REGULATING POLE CONVERTERS 445

This is the same expression as found for the average armature
heating of a converter of normal voltage ratio, when operating
with an angle of lag, 0o, of the alternating current, where fc denotes
the ratio of 'the total alternating current to the alternating
power current corresponding to the direct-current output.

In an ri-phase variable ratio converter (split-pole converter),
the average armature heating thus is given "by:

p ^_ 8fc2 | i 16 fc cos 00

~ ~'

n
where

(1 + 0(14- Pi) cos r«

---- — - —

l£>l

-

cos 61
0o = 0i — ra — Tfr; (10)

and 2 = ratio of third harmonic to fundamental alternating
voltage wave; pi = ratio of loss to output; 0i = angle of lag of
alternating current; ra = angle of shift of the resultant mag-
netic field in opposition to the armature rotation, and T& = angle
of shift of the brushes in the direction of the armature rotation.
244, For a three-phase converter, equation (18) gives (n = 3) :

+-1 -1.621 ft cos

= 1.185 fc2 + 1 - 1.621 fc cos fa. j
For a six-phase converter, equation (18) gives (n = 6) :

O &2

r = »L+ ! _

= 0.889 fc2 + 1 - 1.621 fc cos 00.
For a converter of normal voltage ratio:
t = 0, Ta = 0,

using no brush shift :

T> = 0;

when neglecting the losses :

Pi = 0,

•it is:

- -
— ~ " ^ '
COS 0!
A
= c/i,