Archive for February, 2016

Title 10



Parts 200 to 499

Revised as of January 1, 2015

Containing a codification of documents of general applicability and future effect

As of January 1, 2015

Published by the Office of the Federal Register National Archives and Records Administration as a Special Edition of the Federal Register

Department of Energy


Single-phase transformers Three-phase transformers
kVA Impedance


kVA Impedance


37.5 …….. 1.0–4.5 75 1.0-5.0
50 ……….. 1.5–4.5 112.5 1.2-6.0
75 ···· ·· ···

100 ………







167 ……… 1.5–4.5 300 1.2-6.0
250 ……… 1.5-6.0 500 1.5–7.0
333 ……… 1.5-6.0 750 5.0-7.5
500 ·········

667 ………







833 ……… 5.0-7.5 2000 5.0-7.5
2500 5.0–7.5


Single-phase transformers Three-phase transformers
kVA Impedance


kVA Impedance


15 ……….. 1.5-6.0 15 1.5-6.0
25 ……….. 1.5-6.0 30 1.5-6.0
37.5 …….. 1.5-6.0 45 1.5-6.0
50 ……….. 1.5-6.0 75 1.5-6.0
75 ……….. 2.0-7.0 112.5 1.5-6.0
100 ……… 2.0-7.0 150 1.5-6.0
167 ……… 2.5–8.0 225 3.0-7.0
250 ·········

333 ………







500 3.5–8.0 750 5.0–8.0
667 ……… 5.0–8.0 1000 5.0-6.0
833 ……… 5.0-6.0 1500 5.0–8.0
2000 5.0–8.0
2500 5.0–8.0

Temperature correction means the mathematical correction(s) of meas­urement data, obtained when a trans­ former is tested at a temperature that is different from the reference tem­perature, to the value(s) that would have been obtained if the transformer had been tested at the reference tem­perature.

Test current means the current of the electrical power supplied to the trans­ former under test.

Test frequency means the frequency of the electrical power supplied to the transformer under test.

Test voltage means the voltage of the electrical power supplied to the trans­ former under test.

Testing transformer means a trans­ former used in a circuit to produce a specific voltage or current for the pur­ pose of testing electrical equipment.

Total loss means the sum of the no­ load loss and the load loss for a trans­ former.


Transformer means a device con­sisting of 2 or more coils of insulated wire that transfers alternating current by electromagnetic induction from 1 coil to another to change the original voltage or current value.

Transformer with tap range of 20 per­cent or more means a transformer with multiple voltage taps, the highest of which equals at least 20 percent more than the lowest, computed based on the sum of the deviations of the voltages of these taps from the transformer’s nominal voltage.

Uninterruptible power supply trans­ former means a transformer that is used within an uninterruptible power system, which in turn supplies power to loads that are sensitive to power failure, power sags, over voltage, switching transients, line noise, and other power quality factors.

Waveform correction means the adjust­ment(s) (mathematical correction(s)) of measurement data obtained with a test voltage that is non-sinusoidal, to a value(s) that would have been obtained with a sinusoidal voltage.

Welding transformer means a trans­ former designed for use in arc welding equipment or resistance welding equip­ment.

(70 FR 60416, Oct. 18, 2005, as amended at 71

FR 24995, Apr. 27, 2006; 71 FR 60662, Oct. 16,

2006; 72 FR 58239, Oct. 12, 2007; 78 FR 23433,

Apr. 18, 2013]


  • 431.193 Test procedures for meas­uring energy consumption of dis­tribution transformers.

The test procedures for measuring the energy efficiency of distribution transformers for purposes of EPCA are specified in appendix A to this subpart.

(71 FR 24997, Apr. 27, 2006]


  • 431.196 Energy conservation stand­ards and their effective dates.

(a) Low-Voltage Dry- Type Distribution Transformers. (1) The efficiency of a low-voltage, dry-type distribution transformer manufactured on or after January 1, 2007 , but before January 1, 2016, shall be no less than that required for the applicable kVA rating in the

§ 431.196

table below. Low-voltage dry-type dis­tribution transformers with kVA rat­ ings not appearing in the table shall have their minimum efficiency level determined by linear interpolation of the kVA and efficiency values imme­diately above and below that kVA rat­ing.

Single-phase Three-phase

10 CFR Ch. II (1-1-15 Edition)

Single-phase Three-phase
kVA Efficiency


kVA Efficiency





37.5 ………..

50 …………..

75 …………..





















15 …………..

30 …………..

45 …………..


112.5 ………

150 ·······-····

225 …………

300 …………

500 …………

750 …………

1000 ……….

1500 ……….

