GB208804A - Improvements in and relating to squirrel cage electric motors - Google Patents

Abstract

208,804. Arut³noff, A. Sept. 29, 1922. Alternating-current induction machines.-In a squirrel-cage motor, the rotor bars are connected to subdivided rings which are short-circuited by wedge-shaped contact pieces under centrifugal action, and means may be provided between the subdivided rings and the bars to control the rotor resistance. As shown in Figs. 3 and 4, the wedge contacts 4, which are normally retracted by springs 5, are weighted at 4<a> and at a limiting speed enter between the subdivided end-rings 3. The weights are guided by an end flange 8 and the whole is enclosed in a casing 7. The springs 5 may be replaced by a spiral spring which clasps all the weights and draws them towards the centre, and in place of having plane faces the contacts 4 may have angular ribs on their faces to enter corresponding grooves in the portions 3. They may alternatively consist of a series of conically-arranged washers 15, Fig. 10, or curved or angularly bent plates on a central stem 14 such as to bed flexibly on to the ring segments 11, 12 and give a good contact by sliding slightly on their surfaces under centrifugal action. In the form shown in Figs. 7 and 8, the contact blocks 4 are slotted for the retaining-screws 6 and springs 5 by which they are retracted. The segments 3 are secured to the rotor body by screws 10 and the depth to which these screws are bedded in the body or the pressure which they exert between the segments and the body determines the resistance of the rotor.