
Test Your Knowledge: Construction of DC Machine Quiz
Attention! In this quiz, 23 questions will be asked within 20 minutes. Negative marking of 1/4 is applied.
Important One Liner (Construction of DC Machine Quiz)
- DC machines consist of a stationary stator and a rotating rotor or armature.
- The stator provides a constant magnetic field using field windings or permanent magnets.
- Armature windings are placed in slots on the rotor to cut magnetic flux.
- Commutators and brushes convert the alternating emf induced in the armature into direct current output.
- Field windings on the stator can be series, shunt, or compound connected.
- Series-connected DC machines have high starting torque and variable speed characteristics.
- Shunt-connected DC machines maintain nearly constant speed under variable loads.
- Compound machines combine series and shunt windings for improved performance.
- The yoke is the outer frame providing mechanical support and a return path for magnetic flux.
- The pole core and pole shoe shape the magnetic field and support field coils.
- Varnish or insulating material protects windings from moisture and electrical shorts.
- Armature core is built from laminated steel sheets to reduce eddy current losses.
- Brush gear ensures consistent contact and minimizes sparking at the commutator.
- End connections of windings are insulated to prevent short circuits between coils.
- Bearings mounted at the shaft ends support smooth rotor rotation and reduce friction.
- Cooling ducts and fans help dissipate heat generated during operation.
- Interpole (commutation) poles improve current reversal and reduce sparking.
- Armature reaction refers to the distortion of main field flux due to armature current.
- Compensating windings neutralize the effect of armature reaction under load.
- The air gap between rotor and stator affects magnetic flux density and efficiency.
- Armature winding types include simplex, duplex, and concentric windings.
- Construction quality and material choice influence machine losses and performance.
- Regular maintenance ensures brush replacement and cleaning of commutator surfaces.
- Proper lubrication of bearings extends machine life and prevents overheating.
- Insulation class selection determines maximum operating temperature.
- Voltage regulation is managed by adjusting field excitation or loading patterns.
- Noise reduction techniques involve damping, improved lamination, and precision assembly.
- Protective devices such as fuses, circuit breakers, and overload relays safeguard the machine.
- Testing methods include open-circuit and load tests to determine performance parameters.
- Efficiency of DC machines can exceed 90% with optimized design and materials.
- High-power DC machines often use water or air blast cooling for thermal management.
- Modern applications include traction, electroplating, and emergency power supplies.
- Power losses comprise copper losses, iron losses, brush contact losses, and stray load losses.
- Design advances focus on lightweight materials and compact winding techniques.
- Regenerative braking in DC motors feeds energy back to the supply source.
- Field weakening extends speed range in DC motor drives.
- DC generators require prime movers such as steam, gas turbines, or internal combustion engines.
- End covers support bearing housings and protect internal components from contaminants.
- Generator paralleling involves synchronization, voltage matching, and phase angle control.
- Armature voltage is proportional to the product of flux per pole and speed.
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