2000 ··········

2500 ……….
















immersed distribution transformers with kVA ratings not appearing in the table shall have their minimum effi­ciency level determined by linear in­terpolation of the kVA and efficiency values immediately above and below that kVA rating.

kVA % kVA %
15 97.7 15 97.0
25 98.0 30 97.5
37.5 ……….• 98.2 45 …………•. 97.7
50 ………….. 98.3 75 .. ……….. 98.0
75 ………….. 98.5 112.5 ……… 98.2
100 98.6 150 ………… 98.3
167 98.7 225 ………… 98.5
250 98.8 300 ………… 98.6
333 98.9 500 ··· ········ 98.7
750 ………… 98.8
1000 ………. 98.9

Note: All efficiency values are at 35 percent of nameplate­ rated load. determined according to the DOE Test Method for Measuring the Energy Consumption of Distribution Trans­formers under Appendix A to Subpart K of 10 CFR part 431.

Single-phase Three-phase
kVA Efficiency


kVA Efficiency


15 97.70 15 ………….. 97.89
25 98.00 30 ………….. 98.23
37.5 ……….. 98.20 45 ………….. 98.40
50 …..•……•. 98.30 75 ………….. 98.60
75 ………….. 98.50 112.5 ……… 98.74
100 98.60 150 ………… 98.83
167 98.70 225 ………… 98.94
250 98.80 300 ………… 99.02
333 98.90 500 ………… 99.14
750 …····· ·· 99.23
1000 ……… 99.28


(2) The efficiency of a low-voltage dry-type distribution transformer man­ufactured on or after January 1, 2016, shall be no less than that required for their kVA rating in the table below. Low-voltage dry-type distribution transformers with kVA ratings not ap­pearing in the table shall have their minimum efficiency level determined by linear interpolation of the kVA and efficiency values immediately above and below that kVA rating.

Note: All efficiency values are at 50 percent of nameplate­ rated load, determined according to the DOE Test-Proce­ dure, Appendix A to Subpart K of 10 CFR part 431.

Single-phase Three-phase
kVA Efficiency


kVA Efficiency





37.5 ………..

50 …….. …..

75 …….. …..

100 …………

167 … ……..

250 …………

333 ………..•

500 …… …..

667 …… …..

833 …………











15 …………..

30 …………..

45 ….

75 …………..

112.5 ………

150 …………

225 …………

300 ………..


750 …… …..













99.51 99.53

99.49 1000 ……….

99.52 1500 ···· ····

99.55 2000 ……. ..

2500 ……….


(2) The efficiency of a liquid-im­mersed distribution transformer manu­factured on or after January 1, 2016, shall be no less than that required for their kVA rating in the table below. Liquid-immersed distribution trans­formers with kVA ratings not appear­ing in the table shall have their min­imum efficiency level determined by linear interpolation of the kVA and ef­ficiency values immediately above and below that kVA rating.

Note: All efficiency values are at 35 percent of nameplate­ rated load, determined according to the DOE Test Method for Measuring the Energy Consumption of Distribution Trans­ formers under Appendix A to Subpart K of 10 CFR part 431.

(b) Liquid-Immersed Distribution Trans­formers. (1) The efficiency of a liquid­ immersed distribution transformer manufactured on or after January 1, 2010, but before January 1, 2016, shall be no less than that required for their kVA rating in the table below.

Note: All efficiency values are at 50 percent of nameplate­ rated load, determined according to the DOE Test Method for Measuring the Energy Consumption of Distribution Trans­formers under Appendix A to Subpart K of 10 CFR part 431.

(c) MediumVoltage DryType Distribu­tion Transformers. (1) The efficiency of a medium-voltage dry-type distribution


Bank of America is one of the world’s largest financial institutions, serving individual consumers, small- and middle-market businesses and large corporations with a full range of banking, investing, asset management and other financial and risk management products and services. As part of its $20 billion commitment to support the growth of environmentally sustainable businesses that address global climate change, Bank of America has committed $1.4 billion to meet the U.S. Green Building Council’s LEED® (Leadership in Energy and Environmental Design) certification requirements in all new construction of office facilities and banking centers and invested $1.5 billion to renovate environmentally progressive office towers in Charlotte, N.C. and New York City.


The 30-story Charlotte corporate headquarters building, vintage mid-1970’s, had twenty two (22) low- voltage distribution transformers serving the building that were nearing end of life. Like most Fortune 500 companies experiencing a growing dependence on information technology and integrating controls, as well as supporting expanding data processing and call centers, all served by an aging power system, the decision was made to renovate this 24/7 corporate facility’s power system. The goal was to achieve 100% compatibility of the connected loads with the power system. After extensive building surveys, PQI was challenged to present the case to utilize PQI Harmonic Mitigating Transformers versus K-rated Transformers as part of the renovation strategy of the building’s power system.


