THE CITY'S ELECTRICITY

Lyttelton Times, Volume CXV, Issue 16606, 18 July 1914, Page 15

THE CITY'S ELECTRICITY

PROGRESS OF THE GREAT

SCHEME,

FROM THE LAKE TO THE CITIZEN'S HOME.

THE TRANSMISSION LINES, (By Oto Special Reportek.) 111.

Nearly 1800 ironbark poles have been used in the erection of the two transmission lines from Lake Coleridge to tho city. It is almost incredible that such an enormous amount of power is to bo transmitted along the thin wires on those poles. When it is considered that in tho course of its generation the electricity has necessitated the building of an Bft tunnel a mile and a q'uartef long, of half a mile- of 4ft Gin piping and the erection of some huge machines, it seems difhcult to realise that the current could bo carried along such slender threads. The latent power of Lake Coleridge enters the baso of tho powerhouse, through wide water pipes, and it is sent out through the roof as a ".live" thing along these wires. The six transmission lines forming two units of three wires each leave the station, from annd a collection of weird insulators and " choko coils." and . commence their long overland journey to CTiristchurch on the 42ft poles which are placed 6ft in tho ground. On the head of each pole threo largo insulators, weighing 281 b each, are set, one on the extreme too and tho other two 6ft below on a cross-tree. Below these again is a smaller cross-picco which carries the teleohone wires to the station. J.ho poles aro placed at intervals of .six chains, but in one part, about eight miles out from the powerhouse, three quarter-mile spans were necrssary to cross a gully. Ordinary poles of course, were not strong enough to stand such a strain con^ T ™ treble poles were erected, with treble Bets of*insulators. ERECTING THE LAST POLE.

There aro two transmission lines to Christchurch, but they do not come in bv the same route. For about twelve miles after leaving Lake Coleridge they travel together, and then they separate, >ono taking a southerly course through South Sororata and Charing Cross and the other, moro to the north passing down through Coalgate. the reason why the two courses have been adopted is to minimise as far as possible any electrical disturbance that might be caused by the proximity ot such a largo amount of energy. Altogether there are about 420 miles ot wire between the power station at Lake Coleridge and the sub-station at Addington. Practically all the poles havo been placed in position, and the gang of men, which carried out the work, put up some good records. Tho average number put in each day was thirteen, and the greatest number in any day was twenty-two. The gang went out on the northern courso, and ieturned by the southern one, and last week the writer had tho privilege of witnessing the erection on tho Yaldhurst Road of the last pole of the contract. The gang of six men which followed and wired the poles, did not make such good progress as the other mon. So far the whole of one lino has been wired, and the gang returning by the other line has wired about forty miles, so that the work should be completed within a month.

GOVERNMENT'S GOOD WORK. Before commencing the description of tho Addington sub-station, a word about the difficulties which the Public Works Department has overcome in the way of transport to Lake Coleridge would not be out of placo. For nearly four years now the Department has had chargo of the roads leading to the settlement, and when it is considered that every article to be used in tho scheme, all the supplies and necessary material, incidental to such an undertaking, had to bo transported over a distance of 32 miles from Coalgate, the nearest point of tho railway, the task was by no means an easy one. At one time there were as many as thirteen traction engines on tho route, and the roads have stood the heavy traffic very well. During the time the work has been carried on something like 15,000 tons of material havo been carried over that road. Three thousand tons of coal. 2000 tons of cement and about 1000 tons of machinery have constituted the major portion of tho material, while the supplies for tho men on the works have been considerable. ADDINGTON SUB-STATION.

WHERE THE CURRENT UNDERGOES ANOTHER CHANGE.

