808

THE COLLIERY GUARDIAN.

April 16, 1915.

to open and close feeder or machine circuits occasionally,
and generally with no load on at the time, switches for
three-phase winders frequently have to make and break
circuits from 500 to 1,000 times per day, and the
breaking is usually done under full load. It requires a
very substantial switch to stand up to this sort
of work, and the arcing contacts and the oil have
to be renewed at least once a week. This is a very
‘‘ messy ” and expensive job, and contactor switches are
being insisted upon for all future three-phase winders.
On a three-phase winder at Rose Deep Limited these
switches have made and broken the stator circuits over
388,000 times without any cost whatsoever for repairs
or maintenance.

Ward-Leonard v. Three-Phase Winders.

The author has endeavoured to obtain from his own
experience reliable comparative figures of the costs of
Ward-Leonard and three-phase winders, but the weights
raised, rates of acceleration, speeds of winding, and
depths of shafts are so variable on the mines of the
group which have the two classes of winders, that he
cannot put forward data of any real value. It may be
stated generally that the deeper the shaft (i.e., the
longer the relative period of full-speed winding) the
cheaper is the three-phase system compared with the
Ward-Leonard, particularly if the contactor system of
rotor control is used, because with the latter the
resistance losses are entirely eliminated at full speed.

With balanced (double drum) winders working
without a tail-rope, there is, however, a limit to the
depth at which a three-phase winder is the more
economical, because the weight of the descending rope
ultimately overbalances the weight of the ascending
lo id and reverse current has to be applied to prevent
the winder running away. Such energy has to be paid
for, but with the Ward-Leonard winder the greater part
of the braking energy can be returned to the line.
There is therefore not only the saving of a loss, but a
distinct gain to be made.

For a winder which is frequently or constantly used
for lowering loads, such as men or material, or, in some

WINDING DRUMS

CONTROLLER-

■CONTACTS

___p—NEUTRAL '•05ITI0N

Fig. 2.—Diagram of Philip’s Indicating
Device.

cases of incline shafts, lowering rock to a point where it
can be better raised by a vertical shaft winder, the Ward-
Leonard system is much to be preferred. It is only by
drawing out a diagram for each individual case that a
proper decision can be made as to which type of winder
is the correct one to employ.

One advantage which the 3-phase winder has over the
Ward-Leonard is that geared motors running at 375
r.p.m., or at higher speeds, can be most conveniently
employed in the majority of cases, which not only means
a much cheaper equipment, but a better and more
economical motor than if a direct-coupled one were
used. With the Ward-Leonard system a direct-coupled
low-speed motor, although more expensive, gives a better
working machine.

The largest electric winder in South Africa is of the
Ward-Leonard type and has two motors, each of 2,000
h.p. (R.M.S. rating), one at each end of the drum shaft.
There are two cylin dro-conical drums, each 22 feet
diameter, which wind a net load of 16,000 lb. from a
depth of. 3,540 feet at a speed of 3,500 feet per minute.
The winding ropes are 2 in. diameter. This winder is
one of three at the South Rand shaft of Crown Mines
Limited, and they operate at 54 r.p.m.

The motor-genera tor for the above set runs at 350
r.p.m. and has two generators, one on each side of the
induction motor, each working at 500 volts. They are
connected in series with each other and the two winding
motors. A current of 5,000 amperes is frequently taken
when starting up the winder. The electrical equipment
was madeby the General Electric Company, Schenectady.

A winder with a single cylindro-conical drum, 24 ft.
diameter, and identical electrical plant, is now being
erected at New Modderfontein G. M. Company Limited.
This winder will raise a net load of 12,000 lb. from a depth
of 2,200 feet at a speed of 4,050 feet per minute.

Overwinding Devices.

There is one essential difference between winding coal
and winding gold ore. Coal is comparatively soft and
easily broken, and it is necessary that it should be
delivered in masses as large as possible. The gold-
bearing rock or “ reef ” of the Witwatersrand is exceed-
ingly hard, and the ore is brought to the surface in
steel skips, holding from 3 to 8 tons. The skips are
filled at the bottom of the shaft through chutes from
large underground bins, to which the ore is brought

either in tubs or trucks by the underground haulage
system. The ore is tipped from the skips into bins
situated high up in the headgear, so as to get sufficient
head room beneath the chutes for the operations of
sorting, crushing, &c., on the surface. This means that
the clearance between the skips at the tipping point
and the headgear sheaves is very small, frequently not
more than 5 ft. on many mines, and the care required
from the driver to prevent overwinds is therefore much
increased.

