Field of the Invention
The invention relates to a method and an apparatus for decoupling a high-frequency error signal from a high-frequency electromagnetic field in a heavy electrical machine, having a stator that carries an electric winding.
The invention relates in particular to operational monitoring of a heavy electrical machine and above all to the detecting of defects. Specifically, reference is made to defects that cause spark formation during operation in the heavy electrical machine.
The term "heavy electrical machines" is understood in the present context particularly to mean large generators, such as turbogenerators, having electrical outputs which are 50 MVA and more.
Detecting defects in systems with heavy electrical machines is gaining steadily increasing interest, in an attempt to increase the availability of the system and to detect defects as early as possible, and if at all possible even to predict them, preferably during regular operation. It is also significant that digital computer systems for evaluating the signals from complex monitoring systems are increasingly available at an acceptable cost.
Methods and apparatuses for detecting, and optionally locating, defects in electrical systems, especially systems with heavy electrical machines, are disclosed in German Patent DE 34 08 256 C2, German Published, Non-Prosecuted Application DE 35 26 149 A1, German Published, Non-Prosecuted Application DE 39 18 116 A1, European Patent Specification 0 228 613 B1 corresponding to U.S. Pat. No. 4,814,699, and European Patent Specification 0 241 764 B1. Those references disclose entire systems for detecting and locating defects in electrical systems that involve evaluations of high-frequency error signals, and also disclose details for decoupling high-frequency error signals from high-frequency fields in heavy electrical machines. U.S. Pat. No. 4,949,001 relates to the detection of partial discharges in the stator of a dynamo electrical heavy machine, especially a turbogenerator. According to that patent, a measurement value pickup is made by stripline technology and while acting as an antenna for decoupling a high-frequency error signal, in the manner of a directional coupler, it is placed on the stator and connected to an evaluation device through suitable connecting lines. By evaluating the level and/or the course over time of the error signals, it is possible to locate the point where the error signals have originated. In order to avoid further repetition herein, the content of all of the references cited above is expressly incorporated herein by reference.
One important aspect in decoupling high-frequency error signals from a heavy electrical machine is to make the best possible utilization of components and devices that are present anyway, so that additional components will not impair or even shield the high-frequency electromagnetic fields caused by errors or the like. Moreover, economic aspects which must be considered may make overly complex sensor systems disadvantageous. Finally, considerations of the load capability and efficiency of the heavy electrical machines argue against making overly generous space available for operational monitoring systems.
A heavy electrical machine in the form of an asynchronous motor, having a stator that carries an electrical winding, and in which the winding is placed in slots of the stator and a temperature measuring sensor is disposed in a slot, is known from the article entitled "Messen und Uberwachen von Temperaturen an gro.beta.en Asynchronmotoren" Measuring and Monitoring Temperatures in Heavy Asynchronous Motors!, by W. Raasch, in Elektro-Jahr Electrical Engineering Yearbook! 1979, published by Vogel-Verlag, Wurzburg, Germany, pages 27-30.