To reduce nonlinear load-generated ‘penalty losses’ in the distribution system, increase system and load energy efficiency, improve system power factor, and reduce voltage distortion at the 480-volt loads, The PQI Power System Optimization Plan was implemented resulting in a new low voltage distribution system comprised of the replacement of twenty two 45 kVA harmonic mitigating transformers, in a 24-pulse configuration.


100% compatibility of the connected loads with the power system of the building was achieved. Under the connected loads in the new configuration and based on the cost of power, the annual financial reduction of power exceeded $170,000. This renovation of the bank’s corporate headquarters in Charlotte also resulted in dramatically reducing the building’s carbon footprint while achieving LEED Gold™ certification, the first renovation project in North Carolina to achieve this distinction.


HP is a technology company that operates in more than 170 countries around the world. HP explores how technology and services can help people and companies address their problems and challenges, and realize their possibilities, aspirations and dreams. HP applies new thinking and ideas to create more simple, valuable and trusted experiences with technology, continuously improving the way its customers live and work.


Hewlett-Packard unveiled one of the most ambitious data center consolidation projects ever, which consolidated 85 data centers worldwide into six larger centers located in three U.S. cities – Atlanta, Houston and Austin. However, distributing the power in these mission critical facilities required ultra energy efficiency that was unmatched in the industry.


PQI was selected as the ultra energy efficient transformer source for numerous 500 kVA transformers. These transformers were custom made for HP and were beyond any industry standard for efficiency in the industry.


The consolidation will help HP reduce its IT spending by approximately $1 billion in the coming years. The facilities also will serve as a showcase for HP Adaptive Infrastructure products and services. The data centers will provide HP with more dependable, simplified operations. This effort will enable faster delivery of new technologies, services and information and provide room for growth and improved business continuity, while significantly reducing costs. And HP will enjoy the highest power quality in the industry as a result of the PQI ultra energy efficient transformers.

FedEx called on Power Quality International, Inc. for assistance. They were experiencing dangerous airframe-to-ground arcing, when supplying their aircraft from their hanger’s 400Hz electrical power system. Inside a hanger is considered a potentially explosive environment. Arcing is an unacceptable hazard.

Arcing results when zero-sequence harmonic currents, flowing through the zero-sequence impedance of the aircraft’s metallic airframe, generate zero-sequence harmonic voltages (Eh = Ih x ZH). Any grounding of the airframe will cause arcing. Arcing occurred when the hangar’s grounded hydraulic lines or static grounding cable come into contact with the aircraft. The zero- sequence current, which flows on the airframe, is generated by:

  1. Unbalanced loading in the three-phase, fourwire
  2. Single-phase nonlinear loads, which generate unbalanced positive- and negative- sequence harmonic currents, and
  3. Single-phase, nonlinear loads, which generate third-order, zero-sequence harmonic

In order to eliminate arcing, zero-sequence currents and arc voltage must be eliminated.

The measured arc voltage was 4.1 volts, sufficient to cause continuous arcing. The predominant arc frequency is 1200Hz, the 400Hz system’s third harmonic.


PQI was able to eliminate arc voltage with the application of a 400Hz IoFilter™ – Zero-Sequence Harmonic Filter.

The filter also improved the system’s power quality by:

    • Reducing peak phase current,
    • Reducing average phase current,
    • Reducing transformer losses,
    • Reducing system losses,
    • Reducing total harmonic distortion,
    • Improving power factor,
    • Improving phase current balance, and
    • Improving phase voltage balance.

The zero-sequence current at the aircraft was reduced by 95%. At this level, there is not enough current to sustain an arc should arc voltage increase. In addition, the arc voltage was reduced from 4.1 volts to less than 0.1 volts, which is a reduction of 97.6%. The reduction of zero-sequence current and airframe to ground voltage can be accompanied by applying an ultra low zero-sequence impedance at the load or aircraft end of the three-phase, four-wire radial feeder circuit. The zero sequence filter will shunt all zero-sequence currents, at its point of connection, in proportion to the zero-sequence impedance of the source and the filter.

The Bellagio Resort & Casino, Las Vegas, is part of the MGM Mirage Group, one of the largest hotel & casino operations. Their family of resorts includes Aria, Circus Circus, City Center, Excalibur, Luxor, Mandalay Bay, MGM Grand, Monte Carlo, New York- New York and The Mirage.


