REGULATING POLE CONVERTERS

439

Where the required voltage range above normal is not greater
than can be produced by the third harmonic of a large pole arc
with uniform density, this combination of voltage regulation
by both methods can be carried out with two sections of the
field poles, of which the one (toward which the armature moves)
is greater than the other, as shown in Fig. 211, and the variation
then is as follows :

Pole section .
Max. voltage

Min. voltage

Magnetic Density
2 I7

2'

. +

4-

A

i
2
n
i
2'
|.

FIG. 211.—Two-section pole for variable-ratio converter.

Heating and Rating

240. The distribution of current in the armature conductors
of the variable-ratio converter, the wave form of the actual
or differential current in the conductors, and the effect of the
wattless current thereon, are determined in the same manner as
in the standard converter, and from them are calculated the local
heating in the individual armature turns and the mean armature
heating.

In an n-phase converter of normal voltage ratio, let E$ =
direct voltage; I0 = direct current; EQ = alternating voltage
between adjacent collector rings (ring voltage), and 1° = alter-
nating current between adjacent collector rings (ring current);
then, as seen in the preceding:

n • K

EQ sm -

E° - -JT' «

and as by the law of conservation of energy, the output must
equal the input, when neglecting losses:

jo =

(2)

n sm-

1

i ?fi

n