Oct
30

## How to Avoid Common Mistakes in Data Center Planning and Design

The new, free eBook from Schneider Electric, “A Practical Guide to Data Center Planning and Design” will walk you through the data center planning process, including design and site selection. It also includes some best practices and success stories based on real customer implementations.

Download the eBook now to get some valuable tips that’ll help ensure your next data center is a resounding success – and doesn’t fall victim to any of those common mistakes.

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Oct
23

## Power Quality Tips

Here are some common signs that you might be having problems with power quality and steps to take to begin addressing some of the issues.

How do you know if you have power quality problems?

The answer is you either conduct a battery of specific tests in the course of a power quality analysis, or you produce reports from your power quality monitor. Fully executing either approach requires expertise not typically present in plant engineering.

It might be better to ask how you know to suspect power quality problems. Here are some common signs, but note that their absence does not mean your power quality is necessarily what it should be:

• A high rate of motor bearing failures and/or motor winding failures.

• The mechanics find pitted bearings in mechanical drives and other equipment under their purvey.

• Circuit board replacement is a normal occurrence. Same for PLC module replacement.

• Lights flicker. Lights don’t seem bright enough. Lighting system component replacement is a normal occurrence.

• Neutral conductors appear discolored.

• Nuisance breaker trips occur, but their source is rarely, if ever, identified.

• Insulation resistance (IR) testing shows cable failure at an abnormal rate. Note that a qualified electrical testing firm can tell you from experience whether the rate is abnormal.

If you have any of these symptoms, suspect one or more power quality problems. You may be able to identify some issues with a little sleuthing and some basic measurements, but you’ll probably need a qualified firm to do a complete workup.

If you suspect power quality problems that are due to equipment failures and other symptoms, how do you respond?

It is unlikely you have the required expertise in house, and you probably have to go through a process before you can bring in a firm with that expertise.

While that process is in progress, what can you do to start addressing at least some of these issues?

• Perform voltage measurements on all feeders, then on all branch circuits. Measure line to ground and line to line, RMS. You’re looking for low voltage, high voltage, and voltage imbalance. The sheer scope of the work may require hiring an electrical services firm. While awaiting approval, take the measurements for your critical equipment.

• Inspect for grounding and bonding errors. If you see a ground rod on the load side, that’s a red flag that something is wrong. This rod serves no electrical purpose, and is probably substituting for proper bonding.

• Check all transformers (except auto-transformers) for proper grounding; the National Electrical Code (NEC) considers them to be separately derived sources.

One way to turbocharge this process is to start keeping a spreadsheet of the problems as they occur if they seem related to power quality.

If you note key information, you can sort in a way that will enable you to conduct a Pareto analysis. This will, for one thing, reveal patterns that can lead to quicker resolution.

Include these fields:

• Whether the supply is a branch circuit or feeder.
• Nominal voltage.
• Building or area where load is situated.
• Affiliated production line, if applicable.
• Type of equipment served (use standardized codes, such as 1 for production motor with drive, 2 for production motor without drive, 3 for lights, 4 for HVAC, 5 for computers, etc.).

P3 strives to bring you quality relevant industry related news.

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Oct
16

## Effective Electrical Safety Comes Down to Two Factors

This technical paper on effective workplace electrical safety details the critical question that those responsible for safety must ask.

P3 strives to bring you quality relevant industry related news.

1644 Hits
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Oct
09

## How To Check For Harmonics In Electrical Power Systems

Harmonics are electric voltages and currents on an electric power system that can cause power quality problems. Because equipment and machinery can malfunction or fail in the presence of high harmonic voltage and/or current levels, harmonic distortion has become a growing concern for facility managers, users of automation equipment, and engineers. While the presence of harmonics won't make it impossible for a factory or office to operate, the degree of impact depends on how much the power system can withstand and how susceptible the equipment is to harmonic distortion.

What Causes Harmonics?

Harmonics are created by electronic equipment with nonlinear loads drawing in current in abrupt short pulses. The short pulses cause distorted current waveforms, which in turn cause harmonic currents to flow back into other parts of the power system. Harmonics are especially prevalent when there are many personal computers, laser printers, fax machines, copiers, or medical test equipment, fluorescent lighting, uninterruptible power supplies (UPSs), and variable speed drives all on the same electrical system.

Harmonics degrade the level of power quality and its efficiency, particularly in a commercial building or industrial facility. In general, most buildings can withstand nonlinear loads of up to 15% of the total electrical system capacity without concern. If the nonlinear loads exceed 15%, some non-apparent negative consequences can result.

Common Problems Caused by Harmonics

The three-phase system consists of three individual phase conductors and a neutral conductor. If all the phase conductors carry the same current, the phase currents tend to cancel one another out provided there is a balanced load. This balanced load makes it possible to reduce the size of the neutral conductor. Unfortunately, switched mode power supplies used in computers have a very high third-harmonic current. While harmonic currents cancel out on the neutral wire, the third harmonic current is additive in the neutral. In buildings with a large number of installed personal computers, the neutral wire can carry much higher currents than the wire was designed to accommodate, creating a potential fire hazard.

Overheating Transformers and Increased Associated Losses

For transformers feeding harmonic-producing loads, the eddy current loss in the windings is the most dominant loss component in the transformer. This eddy current loss increases proportionate to the square of the product's harmonic current and its corresponding frequency. The total transformer loss to a fully loaded transformer supplying to a nonlinear load is twice as high as for an equivalent linear load. This causes excessive transformer heating and degrades the insulation materials in the transformer, which eventually leads to transformer failure.

Nuisance Tripping of Circuit Breakers

All circuits containing capacitance and inductance have one or more resonant frequencies. When any of the resonant frequencies correspond to the harmonic frequency produced by nonlinear loads, harmonic resonance can occur. Voltage and current during resonant frequency can be highly distorted. This distortion can cause nuisance tripping in an electrical power system, which can ultimately result in production losses.

How to Diagnose and Fix Harmonics

A harmonics analyzer is the most effective instrument for performing detailed analysis of power quality to determine the wave shapes of voltage and current on respective frequency spectrums. A harmonic analyzer is also useful in instances where the lack of obvious symptoms prevent you from determining if harmonics are a cause for concern.

A harmonics analyzer is used to provide a detailed analysis of the suspect source. Using this data, the harmonic ratio function calculates a value from 0% to 100% to indicate the deviation of non-sinusoidal and sinusoidal waveform. This value indicates the presence of harmonics. This information can be used to prevent or reduce equipment downtime and repair costs.

P3 strives to bring you quality relevant industry related news.

See the origial article at:

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Oct
02

## Puerto Rico's debt-plagued power grid was on life support long before hurricanes wiped it out

A view of downtown San Juan, Puerto Rico, where officials say it will likely be four to six months before power is fully restored across the U.S. territory. (Carolyn Cole / Los Angeles Times)

At a public housing complex just outside the tourist district in Old San Juan, residents must make their way beneath a downed electrical pole to get in the front door. Another broken power pole blocks the road outside, and a third is sprawled next to the parking lot out back.

