Use of a mixed-Weibull distribution for the identification of PDphenomena [corrected version]

The interaction between partial discharge (PD) phenomena occurring in insulating systems is investigated in this paper. In particular, the recognition of two PD phenomena simultaneously active is approached by means of a 5-parameter additive Weibull distribution. Various shapes of the PD height distribution, obtained from measurements performed on specimens of stator bars and windings of ac rotating machines, are considered. It is shown that the proposed probability function fits well the partial discharge height distributions. The probability distribution relevant to each concurring PD phenomenon can be derived, analyzed and identified. Moreover, the standard average quantities are estimated for each phenomenon     

Use of a mixed-Weibull distribution for the identification of PDphenomena [discussion and reply]

The authors of the original paper [see ibid., vol. 2, no. 4, 1995] propose to use a Weibull statistical analysis to identify when two separate PD mechanisms are active simultaneously. Five parameters are needed to be estimated using a complex iterative technique. Their paper raises the following question. In the many thousands of pulse height analysis (PHA) plots I have collected, it has normally been very easy to determine that two (or more) mechanisms are occurring by simply looking at the plots. The author shows such straightforward examples. In fact observation shows it is easier to see the two mechanisms and their demarcations with the PHA plots than the Weibull plots. This makes sense to me since the Weibull transformation fundamentally involves a double logarithm transformation which tends to reduce differences. Furthermore, straightforward regression analysis techniques are readily available to separate `objectively' the two mechanisms from the PHA. In addition, there are now many pattern recognition methods available. Thus why do the authors propose that we should go through the complicated process of transforming the data to Weibull format and using more complicated analytical procedures? A reply is given     

A discharge locating probe for rotating machines

The basic principles of an improved Tennessee Valley Authority (TVA) probe known as the discharge locating (DL) probe are presented. The principal features of the new device are very-high-frequency detection using a capacitive sensor and microprocessor-based signal processing. These features are intended to make the probe easier to use and less ambiguous in the interpretation of results. The coupling technique used permits significantly improved spatial resolution of the discharge source and immunity to radiated electrical interference. Details of the signal processing electronics and field experience are described     

Modeling of skew using the flux-MMF diagram [of PM machines]

The flux-MMF diagram has recently been used to predict torque ripple in different electric machine types. This paper describes a simple and elegant method, based on this technique, for predicting the effect of skew on torque ripple in permanent-magnet machines. Although it is well known that skewing minimizes torque ripple, the paper quantifies the difference in the extent of minimization between the electromagnetic torque ripple and the cogging torque     

Trends in insulation materials and processes for rotating machines

Market pressure for cost reduction and more rapid innovation has taken away the privilege for the insulation design engineers to re-test everything according to time-honored “in-house” methods     

New electric insulating materials for the insulation systems of rotating electrical machines

A wide range of nomenclature and properties for new materials for the insulation of high voltage electrical machines and traction motors of F and H insulation classes developed at Elinar Holding Company are presented in the report.     

Modern electric insulating materials for the insulation systems of rotating electric machines

Modern insulation systems of turbo- and hydrogenerators, large electric machines, and traction motors based on new electric insulating materials (EIMs) produced by the JSC Elinar Holding Company (Elinar HC) are described briefly. The technical characteristics of some new EIMs are given.     

Field-oriented controllers with rotor deep bar compensationcircuits [induction machines]

A rotor deep bar effect compensation circuit for field-oriented controllers is derived from the transient equations of a double-cage induction machine. Torque and flux are decoupled with respect to the airgap flux. Accurate tuning of the field-oriented controller is possible both for steady-state and high-frequency conditions in the rotor. Consequently, an extended static stability region and improved torque dynamics are obtained with the deep bar effect compensated induction motor drive     

Use of transverse-flux machines in a free-piston generator

This paper investigates the use of transverse-flux machines (TFMs) in a free-piston generator, an integration of a combustion engine and a linear electrical machine. For hybrid vehicles (the intended application), this integrated device has benefits in efficiency, emissions, reliability, etc. Conventional TFMs are dimensioned and their shortcomings illustrated. Several surface-mounted TFM designs are suggested. These designs, initially believed to be promising, are later discovered to be poor during the three-dimensional finite-element method (3-D FEM) analysis. These designs suffered from a large axial pole-to-pole armature-flux leakage in the stator. This problem is solved in the proposed buried-magnets TFM variants, for which patents have been filed as well. A 5-kW proof-of-concept prototype of one such design is dimensioned that allowed the near fulfilment of 3-D FEM verifiable system demands. One phase of this dimensioned three-phase prototype is built. Measurements on this prototype showed that the use of short pole lengths in the machine had led to manufacturing defects. Nevertheless, the electromagnetic viability of the design could still be approximately verified.     

