276 The N.Z. Journal of Science and Technology. [Sept. 
that a very large number of the old steam winders have been equipped 
electrically. One of the chief difficulties was the very large amount of 
power a large winding-engine takes in starting, and the necessity of 
providing adequate equipment at the power-station to cope with this peak 
load. 
The subject of electric winding is a highly technical one, and it is not 
possible to deal with it in detail in a short article. Suffice it to say that 
there are two types of winders in use—namely, (1) the three-phase type, and 
(2) the Ward-Leonard type. In the South African mines, where a very 
large number of electric winders are installed, the first type has up to the 
present found favour, but solely on account of the lower capital cost, and 
the tendency is now to install the Ward-Leonard type. The three-phase 
type consists of an induction motor coupled to the winding-drums by 
means of gearing, and is a much simpler machine than the Ward-Leonard, 
but the control is more complicated. The Ward-Leonard consists of a 
motor generator set, the generator supplying current for a direct-current 
motor, either direct-coupled or geared with winding-drums. A great 
advantage of this type is the simplicity of control and the ease with which 
the cage may be manipulated when effecting a landing at the brace or the 
various levels, and also the fact that during braking operations at the end 
of a wind the winding-motor can be converted into a generator, thereby 
returning current to the line and acting as a very efficient electric brake; 
also, when lowering men or large quantities of material for use in the mine 
the greater part of the energy can be returned to the source of supply. 
A winder of this type has been working at the mine of the Waihi Gold¬ 
mining Company for the past four years ; it has cost nothing in the way 
of repairs beyond the renewal of a few brushes, and is preferred by the 
drivers to the steam-engine which was previously in use. 
Whilst on the subject of winding, it is interesting to note that one of the 
steam winding-engines at the Waihi Mine is now being run on compressed 
air, and a considerable saving has been effected. This engine has two 
high-pressure cylinders, each 18 in. diameter by 3 ft. stroke, and handles 
a maximum load of about 6 tons. The supply is taken from the main 
compressing plant at the mine, and efficient receiver capacity is provided. 
No alteration has been made to the engine except that appliances have been 
installed for pre-heating the air. It must, of course, be realized that, on 
account of conversion losses being heavy, such a system is only possible 
where cheap hydro-electric power is available ; but in this particular instance 
it was found cheaper to enlarge the existing compressing plant (electrically 
driven) and utilize compressed air than to electrify the winding-engine. 
Compressing .—Compressed air is one of the most useful and at the same 
time one of the most uneconomical servants of the miner, but is used for 
a variety of purposes in the mine and mill. Its chief use in the mine is for 
rock-drilling, but it is also largely used for winding, hauling, pumping, and 
ventilation, for pneumatic tools in the workshops, and for operating tool- 
sharpeners for the tools used for rock-drilling, whilst in the mill it is used 
for agitating and for air-lifts. 
Dealing first with its use at the mine, it is quite obvious that where 
large quantities of compressed air are required the ideal method is to have 
one main compressing-station and distribute the air to the various depart¬ 
ments. In a mine equipped with a steam-electric power-station it is 
a debatable point whether it is better to generate the compressed air 
electrically or to generate direct by steam. If the amount of air used is 
