I '

236 ELEMENTS OF ELECTRICAL ENGINEERING
generator of the same output, we have

sin2 -
n

• + 1 -

16 cos r

the ratio of the power loss in the armature coil resistance of the
converter to that of the direct-current generator of the same
output, and thus the ratio of coil heating.
This ratio is a maximum at the position of the alternating

leads, r = -, and is

IV

16 cos

n

nir sin —
n

It is a minimum for a coil midway between adjacent alter-
nating leads, r = 0, and is

8 . . 8

To =

n2 sin

2 -
n

7T

•sm -
n

Integrating over r from 0 (coil d) to -, that is, over the whole

¥1

phase or section ax a2, we have

n2 sin2 -
n

the ratio of the total power loss in the armature resistance of
an ft-phase converter to that of the same machine as direct-
current generator at the same output, or the relative armature
heating.

Thus, to get the same loss in the armature conductors, and
consequently the same heating of the armature, the current in
the converter, and thus its output, can be increased in the pro-
portion —T~ over that of the direct-current generator.

The calculation for the two-circuit single-phase converter is
somewhat different, since in this in one-third of the armature
the Pr loss is that of the direct-current output, and only in the

other two-thirds—or an arc ~—is there alternating current.