Unit 4 — Electrical Machines
Unit IV of AR111, written against the GGSIPU 2026-30 USAR syllabus. The two laws every rotating machine runs on — Faraday's e = BLv for generator action and F = BIL for motor action — and why both are present in the same machine at once. The DC machine: sectional construction part by part with what each is made of and what it does, classification by excitation, working principle, the e.m.f. and torque equations and back e.m.f. The single phase induction machine and why it is not self-starting, with the methods used to start it. The three-phase induction motor: rotating magnetic field and synchronous speed, working principle, slip and the rotor quantities that depend on it, the torque equation and the full torque-slip characteristic. Then the losses that occur in electrical machines — copper, iron, friction and windage — and where each one goes, and the applications of DC and induction machines set against the characteristics that suit them to the job. Solved numerical problems and a question bank at the end.