Southern Electric Group Kent Coast Electrification Scheme (Part 3)

Electrification—Power Supply and Control—Phase 1

The lines were electrified at 750V dc throughout. Current was taken from the National Grid at 33 kV 50Hz ac at 5 points in Phase 1—Sittingbourne, Queenborough, Thanet, Canterbury and Folkestone—for distribution through oil-filled cables in concrete ducts for rectification to line voltage at 23 substations. The rectifiers were all of the mercury-arc variety, similar to many in use already in the suburban area. The area normally fed from each feeding station was as follows:

Sittingbourne fed the line from Gillingham to Graveney (between Faversham and Whitstable), the Sheerness branch and the Dover Priory branch as far as Selling
Queenborough was used to supply lines on the Isle of Sheppey in the event of power cables across the Swale being damaged;
Canterbury fed the Dover line from Selling to its junction with the Deal line; Thanet (situated near Margate) fed the Ramsgate line beyond Graveney.

In all, 7 substations were fed from Sittingbourne, 1 from Queenborough, 7 from Thanet, 6 from Canterbury and 2 from Folkestone. The substations were located at 3½ mile intervals. There were 13 on the Gillingham—Ramsgate section, two on the Sheerness branch and 8 on the Dover line. In addition there were 21 track paralleling huts, whose function is to improve the supply current characteristics, and provide additional points at which the power supply can be sectioned. The substations had a capacity of 2500 kW, save those at Queenborough, Broadstairs and Dover, which had double the normal capacity. (The number of substations fed from each grid feed has since altered.)

Conductor rails were 106lb per yard, except on the boat train route between Gillingham and Dover where 150lb per yard rails were used. They were laid in lengths up to 440 yards.

Electrification—Power Supply and Control—Phase 2

Equipment used for electric current supply was similar to that used in Phase 1 with supplies being taken from the National Grid at 4 existing supply points Tunbridge Wells, Canterbury West, Thanet and Folkestone. Tunbridge Wells supplied substations from Sevenoaks to Maidstone West and Headcorn. From here Folkestone became the supply point. Folkestone’s area extended to Walmer, Wye (from Ashford), and Bearstead. Canterbury grid feed supplied the Wye–Minster section and Thanet supplied Sandwich and Betteshanger substations. The number of substations added to other feeds were: Tunbridge Wells 10; Folkestone 16; and Canterbury 6.

30 of the 32 substations had 2500kW mercury arc rectifiers similar to those used for Phase 1, while that at Folkestone had double the capacity. The substation at Hollingbourne was of an experimental type which became the standard for the later Bournemouth line electrification. Instead of mercury arc rectifiers, a 1500 kW silicon rectifier was installed.

The substations, together with 18 track parallelling huts, were controlled from a new electrical control room situated at Paddock Wood. Conductor rails on the lines electrified under Phase 2 were of 150lb per yard on the boat train routes (via Tonbridge and Hollingbourne) and 106lb per yard from Ashford to Ramsgate via Canterbury West and from Buckland Junction (north of Dover) to Minster Junction.

Signalling—Phase 1

Some 97 route miles were resignalled as part of Phase 1, comprising lines from Factory Junction to Ramsgate by both the main line and the Catford Loop, and including the Sheerness Branch. The section from Faversham to Dover was not resignalled. The scheme meant that 9 new power signal boxes were introduced, permitting the abolition of 31 cabins. Other modifications allowed 23 of those remaining to be manned on a part-time basis. Semaphore signalling on the resignalled section was replaced with colour-light, mostly 3 aspect, but with 4 aspect signals in congested areas where close headways were necessary.

The new power boxes were at Factory Junction, Shepherds Lane, Herne Hill, Beckenham Junction, Shortlands Jn, Chislehurst Jn, Rochester Bridge Jn, Rainham, Sittingbourne and Faversham. Existing boxes were retained at Swanley, Gillingham, Margate and Ramsgate. Push-button route setting was installed in all the new signal boxes and included plug-in relay apparatus, thus enabling the relay room to be reduced very much in size.

The Chislehurst Junction box, which replaced no less than 7 former boxes, controlled the very important junctions between the Chatham and South Eastern lines referred to above. At first it linked with semaphore signalling controlled from Grove Park and Orpington, until this was replaced by multiple aspect equipment under Phase 2.

The Sheerness branch was operated from Sittingbourne by the EDICT (Electronic Digital Indicating and Control Transmission) system. This was the first use of centralised traffic control on the Southern Region. Time division multiplex scanning was used, and 160 functions were interrogated during a 3.84 second cycle, the information being transmitted to Sittingbourne.

The new signalling allowed for a 3 minute headway on all lines, save on the slow lines between London and Swanley where a 2½ minute headway was installed to cater with the volume of inner suburban traffic.

The new signalling was introduced during the Spring of 1959 as follows:

Signalling—Phase 2

Phase 2 was similar to Phase 1 regarding signalling in that it extended from well within the suburban area to Dover, and left certain sections—Paddock Wood to Maidstone West, Dover to Ramsgate and Ashford to Ramsgate—unconverted. Indeed, signalling for Phase 2 seems to have been based largely on automatic signalling over long straight sections, with signals being controlled in junction areas. Route setting was achieved by push-button selection once again.

6 new power boxes were built for Phase 2; these were Hither Green, Orpington, Sevenoaks, Tonbridge, Ashford and Folkestone Junction. These replaced 41 mechanical signal boxes, of which 33 were abolished completely. An interesting point to note is that, although the lines through Tunbridge Wells were not electrified, the signalling nevertheless extends as far as Grove Junction (where the Hastings and Uckfield lines diverge). Indeed, Tonbridge controls an extensive area, from Sevenoaks to beyond Paddock Wood, Yalding (exclusive) on the Maidstone branch and Grove Junction (exclusive).

At Headcorn, the down main line and loop were normally under the control of Ashford panel, while Tonbridge controlled the up main line and loop. The existing cabin was retained for shunting freight trains to the goods yard, but that was closed soon after the resignalling. The box remained to take control of either the up or down lines in the event of failure of the automatic control. Sandling was the junction for a siding connection to the up line—the remains of the Hythe branch. The ground frame here was released from Westenhanger box when that box was open, otherwise it was released from Ashford Panel box.

The length of the Elmstead Woods, Polhill and Sevenoaks Tunnels meant that signals had to be installed in the tunnels to maintain the required headways. (It should be noted that this arrangement did not apply on the slow lines through Elmstead Woods tunnel). The original proposal was to allow a train, if it had been stopped at the first signal after leaving a tunnel, to proceed at caution under the authority of a calling-on signal into the occupied section beyond. This arrangement was not approved by the Railway Inspectorate, and in the revised arrangement the signal controlling the entrance to the tunnel will only clear if either the signal in the tunnel or that beyond the exit (or both) are clear. thus a train is prevented from entering a tunnel unless the exit is clear.

The signalling for Phase 2 was introduced during 1962 as follows:

The headway allowed was 2 minutes for fast trains between Hither Green and Sevenoaks, and 2½ for stopping trains on this section. Beyond Sevenoaks the headway was increased to 3 minutes, but these headways were reduced at Sevenoaks, Tonbridge, Ashford and Folkestone to allow fast trains to close up and pass trains which were stopped in platform.

4-aspect signals were used from Parks Bridge Jn to Sevenoaks, at Tonbridge and Ashford, and between Cheriton and Folkestone Junction; elsewhere 3-aspect signals were used.