construction

construction

1. What "Construction" Refers To (DC Machine)

Construction of DC machine = physical parts that make electromechanical conversion possible. The same construction works as motor or generator (reversible), differing only in external connections and energy flow.

2. Main Parts (exam diagram — label 7 parts)

Part	Material / Construction	Function
Yoke (frame)	Cast steel (or fabricated)	Mechanical support and magnetic path (carries flux), outer cover
Pole + Pole shoe + Field winding	Laminated steel pole with copper field coil wound around	Creates magnetic field $B$ (electromagnet) — $Φ$ per pole; pole shoe spreads flux and supports field coil
Armature core	Laminated silicon steel with slots on periphery, cylindrical	Houses armature conductors, reduces eddy currents (lamination), provides low-reluctance path
Armature winding	Copper conductors placed in slots, lap or wave wound	Where emf induced (generator) / force produced (motor) — carries $I_a$
Commutator	Copper segments insulated by mica, cylindrical, connected to winding ends	Rectifies AC in armature to DC at brushes (generator) / reverses $I$ to keep torque unidirectional (motor)
Brushes	Carbon/graphite blocks with springs pressing on commutator	Collect current from rotating commutator to stationary external circuit
Bearings, shaft, etc.	Shaft through armature, bearings support rotation	Mechanical rotation

Cross-section: outer Yoke → inward Pole (with field winding) → air gap → Armature core (with slots + winding) on shaft → Commutator on shaft → Brushes touching commutator → shaft out to prime mover/load.

5. Exam Points

• Draw labelled diagram (yoke, pole, field winding, armature core, winding, commutator, brushes) — 7 marks, very frequent (almost certain to ask construction).
• State function of each part — 5-7 marks, very frequent.
• Mention laminated core to reduce eddy currents — 3-5 marks, frequent.
• Distinguish lap vs wave winding (brief) — 3 marks.