EL19 DC machines Revision

The image shows the major parts of a d. c. machine.

The parts that require regular maintenance are:

• the field windings

• the brush gear and commutator

• the armature windings

• the bearings

• the pole shoes

DC machines are devices which work by the use of electromagnetism just like transformers, solenoids, relays, etc. However, they have an additional hazard which is:

• very strong magnetic fields

• rotating parts

• higher fault levels

Which of these is/are NOT a part of a d.c. generator?

• slip rings

• commutator

• brushes

• armature

Which part of a d.c. generator converts the a.c. produced in the coil into d.c. at the generator terminals?

• field coils

• commutator and brushes

• yoke or frame

• armature

The process of generating an EMF in a conductor is called:

• electro motive force

• electromagnetic induction

• generator energy conversion

• voltage induction

The single loop generator shown, produces maximum output at the:

(select all that apply)

• 0° coil position

• 90° coil position

• 180° coil position

• 270° coil position

• 360° coil position

Generators get their mechanical power from:

• batteries

• prime movers

• transformers

• power capacitors

Generators are devices that convert

_______ energy into _______ energy.

• chemical; mechanical

• mechanical; electrical

• electrical; mechanical

• potential; kinetic

The direction of an induced EMF is determined using:

• Fleming’s left-hand rule

• Fleming’s right-hand rule

• Faraday’s law of electromagnetic induction

• Lenz's law

In Fleming’s left-hand rule, what does the index finger (first finger) indicate?

• the direction of induced EMF

• the direction of the conductor motion

• the direction of the electric field

• the direction of the magnetic field