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VK3ABK > INFO 06.07.02 13:55l 48 Lines 2246 Bytes #999 (0) @ WW
BID : 28930_VK3VSW
Read: DB0FHN GUEST
Subj: RE KB2VXA AGAIN!
Path: DB0FHN<DB0ZWI<DB0CHZ<OK0PKL<OK0PPL<RZ6HXA<WA7V<VE3FJB<ON0AR<ON0BEL<
VK3TE<VK3SPB<VK3FRC<VK3VSW
Sent: 020705/1139Z @:VK3VSW.#WEV.VIC.AUS.OC #:28930 [Geelong] $:28930_VK3VSW
From: VK3ABK@VK3VSW.#WEV.VIC.AUS.OC
To : INFO@WW
Hello Warren.
There may be confusion about what is an induction motor, but consider this.
In electrical engineering, induction electric motors come in single phase,
where the rotor is wound and supplied externally, or inductively coupled
to the stator winding. Often a combination, as in the repulsion/induction
motor. In small shaded pole motors, the rotor winding is no more than a
single turn of heavy conductor. These are induction motors in that
electromagnetic coupling is required for their operation.
In 3 phase motors, the rotor is wound with either wire, and an external
controller for speed adjustment, usually when starting, or they may have
a rotor 'winding' formed as single turns of cast aluminium. (note the
correct spelling) and are called 'squirrel cage'motors for fairly obvious
reasons. A synchronous motor is an induction motor which is excited by an
external voltage supply.
You have introduced the concept of alternator-motor operation, and give an
example of frequency/speed relation where an alternator drives an induction
motor. In my previous bulletin I described the relation between rotation
speed and the number of 'poles' wound in these machines. This is a method
of winding which effectively divides the rotor or field winding into a
series of magnetic circuits. A 3 phase alternator would have multiple poles
which would reduce the required rotational speed to a suitable figure.
Likewise a 3 phase motor connected to the alternator would run at
a speed depending on the number of poles created in the field windings.
A 'synchronous' induction motor is designed to rotate at the supply frequency
divided by the number of poles, but the majority of 3 phase induction motors
'slip' and rotate at about 10% less than synchronous speed as I indicated
previously. A lightly loaded motor may run at near synchronous speed, but a
motor running at rated load would not.
This is normal engineering practice in Australia, and as my first electrical
engineering text was by 'Dawes, Harvard U Cambridge Mass', many years ago,
I expect your training would have a similar background.
You are sounding more like a MAGICIAN than a TECHNICIAN. You can't be both:-)
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