international inc. lineator case study: rambam hospital israel · spectrum of higher frequency sine...

Lineator™ Case Study:Rambam Hospital Israel

Challenge

Solution

International Inc.

Rambam Health Care Hospital and Campus in Haifa, Israel, is a 1,000-bed academic hospital serving more than two million people in northern Israel. Rambam Hospital is also the backup referral center for twelve district Hospitals, the Israel Defense Forces Northern Command, the US Navy Sixth Fleet and the UN Peacekeeping Forces posted in the region.

After the new 240kW Chillers were installed the Hospital maintenance team noted that the power transformer feeding the Chillers were severely damaged and caused unplanned interruptions until it had to be replaced. In addition, it was not possible to operate both new Chillers simultaneously, as the overheating activated the overload protection. Even while

by Mirus International to solve their harmonic challenge. There were several key advantages the LINEATOR™ provided over the other methods:

Maintenance-free passive filteringSeries connected to the gridOne single magnetic core construction with multiple

windingsProvides the lowest losses Very small capacitor bank <15% of the kVA of the load allows

compatible operation with diesel generatorsGuaranteed compliance to IEEE 519-1992 at the input

terminals of the filterThree (3) year standard warranty

P.Q. Tech, a company specialized in analyzing and correcting power quality issues installed two 300HP LINEATORs (Fig. 3) with each unit connected to one drive for maximum filtration and flexibility.

In an effort to save energy the hospital purchased two new Chillers at 240kW each for their cooling system. The new Chillers were to replace an aging and inefficient single 600kW Chiller which was part of the 5000 ton cooling array. The new Chillers were equipped with VFD’s which consume far less energy per cooling ton but draw current from the electrical supply in nonlinear pulses instead of linear sine waves due to their construction (Fig. 1).

As nonlinear pulsing currents (Fig. 2) reached higher values their interaction with the system impedance caused the hospital’s supply voltage to become increasingly distorted. The distorted system voltage affected the reliable operation of sensitive equipment in the hospital that any interruption, even extremely short, may lead to loss of life. Due to the importance of this issue, the IEEE

running a single Chiller, it was hotter than expected and the HVAC plant manager was afraid that the new transformer would fail.

Even though the Chiller VFD’s were supplied complete with series connected input AC line reactors, a common practice for basic harmonic filtration, the reactors did not lower the harmonic current distortion low enough. Series AC line reactors can only lower the current harmonics to about 35%.

Several harmonic mitigation methods were researched by the hospital maintenance team and management team and were considered as possible solutions (Table 1).

After much review the hospital’s management team selected the LINEATOR™ Passive Harmonic Filter

519 1992 Standards specify < 3% Total Harmonic Voltage Distortion (THD (V)) for hospitals and airports compared to other applications where THD (V) of <5% is acceptable.

In addition to the problems created by higher levels of THD (V) the nonlinear pulsing currents (Fig. 2) were made up of a spectrum of higher frequency sine wave currents ranging from the 5th (5 x 50 = 250 HZ), 7th, (7 x 50 = 350 HZ) 11th 11 x 50 = 550 HZ) 13th (13 x 50 = 650 HZ) etc.

These higher frequency harmonic currents caused over heating of cables, transformers and generators due to increased I2R losses and eddy current losses. Over heating will lead to nuisance operation of overload devices and increased risk of fire in transformers, cables and generators.

The harmonic frequencies (Fig. 2) are reflected onto the system voltage waveform. Some of the frequencies have a positive sequence, but those that have a negative sequence actually create counter torque on AC motors that are running directly across the line.

Fig. 1: Variable Frequency 6-Pulse Drive Structure

Fig. 2: Variable Frequency 6-Pulse Input Current Waveform

ResultsThe installation of the LINEATORS enabled the simultaneous operation of the two Chillers by reducing the harmonic pollution by more than 2/3 and lowering voltage distortion from almost 4% to <1.5%, well below the IEEE 519-1992 requirements. The operation temperature of the drives and Chillers was reduced by more than 10°C, increasing their life time and reliability.

Figure 4 shows the current waveform without and with the filtration; Figures 5 and 6 shows the voltage harmonics and the current harmonics respectively. It can be clearly seen that the harmonic pollution exceeded the IEEE 519-1992 levels before the installation of the filters and are well below afterwards.

