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Electrical machines miscellaneous

Electrical Machines

  1. A 220V, 50 Hz, single-phase induction motor has the following connection diagram and winding orientations shown. MM' is the axis of the main stator winding (M1M2) and AA' is that of the auxiliar y winding (A1A2). Directions of the winding axes indicate direction of flux when currents in the windings are in the directions
    shown. Parameters of each winding are indicated. When switch S is closed, the motor

    1. rotates clockwise
    2. rotates anticlockwise
    3. does not rotate
    4. rotates momentarily and comes to a halt
Correct Option: C

ZAUX = r a + jxLa

= 1 + j(2π × 50) ×
10
π

= 1 + j 1000 ∼ 1000 ∠90°

Zm = rm + jxm
= 0.1 + j (2 π × 50 ) ×
0.1
π

= 0.1 + j 10 = ∠ 90°
IAUX =
V
= Ia ∠ -90°
Z0

IM =
V
= IM ∠ -90°
ZM

∴ Starting torque = k Ia Im sin (Ia, I m)
= k' sin (θ) = 0
So motor does not rotate at starting. Obviously 1φ motor is not self starting.



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