cooling of generator or motor

Cooling of Rotating Machines :

Forced Air Cooling : For large machines which may require many tonnes of cooling air/hr. , forced ventilation permits the cleaning of the air by suitable filters , avoiding clogging of the ducts. The air is filtered or washed with a water spray , then baffled against flooded scrubbing surfaces to precipitate the dust. It is then dried by passing over a series of dry scrubbing plates.

Hydrogen Cooling : To build air cooled turbo-generators above 50 MW rating present serious ventilation difficulties, not only in circulating the requisite quantity of air through the machine but also the high fan power required to circulate the air. Therefore the use of air as a coolant for high rating machines is ruled out and hydrogen is used as the alternate cooling media..

Gas Cooling : Large stator cores for turbo-generators are provided with both axial & radial ducts. For machines of rating more than 100 MW, the temperature gradient over the conductor insulation is high enough to call for direct contact between the coolant & the material of the conductor themselves. The rotor conductors comprise rectangular tubes ,ventilated by the cooling circuit separate from that of the stator, the hydrogen gas being admitted to the tubes through insulating flexible connections at the ends from a centrifugal impeller mounted on the outboard end of the rotor shaft. The direct gas cooling of the stator & particularly of rotor winding permits of much higher electrical loading. With ratings of 1000 MW even this is not enough to cope with the very large flow rate & pressure, which might be 15 cu. m of hydrogen at 1.2 atm to absorb an excitation loss of 5 MW.

Water cooling : Turbo-generators of highest rating so far contemplated are likely to have hydrogen cooled stator cores & direct water cooled stator & rotor windings. In the direct water cooling of stator windings, one problem is to device flexible water tube connections with insulation against the high winding voltages and to preserve a low water conductivity. Water cooling of rotor winding, even more desirable because of it?s high electric loading, offers more mechanical difficulty. Water cooled field windings have been used for salient poles of large hydro-generators. The mass of cooling water required is only one quarter of that of air at atmospheric pressure for the same cooling effect.