Installation of the LINEATOR™ Advanced Universal Harmonic Filter on the new Chiller VFD’s ensures compliance to harmonic pollution levels and smooth operation of the Chillers. The no-setup approach, requiring just fitting the filter to the drive rating and motor type, provides the best solution for reduced harmonics in this retrofit system and is also ideal for application at the design stage for new construction. Specifying LINEATOR™ on VFD applications will ensure that harmonic pollution limits are met.

Study conducted by: Mr. Menachem Bercholz, Mr. Al Archambault, Mr. Amir Broshi

Mirus International Inc.31 Sun Pac Blvd.Brampton, OntarioCanada L6S 5P6

www.mirusinternational.com

1-888-TO MIRUS (1-888-866-4787)

About Mirus InternationalMirus designs and develops world class power quality improvement products for mission critical operations. Their uniquely specialized product line includes highly efficient harmonic filters, transformers, autotransformers and Data Center power distribution equipment. Comprised of a leading team of power quality experts, Mirus’ solutions minimize disruption to the power supply, improve reliability and adhere to the strictest of regulatory requirements while also saving energy. Proven to perform, Mirus products are available globally and are real-world tested in its own Harmonics & Energy (H&E) Lab.

ProsSolution

Do Nothing

Series Reactor

Improved Drives(12/18 pulses, AFE)

Traditional LC Trap Filters

Active Harmonic Filter

Passive Harmonic Filter(LINEATORTM)

Low price

Simple low cost

Low harmonic pollution

Low harmonics

Suitable for any load and variable conditions

Excellent filtration guaranteed to meetIEEE 519 at the input terminals of the filter.Very small capacitor bank < 15% of the kVA ofthe load. Most efficient solution.

Cons

Does not work

THD(I) reduced to only 35%

Expensive, 2 to 3% extra losses. Need maximumfloor space.

Capacitor banks must be 40% of the kVA of theload

Very expensive 1% extra losses. Not reliable.Needs large floor space.

Requires some floor space but less than otheroptions.

Table 1: Solutions for Harmonic Mitigation

Fig. 3: Two 300HP LINEATORS at Rambam Hospital

Fig. 4a: Current Waveform without Filtration

Fig. 4b: Current Waveform with Filtration

Fig. 5: Voltage Harmonics with and without Filtration and IEEE 519-1992 Level

Fig. 6: Current Harmonics with and without Filtration and IEEE 519-1992 Level

GENLINK™ Case Study:Fast Food Industry Distribution Warehouse

Mirus International Inc.31 Sun Pac Blvd.Brampton, OntarioCanada L6S 5P6


1-888-TO MIRUS (1-888-866-4787)

Challenge Solution

Results

International Inc.

A large distribution facility servicing the fast food industry in Conroe, Texas had recently decided to expand its standby generation capacity and added a 1000 kW generator to the existing 750 kW unit at the site. The electrical contractor and generator supplier noticed that there was an excessive amount of neutral circulating current when both generators were paralleled and if left untreated could cause the generators to overheat or the circuit protection to trip inadvertently.

What the electrical contractor and generator supplier had failed to do was consider the fact that the winding pitch of the new generator was different than the winding pitch of the existing generator. Neutral circulating current will appear in paralleled generators that have different winding pitches due to the slight difference in voltage waveshape that each generator produces. This neutral current will typically be 3x the fundamental frequency and is often quite significant in magnitude. The amount of current being dependent upon the zero sequence impedance of the generators and cables and the instantaneous voltage difference that exists between the paralleled phase conductors.

The new 1000 kW generator had a 5/6P winding while the existing 750 kW generator was 6/7P. The circulating current that resulted was measured by the electrical contractor to be in excess of 150A. It was imperative that a solution be found to reduce this circulating current to prevent the possibility of generator overheating or false protection trips. Neutral Circulating Current Eliminated –

Mirus’ GenLink DPNL eliminated the neutral circulating current created by paralleling generators with different winding pitches.

• Expert Problem-Solving – Mirus and NSOEM provided the expertise that was needed to diagnose the problem and recommend a solution that met the client’s needs and specifications.

• On-site Support and Real-World Testing – By providing installation support and on-site testing, Mirus and NSOEM were able to ensure GenLink DPNL was installed successfully and performed to expectation.

