Electrical Engineering and Electronics
Core concepts
Master Ohm's law, Kirchhoff's voltage and current laws, series and parallel networks, and power P = U·I. For AC, understand RMS values, phase angle, active/reactive/apparent power and power factor. Know three-phase systems: line versus phase voltage (star: U_L = √3·U_Ph; delta: I_L = √3·I_Ph). In electronics, cover diodes, rectifiers, transistors as switches, operational amplifiers, filters and basic digital logic. Understand protective measures: fuses, circuit breakers, RCDs, earthing, and the difference between overcurrent and residual-current protection.
Traps in questions
- Mixing RMS and peak values (peak = √2 × RMS for sine).
- Applying DC formulas to reactive AC circuits without impedance.
- Confusing protective earthing with neutral conductor.
- Forgetting that an RCD protects people, not equipment, and does not replace overcurrent protection.
- Reversing diode polarity or ignoring voltage drop in a rectifier.
Worked example
A three-phase motor in star connection on 400 V line voltage: phase voltage = 400 / √3 ≈ 231 V. If each winding draws 10 A at cos φ = 0.85, apparent power S = √3·U_L·I = √3 × 400 × 10 ≈ 6.93 kVA; active power P = S·cos φ ≈ 5.89 kW. Rule of thumb: √3 ≈ 1.732 and 400 V/230 V is the standard European low-voltage ratio.
Practical competence
Be able to read a circuit diagram, identify protective devices, and reason about measurement (multimeter, current clamp, oscilloscope). Understand EMC basics: shielding, grounding, cable routing and interference suppression.