Methods Of Cooling Of Rotating Electrical Machines


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This is a presentation for my seminar in college. Its on methods of cooling of rotating electrical machines.

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Methods Of Cooling Of Rotating Electrical Machines

  2. 2. Why is cooling needed ? <ul><li>Energy transfer and energy conversion in rotating machines manifest losses. </li></ul><ul><li>These losses appear as heat and increase temperature of the machine beyond its optimum level. </li></ul><ul><li>Heat is dissipated to surroundings by conduction and convection assisted by radiation from outer surfaces. </li></ul>
  3. 3. What is cooling ? <ul><li>Process by which heat resulting from losses occurring in a machine is given up to a primary coolant by increasing its temperature. </li></ul><ul><li>Heated primary coolant may be replaced by a new coolant at lower temperature or may be cooled by a secondary coolant in some form of heat exchanger. </li></ul>
  4. 4. COOLANTS AND HEAT EXCHANGERS <ul><li>Primary Coolant : lower temperature than machine part </li></ul><ul><li>Secondary Coolant : lower temperature than primary coolant </li></ul><ul><li>Heat Exchanger : Component that keeps two coolants separate but allows transfer of heat energy between them </li></ul>
  5. 5. Methods of cooling <ul><li>Size of a machine of a given duty depends on heat losses in its various parts. </li></ul><ul><li>Small machines ( fractional H.P.) cooled by natural means. </li></ul><ul><li>Modern machines require cooling. </li></ul><ul><li>Cooling by air stream  ventilation </li></ul>
  6. 6. COOLING SYSTEM CLASSIFICATION <ul><li>Based on origin of cooling : </li></ul><ul><li>Natural cooling </li></ul><ul><li>Self cooling </li></ul><ul><li>Separate cooling </li></ul><ul><li>Based on manner of cooling : </li></ul><ul><li>Open circuit ventilation </li></ul><ul><li>Surface ventilation </li></ul><ul><li>Closed circuit ventilation </li></ul><ul><li>Liquid cooling </li></ul>
  7. 7. Enclosures for machines <ul><li>Open machine </li></ul><ul><li>Protected machine </li></ul><ul><li>Drip proof machine </li></ul><ul><li>Pipe/duct ventilated machine </li></ul><ul><li>Totally enclosed machine </li></ul><ul><li>Watertight machine </li></ul><ul><li>Weather proof machine </li></ul><ul><li>Submersible machine </li></ul><ul><li>Flame proof machine </li></ul><ul><li>Totally enclosed gas circuit machine </li></ul><ul><li>Open pedestal machine </li></ul><ul><li>Open end bracket machine </li></ul><ul><li>Screen protected machine </li></ul><ul><li>Splash proof machine </li></ul><ul><li>Hose proof machine </li></ul><ul><li>Totally enclosed fan cooled </li></ul><ul><li>Totally enclosed separately air cooled machine </li></ul><ul><li>Totally enclosed liquid cooled machine </li></ul><ul><li>Totally enclosed closed air circuit machine </li></ul>
  8. 8. TYPES OF VENTILATION <ul><li>INDUCED </li></ul><ul><li>Fan  decrease in air pressure inside machine  air sucked in  pushed out by fan </li></ul><ul><li>Small, medium machines </li></ul><ul><li>FORCED </li></ul><ul><li>Fan  sucks air from atmosphere  forces it into machine  air pushed out </li></ul><ul><li>Temperature of cooling air rises due to heat loss </li></ul><ul><li>More amount of air required </li></ul>
  9. 9. RADIAL VENTILATION <ul><li>Most common, up to 20 kW rating </li></ul><ul><li>Large machines  large core lengths  core subdivided to provide radial ventilating ducts </li></ul><ul><li>Advantages : min. energy loss for ventilation, almost uniform temp. rise in axial direction </li></ul><ul><li>Disadvantages : makes machine length larger, cooling might be unstable with amount of cooling air flowing </li></ul>
  10. 10. AXIAL VENTILATION <ul><li>Used in induction machines (medium o/p, high speed machines) </li></ul><ul><li>Solid rotor  restricts radial ventilation </li></ul><ul><li>Holes punched where heat loss is more </li></ul><ul><li>Disadvantages : non-uniform heat transfer, increased iron loss (ducts in slots of rotor reduce amount of iron  inc flux density in core  increase in iron loss) </li></ul>
  11. 11. AXIAL-RADIAL VENTILATION <ul><li>For Large motors, small turbo-alternators </li></ul><ul><li>axial system  large iron loss  so mixed system is used </li></ul><ul><li>Rotor mounted fan forces out the air. </li></ul><ul><li>As a rule, induction motors having radial ducts in stator & rotor use forced self ventilation. </li></ul>
  12. 12. COOLING OF TOTALLY ENCLOSED MACHINE <ul><li>Totally enclosed machines  heavy, expensive, hence uneconomical </li></ul><ul><li>Air  impurities  destroy insulation </li></ul><ul><li>Natural cooling  ineffective  rating reduces </li></ul><ul><li>Cooled by : </li></ul><ul><li>Self ventilated frame, Ventilated radiator machines </li></ul>
