Power Quality and Harmonic Mitigation 1

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Power Quality and Harmonic Mitigation

AccuSine

Schneider Electric 2- Power Quality Correction Group – May 2009

Agenda

● Overview● Harmonic Basics ● IEEE 519● Conventional Harmonic Mitigation Methods● AccuSine® PCS● Applications & Installation Notes● Specification Recommendations● Summary


Schneider Power Quality Correction Group

●Power Factor Correction and Harmonic Filtering:●Capacitor Systems

●LV & MV up to 15 kV●Fixed, Standard and Detuned Auto Banks

●AccuSine PCS●Voltage Regulation:

●Hybrid VAR Compensator●Electronic Sag Fighter


Fundamental

3rdHarmonic

Harmonic Basics

● What are harmonics?●Proliferated by power semiconductor devices

●Converts power (AC to DC)●A harmonic is a component of a periodic wave

having a frequency that is an integer multiple of the fundamental power line frequency

●Characteristic harmonics are the predominate harmonics seen by the power distribution system

●Predicted by the following equation:●Hc = np +/- 1●hC = characteristic harmonics to be expected●n = an integer from 1,2,3,4,5, etc.●p = number of pulses or rectifiers in circuit

Harmonic Frequency Sequence1 60Hz +2 120Hz 03 180Hz 04 240Hz 05 300Hz -6 360Hz 07 420Hz +: : :

19 1140Hz +

5thHarmonic

7thHarmonic

Resultant Waveform


Multi-pulse ConvertersHn

1 phase 4-pulse

2 phase 4-pulse

3 phase 6-pulse

3 phase 12-pulse

3 phase 18-pulse

3 x x5 x x x7 x x x9 x x11 x x x x13 x x x x15 x x17 x x x x19 x x x x21 x x23 x x x x25 x x x x27 x x29 x x x31 x x x33 x x35 x x x x x37 x x x x x39 x x41 x x x43 x x x45 x x47 x x x x49 x x x x

Harmonics present by rectifier designType of rectifier

Hc = np +/- 1

Hc = characteristic harmonic order present

n = an integer

p = number of pulses


Harmonic Basics●Nonlinear loads draw it●Example: 6-Pulse VFD

InverterConverter

DC bus

M

ABC


Harmonic Basics

● Why a concern?●Current distortion

●Added heating, reduced capacity in :– Transformers– Conductors and cables

●Heating effect proportional to harmonic order squared●Nuisance tripping of electronic circuit breakers (thermal overload)●Blown fuses●Detrimental to generators

– Heating of windings●Detrimental to UPS

– UPS can’t supply the current

Loads

Ih

Vh = Ih x Zh


Harmonic Basics●Voltage distortion

● Interference with other electronic loads●Faulting to destruction

●Creates harmonic currents in linear loads●Generator regulators can’t function

●Shut downs●Not compatible with standard PF caps

●Potential resonance condition ●Excessive voltage

●Overheating of PF correction capacitors● Tripping of PF protection equipment●Shutdown / damage to electronic equipment

Loads

Ih

Vh = Ih x Zh


Total Power Factor

TPF = (DPF) x (Distortion factor)

DPF =KW

KVAf= Cos φ

Distortion Factor =1

1 + THD(I)2

TPF = Total or true power factor

DPF = Displacement power factor

Distortion Factor = Harmonic power factor

= Cos δ


Total Power Factor Example

●Variable frequency drive (PWM type)●DPF = .95

● THD(I) = 90% ●(no DC choke & no input line reactor)

●Distortion Factor =

●TPF = .95 x .7433 = .7061

11 + .92

= .7433


How are harmonics handled today?●Mixed bag of objectives

●Basis of compliance is mixed– THDi, THDv, TDD?– IEEE 519-1992?

●Where is PCC?●What level of harmonics is to be attained?●How to obtain compliance?

