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October, 1960

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An important concentration scheme being carried out by the Durham Division of the National Coal Board has linked together Eppleton, Elemore and Murton collieries and concentrated their output at one new skip-winding shaft at Hawthorn where a new coal-preparation plant has been built to deal with 750 tons of coal per hour. By 1961 it is planned to produce over 8,000 tons of coal per day from this scheme.

In order to achieve this production figure, an extensive system of locomotive haulage roadways has been driven at two horizons to inter-connect the three collieries with the new winding shaft. Altogether some 20 miles of track have been laid. Coal is transported to the winding shaft in two-ton capacity mine-cars, in sets of 24, hauled by battery locomotives. It is planned to operate no less than 24 loading points at the two levels and to do this, about 34 locomotives will be required for coal transport and man-riding duties.

With such an extensive scheme it is essential to have a system of traffic control which will ensure a smooth flow of coal to the Hawthorn pit-bottoms and at the same time provide a maximum degree of safety for the man-riding trains and transport personnel.

Earlier signalling installations

In previously installed schemes at other collieries, traffic control of underground locomotive transport is adequately handled by a Westinghouse system controlled from a centrally-located signal cabin containing a power interlocking frame and track diagram. Basically the above system is such that the presence of a train or vehicle standing at a predetermined position, say at a signal, is indicated to the operator in the signal cabin by the depression of one or more treadles. The operator then operates the points to the required position by manipulation of small point levers, and finally clears the signal authorising a train movement over the route he has set up, by use of a small signal lever, which is electrically released by the actual depression of the treadle or treadles. The signal lever concerned cannot be restored to its full normal position until the train or vehicle has depressed or cleared a further treadle or treadles. Mechanical interlocking is provided between levers so that no conflicting movement can be made until the train has moved out of the area concerned. In this system points are moved pneumatically and controlled electrically from the levers which are equipped with selection contacts which control the electrical relays.

The Hawthorn scheme

As the Hawthorn scheme is much more extensive than others so far encountered, it was decided to approach nearer to fully-automatic practice and adopt a system, dispensing with the interlocking frame and operated by the locomotive drivers. This is the most extensive installation of locomotive haulage traffic signalling of its type yet made underground; it was designed by the Westinghouse Brake and Signal Co. Ltd., and installed under their supervision.

To meet the requirements of the N.C.B. the responsibilities normally undertaken by a traffic controller or signalman are divided between the locomotive drivers in the signalled area. This is achieved by selector switches and plungers situated at the signals concerned and has meant the use of certain equipment which would not otherwise have been necessary.

All interlocking facilities associated with the use of an interlocking power frame are provided and the operation of the respective plungers simulate the movements by a traffic controller or signalman on such a frame.

In view of the fact that it is the driver who selects his own route it was found sufficient only to provide two aspect junction signals except in special cases which will be described later. Therefore, after deciding over which route he intends to travel, the driver operates the plunger control and with the route set up and locked the signal clears from red to green.

The two aspect signals have the following significations :—

(1)	Red (Danger — Stop).
	Green (Clear — Proceed).
(2)	Red (Danger — Stop).
	Yellow (Proceed with caution).

In the former case the green aspect signifies a definite locked route whereas the yellow aspect signifies that the section into which the signal reads has certain restrictions both to speed and possible hand operation of points or special requirements such as shunting, etc. An example of this is found at the Eppleton shaft sidings.

In all cases "ready" lights are provided at the signals and are an indication to the locomotive driver that the section or route over which he desires to travel is clear and that the plunger operation for that route would be effective. These "ready" lights have no implication other than this. Their purpose being solely to prevent useless operation of the plunger control.

At those signals where more than one route can be selected, a special cancel plunger has been provided so that in the event of the driver selecting the wrong route the operation of this plunger releases the hold obtained and reverts the signal to red. It is important to note however that this cancelling feature is only operative provided the train had not passed the signal concerned.

In certain signals, additional aspects have been provided to indicate a particular route requirement, such as a special shunt move, signified by the letter "S" or a special man riding route signified by the letter M." The additional "M" indication is provided at each marshalling point for through running. In general, in this scheme, there is no differentiation between the various classes of traffic, so far as the signals are concerned.

