No abstract

former. This is then a function of the current and voltage, which are both a function of the frequency. Therefore, the conversion factor for the transformer leakage impedance, in Ohms, should theoretically be 1.2. To confirm this relationship with test, the corresponding impedance voltage, which would result in full load current in the winding, should be used and resulting impedances in Ohms, 60 versus 50 Hz, compared. 2) Correct. 3) Yes, the flux density was the same in each comparison. The sound level conversion factor was developed from both measured data and from information available with major power transformer manufacturers who have had a significant database for both 50-and 60-Hz noise level measurements. The analysis in the paper used 16 sets of measurements, which was a fairly large sample size that covered the range of megavolt-amperes, core steel materials, and inductions used in the industry. Data that were outside of the expected range could be attributed to mechanical resonance or testing error. With reference to Table 1, the two manufacturers with a lot of experience in building units for the 50-and 60-Hz market used conversion factors of 3.0 and 3.5 dB, respectively, which closely matched the calculated conversion factor. Thus, the authors are confident that the calculated value matches the experience seen by the industry and is a correct and practical value to use. REFERENCES[1] R. S. Girgis, B. Beaster, and E. G. teNyenhuis, "Proposed standards for frequency conversion factors of transformer performance parameters," inThe authors [1] imply that their combined ampacity/sag computer program is the first of its kind. The program Calculation of Overhead Line Thermal, Electrical and Mechanical Properties (COOLTEMP) has been described previously [2]. Besides calculating the surface temperature and the sag of a conductor, this unified model also calculates the radial temperature and current distributions, tension, stresses, creep, cumulative loss of tensile strength, complex permeability of the steel core, if present, ac resistance, core loss, and total loss.It is surprising that the authors have used a graphical method in their program to calculate sag, rather than a program such as STESS [3]. Was the effect of creep taken into account? It is stated that a unique aspect of their program is the high operating temperature limit. However, other codes have been validated for conductor temperatures up to 275 C, for example [4].