Design and Voltage Supply of High-Speed Induction - Aaltodoc
Design and Voltage Supply of High-Speed Induction - Aaltodoc
Design and Voltage Supply of High-Speed Induction - Aaltodoc
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Cooling <strong>of</strong> the stator could need axial or radial cooling ducts for coolants but in the motors studied<br />
this was not necessary. The fact that the stator was actually divided into two parts by a radial duct<br />
was primarily because <strong>of</strong> the need to have cooling air circulation for the rotor. The cooling fan is<br />
attached to the other end <strong>of</strong> the shaft. The fan either blows or sucks the air through the motor. From<br />
the temperature rise point <strong>of</strong> view it is better to suck the air through the motor, since then the loss<br />
corresponding to the pressure drop over the motor is not warming up the motor.<br />
It is worth remembering that different motor constructions may benefit from different kinds <strong>of</strong><br />
cooling arrangements. Different coolants <strong>and</strong> cooling flow topologies can be chosen. In some cases,<br />
direct cooling <strong>of</strong> a rotor is considered costly <strong>and</strong> efficient stator cooling is used instead (Boglietti et<br />
al. 1992). Fuchs <strong>and</strong> Frank (1983a, 1983b) go on to design a 75 kW 40000 1 /min homopolar motor in<br />
order to avoid direct cooling. This is a good example, showing that the selection <strong>of</strong> a cooling system<br />
<strong>and</strong> a motor type go h<strong>and</strong> in h<strong>and</strong>. The approach chosen by Fuchs <strong>and</strong> Frank is different from the<br />
approach chosen in the project (including this work). The choice between different approaches is a<br />
complicated issue that may be difficult to formulate exclusively. The problem <strong>of</strong> choice comes<br />
down to the definition <strong>and</strong> weighting <strong>of</strong> the objectives, which is strictly speaking never the same for<br />
two different projects.<br />
Hydrogen or helium could be used as a closed circuit coolant because <strong>of</strong> reduced friction <strong>and</strong><br />
cooling loss <strong>and</strong> increased heat transfer (Gilon 1994, Saari <strong>and</strong> Arkkio 1995). Other cooling<br />
systems like cooling <strong>of</strong> the stator with water or R134a could be combined for maximum<br />
performance (Mekhiche et al. 1999).<br />
2.5 <strong>Voltage</strong> modulation for the high-speed induction motor<br />
The following description introduces the subject briefly. The idea is to illustrate the type <strong>of</strong><br />
frequency converter used in this work <strong>and</strong> the basic idea in the pulse amplitude <strong>and</strong> pulse width<br />
modulation. More information can be found e.g. from Mohan et al. (1995).<br />
On the input or supply network side <strong>of</strong> the frequency converter, there is a three phase choke <strong>and</strong><br />
diode bridge rectifier. Together with an intermediate or DC-link capacitor, the AC-voltage <strong>of</strong> the<br />
supply network is rectified into a DC-voltage. On the output or load side, there is a three phase<br />
IGBT inverter bridge changing the DC-voltage back into AC-voltage <strong>of</strong> some amplitude <strong>and</strong><br />
frequency. A schematic diagram <strong>of</strong> the converter can be found in Fig. 5.2 in Section 5.1.<br />
The DC-voltage Ud produced by a diode bridge rectifier depends mainly on the amplitude <strong>of</strong> the<br />
AC-voltage in the supply network Uac. In an ideal case, Ud is<br />
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