– Sometimes defined– Sometimes open ended

●Validation ●Poorly defined●By each equipment vendor●No ‘Total Responsibility’ for harmonics

●Has the User been protected where it matters – inside the facility


Typical Present Situation●Specifications direct manufacturers of nonlinear loads to comply within

equipment specifications●Manufacturers of nonlinear loads have other concerns

●Sell standard equipment at competitive prices●Leads to minimized harmonic solutions●Leads to misleading information about harmonic performance●Leads to operational difficulties

– e.g. Can’t operate on backup generators/UPS● Force the IEEE 519 discussion to the utility PCC

●Many types of solutions are not compatible●Each manufacturer does his own thing without regard to other solutions●Approaches are for ‘my’ equipment only● ‘My’ simulation is for ‘my’ equipment only – I can’t include the others

● ‘Total’ solution not achieved●User has system that exceeds specification objectives●Consulting engineers can’t get overall compliance


ANSI Standard IEEE 519-1992● Issues addressed:

● THD(V) delivered by utility to user (Chapter 11)●THD(V) must be < 5% [< 69 KV systems]

●Defines the amount of TDD a user can cause (Chapter 10)●Based upon size of user in relation to power source●Table 10.3 for systems < 69 kV

●Defines limits for voltage notches caused by SCR rectifiers – Table 10.2

●Defines PCC (point of common coupling)


IEEE 519-1992

●Defines current distortion as TDD● Total Demand Distortion

●Largest amplitude of harmonic current occurs at maximum load of nonlinear device – if electrical system can handle this it can handle all lower amplitudes●Always referenced to full load current●Effective meaning of current distortion

●Defines voltage distortion as THD● Total harmonic voltage distortion

●Does not use THD(I)● Total harmonic current distortion● Instrument measurement (instantaneous values)●Uses measured load current to calculate THD(I)


IEEE 519-1992

Total I, rms

Fund I, rms

Harm I, rms THD(I) TDD

Full load 936.68 936.00 35.57 3.8% 3.8%836.70 836.00 34.28 4.1% 3.7%767.68 767.00 32.21 4.2% 3.4%592.63 592.00 27.23 4.6% 2.9%424.53 424.00 21.20 5.0% 2.3%246.58 246.00 16.97 6.9% 1.8%111.80 111.00 13.32 12.0% 1.4%

Measured

• TDD and THD(I) are not the same except at 100% load

• As load decreases, TDD decreases while THD(I) increases.

• Example:


IEEE 519-1992 Table 10.3Current Distortion Limits for General Distribution Systems (<69 kV)

Isc / Iload <11 11<=h<17 17<=h<23 23<=h<35 h>=35 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% 0.2% 1.0% 15.0%>1000 15.0% 7.0% 6.0% 2.5% 1.4% 20.0%

Isc = short circuit current capacity of sourceIload = demand load current (fundamental)

(TDD = Total harmonic current distortion measured against fundamental current at demand load.)

TDD = Total Demand Distortion


Harmonic Standards

• Most harmonic problems are not at the PCC with utility. Typically harmonic problem occur:

• Within a facility• With generator & UPS operation• Where nonlinear loads are concentrated

• Need to protect the user from self by moving the harmonic mitigation requirements to where harmonic loads are located


Agenda

I. Harmonic Basics II. Conventional Harmonic Mitigation MethodsIII. AccuSine® PCSIV. ApplicationsV. Specification RecommendationsVI. Summary


Harmonic Mitigation Methods

●Typically applied per device● Line reactors/DC bus chokes/isolation transformers● 5th harmonic filters (trap filters)●Broadband filters●Multi-pulse transformers/converters●Active front end (AFE) converter

●System solution●Active harmonic filter

Harmonic mitigation methods - (Applied per VFD)

Solution Advantage DisadvantageTypical %

TDDTypical Price

Multiplier*Increase short circuit capacity Reduces THD(V)

●Increases TDD ●Not likely to occur**

Dependent upon SCR***

Cost of transformer and installation change out

C-Less Technology

●Lower TDD●Simplified design●Less cost

●Compliance is limited ●Application limited●Size limited 30 - 50% TDD 0.90 - 0.95

Impedance (3% LR or 3% DC choke)

●Low cost adder●Simple ●Compliance difficult 30 - 40% TDD 1.05 - 1.15

5th Harmonic filterReduces 5th & total TDD

●Does not meet harmonic levels at higher orders^ 18 - 22% TDD 1.20 - 1.45

Broadband filterReduces TDD (thru 13th)

