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Mehran University College
Of Engineering & Technology,
Khairpur Mir’s
HARMONICS
ENGR. AHSANULLAH MEMON
LECTURER
DEPARTMENT OF ELECTRICAL ENGINEERING MUCET KHAIRPUR MIRS
Actuall sine wave with linear loads
sine wave with non linear loads
INTRODUCTION
 A harmonic of a wave is a component frequency of the
signal that is an integer multiple of the fundamental
frequency,
 if the fundamental frequency is f, the harmonics have
frequencies 2f, 3f, 4f, . . . etc.
 Harmonic frequencies are equally spaced by the width of
the fundamental frequency.
 For example, if the fundamental frequency is 25 Hz, the
frequencies of the harmonics are: 50 Hz, 75 Hz, 100 Hz etc.
 Harmonics are electric voltages and currents that appear
on the electric power system as a result of non-linear
electric loads.
 Harmonic frequencies in the power grid are a frequent
cause of power quality problems. Harmonic components
should be reduced as much as possible.
CAUSES
 In a normal alternating current power system, the voltage
varies sinusoidally at a specific frequency, usually 50 or 60
hertz.
 When a linear electrical load is connected to the system, it
draws a sinusoidal current at the same frequency as the
voltage.
 When a non-linear load, such as a rectifier, is connected to
the system, it draws a current that is not necessarily
sinusoidal.
 The current waveform can become quite complex,
depending on the type of load and its interaction with
other components of the system.
 Further examples of non-linear loads include common
office equipment such as computers and printers,
Fluorescent lighting, battery chargers and also adjustable
speed drives.
EFFECTS
 One of the major effects of power system harmonics is
to increase the current in the system. This is
particularly the case for the third harmonic, which
causes a sharp increase in the zero sequence current,
and therefore increases the current in the neutral
conductor.
 Electric motors experience hysteresis loss caused by
eddy currents set up in the iron core of the motor.
These are proportional to the frequency of the current.
Since the harmonics are at higher frequencies, they
produce more core loss in a motor than the power
frequency would. This results in increased heating of
the motor core, which (if excessive) can shorten the life
of the motor.
 In the United States, common telephone lines are
designed to transmit frequencies between 180 and
3200 Hz. Since electric power in the United States is
distributed at 60 Hz, it normally does not interfere with
telephone communications because its frequency is
too low. However, since the third harmonic of the
power has a frequency of 180 Hz, its higher-order
harmonics are high enough to interfere with telephone
service if they become induced in the line
Mehran University College
Of Engineering & Technology,
Khairpur Mir’s
HARMONICS SUPPRESION
ENGR. AHSANULLAH MEMON
LECTURER
DEPARTMENT OF ELECTRICAL ENGINEERING MUCET KHAIRPUR MIRS
 To maintain output voltage sinosuidal and flux
sinosuidal, no load exciting current must be non
sinosuidal.
 The non linear characteristics of ferromagnetic core
used in transformers causes the magnetizing current
to be non sinosuidal even thogh the mutual flux is
sinosuidal.
HARMONICS IN SINGLE PHASE TRANSFORMER
HARMONICS IN THREE PHASE TRANSFORMERS
STAR-STAR CONNECTION
 If the neutral
connection between the
transformer primaries
and the generator is
broken, then the path
for the third-harmonic
currents is interrupted
and the third harmonics
in the exciting current
will be suppressed.
 As a result, the flux
cannot be sinusoidal, as
it will contain a third
harmonic, which in
turn produces a third
harmonic in the
transformer voltages.
These third harmonics show up only in the line-toneutral voltage if the transformers are identical, and
will not appear in the line-to-line voltages because
the line-to-line voltages are the phasor difference
between the line-to-neutral voltages.
The third harmonics in the line-to-neutral voltages
of all three phases are equal and in phase with each
other and, therefore, cancel in the line-to-line
STAR DELTA
 Third-harmonic current circulate in the delta, thus producing
a substantially sinusoidal flux.
 If, in addition, the primary neutral is closed, the thirdharmonic components of the mmf required by the sinusoidal
flux divide between the primary and secondary, depending
upon their relative third-harmonic leakage impedances.
 Where wye-wye transformation is required, it is quite
common to incorporate a third winding, known as a tertiary,
connected in delta.