“At Fortaleza they have light, but not here,” said Rosa Rivera, 53, a retired maintenance worker, referring to the governor’s official residence. Rivera was sitting outside in her wheelchair Thursday to avoid the suffocating heat inside with no air conditioning.

Angel Perez, who lives nearby in the upscale Condado neighborhood, has called the city repeatedly to find out when the power — out across more than 95% of Puerto Rico since Hurricane Maria hit on Sept. 20 — will be restored.

"No one has come,” Perez said. “They don't pick up the phone."

In downtown San Juan, electric lines lie in the road and poles block apartment complexes, like the Residencia Parque San Lorenzo. (Carolyn Cole / Los Angeles Times)

Puerto Rico officials say it will likely be four to six months before power is fully restored across the U.S. territory of 3.5 million people. The island’s faltering electrical grid, now crippled by the twin blows of Hurricane Maria and Hurricane Irma, already was struggling to keep the lights on after a history of poor maintenance, poorly trained staff, allegations of corruption and crushing debt.

As recently as 2016, the island suffered a three-day, island-wide blackout as a result of a fire. A private energy consultant noted then that the Puerto Rico Electric Power Authority “appears to be running on fumes, and … desperately requires an infusion of capital — monetary, human and intellectual — to restore a functional utility.”

Puerto Ricans in early 2016 were suffering power outages at rates four to five times higher than average U.S. customers, said the report from the Massachusetts-based Synapse Energy Economics.

And then came Maria.

The collapse of the power system has tumbled down the infrastructure chain, making it difficult to pump water supplies — the water authority is one of the power authority’s biggest clients — and also to operate the cellular phone system, which also relies on the power grid.

Residents have been scrounging for scarce fuel to power generators long enough to keep refrigerators and a light or two running. At night, many drag mattresses out to balconies and porches to escape the heat. Hospitals have seen life support systems fail and most business has come to a halt.

Much of the booming capital has been shrouded in nighttime darkness, except for the few restaurants able to stay open with generators — glowing magnets of cool air, iced drinks and salsa music.

Puerto Rico largely survived Hurricane Irma, which killed three people and led to widespread power outages when it sideswiped the island two weeks ago. In relatively short order, the government-owned PREPA was able to restore electricity to 96% of its 1.5 million customers.

But the ferocious winds of Hurricane Maria a week later took out 55% of the island’s transmission towers. Government officials and emergency responders said the island’s power grid was effectively destroyed.

"Our infrastructure and energy distribution systems suffered great damages," Puerto Rico Gov. Ricardo Rossello said.

Mike Hyland, senior vice president of engineering for the American Public Power Assn., a nonprofit organization that sent equipment and utility experts to help with recovery, said officials are conducting a comprehensive assessment of damage to the electrical system, relying in part on drones sent by the New York State Department of Environmental Conservation.

“It is going to be a long and arduous process and patience is the key word,” Hyland said.

Restoring Puerto Rico’s power will involve much more than replacing downed poles and cables. The entire system of generation, transmission and distribution must be rebuilt, including replacement of high-voltage transmission lines Hyland said.

The island has been relying on generators large and small, but fuel shortages have limited their capacity.

At least two people died this week in the city of San Juan after the generator producing electricity that powered life support systems ran out of fuel, city officials said.

The lack of power has brought some water pumps to a standstill, and a growing number of homes are running out of clean water.

U.S. military officials, part of a contingent of thousands of extra troops being brought in to help with recovery, are helping expedite fuel deliveries to hospitals.

By midweek, 689 of the 1,000 gas stations on the island were operating, Puerto Rico officials said. Fuel was delivered to at least 200 of those stations on Wednesday, they said.

The warnings about impending electricity problems that were issued even before Hurricane Maria hit stemmed from the island’s long history of power outages and the lack of substantial refurbishing and maintenance.

Hurricane Georges in 1998 left the island without power for three weeks. The tropical storm destroyed 30,000 houses and damaged at least another 60,000.

Last year, the island suffered a massive blackout after a fire broke out at one of the island’s main electricity plants, leaving half of the territory’s residents in the dark.

PREPA at the time said two transmission lines had failed.

While natural disasters have underscored the problems of the island’s electrical system, over the past few years the island’s and the power company’s money problems made the power grid particularly susceptible to crippling damage by storms.

As of 2014 the government-owned company was $9 billion in debt, and in July, it filed for bankruptcy under the provisions set by the Puerto Rico Oversight, Management, and Economic Stability Act, a law signed by President Obama in 2016. Problems accumulated. Cutbacks in tree pruning left the 16,000 miles of primary power lines spread across the island vulnerable. Inspections, maintenance and repairs were scaled back. Up to 30% of the utility’s employees retired or migrated to the U.S. mainland, analysts said, and the utility had trouble hiring experienced employees to replace them. The neglect led to massive and chronic failures at the Aguirre and Palo Seco power plants. The three-day blackout in September 2016 underscored how fragile the system was, and that the company was "unable to cope with this first contingency," the Synapse Energy report said. This week, for the first time since the storm, electrical crews began appearing not just in the capital, but in neighboring Carolina and Rio Grande. Faced with a tangle of downed poles, lines and transformers on nearly every street, it wasn’t clear how much progress they were making. Across the island, residents have been waiting in gas lines not so much to drive, but to keep their generators running. Eduardo Millan, sweating in the the afternoon heat in one such line, said he needed fuel for the generator at his home near the airport. P3 strives to bring you quality relevant industry related news. See the origial article at: http://www.latimes.com/nation/la-na-puerto-rico-power-20170925-story.html 1999 Hits 1999 Hits Sep 25 ## The Wild World of Electrical Slang Think you're up on your electrical slang? Take a look at 10 of our favorite slang terms, and see if you know which electrical product (or individual) it's referring to. 1. Attic Monkey An electrician with a slim build, best suited for crawling through tight spaces 2. Baloney Bender A person who works with thick or heavy cable 3. Bunny Gun A cable cutter used to cut copper or aluminum wire. 4. Buzzard Tongue Zip ties 5. Chili Bowl An oversized pin-type insulator 6. Dog Bone Extra-high voltage yoke plates — named so for their shape 7. Egg Breaker A guy strain insulator 8. Ice Skates Holds gem box in sheetrock by offering counter pressure to the box ears 9. Music Rack A hot-line tool rack 10. Toilet Seat Cover A weatherproof plate for T11 boxes with either one or two flip-top lids P3 strives to bring you quality relevant industry related news. See the origial article at: http://www.ecmweb.com/training/wild-world-electrical-slang 2545 Hits 2545 Hits Sep 19 ## Ameren Sends 2nd Wave of Workers to Assist Hurricane Irma Recovery With an additional wave of Ameren employees headed to Florida, Ameren now has approximately 1,000 employees and contractors assisting in the restoration and rebuilding efforts in response to Hurricane Irma. The company also announced today an additional$25,000 donation to aid Red Cross relief efforts in Florida, following a similar donation last week for Texas after Hurricane Harvey.