●Large heat losses ●Application limited 8 - 15% TDD 1.25 - 1.50

12-pulse rectifiers●Reduces TDD ●Reliable

●Large footprint/heavy●Good for >100 HP 8 - 15 % TDD 1.65 - 1.85

18-pulse rectifiers●Reduces TDD●Reliable

●Large footprint/heavy ●Good for >100 HP 5 - 8% TDD 1.65 - 1.85

Active front end converter

●Very good TDD ●Regeneration possible

●Large footprint/heavy●Very high cost per unit ●High heat losses < 5% TDD 2.0 - 2.5

* Price compared to a standard 6-pulse VFD.** Utilities and users are not likely to change their distribution systems.*** Increasing short circuit capacity (lower impedance source or larger KVA capacity) raises TDD but lowers THD(V).^ Can be said for all methods listed.


Harmonic mitigation methods

Solution Advantage DisadvantageTypical %

TDDTypical Price

Multiplier*Increase short circuit capacity Reduces THD(V)

●Increases TDD ●Not likely to occur**

Dependent upon SCR***

Cost of transformer and installation change out

C-Less Technology

●Lower TDD●Simplified design●Less cost

●Compliance is limited ●Application limited●Size limited 30 - 50% TDD 0.90 - 0.95

Impedance (3% LR or 3% DC choke)

●Low cost adder●Simple ●Compliance difficult 30 - 40% TDD 1.05 - 1.15

5th Harmonic filterReduces 5th & total TDD

●Does not meet harmonic levels at higher orders^ 18 - 22% TDD 1.20 - 1.45

Broadband filterReduces TDD (thru 13th)

●Large heat losses ●Application limited 8 - 15% TDD

12-pulse rectifiers●Reduces TDD ●Reliable

●Large footprint/heavy●Good for >100 HP 8 - 15 % TDD 1.65 - 1.85

18-pulse rectifiers●Reduces TDD●Reliable

●Large footprint/heavy ●Good for >100 HP 5 - 8% TDD 1.65 - 1.85

Active front end converter

●Very good TDD ●Regeneration possible

●Large footprint/heavy●Very high cost per unit ●High heat losses < 5% TDD 2.0 - 2.5

* Price compared to a standard 6-pulse VFD.** Utilities and users are not likely to change their distribution systems.*** Increasing short circuit capacity (lower impedance source or larger KVA capacity) raises TDD but lowers THD(V).^ Can be said for all methods listed.

AccuSine

AccuSine


Inductors/Transformers/DC Bus ChokesDescription:Converter-applied inductors or isolation transformers.●Pros:

● Inexpensive & reliable● Transient protection for loads● 1st Z yields big TDD reduction (90% to 35% w/3% Z)● Complimentary to active harmonic control

●Cons:● Limited reduction of TDD at equipment terminals after 1st Z● Reduction dependent on source Z


5th Harmonic Filter (Trap Filter)• Inductor (Lp) and Capacitor (C) provide low impedance source for a single frequency (5th)

• Must add more tuned filters to filter more frequencies

• Inductor Ls required to detune filter from electrical system and other filters

• If Ls not present, filter is sink for all 5th

harmonics in system

• If Ls not present, resonance with other tuned filters possible

• Injects leading reactive current (KVAR) at all times – may not need

LoadVs

Zs

Lp

C

Ls


• Mitigates up to 13th order or higher• Each inductor (L) > 8% impedance

• V drops ~ 16% at load• Trapezoidal voltage to load

•Can only be used on diode converters• Prevents fast current changes (only good for centrifugal loads)• When generators are present, re-tuning may be required

• Capacitor (C) designed to boost V at load to proper level (injects leading VARs)• Physically large• High heat losses (>5%)• Series device

Broadband Filters

Load

Source

L L

C

~Lp


Multi-Pulse Drives

Description: Drives/UPS with two (12 pulse) or three (18 pulse) input bridgesfed by a transformer with two or three phase shifted output windings.●Pros:

● Reduces TDD to 10% (12 pulse) & 5% (18 pulse) at loads● Reliable

●Cons:● High installation cost with external transformer● Large footprint (even w/autotransformer)● Series solution with reduction in efficiency● One required for each product● Cannot retrofit


Harmonic mitigation methodsVFD mitigation topologies

6-Pulse converter

“C-less” or 3% reactance min (if included); small footprint, simplified cabling

Current waveform distortedTDD 30% to 40% with 3% reactor (depending on network impedance)

