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Entry type: FAQ Entry ID: 33386716, Entry date: 12/15/2008
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Cooling of electrical machines

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QUESTION:

 

 

 

 

 

How can an electrical machine be cooled?


ANSWER / REMEDY / NOTES:

 

An electrical machine can be cooled as follows:

 

Surface cooling

The heat from the active parts is conducted to the closed external surface of the machine by means of a closed primary cooling circuit (internal air circuit or heat conduit).

Hollow fins or ducts of a surface-cooled motor enables the creation of an

internal cooling circuit. It transports a large part of the rotor losses and the copper losses in the winding heads of the stator winding directly to the cooling fins of the housing. Here, they are dissipated by the external cooling circuit.

 

Natural cooling, convection cooling, free cooling

Cooling takes place due to the natural air flow that is created by the hot air rising above or in the machine.

Heat dissipation by means of thermal radiation can be ignored in the case of electrical machines. How intensive cooling is, depends on the design of the machine and the mounting position. If the shaft is horizontal, the naturally cooled machines are fitted with fins suitably arranged in a circle. The heated air can flow upwards unhindered between the fins.

Naturally, cooled machines are big and heavy. Due to the lack of a forced air flow, these machines easily become dirty and this must be taken into consideration for maintenance.

 

Code

Sketch

Cooling circuit arrangement

 

IC 00

IC 0A0

Free cooling circuit

"silent cooling": no external fan

 

IC 410

IC 4A1A0

Surface cooling

 

 

Self-cooling

Cooling is carried out by a cooling medium that is moved by the machine itself. The cooling medium is moved in relation to the motor speed as follows:

-    -- due to the flow-promoting effect of the rotor alone

-    -- by the fan subassembly directly mounted on the rotor

-- by an installed fan or pump unit directly driven by the machine

 

Code

Sketch

Movement of the secondary cooling medium

 

IC 411

IC 4A1A1

Self-cooling

External fan on motor shaft

e.g. 1LA8 / 1LA4

 

 

External cooling

Cooling is carried out by a built-on subassembly which has its own drive motor and ensures constant cooling irrespective of the main motor's speed.

 

Code

Sketch

Cooling circuit arrangement

 

External cooling of an open cooling circuit

 

IC 06

IC 0A6

Free cooling circuit
Cooling medium = Ambient air
e.g. 1G.5 / 1G.6 / 1PL6

 

IC 16

IC 1A6

Supplied via pipe or duct
Cooling medium is supplied

 

IC 26

IC 2A6

Removed via pipe or duct
Cooling medium = Ambient air

 

IC 36

IC 3A6

Supply and removal via pipe or duct cooling medium is supplied

 

 

Code

Sketch

Cooling circuit arrangement

  External cooling, primary cooling circuit closed, secondary cooling circuit open

 

IC 416

IC 4A1A6

Surface cooling
Cooling medium = Ambient air
e.g. 1PQ8 / 1PQ4

 

IC 516

IC 5A1A6

Built-in heat exchanger
Cooling medium = Ambient air

 

Cooling due to relative movement

Type of cooling whereby the ambient air as the cooling medium is moved due to the relative movement between the machine and its environment.

This type of cooling is frequently used for vehicles or for motors that rest in the air flow of the driven fan (duct-fan motors)

 

Code

Skizze

Cooling circuit arrangement

 

IC 418

IC 4A1A8

Surface cooling
Cooling medium = Ambient air

 

Open-circuit cooling, open-circuit ventilation

Cooling whereby the air as the cooling medium flows directly through the interior of the machine

The cooling medium absorbs the heat almost directly at the source and dissipates it towards the outside. The cooling effect is considerably more intensive than in the case of surface cooling.

For a given rating, less material is needed for the active parts and the machine can be built smaller.

This method of cooling is advantageous if the machine is installed in an environment that is free of dust, dirt and water.

With the cooling air being supplied and removed via pipes or ducts, it is possible to make cooling independent of the indoor atmosphere or transport the heat out of the service room.

 

Code

Sketch

Cooling circuit arrangement

 

IC 01

IC 0A1

Free cooling circuit
Cooling medium = Ambient air
e.g. 1LL8 / 1RA4

 

IC 11

IC 1A1

Supplied via pipe or duct
The cooling medium is the supplied medium

 

IC 21

IC 2A1

Removed via pipe or duct
Cooling medium = Ambient air

 

IC 31

IC 3A1

Supply and removal via pipe or duct
The cooling medium is the supplied medium

NOTICE !

Motors with open-circuit cooling can act like vacuum cleaners; the winding heads work as dust filters and become clogged with the result that the winding is no longer sufficiently cooled and sooner or later becomes scorched.

It is therefore necessary to pay great attention to cleanliness in the service rooms and maintain machines carefully.

Closed-circuit cooling

A method of cooling whereby the primary cooling medium flows in a closed circuit and the heat is transferred to the secondary cooling medium by means of heat exchangers.

Closed-circuit cooling enables intensive heat dissipation with a high degree of protection in spite of the closed type of construction. With closed-circuit cooling, many types of cooling and therefore many ways of adapting it to the operating conditions and conditions of installation are possible:

 

– The heat exchanger can be built into the machine, built onto it or
   installed separately from the machine.

– The secondary cooling medium can be gaseous (air) or liquid (water),
   an ambient medium or other medium.

– The circuit of the secondary cooling medium is brought about by a fan
   belonging to the machine (self-cooling) or by an independent sub-
   assembly that can be built into or on the machine or installed sepa-
   rately
or it can be brought about due to the operating pressure of the
   cooling medium.

 

NOTICE !

The pipes for the secondary cooling medium (water hoses, pipes, ducts) should be connected with elastic connecting elements in order to prevent deformation of the machine housing and the transmission of structure-borne noise.

 

NOTICE !

In the case of motors with a water cooler, the cooling water of the motor must be drained off if it is be transported overland or placed in storage in winter. Danger of bursting due to frost!

 

Code

Sketch

Cooling circuit arrangement

 

IC 81W

IC 8A1W7

Self-cooling in the primary cooling circuit

e.g. 1RN4

 

IC 85W

IC 8A5W7

Primary cooling circuit by means of built-in independent sub-assembly

e.g. 1RN4

 

IC 86W

IC 8A6W7

Primary cooling circuit by means of built-on independent sub-assembly

 

Tube cooling

Method of cooling with a closed primary cooling circuit by which the heat is transferred to the surrounding cooling medium by means of a built-in or built-on bundle of tubes.

 

NOTICE !

Although the conduction of air in a straight line in the smooth tubes ensures that the tubes clean themselves to a large extent due to the external flow of cooling medium, attention must be paid to possible soiling of the cooling tubes during maintenance.

 

Code

Sketch

Cooling circuit arrangement

 

IC 511

IC 5A1A1

Built-in cooling tubes as heat exchangers,

self-cooling, primary and se-condary cooling media are moved by fans on the motor shaft

 

IC 516

IC 5A1A6

Built-in cooling tubes as heat exchangers,

primary cooling medium is moved by a fan on the motor shaft

Built-on independent external ventilator moves the secondary cooling medium

 

IC 616

IC 6A1A6

Built-on heat exchanger

Cooling medium = Ambient air

e.g. 1RQ4

 

IC 611

IC 6A1A1

Built-on tube cooler with bundle of tubes,

self-cooling, primary and se-condary cooling media are moved by fans on the motor shaft

e.g. 1RQ4

 

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