T99 - Harmonic Solutions - Rockwell Automation · Isc=maximum short circuit current at PCC I ... Custom XFMR creates the solution magnetically ... solution for MCC lineups

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T99 - Harmonic SolutionsHarmonic Mitigation, Problems, Limitations and Solutions

PUBLIC Copyright © 2018 Rockwell Automation, Inc. All Rights Reserved. 2

Agenda

Challenges - How do I choose?Solution Strategies

Background on Harmonics


Agenda

Background on Harmonics


Linear Loads vs Non-linear LoadsLoads connected to an AC power source can be divided into two categories: Linear and Non-linear

Smooth Sine Wave Current Draw “Pulsing” Current Draw


Linear Loads vs Non-linear LoadsWhat causes the pulsing current draw?

Diodes have a “Forward Conduction Voltage” (FCV) They block current both ways until the voltage

sine wave reaches the FCV level, then stop again when it drops

DC Bus capacitors charge / draw current instantly

Short steep pulses of current drawn by the capacitors cause distortion in the line voltage

Voltage Sine Wave

FCV threshold Current drawn by the

bus caps in short steep pulses


Linear Loads vs Non-linear Loads

Linear loads draw current from the AC Sine Wave as an AC Sine Wave Resistance heaters, across-the-line (ATL) motors, incandescent

lamps Non-linear loads draw current from the sine wave in “pulses”

Virtually EVERYTHING that is not a resistance heater or ATL motor is now a non-linear load SMPS (Switch Mode Power Supplies), AC and DC drives, Servo Amplifiers, UPS,

HID / Fluorescent / LED lighting…

AC loads can be divided into two categories: linear and non-linear


Harmonics

Can be described as multiples of the fundamental frequency (i.e. 60 Hz) 2nd harmonic = 120 Hz, 3rd harmonic = 180 Hz, 7th harmonic = 420 Hz, etc.

Harmonic frequencies are superimposed (layered) on top of the fundamental 2nd order (multiples of 2 / even) cancel each other out 3rd order (triplen) also cancel each other in a 3-phase system Non-Triplen odd order harmonics are additive!

5th, 7th, 11th 17th, etc.

Harmonics” describes that distortion in the AC sine wave


Harmonics“Harmonics” describes that distortion in the AC sine wave and can be described as multiples of the fundamental frequency (i.e. 60 Hz) Fundamental Add 5th harmonic Add 7th harmonic Add 11th harmonic Sum them Effect on the

fundamental


Why Worry About Harmonics? Harmonics cause additional heating in electrical systems. Increase equipment failure

Due to loss of true sign wave, confused 0 Crossing and other power quality issues Increase the size (aka cost) of required distribution equipment.

Larger Transformers, cables and switch gear to handle the extra harmonic currents Many protective devices assume a 60 Hz sine wave. Too much distortion

can make them less effective, or prone to false trips…(Typical of Power Quality issues)


Why Worry About Harmonics? Harmonics cause additional heating in electrical systems It’s not always accountable to protective devices and can lead to failure,

such as …Transformer winding heating…

Above thermal and daylight images show uneven heating in the windings of a three phase step-down transformer, most likely due to harmonics

Neutral conductor heating…

Above thermal and daylight images show overheated neutral wires, proven to be caused by harmonics

Capacitor failure……

Over heating of terminations…

Even transformer fires!…


How Much is Too Much?If the non-linear load is a SIGNIFICANT portion of the total load (linear + non-linear), there is a potential for harmonic distortion problems

A good rule of thumb is that if your non-linear load is 20% or higher of the total load, then you are a good candidate for a harmonic mitigation.


How Much is Too Much?Other factors for deciding if you must mitigate VFD harmonics:

Service transformer is >80% loaded >60% of the time Power Factor Correction Capacitors are used or planned Harmonic load on a backup generator causes over sizing

to compensate Voltage distortion is already >4%


IEEE - 519

IEEE (Institute of Electrical and Electronic Engineers) published guidelines in 1981 for limits to harmonics and preventing damage to transmission and distribution equipment

Establishes responsibilities for users and utilities to maintain the voltage THD (Total Harmonic Distortion) limits within acceptable levels at the PCC (Point of Common Coupling) Updated in 1992, then again just recently in 2014 Users must limit current distortion in their facility so as to not create voltage THD at the

PCC Utilities must limit voltage distortion going to the PCC by maintaining circuit impedance


IEEE - 519Current harmonics in YOUR facility causes voltage harmonics on the line

Voltage harmonics pass to your neighbors via the utility connection

Voltage harmonics coming in from the utility makes current harmonics worse

Pulsing current draw leads to current harmonics

Current harmonics leads to voltage harmonics

The purpose of IEEE-519 is to control voltage Total Harmonic Distortion (V-THD) at the PCC


IEEE - 519This is how you do it… by limiting the CURRENT (I) distortion in your equipment… As a percentage of your total DEMAND (TDD = Total Demand Distortion)

Current distortion Limits for General Distribution Systems (120V through 69,000V)

Isc/Iload <11 11<=h<17 17<=h<23 23<=h<35 35<=h TDD (%)<20 4.0 2.0 1.5 0.6 0.3 5.0 20<50 7.0 3.5 2.5 1.0 0.5 8.0 50<100 10.0 4.5 4.0 1.5 0.7 12.0 100<1000 12.0 5.5 5.0 2.0 1.0 15.0 >1000 15.0 7.0 6.0 2.5 1.4 20.0 Even harmonics are limited to 25% of the odd harmonic limits above

Isc=maximum short circuit current at PCCIload=maximum demand load current (fundamental frequency component) at PCC

Maximum Harmonic Current Distortion in Percent of Iload


Agenda

Solution Strategies


Strategies - What Do You Do?Mitigate Cumulatively or Mitigate Individually?

