THE COLLIERY GUARDIAN

AND

JOURNAL OF THE COAL AND IRON TRADES.
______________________________________

Vol. CXI.

FRIDAY, MARCH 31, 1916.

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The Calculation of Flywheel Motor=Generator Sets.

A description of a new electric hoist installed by the
North Butte Mining Company is given by Mr. Franklin
Moeller in a paper read before the American Institute of
Mining Engineers, to which is added a note on prelimi-
nary calculation of flywheel motor-generator sets by Mi-.
C. D. Gilpin.

This engine is believed to be the. largest electrically-
driven hoist in the United States, and is working at the
Granite Mountain shaft of the North Butte Mining
Company, Butte, Montana. While the weight of rock
which is hoisted by this machine is not the largest now
being handled by electric mine hoists, the speed of hoist-
ing is so, and the combination of the high speed with
the heavy load has resulted in a machine of considerable
interest to all those actively engaged in mining.

The conditions to be met in this installation were as
follow :—

Weight of rock to be raised per trip, 7 gross tons 15,680 lb
Weight of skip ...............................	8,000 lb

Weight of cage..............................	1,8001b

.............................

Maximum depth of hoisting ___,................. 4,0001b

Diameter of rope............................. 1 i in

Total weight suspend“d on one rope from drum 42,00u lb
Normal hoisting speed per minute ............	2,700 ft

Maximum hoisting speed, per minute ___............ 3,000	ft.

Desired capacity : 200 tons per hour from 4,000 ft.
depth.

At this mine, where the service requires a combina-
tion of high speeds and heavy loads, the’first choice of



Fig. 1.—Hoist Room at Granite Shaft.

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equipment is a hoist direct connected to the motor with
voltage control. In the present instance1, a first motion
hoist with a rhotor-generator flywheel set was chosen as
the most desirable equipment. Fig. 1 shows a part of
the hoist room with the equipment installed. The. hoist
is located 425 ft. from the head frame, the ropes between
the head frame sheaves and the drums being supported
on sheaves mounted on special towers. The hoist con-
sists of two 12 ft. drums fitted with a clutch, post brake
and band brake. The drums are mounted on a shaft
supported in three bearings, this shaft having a flanged
coupling to connect to the motor. The clutches and
post brakes are operated by oil cylinders, the pressure
being supplied by tin, accumulator and an electrically- ,
operated pump. The band brakes are operated by hand
wheels.

The safety devices include :—(1) A mechanism for
moving the control lever to the “ off ” position when
the skip has reached a pre-determined point, holding the
lever in this position until the reverse lever has been
moved to the opposite position, the operator being
thereby prevented from starting in the wrong direction.
(2) Two solenoids which automatically apply the post
brake if the skip is carried too far after the current has
been cut oft'. An indicator with large dial is provided

for each drum; for accurately spotting the skip or cage
the brake rings on the drums next to the middle bearing
are extended 8 in., affording a large surface on which
to paint marks.

The drums are 12 ft. in diameter by 9 ft. 4 in. face,
grooved to hold 5,000 ft. of If in. rope in two layers.
The clutches are designed to take a load of 50,0001b.
on a 12 ft. diameter, with a factor of safety on all parts
of not less than 8. The clutches are of the flat friction
type, consisting of two heavily ribbed annular rings,
faced with wood, supported on a six-armed spider keyed

3800

2800

2400

920

640

000

276

3480

3430

3130

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1700^

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2800 Ft. - 82.2 Sec.-------

- 3000 Ft. - 86.6 Sec.-----

------4000 Ft. - 108.8 Sec.

Lc 25 J i	/

I $ec- *1	1480 -

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I 47.7 Sec. 1

j< 2000 Ft. - 64.4 Sec.

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Fig. 2.—Calculated Hoisting Speed
and Power Curves.

Fig. 3.—Tachograph Record of Typical
Hoisting Speeds.

to the shaft. These rings clamp a flat steel plate bolted
to the drums, and are moved by six sets of toggle arms
connected to a sliding sleeve, and rock shaft operated by
an oil cylinder.

The post brakes are made of plates and angles in the
form of a box girder. They are of the parallel type
applied by weights and released by oil cylinders. The
combined weight of drum shaft with two drums and
two clutches is 300,000 lb.; the radius of gyration is
4-86 ft.

No. 2883.

The electrical equipment consists of a 1,850 horse-
power, 71 revolutions per minute, 550 volt, direct-
current, direct-connected hoist motor, directly connected
electrically to a generator of equivalent capacity, which
is driven by,a 1,400 horse-power, 505 revolutions per
minute, alternating-current motor. A 100,000 lb. fly-
wheel is mounted between the motor and the generator
of the motor-generator set. The flywheel is turned
smooth, and is enclosed in a steel case, which reduces
not only the windage friction, but the noise. Both the
hoist motor and the generator are designed to carry high
overloads. The field current of the generator is not
regulated directly, but by means of magnetic switches
operated by the master controller.

The operation of the hoist is extremely easy, merely
one air brake being commonly used; this air brake, in
fact, is usually not applied until the rope speed is
reduced to almost nothing. Fig. 3 shows some typical
speed records from the tachograph with which the hoist
is provided. Fig. 4 is a power curve taken when the
operator was hoising at a speed about 10 per cent, below
normal from a depth of approximately 2,250 ft. Fig. 2
shows a series of calculated curves. As a matter of
interest, the values from the 1,000 ft. level curve and
3,000 ft. level curve have been applied to equation 4
in the note appended to the paper, with the result that
a flywheel sufficient to smooth out all the peaks is

2575,

>—35 Sec.-

1596

1370

- 2250 FL-80.6 Sec.—

670

<1275

16 Sec.

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Fig. 4.—Power Curve at 10 per Cent, below
Normal Speed.

indicated, based on assumed values for demand and
meter charges. Calculations made from these curves
indicate for the 1,000 ft. level that a 90,0001b. wheel
will be required, while for the 3,000 ft. level a 111,000 lb.
wheel will be necessary, a minimum time of 15 seconds
being allowed for loading in each ease. In these
calculations the slip was taken at 20 per cent.

■ Finally, there are many instances in which a short
inspection of the load cycle and the powfer contract will
make it certain that a flywheel system is necessary.
Just how much of the peak if is desirable to cut off is
not so easily determined. The following method of
calculation may, perhaps, be of interest.

A curve should be plotted, similar to the one shown
in solid lines on fig. 5, this curve to represent the power
at the flywheel shaft. The peak cost per horse-power
per trip (C,) should next be determined by dividing the
peak charge per horse-power per month by the probable
number of trips per month, allowing for the losses in
the alternating-current motor. The current charge
(C2) per horse-power-second should be figured. It is
obvious that the acceleration peak of the curve will be
comparatively easy to do away with, and this point
should be first considered. Assuming a constant
maximum slip, s, for the flywheel (expressed as a
decimal fraction of normal speed), and calling the weight