POWER FAILURES.

New Zealand Herald, Volume LXVIII, Issue 20894, 9 June 1931, Page 5

POWER FAILURES.

PROTECTIVE DEVICES.

INGENIOUS AND AUTOMATIC.

The power line fault which for a time cut off supplies to several of the .suburbs last week serves to direct attention to the many ingenious devices for protection, some of which are in use with every modern installation. Most of these are too complicated and technical to be leadily understood by the layman, but the principles involved and the results obtained are of general interest. For many years past it has been practically essential to protect all high , tension and extra high tension rabies not only against tripping out through overloading but also against faults and leakages. To guard against a short circuit from overloading there is a special apparatus set to record the maximum load that may be safely transmitted. When (hat point is reached the cable is automatically cut out by a trip. Another protection is required to meet the situation when a fault occurs on a cable, breaking down the installation and allowing current to flow to earth. Much . damage might be done to the cable if provision were not made for such an emergency. Many systems are on the market, each quite good in its own way, but some more applicable to certain classes of faults than others. Three different systems are employed by the Auckland Electric-Power Board, the chief being an installation based on the principle that when everything is right there should be an exact balance of current at both ends of the cable. As soon as a fault develops that balance is upset by the leakage that occurs. The devico actuates certain electric relays and the affected section of the cable is cut outIn unattended sub-stations such a» the one at Lincoln Street, where tho fault was recorded last week, there is another provision. When a cable trips out, as that one did, on account of a short circuit or a fault amounting to overloading, there is an automatic equipment that will put the cable back three times at intervals of 20 or 30 seconds. If the trouble has been a merely temporary overloading that has passed away the cable will step in and continue its work. If it is a fault, after tho cable has gone in three times it locks itself out and cannot be put back again until it has been reset by hand. Such equipment is provided at. all the board's unattended sub-stations, and all its cables have the doubla protection against fault.jind against overloading. The same principle is applied to all high tension overhead lines. Immediately a broken line comes in contact with anything, such as the branch of a tree, that would convey current to the earth tho line makes itself dead. This, of course, is a great safeguard against accidents occurring through contacts with live wires. There is no necessity for the same precautions with low tension wires. GRAPES FOR CANADA. QUEENSLAND SHIPMENT. The Queensland Committee of Direction of Fruit Marketing, in a report on Queensland grapes recently shipped to Canada, stated that the fruit arrived in splendid order, the cork dust packing being perfectly satisfactory. Sales realised from 20s lOd to 18s 4d per 251b. box. All l Queensland varieties, including Corni- ! chons, carried well. Earliest possible shipments next year, since the Canadian market is a good one, are advised. | Questioned regarding the possibility of developing an export trade in grapes from Auckland, a leading merchant stated yesterday that there was practically no chance of that meantime. Although there was heavy production of Auckland grapes at certain seasons of the year, the quality was not good enough to stand competition overseas. SOVIET RUSSIA. INDUSTRIAL EXPANSION. The April issue of World Trade contains an article on the industrialisation of Russia. The author does not share all the fears which are entertained in some quarters of the effect on world markets of a Russia filled with factories. "The fiveyear plan will not of itself give Soviet Russia an overwhelming industrial position in the world," he says, "but the balance of evidence indicates that the economic changes of the last three years will leave a permanent mark and it behoves the rest of the world to consider what form of organisation, whether of individual firms or on wider lines, is best suited to deal with the centrally directed national units to which the foreign trade of the U.S.S.R. is entrusted. The most suitable organisation will almost certainly be one of largo size."