244

ELECTRICAL APPARATUS

practical usefulness of rectification, as such readjustment with
every change of circuit condition is hardly practicable.

Short-circuit rectification has been used to a large extent on
constant-current circuits; it is the method by which the Thomson-

A

O

ff

FIG. 92.—Double-brush rectifier.

Houston (three-phase) and the Brush arc machine (quarter-
phase) commutates. For more details on this see " Theory and
Calculations of Transient Phenomena," Section II.

FIG. 93. — Voltage waves of open -circuit rectifier charging storage battery.

Open-circuit rectification has found a limited use on non-in-
ductive circuits containing a counter e.m.f., that is, in charging
storage batteries.

If, in Fig. 93, e0 is the rectified voltage, and ei the counter e.m.f.

i

of the storage battery, the current is n =

Pr\ ,- t

> where r- = ef-

fective resistance of the battery, and if the counter e.m.f. of the