An isometric view of the roadways linking the workings with the Hawthorn shaft is shown in Fig. 5. From this sketch it can be seen that locomotive haulage operates at two levels. All coal from the Eppleton workings is transported on the lower level, whilst some Murton coal is handled on the level above. At the present time, coal from Elemore is hauled outbye by diesel locomotive to an exchange siding on the upper level near the Hawthorn shaft. At this point battery locomotives take over and haul the coal over the remaining distance to the shaft. The Elemore traffic to Hawthorn operates with a local signalling arrangement at present, but it is planned to introduce full signalling protection at a later date. There is, however, a section at the Elemore George shaft area where signalling is provided to cater for traffic movements over two connected triangular junctions involving six sets of power worked points and five signals. This section handles trains of tubs which convey coal to an underground tippler transferring the coal to minecars.

The layout has been planned to include marshalling points so that a train changes locomotives at these points instead of being hauled directly from a loading point to the shaft by the same machine. One advantage of this is that the locomotive driver operates in a more localised area and thus becomes more familiar with his own section of track. These marshalling yards facilitate the use of 24-car trains on main sections to Hawthorn with exchange to smaller trains or tandem locomotives, inbye where gradients are heavier as well as providing a "buffer" stage for stocking full or empty cars should Hawthorn or the district concerned be running slow.

The signalled moves fall into the following categories :—

(1) Signals reading over a junction.

(2) Signals reading over a straight track (traffic running in one direction).

(3) Signals reading over a straight track (traffic running in both directions).

(1) A locomotive driver with a train standing at a junction signal which reads to two routes, has two plungers available to him. In those cases where more than two routes are concerned then selector switches have been provided with one plunger control. In both cases however the selector switch position or plungers are labelled signifying the route applicable. The driver depresses the plunger, depending on which way he desires to proceed, after receiving the visual permission of the appropriate "ready" light. If the points are already lying in the correct direction no point operation follows and the signal changes to green and allows him to proceed forward to the next signal. If the points are lying in the wrong direction then operation of the same plunger moves the points to the correct position. After this operation, and correct detection, the signal changes to green. Detected arrival at the next signal releases the junction signal for further traffic moves.

(2) Over a straight length of track with one-way traffic, the procedure is as follows: On arrival at the first signal, the locomotive driver depresses the plunger provided the "ready" light has been given. This operation clears the signal to green and allows the driver to proceed forward to the next signal. Further use of the first signal is restricted until the train has negotiated the second signal.

(3) On a two-way single track, depression of the plunger at one end gains directional control of the track and locks out the control at the other end. Detected arrival at the signal past the two-way single section releases the section. The contingency of instantaneous depression of plungers has been catered for.

Some examples of traffic control are given below.

Hawthorn/Eppleton lower level

Fig. 8 shows part of the track layout at the lower level and the position of signals. The position of the South Busty loading point and marshalling point Z can be seen in the centre of the layout. It will be noticed that the loading point is situated away from the main track and thus loading operations do not interrupt through traffic making to or from the Hawthorn shaft. Only one locomotive at a time operates in the loading point road, and delivers 24 empty cars and collects 24 full cars each journey.

Signalling at marshalling point Z

Figs. 9 and 10 show the layout of colour signals, track instruments and associated equipment outbye and at marshalling point Z. The numbers associated with the equipment have been prefixed with: ZL — marshalling point Z, lower level; EL — Eppleton shaft area, lower level; MR — man-riding; PU — propelling unit; HL — Hawthorn, lower level; to assist in identification.

Empty traffic from the Hawthorn end gains entry to the single line section by means of Signal No. HL1G shown on Fig. 9. (At this stage we will dispense with the prefix letters ZL.)

Arrival at signal 4G clears the section for routes from signal 3G. Selection for movements into either the marshalling point and the South Busty loading station area are provided by the two plungers A and B at signal 4G.

An empty train for the marshalling point draws forward and stops at signal 7G. The train is then standing over the propelling unit No. 1. Plunger operation clears signal 7G and the locomotive uncouples and moves forward and sets back over the No. 3 spring points on to track instrument 7Q(C). This, with the operation of a plunger situated here starts up the propelling unit No. 1 and feeds the train forward into the empties standage road.

The locomotive then sets back into the fulls standage road, collects 24 full cars and draws forward to signal 5G for entry into the single line section up to signal 3G and thence to the Hawthorn shaft.

Full trains enter the single line section from signal 11G and by way of 8W and 7W points and No. 8 spring points up to signal 8G. If stone cars are to be deposited in the standage, the locomotive sets back through No. 7 spring points accordingly.