The electrical engineer contacted Mirus International and NSOEM Inc., the Sales Representative for Mirus in Texas, for problem analysis and recommendations for corrective action. After review of the 1-line diagram and field measurements provided by the contractor, the application of a Mirus’ GenLink DPNL (Dissimilar Pitch Neutral Limiter) was recommended.

GenLink DPNL is specially designed and engineered to solve the challenges that arise when paralleling generators with different pitch properties and when paralleling 4-wire utility feeds with alternative energy supplies. A multiple winding reactor, GenLink DPNL is installed in the common neutral where it blocks the flow of circulating currents without significantly decreasing the 1-phase fault level of the system. The unique winding configuration accomplishes this by introducing approximately 45% impedance in the neutral circulating path at the triple frequency while adding < 1% impedance in the 1-phase fault path during a fault condition.

Mirus and NSOEM provided additional support with on-site testing, installation supervision and performance verification. Upon GenLink DPNL being installed, tests were run under peak load conditions which found that virtually all of the circulating current was eliminated.

About Mirus InternationalMirus designs and develops world class power quality improvement products for mission critical operations. Their uniquely specialized product line includes highly efficient harmonic filters, transformers, autotransformers and Data Center power distribution equipment. Comprised of a leading team of power quality experts, Mirus’ solutions minimize disruption to the power supply, improve reliability and adhere to the strictest of regulatory requirements while also saving energy. Proven to perform, Mirus products are available globally and are real-world tested in its own Harmonics & Energy (H&E) Lab.

Total neutralcurrent = 160A

G1 G2

N

750kW(6/7 Pitch)

1000kW(5/7 Pitch)

Two Dissimiliarily Pitched Generators

G1 G2

N

750kW(6/7 Pitch)

1000kW(5/7 Pitch)

Two Dissimiliarily Pitched Generatorswith GENLINK™

1300AGENLINK™

24.6A 17.1A

38.4A

"Lineator provided the perfect power quality solutionfor our generator-fed MCC arrangements."

- Dave Challoner

Case Study: Natural Gas Sweetening Plant


1-888-TO MIRUS

ScenarioA natural gas processing and transportation company, located inBritish Columbia, Canada, had commissioned the installation of 8Motor Control Centers (MCC's), each exclusively loaded withadjustable frequency drives, for an upgrade at one of their naturalgas sweetening plants. Since the plant power supply is entirelyfed by on-site turbine generators,the heavy concentration of drivesraised significant concern aboutharmonics and their effect on powerquality.

To process sour natural gas for safetransport, poisonous hydrogensulfide (H2S) must be removed.The process trains at the plant usean aqueous amine solution toabsorb the H2S. The liquid requiresa carefully controlled temperature,which is regulated with cooling fans.The MCC's each contained seven480V adjustable frequency drives(1x40hp, 4x50hp, 2x60hp), runninga configuration of fans to controltemperature in the amine trains.This critical process demanded high reliability and stability in powerquality which could not be assured by using standard methods ofharmonic reduction, such as line reactors, especially with the highimpedance generator source. 12- and 18- pulse solutions werenot practical due to the cost of the technology on each of the smalldrives. Tuned filters posed a risk as knowledge of harmonics fromthe rest of the power system were difficult to calculate making it allbut impossible to determine proper sizing. There was alsouncertainty about the long-term reliability of active filter solutions.

SolutionDave Challoner, the engineer managing the project, turned to theLINEATORTM Universal Harmonic Filter from Mirus InternationalInc. upon recommendations from the drive supplier. "LINEATORTMoffered premium harmonic attenuation, a reliable passive filterdesign, and system independency," remarked Dave.

The ability to apply one LINEATORTM to each MCC also made itcost effective and easy to install."

The installation of the LINEATORTM was a tremendous success.Without correction devices, Total Harmonic Voltage Distortion on

the 480V switchgear supplying the8 amine train MCC's was expectedto exceed 16.5%, with CurrentDistortion as high as 40%. TheLINEATORTM proposed to bringVoltage Distortion below 5% andCurrent Distortion below 8%. Actualperformance exceeded bothpredicted levels, with voltage andcurrent distortion measured at 1.9%and 5.7% respectively while runningat near full load, well below theproject target and IEEE 519guidelines.

