Technical: Electrical, Mechanical, Civil and Electronics Fundamentals
The SJVN JFE/FE Technical domain checks whether you can apply first principles from electrical, mechanical, civil and electronics engineering to hydroelectric plant equipment and structures. Expect numerical questions, unit checks and equipment-selection logic rather than isolated definitions.
Core rules
- Electrical: for a balanced three-phase load, P = √3 V_L I_L cos φ; use line voltage and line current consistently. A transformer reaches maximum efficiency when variable copper loss equals constant iron loss, i.e. at load fraction √(P_i/P_cu).
- Mechanical: turbine type follows head and specific speed: Pelton for high head/low discharge, Francis for medium head, Kaplan for low head/high discharge. Cavitation risk is controlled by net positive suction head and correct setting.
- Civil: in concrete, the water–cement ratio chiefly controls strength and durability; slump measures workability, not strength. Curing keeps hydration going.
- Electronics: ideal op-amp analysis uses infinite input impedance and a virtual short between inputs; check the output against supply rails before trusting the linear result.
Worked example
A 100 kVA transformer has iron loss 1 kW and full-load copper loss 4 kW. Maximum efficiency occurs at load fraction √(1/4)=0.5, i.e. 50 kVA. At unity power factor, output is 50 kW; losses are 1 + 4(0.5)^2 = 2 kW. Efficiency = 50/(50+2)=0.9615, or 96.15%. The trap is evaluating at full load, where copper loss is 4 kW and efficiency is lower.
Traps
Mixing phase and line quantities; using peak instead of RMS; choosing a turbine by power rather than head; treating slump as a strength test; and ignoring op-amp saturation.