Arrival at signal 8G and the depression of the plunger control clears this signal. After uncoupling, the locomotive moves forward, then sets back on to track instrument 8Q(C) which, with the operation of a plunger situated there starts up propelling unit No. 4 to feed the train forward into the fulls standage road.

The locomotive then moves into the empties standage road, collects 24 empty cars and draws forward to signal 9G for entry into the single line section up to signal 12G.

Propelling unit No. 2 (empties) and propelling unit No. 3 (fulls) each automatically start up as the respective train moves up to it to feed the trains further along the standage roads. Track instruments placed suitably in these two roads automatically cause the units to stop when the respective roads become full.

A special "stone" plunger is provided at signal No. 9G so that a light locomotive may move forward to the "limit of shunt" board at 8W points. These points are equipped for special through running when closed to enable the locomotive to set back on to the front of a stone train. Usual operations for the clearance of signal 10G up to signal 12G are in use.

Empty trains for Eppleton are signalled straight through the junction on the single line up to signal 16G (Fig. 11). Full traffic is signalled in the opposite direction from Eppleton from signal 15G to signal 11G.

The materials turnout (Fig. 11) is controlled from signal 15G and the route selected locks out the junction until the train has been detected clear into this road. Signalled protection is available for traffic leaving this materials turnout, the route being direct to signal 16G. The turnout is restricted to one locomotive and train only.

Man-riding traffic, after the operation of the requisite plunger at signal 11G, by-passes the South Busty loading point up to signal 3G, signal 6G being automatic for this move.

Selection at signal 3G obtains routes for either the four-car or eight-car man riding stations. After arrival in the selected station the locomotive detaches and traverses the set as a composite move. Selection from either man-riding signals MR1G or MR2G would gain routes to signal 4G and from this signal via the man-riding route by passing the loading point to signal 12G.

Both at signal 11G and 4G a special "M" manriding aspect is provided.

It is important to note that whilst man-riding is taking place in either direction no traffic moves can take place into or out of the marshalling point Z or loading point until:—

(a) the outbye going train has reached signal 3G

or

(b) the inbye going train has reached signal 12G.

Traffic movements at Lindsay shaft bottom

Empty or stone trains, from the marshalling point Z or stone trains from the stone standage in the East Busty landing (Fig. 12), arrive at signal 5G. Located at that signal is a plunger control and associated 4-position switch to cater for the four routes involved from that signal, i.e. empties road of airlock, stone road of airlock, man-riding standage 2, and those roads involving man-riding standages 1, repair shop, charging station and the collection of "fulls" from the Lindsay shaft.

The "ready" light associated with this signal, apart from its usual function, has the added significance of proving the exit airlock doors closed and indicating the state of the two roads inside the airlock (Fig. 12). Operation of the plunger control therefore opens the entrance door to the airlock and sets the points involved to the appropriate position. With these functions proved the signal clears and the locomotive, after detaching, proceeds via No. 7 spring points and No. 5 spring points to the rear of the train. The train is then propelled into the airlock. The locomotive is again detached and moves out of the airlock up to signal No. 7G. Operation of the control at this signal allows movement to a "limit of shunt" board at points No. 4W which are specially equipped for through running for the light locomotive movement towards the man-riding standages, etc. Detected departure past the airlock door involved and operation of the plunger control automatically closes that door and allows the opening of the appropriate door at the shaft end of the airlock.

The interlocking of the respective airlock doors with two minecar feeders has been provided.

Traffic movements from the man-riding standages Nos. 1 and 2, repair shop and the fulls roads from the Lindsay shaft are allowed from signals Nos. 11G. 8G, 10G and 12G respectively. Hand points are provided inside this area and bounded by automatic signal to allow signalled movement in any direction to any of these destinations by one train or light locomotive at a time. These movements are originated from these signals by the plungers marked (A) located at these signals.

No. 9 signal caters for light locomotive movement into the above area after depositing a man-riding set in standage No. 2.

For a traffic movement past the automatic signal down to signal No. 4G, operation of the plunger controls marked (B) at these signals "sweeps" the area previously described and that beyond and up to signal No. 4G. In addition to the clearing of the particular signal operated, the automatic signal clears to Green and allows the movement to signal No. 4G.

Signalling into and out of Hawthorn shaft bottom

Fig. 13 shows the track layout and signalling arrangements which cater for a total of fifteen separate routes, three of which can be achieved simultaneously. Five signals are involved together with nine sets of power worked points.

