Electrical Machines – I

Magnetic circuits analyse how ampere-turns (MMF) drive flux Φ through iron cores and air gaps — the electric-circuit analogy (ℱ–Φ–R) is the starting point for transformers and all rotating machines in Nagrath & Kothari.

A transformer transfers AC power between circuits by electromagnetic induction at nearly constant frequency — voltage changes but power (ideally) is conserved: V1/V2 = N1/N2.

A DC generator converts mechanical to electrical energy by inducing an EMF E = PΦZN/60A in the armature conductors; the connection of the field (separately excited, shunt, series, compound) sets its load characteristic.

A DC motor develops torque T = KΦI_a and runs at a speed set by N ∝ (V − I_aR_a)/Φ; the field connection makes the shunt motor a constant-speed drive and the series motor a high-starting-torque drive.

Testing methods estimate DC machine efficiency without full-load loading: the Swinburne test uses a no-load run to separate constant losses, while the Hopkinson (back-to-back) test loads two identical machines against each other.