Turbo generator cooling An efficient cooling and ventilating system is needed to keep the temperature of the windings and other components of the generator resulting due to various losses, below certain limits depending on the insulation.
Dissipation in generators appears as heat which must be removed. This heat appears in the armature conductors, field-winding conductors, stator core, rotor surface, and other structural elements of the machine. Cooling of armature and field conductors may be direct or indirect; the difference is direct contact of the cooling medium with the conductor c onductor or contact through electrical insulation. Dissipationa loss of energy from a dynamic dy namic system. Dynamic - !otion
"osses in an ac generator The three losses found in an AC generator are #.$nternal voltage drops due to the internal resistance and impedance of the generator %.&ysteresis losses '.!echanical losses
Cooling methods of turbogenerators #.(tator winding-indirectly air cooled )otor winding-directly air cooled %.stator winding-indirectly hydrogen cooled )otor winding-directly hydrogen cooled '.stator winding-directly water cooled )otor winding-directly hydrogen cooled
Air cooled turbo generator $n this,stator winding is indirectly air cooled whereas the rotor winding and stator core is directly air cooled.This type of cooling is applicable for rating of '* !+ to * !+ generators.
&ydrogen cooled turbogenerator A hydrogen-cooled turbo generator is a turbo generator with gaseous hydrogen as a coolant. Advantages #.)eduction in sie of machine %.$ncrease in life of machine
Coolant-An agent that produces cooling.
&ydrogen cooling system Although hydrogen is a very useful medium for cooling the generator internal components, it is very dangerous if not handled correctly. A dedicated system to handle the supply and control of the hydrogen atmosphere inside the generator is reuired. (ince hydrogen is used at generator casing pressures up to /* psig, the generator is also considered a pressure vessel. v essel. This reuires various sealing arrangements to keep the hydrogen inside the machine.
(upply of the hydrogen to the generator is generally provided by an on-site hydrogen manufacturing plant, or purchased in a pressure container and replenished periodically periodically.. Degas-to remove gas 0urge-to clean thoroughly
$n addition to the hydrogen, a separate supply system is reuired for C1% to purge the generator of hydrogen during filling and degassing. C1% is used because it is inert and will not react with the hydrogen. $f the hydrogen in the generator were to be purged with air, air, this would encroach e ncroach upon both the upper and lower e2plosive limits due to the combustible nature of a hydrogen3o2ygen mi2ture.
&ydrogen at high purity 4above /*56 will not support combustion, and at this level there is no danger of e2plosion since the e2plosive range of a hydrogen3o2ygen mi2ture is 7 to 895 hydrogen in air. To prevent the possibility of an e2plosive mi2ture when filling the generator with hydrogen for operation, air is first purged from the generator by C1%, and the C1% is then purged by hydrogen. +hen degassing the generator for shutdown, hydrogen is first displaced by C1% and then the C1% is purged by air. This way, no e2plosive mi2ture of hydrogen and o2ygen can occur oc cur.. $n some rare cases, other inert gases have been used, such as argon.
During operation, a gas pressure regulator automatically maintains the generator casing hydrogen pressure at a preset 4rated6 value. $f hydrogen leaks occur, occur, the pressure regulator admits additional hydrogen from the supply system until the predeterprede termined pressure is restored. There is always a certain amount of e2pected leakage into the seal oil, through minute leaks, permeation pe rmeation through the stator winding hoses, and so forth, but most generators should be capable of continuous operation below 9** cubic feet per day loss. $f the loss increases to #9** cubic feet per day day,, the source of the leak should be investigated immediately and corrected.
A hydrogen gas analyer is usually present to monitor the hydrogen purity, which should be maintained above /85. Dew-point monitoring is sometimes provided to control the level of moisture inside the generator. The dew point is generally maintained below : #*C and should not be allowed to rise above *C at generator casing 0ressure.
Dew pointThe dew point is the temperature at at which the air will will become completely saturated. Dew 0oint the temperature at which air becomes saturated by water vapor when cooled at a given moisture content and a constant pressure. (aturation is the point at which a solution of a substance can dissolve no more of that substance and additional amounts of it will appear as a separate phase
$nside the generator, generator, the hydrogen picks up heat from the various components as it flows over and through such components as the stator core vents and rotor winding. Then it is routed to pass through heat e2changers inside the generator gene rator,, where the hydrogen leaving the cooler outlet side has been reduced in temperature to complete another cycle of heat pickup as it goes through the same generator components again.
(eal oil system (eal-to close completely
'.The seals may be of the =ournal 4ring6 type or the thrust-collar type, one thing both arrangements have in common is the reuirement of high-pressure oil in the seal to do the actual sealing. The euipment that provides the oil to do this is called the seal-oil system.
(tator cooling water system The stator cooling water system 4(C+6 is used to provide a source of demineralied water to the generator stator winding for direct cooling of the stator winding and associated components. The (C+ is generally used in machines rated at or above '** !>A. !ost (C+ systems are provided as package units, mounted on a single platform, which includes all of the (C+ (C+ system components. All components of the system are generally made from stainless steel or or copper materials.
