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