"Historic storms such as Harvey and Irma require a large collaborative response effort from utilities and relief organizations," said Warner Baxter, chairman, president and CEO of Ameren Corporation. "Being able to assist in power restoration efforts and offer resources to organizations that help those in need can make a real difference in recovery efforts – which is why we are providing both. For those who have been affected by these devastating storms, our hope is to help get these communities back on their feet as quickly as possible."

Ameren resources working in Florida or headed that way include those from Ameren Missouri, Ameren Illinois and Ameren Transmission.

According to the Edison Electric Institute, Hurricane Irma is likely to be one of the largest and most complex power-restoration efforts in U.S. history.

Ameren participates in the electric industry's mutual assistance network through Edison Electric Institute, which means the company is available to help with emergencies in other parts of the country such as Superstorm Sandy in 2012 and Hurricane Katrina in 2005. Customers of Ameren Illinois and Ameren Missouri have benefited from past assistance from other utilities following severe weather in the Midwest, including tornados, ice storms and other weather events.

P3 strives to bring you quality relevant industry related news.

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Sep
11

## IEEE Standards for SPDs

The Institute of Electrical and Electronics Engineers, IEEE, has produced a set of standards known as the “trilogy” to address the surge environment, characterize surges, and define surge testing in low-voltage AC power circuits. The following standards constitute the trilogy.

• IEEE C62.41.1, “Guide on the Surge Environment in Low-Voltage (1000 V and less) AC Power Circuits”
• IEEE C62.41.2, “Recommended Practice on characterization of Surges in Low-Voltage (1000 V and less) AC Power Circuits”
• IEEE C62.45, “Recommended Practice on Surge Testing for Equipment Connected to Low-Voltage (1000 V and Less) AC Power Circuits”

In addition IEEE has produced the following standards for the application and testing of SPDs.

• IEEE C62.47-1992, “IEEE Guide on Electrostatic Discharge (ESD): Characterization of the ESD Environment”
• IEEE C62.48, “Guide on Interactions Between Power System Disturbances and Surge-Protective Devices”
• IEEE C62.62, “Test Specifications for Surge-Protective Devices (SPDs) for Use on the Load Side of the Service Equipment in Low-Voltage (1000 V and Less) AC Power Circuits”
• IEEE C62.72, “Guide for the Application of Surge-Protective Devices for Low-Voltage (1000 V or Less) AC Power Circuits”

These standards have been developed from many years of scientific research and are recognized by American National Standards Institute (ANSI). They are intended for use primarily by surge equipment manufacturers and provide valuable reference for consulting engineers that specify surrge protection devices (SPDs).

IEEE C62.41.1

Guide on the Surge Environment in Low-Voltage (1000 V and less) AC Power Circuits.

This guide, the first in the trilogy, provides readers with a comprehensive information on surges, the environment in which they occur and is a reference for the second document of the trilogy. The surge environment is described using:

• Three location categories (C, B or A) according to their position from the building service entrance.
• Level of exposure to major sources of surges: lightning and load switching.
• Representative waveforms of surge voltages and surge currents are described for each category.

This guide should not be used as a testing document to define performance, survivability or any other related test criteria. Any statement that a SPD “meets the requirement of” or “is certified to”, this document is inappropriate and misleading.

IEEE C62.41.2

Recommended Practice on characterization of Surges in Low-Voltage (1000 V and less) AC Power Circuits.

This guide, the second in the trilogy, presents recommendations on the selection of surge waveforms, amplitudes of surge voltages and currents used to evaluate equipment immunity and performance of SPDs. Two recommended “standard” waveforms are used as a simplified representation of the surge environment:

• 0.5µs/100kHZ ringwave
• 1.2/50/8-20µs combination wave

IEEE C62.45

Recommended Practice on Surge Testing for Equipment Connected to Low-Voltage (1000 V and Less) AC Power Circuits.

This guide, the third in the trilogy, focuses on surge testing procedures (using the simplified waveform representations) for obtaining reliable measurements and enhancing operator safety. The intent is to provide background that can help determine whether equipment or a circuit has adequate ‘withstand’ capability.

• Signal and data lines are not addressed in this document.
• The document does not indicate withstand levels that might be assigned to specific equipment.
• An important objective of the document is to call attention to the safety aspects of surge testing.
• Underwriters Laboratories, Inc. uses these guidelines as a reference in their performance and safety testing of SPDs.

IEEE C62.48

IEEE Guide on Interactions Between Power System Disturbances and Surge-Protective Devices

This guide applies to surge-protective devices (SPDs) manufactured to be connected to 50 Hz or 60 Hz ac power circuits rated at 100–1000 V rms. It describes the effects on SPDs of power system disturbances occurring in these low-voltage ac power circuits. The disturbances are not limited to surges. The effects of the presence and operation of SPDs on the quality of power available to the connected loads are described. The interaction among multiple SPDs on the same circuit is also described. This guide discusses both voltage and current surges. The current surges discussed in this guide are the result of voltage surges. Current surges that are solely the result of load changes and do not result in voltage increases, such as a short circuit, are not discussed in this guide.

An SPD’s primary purpose is to provide surge protection. Devices discussed in this guide contain at least one nonlinear component for diverting surge current and/or dissipating surge energy, such as a metal oxide varistor (MOV), silicon avalanche diode (SAD), thyristor, or spark gap. Uninterruptible power supplies (UPSs), ferroresonators, motor-generators, and filters containing only inductive and/or capacitive components are not considered SPDs in this guide.

IEEE C62.62

IEEE Standard Test Specifications for Surge-Protective Devices (SPDs) for Use on the Load Side of the Service Equipment in Low-Voltage (1000 V and Less) AC Power Circuits

This standard applies to surge-protective devices (SPDs) intended to be installed on the load side of the service equipment connected to 50 Hz or 60 Hz alternating current (ac) power circuits rated at 1000 V (root mean squared [rms]) or less. Performance characteristics and standard methods for testing and rating are established for these devices, which may be composed of any combination of components. The tests in this standard are aimed at providing comparisons among the variety of surge-protective devices available.

IEEE C62.72

IEEE Guide for the Application of Surge-Protective Devices for Low-Voltage (1000 V or Less) AC Power Circuits

The transient overvoltages or surge events that are described and discussed in this guide are those that originate outside of a building or facility and impinge on a power distribution system (PDS) through the service entrance conductors. Transient overvoltages or surge events that originate from equipment within a specific facility are not within the scope of this document.

