DC Machines & Transformers (PCEET303) Syllabus

Constructional details of DC machines — armature winding, lap and wave (simplex, progressive only), winding diagrams of simplex lap wound and simplex wave wound armatures (winding diagram not for evaluation). DC generator — principle of operation, EMF equation, numerical problems. Classification of DC generators — steady-state equations, numerical problems. DC shunt generator — no-load characteristics (critical field resistance, critical speed, voltage build-up), load characteristics, numerical problems. Armature reaction — cross magnetising and demagnetising effect (computation of ampere-turns not required), compensating winding, interpoles, commutation (concept only), numerical problems. Power flow diagram — losses and efficiency, maximum efficiency, numerical problems. Parallel operation of DC shunt generators — load sharing, numerical problems.

DC motor — back EMF, torque equation, numerical problems. Classification of DC motors — steady-state equations, numerical problems. Characteristics of DC motors — numerical problems. Starting of DC motors — 3-point starter. Braking — regenerative braking, dynamic braking and plugging (concepts only). Speed control of DC shunt and series motors — field control and armature control, numerical problems. Power flow diagram — losses and efficiency, numerical problems. Testing — Swinburne's test, Hopkinson's test, retardation test, separation of rotational losses, numerical problems.

Single phase transformers — constructional details, principle of operation, EMF equation, ideal and practical transformer, numerical problems. Operation on no load and on load, phasor diagram at different load conditions, equivalent circuit, voltage regulation, numerical problems. Losses and efficiency, condition for maximum efficiency, numerical problems. Testing of transformers — polarity test, OC test, SC test, Sumpner's test, separation of losses, numerical problems.

Autotransformer — saving of copper, numerical problems. 3-phase transformer — construction, different connections of 3-phase transformers, numerical problems. Difference between power transformer and distribution transformer, all-day efficiency, numerical problems. Scott connection for 3-phase to 2-phase conversion. Vector groupings — Yy0, Dd0, Yd1, Yd11, Dy1, Dy11. Parallel operation of 1-phase and 3-phase transformers — essential and desirable conditions. On load and off-load tap-changers.