HITKARINI COLLEGE OF ENGINEERING AND TECHNOLOGY

MAJOR PROJECT REPORT ON THIRD HARMONICS DISTORTION

METER

DEPARTMENT OF ELECTRICAL AND ELECTRONICS

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)

THIRD HARMONIC

DISTORTION METER

HARMONICSA 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.

CAUSESNON-LINEAR COMPONENTSDiodesTransistorsElectric MotorsSMPS(switch mode power supply)Etc.

EFFECTSOne 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.

WHAT IS THIRD HARMONIC DISTORTIONMost 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

INTRODUCTIONThe 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.

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.

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.

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.

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.

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

.

The amplitude for each harmonic can be computed as

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

32-point sample of half ac wave

CIRCUIT DISCRIPTIONFrom 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.

SOFTWARE USEDMPLAB 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.

 

ADVANTAGESDETECTS 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

DISADVANTAGEIt 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.

CONCLUSIONAs 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.

CONCLUSION (CONT..)WE WILL TRY TO BUILD A CHEAP

INSTRUMENT FOR MEASURING THE THIRD HARMONIC OF AC POWER LINE WITH PIC 18F255 MICRCONTROLLER.