PQI was asked to investigate the cause of several serious operational problems at the Bellagio Hotel & Casino in Las Vegas, Nevada. These problems included corruption of data in the computer and slot machine networks, and poor video quality at the surveillance system monitors. PQI uncovered two significant power quality issues, which were the cause of these network and picture quality problems. The issues included high levels of voltage distortion and neutral- to-ground voltage at these sensitive electronic loads. Power system and load incompatibility problems are common when the loads are nonlinear. PQI was next asked to find a solution and prepare a detailed proposal.


PQI proposed and was authorized to supply zero-sequence harmonic filters for all branch circuit sub- panels and harmonic mitigating transformers for all five targeted sub-systems. The application of these devices was guaranteed to resolve the identified operational and system incompatibility problems.


With annual savings of approximately $241,381 and an installed cost of $363,956, the payback was 1.5 years and the rate-of-return was 66%. If harmonic mitigation had been included in the original design, payback would have been achieved in less than 6 months.

POWER QUALITY INTERNATIONAL is the industry leader in the development, design and manufacturing of harmonic mitigating and energy-efficient transformer technologies. With a passion for solving problems and helping customers achieve power quality and energy efficiency, PQI delivers cost-effective solutions that ensure power quality and energy efficiency for the life of their customers facilities.

Wynn Resorts Limited is a developer and operator of high-end hotels and casinos. The company’s first project, Wynn Las Vegas, opened on April 28, 2005. The Encore, an extension to Wynn Las Vegas, broke ground on April 28, 2006 – the first anniversary of the opening of Wynn Las Vegas.

Wynn Macau, the company’s first project in The Peoples Republic of China, started construction on June 28, 2004. It opened September 5, 2006. The Encore at Wynn Macau, the company’s second tower, opened on April 21, 2010.


On January 15, 2010, PQI received a report regarding a severe harmonic problem at the Wynn Macau Encore tower from JBA Consulting Engineers, who had been retained to evaluate performance issues on the hotel’s electrical distribution systems. During the initial commissioning, JBA observed flickering lights in the guest rooms and unusual humming and vibration in the six distribution panels that supply the hotel’s Diamond Feature. The Diamond Feature is a unique lighting display located on the exterior concave facade of the Encore tower. This display extends from the seventh floor to the fiftieth floor. The feature includes approximately 70,000 randomly controlled, dimmable cold cathode fluorescent lamps.

The average total harmonic distortion of current (THDI) at the lamps’ local controllers was measured at 191%, while THDI at the six distribution panels was between 114% and 156%. High current distortion was thought to be the likely cause of panel humming and vibration. In an Ohm’s law relationship with the

distribution panel, which is most remote from the main switchgear, was 21%. These are the highest levels of current and voltage distortion ever presented to PQI. True Power Factor (TPF) on the riser supplying the Diamond Feature was measured at 0.68. Based on this information, we anticipated very high harmonic-current related “penalty losses” and very low efficiencies in the distribution system and its loads.

Under this load condition, THDV at the facility’s main switchboard was measured at 19%. This level of baseline voltage distortion was therefore imposed on all other distribution system loads. Since a high percentage of these loads are also nonlinear, THDV is expected to be well above 10% at all other loads. IEEE Standard 519-1992 recommends a limit of 5% THDV at a system’s loads. High voltage distortion was thought to be the likely cause of flickering lights in the guest rooms. In addition to diminishing system and load functionality and reliability, the presence of voltage distortion at the linear loads will result in identical current distortion; that is, %THDI will equal %THDV. In this environment, linear loads produce harmonic currents.


To resolve the observed operational issues, reduce distortion and “penalty losses” and improve power factor, PQI prepared a harmonic mitigation plan with guaranteed outcomes. This plan was presented to JBA Consulting Engineers on January 20, 2010 – five days after receiving their report. JBA sent our mitigation plan to the owner’s representative for approval. To resolve all identified issues, our plan proposed the application of five ultra-efficient harmonic mitigating transformers at the line side of the five distribution panels that supply the Diamond Feature. These Distribution TransFilters™ (filters) were to be used to convert the Diamond Feature’s six-pulse loads to a twenty-four-pulse load at their common 400-volt riser. The filters would also create a separately derived grounded neutral adjacent to each distribution panel and reduce the distribution system’s zero-sequence impedance by approximately 200X. We discovered later that PQI’s proposed solution was one of three presented to the owner’s representative.

The Wynn organization elected to proceed with a solution prepared by Schneider Electric (Square D). Their solution required the application of an active harmonic filter (AHF) at each of the Diamond Feature’s five distribution panels. These devices are designed to analyze a circuit’s harmonic current profile then inject harmonic currents, which are equal in magnitude but 180° out-of-phase, into the circuit. This effectively cancels the load-generated harmonic currents. Unfortunately, the Diamond Feature’s lamp controllers produce a current rise time and duration that was well beyond the AHF’s ability to track or mitigate. This problem actually caused the AHF to increase current and voltage distortion. To increase the currents’ rise time and duration and reduce service.

