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Examoogle • User • info@examoogle.com • EE-2024-8821
Chapter 1 of 12 • Page 1 of 248🔒 Protected PDF • Watermarked
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In three phase system coil is placed at
0°
60°
90°
120°
120°
In a balanced three-phase system, the three stator windings are physically displaced from each other by 120° electrical degrees in space. This arrangement ensures that the induced electromotive forces (EMF) are also time-shifted by 120° phase displacement, providing a smooth and constant power delivery.
In a balanced three-phase system, the three stator windings are physically displaced from each other by 120° electrical degrees in space. This arrangement ensures that the induced electromotive forces (EMF) are also time-shifted by 120° phase displacement, providing a smooth and constant power delivery.
Vph=Vmsin(ωt−(n−1)120°) — represents the instantaneous voltage of phase 'n'
When a magnetic field rotates at constant speed, it cuts the three coils placed 120° apart sequentially. This geometric arrangement ensures that the flux linkage varies sinusoidally for each coil, resulting in a three-phase voltage set where the sum of voltages is zero at any instant: va+vb+vc=0.
Three-phase supply provides a constant, non-pulsating power output.
The physical 120° spatial displacement leads to a 120° temporal phase shift in the generated AC voltages.
This configuration is standard for both delta and star (wye) connections in power distribution.
Total power in a balanced 3-phase load is P=3VLILcos(ϕ).
Higher power density compared to single-phase systems.
More efficient transmission due to reduced copper requirements for the same power.
More complex wiring and control requirements.
Unbalanced loads can cause circulating currents and neutral potential rise.
Industrial motor drives and heavy machinery.
National power transmission grids and distribution networks.
The 120° separation is critical for the generation of a rotating magnetic field in induction motors.
Option A (0°) would result in all phases being in-phase, acting as a single-phase system with no phase diversity.
D is correct — In a three-phase system, the coils are physically placed at 120° mechanical degrees apart to produce phase-shifted voltages.
Always remember that 3-phase systems are designed to balance instantaneous power; the 120° shift ensures that the sum of the powers is constant, unlike single-phase which fluctuates at twice the frequency.