August 25, 1916.

THE COLLIERY GUARDIAN.

353

welder, the great manufacturing firms in the kingdom have
been able to keep going at full blast, without any slacken-
ing in production. Bariniar Limited have contributed
in no small degree to the maintenance of the machine shop
efficiency, and the management board of the Metropolitan
Munitions Committee has recently gone out of its way to
testify its appreciation of the prompt and capable manner in
which its services have been rendered.

ELECTRICAL DISTRIBUTION
IN NUNES.*

By H. M. Waeeen,

In consequence of the growing tendency to generate
alternating current, transmit it at a reasonably high
voltage and then convert or transform it to low-voltage
alternating or direct current at or near the point of
application, it is frequently found advantageous to use
both direct and alternating current (usually three-phase)
power in the same mine, direct current being used for
the operation of electric locomotives, coal-cutting
machines, portable track pumps, portable air compressors
or any other equipment that may be operated from a
direct-current trolley line or feeder. The alternating
current is frequently used to advantage in the operation
of equipment requiring medium or large amounts of
power, such as pumps and hoists, although it can also
be employed to advantage in certain cases in the opera-
tion of coal-cutting machines.

In general, however, because of the use of the electric
mining locomotives, with resultant trolley lines extend-
ing to many portions of the mines, the direct current is
used except in equipments requiring considerable power,
in which case low-voltage (250) direct current would not
work out to so good advantage, because of the high cost
of copper involved in the transmission of energy for any
considerable distance.

The active workings of anthracite mines ordinarily
extend over a large area, and for this reason it is fre-
quently advisable to run transmission lines on the surface
and feed the equipment inside by cables suspended in



Fig. 1.—Surface Structure Supporting
Feed Lines.

no reason why a high voltage should not be taken inside
through a borehole, the voltage reduced inside by trans-
formers or supplied directly to the motor at the trans-
mission voltage, if the motor is properly designed and
the entire equipment installed in a correct manner.

However, because of the dampness and conditions
that usually exist, it is not advisable to use a voltage
exceeding 4,000 for the direct operation of an induction
motor, and it might be better practice to limit this to
2,300. This is entirely a question of the insulation of
the induction motor coils and general conditions where
the motor is used.

Transformers used inside should have a case made of
reasonably heavy material of such construction as to
withstand a red heat without coming apart. The top

Fig. 2.—Cable Support between Coal Seams.





should be provided with a cover which would open auto-
matically to relieve any excessive pressure in the trans-
former and permit of the introduotion of a fire extin-
guisher in case of necessity.

Fig. 2 shows the arrangement of supporting cables
where they are dropped from one coal seam to another.
The cables from the surface coming down to this point
through a borehole are taken to a distributing switch-
board, from which point feeders are run off in this par-
ticular seam, and one feeder is carried on down to the
seam below.

The use of 250 or 300 volts direct current for mining
locomotives, while decreasing the danger from a shock
due to contact, increases the amount of copper required
over that which would be necessary with a higher

feeder circuits are brought in from each of two sub-
stations, permitting the load in this section to be handled
from either sub-station as desired. Steel cables on the
grounded return circuit can also be seen in this view, as
well as the method of insulating the positive cables >at
the dead-ending frame by means of heavy porcelain
insulators.

The low-voltage alternating-current feeders can be
installed in a manner similar to those carrying direct
current, but care must be taken in calculating these
circuits to bear in mind the effect of induction and what
is known as “ skin effect,” when large amounts of
current are considered. It may be found advantageous
to split the circuit up, using more wires of a smaller
size, ratheir than to use a smaller number of large size.
A good secondary potential to use is 440 volts, but even
with this the current required for the operation of hoists
or pumps using 200 or 300 horse-power is such as to
cause consideration of these factors when it is necessary
to carry the circuits for any considerable distance.

When the apparatus to be driven is at a considerable
distance below the surface, say, 1,000 or 1,500 ft., the
cost of a borehole becomes an important item, and under
these conditions it would probably be advisable to carry
the high-tension circuit down through the borehole, then
through a conduit system installed under the roadway
or at some convenient location, to the point of applica-
tion to the step-down transformer or transformers. If
the high-tension cable were armoured, it might be sup-
ported along the rib or roof, but unless conditions were
favourable it would be subject to damage by the changing
of timbers, falling of roof and from wrecks. The first
cost of underground ducts is high, but if it can be used
for a long period the expense is undoubtedly justified.
No general rule can be given, but each case must be
carefully considered.

The size of wire for a trolley line depends on the
voltage, the amount of power required and the length of
the circuit, but for 300-volt service it is customary to
use a relatively large wire, one of about 3/0 B. and S.
gauge. Even with the use of a large-sized wire, the drop
in voltage permitted is high, with a maximum permis-
sible drop of about 120 volts, when the direct-current
potential generated is 300. This gives a minimum
trolley voltage at the locomotive of 180. •L’his percentage
drop in voltage would be considered excessive and not
allowable except in mining or some similar service, but
it is good engineering under anthracite-mining condi-
tions when there are various branch trolley lines extend-
ing for considerable distances and over which the loco-
motive operates at infrequent intervals.