With these serious issues unresolved, the owner next engaged JBA to undertake harmonic modeling of the affected distribution system. Upon completion of their study, JBA produced a comprehensive report in January 2011, which described the performance of the existing system under nonlinear loading (baseline). Their calculations closely approximated the site measurements taken one year earlier. The report then described the performance of the system with the addition of Schneider Electric’s active harmonic filters and K-Rated distribution transformer.

JBA’s report then detailed anticipated outcomes based on solutions offered by General Electric and PQI. The report concluded that only PQI’s proposed solution would reduce voltage distortion at the main switchboard to an acceptable level, the key requirement with respect to the flickering light problem, and reduce harmonic current loading at the five distribution panels. Based on this report, PQI was authorized to proceed.


Before installing the five Distribution TransFilters™, PQI took a full set of power and harmonic measurements at the main switchboard that supplies the Diamond Feature and the Encore tower’s guest rooms most affected by voltage distortion, the five Diamond Feature lighting control panels and the five distribution panels that supply them. Upon completion, the proposed filters were installed, the lighting feature was reenergized and a new complete set of measurements were taken. Before and after measurements revealed the following outcomes at the main switchboard: harmonic current magnitudes, Schneider next applied a one-to-one, K-Rated distribution transformer at the line end of the riser. This caused a further increase in voltage distortion. The result was an unacceptable failure rate of the dimmable cold cathode fluorescent lamps, which cost $10.00 US each. As a result, the AHFs and K-Rated transformer were removed from

Before Mitigation | After Mitigation | Reduction

19% THDV 4.4% THDV 77%

This reduction met the IEEE Standard 519 recommendation and resolved the “flickering lights” problem.

The initial measurements revealed a significant but previously unreported problem, that is, high neutral- to-ground voltage at the five distribution panels and lighting controls. Before and after measurements revealed the following average outcome:

Before Mitigation | After Mitigation | Reduction

13.1V 2.5V 81%

This reduction met the Information Technology Industry Council (ITIC) recommendation and will likely reduce lighting controller and/or lamp failures.

With the conversion of the Diamond Feature lighting loads from six-pulse to twenty-four-pulse, current distortion and RMS current were reduced, while power factor was improved, on the 400-volt riser:

Before Mitigation | After Mitigation | Reduction

120% THDI 72.6% THDI 39.5%

0.680 PF 0.979 PF

High neutral currents, which exceeded the phase currents, were totally eliminated on the riser. The efficiency improvement from the reduction in the distribution system’s load losses has resulted in a very attractive financial benefit.

A more complete analysis of these operational and power quality issues, their resolution and the financial outcome are discussed in a paper authored by JBA Consulting Engineers and Power Quality International.

PQI clients and customers benefit from over fifty years of engineering and technical hands-on field experience. With the exception of Antarctica, we’ve completed major assignments on every continent.

With its technical and manufacturing ‘know how’, PQI was first to develop and commercialize a number of leading-edge power magnetic technologies and products. These accomplishments, some of which are listed here, provide cost-effective solutions to various technical, power quality and energy efficiency problems.

2015 First to offer three Transformer Efficiencies that Exceed DOE 2016 efficiency requirements, under the linear or nonlinear load environments for which they were designed.

PQI’s Standard Z3 Efficiency Rating exceeds the US DOE 2016 requirements. Optional Z3+ and Z4 (US DOE CSL 4) efficiencies are available when their additional cost produced an attractive payback and ROI.

2015 – First to receive a UL Certificate of Compliance per UL1562 for our Harmonic Mitigating, Medium Voltage, Cast-Coil Power Transformers. Both CSA and UL have approved our manufacturing facility as a Qualified Product Evaluation and Test Facility.

Measurements and test data generated during product evaluation is now accepted by both CSA and UL for product approval.

Power TransFilters™ have also received Seismic Pre-Certification in accordance with the requirements of the International Building Code 2012 (IBC2012), the California Building Code 2013 (CAB2013) and the National building Code of Canada 2010 (NBC2010). In addition, the transformers specifically met the requirements of OSHPD (Office of Statewide Health Planning and Development of California).

2003 – First to develop a Transformer Excitation & Impedance Loss Measurement Instrument, based on the earlier Voltage & Current Differential, Loss Measurement Method.

Transformer Performance Analyzer™ limits the efficiency calculation error to ±0.033%, when measuring a transformer’s excitation and impedance losses under linear or any nonlinear load condition.