Mitigate cumulatively: Deal with the total problem as it exists at the PCC (Point of Common Coupling)

Mitigate individually: Solve harmonics issues at every source, which ultimately avoids the cumulative effects


VFD Harmonic Mitigation: CumulativeCorrect Current harmonics at the PCC, UPSTREAM of the VFDs Active Harmonic Filters (AHF) systems

Provides corrective current to counter the distortion current

Measures, adapts and mitigates dynamically as the system changes

One AHF can correct multiple smaller VFDs Becomes expensive for larger VFDs

Great for MCC lineups, ≤ 200 HP drives


VFD Harmonic Mitigation: IndividualCorrect current harmonics at EACH and every VFD

Line Reactors and / or DC Bus Chokes Passive Harmonic Filters Multi-Pulse Front End Drives Active Front End (AFE) Drives


VFD Harmonic Mitigation: IndividualCorrect current harmonics at EACH and every VFD Line Reactors and / or DC Bus Chokes Reduces I-THD, but not enough in most cases

From 80-120% I-THD to 20-40% May be OK if VFDs are a small fraction of the total load (TDD) Line reactors beneficial for other reasons, so still recommended

Increases the reliability of ALL VFDs HIGHLY recommended if source kVA is > 10X the VFD kVA


VFD Harmonic Mitigation: IndividualCorrect Current harmonics at EACH and every VFD Passive harmonic filters Tuned RC filter traps 5th, or 5th +7th harmonics

Reduces I-THD to 5-6% typical Effective solution for 75 Hp and below,

small quantities Includes line reactor, so provides

those other benefits


VFD Harmonic Mitigation: IndividualCorrect Current harmonics at EACH and every VFD; ≥250 HPTwo substrategies:

Multi-Pulse Front End drives 18 pulse (North America), 12 pulse (Europe)

Active Front End (AFE) low harmonic drives


VFD Harmonic MitigationSummary of mitigation so far: Line Reactors / Bus Chokes

OK for motors ≤ 25 HP and/or small % TDD Passive Harmonic Filters

Effective solution for 75 HP and below, in small quantities Active Harmonic Filters

Good for MCCs and/or multiple motors ≤ 200 HP What about motors ≥250 HP?


18-Pulse Advantages Simple magnetics

Custom XFMR creates the solution magnetically

Familiarity Used extensively for the past

10+ years in W / WW applications

18 Pulse Solution


18-Pulse Performance Challenges Poor harmonic performance with

any line voltage imbalance Can allow 20 to 50% I-THD at

just 2% imbalance Attenuation can drop below

IEEE-519 requirements as load drops to <60% Little discussed fact…

Advantages and Challenges 18 Pulse

IEEE-519 limit


AFE Drive Advantages NO transformer required Better footprint than most 18 pulse Footprint smaller than thermally

stable “side – x – side” Footprint compares to “stacked”

design (xfmr below drive) Less thermal stress on the

electronics

Advantages and Challenges AFE drives400 Hp Comparison: PowerFlex® 755TL to 18-Pulse S-x-S

80”47”

27”Depth 33”

Width


AFE Drive Advantages NOT susceptible to line

voltage imbalance Software adjusts line inverter

pattern to match changing conditions

Corrects Total Power Factor to as high as 0.999 Displacement PF and Distortion PF combined

Advantages and Challenges


Agenda

Challenges - How do I choose?


“How do I decide which way to go?” Take all factors into consideration: Size of motors requiring mitigation Quantity of motors requiring mitigation Mounting configurations MCC, control panel, standalone, etc.

Electrical supply Stiff supply, end of line, backup generator, etc

Summary


How do I decide which way to go? Size of motors requiring mitigation Motors < 200 HP Individual Mitigation Correct Current harmonics at EACH

and every VFD• Line Reactors and / or DC Bus

Chokes• Passive Harmonic Filters• Multi-Pulse Front End Drive• Active Front End (AFE) Drives

Summary


“How do I decide which way to go?” Size of motors requiring mitigation Motors < 200 HP Multiple Motors

(Cumulative Mitigation)

Summary

Active Harmonic Filters (AHF) systems Typical I-(THD) of 3 to 6% 0.9 - 0.99 PF Good for multiple smaller VFDs Great solution for MCC lineups


How do I decide which way to go? Size of motors requiring mitigation Large Motors (≥ 250 HP)

Summary


Active Front End Drive – New Technology Widely Accepted in Europe Newer Technology in North America, and not as

widely accepted

Harmonics Are a Problem with Many Solutions

Passive Filters Suited to low power ratings < 100 hp Numerous suppliers

Active Filters Showing up on specifications Versatile – used for single drives or

multiple drives

18-Pulse – widely accepted Most often specified Works well Can be expensive and take up space

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T99 - Harmonic Solutions - Rockwell Automation · Isc=maximum short circuit current at PCC I ... Custom XFMR creates the solution magnetically ... solution for MCC lineups