Methods of cooling of electrical machines
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Transcript of Methods of cooling of electrical machines
METHODS OF COOLING OF ELECTRICAL MACHINES
SUBMITTED BY:
NAME : Abinash Nayak
REG. NO. : 1201209177
BRANCH : EEE
Silicon Institute of Technology
Bhubaneswar
What is cooling?
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
Process by which heat resulting from losses occurring in a machine is given up to a primary coolant by increasing its temperature
Why is cooling needed?
Energy transfer and energy conversion in electrical machines create losses.
These losses appear as heat and increase temperature of the machine beyond its optimum level.
Heat is dissipated to surroundings by conduction and convection assisted by radiation from outer surfaces.
COOLANTS AND HEAT EXCHANGERS
Primary Coolant : Its has lower temperature than machine part.Example : Water
Secondary Coolant : It has lower temperature than primary coolant.
Example : Ethylene Glycol, Calcium Chloride, Sodium Chloride
Heat Exchanger : Component that keeps two coolants separate but allows transfer of heat energy between them.
Example : Power Plants, Chemical Plants, Petrochemical Plants
TYPES OF VENTILATION
INDUCED Fan →Decrease in air
pressure inside machine→Air sucked in→Pushed out by fan
Small, Medium Machines
FORCED Fan→Sucks air from
atmosphere →Forces it into machine→Air pushed out
Temperature of cooling air rises due to heat losses
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RADIAL VENTILATIONMost commonly used, Up to 20kW ratingLarge machines → Large core lengths → Core sub
divided to provide radial ventilating ductsAdvantages : Minimum energy losses for ventilation,
Almost uniform temperature rise in axial directionDisadvantages : Makes machine length larger
AXIAL VENTIALTION
Used in Induction Machines (Medium output, High speed machines)
Holes punched where heat loss is moreDisadvantages : Non-uniform heat transfer,
Increased iron loss
AXIAL-RADIAL VENTILATION
For large motors, small turbo alternatorsAxial system → Large iron loss So mixed system is
usedRotor mounted fan forces out the airAs a rule, Induction motors having radial ducts in
stator and rotor use forced self ventilation
VENTILATED FRAME MACHINES
Self ventilated frame, fan enclosed on shaft outside working part of machine
Fan enclosed by cover to secure direction of air flow for machine rating upto 25kW
For rating > 25kW, Internal fan (Primary coolant) + External fan (Secondary coolant)
Internal Fan → Inside machine, Avoids temperature gradiant across air gap
VENTIALTED RADIATOR MACHINES
Internal fan circulates air inside machine
External fan → Sucks hot air from inside → Pushes it back to radiators (Heat Exchanger) on frame of machine
Totally enclosed machines up to 5MW
At higher ratings, Air may be cooled by water if convenient
COOLING OF TOTALLY ENCLOSED MACHINE
Totally Enclosed Machine : Heavy, Expensive and uneconomical
Air Impurities → Destory InsulationNatural cooling → Ineffective Rating reducesCooled By:
Self ventilated frame, Ventilated radiator Machines
WATER AS COOLANT IN DIRECT COOLING
Higher rating : Mechanical limitations for hydrogen coolingSuperior heat transfer property, Low viscosity, No high
pressure heads required for circulationsAdvantages :1) Higher load is possible as no temperature difference
between conductors and water2) For rating upto 600MW
HYDROGEN COOLING SYSTEM
Frame strong enough, all joints gas tightGas pressure maintainedHydrogen pumped from one end to otherHydrogen (4-76%) + Air = Explosive MixtureExplosive Mix avoidedUsed for machines with rating upto 300MW
COOLING OF TRANSFORMERS
HYDROGEN COOLING OF TURBO ALTERNATORS
For machine > 50MW, Air cooling unsuitableNo requisite amount of air, higher fan powerAdvantages :1) Increased efficiency2) Increase in rating3) Increase in life span4) Elimination of fire hazard5) Smaller size of cooler6) Less noise
CONCLUSION :
Cooling is very much essential for modern output machines
Makes the output of machine stableIncrease efficiency, rating of machineIncrease longevity of machines, maintains safe
operationProtects the inner parts of machine from
thermal damages