2003 – First to use a sophisticated computer program that is in compliance with IEEE Std. C57. 110-1998, that allows our engineers to recalculate any transformer’s linear losses and efficiency into its nonlinear losses and efficiency, which is based on a specific harmonic current profile.

The PQI Calculator™ will compare the performance of any two transformers and calculate a payback and return-on-investment.

The PQI Calculator TM
Project Sample
  1. 0
To compare the performance of a 75 kVA, K-13
  1. 0
K13 DY0
Distribution TransFilter, under K-13 loading.
  1. 0
Date August 20, 2008 8.0
Linear Eff. at 35% of TX Rated kVA 95.00%
DY0 kVA Rating 75.0 Losses (kW) vs. kVA Rating (pu)
Zero-Sequence Harmonic Flux Cancellation Yes/No Yes 1.000
Linear Eff. at 35% of TX Rated kVA 98.65%
Installation [ if replaced before end-of-life ] $1,000.00
Air Conditioning Requirement

Months/Year [ direct or indirect ]

12 Efficiency (pu) vs. kVA Rating (pu)
Days/Year for Segment 261 261 104 365
Calculation of Penalty Losses

Actual kW Losses for K13









Actual kW Losses for DY0 0.823 0.460 0.306 0.546
Difference in kW K13 DY0 2.753 1.460 0.923 1.768
Annual Energy Savings, including A/C Costs $1,753.88 $930.03 $492.77 $3,176.68
Calculation of Financial Benefits

Annual Savings, including A/C Costs, when using DY0

$3,176.68 / year
Payback on Incremental Cost [ substitution ]

Return-on-Investment (ROI) on Incremental Cost [ substitution ]

4.7 months

253.1 %

Payback on Installed Cost [ before end-of-life replacement ]

Return-on-Investment (ROI) on Installed Cost [ before end-of-life replacement ]

2.1 years

48.1 %

Reduction in kWh over 25 years of operation 387,298.12 kWh saved
Summary of Environmental Benefits

Annual Reductions per EPA Formula

11.44 tons of CO2 90 kgs of SO2

33,695.74 kgs of coal 39 kgs of Nox

2 acres of trees 2 homes heated 2 fewer cars on the road each year



2003 – First to develop a Technology Demonstration Vehicle that demonstrates all harmonic related ‘power quality’ issues, and compares the accuracy of the Power-In – Power-Out, Loss Measurement Method and the Voltage & Current Differential, Loss Measurement Method.

2001 – First complete line of Harmonic Filtering Transformers that exceed EPA – Energy Star® linear load efficiency requirements under nonlinear load conditions.

PQI HarMitigator™ products, which include harmonic mitigating power, distribution and drive isolation transformers, are approximately 2% more efficient than any competing harmonic mitigating transformers and up to 15% more efficient than typical conventional or K-Rated transformers, under severe nonlinear loading.

2001 – First computed program that will calculate a solution for harmonic current, ‘penalty loss’ and power cost reductions, and system performance and power quality improvement.

The PQI Solution™ includes the consulting services of a professional engineer specialist who will provide guidance in the selection and application of PQI’s technically advanced, ultra- efficient e-Rated® products. This service is offered on a no-fee-basis to system designers. If our recommendations are fully implemented, PQI will guarantee compliance with the power quality requirements of IEEE Std 519-1992 – IEEE Recommended Practices and Requirements for Harmonic Control in Electrical Power Systems. The proper selection of products and application of our engineered solution will result in the most cost-effective optimization of system and load efficiency and compatibility. Implementation of our recommendations will also result in an increase in our standard warranty from 10 years to 20 years.

2000 – First electromagnetic Zero-Sequence Harmonic Filter that shunts zero-sequence harmonic currents at the load-end of a branch circuit.

Mini-Z™ filters provide an alternative to de-rating conventional distribution transformers, applying K-Rated distribution transformers, increasing ‘shared’ neutral conductors or configuring branch circuits with separate neutral conductors, in an environment that is rich with zero-sequence harmonic currents.

1996 – First commercial sale of Medium Voltage Class Sub-Cycle Voltage Regulator Transformers for application in a utility’s distribution system.

PQI TransRegulator™ products mitigate the voltage sags that result from fault clearing events on a utility’s transmission and distribution systems.

1991 – First complete line of Harmonic Filters and Harmonic Mitigating Transformers that shunt or cancel zero-sequence harmonic currents and/or cancel positive- and negative-sequence harmonic currents.

PQI HarMitigator™ products, which include harmonic mitigating power, distribution and drive isolation transformers, reactors and filters, provide the means to implement The PQI Solution.

1990 – First to develop and apply Harmonic Mitigating Transformers that shunt zero-sequence harmonic currents with ultra-low zero-sequence impedance windings and cancel positive- and negative-sequence harmonic currents within their secondary windings.

