1. HITKARINI COLLEGE OF
ENGINEERING AND TECHNOLOGY
MAJOR PROJECT REPORT
ON
THIRD HARMONICS DISTORTION METER
DEPARTMENT OF ELECTRICAL AND ELECTRONICS

2. UNDER THE GUIDENCE OF:-
MRS. SMITA SHRIVASTAVA
H.O.D (ELEX)
SUBMITTED BY:-
ADITI TIWARI(0203ex091001)
BANTY SANODIYA(0203ex091014)
KIRTI RAGHUWANSHI0203ex091022)
NEHA MAHARAJ(0203ex091032)
NIDHI SHUKLA(0203ex091033)
NILESH SANODIYA(0203ex091034)
RAJESH SAKET(0203ex0910)

4. HARMONICS
 A harmonic of a sinosuidal wave is a component frequency
of the signal that is an integer multiple of the fundamental
frequency, i.e. if the fundamental frequency is f, the
harmonics have frequencies 2f, 3f, 4f, . . . etc. The
harmonics have the property that they are all periodic at
the fundamental frequency, therefore the sum of
harmonics is also periodic at that frequency. Harmonic
frequencies are equally spaced by the width of the
fundamental frequency and can be found by repeatedly
adding that frequency. For example, if the fundamental
frequency is 25 Hz, the frequencies of the harmonics are:
50 Hz, 75 Hz, 100 Hz etc.

5. CAUSES
 NON-LINEAR COMPONENTS
 Diodes
 Transistors
 Electric Motors
 SMPS(switch mode power supply)
 Etc.

6. 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. This effect can require special
consideration in the design of an electric system to
serve non-linear loads.
 In addition to the increased line current, different
pieces of electrical equipment can suffer effects from
harmonics on the power system.

7. WHAT IS THIRD HARMONIC
DISTORTION
 Most of the harmonic problem is caused by the 3rd
component. Since the 3rd harmonic is the 2nd highest
energy from the fundamental component.
 Third-harmonic distortion is nothing more than a
measurement of the amplitude of the third harmonic
of the input frequency and is the most prominent
distortion component in analog magnetic recording
systems

9. INTRODUCTION
 The 3rd harmonic distortion meter has been designed for
measuring the quality of AC supply. The meter is built with a
PIC18F2550 project board and the full wave rectifier front-end
circuit. The AC power line, 220VAC is measured through the step
down isolation transformer. The input signal to the 10-bit ADC is
full wave rectified. The software performs DFT calculation
finding the amplitude of the fundamental frequency and the 3rd
harmonic. The distortion is computed by the ratio of the
amplitude of the 3rd harmonic to the fundamental frequency.
The meter has been tested with the square wave signal resulting
33% distortion. For low voltage AC utility, 220V, the reading
showed approx. 3%. The meter can be applied for high voltage
application with the appropriate signal conditioning.

10.  Nowadays an increasing of the electronic devices having
nonlinear characteristics are many used at home and office.
Such devices mostly are computer based equipment with a
low power factor switch mode power supply. The input
circuit of the power supply uses a diode-capacitor at the
front-end circuit. The current drawn is charging capacitor
only near the peak voltage. Thus for a given feeder having
finite impedance, there will be a lost from voltage dropped
near the peak voltage resulting flattened top distortion of
the AC voltage. To measure how high the distortion of AC
voltage is, we may decompose it into the summation of
sinusoid waves using DFT. The PIC harmonic distortion
meter shows a method for finding the amplitude of the
fundamental frequency and the 3rd harmonic. The reading
shows percentage of the 3rd harmonic distortion.

11. DETECTION OF HARMONICS USING
DFT
 In the proposed method a harmonic meter using a
microcontroller is designed. The meter is built with a
microcontroller and the full wave rectifier front-end
circuit. The input signal to the 10-bit ADC is full wave
rectified. The software performs DFT calculation
finding the amplitude of the fundamental frequency
and the 3rd harmonic. The distortion is computed by
the ratio of the amplitude of the 3rd harmonic to the
fundamental frequency. The effectiveness of the
proposed harmonic meter is confirmed by experiment.

12.  Total Harmonic Distortion, THD
 To measure the waveshape distortion, we use the
quantity of the Total Harmonic Distortion, THD
(equation 1). THD is the ratio of the power of
harmonic components to the power of fundamental
frequency. Our concern is the voltage distortion, we
can just find the sum of the rms of the harmonic
components, Vn and the rms of the fundamental
frequency, V1.


13.  Most of the harmonic problem is caused by the 3rd
component. Since the 3rd harmonic is the 2nd highest
energy from the fundamental component. So we
interest to find only the 3rd harmonic distortion using
equation 2.

14.  We may decompose the periodic waveform, f(t) into
the summation of a number of sinusoids waveform
easily using the Discrete Fourier Transform . A0 is the
amplitude of DC components. For AC voltage
waveform, A0 is zero
 .

15. The amplitude for each harmonic
can be computed as

17. FLATTENED TOP AC VOLTAGE CAUSED BY A
LOW POWER FACTOR SWITCH MODE
POWER SUPPLY

18. 32-point sample of half ac wave

20. CIRCUIT DISCRIPTION
 From the above design, first of all input signal is applied to the
circuit which is 220Vac. The bridge rectifier rectifies the ac input
to the pulsating dc, which would further made constant 5V with
the help of filter-capacitor arrangement and voltage stabilizer so
that any change in ac would not proportionally change dc. The
dc output is given to the variable resistor which is used to select
the voltage which in case of PLL cannot be done because it needs
a separate phase detector for different frequencies (voltages) this
is then applied to the digital oscilloscope which shows the total
coverage of half cycle by capturing 32 samples. The output from
this is given to the microcontroller where the software performs
the DFT calculations and the final results are displayed on the
LCD i.e. the fundamental frequency, the third order harmonic
component and the harmonic distortion in percentage.

22. SOFTWARE USED
MPLAB 8.84
 MPLAB development tools for the PIC16F877A
Microcontroller Architecture support every level of
software developer from the professional
applications engineer to the student just learning
about embedded software development. The Keil
8051 Development Tools are designed to solve the
complex problems facing embedded software
developers.

23. ADVANTAGES
 DETECTS 3RD HARMONIC IN A SIGNAL.
 SHOWS THE VALUE OF INPUT VOLTAGE TO BE
GIVEN SO THAT NO 3RD HARMONIC IS PRESENT
 CAN BE USED IN BIG INDUSTRIES FOR CLEARING
LOSSES DUE TO 3RD HARMONIC

24. DISADVANTAGE
 It is designed for very less range of voltage if distortion
more than 5% is present then the microcontroller will
get damaged.
 It can only detect % distortion but cannot filter it out
because as ac is used then this technique of dft is not
possible in this case.

25. CONCLUSION
 As a matter of fact, the frequency analysis of discrete time
signals is conveniently performed on a digital signal
processor which in our case is designed and programmed
in an embedded microcontroller. The project approach
applies a computational convenient representation of
discrete time signals known as Discrete Fourier transform
to estimate the fundamental and third harmonic frequency
of the signal. The computation of this ratio can identify the
distortion in ac voltage while being drawn through
different nonlinear devices so that after detecting the
harmonic component we can improve the quality of an ac
waveform.

26. CONCLUSION (CONT..)
 WE WILL TRY TO BUILD A CHEAP INSTRUMENT
FOR MEASURING THE THIRD HARMONIC OF AC
POWER LINE WITH PIC 18F255
MICRCONTROLLER.