This guide applies to surge-protective devices (SPDs) that are manufactured for connections to 50 Hz or 60 Hz ac power circuits that are rated between 100 V rms and 1000 V rms. This guide applies to SPDs that are specifically identified, labeled, or listed for connections on the load side of the service entrance main overcurrent protective device. This guide does not cover those SPDs identified, labeled, or tested as a secondary surge arrester intended for connections on the line side of the service entrance main overcurrent protective device. The SPDs covered in this guide are those manufactured for use in an association with electrical power distribution equipment such as load centers, motor control centers, panelboards, switchboards, switchgear, and end-use equipment installed in commercial and industrial facilities. This guide excludes SPDs associated with retail and consumer appliances and components for residential use.

The SPDs discussed in this guide contain at least one nonlinear component for either diverting surge currents and/or dissipating surge energy. Examples of such nonlinear components are metal-oxide varistors (MOVs), silicon avalanche diodes (SADs), spark gap tubes, or thyristors. Ferroresonators, motor-generators, uninterruptible power supplies, and filters containing only inductive or capacitive components are not considered SPDs in the guide.

IEEE C62.47-1992

IEEE Guide on Electrostatic Discharge (ESD): Characterization of the ESD Environment

The purpose of this guide is to describe the electromagnetic threat posed to electronic equipment and subassemblies by actual Electrostatic Discharge (ESD) events from humans and mobile furnishings. This guide organizes existing data on the subject of ESD in order to characterize the ESD surge environment. This guide is not an ESD test standard. An appropriate ESD test standard should be selected for equipment testing. The manufacturing, handling, packaging, and transportation of individual electronic components, including integrated circuits, are not discussed, and this guide does not deal with mobile items such as automobiles, aircraft, or other masses of comparable size. ESD results in a sudden transfer of charge between bodies of differing electrostatic potentials. In this guide, the term ESD includes charge transfer whether or not an arc occurs or is perceived.

ESD phenomena generate electromagnetic fields over a broad range of frequencies, from direct current (dc) to low gigahertz. The term ESD event includes not only the discharge current, but also the electromagnetic fields and corona effects before and during a discharge. In this guide the intruder is often a human, but it may be any object that is moved, such as a chair, an equipment cart, a vacuum cleaner, or the equipment victim itself, whether or not it is in conductive contact with a human. The equipment victim is usually a fabricated electronic equipment or subassembly and is generally, although not necessarily, at local electrostatic ground potential.

The equipment victim may be the receptor to which the discharge takes place from the intruder; less frequently, the equipment victim may be the intruder. Alternatively, the equipment victim may be affected by the electromagnetic fields generated by a discharge between an intruder and a receptor. Receptors and intruders that may not themselves are equipment victims include furniture such as metal chairs, carts, tables and file cabinets, as well as other electronic equipment.

This guide discusses and cites references that describe the ways in which a body builds up charge and the characteristics of discharge currents and fields. Descriptions and references are also given for electrical equivalent circuits to be used in understanding and simulating the discharge current between intruder and receptor masses. Publications that are specifically referenced in the text of the guide are listed in the Section 3, while Section 9 cites additional publications in both ESD and related areas.

Most of the work that has been published in connection with actual ESD is related to discharges from humans, usually grasping or in association with a metal object. Far less published data exists for discharges from humans without metal objects, and from mobile furnishings, and virtually no data exists for discharges from human torsos or clothing. For this reason, primary emphasis is placed on discharges from humans with associated metal objects, with some additional material relating to ESDs from mobile furnishings. All discharges are assumed to take place in an air environment.

Finally, all of the published time-domain data on which this guide relies were taken using instrumentation with either a 400 MHz or a 1 GHz bandwidth.

IEEE Std 1100™-2005

IEEE Recommended Practice for Powering and Grounding Electronic Equipment

This document presents recommended design, installation, and maintenance practices for electrical power and grounding (including both safety and noise control) and protection of electronic loads such as industrial controllers, computers, and other information technology equipment (ITE) used in commercial and industrial applications.

IEEE Std. 142-2007

IEEE Recommended Practice for Grounding of Industrial and Commercial Power Systems

The problems of system grounding, that is, connection to ground of neutral, of the corner of the delta, or of the midtap of one phase, are covered. The advantages and disadvantages of grounded vs. ungrounded systems are discussed. Information is given on how to ground the system, where the system should be grounded, and how to select equipment for the ground of the neutral circuits. Connecting the frames and enclosures of electric apparatus, such as motors, switchgear, transformers, buses, cables, conduits, building frames, and portable equipment, to a ground system is addressed. The fundamentals of making the interconnection of a ground conductor system between electric equipment and the ground rods, water pipes, etc., are outlined. The problems of static electricity— how it is generated, what processes may produce it, how it is measured, and what should be done to prevent its generation or to drain the static charges to earth to prevent sparking—are treated. Methods of protecting structures against the effects of lightning are also covered. Obtaining a low-resistance connection to earth, use of ground rods, connections to water pipes, etc., are discussed. A separate chapter on electronic equipment is included.

IEEE standards can be obtained online in the IEEE Standards Store

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See the origial article at: http://www.nemasurge.org/ieee-standards-for-spds/

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Sep
05

## Understanding Surge Protective Device Ratings

How to know what kA rating to use

Selecting the appropriate surge protective device (SPD) can seem like a daunting task, especially with all of the different types on the market today. The surge rating or kA rating of an SPD is one of the most misunderstood ratings. Customers commonly ask for an SPD to protect their 200A panel. There¡¯s also a tendency to think that the larger the panel, the larger the kA device rating needs to be for protection. As you will see in this article, this is a common misconception.

When a surge enters a panel, it does not care or know the size of the panel. So how do you know if you should use a 50kA, 100kA, or 200kA SPD? As discussed in the IEEE standard C62.41, a building's wiring adds impedance that will limit the surge current. The standard also states that 10kA devices have been adequately limiting surge currents at the service entrance for several years. Therefore, it's reasonable to say the largest surge that can enter a building's wiring system is 10kA; however, a direct lightning strike would produce a much larger surge. The extremely high voltage associated with a direct lightning strike would most likely flashover, thereby "self-limiting" the surge. So why would you ever need an SPD rated for 200kA? Simply stated — for longevity.

You might think: If 200kA is good, then 600kA must be three times better, right? Not necessarily. At some point, the rating diminishes its return, only adding extra cost and no substantial benefit.

Because most SPDs on the market use a metal-oxide varistor (MOV) as the main limiting device, we can explore how/why higher kA ratings are achieved. If an MOV is rated for 10kA and sees a 10kA surge, it would use 100% of its capacity. This can be viewed somewhat like a gas tank, where the surge will degrade the MOV a little bit (no longer is it 100% full).

If the SPD has two 10kA MOVs in parallel, it would be rated for 20kA. Theoretically, the MOVs will evenly split the 10kA surge, so each would take 5kA. In this case, each MOV has only used 50% of its capacity, which degrades the MOV much less — leaving more left in the tank for future surges.

Does this translate into surge "stopping power"? No. Just because an SPD has two or 20 MOVs in parallel doesn't mean it will limit the 10kA surge any better than a single SPD of the same rating. The main objective of having MOVs in parallel is to increase the longevity of the SPD. Again, keep in mind that this is subjective — at some point you are only adding cost by incorporating more MOVs and receiving little benefit.

