This invention relates to electrical power units, and is particularly although not exclusively concerned with electrical power units that are suitable for use in hazardous environments, such as, for example, in underground mining.

Safety in mines has improved considerably over recent years. However, developments in mining technology have led to the use of extremely large and powerful machinery at the coal face, and in the vicinity thereof.

Due to the nature of mining, such machinery is regularly moved. Consequently, face workers in a modern mine can still face great hazards from the complex of machinery, ancillary equipment, cables, etc. in and around the work area.

Such hazards are aggravated by the fact that, despite advances in technology, it has not yet been found possible to provide efficient artificial lighting of coal faces. Because of the potential dangers from moving machinery, regulations prescribe that electric cables over specific voltages may not be provided within a specific distance of coat faces. This is because of the high risk of rupturing such cables, with the consequent risk of electric shock, and gas explosion from electric arcs.

Thus, face workers have to work in these extremely hazardous areas with virtually no lighting. The risks of accident are therefore gravely accentuated.

Lighting systems that have been adopted in mining environments do tend to have a number of inherent problems. For example, previously proposed wholly electrical systems

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have the disadvantage that a high voltage source is required near the point of use, and bulky transformers and converter units are required at frequent intervals along. he power distribution system. It is possible only to run five single lamps each of seven watts output from one converter, and it is possible only to run a seven metre length of cable from each converter to each single lamp unit (thus limiting the positional capability of each lamp, with respect to the converter source). Thus, there are numerous cables required, which can be severed and. cause shock or sparking, the cables carrying live current at 110/125 volts.. Such wholly electrical systems require a high consumption of electrical power, and for transmission of power over 200 metres or more, there is inefficient striking of the lamps, due to power drop.

Another system that has been proposed uses lamp units that are driven by pneumatic power, which power is converted to electrically energy by a generator within the ^" lamp unit. However, such a system ^" has not been adopted for a number of reasons. For example, the generators tend to be very bulky, causing the individual lamp units to be bulky, and only single lamp units are available, of relatively poor lighting capability. There is present a high noise level upon starting and during operation of such units, and a large amount of heat is generated from each unit in continuous use. TheVe fends to be a rapid power drop of pneumatic power with distance, which severely restricts the distances over which light units can be used. Overall, such lamp units tend to be unreliable.

We have also become aware of lamp units similar to the above, but in respect of which- it is said that they may be driven by hydraulic power. However, the only design of such lamp units that we have seen can not possibly afford safe running in present day mining conditions tJϊ -

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and has attendant disadvantages similar to the pneumatically driven lamp units mentioned above.

Preferred embodiments. of the present invention aim to overcome these disadvantages, by providing reliable lighting units that may be used safely in hazardous conditions. However, the invention generally is of wider application.

According to a first a.spect of the present invention, there is provided an electrical.power unit comprising an hydraulic motor and an electric generator arranged to be driven by the motor, characterised in that said motor and said generator are each disposed within a flameproof housing.

It may be appreciated that power units in accordance with the. invention can be designed to be safe for use in hazardous areas - e.g. where there is a risk of cable severance or explosive gas. Then, severance of an hydraulic pipe can be of relatively minor consequence. Preferably, means is provided for blocking flow in an hydraulic pipe supplying a power unit in accordance with the invention, in the event of a loss in pressure greater than a predetermined -value, as may occur, for example, in a pipe fracture.

Numerous advantages and optional features of the invention will be apparent from the following description of preferred embodiments thereof.

For a better understanding of the invention, and ^' to show how the same may be carried into effect, reference will now be made, by way of example, to the accompanying diagrammatic drawings, in which:

Figure 1 is anhydraulic flow diagram of a ^' lighting system embodying the invention;

Figure 2 is an electrical circuit diagram of a lamp unit embodying the invention;

Figure 3 shows one example of a lamp unit, in cross-section;

Figure 4 shows another ^" example of a lamp unit, in cross-section;

Figure 5 shows, in plan view, a coal face provided with a lighting system embodying the invention;

Figure 6 shows the coal face in front elevation;

Figures 7, 8 and 9 show lamp units fitted to respective roof supports or shields as seen respectively on the lines C-C, B-B and A-A.of Figure 5;

Figure 10 is a perspective view of one example of a lamp unit as used in Figures 5 to 9;

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Figure 11 is a perspective view of another example of a lamp unit; and

Figure 12 is a circuit diagram of a curre'nt limiting circuit of the lamp unit of Figure 11.

In the figures, like reference numerals denote like or corresponding parts.

The lighting system illustrated in Figure 1 is suitable for use in underground mining, where it can be used with relative safety. The system comprises a reservoir 1 of hydraulic fluid, and a. pump 2 which is arranged to be driven by a motor 3. The motor 3 can be an any suitable prime mover, such as/electric or diesel motor, and may be of 40 horse power or less. ^' The pump 2 is arranged to pump hydraulic fluid around the system at a rate of 27.5 gallons per minute, at a pressure of about 1600 P.S.I. A relief valve assembly.6 is provided between flow and return lines 4 and 5, to relieve excess pressure in the system. The .

p-rts 1 to 6 thus der-cribed afford an hydraulic fluid supply system, ha ing flow and return ports 7 ^a "d 8. .