Experience has shown, however, that most of the
so-called overwinding accidents which have occurred on
the Rand have been caused, not by any failure to stop
the skip, but by starting the winder in the wrong
direction when one skip is at the tipping point. In
such cases the skip is pulled into the headgear sheaves
before the winder drum has made half a turn. Over-
winding devices which cut off the supply of energy
when the skip has reached a predetermined point are
not of much use for avoiding such accidents, because
the driver must retain full command of the winder, in
whatever position the skip is, to be able to bring the
skip to the exact tipping point. This operation
frequently calls for slight movements of the winder
after it has first been stopped.

In 1912 the author’s attention was directed to an
electrical device in use on certain winding engines at
the Simmer and Jack East mine, near Johannesburg,
the invention of Mr. W. Philip, the resident engineer,
which it was claimed would give unmistakable warning
to the driver if he attempted to start the winder in the
wrong direction with the skip in the tip, without in any
way taking away from him the full command of the
winder. On investigation this claim was found to be
fully justified, and since that date the whole of the
winders on the mines of the group have been fitted with
the Philip device. Its principle is illustrated in
fig. 2, which shows a diagrammatic arrangement, and
the action is as follows:—A two-way controller switch
is connected to the driver’s operating lever, so that the
contacts are open when the lever is in the neutral or
“ off ” position. A slight motion of the lever in either
direction closes the contacts on one side or the other.
An insulated disc, with a short metallic insertion on the
edge, is fixed on the spindle of each depth indicator
dial, with two contacts arranged so that the circuit is
closed when th? depth indicator shows the skip to be
anywhere in the region between the headgear sheaves
and, say, 150 ft. below the collar of the shaft. A
battery and a loud warning hooter complete the
apparatus, which is connected up as shown in fig. 2. In
the case of winders with loose drums operated through
clutches (a great many of these winders are in use on
the Rand to wind from different levels) an auxiliary
contact is provided which is broken when the clutch is
open and the brakes are holding that drum.

By following through the connections it will be seen
that when a skip is within what may be called the
“danger zone” the smallest movement of the operating
lever in the direction to raise the skip will sound the
hooter, which is placed close to the driver. He is at
once warned, and unless he has deliberately put his lever
into that position he quickly pulls it back before any
damage has been done. He can only raise the skip
within the danger zone with the full knowledge of what
he is doing, and he is also warned by the hooter if he
keeps the power on past the predetermined point in
the shaft. This simple apparatus has already been the
means of preventing a great many accidents.

There are many designs of overwinding devices, both
electrical and mechanical, which come into operation
when the skip has passed a certain point in the shaft or
headgear and stop the winder by cutting off the power
and applying the brakes. Some act through a centri-
fugal governor and prevent the driver from winding at
too great a speed within the danger zone. Others only
act when the skip has actually come to a few feet above
the correct stopping place. One of the most common
and effective types employs cams or screws with running
nuts gradually to bring the control lever back to the off
position if the driver has not already done so.

Depth Indicators.

The most general form of depth indicator used on
winders on the Rand is that of the dial pattern, as
indicated in fig. 2. The dials are usually about 5 ft.
diameter, and are mounted on high cast iron^ pillars,
placed one at the right hand and one at the left hand,
either in front of or behind the winding drums, facing
the driver’s platform.

When the old steam, winders were converted to electric
driving the original depth indicators were kept in use,
and the electrical instruments, being of a small size, had
to be mounted on or close to the driver’s platform so that
they could readily be seen. Even for new electric
winders the same arrangement of large depth indicators
at a distance and small electrical instruments close to
the driver was retained. Only in a few cases has the
vertical screw pattern of indicator been used, still with
electrical instruments mounted separately.

It appeared to the author that it was a wrong
principle to make the driver have to watch two sets of
indicators, one mechanical and one electrical, in such
different positions and at such different distances, and
that the eye strain must be detrimental. He therefore
endeavoured to bring all the indicators to one place,
namely at a distance of about 6 ft. in front of the driver,
and to reduce the size of the dial of each depth indicator
so that it would have the same angular diameter as at
the greater distance. For example, a dial 5 ft. diameter,
at a distance of 20 ft., would appear no larger than one
18 in. diameter at a distance of 6 ft. It is obvious, also,
that as the angular movement of the pointer would be
the same whatever the diameter of the dial, the indica-
tions would be just as visible on the smaller dial at the
reduced distance, as on the larger dial at the original
distance.

