# Basic Electrical Engineering (3110005)

BE | Semester-1   Winter-2019 | 11-01-2020

## Q4) (c)

#### Generation of Rotating Magnetic Field (RMF)

• When stationary three phase winding coils are supplied by an alternating 3-phase supply then uniform Rotating Magnetic Field (or flux) of constant value is produced.
• The principle of 3-phase, 2-pole stator having three identical winding coils are placed by 120° electrical apart. The sinusoidal flux due to three phase windings is shown in Fig. 2.
• The directions of the positive fluxes are shown individually below at different positions.
• Let us say that the maximum value of the flux due to any one of the three phases be ${\varnothing }_{\mathrm{m}}$ . The resultant flux ${\varnothing }_{\mathrm{r}}$ , at any instant is given by the resultant sum of the individual fluxes ${\varnothing }_{1}$${\varnothing }_{2}$, and ${\varnothing }_{3}$, due to three phases.
• We have considered the $\frac{1}{6}$th time period apart corresponding to points marked 0, 1, 2 and 3 in Fig. 1.

We have,

Now,

We have,

Now,

We have,

Now,

#### When  (at point 3),the Resultant flux,

We have,

Now,

FOR UNDERSTANDING ONLY

Note: Any above cases, any one vector has zero value and 60° is the angle between other two present vectors as per law of parallelogram, hence, in each above cases cos60 is considered. The value of θ is considered with sin function, as the waveforms are sinewaves.