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Three phase motors I: The rotating magnetic field
The rotating magnetic field RMF is the basis of the three-phase motors - whether synchronous or asynchronous / induction motor. This video explains how a rotating field is generated, how the number of pole pairs influences the synchronous speed, how the synchronous speed can be calculated, etc..
Example 1: A 6-pole synchronous motor has a rotational speed of n = 1200 min-1. At which mains frequency is it operated?
Example 2: In the USA the frequency of the power supply has 60 Hz, in Europe 50 Hz. How much does a synchronous motor with 8 poles, that means a pole pair number of 4, run faster in the USA than in Europe? Note: 6 poles Δ pole pair number = 3
Example 1: nRMF = f / p => f = nRMF × p = 1200 min-1 * 3 = 60 s-1 or 60 Hz Note: 6 poles Δ pole pair number = 3 Example 2: Europe: f = 50 Hz => nRMF = f/p = 50 Hz/4 = 12,5 s-1 Δ 750 min-1 USA: f = 60 Hz => nRMF = f/p = 60 Hz/4 = 15 s-1 Δ 900 min-1 => Δn = 150 min-1 Δn = 150 min-1 / 750 min-1 × 100% = 20%
. 60 s/min
