HARMONICS AND THEIR EFECTS ON POWER SYSTEM PRESENTED BY: S.M.JAFFER-1CR07EE048 IV Year, EEE,BE

Seminar Flow Why we need to study harmonics. What are harmonics How are they generated What effect these harmonics have. What are the measures to counter them.

Why study Harmonics Presence of harmonics in the power system severely affects its operation and stability. Everyday more and more no. of non-linear loads are being connected to the power system. Harmonics have the potential to disrupt or outright destroy the power system under right conditions. Overall power efficiency, quality and reliability are affected. Cost of power to consumers increases due to metering difficulties in presence of harmonics. When dealing with such a large system small disturbances cannot be allowed to prevail as they can easily lead to very large catastrophes.

HARMONICS Harmonics are those voltage or current signals which have frequency as the integral multiple of the power frequency. Any distorted periodic waveform can be broken into signals which are harmonics of the power signal. This treatment to the distorted waveform is done using Fourier theorem. In power System usually symmetric harmonics are generated, i.e. they are all odd harmonics of the fundamental power frequency.

FOURIER REPRESENTATION

DISTORTED WAVEFORM HARMONIC COMPONENTS OF A SIGNAL

AVERAGE ENERGY AND POWER

ORTHOGNALITY AND DEPENDENCE OF AVERAGE POWER ON FREQUENCY

EXAMPLES

GENERATION OF HARMONICS GENERATORS They possess distributed windings on stator and field windings on rotor. Air gap flux in not perfectly symmetric due to odd symmetry of poles. Distribution of windings is not perfect around the stator inner periphery.

For salient pole generators flux at the pole shoe remains almost constant and between the poles reduces to zero. This leads to generation of a 3 rd harmonic which distorts the fundamental waveform. Magnitude of 3 rd harmonic is negligible and constitutes about 2% of the fundamental waveform. The distribution factor of harmonics is given by Kb=sin(mnα/2)/msin(nα/2)

LOADS LINEAR LOADS: Linear loads are those loads whose voltage-current relationship is linear. When a sinusoidal voltage is applied to a linear load, the current drawn by the load is proportional to the voltage and impedance and follows the envelope of the voltage waveform. They ‘DO NOT’ contribute to the generation of harmonics in the system. Typical examples: Incandescent lamps Heaters Motors etc

NON-LINEAR LOADS Non-Linear Loads are those loads which possess a non-linear relationship between voltage and current. Whenever a sinusoidal voltage is applied to a non-linear load the current wave varies disproportionately with the voltage. Hence these are major sources of harmonics. This current waveform can be, using Fourier series broken into harmonics of the fundamental power frequency. This distorted current waveform goes back into the power system and through various power system impedances produces distorted voltages which ultimately lead to a distortion of the fundamental voltage wave. This happens due to: Non-Stiff Voltage source. Very large Non-linear loads.

EFFECTS OF HARMONICS ON POWER SYSTEM AND ITS COMPONENTS HARMONICS EFFECT VARIOUS POWER SYSTEM COMPONENTS LIKE: NEUTRAL CONDUCTORS. TRANSFORMERS MOTORS AND GENERATORS TRANSMISSION CABLES SWITCHGEAR LIKE : FUSES CIRCUIT BREAKERS RELAYS METERING LIGHTING

MEASURES TO COUNTER HARMONICS SOME OF THE MEASURE TAKEN TO COMBAT HARMONICS ARE: OVERSIZING THE NEUTRAL CONDUCTOR. USING SEPARATE NETURAL CONDUCTORS FOR DIFFERENT NETWORKS. USING K-RATED TRANSFORMERS. USING CABLES AND CAPACITOR BANKS OF HIGHER RATING. USING ANTI HARMONIC REACTANCE.