As mentioned before, panel size does not really play a role in the selection of a kA rating. The location of the panel within the facility is much more important. IEEE C62.41.2 defines the categories of expected surges within a facility as:

Category C: Service entrance, more severe environment: 10kV, 10kA surge.
Category B: Downstream, greater than or equal to 30 ft from category C, less severe environment: 6kV, 3kA surge.
Category A: Further downstream, greater than or equal to 60 ft from category C, least severe environment: 6kV, 0.5kA surge.

Category C devices can be used in Category B or A locations; however, a Category C device would be excessive for a Category B location. Some engineers may decide to specify Category C devices to have a conservative design, but this will also only add cost while adding little to no benefit.

Although UL 1449 third edition does not use the exact category terminology as IEEE C62.41.2, it does define three major types. Type 1 can be installed on the line side of the service entrance overcurrent device (no extra overcurrent device needed), which is similar to Category C. Type 2 is similar to Category B and can only be installed on the load side of the service entrance overcurrent device. Type 3 and Category A are point of utilization devices like a surge power strip that is plugged into a wall outlet. While UL types and IEEE categories are similar, they are not 100% interchangeable. UL Type 1 devices are often used in Type 2 locations. The benefit of doing this is that there is no extra overcurrent device needed.

How do you know what kA rating to use? The IEEE categories provide a good base for selecting kA ratings. There are many "right" sizes for each category, but there must be a balance between redundancy and added cost. Qualified judgment should always be used when selecting the appropriate kA rating for an SPD.

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See the origial article at:

1949 Hits
1949 Hits
Sep
05

## Surge Damage: What is at Risk?

Surges or transients can damage, degrade or destroy the sensitive electronic equipment in offices or businesses resulting in:

• Equipment damage
• Equipment downtime
• Losses in resulting revenues
• Productivity losses due to downtime

Page content:

What is at risk?
What are signs of damage?

There are three main types of effects that transients have on your electronic equipment:

Disruptive effects:

These effects are usually encountered when a transient enters the equipment by inductive coupling. The energy source for this inductive coupling can act on the data output lines that integrate an electronic installation. The electronic components then try to process the transient as a valid logic command. The result is system lock-up, malfunction, erroneous output, lost or corrupted files, and a variety of other undesirable effects.

Dissipative effects:

These effects are associated with repeated stresses to IC components. The materials used to fabricate IC’s can only withstand a certain number of repeated energy level surges. After long-term degradation, the device fails to operate properly. The failure is due to the cumulative build-up of transient-created stresses which result in arc-overs, shorts, open circuits, or semiconductor junction failures within the IC.

Destructive effects:

These effects include all conditions where transients with high levels of energy cause equipment to fail instantaneously. Very often, there is actual physical damage apparent, like burnt PC boards or melting of electronic components.
Destructive effects can occur when noise pulses are too fast for power supply regulator circuits to respond by limiting transient voltage to acceptable levels. Also, transients on the power line may subject electronic components to overwhelming voltage levels. For example, components like rectifier diodes can fail immediately when their Peak Inverse Voltage (PIV) rating is exceeded. PIV diode ratings in a well-designed computer can be in the 1 kV – 1.5 kV range. Transients on AC lines can easily exceed 1.5 kV.
What are the Symptoms of Surge Damage?

There are several possible symptoms to look for to determine whether surges are affecting your office or business.

• Computer lock-ups or latch-ups
• Unexplainable data corruption
• Equipment shutdown
• Flickering lights
• Premature failure of electronic ballasts or printed circuit boards

There is no such thing as a transient free facility. Many people do not realize that their company’s productivity and profitability is being significantly impacted by the effects of transients. The problems described above result in billions of dollars of lost profits to U.S. businesses every year.

P3 strives to bring you quality relevant industry related news.

See the origial article at: http://www.nemasurge.org/surge-damage/#symptoms

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Aug
28

## Improve System Efficiency by Addressing Waste Heat

Actively search out sources of waste heat and pursue techniques to recover the wasted heat.

What kind of gas mileage would you expect if you were driving your car with one foot on the gas and the other on the brake? The results from this approach would be pretty poor.

Many facilities have a similar dynamic going on with “waste heat.” Continuing on with the car example, if you look under the hood (and understand what you’re looking at), you’ll see some waste heat recovery techniques in play.

What kinds of techniques might your facility use? Before you can really answer that question, you need to identify the waste heat sources and quantify the amount of waste heat from each source.

Once you have that information, look at processes or equipment that requires additional heat. Many waste heat recovery techniques involve providing at least some of that heat by redirecting waste heat.

Consider a plant that had a small annealing furnace. This furnace used outside air, which had to be preheated in the winter just to get up to the inside air temperature. Meanwhile, several hot process situated nearby were ducting their waste heat air to the outside (and pulling already heated ambient air out as well). Some reducting (along with pressure controls and approval by the boiler inspector prior to actual implementation) changed much of the waste heat into process-used heat.

Another plant had a row of small cooling towers outside the building. A closed piping system ran through the towers. The water cooled a manufacturing process and was simply circulated through the pipes. Hot water ran to the cooling towers, and cooled water ran back to the equipment that needed cooling. This system is very much like the cooling system in a car, except the car has a radiator instead of a row of cooling towers.

The plant had recently hired a new plant engineer, and he noticed almost none of the pipes in the ceiling were color coded or even labeled. So he hired an industrial services firm to identify the pipes. In the process of identifying these, they were amazed to discover that the uninsulated cooling tower return pipe was run between two hot water pipes for about thirty feet. And the pipes were touching each other, causing a loss of energy in the heated water while degrading the cooling system.

Don’t wait to incidentally find instances of gas and brake. Actively look for them. Where are you running hot air, water, etc., and where are you running cooling air or water supply? Where are you generating heat for use, and where are you exhausting heat instead of using it?

P3 strives to bring you quality relevant industry related news.

1833 Hits
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Aug
21

## Watch the North American power grids respond to the 2017 eclipse, live!

On Monday, August 21, the North American power grid will be the subject of a celestial experiment: now that we have lots of grid-connected solar power, what happens when the sun goes away?

You can watch this experiment unfold, live, on instruments at two free web sites: LiveEclipse.PQube3.com/West and LiveEclipse.PQube3.com/east. (After the eclipse finishes, the data gathered by these instruments will be shared with scientists around the world.)

The eclipse will pass through the two largest North American power grids, informally called the Western Interconnect and the Eastern Interconnect. The eclipse will miss the other two main grids: Texas and Quebec.

Minute by minute, grid operators carefully balance the output of thousands of grid-connected generators against the varying total load on the grid. This balancing act is eased by two characteristics of grid load called “diversity” and “predictability”.

