerical method for calculating the self and mutual reactances of all the electrical circuits in a machine on the basis of field computation and the given machine constructional dimensions. Subsequently, the asynchronous starting characteristics as well as the damper-bar currents are also computed. Each of the damper bars is treated individually so that it can assume any arbitrary spatial position, e.g., along the pole surface or in the interpole region. Furthermore, the damper cage can either be complete (with damper ring) or be of the pole-grid type (without pole connection). In the analysis provision is also made for a pole-shoe collar under the lower face of the pole shoe. All feasible types of airgap patterns can be precisely accounted for. The saturation influences are neglected, however, it is also possible to consider these approximately by modifying the virtual airgap and the damper-slot opening.

ADDITIONAL LOSSES IN SOLID-ROTOR SALIENT-POLE SYNCHRONOUS MACHINES ASSOCIATED WITH STATIC CONVERTORS

Abstract In solid-rotor synchronous machines associated with static converters, the harmonics generated by the operation of converters result in additional losses in the different parts of the machine. These losses are investigated in this paper. The rotor harmonic currents are determined, the machine equivalent-circuits are derived, and the losses are obtained for the general case of salient-pole machines. The results show that the additional losses are considerable and that constructing the solid-rotor machines with simple damper cages and laminated pole faces has the most prominent effect on reducing these losses.