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January, 1942

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Ward-Leonard controller

As mentioned at the commencement of this article, the winder is controlled by a new design of servomotor-operated Ward-Leonard controller which offers several advantages over the normal direct-operated faceplate controller. Electrically the Ward-Leonard principle is unchanged, except that, as already explained, the use of an exciter-exciter on the motor-generator set reduces the currents to be handled by the controller to a small value and enables miniature apparatus to be employed. This applies not only to the electrical portions of the controller but also to the camgear, which can be made on precision lines, built up on a single bedplate, and shipped from the works as a complete unit as depicted in Fig. 10. The effort required to operate the driver's lever is also much reduced, a feature which combines very happily with the desk control which is a Metrovick speciality. But perhaps the most important advantages of the new controller are that acceleration and retardation are automatically controlled at any point in the wind, and that the rate of emergency electrical braking is similarly controlled.

Basically the apparatus consists of a Ward-Leonard faceplate controller rotated by an oil-operated servomotor which rises under oil pressure to bring the winder up to speed, and falls under the influence of a weight to bring the winder to rest. The employment of a weight ensures that the controller will fail to safety; nevertheless, a safety device is incorporated to apply the mechanical brakes even in the unlikely event of the controller sticking. Acceleration and retardation are adjusted independently by orifice plates which control the rate of oil flow into and out of the servomotor. In the event of an emergency trip which calls for electrical braking, the servomotor is emptied through a further orifice plate which controls the rate of electrical braking. When the controller is first adjusted the acceleration is naturally set with a view to winding coal, but when winding abnormally heavy loads, such as stone, an acceleration which is correct for coal would impose an overload on the winder. A control is therefore introduced which reduces the acceleration to a safe value when an abnormal load is raised.

Although the Ward-Leonard camgear normally imposes effective control over the winder, a Lilly controller is included to take account of any abnormal condition. It is of the duplex type with provision for men-riding control in accordance with current Regulations.

A general view of the control gear appears in Fig. 11. The servo control for the Ward-Leonard controller can be seen on the left and the camgear on the right. The Lilly controller is behind the camgear and the friction-driven overwind-limit switch can be seen on the left-hand side of the camgear bedplate with a rod passing up through the winder-house floor to the resetting lever on the driver's control desk.

Control desk

All the control gear just described is housed in a chamber immediately below the driver's cabin, the rods from the driver's control levers passing directly down through the floor of the cabin into this chamber. A view inside the cabin appears in Fig. 13, and shows the control desk in detail. The brake and controller levers are on the left and right respectively, and in the centre of the desk is a drum-type depth indicator. This is a large drum sprayed with a special matt cellulose white paint which makes a complete revolution for every revolution of the winder drum, and over which two travelling pointers follow the positions of the cages. Any required shaft indications, positions of insets, &c., are marked in ink on this drum, and its readings are, in fact, so precise that there is little need to refer to the markings on the winder drum when bringing the cage to bank. The men-coal lever is not visible in the photograph but it is located in the recess in front of the driver's feet. On either side of the depth indicator are trip recorders totalling the number of coal winds and men winds respectively.

The usual shaft signals are assembled in the panel to the left of the depth indicator, and a pushbutton on the left-hand jamb enables the driver to call for a repeat signal if desired. On the right-hand panel is a series of luminous indicators showing the condition of various vital items of equipment, such as the position of the men-coal lever, the position of the main circuit breaker, and which oil pump is running. This panel also includes signals for "keps out," overspeed warning, and resetting of primary and secondary trip circuits. Immediately to the driver's right hand is a large plunger switch which enables him to stop the winder at once in case of emergency. A similar plunger to his left hand resets the emergency circuits after a trip from any cause of a kind which clears itself as soon as the winder has come to rest.

The remaining instruments on the desk include an ammeter and voltmeter, an exciter voltmeter, oil-pressure indicator, clock, and a rope-speed indicator; the last-named instrument is particularly useful in keeping the driver informed whether he is complying with the banking speed of 5 ft. per sec. when riding men. It consists of a specially calibrated voltmeter energised from a tachometer generator driven from the winder. The oil pumps for the brakes are controlled by on and off pushbuttons on the left-hand jamb of the desk.

