INSTRUCTIVE LECTURE

Bay of Plenty Beacon, Volume 9, Issue 94, 3 July 1946, Page 2

INSTRUCTIVE LECTURE

N.Z. INSTITUTE OF ELECTRICCIANS On Thursday the 27th June the members of the above Institute met in the Test Room of the Borough Council Electrical Department. A good attendance ©f members, showing their continued interest, was presided oyer firstly by the President, Mr Lysaght, who found it necessary to leave half way through to attend another meeting, and in the second case by the Vice-President. The first part of the evening was devoted to routine business which included a discussion on Associate Members. It was decided to hold the next meeting on the 25th of July in Opotiki, and the vice-president, Mr R. Combes, agreed to give the lecture on a suitable subject. During the second part of the evening, Mr J. Ditchfield of the staff of the Whakatane Paper Mills, gave a most interesting and skilful lecture of over an hour’s duration, illustrated with large scale diagrams on the Control and starting gear of the variable speed three-phase commutator motors. This lecture was l’eally a continuation of a previous lecture of Mr G. W. Marklands bn the motors themselves. At the Whakatane Paper Mills there are two of these variable speed three-phase 400 volt commutator motors of 140 horse-power each driving the main line shaft. In paper board making constant speed is essential to maintain a regular thickness of board. The diagrams already mentioned were six in number and must have taken Mr Ditchfield a considerable amount of time to prepare, the first and second of which dealt with the starting and control operations of the motors. '

The third diagram dealt with the balancing of the load on the two motors and illustrated how if the load was increased or decreased on the one motor an automatic adjustment was made on the other motor so that each did its fair share.

The fourth diagram dealt with the automatic speed control of the motors so that a certain standard of paper board might be produced. This arrangement of circuits allowed for either a change of frequency or voltage in the source of supply, either of which factor could affect the speed of the motors. The fifth diagram illustrated how in the event of a» failure of the automatic speed control the same control could be effected by hand. This was so rarely used as to cause the remark to be made that it’s only use was probably so that the inquisitive might ask ridiculous questions.

The sixth diagram dealt with Brushgear control on the motors and showed how when the main motors were stopped the brushgear returned to its normal position so as to be ready for the starting operation which can only be effected when this brushgear is in its true position. Mr Combes expressed and Mr Hurndell seconded a motion of thanks to Mr Ditchfield for his instructive lecture, and this was carried by acclamation. In moving this motion the vice-president added that to obtain motors of sufficient horse-power and at the same time having a great range of speed was most difficult and costly and the best results could be obtained with two motors of the type mentioned and of half the horse-power at a more economical figure. Dealing with relays, Mr Combes mentioned that the Swedish manufacturers considered thermal relays the best possible protection, not against faults but overload and an expensive type of motor could be secured with the relays actually built into the motor.

The evening was brought to a close with supper and an opportunity for the members to cultivate that social friendship as laid down as an object.