BenefitsLINEATORTM proved to be the rightsolution for this installation,because:

• The LINEATORTM was system independent and did not requirevaluable engineering time spent evaluating exact fault levelsand harmonics on the rest of the power distribution system

• Installation of a single LINEATORTM on multiple drives (in thiscase, an MCC line-up) was simple, space-saving, and relativelyeconomical

• The simple yet robust LINEATORTM filter design was consideredto be inherently more reliable than a complex electronic active-filter system

• The measured performance of the LINEATORTM exceededexpectations

SummaryResolving the potential harmonic problems with the generator-fed MCC application of drives was a real challenge. LINEATORTMdelivered, solving the installation and power quality concernsreliably and cost-effectively.

Mirus International, Inc.31 Sun Pac Blvd.Brampton, OntarioCanada L6S 5P6

At Chevron, we want to achieve themost harmonic reduction for ourdollar.

- Peter O'Brien, Chevron

Case Study: Chevron’s Simonette Well Site

ScenarioWhen Chevron uses adjustable speed drives to control motors that operate submersible pumps inremote, unmanned oil wells, they require high reliability in power systems to achieve financialobjectives. Therefore, harmonic control to ensure power quality is paramount.

Each well in far Northern Alberta features a single, low voltage adjustable speed drive and supplytransformer. Since the drive is the only load on the transformer, current in the system is rich inharmonic frequencies. In addition, since well sites are unmanned, control and communicationsystems must be safeguarded against interference or failure. The combination of the risk of highharmonics, and the need for high-reliability in these systems, drove Chevron to evaluate all of theiroptions.

Engineers at Chevron decided to take preventive measures tolimit harmonics at well sites. For applications where a lowvoltage drive is the only non-linear load, and when it is arelatively low horsepower (1000 HP or less), Chevron selectedMirus' LINEATOR™ Universal Harmonic Filter (UHF).

Solution"LINEATOR™ did as promised", said Peter O'Brien, ChevronElectrical Engineer. "Our experience was with multi-pulsedrives. We have used 12-pulse drives. However, in order toachieve the harmonic limits that we need, we realized that wemust either purchase 18-pulse drives or evaluate otheroptions. Our drive supplier had fully tested and recommendedLINEATOR™ as a power quality solution, and that was enoughfor us."

Chevron's Simonette well site features a 200 kVA servicetransformer, a 150 kVA, 480 volt adjustable speed drive and a150 horsepower UHF.

BenefitsLINEATOR™ proved to be the right solution for Chevron, because:

The LINEATOR™ was 9% less expensive than the cost to configure a drive for a 12-pulseoperation in this application.Installation was easier for Chevron. The LINEATOR™ is essentially "plug and play".The LINEATOR™ required no factory testing. (A multi-pulse system may have requiredtesting to ensure correct phase shift and load sharing.)The LINEATOR™ provided better-than 18-pulse performance.

SummaryAt the Simonette well site, Chevron achieved two goals with LINEATOR™. They ensured highreliability in critical systems and did it cost effectively.

Mirus International, Inc.


1-888-TO MIRUS

31 Sun Pac Blvd.Brampton, OntarioCanada L6S 5P6

A New Solution for HarmonicsGenerated by Variable Speed Drives

In addition to its harmonic mit-igating capabilities, this widespectrum harmonic f ilter helpsprotect a VSD from transientovervoltages caused by capacitorswitching and other fast changingloads. It is suitable for virtuallyany application involving a VSDor similar 3-phase, 6-pulse diodebridge rectif ier load.

Harmonic ProblemsThe front-end diode bridge recti-

fiers of 3-phase, 6-pulse static powerconvertors (ac-dc), such as those foundin variable speed drives, are considerednonlinear because they draw current ina non-sinusoidal manner. The currentharmonics they generate are defined

by the following formula:

h = np ±1

Where:

h = the harmonics generated

n = any integer (1, 2, 3, etc.)

p = the rectifier pulse number

A simple 6-pulse rectifier (p =6) is shown in Figure 1. Withoutany harmonic treatment, the totalharmonic current distortion (THID)of this rectifier would be in the100-140% range with the predomi-nant harmonics being the 5th and7th. The 11th, 13th, and other higherorders are also present but at lowerlevels. In the example shown in

Figure 1, the 5th harmonic currentis about 75% of the fundamental(60Hz) current and the 7th nearly60%. This means that a rectifier ofthis configuration, which draws100A of 60Hz current, will alsodraw 75A of the 5th harmonic cur-rent and 60A of the 7th harmonic.