The connecting link between the works at Lake Coleridge and the City Council's plant in the Addington substation forms an important factor in the scheme. Hero the current from Lake Coleridge enters at 66,000 volts, and is transformed through a series of wonderful contrivances to 11.000 volts on cables of greater dimensions than the aluminium wires from the lakeThis fact can be even more readily understood when the two kinds of cable are compared. The lake transmission wires consist of seven strands of aluminium wire, a little more than oneeighth of an inch in thickness. On the other hand the current leaves tho Addington sub - station through specially prepared copper cable consisting of thirty-seven strands interwoven into a diamond shape. Whereas the aluminium wires are not insulated except for the large porcelain insulators on tho transmission poles, this copper cable is insulated Dy several layers of different material, and. the whole is encased in lead, making a thickness of about two inches. .As such it goes underground to the city, in a peculiar kind of concrete pipe, across Hagley Park and along Oxford Terrace and Armagh Street to the plant at the destructor, whero the current will undergo another transformation before it is finally distributed to the consumers. The current will enter the sub-sta-tion a three-phase alternating current of fifty cycles per-second at a pressure of 66,000 volts. On the west side of tho roof, which has been prepared with a special rubberised composition, aro situated tho insulators to which aro attached the incoming wires. These glased insulators stand about two fest high, and some are of a peculiar French-grey- colour, while others J aro of a dark brown hue.- Alongside each set of insulators is a lightning arrester, which consists of what is called a " choke-coil," moro resembling ail extra large-sized spring used in furniture making than anything else. This particular pieco of mechanism serves to choice off any lightning discharges and| dissipate the atmospheric current through proper channels to the earth, without caushig any injury to the transformers below. THE TRANSFORMERS.

The current enters by way of the root and immediately commences its process of transformation- The interior view of the sub-station is quite different from what the ordinary individual would expect in an eleotnc station. One is accustomed to see switchboards of marble panels with shining metal dials The reverse, however, is met, for in this instance the switchboard itself, although, allimportant i» a comparatively small portion of the works. The first things that impress one most are the huge transformers which arc arranged ?n SrfiS?" $ thr , ee nt each end of the station, riiey look more like inverted

steam boilers, and stain 7 ibout twelve feet high, with a diam .-. r of five or six feet. Each transformer weighs eight tons, while- the mechanism inside weighs another six tons. Through tho top of tho roof the electrical energy is conducted by means of a network of copper wires, which are supported on a number of tho large insulators (similar to those used on the roof) to the three ungainly-looking oil-switches. From tho oil-switches tho current is conveyed to tho transformer terminals, which protrude above tho transformer it-self, for about thirty inches, like two great black horns. What actually occurs inside tho transformers is puzzling to the layman. Each transformer contains thousands of coils of copper wire wound round iron cores. All the coils are not of the same thickness, and the current which enters it 66,000 volts traverses the coils of thinner wire first, and induces a current of lower voltage into tho next coil, having a wire of greater thickness. Finally the current emerges at a voltage of 11,000, whenco it is distributed to the other switches before finally, leaving the station for the city. In between the coils of tho transformers a special oil is filled, which is kept circulating all tho while the current is flowing through. . Serving as an insulator as well, this mineral oil, before being used, is subjected to a thorough process of filtration. The building for doing this work is being erected adjacent to the station, and there the oil will bo forced at a pressure of 2001 b to the square inch through three hundred sheets of thick blotting paper, which will remove all impurities and absorb all traces of water. Tho oil capacity of each transformer is about 800 gallons, so that altogether nearly •■3OOO gallons of oil will be used at the samo time.

OIL-SWITCHES. Whon it is considered that such a tremendous amount of electricity is being handled, and at such dangerous voltages, the greatest precautions are absolutely necessary. The switches at tho Addington substation are of special design, and are automatic; that is to say, they are worked by means of hand switches from the switchboard which overlooks the wholo of tho machinery. Oil plays an important part in the manipulation of these huge switches, of which there will bo about fifteen when tho station is in full working order. The mechanis mthat operates the switch is built into a concrete partition about five feet high and four feet across. Tho contact pieces aro immersed in oil chambers, which prevent any escape of current, because if it were switched on in the air, tho flash that would occur, when they were being worked, would burn the metal surrounding it. A largo electro-magnet is the secret of this automatic operation. When tho lever is turned on the main switchboard an electric current is set up, and the magnet immediately draws the two contacts together. Tho reversal of the lever throws into action another smaller olectro-maguot which in turn releases a catch, and the switch opens. Thero are three main switches for each triple set of transformers. Incidentally there is a similar oil-switch controlling each outgoing cable. Overhead the main switches aro connected to the sub-switches by a series of busbars. These are long strips of copper about an inch wide, and extending the whole length of tho twelve switches through which tho transformed current will be distributed. THE SWITCH-BOARD.

