THE MYSTERY AT ARAPUNI

Taranaki Daily News, 14 April 1932, Page 9

THE MYSTERY AT ARAPUNI

vibration in generator

LOCATING THE TROUBLE.

SMALL FLAW IN MACHINERY.

It is believed that the cause of vibration in No. 1 generator at the Arapuni power station, which has been a source of mystery for nearly two years, has been determined. Careful. tests and calculations have narrowed down the possible cause to an unbalanced hydraulic condition in the turbine, due, it is feared, to a small flaw in the manufacture of the runner, which is a cylindrical Spinning part. If this is the cause, states a correspondent of the New Zealand Herald, and it can still only be a surmise, the vibration set up by the unbalanced condition of this part of the machinery would be easily transmitted to the generator, in .which the trouble first became noticeable. No information could be gained as to the cause of the trouble from the power station superintendent or the engineers at Arapuni on Tuesday, but it was reliably learned from an outside source that the suspicions of the experts are as stated. ADVICE FROM ABROAD POSSIBLE. , Jt is possible that the Government may see fit to check the theories of its engineers 'by forwarding a considerable amount of data to England and Sweden for confirmation by world-rccognised experts in .hydraulics, as the task of acs curately ascertaining the cause of the trouble bristles with highly technical problems. If this should be the Government’s decision, the remedying of the trouble will be a lengthy business, as the mass of data will have to be sifted, and if the diagnosis outlined. received confirmation, the part of the machinery affected will have to foe ( replaced. The surmised location of the trouble definitely discountenances the rumour frequently, heard that the fault lies in the power-house foundations. Not only is this theory rendered untenable by the mere process of elimination, but it is flatly disproved by exact observations tarried out by such instruments as a seismograph, which is located inside the Eower station and a number of extremer sensitive levels. EARTH MOVEMENT RECORDED. Few people know of the existence of these instruments. They were installed to measure earth deflection at the time the fault developed in the country as a result of water percolation causing the whole area between the gorge and the headrace to tilt toward the river. They showed that when the water was removed from the headrace the country sprang back to its original position, leaving the power-house and its foundations the same as before. These instruments, aftei- being employed to record how the country behaved when the water entered the headrace, have now been used to determine whether any portions of the foundations have moved or are moving so as to account for the vibration in No. 1 generator. They show conclusively that no such movement has taken or is taking place. The seismograph is of such a sensitive character that it can measure and record movements of one-millionth of an inch in the earth’s crust. Subterranean disturbances 5000 miles away in the Pacific Ocean have been clearly recorded and during , the Napier earthquake the recording needle jumped completely off the chart. The seismograph records in the form of a wavy line the minute contractions and expansions of the concrete foundations during and immediately after a night of frost, but it records no seesaw movement or vibration of the concrete foundations such as might account for the trouble with No. 1 generator. FOUNDATIONS STEADY AS ROCK. The sensitive, levels in use show no difference between the permanent horizontal level of the foundations at the spot where'No. 1 unit operates and the beds of Nos. 2 and 3 units, which are both running without vibration. All parts of the foundations are as steady as a rock. A theory has been advanced that the cause of the vibration may be trace! to an underground river said to have been located -by a water diviner close to the power-house. If such were the case it may be assumed that not only would No. 1 unit vibrate, but all the others resting on the same foundations. Yet that is not so. Whatever may be the truth of the water diviner’s findings the fact remains that 6ft from the corner of the power-house, a few feet from the place where the diviner ( sensed , water and only some 30ft from No. 1 turbine, is an observation bore that goes vertically into the ground for 400 ft. No underground stream has been tapped by it. If such a stream exists it must be so far below the surface as not to affect in the slightest the steadiness of the foundations.