Power distribution systems carry-ing a heavy nonlinear load compo-nent will often experience problemscaused by excessive harmonic cur-rents. Problems that arise include:

• Power factor correction capaci-tor failures due to overloadingand/or system resonance

he need for harmonic mitigating devices is

growing because of the rapid increase in vari-

able speed drive (VSD) usage in industrial and

commercial applications and the corresponding growth

in harmonic-related problems. A new state-of-the-art

passive universal harmonic filter (UHF) is designed to

enhance the conversion of ac power to dc power within a

VSD or other equipment with a 3-phase, 6-pulse diode

bridge rectifier front-end.

Tony Hoevenaars, P.E., MIRUS International Inc., Toronto, Ontario

T

Editor’s Note:This article focuses on a

specif ic new product fromMIRUS International Inc.Although this article is manu-facturer-oriented, based uponthe information we observedwhen the product was dis-played at our recent PowerQuality ’99 conference, PQMagazine believes this prod-uct deserves to be presentedto our readers so that theymay investigate its claims ontheir own.

DECEMBER 1999

• Overheating cables, transformersand other distribution equipmentreducing their life span

• High voltage distortion (typical-ly in the form of flat-topping),especially when operating onweak sources such as emergencygenerators

• False tripping of circuit breakers

• Premature failure of rotatingequipment (motors, generators,etc.)

• Misoperation or component fail-ure in PLCs, computers or othersensitive loads

Existing Methods ofHarmonic Treatment forVSDs

There are several methodsavailable for treatment of VSDharmonics. Ac input reactors(either 3 or 5% impedance) arethe most commonly used treat-ment. They have a relatively lowcost but are only moderatelyeffective in reducing harmoniccurrent distortion (see Figure 2and Table 1 for typical values).The high impedance of ac inputreactors helps protect the drivefrom transient overvoltagescaused by capacitor switchingand/or fast changing loads butthey can often introduce trouble-some voltage drops at the rectif ierinput. Some VSDs are equippedwith a dc link reactor that isslightly more effective at reducingharmonic currents than the acreactor, and it does not cause anac voltage drop. The dc link reac-tor, however, is somewhat lesseffective than the ac reactor inovervoltage protection.

Conventional tuned LC or trapfilters, as their name implies,require tuning to a specif ic har-monic frequency. Usually, 6-pulserectif ier loads are tuned to themost predominant harmonic – the5th. Their effectiveness is limited,

however, unless multiple tunedelements are incorporated toremove the 7th and other higherorder harmonics. They are proneto problems such as importationof harmonics from upstream non-linear loads and the introductionof a leading power factor.

By treating a wider spectrum ofharmonics, low-pass filters aremore effective than tuned filters,but are also more expensive.Although they address some of theissues associated with tuned fil-ters, they are not problem-free.Specifically, their large seriesinductor necessitates the use of alarge capacitor bank to compen-sate for voltage drops. Thesecapacitors create a leading powerfactor that may cause excitationcontrol and voltage fluctuationproblems with generators.

In multipulsed systems, thedrive manufacturer will phase shiftbetween multiple front-end recti-fiers to cancel harmonics. Some18 and 24-pulsed systems canachieve THID levels of < 8%, butthey require a large footprint andare quite expensive. The applica-tion of phase shifting transformerscan be a very cost-effectivemethod of harmonic treatmentwhere multiple 6-pulse VSDs arein operation. A quasi 12-pulsescheme (i.e., cancellation of 5th

and 7th harmonics) can be createdby phase shifting one VSD againsta second similar VSD. The 18 and24-pulse schemes require threeand four VSDs, respectively.

Active f ilters treat harmonicsby measuring the level of harmon-ic current present in the systemand injecting currents of oppositepolarity to cancel them out.Excellent performance can beachieved but reliability is some-times an issue and their high costhas limited their use. Due to thedynamic characteristics associatedwith detection and treatment, fastchanging conditions may not beadequately addressed.