The North Harvey and Harvey West districts are each confined to one locomotive and train and once a train has entered either of these districts its section behind is cleared for further traffic moves over the junctions. Not until the train has been detected out of these districts can further traffic moves be permitted.

An example of the three simultaneous moves is as follows:—

A train could be proceeding into the North Harvey district from signal HL3G, a train could be proceeding from signal HL6G to the Harvey West district and a train could be proceeding from signal HL2G into the Hawthorn bottom. This is by no means the only example.

A special relay of the polarised type is used in the signal and point control circuits. The feature of this type of relay is that once it has been operated, say from normal to reverse, it requires a current of reverse polarity to normalise it. Until this is applied to the coils it becomes a "stayput" relay.

One application to which the relays are put is to correspond with each locked section, as will be seen on Fig. 13 and shown as LR (Lock Relay).

It will be noted therefore that from say signal HL6G four separate routes are available:—

A To Harvey West	6ALR Locked Section
B To Hawthorn	6BLR
C To Eppleton	6CLR
D To North Harvey	6DLR

Therefore considering the route to Hawthorn the operations are as follows

Arrival of a train at signal 6G is detected. Selection at this signal for Hawthorn obtains a "ready" light with the section ahead clear of traffic. Operation of the plunger control initially sets the route, i.e. 4/7 route and 2W points reverse. With the complete route detected 6BLR operates which, together with other relays, clear the signal 6G to green.

All other controls into this area are suspended and the train passing signal 6G reverts it to red. The train proceeds into the now locked section and last vehicle detection at 3Q(D and E) resets 6BLR to normal and so frees the section once more.

It is important to note that not only is the correctly detected route used in the clearing of the signal but also in the release or resetting of the lock relay. This means that only the train which accepts the signal can reset the locked section into which the signal reads.

Head to tail running is in operation along the shaft approach road up to signal 12G. One locomotive and train is permitted beyond this signal to the 12Q (D and E) clearance, point. Beyond this point and up to signal 3G head to tail working is in operation. This is the only place where head to tail working is permitted in the whole signalled area, and was decided upon to allow a maximum number of trains into the shaft area if a winding delay occurred.

From the foregoing it will be possible to trace, in conjunction with Fig. 13, each of the routes from a particular signal. Where no confliction occurs, simultaneous traffic movements are permissible.

In the dispatcher’s cabin is a track diagram which indicates the movements of the traffic along the roadways to and from the Hawthorn shaft. The extent of the area so covered on this diagram is the Murton shaft sidings and inbye to a marshalling point in one direction and the approach roads from Eppleton in the other.

A composite description of the entire scheme in the form of circuit diagrams and tables of signal controls has been prepared by the Westinghouse Brake and Signal Co. Ltd. and issued to N.C.B. personnel involved in the scheme. These sets of tables and diagrams have been prepared for each individual section and have proved of great value for maintenance and fault location purposes. A page of one such set of tables is reproduced here as Table I. In the bottom division of the table, the route from signal HL6G (Fig. 13) to the Hawthorn shaft bottom is described.

Signalling at the East/West junction Murton upper level

Signalling caters for some 16 separate traffic moves over this junction (Fig. 17) made up from six through routes, the remainder being special routes for stocking and unstocking coal and stone.

From Fig. 17, the through traffic moves will be evident, i.e. —

From signal 11G to Murton shaft or inbye to marshalling point X.

From signal 16G to Murton shaft or to Hawthorn.

From signal 36G to Hawthorn or marshalling point X.

An example of the coal stocking procedure is as follows :—

A train arrives at signal 16G and the driver selects a route to the stocking ground. On receipt of the appropriate signal — in this case "5," signifying Shunt for stocking — the locomotive is detached and proceeds to signal 17G by way of the spring points SP14. Selection at signal 17G enables the locomotive to complete the traversing move. The full set is then breasted into the stocking ground. An empty set is then hauled out to signal 17G selection at which gains entry to the marshalling point area. During the complete shunting operation and until the empty train arrives at signal 17G the junction is held locked.

Unstocking procedure is as follows :—

A train is signalled from signal 11G and arrives at the L.O.S. board at signal 17(A)G (shunt signal). Operation of a plunger here sets the route into the stocking ground. When the route is detected signal 17(A)G indicates this and the empty set is breasted back. A full set is then hauled out of the stocking ground up to signal 17G. Selection at this signal enables the locomotive to move to signal 16G. At this signal selection is made for Hawthorn and on receipt of the green proceed signal the locomotive completes the traversing move and picks up the full set and proceeds to Hawthorn.

