2. Electrical Drives & Instrumentation
EEE-105
No. Marks obtained
(Out of 100)
Letter
Grade
Grade Point
(4 point scale)
1 80% or above A+ 4.00
2 75% to less than 79% A 3.75
3 70% to less than 74% A- 3.50
4 65% to less than 69% B+ 3.25
5 60% to less than 64% B 3.00
6 55% to less than 59% B- 2.75
7 50% to less than 54% C+ 2.50
8 45% to less than 49% C 2.25
9 40% to less than 44% D 2.00
10 Less than 40% F 0.00
11 Incomplete I -
12 Withheld W -
No.
Theory
Description Ratio
1 Class Attendance 05%
2 Class Test or Quizzes 10%
3 Assignment & Presentation 10%
4 Mid-Term Examination 25%
5 Final Examination 50%
Total- 100%
3. Electrical Drives & Instrumentation
EEE-105
Text Book: Electric Machinery Fundamentals,
5th Edition, by Chapman
4. Transformers_(Chapter-2)
Why TRANSFORMERS are important to modern life:
The first power distribution system in the United States was a 120-V
dc system invented by Thomas A. Edison to supply power for
incandescent light bulbs. Unfortunately, his power system generated
and transmitted power at such low voltages that very large currents
were necessary to supply significant amounts of power.
These high currents caused huge voltage drops and power losses in
the transmission lines.
The fact that power could not be transmitted far with low-voltage in
dc power systems.
The invention of the transformer and the concurrent development of
ac power sources eliminated forever these restrictions on the range
and power level of power systems.
5. Transformers_(Chapter-2)
Why TRANSFORMERS are important to modern life:
A transformer ideally changes one ac voltage level to
another voltage level without affecting the actual power
supplied.
If a transformer steps up the voltage level of a circuit, it
must decrease the current to keep the power into the
device equal to the power out of it.
Therefore, ac electric power can be generated at one
central location, its voltage stepped up for transmission
over long distances at very low losses, and its voltage
stepped down again for final use.
6. Transformers_(Chapter-2)
TYPES ofTRANSFORMERS:
The principal purpose of a transformer is to convert ac power at
one voltage level to ac power of the same frequency at another
voltage level.
Transformers are also used for a variety of other purposes (voltage
sampling, current sampling and impedance transformation).
But this course is primarily devoted to the power transformer.
7. Transformers_(Chapter-2)
TYPES ofTRANSFORMERS:
In addition to power transformers, two special-purpose transformers are
used with electric machinery and power systems.
The first of these special transformers is a device specially designed to
sample a high voltage and produce a low secondary voltage directly
proportional to it. Such a transformer is called a potential transformer.
The second type of special transformer is a device designed to provide a
secondary current much smaller than but directly proportional to its
primary current.This device is called a current transformer.
8. Transformers_(Chapter-2)
TYPES ofTRANSFORMERS:
Both the Potential and Current transformers are called Instrument
Transformer in general.
There are other type of transformer called AutoTransformer.
On some occasions it is desirable to change voltage levels by only a small
amount. For example, it may be necessary to increase a voltage from 110
to 120V or from13.2 to 13.8 kV.These small rises may be made necessary
by voltage drops that occur in power systems a long way from the
generators. In such circumstances, it is wasteful and excessively expensive
to wind a transformer with two full windings, each rated at about the same
voltage. A special-purpose transformer, called an auto transformer, is
used instead.