The Universal HarmonicFilter vs. OtherConventional PassiveFilters

The UHF is a purely passiveseries connected device, whichcan be installed at the input ofany 3-phase, 6-pulse diode bridgerectif ier to dramatically reduce itsinput current harmonics. Its revo-lutionary design achieves cancel-lation of all the major harmoniccurrents generated by the rectif ier,resulting in THID of <8% andoften as low as 5%. This meetsIEEE std 519 harmonic currentlimits for all but the weakest ofsupply sources. The unique fea-ture of the UHF is its 3-phasereactor design consisting of multi-ple windings on a common mag-netic core. This reactor allows forthe use of a much smaller capaci-tor bank without sacrif icing f ilterperformance or introducing unac-ceptable voltage drops. Capacitivereactive power is typically 3-4xlower than that of conventionalf ilters. This is signif icant inreducing cost and space require-ments. Moreover, it preventspower system interaction prob-lems that often result from a lead-ing power factor.

The large capacitor banksfound in both tuned and low-passf ilters present a capacitive reac-tance to the system, especiallyunder light loads. This is a bene-f icial feature where inductiveloads require a compensatingreactance to improve a low dis-placement power factor. But inmost VSD applications, displace-ment power factor is close tounity even though overall powerfactor may be low due to the har-monic content in the current.Compensation for inductive loadsis usually not necessary and, infact, can cause problems, espe-cially when supplied by an emer-gency standby generator. To

address this issue, some f ilter manufacturers offermechanisms for switching out the capacitors underlight loads, which increases cost and complexity.Even under no load conditions, the capacitive reac-tance of the UHF is so low that switching out thecapacitors is unnecessary.

Another concern with tuned f ilters is that unlessthey incorporate a detuning reactor in series with thesupply feeder, they can easily be overloaded byattracting harmonics from upstream sources. Thedetuning reactor will introduce a voltage drop at thedc bus as load is applied to the VSD. The multiplewinding configuration of the UHF, on the otherhand, prevents the attraction of harmonics fromupstream sources without introducing an excessivevoltage drop as VSD load increases.

The f iltering effectiveness of a tuned f ilter isdependent upon the amount of harmonics present atuntuned frequencies as well as the residual at thetuned frequency. To obtain performance better than15% THID, multiple tuned branches are oftenrequired. Low-pass f ilters achieve <12% THID butrequire relatively large capacitor banks. Even largercapacitors are required if further reduction in THIDis desired. The UHF reduces current distortion to<8% over the entire operating range and typicallyachieves near 5% THID at normal operating levels.

Simulation of Harmonic FilterPerformance

As previously mentioned, many of today’s VSDsare equipped with either ac line reactors or dc linkchokes to reduce harmonic current distortion.Computer simulation allows us to compare thesesolutions with the UHF. The circuit diagram shownin Figure 1 was used to simulate a 5kW, 380V 6-pulse diode bridge rectif ier. Five different harmonictreatment schemes were analyzed as follows:Scheme 1 – No harmonic treatment

Scheme 2 – With 3% ac line reactor

Scheme 3 – With 8 mH dc link choke

Scheme 4 – With both ac line reactor and dc link choke

Scheme 5 – With universal harmonic filter

The chart in Figure 2 plots the THID for eachscheme over the full operating range of the rectif ier.With no harmonic treatment, THID ranged fromnearly 180% at extremely light loading to 140% atfull load. The reactors implemented in Schemes 2, 3and 4 reduced the THID by approximately the sameamount. THID ranged from 100% near no load to 30-

Figure 1. Simple 3-phase, 6-pulse diode bridge rectifier withno harmonic treatment.

Figure 2. Total Harmonic Current Distortion through computersimulation of a 5kW, 6-pulse rectifier with various forms of pas-sive harmonic treatment.

Figure 3. dc bus voltage through computer simulation of a 5kW,380V 6-pulse rectifier with various forms of passive harmonictreatment.

35% at full load. The UHF was byfar the most effective in reducingTHID. At full load the THID wasreduced to about 5% and itincreased to 8% under more light-ly loaded conditions.

The computer simulations areconfirmed by f ield tests on a

60HP, 480V PWM variable speeddrive (see Table 1). While thereactors reduced current distor-tion by about 50%, the UHFachieved more than a 10 timesreduction. The current waveformwas nearly sinusoidal with itsspectrum containing only small

traces of harmonic content. Inaddition, removal of the harmoniccurrent improved power factor tovirtual unity.

