Electrical Machinery in the Coal Industry
The nature and extent of the application of electrical machinery in Illawarra coal mines very much reflects the progress of the industry itself as it developed. Over the period in which the industry has evolved in the Illawarra, it has moved from one where the process of production was dominated by the labour of men and horses, to one in which huge tonnages of coal are able to be extracted by automatic, computer-equipped longwall machines whose operations can be monitored from many kilometres away. Importantly, the safety of those in the industry has notably improved over the same period.
Typical initial uses for electric power included lighting, water pumping, and later, coal haulage systems. Coal cutting machines were those devices used to replace what had previously been a laborious manual method of preparing a coal face for blasting.
Coal Cutting Machines
The coal cutting machine was developed to undercut the coal face, prior to it being “bored and shot’’ using explosives. While the machine eliminated the need for the miner to manually undercut the face by hand, it had the effect of increasing the amount of small coal included in the mined product. As no market existed for this coal, it was dumped as waste in the face area by the miner, or on the surface at the pit top. However, soon after the introduction of the ‘coal cutter’, a market was found for this coal to make coke, a product in high demand from smelting plants in Victoria and Broken Hill. Cokeworks were erected at many mines and adjacent sites elsewhere in the Illawarra to satisfy the market for coke both in Australia, and overseas.
Both compressed air and electricity could be used as the power source for the coal cutter drive motors. The compressed air driven machine was favoured by the Mines Inspectorate, colliery management and the coal miners over the electrical equipment of the day because of the open sparking created by the direct current (DC) drive motor, and the supporting motor control equipment. These latter operating features were considered, with some justification, to create a potential source of ignition of methane gas, in the coal face area. The compressed air motor driven coal cutting machines were also considered to have the advantage of exhausting “spent compressed air’’ that could assist in ventilating the coal face area. Compressed air drives could be supplied by either steam- or electrically-powered compressors.
Disputes arose on the use of the electric motor driven machines between the mine owners, miners and the Mines Inspectorate. The early designs of DC driven coal cutters installed at the Mount Kembla and the Bulli mines were, for the above reasons, removed from service for an unspecified period. The development of the AC electric motor and its application to coal cutters later overcame the problems encountered with the brush sparking of the DC motor used on the earlier machines.
The growth in the use of electricity in coal mines in Australia, followed its earlier and increasing use in mines in the USA and the United Kingdom (UK). The development of the AC drive motor and the ‘flameproof enclosure’ to enclose both the motor and control equipment led to the abandonment of the DC drive motor on coal cutters, and the adoption of the AC drive motor and control enclosure. This growing use of electricity in the UK led to “Rules for the Use of Electricity in Coal Mines’’ being prepared and adopted in that country. A review of these Rules was undertaken by the NSW Mines Inspectorate and they were put into effect in NSW in 1907/8.
The use of machines to undercut the coalface was to be but the first step in the long process towards the full mechanisation of the mining task. This was to progressively increase the demand for electric power – until most mining operations in the Illawarra sourced their electricity from the state PWD supply, then largely based on the Port Kembla power house, linked to the Burrinjuck Dam hydroelectric power plant.
The Mechanised Mining System
The first small steps, in the use of machines in the coal mining industry had commenced in the 1930s, when a number of mines installed rail mounted coal cutters, and coal loading systems that included a ‘scraper loader’ and the ‘duckbill shaker pan loader’.
The coal cutting machines were used to support a modified version of the Contract mining system in the development of the working areas created for that system. The Contract system involved the manual boring of shot holes in the face to “shoot the face down’’ using explosives, and the coal miners loading the coal using a pick and a shovel, into small carrying capacity coal skips.
In 1938/9 the Minister for Mines granted approval for the use of the scraper loader and similar type loading machines to extract pillars at the Coalcliff and Bulli Collieries. Following industrial actions and unrest on the part of the miners and their union leaders in the use of this system of mining the approval granted by the Minister was withdrawn, in 1941.
From the outset the mechanised system of mining was not accepted by the Miners Union and its members for many reasons, primarily their perceived loss of employment in the industry, and these fears and attitudes lead to frequent strikes and other disputes. These disruptions resulted in the mine owners being reluctant to invest the large capital expenditure required, to fund the purchase of the plant needed to adopt the mechanised system. The Joint Coal Board (JCB) was to be the agent through which this situation was resolved, with the process of mechanisation continuing. In 1949 there were only five mines of the total mines in the state, that could be claimed to be effectively mechanised. In 1959, as a result of the activities of the JCB, and the support of the mine owners and the miners, some forty mines had adopted the mechanised system of mining, and others were in the process of adopting that system.
