Electrical Supply.

Arrangements were made to obtain supply from the Public Works Department's substation at Khandallah at 11,000 volts, in order to feed the Railway substation at Khandallah, the balance of the supply for the line being supplied from the Kaiwarra substation, which is fed by an alternative 11,000 volt line via the Tawa Flat tunnels.

The substation equipment consists of 11,000 volt armour-clad switchgear, supplied by Messrs. Reyrolle and Company, for the purpose of connecting the 11,000 volt supply to the transformers and rectifiers. The supervisory and remote control equipment was also supplied by Messrs. Reyrolle and Company.

For the purpose of converting the 11,000 volt alternating current supply into 1,500 volt direct current to drive the multiple units, converting apparatus consisting of transformers and glass-bulb rectifiers was installed. The glass-bulb rectifiers were supplied by the Alliance Electrical Company, Ltd., Wellington, on behalf of their principals, the Hewittic Electric Company, Ltd. These rectifiers work in pairs, each bulb being capable of supplying continuously 300 k.w., so that a pair of rectifiers can continuously supply approximately 800 h.p. These bulbs, which are capable of supplying four times this amount for short periods, are of the largest size made for 1,500 volt traction work.

After the power has been rectified to 1,500 volts it is connected to the overhead line through high-speed circuit breakers. The breakers are capable of disconnecting the supply on the occurrence of any fault in .02 of a second. They are provided not only to form a connecting link between the substation and the overhead, but also to prevent the substation being damaged in event of a fault occurring on the overhead.

New Zealand Skill.

The overhead equipment was designed in New Zealand, and many of the detailed parts were manufactured at the Department's Workshops at Woburn. The contact wire, consisting of hard-drawn copper, is .25 sq. ins. in section, and the catenary wire, which supports this, is stranded hard-drawn copper of the same sectional area. There is a total length of 8¾ miles of contact wire installed, including the sidings and the Johnsonville Station-yard.

As soon as normal running is begun on the Johnsonville line the substations will be run without any attention, the necessary switching being carried out by remote control from the control station situated in the main power-house at Wellington. The movement will be accomplished by operating small telephone keys, and every movement made is checked back to the operator before final movement to complete the operation of the circuit-breaker is carried out. The positions of all circuit-breakers are indicated by means of coloured lights, not only in the substations, but also in the remote control station in Wellington, and, in addition to this, indicators are provided in the District Traffic Manager's Train Control Office, so that the train-control operator has a continual indication of the condition of the line always in front of him.

Special Signalling System.

That is a brief description of the electrification system as apart from the rolling-stock, but, in addition to this part of the work, mention should be made of the special signalling system which has been installed. This system, designed by the Railway Department, presents a number of entirely original features. Full automatic working will be provided between Wellington and Johnsonville, the movement of the trains thus causing the points to operate at the various stations—depending upon the condition of the line. Arrangements are made whereby the points will not operate and allow a train to enter a single-line section unless that section is clear for it to do so, and the starting signal will not go toz page break page 23 clear until the points have operated. Provision is made whereby a train, having claimed a section, can be cancelled by a member of the train crew using a special key for the purpose, so as to enable an opposing train on the section in advance going forward to make its crossing instead of having to wait until the first train had gone forward to the next station.

Other Safeguards.

At Johnsonville special provision is made so that during certain hours of the day electric trains will go on one side of the platform and at other times of the day to the other side of the platform, and, further, if one side of the platform is already occupied, then the points will automatically set to divert the following train on to the other route.

Train-control telephones will be provided at all stations, and an indicating light will warn train crews that they are required to stop and speak on the telephone.

Provision is made at Ngaio and Khandallah for the signal cabins there to be switched into use, so that shunting of certain trains can be accomplished by means of the operation of the signal-levers, but under normal working conditions the operation of these stations, including certain specified shunting movements of multiple units, can be carried out automatically without having to switch the signal boxes into use.

In addition to the signalling there is the provision of mechanical train-stops for trains travelling down the grade, so that, if the points are not correctly set, power will be cut off the train and the brakes automatically applied. At the Wadestown crossing-loop, in addition to these facilities, an electrical train-stop is installed which will again cut off power and apply the brakes if the speed of a train is higher than is prescribed.

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