Due to the fact that only comparative results were sought, the
investigation was greatly simplified. On a comparative basis, the effects
of external influences were largely eliminated from positions of vital
importance and the use of an elaborate test, circuit was unnecessary.
The equipment consisted of a high-voltage test transformer which
supplied the test voltage; an induction regulator, auto transformer and
generator field rheostats for voltage control; overload relay and aircore
inductances for circuit protection; motor-generator set for a
source of 60 cycle alternating voltage. The electrodes were circular,
square edge brass discs.
Specimens were immersed in lubricating oil for periods up to 40
hours and then tested for puncture strength. Following this, specimens
were immersed for one hour and 24 hours and each of the two groups tested
at intervals of time up to 720 hours. In each test the voltage was raised
in steps of 200 volts, starting at 1000 volts. The puncture strength
of the untreated paper was determined by testing a sufficient number of
specimens over a period of days.
The results obtained indicated no immediate deleterious effects
of lubricating oil on paper. On the contrary, there was an improvement in puncture strength, accounted for by the fact that the relatively low
voltages-used'did not make ionization a serious factor.- The results of
tho long-time tests were unsatisfactory, as explained previously. However,
they did permit the conclusion that deterioration of paper impregnated
with lubricating oil would become apparent much sooner than if insulating
oil were used. Oxidation, although probably existing, was apparently too
slow to affect the results.
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