The computer simulationshowed the variation in dc busvoltage at the output of the recti-f ier with the various forms ofharmonic treatment. With no har-monic treatment, the dc bus volt-age was fairly stable over theentire operating range (between545V to 520V). Additionalimpedance introduced by thereactors had a fairly signif icantimpact on the dc voltage level. Asexpected, the worst case was withScheme 4 when both the ac linereactor and the dc link chokewere in the circuit. At the fulloperating mode, the dc bus volt-age was nearly 10% lower thanfor the rectif ier with no treat-ment. In contrast, when equippedwith the harmonic f ilter, the dcbus voltage remained very stable,always at or above the valueswithout treatment.

Table 1. Performance comparison of various passive harmonic treatments on a 3-phase, 6-pulse, 60 HP Variable Speed Drive.

HARMONIC MITIGATING PRODUCTS

Onics HMPCHarmonic Mitigating

Power Center

Harmony SeriesHarmonic Mitigating

Transformers

Essential For:• Banks and Financial

Institutions• Software Developers• Internet Service

Providers• Broadcasting Studios• Telecommunications

Sites• Data Centers• Office Buildings

- new and old• School Computer Labs• Variable Speed

Drive UsersMirus International Inc.

6805 Invader Cres., Unit #12, Mississauga, ON, Canada L5T 2K6www.mirusinternational.com • [email protected]

1-888-TO MIRUS or 905-565-6900 • Fax: 905-565-6911

LineatorUniversal

Harmonic Filter

Eliminator SeriesZero SequenceHarmonic Filters

Reprinted with permission from the December 1999 issue of Power Quality Assurance.®

Copyright 1999, PRIMEDIA Business Magazines & Media Inc. All rights reserved.

CALL:

COMCAST OF NEW JERSEY 800 RAHWAY AVE., UNION, NEW JERSEY

MIRUS NEUTRAL CURRENT ELIMINATOR

PERFORMANCE REPORT

OCT. 16, 2001 MIRUS PROJECT # 1992-01

Prepared for: JOHN DUANE CHIEF ENGINEER COMCAST OF NEW JERSEY Prepared by: TONY HOEVENAARS VICE PRESIDENT MIRUS INTERNATIONAL INC.

MIRUS INTERNATIONAL INC. 31 Sun Pac Blvd., Brampton ON, CANADA L6S 5P6 . 1-888-TO MIRUS OR 905-494-1120 FAX: 905-494-1140 WWW.MIRUSINTERNATIONAL.COM

COMCAST: NEUTRAL CURRENT ELIMINATOR PERFORMANCE REPORT 2 _______________________________________________________________________

EXECUTIVE SUMMARY On Oct. 3, 2001 a 400 amp Neutral Current Eliminator™ (NCE™) was put into service at the Comcast Cable facility in Union, New Jersey. The NCE™ is a triplen harmonic filter and had been purchased to address harmonic concerns within the facility. These concerns included:

• An 80 kVA EPS 2000 UPS System supplying critical power to computer systems and broadcasting equipment within the facility that was running excessively hot while being loaded at about 85%. External fans had been installed to remove heat and cool down the UPS.

• Voltage distortion downstream of the UPS System was in excess of 10%. • Harmonic currents, more specifically the 3rd harmonic, were creating high neutral

current at the main power panel downstream of the UPS. • Neutral-ground voltage was above the commonly accepted maximum limit of 2

volts. The NCE™ was connected in parallel at the main power panel downstream of the UPS. By providing a low impedance path for the 3rd harmonic and other triplen harmonic currents, the NCE™ offloaded the neutral conductor and upstream electrical equipment. The NCE™ was extremely effective as demonstrated by the following improvements:

1. Neutral current returning from the main power panel back to the UPS was reduced from 144 amps to 18 amps, an almost 90% reduction. 2. Voltage distortion was reduced from over 13% to less than 3%, an over 80% reduction. 3. The reduction in harmonic currents reduced the loading on the UPS system from 85% to 78%. This resulted in a noticeable reduction in the UPS’s operating temperature. 4. Neutral-to-ground voltage at the main power panel was lowered from 2.4V to 0.4V.

5. Phase current imbalance at the main panel was substantially improved. By achieving the principle goals of reducing neutral current and offloading the UPS system, the NCE™ installation was extremely successful. Evidence of further benefits are expected to appear as improved equipment operation results from the dramatically lower voltage distortion and neutral-to-ground voltage at connected equipment.

