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Topic: Elmo GS1200 great condition $850.00
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Andrew Woodcock
Film God
Posts: 7477
From: Manchester Uk
Registered: Aug 2012
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posted April 17, 2015 06:56 PM
Rik you are right except you are quoting the UNIT of electrical Alternating Current by which an a.c. motor is governed, rather than the actual force which governs an A.C. Induction Motor which is the FREQUENCY of electrical alternating current.
Frequency when applied in terms of an AC current, is how many times per second the wave form alternates from +1 per second to -1 per second.
ie, a 2 pole ac 3 Phase induction motor rotates @3000rpm.
Why? Because it has 1 north pole and 1 south pole in every revolution that it makes.
Given that an A.C. Sinusoidal Wave Form consists of either 50 or 60 individual North & South Poles,dependant on your location in the world, in every one second due to the reciprocating sinusoidal wave form, it can be deduced that a 2 pole, 3 phase a.c. induction motor running at synchronous speed therefore rotates at 50 Cycles Per Second or 50Hz (Uk Mains Frequency) x 60 (seconds per minute) which equals 3000 RPM.
Similarly, in the U.S. A 2 Pole, 3 Phase A.C Induction Motor whose Electrical Mains Frequency is 60Hz (60 Cycles Per Second), will travel at a synchronous speed of 3600RPM due to the calculation of North & South Poles being 60Hz ( 60 North & South Poles Per Second) x 60 (seconds in a Minute of time).
Therefore as 4 Pole, 3 Phase a.c Induction Motor has twice as many poles, ie 2 Norths and 2 Souths, then it takes the 50 or 60hz Mains Frequency twice as long to complete one singular rotation.
Therefore the Synchronous Speeds for a 3 Phase 4 Pole motor are in the UK, 1500 RPM and in the U.S. 1800 RPM and so on as the number of poles expand ie 8 pole UK a.c. induction 3 phase motor =750 RPM Synchronous speed vs 900 RPM U.S. Synchronous Speed...
and so on and so forth...
The same principles apply to single phase A.C. Electrical Motors except they need a phase shift (or lag) to get them going I.e at least two phases or a capacitor to cause a phase shift.
Once locked on at synchronous speed they can happily run on just the one phase which is why the Cap Start method is used just for that... starting the motor.
[ April 17, 2015, 08:38 PM: Message edited by: Andrew Woodcock ]
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"C'mon Baggy..Get with the beat"
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