CLOCKS RUN SLOW

Dominion, Volume 26, Issue 219, 12 June 1933, Page 10

CLOCKS RUN SLOW

Caused by Power Trouble EFFECT ON CITY USERS Users of hydro-electric power in the city about 8.41 on Saturday morning noticed that their motors were slowing down, and that all lights were losing their brilliancy. Electric ranges and radiators were also affected. Upon inquiries being made, it was ascertained that the trouble was caused through a fault in one of the main switches in the combined system cuttingloff the power from Waikaremoana and throwing the whole load on to Mangahao, whose generators were consequently overloaded. As a consequence thej voltage over the transmission lines fell. The city feed line voltage dropped from 11,000 to 9000 volts, and there was a corresponding drop in voltage right down to the 230-volt supply which reaches the city user. The heavy load also slowed up the generators, and this resulted in a reduction in Hie number of frequencies, or cycles, per second from the standard of 50 to perhaps 45. Lower voltage meant that all lights burned with much less brilliancy, and electric ranges, radiators, etc., were also affected.

The lower frequency affected motors of all kinds, and a curious effect was found in many electric clocks. Some more modern types of electric clocks (Mangahao time clocks) are driven by tiny motors, the speed of which is fixed by the frequency. If the frequency of the alternations (in a.c. supply the current does not run smoothly through a circuit, but flashes clockwise and anti-clockwise) rises about 50 per second such clocks run fast, and if the frequency drops tlie clocks run slow. Saturday morning’s complication, therefore, resulted in the clocks losing about four minutes in half an hour. The engineers at the power stations undertook to put them right again by the simple method of running the generators just a trifle fast, say, 51 cycles per second, until the four minutes wore exactly made up, after which the generators were brought back to tlie unvarying 50 cycles per second. The Evans Bay steam station was brought Into operation, but within half an hour the supply was normal again.