A method for wide frequency range modeling of power transformersand rotating machines

Wide frequency range representation of power system components such as power transformers, reactors and rotating machines is mainly needed for the analysis of electromagnetic transients in power systems. In this paper, a method is presented for state space formulation of machine windings. The described procedure is completely based on external terminal impedance measurements and data related to the internal structure is not required. First, the wide frequency behavior of machine windings is reviewed and the nonlinearity effects of the iron core are discussed. A numerical method is given for calculation of the state equation parameters directly from the measured terminal impedance characteristics. The presented modeling method is applicable to any transformer, reactor or rotating machine in service where sufficient information on the internal design is not available. Besides, the canonical structure of the model offers advantages in terms of computer memory and computation effort in time domain analyses of complex power systems     

Experience with development and evaluation of corona-suppression systems for HV rotating machines

This paper presents the results of a project aimed at the development of reliable corona-suppression systems for high voltage rotating machines. These systems are based on both conducting and semi-conducting dry and B-stage tapes as well as paints of different resistivity. Three groups of anti-corona systems were developed; namely, paint (on the slot portion) - paint (on the slot exit) system, paint (on the slot portion) - tape (on the slot exit) system, and tape (on the slot portion) - tape (on the slot exit) system. Sample results of standard evaluation and acceptance tests are presented. The accelerated life-aging test was run on test coil samples at the National Electric Coil HV testing facility. A numerical 2-dimensional finite difference model for the electric potential and field analysis along the end-turn zone was developed and the model results are used as guidelines through the design process of the grading system. Laboratory test results on randomly selected sample coils were confirmed by an independent testing facility. The proposed corona-suppression systems were applied on thousands of production coils.     

Computer aided instruction of rotating electric machines viaanimated graphics

A menu-driven interactive graphics software package has been developed for use as an instructional aid for the electric machines course in the electrical engineering curriculum. The main purpose of this tool is to give the students a clearer understanding of the basics of the operation of rotating electric machines. The animation program was developed for displaying live and rotating diagrams depicting different modes of operation of synchronous generators. Different parts are identified with different colors. The interaction of the magnetic poles on the stator and on the rotor, and the relative spatial positions and time variations of the magnetic and electric quantities are demonstrated through moving images. The software features are described     

New practices for partial discharge detection and localization in large rotating machines

This paper presents a new technique for detection and localization of partial discharges (PD) in large rotating machines. In this technique, denoted "InTech", a stator winding with (n) coils is equipped with (n + 1) inductive sensors; as a result, every stator coil is situated between two sensors. The measurement is then focused on the individual stator coils. In this way common difficulties facing partial discharge measurements in rotating machines such as attenuation and distortion of the signals in the stator winding, noise reduction, and the calibration accuracy are reduced considerably. The treatment of the sensor signals, using a special method, results in a measurement of PD in each respective stator coil. In addition, the stator coil from which the PD originates is identified. Results from field measurements on both hydro and turbo machines are presented and discussed.     

Parameter identification of vector-controlled induction machines

Contents This paper describes the identification of electromagnetic time constants and stator resistance for field oriented induction motor drives. The model of an induction motor at standstill in terms of state representation is discussed. A direct continuous-time identification from the standstill time-domain test data is based on the parametrized observer state vector. In a laboratory configuration the stator resistance is influenced by the non-linear inverter gain function. Two categories of current responses to voltage steps and to pseudo random binary sequences are examined. The current transients indicate saturation effects. Parameter estimates of a linear machine model are determined using least squares algorithms. Simulation and experimental studies are carried out in a Matlab software environment. Corresponding results obtained for two induction motor drives of different power ratings are included.

---

Parameteridentifikation von vektorgeregelten Asynchronmotoren

Übersicht Der Aufsatz beschreibt die Identifikation der elektromagnetischen Zeitkonstanten und des Statorwiderstandes für Antriebe mit vektorgeregelten Asynchronmotoren. Das Modell eines Asynchronmotors im Stillstand wird in der Zustandsform beschrieben. Die direkte zeitkontinuierliche Identifikation aus den Meßdaten im Stillstand beruht auf dem parametrierten Beobachter Zustandsvektor. In einer Laboranordnung wird der Statorwiderstand durch die nichtlineare Kennlinie des Umrichters beeinflußt. Es werden zwei Kategorien der Stromantwort auf Spannungssprünge und PRBS-Sequenzen untersucht. Der transiente Stromverlauf weist Sättigungseffekte auf. Parameterschätzungen an einem linearen Maschinenmodell werden mittels der Methode der kleinsten Fehlerquadrate bestimmt. Es werden Simulationsrechnungen und experimentelle Studien in einer Matlab Umgebung durchgeführt. Die Ergebnisse für zwei Antriebe mit Asynchronmotoren unterschiedlicher Leistung werden vorgestellt.

---

---

This work was supported in part by the Deutscher Akademischer Austauschdients, Ref. 323, and by a grant from the State Committee for Science Research (Poland) Contract BW959050.