6. In the Brookhouse downcast shaft there are two double-deck cages, each deck holding two tubs of coal or 22 persons. Each cage is guided through the shaft by means of four wire rope guides that are suspended by clamps in the headframe and tensioned by deadweights in the shaft sump below the Silkstone Seam entrance.

7. At this entrance the cages are landed on four large wooden baulks which are supported by two steel compound girders 26 inches deep by 14 inches wide built into the shaft wall. The entrance is provided with two platforms so that both decks of a cage resting on the landing baulks may be loaded or unloaded simultaneously with mineral, material or persons.

8. The steel headframe above the shaft supports, and is connected to, some of the winding apparatus, including: two pulleys for the winding ropes attached to the cages and the winding engine, eight wire ropes for guiding the cages, two detaching plates that form part of the gear by which either cage is detached from its winding rope if it ascends too far when overwound, four sets of safety catches of the multiple type which are designed to support a cage that has been detached from the rope, and the equipment used for loading and unloading the cages. This equipment is located on two platforms, as at the Silkstone Seam entrance, so that both decks can be dealt with simultaneously.

9. The headframe is constructed so that a cage may ascend a distance of 21 feet 3 inches above its normal position at the loading and unloading platforms before it is detached from the winding rope.

General

10. The winding engine involved in the overwind was supplied by The General Electric Company, Limited, Witton, and it was installed in the year 1929. Between that date and 1942 the engine was used infrequently to provide another means of egress from the mine that was being worked from the Beighton shafts. The engine was not used to raise coal until the mine and its equipment had been reorganised both on the surface and below ground so as to handle a projected output of about 15,000 tons of coal per week. In order to raise this output the nominal maximum speed of the winding drum was increased from 45.3 to 53.7 revolutions per minute as a result of modifications made to some of the electrical components. Technical particulars of the winding apparatus, including the winding engine, are given in Appendix I.

11. The engine has a bi-cylindro-conical drum (see Drawing) on to which the winding rope attached to one cage is coiled whilst the rope attached to the other cage is uncoiled. The drum is coupled directly to a D.C. winding motor that bears a name plate on which the following particulars are included: 1,200/2,040 h.p., 53.7 r.p.m., 425 volts, 2,260/4,000 amps. This motor is supplied with electrical energy by an induction-motor-driven Ward Leonard set with flywheel and slip regulator, which runs at a speed in the range of about 1,000 to 820 r.p.m. according to the magnitude and direction of the unbalanced load in the cages. The set includes a 900/1,700 kilowatt, 425 volt, D.C. generator, a flywheel weighing 11¼ tons and a 900/1,800 h.p., 3,300 volt, 3 phase, 50 cycles, slip-ring induction motor, which is controlled by a combined liquid starter and slip regulator.

12. The speed and direction of rotation of the winding motor are determined primarily by three field windings on the Ward Leonard generator. These windings consist of a self-excited field, a separately excited field regulated by the engineman's hand control lever and a differentially compounded field which is connected in series and is in opposition to the self-excited field during motoring conditions. The self-excited field is connected across the terminals of the generator and is subject in addition to two steps of resistance control introduced by the position of the engineman's hand lever. The three fields are so arranged that the armature current is limited to a safe value irrespective of the movement of the hand lever. The speed of the winding motor is also determined by the speed of the motor-driven Ward Leonard set and the magnitude and direction of the unbalanced load in the cages. The speed/load regulation of this control system between no load and full load is stated to be 11 per cent. but the actual regulation is about 19.75 per cent. owing to the large variation in the speed of the Ward Leonard set introduced by the slip regulator. The engineman's hand control lever moves inside a quadrant and it has three main positions, namely, a full speed "Forward" position at the end of the quadrant remote from the engineman, an "Off" position in the centre of the quadrant and a full speed "Reverse" position at the other end of the quadrant.

13. In order to lower a cage, for example, the under-rope cage, from the landing places in the headframe to the Silkstone Seam entrance, the engineman after receiving the necessary signals moves the control lever towards the "Reverse" position and releases the mechanical brakes on the drum. Consequently the winding engine accelerates and the motor generator set decelerates to allow the flywheel to give up some of its kinetic energy and thereby reduce the peak demand for electrical energy to drive the induction motor. This continues until the winding motor and the motor generator set attain speeds determined by the position of the control lever, the slip regulator and the magnitude and direction of the unbalanced load in the cages. When the cage is travelling at the appropriate speed at a certain place towards the end of the wind as shown on the depth indicator, the engineman normally moves the control lever towards the "Off" position and allows some of the kinetic energy in the winding engine to be converted into electrical energy which accelerates the flywheel and the motor generator set and thereby decelerates the engine. In other words he obtains regenerative braking. At the appropriate place the engineman applies the mechanical brakes and eventually brings the cage to rest where required. Abnormally if the engine is travelling at a greater speed at this place, the engineman may move his control lever through the "Off" position towards the "Forward" position to try to obtain a greater rate of deceleration or regenerative braking, a matter which is considered later in this Report.

14. At the commencement of a wind the rope attached to the cage at the landing places in the headframe is on the large diameter of the drum, namely, 17 feet 6 inches, whereas the rope attached to the cage at the Silkstone Seam entrance is on the small diameter of the drum, namely, 11 feet 0 inches. Consequently the effort required to start or accelerate the winding engine is much less than it would be if both ropes coiled on to and off the same diameter of the drum. The speeds of the two cages at any instant are directly proportional to the varying diameters of the drum on to which the ropes are coiling and thus the cages travel at the same speed for a long distance in the shaft, but their speeds are in the ratio of 1 to 1.59 when they are in close proximity to the Silkstone Seam entrance and the landing places in the headframe, respectively. For example, a landing speed of 5 feet per second at the Silkstone entrance corresponds to a speed of nearly 8 feet per second at the above landing places.

