36 ELECTRIC DISCHARGES, WAVES AND IMPULSES.
__From this polar diagram of the rotating field, in Fig, 19, values
OC can now be taken, corresponding to successive momenta of
time, and plotted in rectangular coordinates, an done* m Fig, 20.
As seen, the rotating field builds up from ssero at the moment of
closing the circuit, and reaches the final value by a series of oscil-
lations; that is, it first reaches beyond the permanent value, then
drop's below it, risen again beyond it, etc.
time, and plotted in rectangular coordinates, an done* m Fig, 20.
As seen, the rotating field builds up from ssero at the moment of
closing the circuit, and reaches the final value by a series of oscil-
lations; that is, it first reaches beyond the permanent value, then
drop's below it, risen again beyond it, etc.
I 4
Fig. 20, <— Starting Transient of Rotating Field; Rectangular Form.
We have here an oscillatory transient, produced in u system
with only one form of stored energy (magnetic energy), by the
combination of several simple exponential tranwralH. How-
ever, it must be considered that, while energy can be stored
in one form only, as magnetic energy, it can bo stored in three
"electric circuits, and a transfer of stored magnetic energy between
the three electric circuits, and therewith a surge, thus can
occur.
with only one form of stored energy (magnetic energy), by the
combination of several simple exponential tranwralH. How-
ever, it must be considered that, while energy can be stored
in one form only, as magnetic energy, it can bo stored in three
"electric circuits, and a transfer of stored magnetic energy between
the three electric circuits, and therewith a surge, thus can
occur.
It is interesting to note that the rotatmg-field transient is
independent of the point of the wave at which the circuit m
closed. That is, while the individual tranment** of the three
three-phase currents vary in shape with the point of the wave at
which they start, as shown in 1%, 17, their polyphase rwulttmt
always has the same oscillating approach to a uniform rotating
independent of the point of the wave at which the circuit m
closed. That is, while the individual tranment** of the three
three-phase currents vary in shape with the point of the wave at
which they start, as shown in 1%, 17, their polyphase rwulttmt
always has the same oscillating approach to a uniform rotating
field, of duration T - - •
The maximum value, which the magnetic field during the transi-
tion period can reach, is limited to less than double the final value,
as is obvious from the construction of the field, Fig* 19, It IH
evident herefrom, however, that m apparatus containing rotating
fields, as induction motors, polyphase j&ynchronoiw machines, etc.,
the resultant field may under transient condition** reach nearly
double value, and if then it reaches far above magnetic saturation,
excessive momentary currents may appear, wimilar an in Hturtmg
transformers of high magnetic density. In polyphmw rotary
tion period can reach, is limited to less than double the final value,
as is obvious from the construction of the field, Fig* 19, It IH
evident herefrom, however, that m apparatus containing rotating
fields, as induction motors, polyphase j&ynchronoiw machines, etc.,
the resultant field may under transient condition** reach nearly
double value, and if then it reaches far above magnetic saturation,
excessive momentary currents may appear, wimilar an in Hturtmg
transformers of high magnetic density. In polyphmw rotary