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Appendix
IEEE Standard C57.19.01 specifies a limit 0.5% for C1 power factor for oil
impregnated paper insulated bushings, Type O Plus C, AB, and T condenser
bushings C1 power factor values are well below this limit.
Condenser bushings rated 69 kV and below as mentioned earlier, have the main
C1 capacitance, which is strictly controlled by design. Like the bushings rated
115 kV and above, the C1 power factor and capacitance test values of these
bushings are not affected too much by external factors under normal
circumstances. However, under conditions of contamination and high humidity,
these measurements may be significantly affected. Also, these measurements
may be affected by supporting structure, wooden crates that are moist/wet,
resistance between bushing mounting flange and the transformer tank, stray
effect from other objects, and external connections during testing. These
bushings have an inherent C2 capacitance, which is dependent upon a few
outer layers of paper with adhesive, an oil gap between the flange and the
condenser core, and the tap insulator. Variations in adhesive in the outer paper
layers and other factors can result in PF variations in bushings of the same style
number. In addition, the close proximity of the C1 layer (see figure 12-3) with the
mounting flange results in greater fringing effect between the two parts. As a
result of this, the porcelains, oil, and air surrounding the bushing can have some
affect on the C2 power factor test values. In particular, high current Type T
condenser bushings with a short mounting flange and a long internal C1 layer/
foil tend to exhibit higher power factors because of greater coupling effect
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