HarmonicsTheirCauseandControl.ppt

Power Line Harmonics: Their Cause and Control Power Line HarmonicsTheir Cause and Control What are harmonics? Low frequency interference on the power line Caused by non-uniform current flow from the power line Caused by the input stage of the power-consuming device PWM Drive Design The rectifier converts the AC line voltage to pulsating DC The DC bus capacitors filter the pulsating DC and maintain a constant DC bus voltage Rectifier Changes AC to DC The rectifier converts the AC line voltage into pulsating DC The peak voltage of a 460 V AC power line is about 650 V DC Rectified AC Charges the DC Bus Intermittent Current Intermittent 3-Phase Current AC Current Flow Effect on Line Voltage Effects of Voltage Distortion Effects of Voltage Distortion Carrier current signals Lighting systems (Leviton) Some security systems Sensitive electronic equipment Communication Medical Security Research Computer Stand-by generators How Much Distortion? Harmonic analysis can be used to describe any repetitive wave Describe the wave in terms of a base frequency and multiple frequencies (harmonics) 1st harmonic = 50 Hz 2nd harmonic = 100 Hz ... Total harmonic distortion (THD) is the square root of the sum of the squares of the harmonic amplitudes Harmonic Analysis Even harmonics Harmonics which are multiples of 3(180, 540,  900 Hz...) 5th, 7th, 11th, 13th...(300, 420, 660, 780 Hz...) Half-wave rectification Single phase loads: computers, copiers, electronic ballasts... Three phase machines or any of the above Voltage Distortion Total Harmonic Voltage Distortion = 5.1% 5th 2.0% 17th 1.8% 7th 1.9% 19th 0.8% 11th 1.9% 23th 0.4% 13th 1.0% 25th 1.1% IEEE 519-1981: Voltage THDTotal Harmonic Distortion 3% Sensitive applications Airports Hospitals Telephone companies 5% General applications Office buildings Schools 10% Dedicated systems Factories Voltage Distortion Depends On... The non-linear load Power Voltage Design Additional harmonic filters The building’s power system