Distribution TransFilters™ provide an alternative to de-rated conventional distribution transformers or applying K-Rated distribution transformers. These ultra-efficient transformers meet their published efficiency in the nonlinear environment for which they’re designed.

1986 – First electromagnetic Zero-Sequence Harmonic Filters that shunt zero-sequence harmonic currents from a three-phase, four-wire sub-system.

I0Filter™ provide an alternative to de-rating conventional distribution transformers, applying K-Rated distribution transformers or increasing feeder circuits’ neutral conductors, in an environment that is rich with zero-sequence harmonic currents.

1983 – First to develop a Three-Phase Power Harmonic Analyzer that measures harmonic currents, voltage magnitudes and phase angles, up to the 50th harmonic, then calculates total harmonic distortion of current and voltage, harmonic power flow for each individual harmonic, system impedance at each harmonic frequency, kVT or IT products for each harmonic and Telephone Interference Factor. This project led to the development of the first Fluke, Model 41 Harmonic Analyzers.

1982 – First ‘on-line Partial Discharge Analyzers that monitor the condition of stator winding insulation systems in hydroelectric generators.

PDA-H® technology remains the ‘world standard’ for failure avoidance and maintenance optimization. This technology is now used on turbo-alternators and medium voltage class motors.

1965 The founder of PQI, while an employee of Ontario Hydro-Electric Power Commission, developed the first Three-Phase Transformer Ratiometer. This instrument measured the true turns-ratio of any single- or three-phase power transformer, distribution transformer or voltage transformer with an accuracy of 1 turn in a 100,000 (±0.001%) or a current transformer, with an accuracy of 1 turn in 10,000 (±0.01%). The instrument was also capable of detecting internal impedance changes, such as loose connections, burned tap-changer contacts or turn- to-turn insulation deterioration.

The Transformer Ratiometer™, after 50 years of service, remains the most accurate and reliable field instrument for confirming a transformer’s turn-to-turn windings ratio.

Case Study:
Generator Compatibility with UPS Incorporating an IGBT-Based Front End


Lack of generator compatibility with uninterruptible power supplies (UPS) has been an issue since continuous power solutions have been in use. Typical applications involve a double conversion UPS with an input composed of a six pulse rectifier and an input filter (See Figure 1). With this input, typical input current harmonics range from 10% current total harmonic distortion (THD) at 100% load to over 30-40% current THD at 25% load or less.

It should be noted that for generator applications a tuned L-C (inductor and capacitor) filter is added to the line side of the rectifier of the traditional UPS. It is tuned to work optimally at 100% load and is connected to the input by a contactor. In situations where the load drops below ~25% (NOTE: It is common for UPS systems to be loaded to only 15% to 50% of their full load rating since most people unknowingly oversize the UPS to support the nameplate rating of the downstream equipment.), the tuned filter must be removed from the circuit to prevent a leading power factor from being presented back to the input source which is of grave concern when operating on generator power. When the UPS load drops below 25%, the input filter is removed from the circuit and over 30 to 40% current THD is reflected back to the source. Therefore, one can expect to see the traditional UPS manufacturer’s published 8-10% input current THD specification at 100% load only. The tuned filter has fixed parameters and as the load decreases, the filter becomes less efficient in mitigating harmonics and thus, harmonic content will increase.

High harmonic current reflected from the UPS input to the generator causes generator compatibility issues including excessive heating in the generator windings and high voltage THD. A catastrophic situation may occur if the input filter of the UPS is not taken off-line at light loads. If the filter fails to disengage, the input power factor will be extremely leading, causing current to flow back to the genset and excite the generator windings. This causes the generator windings to see a much higher voltage and shutoff for self-protection, dropping the generator from the circuit. While this occurrence is rare, it is obviously a potential point of failure. Regardless, when the UPS performs normally and disengages the filter, input current distortion will always rise to over 30%-40%.

To lessen the occurrence of these problems, most generator manufacturers recommend over-sizing the diesel genset by a factor of two (2X) and over-sizing natural gas gensets by a factor of three (3X) when feeding a traditional 6-pulse rectifier-based UPS. This is a costly and non-ideal solution.

The Optimal Solution:

Traditional UPS designs have been greatly improved by putting an IGBT converter in the front end, in lieu of a six pulse rectifier with an input filter. The input IGBT’s switch at 22 kHz (converting AC power to DC power) and at this rate, the harmonics reflected back to the source are almost non-existent (See Figure 2):

The following harmonic graph for the Toshiba UPS with an IGBT-based front end shows that the current harmonic distortion is well below the published 3% specification (See Figure 3):

The Test:

Testing was done at the Onan facility in Fridley, Minnesota using a Dranetz PP4300. The Toshiba 15kVA 4200 Series UPS was loaded to 100% load with a standard three-phase load bank. The test simulated the elevation in source impedance and the interaction between the UPS and the Onan generator. The Onan test engineer concluded that the Toshiba UPS performed like a nearly perfect linear, power factor corrected, resistive load.

