Patent GB-294249-A (GB)
Title: Improvements in and relating to liquid film seals for use in gascooled dynamo-electric machines
IPC: F16J15/40
Filed: 1928-07-17
Abstract: 294,249. British Thomson-Houston Co., Ltd., (Assignees of Rice, C. W.). July, 22, 1927, [Convention date]. Dynamos and motors, cooling.-In a dynamoelectric machine which is cooled by hydrogen or another gas circulating within the closed machine casing, and sealed with a liquid seal between the casing and shaft to prevent escape of the gas or entry of external air, a double liquid sealing film is used, one film being saturated with the cooling gas and the other with air. Means are also supplied for indicating the density, and thus the purity, of the cooling gas. The invention is illustrated in connection with a cooling system as described in Specification 104,250 in which gas passes from containers 15 and a drier 16 to the dynamo casing where a fan 17 directs a part of it against a deflecting wall 18 and then through the air-gap and ducts 19 between the stator laminae to ducts 20 between the stator and casing; and a part through a passage 21 to a central passage 22, inwards on to the rotor surface and then outwards to the ducts 20. From the ducts 20 the gas passes over a cooler 23 and again to the fan for renewed circulation. The two sets of grooves for the liquid sealing films 25, 26 are formed between the shaft and the bearing, the former being saturated with the internal gas and the latter with air. The gas-saturated liquid is drawn from a tank 27 by a feed-pipe 28 having a valve 29 for adjusting the head and passes to overflow grooves 30 and a down-pipe 31 to a receiver and gas detainer 32. Constant head is maintained in the tank 27 by means of a pump 33 which delivers liquid through a pipe 34 to the tank in excess of the amount required by the groove 25, the excess passing back to the receiver by a pipe. 35 terminating at a high level in the tank. The tank and receiver, which form a system sealed against air entry, are coupled by a pipe 36 which has an opening 37 into the machine casing whereby the liquid in the system is kept saturated with the cooling gas. The outer groove 26 is similarly supplied with air-saturated liquid circulated in excess of the groove requirement by means of a pump 45 between a tank 38 and a, receiver and air detainer 44. This system is open to air so that the liquid is air-saturated. The result is to prevent interchange of gas and air between the sealed casing of the machine and the external atmosphere. A difference of pressure between the liquids in the two sets of grooves 25, 26 might result in excessive interchange of liquid between the two systems and this is prevented by providing means for maintaining a definite ratio between the quantities of liquid in the two systems. This is effected by means of a float 48 in the receiver 44 with a. counterweight 52 and cord controlling a valve 51 in the pipe 28 through which gas-saturated liquid passes to the grooves 25. A rise of level in the receiver 44 tends to close the valve 51, and the resulting fall of pressure in the grooves 25 will cause liquid to flow from the groove 26 to the grooves 25 until the level in the receiver 44 falls sufficiently to open the valve 51 and establish equilibrium of pressure between the grooves. A fall of level in the receiver 44 has the converse effect. Thus, the quantity of air-saturated liquid circulating in the system will be maintained in accordance with the adjustment of the float and may be given any desired ratio to that in the other system. The float may alternatively be provided in the system of the gas-saturated liquid. Gauges 25a, 26a in the two systems enable the presures in the system to be adjusted to the requisite values to prevent cross-flow between the systems. A bleeder tube may be provided in the receiver 44 for allowing slow escape of the liquid and causing a slow transfer between the grooves 25, 26. The purity of the cooling gas is kept under observation by causing the gas to circulate at constant velocity and indicating its velocity head in a U-tube 60 connecting two Pitot tubes 61, 62 opening respectively in and contrary to the direction of flow of the gas in the passage 21. Variation in the density of the gas causes a variation in the velocity head indication at 60 and the device is calibrated to indicate the density or purity of the gas. Specification 225,244 also is, referred to.