Harmonic Data Comparisons 1336 PLUS, 1336 PLUS II, 1336 IMPACT and 1336 FORCE AC Drives with 6-Pulse, 12-Pulse, and 18-Pulse Front-Ends
Topologies 6-Pulse drive 12-Pulse drive 18-Pulse drive Harmonic Spectrum Comparison This document provides a comparison of the harmonic spectrum for 1336 PLUS, 1336 PLUS II, 1336 IMPACT and 1336 FORCE AC drives utilizing various AC/DC converters (front-end) topologies. The comparison is based on the following topologies: 6-Pulse drive using a 6-Pulse SCR bridge, 12-Pulse drive using a 12-Pulse phase shifting auto-transformer with a 12- Pulse diode bridge, and 18-Pulse drive using an 18-Pulse phase-shifting auto-transformer with an 18- Pulse diode bridge. All three topologies utilize the same Pulse Width Modulated (PWM) inverter and 1336 PLUS II control board. A customer s specific electrical power distribution system should be considered in the selection of a harmonic mitigation solution. Table 1 is a summary of the typical harmonic current spectrum for the various front-ends of the PWM AC drives. Keep in mind that harmonic distortion levels for PWM AC drives are significantly impacted by varying the customer s power system impedence. When looking up limits in IEEE 519-1992, the ratio of short circuit current, which can be estimated from supply transformer impedence, to load current must be considered. Category 6-Pulse Drive 12-Pulse Drive 18-Pulse Drive 1. Current THD 30 35% 6.5 9.5% 4.5 5% 2. Power Factor 0.92 0.95 0.97 0.98 0.98 0.99 3. DPF 0.95 0.97 0.96 0.98 0.98 0.99 4. K-Factor 3.0 5.0 2.0 3.0 1.0 2.0 5. 5 th Harmonic 20.0 30.0% 4.0 6.0% 2.0 3.0% 6. 7 th Harmonic 4.0 7.0% 2.0 4.0% 1.5 2.5% 7. 11 th Harmonic 3.0 5.0% 4.0 7.0% 1.0 2.5% 8. 13 th Harmonic 2.5 4.5% 3.5 5.0% 1.0 2.0% 9. 17 th Harmonic 1.5 2.5% 1.0 2.0% 0.5 1.5% 10. 19 th Harmonic 1.0 2.0% 1.0 1.5% 0.5 1.0% Table 1 Typical normalized harmonic current spectrum of PWM AC drives. The data obtained from factory floor measurements is presented in the graphs (Figures 1-4). The Point of Common Coupling (PCC) was picked at the input terminals of the 1336 PLUS II AC drive (460 volt AC, 3-phase, 350 horsepower) which supplied a 3-phase, 460 volt AC, 400 horsepower, 4-pole induction motor with base speed of 1785 RPM. The load to the AC motor was a DC motor connected to the shaft. The DC motor was rated at 400 horsepower, 500-volt armature, and was operated by a 460V AC, 400 horsepower 1395 DC drive. The test measurements were taken at intervals of 15 minutes.
Figures 1 and 2 indicate that the voltage Total Harmonic Distortion (THD) increases with speed and load. Also note that load and speed affect the 6-Pulse drives more than the 18-Pulse drives. Voltage THD of 6 pulse vs 18 pulse Drives THD, % 8.00 7.00 6.00 5.00 4.00 3.00 2.00 1.00 0.00 7.33 5.24 3.21 1.98 1.82 2.14 1.15 1.28 0 500 1000 1500 2000 Speed, RPM 6 pulse Voltage THD Rms, % 18 pulse Voltage THD Rms, % Figure 1 Voltage harmonics of the Allen-Bradley AC drives at different speeds. Voltage THD of 6 pulse vs 18 pulse Drives THD, % 8 7 6 5 4 3 2 1 0 7.19 5.42 3.31 2.39 1.45 1.68 1.91 2.03 0 25 50 75 100 125 Load, % of rated current 6 pulse Voltage THD Rms, % 18 pulse Voltage THD Rms, % Figure 2 Voltage harmonics of the Allen-Bradley AC drives at different loads.
Figures 3 and 4 show that current THD decreases with increasing load and increasing speed. As expected, the 18-Pulse front-end has much lower current distortion than the 6-Pulse front-end. 60 50 Current THD of 6 pulse vs 18 pulse Drives 52.45 TH D, % 40 30 20 37.63 35.12 31.24 10 0 10.22 6.83 5.27 4.90 0 500 1000 1500 2000 Speed, RPM 6 pulse Current THD Rms, % 18 pulse Current THD Rms, % Figure 3 Current harmonics of the Allen-Bradley AC drives at different speeds. Current THD of 6 pulse vs 18 pulse Drives THD, % 60.00 50.00 40.00 30.00 20.00 10.00 0.00 55.50 38.71 33.50 30.11 11.30 7.18 5.32 4.81 0 25 50 75 100 125 Load, % of rated current 6 pulse Current THD Rms, % 18 pulse Current THD Rms, % Figure 4 Current harmonics of the Allen-Bradley AC drives at different loads.