Such roads are used for limited periods, and when
this section becomes worked out, the wire is taken down
and used elsewhere. This condition, together with the
low cost of power, would.not warrant the investment in
copper and labour necessary to provide circuits of such
capacity as to give a small drop in voltage. Experience
indicates, however, that it is not advisable to allow the
pressure to drop below about 180 volts.

Ot-her apparatus driven by direct-current motors of
the series type, such as hoisting equipment, will
operate satisfactorily under this voltage, but if motors
not. of the series type are used for the operation of any
equipment such at pumps, requiring a fairly constant
speed, care should be taken to see that these motors
are designed to operate satisfactorily under this condi-
tion, and it is customary to use what is known as an
“ accumulative -wound motor ” for this purpose. This
type has, in addition to the shunt fields, a series field,
so connected as to assist in maintaining the strength of
the field when the voltage is low’.

The trolley wire is supported by means of special insu-
lators with various arrangements for attachment to the

boreholes. There are four ways of taking the feeders
into the mines—through a drift, down a slope, a shaft, or
a borehole.

Where it is at all practicable, a borehole properly lined
is most desirable, for the cables are then free - from
mechanical injury, and not liable to be subjected to the
action of bad water. In shafts where there is sufficient
space to suspend the cable so that it is entirely free from
contact with any portion of the shaft, piping or other
material and not likely to be damaged by falling ice or
coal, there is no serious objection to suspending it in the
shaft. But even in cases of this sort where the shaft is
clear, there remains the possibility of damage by work-
men or a wreck in the shaft. However, these instances
are few, as the space in most shafts is taken up by steam,
air, or water lines.

There is no reason why cables should not be taken in
through a drift or down a slope if conditions are favour-
able to this method, but as compared to a borehole they
are still subject to greater liability of damage.

Fig. 1 shows a structure on the surface supporting the
feed lines where they are “ dead-ended ” and from which
the borehole cables are suspended. This installation is
for a direct-current circuit, but a similar type of
structure is used for alternating-current circuits.
Whenever a borehole is. used in connection with an
alternating-current circuit and the distance from the top
of the borehole to the place where the power is to be
used and the amount of power required is not too great,
it is advisable to place the transformer at the top of the
borehole and reduce the voltage from the transmission
circuit at that point rather than to place the trans-
formers inside. This arrangement permits taking the
lower voltage into the mine, the transformer can be
easily inspected, the coils (which require considerable
headroom for their removal) can be removed for repair,
and the cost of providing space for the transformer
inside is eliminated.

When using alternating current for the operation of
equipment requiring a large amount of power, there is

* Coal Age.

Fig. 4.—Tightening a Cable
with a Turnbuckle.



Fig. 3.—Cable Anchorage and
Bond Attachment.

voltage. In an endeavour to keep down the cost of
copper, second-hand steel cables are used for reinforcing
the grounded return circuit. As these are usually old
hoisting cables an inch and a quarter in diameter or
larger, they are quite heavy to handle, and require
special means of support to keep them in good condition',
as, from past experience, it is found unsatisfactory to
lay them along the roadway or support them in the
manner of supporting the ordinary feeder—that is, by
means of pins and insulators.

Fig. 3 shows the method of anchoring two cables, and
also the way of taking off copper bonds at a point near
the end of the cable.

Fig. 4 shows the process of pulling up the cable by
means of a turnbuckle, with the copper bond around the
connection. In making the bond connection, the old
steel cable is first cleaned and thoroughly tinned. The
copper bond wire is then wrapped around the cable and
thoroughly soldered, after which the joint is taped and
the entire cable painted.

Fig. 5 is a view of a distributing board at a point where

roof or timber. These are manufactured in a variety
of forms adapted to meet the different conditions. The
grooved trolley wire is ordinarily used. This is rolled
in such a manner as to provide two depressions in the
wire, the insulator or hanger being so designed that the
metal portion below the insulator grips the wire in the
grooves. The type of hanger used is entirely a matter
of selection and judgment to meet the conditions under
consideration.

Protection of Trolley Wire.

For the protection of trolley wires, particularly at
points where men or animals are required to cross under
them, it is customary to instal a board on each side. In
low veins, however, these boards present a certain
hazard in that they are rigidly supported, and if a
person’s head should come in contact with one of them,
serious injury might result. With this in view, a pro-
tective device has been tried, consisting of a grounded
steel messenger wire, supporting, by means of heavy
twine, a section of second-hand hose installed as shown.
This has been carefully tested out when wet, and so far