64 The N.Z. Journal of Science and Technology. [Feb. 
load, while the advantage of method (d) over methods (a), ( b ), and (c) lies 
in the fact that the boosting voltages are more easily controlled, but, since 
the boosting generator must have the same number of poles as the balancer, 
it cannot be built very cheaply even though the output is small and the 
cost of exciter and regulating-gear is by no means negligible. 
Several methods of producing an oppositely rotating magnetic field of 
double frequency are described, but all involve the use of several auxiliary 
machines in addition to the main translating apparatus required to furnish 
the single-phase load. 
Before describing the rotating balancing transformer designed by him 
the author deals with the advantages and requirements of single-phase 
furnaces from an electrical point of view. In the first place, only two 
electrodes are required instead of three, and as these can be brought 
into the furnace at two diametrically opposite points the liability of the 
arc to cause a short circuit through the hot semi-conducting lining is very 
much reduced. This enables the voltage to be raised to a value almost 
double that which is practicable for a polyphase furnace. As the electrode 
losses are dependent upon the surface of carbon exposed and also upon 
the amount of air-leakage through the furnace, the reduction in the 
number and size of the electrodes and in the number and size of leakage- 
holes results in a great saving in electrode consumption. There is also a 
reduction in radiation losses due to the spherical form. 
It is pointed out that with an inductance in circuit sufficient to make 
the current lag 45° behind the voltage the input to the furnace cannot 
exceed the full-load value, however the resistance of the circuit may be 
varied. This is the ideal condition for steady running from the user’s 
point of view. From the power company’s point of view, however, the 
inductance is not an unmixed blessing, but so greatly does the stability 
given by the inductance help towards economy in furnace-linings that 
large numbers of furnaces in both England and America are run at 0*7 
power-factor. 
The rotating balancer designed by the author ensures that the single¬ 
phase current supplied to the furnace lags the required 45° behind the 
voltage, while at the same time the three-phase windings may be operated 
at unity power factor, thus satisfying the requirements of both supply 
station and consumer. These conditions are met by building a three- 
phase synchronous motor, having an ordinary three-phase armature winding 
lying in slots near the working-face of the stator, and provided with a 
single-phase winding lying in slots farther removed from the rotor than 
the three-phase slots, and arranged so that very considerable magnetic* 
leakage occurs between the two windings at full load. 
These machines are in successful operation in conjunction with the 
Snyder electric furnace in both England and America. 
A 400 kw. machine designed for furnaces making steel for war purposes 
is described in detail. The test sheets show an efficiency of 904 per cent. 
The machine fulfils the functions of (1) voltage transformers, (2) balancer, 
(3) reactance, (4) power-factor corrector. These functions can, of course, be 
performed by a motor-generator set designed with suitable characteristics, 
but the first cost of the motor generator is higher than that of a balancer 
of the same output and the efficiency is lower. 
Comparative costs of the two types of machine fulfilling the same 
function are, unfortunately, not given. A. C. 0. 
By Authority : Marcus F. Marks, Government Printer, Wellington. 
[ 1 , 800 / 12 / 19-21276 