Externally mounted 3 winding transformer; more wire andcabling; complicated

Current slightly distortedTDD 8% to 15% (depending on network impedance)

12-Pulse converter 18-Pulse converter

Large footprint, more steel& copper (losses)

Current wave form goodTDD 5% to 7% (depending on network impedance)

0

100

A

6 pulse

0

100

A

12 pulse

0.0s 0.02s

0

100

A

18 pulse

+

-

DC Bus Load

Delta

Delta

Wye

AC Line

A

B

C

DC+

DC-

LineReactor

Rectifier Assembly

TransformerTertiary

MultipulseTransformer

A

BC

1

2

3

4

56

7

8

9

DC LinkReactor

M


Active Front End (AFE) Converters●Used in UPS and VFD●Replaces diode converter with IGBT converter●The hype

●Permits current smoothing on AC lines (< 5% TDD)●Permits 4-quadrant operation of VFD●Maintains unity TOTAL PF ●Meets all harmonics specs around the world

AC

Source

Filter Converter Inverter

DC Bus

AC Motor

IGBT IGBT

VFD

Input Filter Required to limit THDv to <5%


AFE ConvertersSignificant harmonics above 50th order

American Bureau of Shipping (ABS) requires examination to 100th order when AFE applied

Higher frequencies yield higher heating of current path & potential resonance with capacitors


AFE Converters●Cons

● Larger and more expensive than 6 pulse drives●Approximately twice the size & price

●Mains voltage must be free of imbalance and voltage harmonics

●Generates more harmonics●Without mains filter THD(V) can reach 40%●Requires short circuit ratio > 40 at PCC●Switched mode power supplies prohibited●Capacitors prohibited on mains● IGBT & SCR rectifiers prohibited on same mains

●No other nonlinear loads permitted

200 KVA rated

PWM VFD

DC Drive

PF caps

100 KVA rated

AFE VFD


Agenda

I. Harmonic Basics II. Conventional Harmonic Mitigation Methods

III. AccuSine® PCSIV. ApplicationsV. Specification RecommendationsVI. Summary


The System Solution●The System Solution:

●Single point of responsibility for the ‘total’ harmonics●One specification for harmonic definitions●One validation responsibility and guarantee

● Standard nonlinear products● 3% input line reactors on most non-linear devices, 3% DC bus choke okay for

PWM VFD● Limits rms current at load for diode rectifiers● Avoids interaction with snubber circuit for SCR rectifier

●Best cost and performance

● Compatible with all nonlinear products●Compliance with harmonic specifications●Controls harmonic levels with facility


Schneider Electric’s Solution

● AccuSine Power Correction System (PCS)● Active harmonic filter

● Provides 5% TDD per load or system● Cancels everything from 2nd to 50th harmonic order● Used on any/all nonlinear load

● Active reactive current correction ● Does not use PF capacitors● Used to correct Displacement PF● In conjunction with or independent of harmonic control (dual mode)● High-speed reactive power


Active Harmonic Filter System Solution

● Applied to one or many nonlinear loads● VFD, UPS, UV, DC drives, DC power supplies

● Provides DPF correction● More cost effective for multiple loads

● For two or more drives, AccuSine and 6 pulse drive combination has lower initial and operating costs than 18 pulse drives● For installations with redundant drives, size AccuSine for the operating drives only

● Saves space● Lower heat losses● Not critical to operation

●Parallel connected


Comparison of 18-P VFD to AccuSine PCS + standard VFD

●Footprint required●AccuSine PCS+ Std VFD less than 18-P VFD

(w/autotransformer) for all conditions●Heat losses

●AccuSine PCS+ Std VFD less than 18-P VFD ●Exception at single units of 50-75 HP, advantage 18-P VFD

●Less costly to operate AccuSine PCS+ Std VFD● Less site cooling required with AccuSine PCS + Std VFD