Situated on a gallery, and command-' ing a position overlooking the whole of tho machinery beneath, the switchboard forms another interesting section of tho sub-station. Altogether there are fifteen panels, three for the three main switches, and twelve ordinary panels to control the outgoing feedors. The main panels, which are in the centre of tho switch-board, will practically form the key to the whole station. Each panel, which stands about six feet high, is fitted up with the latest electrical appliances, and everything has been provided to ensure the utmost precaution against danger and against tho interruption of tho supply. Red and green tell-tale electric lamps aro fitted on each panel showing whether the particular wires passing through it are in use. STORAGE BATTERIES. At the end of the main switchboard, there are two more panels, but these will control the current generated by a small dynamo for charging the storage batteries. Throughout the station the lighting current is entirely separated from the Lake Coleridge current, and will be supplied by the storage batteries, of which there are fiftysix situated in a room at the southern end of the gallery. These batteries will produce a voltage of about 110. The object of tho lighting being supplied by such means is to prevent tho station being thrown into darkness should a breakdown occur in the supply from tho headquarters. LIGHTNING ARRESTERS. It can be easily understood that with such an accumulation of electrical energy tho need of efficient apparatus to ward off any atmospheric attack is all tho moro apparent. A lightning discharge could do much damage in a few seconds. Ascending from the roof a number of hollow copper tubes, of about half an inch in thickness, form the channed by which any electrical disturbance in the air will be connected to the arresters and thence to the earth. These arresters, which are arranged in a. row on the western side of tho building, are each about Bft high, cylindrical in shape and tapering off at tho top to a point through which the copper conductors enter. As each discharge is. caught by the choke coils on the roof, it is passed down to these oylinders, where its strength is exhausted. Inside the arresters there are about 300 aluminium discs filled with a special substance called electrolyte. The high resistance set up by. this substance breaks down the electrical. discharge on its way through, and it leaves tho arrester as a harmless current by means of copper bands, which run all over the station, Outside, these wires are connected to rods, which go down about 14ft into the earth. AUTOMATIC RECORDER. Connected with tho lightning arresters is. an interesting yet intricate little machino which records each discharge as it passes through. The recorder consists of a strip of paper passing over a revolving clockwork drum. Tho lightning in its actual courso earthwards registers its presence by the perforation of tho paper on the recorder. There is thus given a permanent record of evory discharge, no matter at what time it may happen. Simultaneous with the recording of the flash a bell rings' on the madn switchboard, and the man* in charge at once prepares for any emergency. MACHINERY DUPLICATED. There is little moro to be written about this wonderful place. Throughout the main idea has been to prevent interruption of supply. The machinery has been so arranged that should one section go out of order, or one of tho main transmission wires break down, tho remaining plant, with the assistance of connecting switches and intricate gear, could take on the full load. Every part of the transforming works is in duplicate. The building is a plain two-storeyed structure, built entirely of reinforced concrete. It was erected by contract by Messrs Paynter and Hamilton, a Chnstchurch firm, at a cost of about £3500. The trans-

formers wero supplied by the General Electric Company" of America, and the switchboard, oil-switches and the necessary equipment wero supplied by the British Westinghouse Electrical Company of- England. There is little- remaining to be done at the station. At present the transformers are being dried by hot air pumped in at a temperature of about 190 degrees Fahrenheit, and it is expected that they will soon be dry enough to safely undertake any experimental tests. Several of the oilswitches, including the two for the city current, have been equipped, and have been put through the first tests, with satisfactory results. Practically only the finishing touches are now required to make this station one of the most up-to-date of its kind in the dominion. (To bo continued.)