Improvements in and relating to the ventilation of dynamo electric machines

Abstract

Abstract 163,079. British Thomson - Houston Co., Ltd., and Taylor, H. W. Jan. S, 1920. Dynamos, cooling and ventilating; enveloping in special media.-In a system of ventilation for dynamo-electric machines in which the air circulates in a continuous circuit, means are provided for equalizing the air pressure at points where it tends to be at a minimum value. In the form shown in Fig. 1, air which is driven by a fan A over a cooler N and through an alternator forms high and low pressure regions at B, D respectively. These regions are connected by air pockets or ducts C, of substantially the same construction as those described in Specification 160,307, formed in the end shields which open into the regions D so as to lead to these regions any air which may leak through the inner joints of the shields. Pockets or ducts may be similarly provided at the low-pressure regions E, F. According to the Provisional Specification, the air pockets mav be connected to the air system by nozzles which are adjustable, by hand or automatically by electromagnetic means operated by a manometer, so that they point against or with the direction of the circulating draught and maintain the air in the pockets at atmospheric pressure. Fig. 2 shows an arrangement for reducing the rarefaction which is caused behind the fan M when it is started from rest. Places of minimum pressure, such as F, are in connection with the external air, preferably through a filter G, through which the make-up air enters the system when the fan starts. Air pockets, as described above, or high-pressure connections as described in Specification 160,307, may be employed in combination with the openings to atmosphere. In another form, the minimumpressure points in the system are kept above atmospheric pressure by throttling at these points and drawing in the make-up air at increased velocity at these regions so as to cause an accumulation of air in the system. Or, alternatively, the make-up air may be introduced under pressure by means of a motor-driven compressor or a fan M, Fig. 3, and filter G, the main circulating pressure being given by fans K on the rotor. In place of air, carbonic acid or other gas from reservoirs may be used for the make-up, and the internal pressure may be so adjusted that the windage losses are a minimum when the machine is running light.

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