In use, an hydraulic distribution system having 5 flow and return pipes 9 and 10 is connected to the ports

7 and 8 of the supply system. At desired intervals, there are provided pairs of tees 11, 12, etc. in the pipes and 10. Each tee is provided with a respective.non-return valve

13, to provide a connection to the respective flow or

10 return pipe or 10 via the respective tεe _β A respective lamp unit 14-, 15 etc. is connected between each pair of tees 11, 12 etc., vi the one-way valves .13- Eac lamp unit

14, 15 etc. compri-BS an hydraulic motor which is arranged to drive an electric generator, which in turn supplies a

15 respective light.

Fig-ire 2 is an electrical circuit diagram showing one example of a laxp unit 14. The lamp unit 14 comprises an hydraulic motor 16, through which hydraulic fluid passes

20 via flow and return lines 17 and -18. The output shaft of the hydraulic motor 16 is connected to an electric generator 19 ^" by means ofa flexible coupling 20. The output of generator 1 is regulated by a regulator 21, and is fed to three ballast units 22, in parallel. Each ballast unit 22 supplies a

25 respective fluorescent tube 23.

The hydraulic motor may be of approximately y horse power rating, ^" and have a drive speed in the range SOO to 2000 r.p.m. The generator may be a 12 volt - 60 watt DC dynamo. 0 Ballast units 22 and fluorescent tubes2 may be of about 8 watts rating.

Figures 3 and 4 show alternative examples of construction of a lamp unit 14. In Figure 3, the flow and return hoses 1 35 and 18 make connection at one end of a housing 24, to the

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hydraulic motor 16. The hydraulic motor 16, coupling 20 and electric generator 19 are all mounted in one section of the housing 24, and the regulator 21, ballast 22, and tubes 23 are mounted within another-section of the housing 24. The housing 24 is sealed by a cover 25, n a flameproof and fluid-tight manner.

In Figure 4, a fluorescent tube 23 extends perpendicularly to the axis of the generator 1 _. rather than parallel to it. In Figure 4, there can be seen a glass 26, which seals the housing 24. In both Figures 3 and 4, the electrical circuitry may be sunk within epoxy resin gel, to protect components from shock load or external vibration transmitted from local machinery, etc.

In the illustrated system, the hydraulic fluid may comprise exclusively oil, or of an emulsion of 60/40 or

95/5 mixture oil/water, for example. Alternatively, the - hydraulic fluid may be water alone. In the illustrated arrangement, the hydraulic supply system may be sufficient to light 100 lamp units spaced over a distance of 200 metres. Within each lamp unit such as 14-, it is possible to light either 10 six inch fluorescent tubes, each 4 watt; twelve inch fluαescent tubes, each 8 watt; 4 twenty-one inch fluorescent tubes, each 12 watt, or 2 tungsten spotlight units, each 25- watts. Each lamp unit has no external electric circuitry, and operates on ver low voltage - for _example, 18 volts maximum across each fluorescent tube.

Each lamp unit such as 14 may be a hand held inspection lamp, or may be designed for securement to a surface. Lamp units such as 14 may be fitted into any existing type of equipment whichhas a suitable hydraulic luid system incorporated therein.

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In the system shown in Figure.1, each lamp unit 14, etc, may be removed safely from the system without switching off the other lamps in the system. Also, each lamp unit 14- is so designed as to allow any one light within that unit to ail whilst the others within the unit remain lit.

Figures to 9 show how a lighting system as illustrated in Figure 1 may be installed at a coal ace.

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A plurality of roof supports and/or roof shields 2 is arranged across a coal ace 28,- and at ace ends 2 o Various mining machinery is installed at the coal face, although this machinery is not shown in detail. Coal

« mined from the face 28 is carried away on a stage loader conveyor 30, at the main gate 31 to the face 28 ₀ An hydraulic pressure-fluid supply system, such as that shown in Figure 1 (parts 1 to 6) is mounted on the stage loader. A lamp unit 32 (equivalent to the lamp units 14, 15, etc)

20 is mounted on each of the roof supports 27, and is connected to low and return pipes supplied by the hydraulic pressure- fluid supply system 33- Each lamp unit 3 is arranged to light both the gallery JA- and the coal face 28. A face conveyor 40 conveys coal from the face 28 to the stage loader conveyor

Figure 10 illustrates one example of lamp units 32. Each lamp unit 32 has a totally sealed lameproof housing 35- At a centre part of the housing 35, there are provided low _.

30 -J-d return ports 3 and 37, which lead to an hydraulic motor and electrical generator within the housing 35« At one side 38 of the housing 35, there are mounted two fluorescent tubes which are arranged to project light downwardly, as shown by the arrow A _β At an opposite side 39 of the housing 35, there

35 are mounted three fluorescent tubes, which are respectively

arranged to project light horizontally, obliquely downwardly, and vertically downwardly, as shown by the arrows B, C and D. The housing 3S is arranged to be secured to the canopy of a roof support 27, as shown in Figures 5 to 9, such that the two tubes at the side 38 of the housing 35 project light downwardly into the gallery 34, whilst the three tubes at the opposite side 39 project light into the coal face 28.