“Diversity”, in this context, means that all the loads on the grid never turn on and off at exactly the same time. For example, when some air conditioners happen to be cycling on, others happen to be cycling off; and the grid-wide average, over the entire Western Interconnect, is far steadier than any individual load. “Predictability” means that the grid operators know the general pattern of loads, and the general pattern of generators, including solar. For example, solar is predictably on during the day and off at night, and local weather forecasts can make fairly precise predictions about solar generation.

The eclipse will challenge, for the first time, both the diversity and predictability of a significant amount of solar power generation.

The eclipse hits large swaths of solar power generators simultaneously, reducing diversity; fortunately for the grid operators, we know the exact eclipse path and timing, so grid operators can plan for solar power losses.

But grid operators lack complete information about how much solar generation exists, and where it is located. The operators know exactly where the large solar arrays are, but there’s less information about where all the smaller rooftop solar arrays are, or how much power they can generate. And that’s what makes this experiment interesting.

You can see the balance between grid generation and grid load in the grid frequency, which is kept at 60 cycles per second, or 60 Hertz. Higher than 60.000 Hertz means there’s slightly more generation than load; lower, there’s slightly more load than generation. The grid operators dance with the frequency, adjusting the generator settings throughout the grid to maintain a steady flow of power.

Power Standards Lab is a private company in Alameda, California, that does research projects with the U.S. Department of Energy.

As a public service, PSL has set up two public instruments that show the “solar irradiance”, which is the amount of sun power available right now, and the “Frequency”, which is the balance between grid generation and grid load. One of these instruments is on a rooftop in sunny Windsor, California, monitoring the Western Interconnect grid; the other is in a pasture in Zebulon, North Carolina, monitoring the Eastern Interconnect grid.

Readings from both instruments are available to the public at LiveEclipse.PQube3.com/West and LiveEclipse.PQube3.com/east.

It’s an entirely different way to watch the eclipse unfold!

P3 strives to bring you quality relevant industry related news.

See the origial article at: https://www.powersurvey.com/blog/watch-the-north-american-power-grids-respond-to-the-2017-eclipse-live/

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Aug
07

## Report: Lithium-Ion to Gain One-Third of Data Center UPS Market by 2025

Lithium-Ion batteries, widely used in consumer electronics, including smartphones, and electric cars, have just started being adopted for energy storage in data center backup systems. While vendors that sell this equipment claim that its total cost of ownership in the long run is lower than the traditional lead-acid-based energy storage, the upfront cost is high enough to prevent the technology from taking off in the data center market today.

That’s not going to be the case in a few years, according to a new report by the research firm Bloomberg New Energy Finance, which says lithium-ion batteries will command a quickly growing portion of the data center UPS market in North America and Europe.

BNEF expects overall demand for battery backup in data centers in two regions to go from 3.5 gigawatt-hours in 2016 to 14 gigawatt-hours in 2025. During the same period, lithium-ion’s share of the market will rise from 1 percent to 35 percent, the analysts predict.

Annual data center lithium-ion penetration in North America and Europe, 2016-25 (GWh); (Source: Bloomberg New Energy Finance)

According to Schneider Electric, which sells data center UPS systems of both types, lithium-ion’s key advantages over the incumbent technology include:

• Fewer battery replacements (perhaps none) required over the life of the UPS eliminates the risk of downtime posed by battery replacement
• About three times less weight for the same amount of energy
• Up to ten times more discharge cycles depending on chemistry, technology, temperature, and depth of discharge
• About four times less self-discharge (i.e. slow discharge of a battery while not in use)
• Four or more times faster charging, key in multiple outage scenarios

(Source: Schneider Electric whitepaper)

The major drawbacks of lithium-ion, again according to Schneider, are:

• About two to three times more capex for the same amount of energy due to higher manufacturing cost and cost of required battery management system
• Stricter transportation regulations

Simon Zhang, a marketing manager at Schneider, wrote in a blog post that lithium-ion battery cost will go down as a result of greater and greater adoption, driven primarily by growth in the electric-car industry:

“Li-ion technology will snatch 40% of market share in just 8 years. In a market that’s not exactly known for making rapid technological shifts, that is nothing short of remarkable. While VRLA has much lower upfront cost today, lithium-ion batteries will experience significant cost reductions, driven by sizeable ramp-up in demand in the coming decade, much of which will be for electric vehicles. This cost reduction and increasing familiarity with the use of lithium-ion batteries for back-up in data centers will help ramp up adoption in this timeframe.”

P3 strives to bring you quality relevant industry related news.

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Jul
31

## Uncovering PQ Problems with Industrial LED Lighting

### Raising awareness of power quality issues with high-bay LED lighting systems operating in plant settings

The deployment of electronic LED lighting has grown dramatically over the past five years. Most luminaire manufacturers now offer a family of high-bay industrial LED products operating at AC line voltages (347V to 480V). Many industrial plants installed anywhere from a few hundred to a few thousand high-bay LED luminaires in their facilities. However, electronic LED drivers and fixtures were designed without truly understanding the electrical environments of industrial plants once using magnetic high-intensity discharge (HID) lighting operating at 480V.

As with other new electrotechnologies, manufacturers rushed to market with high-bay LED products to replace the inefficient magnetic HID technologies’ poor light quality. No efforts were made to understand the power quality performance of 480V lighting branch circuits. Stemming from the philosophy to protect outdoor LED street lighting, manufacturers assumed the only power quality threat to their drivers was voltage surges — ring wave and combination wave. Thus, large surge protective devices (SPDs) rated for 10kV at 10/20kA were included in LED luminaires as “add-on” SPDs to protect the driver(s).

Unfortunately for many end-users, high-bay LED luminaires installed in industrial plants failed at unacceptable rates from about 1% to as much as 50% two months to two years after installation. In some cases, failure rates would escalate within one year of the end of a five-year warranty. Reacting to failing LED lighting investment, users were forced to exercise their warranties.

Reacting to their customer demands, most manufacturers delivered replacement drivers. The cost of replacement drivers, however, was the smallest cost element required to get the lights back on in industrial plants where lighting is critical to maintaining safe work environments. With fixture counts ranging from a few hundred to a few thousand, many users were forced to absorb high electrical labor costs to remove failed luminaires, replace drivers, and re-hang fixtures. Re-hanging their old HID lighting fixtures was not an option, especially since installing industrial LED lighting was a much larger investment than repairing or replacing their HID technologies. The cost of interruption to plant operations was also difficult to absorb. This cost can range from tens of thousands to millions of dollars. After enduring the high total costs of repairing and replacing their industrial LED lighting — a cost that can be as high as \$1 million — end-users quickly realized that the cost of power quality preparedness before engaging in an LED lighting retrofit project or new installation was many times less than the cost of recovering from failing LED lighting. The number of reactive power quality projects Electrotek has conducted for end-users and manufacturers is the stimulus for this article.

Fig. 1(a). Voltage trending in an industrial facility with LED lighting powered at 480V.