The Mining Plant
The plant items required to operate a typical bord and pillar mechanised mining system (panel) comprised
– a self-propelled, track mounted coal cutter and a coal loader, each supplied with power by a trailing cable;
– a number of five tonne capacity rail wagons;
– two battery powered locomotives; and a battery charging station located either underground or on the surface to support the locomotives.
The coal cutter cut a slot (‘kerf’) into the coal face, and a hand held electrically powered boring machine was used to drill shot holes into the coal face. Explosives and detonators were inserted in each shot hole to “shoot the face’’ and break the coal down.
The coal loader followed to gather the coal shot from the face off the floor and load it into a waiting empty wagon. The full wagon was then hauled by battery locomotive to a rail shunting area or coal bin located adjacent the working panel (the term ‘panel’ refers to the block of coal currently being mined) to deposit the full wagon, collect an empty wagon and return into the panel (a working panel in the ‘bord and pillar’ system of mining is comprised of say five to seven main heading roadways with cut throughs driven between to create coal pillars). In the meantime, the other battery locomotive had delivered an empty wagon to the face for loading.
On completion of the loading out approximately 100 tonnes coal from that ‘place’ as it was known, the loader moved on to the next place in the panel to repeat the process until all places in the panel had been loaded out. The erection of wooden roof bars and ‘props’ followed the ‘loading out’ of the place and the extension of the rail track on wooden or steel sleepers toward the coal face. More information on the process may be found here.
The flexible trailing cables supplying power to the coal cutting and loading machine were hard wired to the machine at one end and fitted with a trailing cable plug that was inserted into a flameproof ‘Gate End Box’ (power outlet) located adjacent to each of the working places in the panel. These boxes were supplied at 415 Volts three phase from a 100 kVa capacity panel transformer. The original hard wired terminal box provided on each coal cutting and loading machine to attach the trailing cable was later replaced by a cable plug receptacle attached to each of these machines. This change enabled the trailing cable to be fitted and removed, without the assistance of an electrician. (The name “Gate End Box” originated from the United Kingdom coal mines where the longwall advancing system of mining was used; ‘Gate Roadways’ were driven, and ‘Gate End Boxes’ were installed.)
The single power outlet Gate End Boxes were later abandoned as the power demand, and operating voltage of the mining equipment being used in the mining panels increased from 415 to 950 volts. The single outlet gate end box was replaced by a flameproof ‘load centre’ fitted with multiple outlets capable of supplying all the equipment in the panel from one location. Later developments in the face mining machines and haulage systems resulted in a move away from railway track to Caterpillar (track- mounted) coal cutting and loading machines.
In the early 1950s the ‘continuous miner’, developed by the Joy Manufacturing Company, arrived in Australia and was followed soon after by the ‘shuttle car’, which took the coal from the continuous miner. Other developments in machinery and plant in each panel included the installation of a conveyor belt and at some mines a Caterpillar track mounted ‘belt feeder’. This feeder enabled the shuttle car to rapidly unload into the feeder and return into the panel while the feeder discharged the coal on to the panel conveyor at a pre-determined rate.
Auxiliary coal face ventilation fans were installed as required in each panel to support the main mine ventilation system to ventilate the advancing coal face. The air flow developed by the fan was carried to the face using ventilation tubing laid on the floor or supported from the roof as the coal face advanced.
Support of the roof using half round wooden roof bars and pit props was progressively replaced by the ‘roof bolt’ – a long bolt installed in a hole drilled in the roof, and which expanded when in position to lock the roof into place. The bolts were initially of a split and wedge design, followed by the expansion shell roof anchor. The ongoing developments in the design of roof bolts and types of anchors has led to their widespread use, along with ‘W’ shape steel roof support strap and the abandonment of wooden bars and props. The ‘roadway support’ topic is covered in more detail elsewhere in these notes.
The continuous miner combined the operations of the coal cutter and loader into one machine and eliminated the use of explosives, by shearing the coal down from the face using ‘ripper chains’, fitted with replaceable ‘cutter picks’, mounted at the front of the machine and using rotating scrolls to load the coal on to a chain conveyor delivering the coal into a waiting wagon or rubber tyred shuttle car.