BACKGROUND Computer systems and audio/video equipment, like most of today’s electronic equipment which utilize switch-mode power supplies, produce troublesome amounts of harmonic currents. By drawing current in a non-sinusoidal manner, these non-linear loads create


harmonics which circulate through the electrical distribution system. The most common problems which result are:

• Overheating neutrals, transformers and other electrical distribution equipment • Excessive voltage distortion and neutral-ground voltage which can cause

equipment malfunctions, component damage and shortened equipment life span • Ground currents which, among other things, can cause video noise problems.

Over heating due to harmonics: The 3rd and other triplen harmonic currents are additive as they return in the neutral conductor. Because of this, neutral conductors will often carry very heavy currents when non-linear loads are present. These currents have been known to cause overheating and failures of the neutral conductor.

In addition, harmonics will increase I2R and eddy current losses in transformers and other distribution equipment such as UPS systems. These excessive losses can cause transformers to overheat even when they are relatively lightly loaded.

High voltage distortion and neutral-ground voltage: Harmonic problems which have been less well documented, but are potentially even more troublesome, are the heavy voltage distortion and high neutral-ground voltages (common mode noise) that are common where high densities of non-linear loads exist. Most of the distortion is the result of the interaction of the harmonic currents with the impedance of the electrical distribution system. That is, as the harmonic currents circulate through the electrical distribution, they produce voltage drops at each harmonic frequency in relation to Ohm's law - Vh = Ih x Zh. The combined effect of the voltage drops at each harmonic frequency is what creates the overall voltage distortion. This problem becomes even more serious when the distribution system is serviced by a weak source, such as an UPS system or diesel generator. Distortion levels are higher when system impedance is higher. System impedance is generally high when fairly long cable runs are serviced from a supply with high source impedance, such as a UPS. Voltage flat-topping is the most common form of voltage distortion. Flat-topping results from the fact that non-linear loads draw currents in pulses at the peak of the voltage waveform. The same Ohm's Law relationship is what creates high neutral-ground common mode noise voltages. Heavy neutral currents, resulting from the additive effect of the triplen harmonic currents, 3rd, 9th, 15th, etc., in the neutral will produce a voltage drop along the neutral conductor. This voltage drop will appear as a potential difference between neutral and ground near the harmonic generating loads (ie. at the power panels and power receptacles). Commonly referred to as common mode noise, this voltage can have a very adverse affect on the operation of equipment which is subjected to it. An effective strategy for harmonic mitigation is to isolate the harmonic currents near the loads themselves through phase shifting and zero sequence filtering. By reducing the current harmonics, the voltage distortion, neutral-ground voltage and overheating that these harmonic currents produce will be dramatically reduced.


Ground Currents: Most electronic equipment which utilize switch-mode power supplies are equipped with π-Filters to reduce the high frequency EMI emissions. These filters are effective at reducing EMI but may allow some low frequency harmonic leakage currents (ie. 180 Hz) to pass through to the ground wire. This can result in troublesome ground currents circulating through the power system.

PERFORMANCE MEASUREMENTS Measurements taken Oct. 3rd on a Fluke 41 meter confirmed that the NCE™ was very effective in addressing the harmonic concerns at Comcast. Figure 1 shows measurements taken on the neutral conductor before and after the installation of the NCE™. Neutral current was reduced by almost 90% (from 144 amps to 18 amps). The largest reduction was in the 3rd harmonic which went from 134 amps to 15 amps. This has offloaded the neutral conductor and the upstream UPS system allowing them to run much cooler. Also, by reducing the neutral current, neutral-to-ground voltage dropped from 2.4V to 0.4V. Other improvements can be seen in the phase current measurements shown in Figure 2. Voltage and current measurements on Phase B are shown both before and after the

Figure 1: NCE Performance – Neutral Conductor


installation of the NCE™. Removal of the 3rd harmonic current in the phase conductor has reduced the overall current distortion from 35% to 25%. With fewer harmonics in the current, voltage distortion which is caused by these harmonics, was dramatically reduced (13% to 2%). The improvement in voltage distortion is also demonstrated by the elimination of the voltage flat-topping. The NCE™ increased the peak voltage to 165V from 150V (a 10% improvement) . This reduction in current harmonics is reflected in the lower current peak.

Figure 2: NCE Performance – Ph B

international inc. lineator case study: rambam hospital israel · spectrum of higher frequency sine...

Documents