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From the Rolls-Royce experimental archive: a quarter of a million communications from Rolls-Royce, 1906 to 1960's. Documents from the Sir Henry Royce Memorial Foundation (SHRMF).
Page describing the electrical phenomena of current oscillation in primary and secondary circuits.

Identifier  ExFiles\Box 4\5\  05-page084
Date  1st August 1920 guessed
  
-15- Contd.

current will overshoot the zero and become negative, and
current oscillations will proceed for a while as already
explained. The fall of current referred to takes place
coincidently with a change of flux corresponding to this
fall of current. Corresponding to this change of flux there
is not only an E.M.F. in the primary winding and across the
condenser terminals, rising perhaps to several hundred volts,
but there also exists an E.M.F. in the secondary winding
proportionally greater in the ratio of the numbers of turns,
(see foot note p.12). An instant arrives very shortly after,
but not absolutely coincidently in time with the instant of
break, at which the secondary voltage has risen high enough
to break down the secondary gap. The moment this occurs
it may be considered that there is a complete secondary circuit
inductively coupled with the primary, with a high value of
coupling coefficient. It can be shown mathematically that the
effect of this sudden introduction of the secondary circuit is
to cause the primary current oscillation to be converted into
an oscillation of very much greater frequency, greater amplitude,
and much more damping than previously, so that the primary
current, although consisting of a number of quick oscillations
between the primary winding and the condenser, can be said to
be reduced to zero almost instantaneously. Corresponding
to this there is at the same time an oscillatory current in
the secondary and across the high tension gap, of similar
frequency and damping, but of amplitude reduced in the ratio
of the numbers of turns, and of phase exactly opposite to that
Contd.
COPY TO BE SENT TO W.O.V. REED. H.R.S.
  
  


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