It may be appreciated that the illustrated arrangements provide a lighting system which is inherently safe for use in hazardous areas, such as are found in mines, chemical storage vessels, and areas where chemicals or gaseous elements exist. Experiments have shown that lamp units as illustrated can have excellent light output, whilst being of relatively modest power consumption, and light in weight. At any particular installation, an hydraulic fluid distribution system may be supplied with tees such as 11 and 12 at any desired intervals, such that inspection lamp units or semi-permanent lamp units may be connected thereto.as desired- Preferably, the hydraulic pressure-fluid supply system is provided with means for blocking flow in the flow and return pipes, in the event of a loss in pressure greater than a predetermined value, as may occur, for example, in a pipe fracture. Thus, in the event of a fracture of an hydraulic pipe in the illustrated system, potentially the most serious event would simply be loss of light. The arrangement nay be such that, in the event of such light loss, associated machinery is automatically turned off.

As noted above, lamp units in accordance with the invention may be provided integrally on apparatus which has its own suitable supply of hydraulic pressure-fluid, such as, for example, a powered roof support.

Although the illustrated arrangements are concerned with lighting units, it may be appreciated that the invention may b.e extended to provide portable power units for any requirement. For example, each housing 24 may contain any desired electrically driven device or apparatus. Alternatively, each housing 24 may be provided with electric terminals for connection to ^' electrically driven apparatus. Such units may advantageously provide an electrical supply at ^■ low voltage, in a safe and convenient _anner»

As an alternative to the hydraulic pressure fluid supply system shown in Figure 1, there may be provided two 20 horse power motors, each driving a respective pump and independent hydraulic fluid distribution system, the two pumps being supplied from the common reservoir 1.

The two hydraulic fluid distribution systems are preferably interlaced in a lighting system. Then, in the event of . .failure of one of the distribution systems, only a portion (e.g.-a half) of the lights in the lighting system may be extinguished. This is particularly advantageous from the aspect of safety.

The alternative lamp unit 40 which is shown in Figure 11 comprises an hydraulic motor 41 and an electric generator 42, each of which is disposed within its own flameproof housing, which housings are bolted one to the other. Flow and return hoses 43 and 44 are connected to the hydraulic motor 41. A current regulator 45 is disposed in its own flameproof housing, which is secured directly to that of the generator 42. In the illustrated example, five fluorescent light units 46 are connected by respective cables 47 to the regulator 45.

Thus, .the hydraulic motor 41, generator 42 and regulator 45 are all arranged in a completely fla-neproof manner, providing a high degree of safety. The cables 47 are connected to the regulator 5 by conventional gland typ ^ ^:

connectors, and the regulator 47 includes a current limiter circuit to ensure that the current flowing through the cables 47 cannot exceed 0.7 amps, to ensure that the cables 47 and light units 46 are "intrinsically safe" ^* " Limiting the current in the cables 47 to 0.7 amps ensures 5 that any sparking cannot be sufficiently strong to cause an explosion in an atmosphere of methane.

In a variation of the arrangement shown in Figure 11, the regulator 45 ^' ay be connected to the generator 10 . 42 by a flexible electric cable, which again will be

"intrinsically safe". The cable between the generator

42 and the regulator 45 will only carry low voltages - for example, 6 volts, 12 volts or, at the very most, 24 volts.

15 Figure 12 shows one example of a current limiter circuit 50, such as may be used in the regulator 45 of Figure 11.

The current ^' limiter 50 has supply input terminals 20 -V+ and V-, across which a-Zener diode ZD1 and a resistor R2 are connected in series. A further resistor HI is connected between the junction point of the resistor R 2 and Zener diode ZD1 and a control electrode of a Thyristor TH1, which is connected across the supply rails. In 5 the illustrated example, there are provided seven pairs of output terminals 0P1 to 0P7. The positive terminal of each pair 0P1 to 0P7 is connected to the main positive rail via a respective fuse F1 to F7 and series diode D1 to O7. 0

In normal use, current flow simply from the positive supply terminal V+, through the respective fuses F1 to F7 and diode D1 to D7, to the output terminals 0P1 to 0P7. In the event of the supply ^' voltage rising unacceptably 5

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high, the Zener diode ZD1 breaks down, to pass current •through the τesistor R2. The voltage at the control electrode of the Thyristor TH1 then rises, via the resistor R1, to cause the Thyristor TH1 to conduct, and thereby bypass the output terminals 0P1 to 0P7.

In the event of serious external loading of the circuit, such that the output voltages at the terminals 0P1 to 0P7 fall -, the fuses F1 to F7 will go open circuit. If, due to induction, surges are fed back into the circuit 50 via the output terminals 0P1 to 0P7, the

Zener diode action will take place, ^" as described above, to cause the Thyristor TH1 to conduct.

The illustrated circuit 50 offers a good degree of current overload protection, against,both current and voltage surges, with a very rapid initial reaction time.

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