4 ELECTRIC DlSCttAROKtit WAVKR AND IMMtt&Kti.
is the phenomenon by which the circuit road justs itself to the
change of stored energy. It may than be said that the perma-
nent phenomena are the phenomena of elwtrb power, thu tran-
sients the phenomena of electric energy.
3. It IB obvious, then, that transients are not ttpwifwally t»l«»t*tri-
cal phenomena, but occur with all forms of energy, under all condi-
tions where energy storage taken place.
Thus, when we start the motors propelling an electric oar, a
transient period, of acceleration, appearn between tlw previous
permanent condition of standstill and the final {xwnancnt con-
dition of constant-speed running; when we shut off the motors,
the permanent condition of standstill is not reached instantly,
but a transient condition of deceleration interwwu Whm wo
open the water gates leading to an empty canal, a tramdont
condition*"of flow and water level intervenes while the* canal in
filling, until the permanent condition SH reached. Thus in the* cam*
of the fan motor in instance Pig, 1, a transient pwiod of $\nml
and mechanical energy appeared while the motor WEH «pmimg up
and gathering the mechanical energy of its momentum. When
turning on an incandescent lamp, the filament pas»oi a transient
of gradually rising temperature,
Just as electrical transients may, under certain condition*** rt»
to destructive values; BO transients of other formn of wergy may
become destructive, or may require serious eoniideration, aw, for
instance, is the case in governing high-head water powcra. The
column of water in the supply pipe represents a conHidorublo
amount of stored mechanical energy, when flowing at velocity,
under load* If, then, full load is suddenly thrown off, it in not
possible to suddenly stop the flow of water, since a rapid stopping
would lead to a pressure transient of destructive value, that in,
burst the pipe. Hence the use of surge tanks, relief valvon, or
deflecting nozzle governors. Inversely, if a heavy load comoH on
suddenly, opening the nozzle wide does not immediately take raw
of the load, but momentarily drops the water pressure at tin*
nozzle, while gradually the water column acquirea velocity, that
is, stores energy.
The fundamental condition of the appearance of a tranmient
thus is such a disposition of the stored energy in the system ti«
differs from that required by the existing conditions of the system;
and any change of the condition of a system, which requires a