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58 ELECTRIC DISCHARGES, WAVES AND IMPULSES,
This gives |
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Assuming i0 = 10 amperes for to = 0, gives from (10) the equa-
tion:
T = 2.92 - \ 9.21 kg" r _.-',-;. -f .921 toy i + , -1^ j .
^ 1, ~j" *0 % I *i *) I' )
Herein, the logarithms have been reduced to the base 10 by
division with logu = .4343.
For comparison is shown, in dotted line, in Fig. 29, the transient
of a circuit containing no iron, and of such constants as to give about the same duration:
i- 1.085 logl*i- ,507.
As seen, in the ironclad transient the current curve i« very
much steeper in the range of high currents, where magnetic sat- uration is reached, but the current change is Blower in the range of medium magnetic densities.
Thus, in ironclad transients very high-current values of abort
duration may occur, and such transients, an those of the starting current of alternating-current transformers, may therefore be of serious importance by their excessive current values.
An oscillogram of the voltage and current waves in an 1 1,000-kw.
high-voltage 60-cycle three-phase transformer, when switching onto the generating station near the most unfavorable point of the wave, is reproduced in Fig, 30. As seen, an excessive current ruwh persists for a number of cycles, causing a distortion of the volt- age wave, and the current waves remain unsymmetrical for many cycles. |
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