ELECTRIFICATION

Evening Post, Volume CXIX, Issue 30, 5 February 1935, Page 10

ELECTRIFICATION

TAWA FLAT PROGRESS

CABLES AND LINES STARTED

POLES NEARLY ALL UP

A great deal more has been done in preparation for the electrification oi! the Main Trunk railway line to Paekakariki than is generally realised. Poles have been erected over most of the line, and though running the cables and ■ transmission lines is highly specialised work and takes time; a start has been made, and a good deal has been done. By the courtesy of Mr. G. W. Wyles, the Bailways Signal and Electrical Engineer, a "Post" reporter was taken over the work by Mr. S. G. Sargent, who is in charge of the installation. This is being carried out with particular attention to the vital points, such as perfect cable jointing and perfect insulation, especially in the tunnels, to avoid electrolysis. Though only some 60 men are at present employed in all departments the poles are practically all up, and the laying of the cables, transmission line, and overhead wires is on the way. The erection of the overhead wires is expected to be done in three months. The transmission line is completed from No. 4 portal to near Pukerua, and from this point to Paekakariki only remains to be done. POWER CABLES. The power will be brought in from the Khandallah sub-station by 11,000----volt aerial feeders, 'vrossing underneath the railway . lines at the Ngahauranga Gorge tnd of No. 1 tunnel in armoured cable housed in a concreted tunnel. From that point it is taken through the tunnel to the main Kaiwarra sub-station, and distributed to four other sub-stations, one half-way between Tawa Flat and Porirua, one half-way between Paremata and Plimmerton, one at Pukerua Bay, and one at Paekakariki. From the end of the 11,000 volt cables at the mouth of the big tunnel near Glenmore (No. 4 Portal) the 'power to the sub-stations is stepped up to 33,000 volts, and runs aerially to Paekakariki. The transmission lines and cables provide for duplicate circuits, either of which could carry on a sub-station, in the event of the breakdown of the other. The cables are carried along the embankment on reinforced concrete "pegs," or posts, on horizontal insulators. Above there are two 11,000-volt cables, below' them two 3300-volt cables, and below them the telephone cables. Some of the drums of cable weigh six tons. The drums are jacked on to a wagon, which is drawn slowly along, unwinding the cable as it goes. POLE PROBLEMS. Erecting the poles presents some unusual problems. All are seated in concrete. They are Australian desapped hardwood, and run from 52ft in length for special purposes to 25ft. They are sunk seven feet in the ground. From Paekakariki yard, with a small exception, the poles are up practically all the way to Kaiwarra. The tides gave some trouble with the transmission poles along the Porirua Harbour. These poles have to be placed well .->"i«ide the overhead pole?, and in some cases they were set in the sea. In •Hose cases the cement was rmV~rt w;th salt water. The poles are raised by means of jacks and huge props with steel jaws, and sometimes problems are presented by the nature of the ground. The soft , surface along the Porirua Harbour was not the best for jacks or props. A 60ft transmission pole was needed to clear the railway bridge at Paremata. Apart from the transmission line poles, approximately 1000 overheadpoles have been erected between Paekakariki and Kaiwarra. The bracing of the poles upon the ramp from Kaiwarra to the bridge has been specially attended to on account of the slightly less stable nature of the ground in which they are set. The poles are tied across below the rails at their bases by steel rails, and in place of the ordinary wires above they are joined by steel bars. OVERHEAD CONTACT WIRES. The suspension of the contact overhead wires from which the locomotives draw their power is from cross catenary wires by special brass clips into which the contact wires are wedged. Sag in the,wires is taken up by droppers. There is six feet of sag in the 240 ft spans. In the tunnels the contact wires are suspended from the roof, in which holes are drilled and plugged to receive the insulators. Putting these into the old tunnels on the way to Paekakariki was something of a snatch job. 'It had to be done between 8.30 on Sunday night and 6-a.m. on Monday, "on account of the frequency of trains at other times. Boring was done on three nights by compressed air from a "X" type locomotive, which is fitted with larger capacity air pumps than other types, boring and. grouting being, done from wagon platforms'. In the double-track tunnels there is 100 ft between each pair of insulators, but in the iower single-track tunnels the contact wire insulators are only 50ft apart. In yards and where there are double ■wires the contact wires are supported . from catenary cross-wires, but in the case of single lines the catenary wires are supported on a "T" iron bracket with an angle in it,. which leans out from the top of the pole, from the top-of which it ■is I stayed.

TELEPHONE SYSTEM.

One of the features of the installation is the complete telephone' system, which will be linked up with the rest of the North Island. A 40----pair telephone cable runs from Kaiwarra to the Hutt Road overbridge, where it is divided into two 20-pair cables, • one going up- the Wairarapa line and the other up the Main Trunk. The telephone cable will be supported where possible from the overhead poles, and where this cannot be done short poles will be put in between on a "messenger" wire. The cable is what is known as a "loaded" one, the .first of the kind to be erected in New Zealand. Every 2000 yards between Wellington and Paekakariki there are what are known as loading coils, which are built into the telephone circuits, and do away with certain losses. The result is that transmission is obtained through the cable with as few or fewer losses than if the wires were run as aerials, and it is possible to talk through 26 miles of cable perfectly. . " At Paekakariki the telephone cable terminates, and the wires radiate away over the North Island. A "D.1." carrier operates from the cable termination to Ohakune. At present only one channel is provided in the carrier, but provision is made to increase this if the traffic warrants it. The carrier circuit is a form of radio telephony, and when normal speech is on the line it cannot be heard on the carrier circuits. ' ■ ■ r

TWO SUPPLY DEPOTS,

Paremata is a secondary depot lor the job, as Kaiwarra is too far away. There overhead wires are at present being accumulated ready for starting the work.

The Kaiwarra sub-station contains a vast amount of material. Many of the fittings used in the electric installa-

tion are made at the Woburn railway shops. When compared with the imported article there is no apparent difference. The assortment of insulators, twelve-foot tallow-wood arms for the transmission poles, twenty-nine pound insulators, clips, wire droppers, clamps for poles, stays, special boxes for ensuring perfect cable joints, and a tremendous amount of special fittings for special purposes is confusing to the layman.