Common Cure for Harmonics - ABB Ultra Low Harmonic Drive
Common Cures for Harmonics Copyright 2008 ABB. All rights reserved. - 1 2/29/2008 Larry Stanley RSE,Nashville,TN Results-Driven Roadshow Cincinnati, 2008 Copyright 2008 ABB - 2 - Harmonics What? Harmonics What? Copyright 2008 ABB - 3 - Non-linear loads draw non-sinusoidal current from a sinusoidal line (current doesnt look like voltage): Non-incandescent lighting Computers
Uninterruptible power supplies Telecommunications equipment Copy machines Battery chargers Electronic variable speed drives Any load with a solid state AC to DC power converter The Real World, 6- Pulse Drive Copyright 2008 ABB - 4 - PWM Drive Input Current ( ) th p ) f7 = 420
w 7 = 2pFundamental, f7 i7 ( t) = 0.09 cos ( w5 7 t - and The Theory: 7th Harmonics f5 = 300 w 5 = 2p f5 i5 ( t) = 0.32 cos w 5 t - p 1 Fundamental i 1 ( t) i 5 ( t) 5th 0.5 Components 0 i 7 ( t) 0.5 7th 1
Why worry? Harmonics Why worry? Harmonic Current Distortion Added heating in transformers and cables, reduces available capacity May stimulate a PF correction resonance condition Copyright 2008 ABB - 8 - Excessive voltage Overheating of capacitors Tripping of protection equipment Shutdown / damage to electronic equipment May cause telephone or electronic interference Harmonics Why worry?
Copyright 2008 ABB - 9 - (cont.) Harmonic Voltage Distortion Increased heating in motors and other electromagnetic equipment Noisy operation of electromagnetic equipment Malfunction of sensitive electronics Nuisance tripping of electronic circuit breakers Equipment downtime Premature component failures
Failed transformers, motors and capacitors Compliance with codes or specifications Harmonics A System Issue! Harmonics produced by an individual load are only important to the extent that they represent a significant portion of the total connected load (Harmonics are expressed as a percentage) Linear loads help reduce system harmonic levels TDD (Total Demand Distortion) equals the THD (Total Harmonic Distortion) of the nonlinear load multiplied by the ratio of nonlinear load to the total (demand) load: (percentages) NL TDD =THDNL TL Copyright 2008 ABB - 14 - Where TDD THDNL NL = TL =
= TDD of the system = THD of the nonlinear loads kVA of nonlinear load kVA of total load (nonlinear + linear) Harmonics By the Numbers IEEE 519 - 1992 Table 10.2 Low-Voltage System Classification and Distortion Limits Special Applications General System Dedicated System Notch Depth 10% 20% 50% THD (Voltage) Notch Area, mVs 3% 5%
10% 16,400 22,800 36,500 Copyright 2008 ABB - 15 - Note: Notch area for other than 480 V systems should be multiplied by V / 480. Harmonics By the Numbers (cont.) RSC IEEE 519 - 1992 Table 10.3 Current Distortion Limits for General Distribution Systems ISC / IL <11 11h<17 17h<23 23h<35 35h TDD <20
1.5 0.7 12.0 100<1000 12.0 5.5 5.0 2.0 1.0 15.0 Copyright 2008 ABB - 16 - Note: All harmonic current levels are in percent with fundamental current IL as the base. Harmonics Copyright 2008 ABB - 17 - Will it be a problem? Harmonic Voltage, Will it be a problem?
THD (Voltage) will be acceptable (<5%) if the % drive load times the % impedance feeding the drive load is <3% %DriveLoad x %Impedance < 3% Copyright 2008 ABB - 18 - E.g. a 45% drive load fed from 6% impedance feeder bus: 45% x 6% = 2.7% 2.7% < 3% Acceptable E.g. a 70% drive load fed from 5% impedance feeder bus: 70% x 5% = 3.5% 3.5% > 3% Not Acceptable (Approximate rule of thumb for 6-pulse drives with 3% reactor, all other loads assumed to be linear) Harmonic Current, Will it be a problem? THD (Current) on a network with a short circuit ratio <20 (20<50, 50<100, 100<1000) will be acceptable if the % drive load times 45% is <5% (<8%, <12%, <15%) %DriveLoad x 45% < 5% (RSC <20) %DriveLoad x 45% < 8% (RSC 20<50) %DriveLoad x 45% < 12% (RSC 50<100) %DriveLoad x 45% < 15% (RSC 100<1000) Copyright 2008 ABB - 19 -
E.g. a network with a short circuit ratio of 35 has 15% drive load: 15% x 45% = 6.75% 6.75% < 8% Acceptable E.g. a network with a short circuit ratio of 65 has 30% drive load: 30% x 45% = 13.5% 13.5% > 12% Not Acceptable (Rule of thumb for 6-pulse drives with 3% reactor,, all other loads assumed to be linear) Copyright 2008 ABB - 20 - Harmonics What can I do? Copyright 2008 ABB - 21 - Harmonics What can I do? Reactors (Chokes) Passive Filters Harmonic Trap Hybrid High Pulse Count Rectification
