The rotor bearings of electricity meters

Abstract

In this paper an accumulation of experimental and statistical data which have been obtained by the author has been brought under review for the purpose of discussing the leading problem in the sphere of meter maintenance, namely that of worn bearings.Attention is drawn to the necessity for improving the reliability of meters in service in consequence of the vast number to be dealt with under modern conditions. The period of sustained accuracy needs to be extended in order to reduce the work of periodically exchanging meters, which is becoming increasingly difficult to contend with.It is submitted that the solution lies in increasing the durability of the bearings and particularly the combination of bottom jewel and pivot which constitutes the footstep bearing.The subject is dealt with in five main sections, which are outlined in the following:In Section (1) typical bearings to be found in electricity meters are illustrated and described and the principal features of design are pointed out. Reference is also made to methods of examining the condition of bearing jewels.Section (2) is directed to a study of the movements of the pivots of meters under load which contribute to the wearing of the bearings. Included in this section is an explanation of the method devised by the author for compensating for fluid friction in mercury motor meters, in which the upward movement is put to practical advantage. The vibratory movements of the rotors of a.c. meters produced by the action of the voltage and current fluxes are dealt with, and the differences observed in the amount of vibration exhibited by different designs are commented upon.In Section (3) the condition in which bearings are found after the meters have been removed from service is discussed. The frequency of the occurrence of defects in the bottom jewel is pointed out and the variety of forms which they take, as revealed by the microscope, is described. Examples of long-life jewels are given and the difficulty of drawing any conclusion as to the cause of wear from the contradictory evidence of life statistics of jewels is pointed out. The extreme obscurity of the problem is recognized, but the author suggests some possible explanations and certain lines along which laboratory research might prove fruitful.Section (4) deals with a special application of the diamond cupped bearing in connection with h.t. polyphase meters working under low-load conditions in exceptional circumstances. Extensive experiments with agate pivots working in sapphire cups are described.In Section (5) the author endeavours to formulate some opinions on various aspects of the bearing question, based on the experience and investigations set out in the paper.