●Price (first cost)●When more than one VFD, AccuSine PCS + Std VFD always

beats 18-P VFD● If only one VFD involved, 300-500 HP sizes favor 18-P VFD


AccuSine Active Harmonic Filter

AHFLoad

CT

Source L

Is

Ia

I l

~

AHF•Parallel connected

•Is + Ia = Il•Ia includes 2nd to 25/50th

harmonic current

•Is <5% TDD


AccuSine® PCS Power Diagram

+C

E

C

E

C

E

C

E

C

E

C

E

C

LineInductor

FilterBoard

Pre-charge Contactor

Inductor

Fuse

Fuse

Fuse

ACLines

DC Bus Capacitors

S4

S5

S6

S1

S2

S3

IGBT Module


System Solution

AccuSine® PCS Sizing Example

● A 125 HP variable torque 6-pulse VFD with 3% LR● Required AHF filtering capability = 47.5 amperes

● Two 125 HP VT 6-pulse VFD w/3% LR● Required AHF size = 84.4 amps

● Three 125 HP VT 6-pulse VFD w/3% LR● Required AHF size = 113.5 amps

● Six 125 HP VT VFD w/3% LR● Required AHF size = 157.6 amps

● (not 6 x 47.5 = 285 amps)


AS off AS onOrder % I fund % I fundFund 100.000%100.000%3 0.038% 0.478%5 31.660% 0.674%7 11.480% 0.679%9 0.435% 0.297%11 7.068% 0.710%13 4.267% 0.521%15 0.367% 0.052%17 3.438% 0.464%19 2.904% 0.639%21 0.284% 0.263%23 2.042% 0.409%25 2.177% 0.489%27 0.293% 0.170%29 1.238% 0.397%31 1.740% 0.243%33 0.261% 0.325%35 0.800% 0.279%37 1.420% 0.815%39 0.282% 0.240%41 0.588% 0.120%43 1.281% 0.337%45 0.259% 0.347%47 0.427% 0.769%49 1.348% 0.590%TDD 35.28% 2.67%

AccuSine Performance

AccuSine injection

Source current

At VFD Terminals


700 HP Drive – AccuSine ON – OFF


Applications

● Most common – VFD sites●Centrifugal pumps and fans

●Pumping Stations– Potable – Wastewater

●Wastewater Plants●Water Purification (potable)

● Disinfectant Systems●UV systems (ultraviolet)

– Electronic ballasts – 3Φ●Ozone generators (SCR power supplies)

● Industrial – in-rush support


AccuSine PCS Specifications

● Universal Application● 208 – 480 VAC

● No user action required to set● Highly customized transformers for higher voltages (to 15 kV)

● 50 or 60 Hz● Fuse protected (200,000 AIC)● UL 508 & CSA approved● CE EMC - 400V● Logic ride through – 1 to 10 minutes


Specification Discussion

●Write a specification in Section 16 for an active harmonic filter● Specify any points of concern for insertion of AHF

●Size of AHF ●Located per electrical bus

● Specify total responsibility for all harmonics in facility● Specify TDD levels desired at each location

●5% TDD guarantees 5% THDv (caused by the loads) with any source● Specify compliance tests for each location

●Write standard nonlinear load specification●Reduces harmonic incompatibilities and product interactions●Need 3% impedance on each nonlinear load

●Universal solution● Good for all nonlinear loads● Apply AccuSine per electrical bus (best economics)

●Can attain 5% TDD per load or bus inside the plant● Avoids harmonic problems – both TDD and THD(V)

●Write TDD specs not THD(I) at 5%


AccuSine Tools● Internet Tools

●Active Filter Guide Spec (www.reactivar.com)● Stand alone spec section (Section 16)● Includes harmonic and PF correction requirements

●Selection Program (www.squaredleantools.com)● Easy selection based upon loads not source (same selection for utility or generator)● Simple tool to use● We guarantee results if used properly during design/layout stage

●Brochure●Application Notes

● Water/wastewater and other applications● Installation Bulletin

● Best/total information for consultant●MCC Selector


Product Package●Standard (UL only)●Enclosed – NEMA 1

● 50 amp – 48”H x 21”W x 19”D, 250 lbs● 100 amp – 65”H x 21”W x 19”D, 350 lbs

●Wall mounted● 300 amp – 75”H x 32”W x 20”D, 775 lbs

●Free standing●Chassis & NEMA12 Also Available


Product Package

● International enclosures●NEMA 12, IP30, IP54

●50 amp – 75”(1905mm) x 31.5”(800mm) x 23.62”(600mm)●Weight – 661Ib(300Kg)●100 amp – 75”(1905mm) x 31.5”(800mm) x 23.62”(600mm)●Weight – 771Ib(350 Kg)●300 amp – 91”(2300mm) x 39.37”(1000mm) x 31.5”(800mm)●Weight – 1212Ib(550 Kg)

