Wide frequency range analysis of the electromagnetic emissions of electrical machine for diagnosis

Abstract

Abstract. The paper presents the possibilities to evaluate the health of an electrical machine by analyzing its electromagnetic emissions. Different piece of information can be detected according to the frequency range. First of all, a monitoring system sensitive to the degradation of the turn-to-turn insulation quality of the stator winding is presented; it is based on high frequency electromagnetic emissions. The second part of the paper is based on the medium and low frequency emission analysis. It explains how to detect turn-to-turn short circuits in stator windings or in the excitation coils of synchronous machines. PACS

Survey of models and reference data for prediction of e.m. field emissions from electrical machinery

“…at the air-gap [37], [38]. This limits the frequency range to tens of kHz and thus the considered e.m. emissions are purely magnetic.…”

“…• The change of winding capacitance is quantified by a direct measurement of conducted voltage/current in [37], [38], where further references on the subject may be found, but further effects on the e.m. emissions external to the machine can be investigated as well, with the advantage of a non-intrusive diagnostic system; • Partial Discharges, (PD), are well known low-level impulsive phenomena occurring between winding turns and are normally detected either on-line or offline by conducted emissions measurements; in [40] an antenna is used and a sample spectrum measured up to 2 GHz indicate a PD signature in the range of 400-700 MHz; it is underlined that the technique is preliminary in that it is not even clearly stated where the antenna is located, either externally to capture the emissions of the whole machine or internally at the air-gap, where PD phenomena have a favorable signal-to-noise ratio.…”