## Power quality voltage trends on branch circuits at four different facilities

Figure 1(a) illustrates a voltage trend in a heavy industrial plant where LED driver failures occurred. You can see there is noticeable separation between the average RMS voltage from phase to phase. There are also noticeable steps in the phase-to-neutral voltages with one major step occurring on Saturday, April 25. Prior to this date, the voltages were running a little low, but still within industry limits. You can also see that after the major step, there were significant excursions in the phase-to-neutral voltage over the next several days. There was also a voltage sag on April 24. The other interest point here is that after reviewing recorded disturbances, many of these characteristics actually represent voltage transient events with high dV/dt. (High dV/dt values indicate the line voltage changed quickly with respect to time. The change in volts can only be 50 to a few hundred volts, but the change in time can be in the one microsecond (1 × 10-6 second, or 1 µsec) range. Values of dV/dt may be high enough to damage driver electronics but not have a high enough voltage to cause a metal-oxide varistor (MOV), external or internal to a driver, to clamp. Take a look at the date/time event markers. There are four groups of power quality disturbance sets. The first set (occurring on April 22 at 18:58:32) involves mutliple events as well as the second and third sets. The fourth disturbance seems to be a single event.

Figure 1(b) illustrates a voltage trend in a commercial facility where LED driver failures also occurred. Here, there seems to be about a 24-hour cyclic pattern to the phase-to-neutral voltage. The average voltage appears to be around 283V and is still within industry limits. However, there were four voltage sags that occurred at different times. The first one seems to be dominant on Phase B while the others seem to be dominant on Phase A. All of the sags occur at a different time each day. You can also see that there were multiple sets of power quality disturbance events here. Many who set a power quality monitor do not activate the right recording functions and fail to record critical disturbance data that helps to explain why LED drivers fail. Many simply look at a voltage trend like the ones presented in this article and determine that there are no power quality problems at a lighting panel or on a lighting branch circuit. However, many of these disturbances, in fact, were also recorded as voltage transients with high dV/dt values.

Fig. 1(b). Voltage trending in a commercial facility with LED lighting powered at 277V.

Fig. 1(c). Voltage trending on an LED outdoor street lighting system powered at 120V.

Figure 1(c) illustrates a voltage trend for a commercial outdoor LED street lighting application where LED driver failures occurred. At this location, the voltage has lots of transient activity characteristics. Transient activity always seems to occur in the morning hour when the lights turn off and in the evening hour when the lights turn on. The other times where disturbances were indicated by a time stamp in between “turn off” and “turn on” are when voltage transients occur upstream of the 120V circuit derived from utility distribution power also serving residences in the area. Reviewing properly recorded disturbances along with voltage trends helps explain why the LED failures occurred.

Fig. 1(d). Voltage trending in a commercial facility with LED lighting powered at 480V.

Figure 1(d) illustrates a voltage trend in a commercial facility where LED drivers also failed. At this location, there is no distinct pattern to the dates/times in between the 24-hour cycles when the line voltage produced a maxima and minima. However, there seems to be more transients at the voltage maxima and minima, especially for the four maxima in the center of the trend. This indicates the turning on and turning off of a heavy load, which produced voltage transients with high dV/dt values.

Notice that in the above four figures of a one-week voltage trend, the power quality at each monitoring point at these four voltage levels was significantly
different. However, it is difficult to identify enough information about the quality of the line voltages and currents by only conducting a one-week monitoring period. Monitoring periods here were at least one month.

## Power quality disturbances and plant electrical systems

Power quality disturbances may originate from the incoming electric utility power feeder to a plant, but most are generated inside the plant’s electrical system, following the well-known ‘rule of thumb’ that most disturbances that cause malfunction and damage to electronic equipment originate inside customer facilities. Many industrial plants are fed at 4,160V to the switchgear. The voltage is then dropped down to 480V at the first transformer location. However, some plants are fed directly at 480V from the electric utility.

Non-linear loads, such as variable-frequency drives (VFDs) and other high-power equipment like induction motors, are powered at the 4,160V and 480V levels. These loads are powered at these higher voltage levels due to the amount of current they require to start up and operate. Powering them at these levels helps keep the conductor sizes smaller. Unfortunately, these loads generate power quality disturbances, which contain both low- and high-frequency content.

Fig. 2. These graphs show two cycles of high-frequency power quality disturbances in a steel plant.

Other power quality phenomena, such as that shown in Fig. 2, can be generated by the switching of contactors. Here, two cycles of high-frequency power quality disturbances are generated on a 480V lighting circuit. Notice from the harmonic spectrum of the voltage out to the 64th harmonic that the voltage contains disturbance energy above 1 kHz. Noticeable harmonic components are the 5th, 7th, 11th, 13th, 17th and 19th harmonic, which can be clearly seen in the low-frequency range.  Other noticeable harmonics in this heavy industrial plant are the 17th, 19th, 23rd, 25th and 28th. However, interharmonics can be seen all across the spectrum, and some interharmonic components near the 64th are as high as the 11th harmonic.

Electrical systems in industrial plants commonly use the 480V bus to support lossy magnetic HID (high-pressure sodium and metal-halide) lighting systems across an entire plant. Regardless of the disturbances generated by the loads on the 480V circuits, the HID magnetic ballasts, made of copper and iron, can tolerate just about any disturbance and keep right on going. The thermal energy generated by operating these core-and-coil ballasts increases plant heat load and actually degrades the ballast design faster than the poor power quality does. What can be done about the poor power quality on 480V circuits if you want to install high-efficiency, high-bay electronic LED lighting in these spaces?

The first thing a plant manager can do is document the non-linear and high-power loads operating on the 480V buses. Most 480V buses are tied together at least through a tie breaker at the switchgear level. If the plant has two electric utility feeds and operates with the tie breaker open, then it is wise to assume that at some point that breaker will be closed, linking the 480V buses together.

The Table outlines the information you should document about the loads on all 480V buses in the plant.

Conduct power quality monitoring on your 480V buses and panels currently powering HID lighting. Knowing what types of disturbances are occurring on each 480V bus and lighting panel which will power LED lighting is a critical part of managing the power quality for your high-bay electronic LED lighting system. There is likely more than one 480V bus in your industrial plant powering lighting. These buses may be fed by different sections of switchgear on different electric utility feeds. Each bus likely supports different types of high-power non-linear with different degrees switching of these loads. Errors in the phase and neutral wiring will also cause disturbances generated by load operation to be worse when they reach the industrial LED lighting. You must also have a well-designed grounding system. Grounding must be of low impedance and able to support high-frequency disturbance currents. In older plants, these buses may be made from duct work or may use locking male-to-female connectors. There may be loose connections or worn terminals on connectors where fixture drop cords plug into bus networks. This will add to the voltage-related power quality problems that are already present.

Use portable advanced power quality monitoring instruments capable of measuring high-frequency transient voltages. Monitors that have Ethernet communication ports capable of being used with remote power quality monitoring systems will best serve these monitoring needs and eliminate plant personnel from having to manually retrieve data. All phases (including neutral and ground) should be measured during monitoring. Keep in mind that monitoring on 480V buses should be carried out long enough to capture disturbances characteristic of plant operating schedules and cycles as not all plant shifts use the same equipment. This should be done at least across two season changes — winter to spring and spring to summer are the two best seasons when thunderstorm activity is the highest.

