Properties of electrical insulation at ultrahigh temperatures

Abstract

Mr. Hanrahan's comments with regard to the assumption of constant stator winding and iron temperatures are a valuable criticism. H. Cooke of the TKM Electric Corporation has made the same comment and has suggested that the temperature rises of the stator winding and of the core of a typical 400-cps permanentmagnet alternator are on the order of 50 C, well below the allowable maxima.To illustrate a more realistic functional relationship between frequency and the various alternator characteristics, an analysis has been made assuming the full-load flux density B mi and the full-load demagnetizing armature mmf H d are constant. The results are shown in Table IV and in Fig. 9. Also shown in the figure for comparison are the other weight-frequency curves shown originally in Fig. 2 of the paper. These results show a very substantial decrease in weight with increasing frequency. Furthermore, the table shows that the winding and iron temperature rises increase significantly with increasing frequency. However, owing to the low values of temperature rise in the 400-cps model, the temperature rise in the winding is 115 C and the core is 216 C at 5,000 cps, values still below the allowable maxima for short-duty-cycle operation.The full-load flux density and direct-axis demagnetizing ampere-turns are assumed constant in view of the following reasoning. If the rotor is air-stabilized, the intersections of the magnet B-H curve and the out-stator permeance line 1 and of the B-H curve and the air-gap permeance line Fig. 9. Relative weight of alternators as a function of frequency Curve 1-Woundfield synchronous alternator Curve 2-Permanent-magnet alternator Curve, 3-Induction alternator The dashed curve shows curve 2 of ; Fi S . 2 2.0