While the use of track mounted wagons – mine cars hauled by battery locomotives – continued for some time these items of plant were rapidly replaced in the mining panels by the Joy rubber tyred, four-wheel-steered, shuttle car. These cars included an internal conveying chain designed to accept and move the coal through the car; when they were fully loaded, they would transport and unload the coal into a waiting rail mounted a mine car, and later, on to a panel belt conveyor. The panel conveyor unloaded on to mine-wide, underground to surface, trunk conveyor belt or a high capacity underground to surface rail haulage system.
The Joy Shuttle Car
The first shuttle cars to arrive in Australia were battery powered, and a relatively small number of these cars were purchased. That first model of car was closely followed by the 10SC, 250 Volt direct current (DC) ‘cable reel’ shuttle car, taking its external DC power supply from either an alternating current (AC) powered motor/DC generator set (‘MG Set’) or an AC/DC mercury arc rectifier (‘MAR’).
In the early 1950s the 10SC, and an increased load carrying capacity 15SC cable reel shuttle car became available to operate on a 415 Volts AC supply and later a 950 Volts AC supply. Shuttle cars manufactured by Joy and other USA suppliers were installed in large numbers throughout the coal industry and these vehicles remain to this point in time the preferred choice in the bord and pillar system of mining using the continuous miner.
The coal loader and continuous miner panels employed two shuttle cars, one with the operator seated on the right-hand side of the car, and the other with the operator on the left-hand side of car.
Track mounted coal cutting machines were first introduced in the 1930s and coal loading machines followed in the late 1940s. As the flexible trailing cables supplying 415 Volt AC to these machines were frequently damaged in use, a replacement trailing cable was stored in the panel, and any damaged cable was taken to the surface for repairs and testing, before being returned underground.
The DC powered cable reel shuttle cars supplied in the 1950s included a twin core, flat cross section trailing cable to supply power to the car. The later cars were AC powered and could be accommodated by the AC power supply system already existing in the mining panel to supply the loader and cutter or the continuous miner.
Cable Repair Workshops
The introduction of the above mining plant created a major increase in the number and types of trailing cables required to support the mining operations and led to the setting up of cable repair shops at the mines. These shops were staffed by existing mine employees, considered capable of acquiring the skills required to repair, test, and assemble trailing and other types of cables required.
The volume of this work increased to a point where the assembly, repair, and testing of the wide range of size and types of trailing, medium voltage reticulation and high voltage power cables led to the abandonment of mine cable shops. Companies experienced in this work were engaged, to carry out this work at cable shops located remote from the mine site.
These companies provided the staff and plant required to inspect, test and repair each damaged cable, assemble new and replacement cables and maintain records of the history of all cables handled, on behalf of the customer. On completion of the repairs to a damaged cable, and/or the assembly of new or replacement cables, a series of final tests was carried out, the results recorded, and the cables delivered back to the mine. Shuttle car cables were in many cases wound on to a cable drum, ready for delivery back in to the mine.
Trailing Cable Repairs
The repair of the bunched strands of damaged core/s of the flexible trailing cable was carried out using small diameter, tinned copper, soldered jointing ferrules, to retain the original flexibility of each conductor. This work was carried out by female employees, who were considered to have the necessary skills to fit and solder these small diameter ferrules, apply the covering insulation of the conductor and the outer sheathing of the assembled cable, prior to vulcanising.
The duty imposed on the shuttle car trailing cable was particularly onerous. The trailing cables supplying power to the two cars operating in a bord and pillar panel were required to be ‘anchored’ at a chosen point on the cable. This anchoring enabled two opposite handed shuttle cars to share a common roadway to and from the face and the coal unloading point.
This sequence of events commences with one car, having been fully loaded at the face by a continuous miner, travelling to the coal unloading point, passing by the second (empty) car standing in a ‘shunt’ clear of the roadway. Once the loaded car has passed the empty car then emerges from its shunt and travels to the face to be filled.
In the meantime the first car, having discharged its load, travels back into the panel to park in its chosen shunt clear of the roadway to enable second (now fully loaded) car to travel past on its way to the unloading point. Once the second car has passed, the first car then emerges from its park in its shunt, and travels to the face to be loaded – and this cycle of car movements continues.