Brakes

15. The winding drum has two brake paths each 12 feet 6 inches in diameter and 8 inches wide, to which brakes of the bottom-anchored four post type, with rigid shoes having Ferodo C R friction linings, are applied by a dead weight that is controlled by a brake engine actuated by compressed air at 60 p.s.i. The brakes are applied or released, respectively, when compressed air is exhausted from or admitted to the underside of the piston in the air cylinder of the brake engine. The movement of the air is controlled by two valves, namely, a valve of the Iversen type and an air escape valve.

16. The Iversen Valve is designed to produce a braking effort directly proportional to the displacement of the winding engineman's hand brake lever. But this object may not be attained without proper adjustment and maintenance of the complete valve, which incorporates a small piston valve that moves inside a sleeve that also moves inside the valve box. The Iversen Valve is actuated for normal braking by the hand brake lever and for emergency braking by an emergency solenoid that is controlled by the safety equipment of the winding engine. This includes the Lilly Controller or automatic contrivance that is fitted to the winding engine in order to prevent overwinding of the cages as required by Regulation 7 of the Coal and Other Mines (Shafts, Outlets and Roads) Regulations, 1956.

17. The air escape valve is actuated by the combined action of the emergency solenoid and the apparatus that controls the movement of the throttling valve in the cataract cylinder of the brake engine in such a way that the air escape valve may function only during "Fast Braking" as described in the next paragraph.

18. There is a cataract or damping cylinder incorporated in the brake engine to provide for "Fast Braking" or for "Slow Braking". This is achieved by the movement of a throttling valve in the pipe that connects the two ends of the cataract cylinder, which is kept full of fluid and contains a piston. The throttling valve is connected to cams on a dial driven by the winding engine so that "Fast Braking" is available for about two revolutions of the winding drum from either end of a wind and "Slow Braking" is enforced for the remainder of a wind.

Safety Equipment

19. The Lilly Controller referred to in paragraph 16 is designed :—

20. The elements provided on the Controller for the purpose of attaining the aforesaid objects include centrifugal governors and dial-mounted cams, overspeed and overwind switches that work in conjunction with backing out switches, accelerating solenoids, electrical safety circuits that are designed to "fail to safety" and a man-safety element which makes one of the governors of the Controller more sensitive when persons are being carried in the cages. The latter element is controlled by a man-safety lever located in the engineman s cabin. When this lever is moved into the man-winding position an indicator in the engine house and indicators at the landing places in the headframe are illuminated automatically, indicating to the banksman that the Controller or automatic contrivance to prevent overwinding is fully engaged before he allows any person to enter the cage.

21. The safety features of the winding engine are divided into two sections, namely, a "Slow Braking Group" and a "Fast Braking Group". The "Slow Braking Group" contains four features by which the emergency brake contactor coil circuit may be tripped, namely, overload of the exciter, overload of the winding motor, the winding engineman's emergency stop button and the overspeed switch of the Lilly Controller. When any of these features cause a trip in the "Slow Braking Zone" described in paragraph 18, regenerative braking is produced and maintained automatically by means of two pressure switches which retain the excitation contactor closed and thereby keep the motor field energised until the mechanical brakes become effective after a lapse of some seconds. One switch is connected to the lower side of the air cylinder and so arranged that its contacts, which are normally closed, are opened automatically as soon as the pressure of the air in the cylinder is reduced when the Iversen Valve is moved into the exhaust position as a result of the "trip". The other switch is connected to the lower side of the cataract cylinder and so arranged that its contacts, which are normally open, are closed automatically as soon as the falling piston in the cylinder establishes pressure and that they remain closed until the pressure is reduced to a low value as the mechanical brakes are applied effectively. At that moment the switch opens to drop out the excitation contactor and thereby remove the winding motor field. When any of the above features causes a trip in the "Fast Braking Zone" the mechanical brakes are applied relatively quickly without regenerative braking because both pressure switches open quickly and trip the excitation contactor.

22. The "Fast Braking Group" comprises four features by which the excitation contactor coil circuit is tripped, namely the overspeed switch of the motor-driven Ward Leonard set, the failure of the winding motor field, the failure of air pressure for the mechanical brake and the overwind switches of the Lilly Controller. When any of these features causes a "trip" in the "Fast Braking Zone" described in paragraph 18, regenerative braking is not produced because the emergency brake contactor is opened to apply the mechanical brakes relatively quickly and consequently the pressure switches do not prevent the excitation contactor from opening and removing the winding motor field.

23. When a trip is caused by any of the above features the winding engine is brought to rest automatically and it cannot be moved until any defect in the safety equipment has been rectified and the winding engineman has reset that equipment. For this purpose the control lever is put into the "Off" position and the brake lever into the "Reset" position and the "Reset" push button is pressed. In the event of an overwind, however, the engineman must first leave his cabin so as to close the appropriate backing out switch on the Ward Leonard controller which is operated by the control lever. This switch then short circuits the overwind switch on the Lilly Controller and enables the engineman to reset the equipment in the manner described. He may then apply power to the winder motor, but only in the opposite direction to that in which the overwind occurred because any attempt to apply power in the other direction would cause the backing out switch to open and cut off the power and apply the brakes.