Electrical, Electronics & Telecommunication Engineering
Electrical, Electronics & Telecommunication Engineering in IESL Part I covers circuit laws, AC power, three-phase systems, transformers and machines, analogue electronics, and communication fundamentals. Numerical questions often test whether you distinguish rms from peak, line from phase, and real from reactive power.
Core rules and concepts
- Ohm’s law, KCL and KVL; Thevenin and superposition for linear circuits.
- AC: Vrms = Vpeak/√2; impedance Z = R + jX; power triangle P = VIcosφ, Q = VIsinφ, S = VI.
- Three-phase: P = √3·VL·IL·cosφ for a balanced load; star and delta relationships differ by √3.
- Transformer: V1/V2 = N1/N2; efficiency = output / (output + core loss + copper loss).
- Induction machine: synchronous speed ns = 120f/p; slip s = (ns − nr)/ns.
- Electronics: transistor bias, op-amp virtual short, and gain bandwidth limits.
Worked example
A load draws 100 kW at 0.8 power factor lagging. S = 100 / 0.8 = 125 kVA and Q = √(125² − 100²) = 75 kvar. To improve the power factor to 0.95, new Q = 100 × tan(cos⁻¹0.95) ≈ 32.9 kvar. Capacitor rating = 75 − 32.9 = 42.1 kvar. The reasoning is to resolve the load into P and Q, set the target reactive power from the desired power factor, and subtract.
Traps that cost marks
- Using peak voltage in power calculations instead of rms.
- Mixing line and phase quantities in star or delta circuits.
- Applying the wrong sign for leading and lagging reactive power.
- Ignoring transformer no-load current or copper loss variation with load.