Electrical Engineering
Electrical Engineering is the technical core of UPPCL JE. The paper tests circuit laws, AC and three-phase quantities, transformers, rotating machines, transmission and distribution, and basic measurement and protection.
Circuit and AC fundamentals
- Ohm's law, KCL and KVL, series-parallel reduction, and Thevenin/Norton equivalents.
- For a sine wave, RMS = Vm/√2, half-cycle average = 2Vm/π, form factor = 1.11, peak factor = 1.414.
- Three-phase: P = √3 VL IL cos φ. In star, VL = √3 Vph and IL = Iph; in delta, IL = √3 Iph and VL = Vph.
Machines and power systems
- Transformer EMF: E = 4.44 f N Φm. Rating is in kVA because copper loss depends on current and core loss on voltage, not on load power factor.
- Induction motor: Ns = 120f/P; slip s = (Ns − Nr)/Ns; rotor frequency = sf.
- Transmission loss is I²R, so raising voltage for the same power lowers current and loss.
Worked example
A 4-pole, 50 Hz induction motor runs at 1440 rpm. Ns = 120 × 50 / 4 = 1500 rpm. Slip = (1500 − 1440)/1500 = 60/1500 = 0.04, or 4%. Rotor frequency = s f = 0.04 × 50 = 2 Hz. The reasoning uses synchronous speed first, then the slip definition; do not subtract from rotor speed.
Traps
- Mixing line and phase values in √3 formulas.
- Using peak voltage where RMS is required in power calculations.
- Treating transformer kVA rating as kW at unity power factor only.
- Forgetting that slip is positive in motoring and negative in generating.