AC Machines: Engr. Jessica Laine M. Tumbaga
AC Machines: Engr. Jessica Laine M. Tumbaga
AC Machines: Engr. Jessica Laine M. Tumbaga
NEE 423
General policies
Absence in excess of 20% of total required number of meetings
per term will be given a mark of D Dropped unofficially.
Late in excess of 25% of the scheduled class duration will be
considered absent (15 minutes for a 1 hour class; 23 minutes for
a 1-1/2 hour class; 30 minutes for a 2 hour class). Reference time
is DOSTs JUAN TIME.
Only missed major exams may be given a special make-up exam
with valid reasons and upon presentation of related documents.
Missed quizzes will be given a score of 0.
Cheating will be automatically penalized with a final grade of
5.0.
Going out of the class during exams is NOT ALLOWED.
Grading system
Prelim
Midterm
Finals
Quizzes (Q)
33%
Quizzes (Q)
33%
Quizzes (Q)
33%
67%
67%
67%
Tentative Midterm
Grade (TMG)
100%
100%
Midterm Grade=
Final Grade=
COURSE OUTLINE
Alternator
Principle of operation
Parts and Construction
Generation of voltage, breadth factor and pitch factor
Voltage Regulation, power developed and efficiency
Parallel Operation
Synchronization
Synchronous Motor
Principle of operation
Exact and approximate equivalent circuits
Method of starting
Power flow diagram
ALTERNATOR
(SYNCHRONOUS GENERATOR)
A machine which
produces electrical power
from mechanical power. It
operates with the same
fundamental
principle
of
electromagnetic induction as
a dc generator.
frequency
The frequency of the induced e.m.f. in the armature
conductors depends upon the speed and the number of poles.
=
120
Where:
f frequency of e.m.f. in Hz
P number of rotor poles
n rotor speed in rpm
10
11
12
(cont.)
Only two slip rings are required for d.c. supply to the field
winding on the rotor. Since the exciting current is small, the
slip rings and brush gear required are of light construction.
Due to simple and robust construction of the rotor, higher
speed of rotating d.c. field is possible. This increases the
output obtainable from a machine of given dimensions.
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14
Construction of an
alternator
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1. STATOR
16
2. ROTOR
carries the field winding which is supplied with
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SALIENT
(OR
PROJECTING)
POLE
TYPE
are mounted on a large
circular steel frame which is
fixed to the shaft of the
alternator. The individual field
pole windings are connected in
series in such a way that when
the field winding is energized by
the d.c. exciter, adjacent poles
have opposite polarities.
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19
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Applications:
Salient pole type
NON-SALIENT POLE
type
HIGH SPEED
ALTERNATORS (1500
OR 3000 rpm)
- Steam turbines
Mechanical robustness and
noiseless
Better e.m.f. waveform
because of a nearly sine
wave flux distribution
around the periphery.
2/4 poles = small diameters
and very long axial lengths.
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Problems
1. An alternator has 6 poles and runs at 1000 rpm. What is its
generated frequency? What must be its speed if frequency is to
be 25Hz?
2. The Binga Hydroelectric plant has a synchronous generator
whose rating is: 3; 27,800 kVA; 0.9 pf; 60Hz; 13,800V; 327.3
rpm. How many poles are there in the alternator? What is the
rated current? Assuming that the generator efficiency is
83.85%, what must be the horsepower rating of the hydraulic
turbine driving the generator?
3. A steam turbine is rated at 50,000kW, 0.8 pf, 3, 13.8kV,
60Hz, and there are two poles. What mist be the rated rpm in
the machine? What is the rated current? If the generator
efficiency is 90%, compute for the torque in pound-feet applied
to the shaft of the generator at rated speed.
Engr. J.L. Tumbaga
22
Problems
4. A diesel-engine generator is rated at 30kW, 0.85pf, 240V,
single-phase, 1800rpm. Fuel consumption is 2.2 gallons per
hour at full-load conditions. (1 US gallon = 3.785 liters). What
is the ampere rating of the generator? How many poles are
there in generator? Assuming that diesel fuel costs Php 3.50
per liter, how much will it cost to run the generator
continuously for one month under full load conditions? Only
30% of the BTU from the fuel is converted into electricity. If
BTU content of diesel oil is 140,000 BTU per gallon, how much
heat is wasted per hour of operation?
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Charles R. Swindoll
~The End~
Engr. J.L. Tumbaga