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Unit 51: Electrical Technology
The Characteristics and Principles of
AC and DC Generators and the
features of a Range of difference
Power Station
Course Aims
At the end of this course the learner will be
able to…
1. Know the methods used to produce electrical
2. Know the properties and applications of conductors,
insulators and magnetic materials
3. Know the physical arrangements of supply,
transmission and distribution equipment
4. Know how electrical energy is used to support
applications of electrical technology
• At the end of the session the learner will
be able to…
– Describe DC Generators
D.C. Generation
DC Generator - Molecular Expressions Florida State University
D.C. Generators
D.C. Generators
• A rotating armature coil passes through a
magnetic field that develops between the north
and south polarities of permanent magnets or
• As the coil rotates, electromagnetic induction
causes a current to be induced into the coil.
• The current produced is an alternating current.
• However it is possible to convert the alternating
current into a form of direct current (DC)
D.C. Generators
• This AC to DC conversion is accomplished
though the use of a split-ring commutator.
• The purpose of the split-ring commutator
is to reverse the armature-coil connection
to the external load circuit at the same
time that the current induced in the
armature coil reverses.
• This causes DC of the correct polarity to
be applied to the load at all times
D.C. Generators
Coil Rotation
Pulsating DC developed by a simple single-coil generator
Pure DC developed by a more complex generator using many
turns of wire and many commutator segments
Factors affecting
the voltage developed
• The voltage developed by a DC generator
depends upon…
– The strength of the magnetic field
– The number of coils in the armature
– The speed of rotation of the armature
• The voltage can be increased by
increasing any of these factors
The Voltage Developed
by a DC Generator
• Vo = (Z x n x Ф) / 60
• Where Vo is the voltage developed across the
generator brushes in volts
• Z = the total number of armature conductors
• N = speed of rotation in r.p.m.
• Ф = magnetic flux per pole in webers
• Given: A 4-pole DC generator rotates at 1200
r.p.m. The armature has 36-slots and each coil
has 4-turns of wire. The magnetic flux per pole
is 0.05 webers. Find the voltage output of the
DC generator?
The Voltage Developed
by a DC Generator
• Note each turn of the wire has two
conductors, thus…
• Z = 2 x 36 x 4 = 288
• Thus Vo = (288 x 1200 x 0.05) / 60
• Vo = 288 volts