Safety arrangements

With a Ward-Leonard winder the primary safeguard is of course, the camgear, the setting of which determines the maximum acceleration at the beginning of the wind and imposes a definite deceleration as the cage approaches bank. The camgear suffices for a normal condition, but to guard against abnormal conditions of overspeed, either in mid wind or when approaching bank, a Lilly controller is introduced as already described. This controller not only guards against overspeed, but imposes the more rigorous control required when riding men and also trips in the event of overwind. When the men-coal lever is put into the men-riding position the setting of the Lilly controller is changed so that the controller imposes its control at a correspondingly lower winder speed. A transfer is also made from the coal cams to the men cams of the Ward-Leonard camgear, and additional resistance is inserted in the generator exciter field so that the maximum winding speed is reduced from 40 to 35 ft. per sec. Overwind is guarded against by limit switches on the Lilly controller, and in the event of one of these switches being operated the driver can restore the cage to banking level by depressing a foot-operated backing-out switch and reversing the winder. To guard against any mishap to the limit switches on the Lilly controller, an additional friction-driven overwind switch is provided actuated from the camgear. This switch is not included in the backingout circuit, but can be reset by means of a handle in the front of the driver's control desk.

An important device in this particular installation is a kep interlock, which prevents the winder being started until the keps have been withdrawn. This is a necessary precaution because the tail rope might be seriously damaged if the driver attempted to wind with the cage on the keps. As already mentioned, an indicator light notifies the driver when the keps have been withdrawn.

Apart from the safeguards already mentioned, and which have to do more particularly with the actual winding, there are, of course, various emergency appliances which operate in the event of failure of any part of the electrical equipment. All these emergency devices are connected into one of two tripping circuits; the primary circuit, which shuts off the power and applies the mechanical brakes, and the secondary circuit, which returns the Ward-Leonard controller to the off position but does not apply the mechanical brakes. Unless the failure is electrical in character, the secondary circuit only is tripped, the braking then being regulated entirely by the Ward-Leonard controller, which, as already explained, can be adjusted to give any desired rate of emergency electrical braking. Actually the controller is adjusted to bring the winder to rest from full speed in about 10 sec. This procedure has the advantages of bringing the winder to rest without shock and of minimising wear on the mechanical brakes. In the event of an electrical failure, however, or of a condition such as an overwind, the primary circuit is tripped, upon which the mechanical brakes bring the winder to rest in the shortest possible time. The curves given in Fig. 14 are speed-time records of secondary and primary trips, and clearly show the difference between electrical and mechanical braking.

In the event of a trip, the driver restores his levers to the off position and depresses the resetting plunger, upon which, if the failure is of a transient description, the circuit will automatically reset and the fact will be indicated by the illumination of the appropriate indicator light.

In the event of a permanent trip, it is necessary to locate the fault and rectify it before winding can be resumed, and in default of any means for facilitating location a good deal of time can be lost in identifying the fault. Metropolitan-Vickers Electrical Co. Ltd. have therefore introduced a useful piece of apparatus which informs the driver immediately of the cause of any emergency trip whether transient or persistent. The instrument, which is known as an emergency trip indicator, is housed in a metal case about 8 x 8 x 20 in. mounted on the wall of the cabin by the side of the driver. A rotary switch located in the front of the case causes a succession of numbers to appear in sequence in a window, each number being simultaneously illuminated from behind by an indicator lamp. When the faulty circuit is reached, the indicator lamp does not light, and reference to a panel on the front of the case gives particulars of the circuit corresponding to the number in question.

Changeover from steam winder

The winder we have described replaced an old steam winder, and owing to site difficulties the changeover was a particularly interesting piece of engineering. Owing to the method adopted, the conversion was effected without the loss of a single day's output, although the electric winder had to be erected so close behind the steam winder that the ropes would have fouled parts of the steam installation.

The site difficulties were very real. It was not possible to erect the new winder in the existing winder house because of the loss of output that would have been entailed but the presence of the other surface buildings prevented the selection of a position for the new winder house which would have left the old house undisturbed. The new house was therefore built immediately behind the old one — in fact, so close that the rear wall of the old house had to be taken down and the steam pipes to the winder re-run. This was necessary not only on account of the lack of space, but also because care had to be taken to avoid giving the ropes an excessive lead to the headgear. The lead chosen is well within the limits of safety, and the ropes have been found to run without lashing. Before the ropes could be put on to the new winder, it was necessary to dismantle part of the steam winder, and to keep the pit running during this period a second-hand steam winder was procured and erected in front of the old steam winder. When the electric winder was complete the ropes were transferred to the temporary winder while the old machine was partially dismantled. The new ropes were then put on the electric winder, and when all was ready the cages were transferred to them.

A similar procedure is being followed in the case of the second winder now being installed; in fact, when we visited the colliery, the back of No. 2 engine house had been taken down, a temporary partition erected, the steam pipes rearranged, and the foundations for the new winder were being laid down.

Drawings and Photographs accompanying the article