ARAPUNI POWER

Otago Daily Times, Issue 22505, 25 February 1935, Page 10

ARAPUNI POWER

FAULT DEVELOPS AT STATION UNIT THROWN OUT OF COMMISSION OUTBREAK OF FIRE FOLLOWS (Pbb United Pbess Association) AUCKLAND, February. 24. It is now learned that serious damage, estimated at several thousand pounds, was done at the Arapuni power station on February 15, when the windings of the So. 1 generator caught fire and the unit was'thrown out of commission. •

A chapter of accidents happened at Arapuni on that date. An insulator fault in the outdoor station interrupted the aervice in the whole district supplied by Arapuni for six minutes. A second insulator fault occurred in the outdoor station later, and there was another dislocation of the service for a time.

The major calamity occurred at 1.25 p.m., when an electrical fault, the cause of which will probably never be known, developed in the generator -windings of the No. 1 unit. The automatic " cut out" apparatus- came into play immediately, and the load, generated by the plant was taken up by another unit which previously had not been in operation. Except for a "jump" in the lighting and power services, the accident wag not noticed by anyone outside the station. From the time the fault occurred to the time the. rotation of the unit could be stopped by the application of the air pressure brakes six minutes elapsed. During that period the cambric and cotton tape insulation covering the copper windings surrounding the stator burst into " flames, , and an awe-inspiring sight was presented. The etation staff, under Superintendent A. C. Thompson, did excellent work with the fire-fighting equipment, and it was not long before the fire was suppressed. Extensive damage was done to . tne windings and it was-at first thought that the major portion of the plant would have to be replaced. An order was sent to the manufacturer* of the unit, the Asea Company of Sweden, for new parts, but the company cabled a reply suggesting that the order 'should be delayed pending the receipt of a detailed description of the requirements. The return cable embodying this description cost £SO to send, so intricate and technical were the details of the parts affected. A reply to this message is being awaited. In the meantime the superstructure and rotor of the unit have, been removed, leaving a cavity which discloses the burnt windings of the stator and the effect of the severe heat which has generated between the time the fault occurred and the rotation of the unit was stopped. No' damage Was done to the building. • Mr S. Lamburd, managing director for New Zealand of the Asea Company, has •pent two days at Arapuni co-operating With the staff of the Public Works Department in assessing the extent of the damage. Mr F. T. M. Kissel, chief electrical engineer of the department in Wellington, and Mr T. MacLennan, district engineer at Hamilton, visited the works . yesterday. . ■ : - ,■ Of the four main., units installed at Arapuni three are .operating and are able to cope with the needs of the district served by the station. It is expected that several months will elapse before the No. 1 unit will again be in working order. It was this unit which gave the engineers a great deal of trouble ..when it was • first installed. It was at first believed that'it was slightly off the balance, but after it had been . dismantled the fault. was found to be due to a defective part. When this fault . wag corrected the machine operated successfully.' ■ .The engineers are satisfied that the. recent fire had nothing to-do "With the defect which caused so much inxiety two years ago. ..-■■_ CAUSE OF THE FAILURE SHORT-CIRCUIT DUE TO STRAIN CHIEF ENGINEER'S THEORY (Special to Daily Times) ; AUCKLAND, February 24. "The department does not look upon the Arapuni trouble as a. major disaster, and the cost of repairs, about £SOOO, wilt be met from the reserve funds." said Mr Kiitel, who arrived in Auckland las* ■night. The repairs, he added,'would take 'four or five months to complete. | "The damage," Mir Kissel said, "was caused by a short circuit developing. on the windings of the stator of the No. 1 machine. Before the machine could be shut down "this electrical fire developed into an ordinary fire, destroying a large proportion of the lower ends s of the windings. Provision is made in the deßign of machines of this nature to cut off the current and to close the passages-which admit and exhaust the air. • "In this particular instance there was some delay in the functioning of the automatic" gear controlling the gates, and the fire in consequence obtained a somewhat greater start than it should have done. Although the power was cut off and the doors were closed within a.very short period, the draught created while the machine was still rotating was sufficient to draw the flames from the part immediately affected to other sections of the windings. "• ' •' "There have been several short circuits at the station during the past month due to lightning and to insulator defects. Although we cannot trace the present failure to any one of these happenings in particular, there is no doubt that some sections of the installation may have been strained, thus resulting in a gradual short circuit which caused the •'fire. ■', -'V . "The department does not anticipate that there will be any shortage of power consequent upon this," continued Mr Kissel. " For some time Arapuni has had a machine in reserve. If necessary. power can be drawn from Waikareiuoaiin or the King's wharf, although it is hot likely that it will be required." Mr Kissel said the department already had in stock some of the material necessary for repairs, although it would have to import N other material direct from the manufacturers' factory in London. The fact that the No. 4 unit had had to be be brought into operation, he added, would not affect the completion of the excavations for the two additional units that were to be installed.