A similar procedure as described for stocking and unstocking of coals from the 5/4 North district beyond the Murton shaft is in operation.

Stone cars are shunted off from a full set into the stone standage and when this standage is full an indication to this effect is given to the despatcher at Hawthorn. Arrangements are made for a light locomotive to proceed from either signals 16G or 36G to the front of the stone train for transport to the Murton shaft.

All the above moves are fully signalled.

Westinghouse signalling and control equipment
Plug-in relays

For control purposes, relays form a very important part of any traffic control scheme. As a result of long years of experience, special relays have been devised by Westinghouse to meet B.S.I. requirements for railway signalling purposes. These standards are very stringent and it is felt that where lives are involved, the same standards should be accepted for colliery use. In railway signalling, all circuits should be of a type that failure will interrupt a circuit, causing a relay to become de-energised, i.e. failing to safety. This principle is adhered to throughout.

Plug-in type relays are designed and manufactured to the above exacting requirements. They are fitted with plug-in features so that they can be easily removed and replaced when servicing. A relay having certain characteristics cannot be plugged into a mounting base for a relay having different characteristics if, by so doing, dangerous conditions might be created.

Westinghouse plug-in relays include a bridge rectifier to absorb any energy stored in the relay magnetic system, thereby ensuring spark suppression in the circuit. The contact and action are visible through a perspex case and the relay is provided with an interior deenergising switch for testing purposes.

The relay mounting bases are provided on pre-wired racks and fitted into apparatus cases which serve as wayside locations. The apparatus cases are of strong construction and fitted with facilities for padlocking to prevent illegal entry.

Flameproof colour light signals

The signals are shown in Fig. 4 and the two aspect units are fitted with a blanking plate in place of the bottom lens unit.

The signals are of sound construct ion and are certified fully flameproof. The main case which houses the electric bulbs has two lens units attached to the front face. Each lens unit is fitted with armour plate glass, fronted by a substantial wire mesh guard, hinged to allow for cleaning the outer face of the lens.

Double doors are provided at the rear. The outer door swings open, disconnecting the bulb circuits at two shrouded two-pin plug and socket connectors in the inner door. The inner door swings open in the opposite direction to enable bulbs to be replaced and other internal maintenance to be done as and when is necessary.

The electric signalling bulbs used are 6 volt 6 watt double-contact S.B. cap type.

Point operation

The sets of controlled points are operated by 4 in. diameter by 4½ in. stroke double-acting cylinders, which are controlled by solenoid-operated air valves (electro/pneumatic valve units style A). Two such units are used for each set of points.

The valve unit consists of a d.c. solenoid supplied from a bridge-type rectifier adjacent to the solenoid, both components being contained within a case fitted with a removable side cover. The a.c. leads from the rectifier are connected to two terminals mounted in a terminal chamber at the side of the case.

A pressure inlet and outlet assembly mounted below the solenoid case, together with the valve housing, completes the remainder of the unit.

To ensure that the point tongues are safely closed in the desired position, detectors have been provided to control the relays.

Track instruments

These instruments provide an automatic means of detecting the presence of a train or locomotive in a particular part of the tracks. They are fitted with two normally-made and two normally-broken contacts.

A long depression bar which is arranged parallel to the running rail is pivoted and is depressed by the passage of a wheel flange along it. The bar is connected to two arms which in turn are arranged to open and close the contacts. Springs and counterweights are provided to return the bar to its normal position when vehicles run clear.

Transformers

The transformers which are used for feeding the electrical circuits are intrinsically safe and flameproof. The output is rated at 24 volt amps., 15 volts on open circuit, the input being 240 volt 50 cycles supplied from the colliery lighting mains.

All the equipment used in the signalling scheme is fully approved and certified by the Ministry of Power.

Acknowledgments

For permission to publish this article we are indebted to Mr. S. W. Potts, General Manager, No. 2 (Mid-East Durham) Area, Durham Division, National Coal Board, and we would very much like to express our thanks to Mr. R. Davis, "B" Group Electrical Engineer and to The Westinghouse Brake and Signal Co. Ltd., for their assistance in the preparation of this article.

Drawings and Photographs accompanying the article