ISRO Scientist Electrical case studies
ISRO Scientist Electrical · Put your knowledge to work in context.
The ISRO Scientist/Engineer (Electrical) recruitment exam is the written selection gateway to engineering posts at the Indian Space Research Organisation, conducted by its central recruitment board. It suits electrical engineering graduates, including final-year students, who want a research-and-development career in space systems rather than conventional utility or manufacturing work. The ISRO Scientist Electrical case studies are 5 cases and about 4,038 words.
1Freewheeling Diode and Brake Release Time in a 220 V DC Circuit
During commissioning of a 220 V DC station-battery panel, a holding brake is switched by an IGBT with only a freewheeling diode connected across the brake coil. Coil data: R = 44 Ω, L = 0.80 H, steady current 5 A.
767 words, about 4 min2Adding a 250 kW Motor to an Existing 1 MVA Board: DOL, Star-Delta or VFD
An 11 kV/415 V, 1 MVA, 6% transformer feeds a 250 kW, 415 V, 4-pole, 50 Hz cage induction motor through 25 m of 4-core 185 mm² cable (r = 0.10 Ω/km, x = 0.08 Ω/km per conductor). Motor data: full-load efficiency 0.94, power factor 0.88, full-load slip 1.33%, direct-on-line starting current 6.5 times full-load current.
709 words, about 4 min3CT Knee-Point Voltage for an 11 kV Feeder and Nuisance Earth-Fault Tripping
An 11 kV feeder uses a 400/1 A, 5P20, 5 VA bar-primary CT with a secondary winding resistance of 3.5 Ω. The numerical relay sits 180 m away in the switchgear panel and is wired with 2.5 mm² copper cable whose loop resistance is 0.0148 Ω/m.
836 words, about 4 min4Tuning a Furnace Temperature Loop with 30 s Dead Time
A reheat furnace temperature loop runs at a 1 s controller sample. The identified process from controller output (%) to temperature (°C) is first-order plus dead time: gain 2.5 °C/%, time constant 180 s, effective dead time 30 s (24 s transport plus 6 s sensor lag).
867 words, about 4 min5Retrofitting a 30 kW Pump with a 6-Pulse VFD: Overheating and Harmonics
A 30 kW, 415 V, 4-pole, 50 Hz IE3 pump motor (nameplate 55 A) is retrofitted with a 6-pulse PWM voltage-source drive fed from a 415 V board with a 1 MVA, 5% transformer. The board's short-circuit current is 18 kA and the drive's fundamental input current at full load is 48 A.
859 words, about 4 min