coal trade bulletin - Clpdigital.org

a sealing compound covering the junction of the
leads and the terminals. At the right-hand side
of the box, facing it, is a handle which closes
and opens the service switch. The acceleration
of the motor is accomplished by limiting the current
peaks with series wound switches.
It might be well to mention here a rather interesting
alternating-current controller. This is
a 125-h.p. 2200-volt, three-phase, 60-cycle automaticstarter
for a slip ring motor. The starter is "explosion
proof" and is mentioned for this reason.
The switches are magnetically operated and the
circuits are made and broken under oil. This controller
was installed in the Homestake Mining
Co.'s gold mine at Lead, S. D. The outfits starts
a pump automatically from a float switch. The
control circuit is stepped down to 220 volts so
that the float switch does not have to handle the
high voltage.
A subject which is occupying much thought
among coal mining engineers is the mine locomotive.
The tendency is to eliminate the overhead
trolley where there are low ceilings. This
may be done either by the use of a trailing cable,
kept taut by a tension reel, or by the use of
storage battery locomotives. The trailing cable
was not very popular until the automatic motordriven
cable take-up was developed. Without this
device the dragging cable was always in the way.
The motor driving the table take-up is connected
across the line in series with a
STEP OF RESISTANCE.
When the cable is to be hauled in, the motor
winds it up, and when paying out is required
the cable overhauls the motor.
On account of the difficulties attending the use
of trailing cables, it would seem that the coming
mine locomotive, when not in main entries, will
be operated from a storage battery carried on
the locomotive. The present trouble with storage
battery locomotive is the necessity of laying
them up for charging or of having two sets of
batteries and charging them at intervals. The
battery must be carefully watched and attended.
If the batteries could be automatically charged
without delay, the usefulness and reliability of
the storage battery locomotive would be materially
increased. This may be accomplished by the
use of an automatic reverse current cut-out, so
arranged that when the locomotive picks up the
trolley, the battery will be automatically put on
charge. If however, the line voltage is for any
reason lower than the battery voltage, the battery
will be automatically cut off from the line.
The same applies when the line voltage fails, so
that the battery will not be discharged into the
line. In this way the same locomotives may be
used for gathering and hauling trips. This will
THE COAL TRADE BULLETIN. 53
result in the battery frequently receiving a boosting
charge. The nickel-iron battery, which seems
the most popular for mine locomotive work will
show its maximum efficiency when so charged.
Manually operated drum controllers are almost
universally used for mine locomotives. These
are usually of the series parallel type and there
are two prevailing styles, each of which has its
advocates. The first operates the same as a standard
street railway drum which has two levers,
one reverse and one for accelerating. The other
style also has two levers as above, but the reverse
has two positions each side of the "off"
position, one for motors in series and the other
for motors in parallel. This
LATTER SCHEME IS ADVANTAGEOUS
because it is easier to get straight series only,
during gathering.
Rheostatic drum type control is sometimes used
for underground haulage engines.
For slope mines, the winding drum for haulage
is generally installed in the tipple and whole
trips of cars are hauled up at once. These winding
or mine haulage machines are usually alternating-current
motor-driven with secondary control,
either by means of a secondary resistance
drum or by means of a liquid rheostat. It is
sometimes advantageous to be able to change
gears for pulling strings of cars in from the
sidings. There has been a tendency of late to
put in safety cut-offs so that the current to the
motor is interrupted before the cars get to the
top. Variable inertia plays an important part in
the stopping point, and in fact, the variable
stopping point sometimes becomes so annoying
that a flyball-governor limit switch in addition
to the ordinary limit switch is installed, so connected
that if the speed is high the governor allows
the first limit switch to trip. If the speed
is low, the first limit switch is "shunted" by the
governor and the haulage may continue until
the second limit switch is engaged.
A straight vertical hoist is used to a limited
extent. Almost invariably this type of hoist can
be best electrified by the use of the variablevoltage
system, because the hoists are short and
therefore acceleration is an important consideration.
A flywheel is used to store the energy for
acceleration. Even with this arrangement, electrification
is in many cases of questionable economic
value.
An equalizer hoisting set is driven by a shuntwound,
direct-current motor, the
MOTOR RECEIVING
its energy from a motor-driven generator. The
motor-generator set has a heavy flywheel which
absorbs energy when the load falls below a certain
value and gives up energy when the load is