● Free standing with door interlocked disconnect

●CE Certified, C-Tick, ABS, UL, CUL


Product Re-packaging

●Maximum ambient into air inlet – 400C●Must meet air flow at inlet of AccuSine

● 50 amp – 300 CFM● 100 amp – 500 CFM● 300 amp - 1250 CFM

●Heat released● 50 amp – 1800 watts● 100 amp – 3000 watts● 300 amp – 9000 watts

●DIM considerations required●On chassis●Remote with cable


Product Re-packaging●MCC Packaging

● 50 & 100 amp models only●Requires one vertical 20” x 20” section● Includes circuit breaker


AccuSine PCS Current Transformers●AC lines

●Class 1● 400 Hz● Four sizes

●500:5/1000:5/3000:5/5000:5●Stock split core – round units

●Added to AccuSine (when parallel connected & source sense)●Use solid core at equal ratio as AC lines CT


AccuSine PCS Performance

Source XFMR

Load(s)

Is

Ias

•AccuSine Logic

•Is + Ias = Il

•AccuSine injects the harmonics the loads want

DEFINITIONS

Is = source current

Ias = AccuSine current

Il = total load current

(vector representations)

Il


AccuSine PCS Performance

●Obtain 5% TDD (current distortion)●Overall 10:1 attenuation

●Cos δ = .998●Obtain near unity lagging DPF (Cos φ)

●Optional: Inject to obtain a user set point ●Either or both functions●VAR compensation

● 100 μsecond detect-to-inject●Dynamic response

●½ cycle to full control for step load changes


AccuSine PCS Overall Performance●Harmonic compensation

● 2nd through 50th order ● Includes inter-harmonics● Independent of source impedance

●Selection and operation same whether on AC line or backup generator or UPS output

●Reactive current injection●Secondary function to harmonic mode●Defaults to unity lagging set point● Injects leading or lagging reactive current


AccuSine PCS Cos φ Performance● In dual mode (Cos δ + Cos φ)

●Reactive current injection is secondary to harmonic mitigation●Activation of Cos φ in the field via DIM●Default to unity lagging Cos φ

●Can enter a set point (i.e. 0.90 lagging)●Can inject leading (capacitive) or lagging (inductive) reactive current


Dual Mode Operation

Ias = rms output current of AccuSine

Ih = rms harmonic current

Ir = rms reactive current

Ias = Ih2 + Ir

2

Ias Ih Ir100.0 10.0 99.5100.0 20.0 98.0100.0 30.0 95.4100.0 40.0 91.7100.0 50.0 86.6100.0 60.0 80.0100.0 70.0 71.4100.0 80.0 60.0100.0 90.0 43.6100.0 95.0 31.2

Examples


AccuSine PCSInstallation Considerations(When in ‘harmonic mode’ – does not apply for ‘reactive mode-only’)


AccuSine PCS Installation Considerations● For Optimal Performance:

● Impedance – 3% input line reactors (minimum) on every nonlinear load● Transformer, 3% DC bus choke for PWM VFD or long power cables (not encapsulated type) can substitute for line reactors● Standardizes selection of AccuSine ●Diode rectifiers: Need to limit rms current at load (limits rise of Ihrms at load)●Thyristor rectifiers: Need to protect snubbers (capacitors) on thyristor

●No capacitors downstream of CT


AccuSine PCS Installation Considerations

This configuration provides individual AccuSine operation per side regardless of breaker positions.

Main – Left Main – Right

CBml CBmr

Tie

CTml CTtl CTtr CTmr

AccuSine RAccuSine L

CBal CBar

Main-tie-main


Summary

●Universal solution●Good for all nonlinear loads (3-phase)●Apply AccuSine per electrical bus (best economics)

●System Solution●Can attain 5% TDD per load or bus inside the plant

●Guarantees 5% THDv●Requires 3% impedance at loads

●Selection based upon loads●Easy to use on-line tool

●www.squaredleantools.com

http://www.squaredleantools.com/


Thank You

Questions?

Power Quality and Harmonic Mitigation 1

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