238

ELECTRICAL APPARATUS

tage, e0, but the alternating current, i, is as shown in Fig. 81 as i.
If the circuit is inductive, vicious sparking occurs in this case
with open-circuit rectification, as the brush when leaving the

FIG. 81.—Voltage and current waves in open-circuit rectifier on non-induc-
tive load.

commutator segment must suddenly interrupt the current. That
is, the current does not stop suddenly, but continues to flow as
an arc at the commutator surface, and also, when making con-

FIG. 82.—Voltage and current wave in open-circuit rectifier on inductive
load, showing sparking.
tact between brush and segment, the current does not instantly
reach full value, but gradually, and the current wave thus is as
shown as i and i0 in Fig. 82, where the shaded area is the arcing
current at the commutator.
Sparkless rectification may be produced in a circuit of moderate