The values increase only slightly when the UPS is supplying a fully nonlinear load.

Additionally, performance was monitored at a field installation at a major software company in Minnesota. A 175kVA 7000 Series Toshiba UPS was applied to an available 160kW generator load. It has been in service for over three years with monthly generator exercising and outage events and has had none of the generator overheating or compatibility problems associated with the typical, commercial grade UPS.

In Conclusion:

Toshiba guarantees generator compatibility on all of its UPS systems from single phase to large three phase. The formula used is:

Generator kW Rating = Toshiba UPS Output kVA

An example of this would be that a 50kW standby diesel genset would be adequately sized to support a 50kVA Toshiba UPS. It should be noted that other loads such as air conditioners and lighting circuits are often required for a true continuous power system and that the generator should be sized to support these additional loads.

Toshiba is the recognized worldwide leader in IGBT design and has been supplying complete UPS systems from its Houston, TX factory since 1986. From small point-of-use single phase systems to large, multi-MVA three phase applications, Toshiba has a double conversion, front end IGBT-based to UPS to handle any critical application.

The G9000 is a transformerless UPS, and is designed to go to bypass to provide fault‐clearing current once a fault is detected.

In the G9000, faults are sensed many ways:

  • Faults sensed on the AC output:
    1. AC Ground Fault on the output: Phase to Ground: in this case a monitoring circuit detects when the zero sequence voltage changes. In other words, the vector addition of all three phases should be zero; when that voltage (or leakage current) rises above a certain setpoint, the unit activates the ZERO PHASE OVERCURRENT alarm, and sends the unit to This function can be disabled.
    2. Phase to Phase: here the CT’s and voltage monitoring on the output sense a rapid rise in current and simultaneous drop in voltage, and gives the INVERTER OVERCURRENT alarm, and again goes to bypass. This function cannot be disabled.
  • Faults on the DC bus/internal to the UPS:
    1. DC ground fault: there is a separate circuit in the G9000 that detects DC ground faults. This measures the difference between the unit’s virtual neutral and the input/output phases, and will detect an alarm in the case of:
      1. Leakage of one of the components in the rectifier/inverter/charger‐chopper circuits
      2. An electrolyte trail from battery to ground
      3. An output AC Phase to Ground fault in systems with ungrounded or HRG (High Resistance Grounded) source: this circuit will detect a fault in HRG systems when the voltage in the UPS’s internal virtual neutral rises to phase voltage (277V).
      4. The result will be a DC GROUND FAULT alarm and the unit will be sent to bypass. This function can be disabled.
  1. DC Short circuit: A similar circuit measures the balance between the + and – legs of the DC bus, and is there to detect a hard fault in the battery This function cannot be disabled.
  2. Note On The G9000’s Bypass Path
    The bypass path has no fuses or breakers in it and therefore has a no interrupt rating, but rather the withstand rating, required by UL from the factory. However, if an interrupt rating is specified, or if fuse protection in this path is desired, there is a provision to add fuses to the bypass path, at 65 kAIC for 80‐225 kVA models, and 100 kAIC for 300‐750 kVA models.

Distributed Bypass systems add no additional cost as there is when a centralized bypass switch is required.  The integral bypass switch is built into each UPS, and so does expand the system footprint.  The Tie cabinet does not need any intelligence. It is simple, reliable, and vendor-independent.  In an N+1 configuration, the distributed bypass design provides redundancy in the event of a failed static switch.


The argument for centralized bypass is simply that simplicity = reliability. The contrary truth is made evident when one considers that a parallel UPS system is more complex than a single large UPS, though parallel UPS systems are commonly designed to provide redundancy and therefore reliability. Likewise, distributed bypass adds a very simple device to each static switch circuit (a contactor) indeed making the bypass path only marginally more complex, yet far more reliable as a result.

Other considerations are:

  • Increased cost: The centralized Static Switch would have to be purchased in addition to the UPS.
  • Increased footprint: The centralized SS would be in a dedicated stand-alone cabinet in addition to the rest of the system
  • Dependence on a single switch, breaker, and motor operator if the switch is momentary, introducing a single point of


In the G9000, the hybrid bypass switch is incorporated in each UPS module. This simple circuit incorporates a thyristor/contactor switch that adds minimum complexity in exchange for greatly increasing each units bypass MTBF to 3,000,000 hrs.