Figures 5 and 6 are typical scope plots of input current waveforms for the various PWM AC drive front-ends. Notice that the waveforms more closely resemble a sine wave as the level of distortion decreases. Input Current Input Current Amps Amps Time (msec) Time (msec) Current THD = 31.4% Current THD = 24.2% 6-Pulse Front-end 6-Pulse Front-end plus 3% Line Reactor Figure 5 Input Current Waveforms for PWM AC drive front-ends Input Current Input Current Amps Amps Time (msec) Time (msec) Current THD = 9.1% Current THD = 4.8% 12-Pulse Front-end 18-Pulse Front-end Figure 6 Input Current Waveforms for PWM AC drive front-ends
Harm. Number Freq. Hertz Table 2 contains data collected for the different front-ends during these tests. The harmonic components that are typically significant in PWM AC drives are highlighted in bold italics. 6-Pulse w/ Bus Choke %I RMS Pulse Width Modulated Variable Frequency Drives 12-Pulse w/ 12-Pulse w/ Bus Choke Bus Choke %I RMS I, θ (phase 6-Pulse w/ Bus Choke I, θ (phase angle) 18-Pulse w/ Bus Choke %I RMS 18-Pulse w/ Bus Choke I, θ (phase angle) angle) 1 60 96.98-15 99.22-11 99.55 9 3 180 0.57 106 3.59-146 0.89-75 5 300 22.81 96 4.41 89 2.05-67 7 420 5.9 94 1.65-132 1.31 22 9 540 0.09 176 0.43 146 0.37 162 11 660 4.43-173 6.49 45 1.31 94 13 780 4.07 167 4.91 53 1.03 136 15 900 0.06 22 0.24-118 0.14-178 17 1020 1.75-109 0.47 115 0.19 168 19 1140 1.33-107 0.42-135 0.33-180 21 1260 0.03 179 0.28 84 0.09 101 23 1380 0.73-85 0.85 55 0.47 89 25 1500 0.54-85 1.08 62 0.28 123 27 1620 0.04 75 0.09-131 0.14-97 29 1740 0.48-35 0.12 171 0.05 162 31 1860 0.52-8 0.14 176 0.14-77 Table 2 Typical normalized harmonic current spectrum for input current waveforms of Allen-Bradley AC drives. This document allows the designer of an electrical power system including Allen- Bradley 1336 PLUS, 1336 PLUS II, 1336 IMPACT, and 1336 FORCE AC drives, using this data, a computer model and one of the previous mitigation techniques, to help evaluate and reduce the harmonic distortion within the customer s power system.
NOTES Harmonic Mitigation
1336 IMPACT and 1336 FORCE are trademarks of Rockwell Automation. www.rockwellautomation.com Corporate Headquarters Rockwell Automation, 777 East Wisconsin Avenue, Suite 1400, Milwaukee, WI, 53202-5302 USA, Tel: (1) 414.212.5200, Fax: (1) 414.212.5201 Headquarters for Allen-Bradley Products, Rockwell Software Products and Global Manufacturing Solutions Americas: Rockwell Automation, 1201 South Second Street, Milwaukee, WI 53204-2496 USA, Tel: (1) 414.382.2000, Fax: (1) 414.382.4444 Europe: Rockwell Automation SA/NV, Vorstlaan /Boulevard du Souverain 36-BP 3A/B, 1170 Brussels, Belgium, Tel: (32) 2 663 0600, Fax: (32) 2 663 0640 Asia Pacific: Rockwell Automation, 27/F Citicorp Centre, 18 Whitfield Road, Causeway Bay, Hong Kong, Tel: (852) 2887 4788, Fax: (852) 2508 1846 Headquarters for Dodge and Reliance Electric Products Americas: Rockwell Automation, 6040 Ponders Court, Greenville, SC 29615-4617 USA, Tel: (1) 864.297.4800, Fax: (1) 864.281.2433 Europe: Rockwell Automation, Brühlstraße 22, D-74834 Elztal-Dallau, Germany, Tel: (49) 6261 9410, Fax: (49) 6261 1774 Asia Pacific: Rockwell Automation, 55 Newton Road, #11-01/02 Revenue House, Singapore 307987, Tel: (65) 351 6723, Fax: (65) 355 1733 Publication DRIVES-WP012A-EN-P September, 2001 Copyright 2001 Rockwell Automation. All rights reserved. Printed in USA.