248

ELECTRICAL APPARATUS

voltage, e0, is one-half th& alternating voltage, e, and the rectified
current, i0, is twice the alternating current, i. However, the i*r
in the secondary coil, ab, is greater, by V2,
than it would be with the alternating cur-
rent, i = iQ/2.

Inversely, in the contact-making rectifier,
Fig. 98,' the rectified voltage is twice the
alternating voltage, the rectified current
half the alternating current.

Contact-making rectifiers of the type
Fig. 97 ^re extensively used as arc recti-
fiers, more particularly the mercury-arc
rectifier shown diagrammatically in Fig.
FIG. 101.—Mercury- 101. This may be compared with Fig.
97. That is, the making of contact during
one half wave, and opening it during the
reverse half wave, is accomplished not by mechanical syn-
chronous rotation, but by the use of the arc as unidirec-

hP-HH

arc rectifier,
making.

contact

FIG. 102.—Diagram of mercury-arc rectifier with its reactances.
tional conductor:1 with the voltage gradient in one direc-
tion, the arc conducts; with the reverse voltage gradient
1 See Chapter II of "Theory and Calculation of Electric Circuits."