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No. 439, August 1994

REMOTE RESET SYSTEMS FOR CONTINUOUS MINING
MACHINES USED IN EXTENDED CUTS

Objective

Provide the technology to remotely reset circuit break-
ers on continuous mining machines used in extended cuts.

Background

The popularity of extended cut mining is increasing in
US. coal mines. With this mining method, remote-
controlled continuous miners are used to drive entries in
excess of 6.1 m (20 ft) inby permanently supported roof.
Industry-wide attention is focusing on safety considerations
in extended cut mining. A particular problem area is the
interruption of power to the continuous miner during an
extended cut. Mine workers are tempted to dart under
unsupported roof, disregarding regulations and personal
safety, to reset circuit breakers on the conlinuous miner.
Information was solicited from various organizations to de-
termine the circumstances that cause power interruptions
to extended cut continuous miners, The data accumulated
permitted several conclusions to be drawn about why bigh-
voltage circuit breakers trip. From this information, de-
signs for remote reset systems were developed.

How It Works

Two reset systems were developed, a mechanical system
and an electrohydraulic system. These system designs
allow for installation on most brands of remotely
controtled continuous miners employed in extended cuts.

The manual reset version, shown in figure 1, is the
simpler of the two designs and can be easily implemented
by any extended cut mine operator. This system essen-
tially consists of two pull cables anchored to opposite sides
of the circuit-breaker lever and associated guide pulleys.
Minor modification to the breaker lever is required to

accommodate attachment of the two pull cables, The pul-
leys are used to route the two pull cables to the inby cnd
of a length of hose conduit anchored to the continuous
miner. At the outby end of the hose conduit, each cable
is terminated with a color-coded pull handle, typically red
for breaker trip action and yellow for reset. The lengths
of the hose and cables are dictated by the depth of the ex-
tended cut operation. During mining operations, the pull
handles are located near the continuous miner operator.
Where practical, the hose conduit can be located alongside
the continuous miner trailing cable.

The electrohydraulic system is a more elaborate design.
A schematic diagram of this system is shown in figure 2.
This version is more suitable for incorporation into new
equipment by the manufacturers but, if adequate space
exists, could be retrofitted on any continuous miner.

On board the continuous miner, the electrical portion
of this reset system contains the radio remote-control
decoder-receiver unit interfaced to an intrinsically safe
(IS.) solenoid valve. Modification to tbe radio remote-
control system may be required to dedicate two spare
discrete-function outputs to control the dual coils of the
solenoid valve. If multiple breakers are to be controlled
independently, each breaker will require a separate sole-
noid valve and a pair of radio remote-control, discrete-
function outputs. The operator’s encoder-transmitter unit
will require modification to include "TRIP" and “RESET”
console function switches for each remotely controlled
circuit breaker. The power source for the continuous
miner’s radio remote decoder-recciver must remain active
after any breaker bas tripped, This can be accomplished
by powering the decoder-receiver unit from an uninter-
rupted ac voltage source on the continuous minee or pow-
ering the decoder-receiver with a battery pack that is
trickle charged during normal operations. Ideally, the
solenoid valve and decoder-receiver should be powered

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from the same source. Intrinsically safe solenoid valves
are available with a variety of alternating and direct cur-
rent type coils,

The design of the hydraulic-mechanical portion of the
system is simple and consists of a few inexpensive com-
ponents. A small, double-acting cylinder is mechanically
linked to the circuit-breaker lever. The cylinder is mount-
ed to both trip and reset the circuit breaker. This requires
a custom installation for each circuit breaker.

A small accumulator, charged by the continuous miner
hydraulic system, powers the hydraulic cylinder. The
charge in the accumulator is retained by a check valve
after the continuous miner's hydraulic pump is turned off
or shut down because of a breaker trip. Other compo-
nents include a pressure-reducing valve and an I.S., 4-way
solenoid valve. For testing purposes at the U.S. Bureau of
Mines (USBM), the available components were connected
with hydraulic hoses and fittings. A more compact hy-
draulic subsystem would use National Fluid Power Asso-
ciation subplate-mounted, stackable components. All of
the components, except the accumulator, can be combined
and mounted on a single subplate or manifold. Depending
on the space available, the accumulator can be dircetly or
remotely connected to this manifold or valve stack.

The pressure-reducing valve is necessary to provide a
constant and limited force to the hydraulic cylinder. For
the prototype test setup, 1,724 kPa (250 psi) was adequate
to generate the required force to operate the continuous
miner’s main circuit-breaker lever. Because the internal
Jeakage of the pressurc-reducing valve will eventually drain
the accumulator, the remote reset capability will exist only
for a finite time after the continuous mining machine is
shut down. Since the volume of the accumulator is large
compared with the internal leakage of the pressure-
reducing valve, a period of several hours can be realized
and is considered adequate for most breaker resetting
situations, A larger accumulator will yield a longer time
interval. To achieve an infinite time period, an LS., zero-
leak, solenoid poppet valve could be installed in the

Figure tMechanlcal ‘aystom installation on the USBM's
Jeffrey 101MC continuous miner.

pressure-reducing valve inlet circuit. This solenoid valve
would have to be activated when the 4-way valve is
activated in cither direction.

Test Results

Both of the reset systems have been installed and tested
on a Jeffrey 101MC' continuous miner at the USBM’s
Pittsburgh Research Center. The mechanical reset was
also successfully tested on the USBM’s JOY 14CM con-
tinuous miner. The systems have been successfully dem-
onstrated to personnel from the Mine Safely and Health
Administration and the Bureau of Deep Mine Safety of
the Commonwealth of Pennsylvania’s Department of Envi-
ronmental Resources. Both agencies found the designs to
be practical and did not expect to require any special
approval for use in underground coal mines.

Cooperative Research Opportunity

The USBM is seeking cooperators to assist in further
research and development of this technology. Additional
information on cooperative research may be obtained by
contacting Jacqueline H. Jansky, Technology Transfer Of-
ficer, Pittsburgh Research Center, U.S. Bureau of Mines,
Cochrans Mill Road, P.O. Box 18070, Pittsburgh, PA
15236, (412) 992-6615.

For More Information

Further details can be obtained from the principal
investigators at the Pittsburgh Research Center, U.S.
Bureau of Mines, Cochrans Mill Road, P.O. Box 18070,
Pittsburgh, PA 15236: August J. Kwitowski, (412) 892-
6474; or Albert L. Brautigam, (412) 892-6470.

‘Reference to specific products does not imply endorsement by the
U.S. Bureau of Mines.

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Figure 2.-Schematic diagram of the electrohydrauile reset
system.