UHF-kalibrierte Messungen
Prof. Dr.-Ing. Stefan Tenbohlen studierte und promovierte an der RWTH Aachen zum Thema Isolationsfestigkeit von SF6. Von 1997 bis 2004 war er Mitarbeiter der ALSTOM Schorch Transformatoren GmbH in Mönchengladbach. Er begann 1997 als Leiter der Abteilung Produkt- und Grundlagenentwicklung. In dieser Funktion war er verantwortlich für die Entwicklung von online Monitoringsystemen zur Zustandsdiagnose von Leistungstransformatoren. Von 2002 bis 2004 leitete er die Hauptabteilung zur Entwicklung, Berechnung und Konstruktion von Leistungstransformatoren. Am 1. Juli 2004 übernahm er die Leitung des Instituts für Energieübertragung und Hochspannungstechnik an der Universität Stuttgart. Seine Forschungsschwerpunkte sind die Hochspannungstechnik, Netzintegration erneuerbarer Energien und elektromagnetische Verträglichkeit. Er ist Mitglied in zahlreichen nationalen und internationalen Fachgremien, Mitglied im Beirat der Energietechnischen Gesellschaft im VDE (ETG) und im internationalen Studienkomitee A2 (Leistungstransformatoren) der CIGRÉ.
Calibration of UHF partial discharge measurements for power transformers
The application of regular condition checks and continuous monitoring of power transformers gains in importance. Common objective is to detect damages in the insulation system at early stage and thus to avoid outages. In addition to the electrical partial discharge (PD) measurement according IEC 60270, the electromagnetic measurement method starts to become common practice. It is suitable for diagnostic measurement on-site and also as continuous PD monitoring system because of its lower sensitivity to external interference compared with the electrical measurement. For electrical PD measurement a calibration procedure for the ratio between transformer capacitance and coupling capacitor is available. Although the actual PD charge still remains unknown, the associated comparability of electrical PD measurement systems has led to an acceptance level at transformer routine tests. A similar calibration of the electromagnetic UHF (ultra-high frequency: 300 MHz – 3 GHz) measurement has not been im- plemented yet, but is necessary for further standardization of this method. In this contribution, a calibration procedure for the ultra-high frequency (UHF) method is proposed as it is necessary to ensure reproducibility and comparability of UHF measurements. Afterwards, a calibrated UHF method can be introduced supplementary to IEC60270 in acceptance tests of power transformers. This contribution compares the calibration procedures of the conventional electric method (IEC60270) and the electromagnetic method. A characterization of UHF sensors by the antenna factor (AF) is a precondition for the UHF calibration procedure. To provide profound knowledge of the equipment, the AF of the UHF sensor is determined under inside transformer conditions. To meet these conditions, an oil-filled GTEM cell is used for correct permittivity. Additional to the calibration procedure, the performance of the installed sensor has to be determined. The evaluation is based on the idea of transmitting electromagnetic waves through the transformer tank from one UHF sensor to another which is called performance check procedure.