Qwestrum Engineering360 · Electrical & Electronics · Network Analysis
What is three-phase power?
Three-phase AC uses three voltages 120° apart — delivers constant power to motors and loads with less copper than single-phase for the same kW. Standard in Indian industry (415 V line).
Exam tip: keep SI units consistent end-to-end, write the governing relation symbolically before substituting, and sanity-check magnitude and sign.
Quick revision
Skim these first — then read the full notes below.
- VL = √3 × Vph in star; IL = Iph in star
- Power P = √3 VL IL cos φ for balanced load
- Indian distribution: 11 kV / 415 V, 50 Hz
- Phase sequence matters for motor direction
Exams & GATE
- 1Basic but high-scoring GATE/network questions.
- 2Practice star-delta conversions until automatic.
Interview prep
Panel interviews: read a motor nameplate (kW, V, A, pf, RPM). Explain how to calculate line current.
📖 Standard books (India)
Electrical Power Systems — CL Wadhwa
Read: Ch. 2–3
Generation, transmission, and fault basics
Understand the concept
Every electrical diploma and B.Tech student in India learns three-phase before machines — it is the language of shop floor electrical maintenance.
Schematic diagram for study — aligned with standard B.Tech / GATE syllabus.
Three-phase phasor diagram (balanced). V_L = √3 V_ph (star). Phase sequence R-Y-B at 120° spacing.Explore related topics
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