  13. 13. VENTILATED FRAME MACHINES <ul><li>Self ventilated frame, fan enclosed on shaft outside working part of machine </li></ul><ul><li>Fan enclosed by cover to secure direction of air flow for machine rating < 25 kW </li></ul><ul><li>For rating > 25 kW, internal fan( primary coolant)+ external fan( secondary coolant) </li></ul><ul><li>Internal fan  inside machine ,avoids temp. gradient across air gap </li></ul>
  14. 14. VENTILATED RADIATOR MACHINES <ul><li>Internal fan circulates air inside machine </li></ul><ul><li>External fan  sucks hot air from inside  pushes it back to radiators (heat exchangers) on frame of machine </li></ul><ul><li>Totally enclosed machine upto 5 MW </li></ul><ul><li>At higher ratings, air may be cooled by water if convenient </li></ul>
  15. 15. COOLING CIRCUIT <ul><li>OPEN CIRCUIT VENTILATION : </li></ul><ul><li>Cold air drawn in, forced out after passing over heated machine parts </li></ul><ul><li>filters required to clean air, driers to remove moisture </li></ul><ul><li>Unsuitable for large machines </li></ul><ul><li>CLOSED CIRCUIT VENTILATION : </li></ul><ul><li>Same volume of air passes through a closed ckt  path has fans,coolers, drying agents  hot air from outlets is cooled  cool air enters through the inlets </li></ul>
  16. 16. COOLING OF TURBO-ALTERNATOR <ul><li>Closed circuit ventilation </li></ul><ul><li>Long core length, small diameter </li></ul><ul><li>Methods : </li></ul><ul><li>air cooled (one side axial, two side axial , multiple inlet system) </li></ul><ul><li>hydrogen cooled </li></ul><ul><li>Direct cooled </li></ul>
  17. 17. AIR COOLED TURBO-ALTERNATORS <ul><li>For small units used as auxilliaries in large power stations </li></ul><ul><li>1 side axial ventilation : upto 3MW </li></ul><ul><li>Air supply by propeller fan  air enters at an end, leaves by the other </li></ul><ul><li>In long machines, temperature rise is high along the length </li></ul>
  18. 18. AIR COOLED TURBO-ALTERNATORS <ul><li>2 sided axial ventilation : </li></ul><ul><li>Air forced from both sides, both windings have same temperature rise </li></ul><ul><li>Used for machine rating up to 12MW </li></ul><ul><li>Multiple inlet system : larger machines </li></ul><ul><li>Outer stator  many chambers  alternate inlets and outlets  up to rating 60MW </li></ul>
  19. 19. HYDROGEN COOLING OF TURBO-ALTERNATORS <ul><li>For machines > 50MW, air cooling unsuitable </li></ul><ul><li>No requisite amount of air, higher fan power </li></ul><ul><li>Advantages of hydrogen cooling : </li></ul><ul><li>Increased efficiency </li></ul><ul><li>Increase in rating </li></ul><ul><li>Increase in life span </li></ul><ul><li>Elimination of fire hazard </li></ul><ul><li>Smaller size of cooler </li></ul><ul><li>Less noise </li></ul>
  20. 20. HYDROGEN COOLING SYSTEM <ul><li>Hydrogen(4-76 %)+air  explosive mixture </li></ul><ul><li>Frame strong enough, all joints gas tight </li></ul><ul><li>Hydrogen above atmospheric pressure, so leakage is from machine to atmosphere </li></ul><ul><li>Gas pressure maintained </li></ul><ul><li>Explosive mix avoided </li></ul><ul><li>Purity of hydrogen checked by measuring its thermal conductivity </li></ul>
  21. 21. DIRECT COOLING OF TURBO-ALTERNATOR <ul><li>Conventional cooling </li></ul><ul><li>Direct cooling : Losses dissipated to medium circulating in windings </li></ul><ul><li>Called supercharged/conductor cooled/ inner cooled machines </li></ul><ul><li>Advantages : increase in rating,winding temperature goes down and higher output </li></ul><ul><li>Coolants used : hydrogen, water, oil </li></ul>
  22. 22. Coolants in direct cooling <ul><li>Hydrogen : </li></ul><ul><li>Stator, rotor made hollow </li></ul><ul><li>Hydrogen pumped from one end to other </li></ul><ul><li>Used for machines with rating up to 300MW </li></ul><ul><li>Oil : </li></ul><ul><li>High grade transformer oil </li></ul><ul><li>Used in US-direct cooling of stator conductors </li></ul><ul><li>Flash point, can be reached in fault conditions, damages insulation </li></ul>
  23. 23. Water as coolant in direct cooling <ul><li>Higher rating  mechanical limitations for hydrogen cooling </li></ul><ul><li>Water : superior heat transfer property, low viscosity, no high pressure heads required for circulation </li></ul><ul><li>Advantages : smaller pumping power </li></ul><ul><li>Higher load is possible as no temperature difference between conductors and water </li></ul><ul><li>For rating up to 600 MW </li></ul>
  24. 24. Thank You ! Anwesa Nanda Reg. No. 0711014018 Branch EEE
  25. 25. Q&A Session