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December, 1933

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As stated in our previous article, a bulk supply of electrical energy for this group of collieries is purchased from the North Eastern Electric Supply Co. Ltd. A diagram, showing the connections and distribution at Boldon colliery, is given in Fig. 5. It will be seen that two feeders are available, the older of which, at 5,500 volts, dates from as long ago as 1908, the Harton Coal Company being one of the pioneer companies in the coalfield to utilise electrical power. This supply is used on the two fan motors direct, but is stepped down to 2,750 volts and 600 volts for use in the other motors.

The 20,000-volt supply is brought by duplicate feeders, which are controlled by the Reyrolle ironclad gear, illustrated above. Two 4,000-kVA. transformers step down this current to 5,000 volts, the winders and compressors being supplied at this pressure through a second Reyrolle board, part of which is also shown in our picture. A view of one of the transformers, which, incidentally, are of Brush manufacture and weigh 16½ tons each, is given in Fig. 4. To safeguard the position so far as the supply to the old board is concerned, a connection has been teed off from the secondary side of one of these transformers to run in parallel with the two 5,500 feeders.

The new 20,000-volt feeders have, of course, been necessitated by the closing down of the boiler plant and the electrification of the winders and air-compressing plant. As particulars of the compressors and their motors were given in our previous article, all that remains to be said here is that the plant is controlled by an English Electric draw-out type board, which also contains a panel for the No. 1 pit winder. All this equipment is housed in the one building — an old engine house, which has been extended and partitioned off to isolate the winder from the compressing plant. The winder is for handling men only and is capable of raising from 45 to 60 persons per wind of 90 secs., the acceleration and retardation periods each being 15 secs., with 60 secs. of full speed wind. Three-decked cages are in use, the depth of shaft being 1,560 ft. Views of this equipment, the electrical portions of which were supplied by Metropolitan-Vickers Electrical Co. Ltd., are reproduced in Figs. 6 and 7. The drum is of the bi-cylindro-conical type, and rises from 10 ft. to 14 ft. in diameter, with four turns of rope on the scroll portion Two spare-rope reels are provided, each capable of accommodating 140 ft. of rope. Both reels are free to revolve on the shaft, and are fitted with reduction gearing, which can be operated externally by hand. A special locking device is incorporated to enable the ropes to be adjusted to within exceedingly fine limits.

An induction motor, designed for dual frequency, provides the drive, having a continuous rating of 380 h.p. at a normal full load speed of 285 r.p.m. and a "pull-out" torque equivalent to 800 h.p. Single-reduction gearing is employed, this being of the double helical type, manufactured by David Brown & Sons (Huddersfield) Limited. As already mentioned, the main electric supply is brought from the substation at 5,500 volts; for use in the winder motor it is stepped down to 2,700 volts in a 360-kVA. Metrovick transformer, situated in the winder house. At present, of course, the motor is running on the 40-period supply and is operating as a 16-pole machine. When the frequency is changed over, however, the end connections of the winding, which is of the basket type, will be modified to give a 20-pole machine. Thus the speed of the motor will be the same as at present and in consequence, the output of the winder will be unaffected by the change in frequency. Control of the motor is effected by means of oil immersed reversing contactors in the stator circuit, and a moving electrode-type controller in the rotor circuit. Power for the various auxiliaries, such as the standby air compressor, is derived from the secondary side of a 20-kVA. transformer at 600 volts.

The mechanical portions of the winder were manufactured by Robey & Co. Ltd., of Lincoln, and include compressed-air brakes designed to operate at a pressure of 65 lb. per sq. in. Normally the compressed air is derived from the main colliery supply, but a motor-driven auxiliary compressor is arranged to start up automatically in the event of the main pressure falling below a predetermined level. Post type brakes are fitted, Ferodo-lined, and are capable of holding the cages indefinitely in any position in the shaft with the full total load of 23,460 lb. Each cage, together with its chains, weighs 4 tons 5 cwt., and the locked-coil rope, which was supplied by Latch & Batchelor Limited and is 4 in. in circumference, weighs 24 lb. per fathom. A Lilly overwind-prevention gear is incorporated and also operates the brakes in the case of overspeed, or failure of the electrical supply; also a slow banking device is included, in keeping with the best modern practice.

