SURGING OF SYNCHRONOUS MOTORS

299

1. An elimination of the term A2, or reduction as far as possible.

2. A sufficiently large term, c2, or

3. A sufficiently large term, pPQ.

(1) refers to the design of the synchronous machine and the
system on which it operates. (2) leads to the use of electro-
magnetic anti-surging devices, as an induction motor winding in
the field poles, short-circuits between the poles, or around the
poles, and (3) leads to flexible connection to a load or a mo-
mentum, as flexible connection with a flywheel, or belt drive of
the load.

The conditions of steadiness are:

>

0,

(c2 + pPQ - A2)2 ee0J|mJ> - 0)

16 " ....... "~" .....

and if:

no oscillation at all occurs, otherwise an oscillation with decreas-
ing amplitude.
As seen, cumulative oscillation, that is, hunting or surging,
can occur only, if there is a source of power supply converting
into low-frequency pulsating power, and the mechanism of con-
version is a lag of some effect—in the magnetic field of the
machine, or external—which causes the forces restoring the
machine into step, to be greater than the forces which oppose the
deviation from the position in step corresponding to the load.
For further discussion of the phenomenon of cumulative surging,
and of cumulative oscillations in general, see Chapter XI of
"Theory and Calculation of Electric Circuits/7