Active Filters Drive Front End Stand Alone Reactors, AC Line or DC Link A C L in e R e a c to r Different design techniques Equal harmonic reduction for same normalized % reactance Typical full load THD (current) at drive input terminals 28% 46%
M D C L in k R e a c to r Copyright 2008 ABB - 22 - M Existence not position is what is important Reactor Effectiveness THD (Current) vs. % Reactor 120 Current harmonic content (THD) at drive input terminals as a function of normalized % reactance and network short circuit ratio %THD (Current) 100 80 60 40 Copyright 2008 ABB - 23 - 20 0
reduced current Reduce harmonics up to 30% more than traditional designs Swing portion of choke characteristic significantly improves harmonic performance at reduced loads Swinging DC Link Choke Designed to reduce harmonics at full and partial loads Perfect for Variable Torque Centrifugal Loads Equivalent to 5% line reactor More inductance per volume/weight of material Copyright 2008 ABB - 25 - Swinging Choke Vs. Fixed Choke Current Distortion vs % Speed for Variable Torque Load 45 40 %TDD (Current)
High Pulse Count Rectification Typical configurations are either 12 pulse or 18 pulse Phase shifting transformer is required Additional drive input bridges are needed Typical full load THD (current) at transformer primary 8% 12% (12 pulse), 4% 6% (18 pulse) Performance significantly reduced by line imbalance (voltage or phase) Excellent choice if stepdown transformer is already required Active Filter Front End with LCL Filter Drive L L
C LCL filter Copyright 2008 ABB - 29 - DC Link M Line inverter (rectifier) Motor inverter Motor Active Filter Line Inverter (rectifier) removes low frequencies < 1kHz LCL Filter (passive filter) removes high frequencies >1 kHz. (Current and voltage) Full output voltage is available with 80% input voltage (400VIn = 480VOut) Full regenerative capability (ACS800-U11/-17) No transformer required Not affected by line imbalance Beauty Instead of Beast IGBT line supply controls the current Active supply
Sinusoidal line current Low distortion below switching frequency Current spectrum of low harmonic drive LCL Line filter removes high frequency distortion 1 0,1 0,01 0,001 0,0001 Diode supply Copyright 2008 ABB - 30 - Cleans the waveform above switching frequency 10 Percentage [%] 100 0
Total current distortion less than 3.5% to 4.5% Total voltage distortion less than 5% Power factor adjustable from 0.85 (leading or lagging) to 1.0 1 0 1 7 13 19 25 31 37 43 49 55 61 67 73 79 85 91 97 %THD (Voltage) = f(RSC) 5 4 3 Copyright 2008 ABB - 31 - 2 1 0 10 20 30 40 50
0 10 5 0 0 0 0 12 15 20 25 30 HP 0 0 0 0 35 40 50 60 0 0 0 0 70 80 90 100 18-Pulse Impedance and Imbalance Dependencies Current Distortion Vs. Line Imbalance 25% 12/18-Pulse drives have 3% internal reactance. Drives are only load present. %TDD Current Distortion 20%
ULH Clearly Superior 12-Pulse 0% Voltage Imbalance Reference Curve 10% Total Network Impedance 18-Pulse 5% Total Network Impedance (Utility + Multi-Phase Transformer) 15% 18 Pulse with 12 Pulse Performance 18-Pulse 10% Total Network Impedance (Utility + Multi-Phase Transformer) 10% ULH 1% Total Network Impedance Copyright 2008 ABB - 36 - 5% ULH 10% Total Network Impedance 0% 0.0% 0.5% 1.0%
1.5% 2.0% 2.5% Voltage Imbalance 12-Pulse Reference 18-Pulse Direct 18-Pulse Xfmr ULH 1% Net Imp ULH 10% Net Imp 3.0% Harmonic Reduction Summary Effectiveness of Harmonic Mitigation Techniques (Assuming 100% Nonlinear Loading, ISC / IL = 60) THD (Current) No mitigation (reference level) 72% Harmonic Reduction
3% line reactors (or equivalent DC link reactor) 39% 45.8% 5% line reactors (or equivalent DC link reactor) 33% 54.2% 5% line reactors + 5th harmonic trap filter 12% 83.3% 12 pulse input rectifier with 5% impedance transformer 10% 86.1% Hybrid filter 7% 90.3% 18 pulse input rectifier with 5% impedance transformer 5%
93.1% 12 pulse input rectifier with 5% impedance transformer + 11th harmonic trap filter 4% 94.4% 3.5% 95.1% Technique Copyright 2008 ABB - 37 - Active harmonic filter Remember! An 80% THD nonlinear load which a will result in only 8% TDD if the nonlinear load is 10% and the linear load is 90%. (80%(10%/(10%+90%))=8%) Copyright 2008 ABB - 38 -
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