The No, 2 winder operates on the Ward-Leonard principle and has two cylindrical drums each 16 ft. in diameter and 5 ft. 6 in. wide. One drum is keyed to the shaft while the other, which is gunmetal-bushed, is connected by means of a multiple-toothed clutch. As the degree of adjustment is fixed by the pitch of the clutch teeth these have been kept as small as possible. David Brown single-reduction double-helical gears are again employed and power is provided by a 600-volt d.c. motor, the normal full load speed being 400 r.p.m. The motor, which is connected to the pinion shaft through a Wellman-Bibby flexible coupling, has a normal rating of 1,860 h.p., but is capable of exerting an overload torque equivalent to 3,720 h.p. It is of the compensated shunt-wound separately-excited type and takes its main supply from a 1,200-kW., 600-r.p.m. motor generator set. A view of the latter equipment is given in Fig. 13; it consists of a 1,200-h.p. self-starting salient pole synchronous motor direct-coupled to a d.c. generator capable of a peak of 3,000 kW. The motor takes its supply via a main switch cubicle from the 5,500-volt lines, and has a pull-out torque equivalent to 4,200 h.p. It is designed to give its most efficient performance when working with a power factor of 09 leading, and sufficient wattless current is thereby circulated to improve the overall power factor of the colliery.

There are two overhung exciters on the motor generator set, one for supplying the d.c. generator and the other for the excitation of the synchronous motor field coils. The synchronous motor is arranged for dual frequency operation, being at present run as an 8-pole machine; when the frequency is changed over to 50 cycles, however, the number of poles will be increased to 10 by altering the end connections of the stator windings and replacing the present rotor.

The winder was designed to raise a net load of 11,200 lb. in four decks from a depth of 1.560 ft., corresponding to a maximum delivery of 250 tons of coal per hour. To achieve this two decking levels will be in service, but as yet only one is being used, and the changing time is 52 seconds instead of 22. The output is thus reduced to 175 tons per hour. Figs. 10 and 12 show the h.p.-time diagram for this winder; the peaks during the decking period are due to the number of changes required. Keps are fitted at both the top and bottom of the shaft. The weight of each cage with its chains is 5.9 tons and the coal handled per wind is 5 tons. Locked-coil winding ropes by Latch & Batchelor are again fitted and in this case are 5 in. in circumference; also a flat balance-rope is provided weighing 42 lb. per fathom.

Fullerton, Hodgart & Barclay Limited were responsible for the mechanical portions of the winder. In this case the brakes are oil-operated and are of the suspended type — an arrangement which permits a uniform horizontal movement, so that a reasonably uniform pressure is given over the whole of the brake shoe. Provision has been made for the addition of a deceleration governor to be added at some future date.

An oil-pressure engine is also fitted for operating the clutch of the loose drum, and is so interlocked with the brake engine that the clutch cannot be withdrawn unless the brakes are full on. A spray lubrication pump driven from the end of the drum shaft is fitted for lubrication of the gears, which are enclosed in an oil-tight bath, the pump taking its supply from the gearcase sump.

Both these winders are controlled on Metropolitan Vickers "two-lever" system — an arrangement which eliminates the separate lever for emergency tripping and resetting of the brakes. With this system a rocking lever, which interconnects the driver's brake lever and the brake engine, is supported on a fulcrum which can be moved vertically. Normally this fulcrum is maintained at its highest position by a solenoid, and emergency braking is carried out by de-energising the solenoid, which permits the fulcrum to fall, so applying the brakes fully, regardless of the position of the driver's brake lever. For resetting. the brake lever is moved to the "on" position, thereby lifting the solenoid plunger and fulcrum and so relieving the solenoid of the duty of raising the weight of the mechanism. In this way the large number of lay-shafts usually required are obviated.

This winder is also served by a Lilly overwinder and, in addition, cam. gear is fitted on the Ward Leonard equipment to control the acceleration and deceleration periods. This gear prevents the driver from accelerating too quickly and brings the controller back to the "off" position at the end of the deceleration period. The Lilly overwinder, however, shadows, as it were, the cam gear and provides much more discriminative control, co-ordinating the cage position with speed.

The precision and reliability with which this overwinder works mark a great advance on the older types still in common use; the apparatus is merely called upon to open an electric contact when prearranged limits are exceeded, and in consequence is constructed as an instrument of the highest refinement.

Underground Operation

Since 1930 the system of mining at Boldon colliery has been completely changed, the old hand-worked bord-and-pillar method having given way to longwall faces operated by machines. The coal is won from double-unit faces, each, as a rule, 100 yards in length. Belt conveyors are used for both face and gate work, and the faces are cut by Mayor & Coulson "Samson" coalcutters operated by compressed air. The face belts are operated by electricity through a rather novel type of rope drive, a drawing of the arrangement being reproduced in Fig. 14. The mechanism consists of fleeting wheels driven by 10-h.p. motors through oil-immersed worm reduction gears. The rope drives are carried up to the face to operate the conveyor heads, the driving motors being kept a minimum distance of 25 yards away. As will be seen from the view in Fig. 15, which shows one of the units taken in the pit yard, the conveyor heads are of special design and incorporate a further set of enclosed reduction gearing. They were manufactured by Mayor & Coulson Limited, and, as no electricity is allowed within 25 yards of the face they enable the advantages of an electric drive to be secured for the conveyors. In the gate itself a 24-in. gate belt is in service, and is extended up to a maximum distance of about 400 yards.

Drawings and Photographs accompanying the article