Owing, however, to a recent (1914) requirement of
the Transvaal Government Mines Department, that the
tip of the pointer of the indicator should have a move-
ment of not less than 1 in. for each complete revolution
of the winding drum, a dial 18 in. in diameter was found
to be too small for most of the winders, as with an 8 ft.
winding drum it would only indicate to a depth of about
1,000 ft. The Government requirement was based upon
the practice of the drivers, viz., to watch for rope or
drum marks during the last revolution of the drum, to
guide them in bringing the skip to the correct spot, and,
with a pointer movement of less than 1 in. per revolu-
tion, it was considered difficult to determine when the
last revolution had arrived. This restriction makes the
vertical-screw type of indicator quite unwieldy, unless a
magnifying pointer be used for the last 100 ft. of the
wind, and even then it requires a somewhat extended
movement of the head and eyes to follow the positions
of the ascending and descending skips and the indica-
tions of the electrical instruments.

The author therefore decided to use a depth indicator
of the dial pattern, of the type in which the pointer moves
through a very wide angle, covering at least 1| turns,
in a circular path of constantly and regularly increasing
(or decreasing) radii. So far as he is aware, this type
was first designed and used by Mr. Roberts, of Knights
Central Limited, Germiston. The final arrangement is
shown in fig. 3, from which it will be seen that the
electrical instruments and the air pressure gauge for
the brakes are mounted between two dials. The indicator
pointer is carried in a rectangular groove at the front end
of the pointer spindle, and is guided in its circular
motion by a small roller on the under side, which engages
in a roller path formed in the depth of the dial face. A
small screen is fixed at the outer end of the pointer,
which covers up the markings on the inner ring when
the pointer is indicating on the outer ring.

The dials are of only 27 in. diameter, and the end of
each pointer can move through a total path of about
116 inches. This, with only an 8 ft. diameter drum,
will serve for a depth of 2,900 feet, on the basis of 1 in.
of movement for each revolution of the drum.

Fig. 3.—Combined Indicators for Electric
Winders.

The complete indicator set is mounted on two pillars
immediately in front of the driver’s platform, with the
tops of the dials at a height of about 4 ft. above the
platform level. The driver is thus able easily to see
over the top, to watch the drum marks, ropes, etc., when
necessary.

The driving spindles for the dials are connected by
gearing to the drums in the usual way.

Immediately beneath each dial in fig. 3 will be
noticed a small square box, with two arrows on the
front side. Each box is divided into two vertical com-
partments, with an incandescent lamp inside each. The
arrows are stencil cut through the cover, each right-
hand arrow being covered by red glass and each left-
hand arrow by green glass. A small control switch is
connected to the operating lever, so that when the skip
in the left-hand shaft compartment is being raised (and
the skip in the right-hand compartment being lowered),
the right-hand arrow (red) under the left-hand dial, and
the left-hand arrow (green) under the right-hand dial are
illuminated. The reverse action takes place when the
skip in the right-hand shaft compartment is being raised.
The driver has therefore an instant indication as to
which skip is being raised, and follows the movements
of that dial indicator pointer which has the red arrow
under it.

Immingham Coal Exports.—Returns tfor the week ending
Friday, 9th inst., show that the coal exported from Imming-
ham was as follows:—Foreign : To Bergen, 950 tons;
Dieppe, 628; Genoa, 4,851; Havnefjord, 900; Huelva, 3,292;
Reykjavik, 1,066; Rotterdam, 13,181; Ystad, 1,398 tons.
Coastwise : To London, 940 tons. Total, 14,403 tons
foreign and 940 tons coastwise, as 'against 29,211 tons foreign
and 2,000 tons coastwise during the corresponding week last
year.

Partnerships Dissolved.—The London Gazette announces
the dissolution of the following partnerships :—T. E.
Frearson and F. D. Bartholomew, steam cultivating con-
tractors, at West Barkwith, Lincoln, under the style of
Frearson and Bartholomew; E. Mills and A. J. Vaughan,
the Victoria Stamping Company, at Manor Works, Wednes-
field-road, Willenhall, Stafford, as manufacturers of drop
forgings; W. Barry and F. O. Gibson, pump makers, at
Dronfield, Derby, under the style of the Dronfield Engineer-
ing Company; H. Tapp and A. Tapp, ironmongers, at
Lydney, Gloucester, under the style of Tapp Brothers; T.
Boulton, W. Burletson, and E. Wilson, consulting engi-
neers, at Exchange-buildings, Quayside, Newcastle-upon-
Tyne, under the style of Thomas Boulton and Company.