These car movements up and down the shared roadway and in and out of the chosen shunt involve the repeated ‘paying out’ and ‘reeling in’ of the trailing cable by the cable reel mounted on the shuttle car. This requires the cable supplying each car, to be anchored in the shunt using a spring loaded ‘shuttle car cable anchor’ attached to a roof support pit prop. This anchoring device is intended to reduce the tension imposed on the cable when it is suddenly reeled on and off the cable reel mounted on the car and restrained by the cable anchor when the car moves in and out of its chosen shunt. These reeling and unreeling operations, and the need to employ a restraining cable anchor, all contribute to severe stress and stretch of the trailing cable and contributes to the relatively short operating life of the shuttle car trailing cable.
The arrival of the shuttle car in Australia is discussed above. The first cable reel shuttle cars required a direct current (DC) power supply. The trailing cables for those cars were supplied from the USA, and were of a flat cross section in shape. They presented difficulties in repairing the power cores and providing the flexibility required of shuttle car trailing cables. This led to the local manufacture of trailing cables and the development of an Australian Standards for the design and manufacture of trailing cables for DC and later AC shuttle cars, and other coal mining machinery.
The development of designs for these cables included consideration of the flexibility of the laid-up power cores, and the minor cores, the individual or collective metal and/or conductive rubber screening of each power core, and the assembly of the complete cable, including its outer sheathing. These developments involved a close association between the cable users and the cable manufacturers, a standard of repairs to be practiced by cable repair workshops and the publication of relevant Australian Standards.
Shuttle Car Trailing Cable Plug and Receptacles
Initially the replacement of a damaged shuttle car trailing cable required the services of an electrician to disconnect the damaged cable and connect the replacement cable to the car via a hard wired terminal box mounted in the cable reel. This was a time-consuming exercise requiring the services of a qualified electrician. To reduce the time taken to replace a cable and enable this change to be made by a person in the mining crew, an angle-shaped cable receptacle was fitted into the cable reel on the shuttle car and a matching plug fitted to the trailing cable.
Shown below is a typical cross section of the shuttle car cable reel receptacle mounted on the cable reel and the matching trailing cable plug, and a cross sectional view of a modern design of a shuttle car trailing cable.
Whilst the earliest designs of trailing cables included a flexible copper metal screening covering the insulated power cores, the modern design of trailing cable employ a conductive rubber sheathing covering each insulated power core and conductive rubber cradle separator of the major and minor cores of the core assembly.
The screening is applied to induce an earth fault (as opposed to a short circuit between the power cores) should the cable be damaged, so as to initiate a system at the power outlet source that would isolate the power supply to the cable, and hence reduce the potential of electric shock and possible death to a person handling the cable.
All flexible trailing cables used in the mine are manufactured using the most up to date materials and processes in compliance with the requirements of Coal Mining Regulations.
While continuous miner/shuttle car systems remain in service, with very significant ongoing changes and improvements in design and features, their primary role is in the development of roadways for future longwall mining panels.
The underground workings of mines originally opened in the coal seams outcropping on the escarpment, and progressively moved west of the escarpment, under deeper surface cover and changed roof conditions. The levels of production which could be realised from the bord and pillar system of mining using continuous miners and shuttle cars became increasingly uneconomic in these conditions, and alternative mining systems were investigated. In the 1960s these investigations led to the introduction of the mechanised ‘retreat longwall’ mining system at the Coalcliff, Kemira and South Bulli Collieries.
The longwall equipment packages purchased at that time were manufactured in the United Kingdom and required an 1100 Volt power supply system, as opposed to 415 Volt used at that time in Australia. The electrical components of the package included gate end boxes, hydraulically powered ‘roof supports’, a ‘shearing machine’, an ‘armoured face conveyor’, and a hydraulic power pack to supply hydraulic fluid to the roof supports, and a power supply for ancillary items including signaling and lighting.
Many problems were encountered with individual mechanical/hydraulic components of the longwall packages supplied in the early years of the application of this system of mining. A number of overseas suppliers were used to supply this equipment before the longwall system finally achieved an acceptable level of production output. The roof supports supplied with the early packages were unable to support the roof of the Bulli Seam, and ongoing problems were experienced, in the design features of the armoured face conveyor. These problems were overcome over time, with perseverance by all concerned and major changes in the design of the equipment. The longwall mining system has now become the most widely adopted, and highly efficient, state of the art system, capable of achieving very high levels of production.
Features of a present-day longwall mining equipment package include a high degree of automation, and an increase in demand for electric power and the primary system operating voltage. A supply voltage of 11000Volt has now been adopted, on some installations, as a primary power supply and the supply voltage to individual items of the longwall package.
More information on the longwall system, the equipment used to deploy it, and the experiences of mining companies over the period of its introduction may be found here.