## Analyzing the power quality data

Hooking up a power quality monitor is not that difficult and can be carried out by qualified electricians. However, analyzing (or reading) monitoring data is a different story. Monitoring data files are best analyzed by power quality experts with years of experience. Even experts in the industry experience challenges when trying to analyze files. Custom software tools provide many data analysis functions to power quality experts. Proper analysis techniques yield the right trends, charts, disturbance waveforms, and statistics, which are critical to determining the types of disturbances, their severity, and likelihood of causing malfunction or damage to electronic LED lighting systems operating on 480V buses.

Determining the source (or cause) of the power quality disturbances captured during the monitoring period is also important prior to making a decision to purchase electronic LED luminaires. Determining the cause of a disturbance (or series of disturbances) can be very challenging and time-consuming. There’s room for significant error during the power quality data monitoring and analysis process if one has little to no experience in power quality. Additional information must always be gathered about the loads and plant operations as well as the customer’s business to determine the sources of disturbances measured by the monitor. Knowing the right questions to ask is critical. Disturbances may also be linked to operations occurring on the electric utility power distribution circuit or the utility transmission feeder, if the plant is fed at a higher voltage level.

## Identifying power quality mitigation measures

Once the power quality data has been analyzed, the disturbances identified, and the causes determined, it is time to identify potential mitigation equipment to reduce or eliminate the disturbances. Here are some important points to keep in mind:

• No two power quality mitigation equipment or devices are the same.
• Mitigation at different points along the plant’s electrical system must be handled individually and has different performance, costs, and ROI.
• Different mitigation equipment or devices are typically required at different points along the plant’s electrical system to achieve effective mitigation across the plant’s power system. In other words, don’t expect one type of mitigation equipment or device to solve all of the power quality problems for the LED lighting installation.
• The high-bay LED luminaire may include a mitigation device as part of the lighting purchase. The type and level of mitigation device included in the luminaire must be included in an engineering analysis to determine what other mitigation equipment or devices are required in the plant to achieve proper mitigation on all of the lighting system branch circuits. In fact, many luminaire manufacturers miss-specify the mitigation device used in a luminaire to provide the required level of protection important to driver life in industrial plants.
• The type and level of mitigation included in the LED drivers is also important and must be included in the mitigation analysis. No type and level of mitigation internal to a driver is the same as what’s included in another model driver. Driver manufacturers don’t use the same type or level of mitigation in their driver designs.

In many cases, it may be necessary to identify and implement measures other than selecting and installing mitigation equipment and devices to eliminate a power quality problem. Changes to a plant’s wiring and grounding system and/or loads may be necessary. Power quality experts can model and simulate plant electrical systems and study potential changes to a system and/or load before money is spent actually implementing changes to a plant’s electrical system.

With the cost of high-bay LED luminaires still considered as an investment in plant infrastructure, verification that any power quality mitigation equipment or device installed in 480V switchgear and on 480V lighting branch circuits is still operational and can provide the required mitigation is critical before LED luminaires are installed. You should conduct another round of power quality monitoring on each lighting circuit undergoing mitigation before LED luminaires are installed. The second round of monitoring will determine the effectiveness of the mitigation equipment or device installed.

## Conclusion

Understanding, identifying, solving, and preventing power quality problems in an industrial plant is critical to the success of any high-bay LED lighting project — retrofit or new industrial construction. Investing in the design and installation of new LED lighting for a plant is a major undertaking and should be handled carefully before signing off to start a project. Most LED luminaire and driver manufacturers, as well as lighting designers, are not fully prepared to help their customers overcome power quality issues. Reaching out to an expert power quality consultant prior to the installation of a LED high-bay lighting system in these settings can ensure a smooth installation and reliably operating system.

P3 strives to bring you quality relevant industry related news.

See the origial article at: http://www.ecmweb.com/power-quality-reliability/uncovering-pq-problems-industrial-led-lighting

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Jul
31

## Understanding Total Harmonic Distortion (THD) in Power Systems

Introductions to AC circuit analysis typically focus on power factor as being determined by the phase relationship between the voltage and current in a circuit while generally ignoring the effect of THD on power factor. Specifically:

Where 0v is the phase of the voltage and 0i is the phase of the current.

This is not the full definition of power factor and this equation, which is called the displacement factor, is only true if both the voltage and the current are completely sinusoidal. The displacement factor aspect of power factor is well covered here and here.

To be fair, most people new to AC circuits are introduced to the proper definition of power factor, but after this introduction they typically focus only on the displacement factor and not the effect of THD. The full definition of power factor is:

Power factor is applicable to circuits with the general form of Figure 1 where there is an AC voltage source that provides an AC current for some kind of load. It is the nature of the load that determines the nature of the current and therefore the power factor.

### Power Factor without THD

If the voltage and current are purely sinusoidal, then the RMS voltage and current can be determined directly from the peak voltage and current:

pk2

If the load is purely resistive, then the average power and apparent power would be equal and the power factor would be 1. If the load also has capacitive and/or inductive elements then the phase difference between the voltage and current could be measured to determine power factor from the equation 1. Figures 2 to 4 show three types of loads along with the relationship between the phases of the voltage and current as well as the relative power factors. Remember, these power factors can be calculated directly from equation 1 because the voltage and current are purely sinusoidal.

##### Figure 4. Resistive and capacitive load with waveforms (Power Factor < 1 and current leads voltage)

Improving the power factor in systems like those in Figures 3 and 4 requires placing a component with the opposite amount of reactance into the system to counteract the reactance already in the system. This type of compensation is explained here.

### THD in Power Factor

Most electrical systems do not have loads with only resistors, inductors and capacitors. Most loads also include power conversion of some kind (such as AC/DC, DC/AC, or DC/DC converters) or some other kind of non-linear load (e.g. fluorescent lighting). These power converters and other non-linear loads change the nature of the current so that it is no longer sinusoidal. Switching power supplies, in which the power element rapidly transitions between a fully-on and a fully-off state, can be especially non-linear. Tricks such as filtering or adding control systems to force current flow to follow a reference signal are often used to reduce the effect of the switching. Even "linear" AC/DC converters significantly change the nature of the current so that it is no longer sinusoidal. Current in these types of converters is "bursty", and this article describes exactly why that is the case.

Since the current in these non-linear systems is still periodic (just not sinusoidal), this change in the nature of the current can be described in terms of the harmonic distortion of the current. Each one of the harmonics in the current has an RMS value, so calculation of the RMS current of the whole signal (as you would need to do when calculating power factor) involves summing the RMS value of each harmonic.

Irms=I2dc+k=1I2k_rms

If you assume that you have a good voltage source that provides a sinusoidal voltage, then there is no voltage at frequencies other than the fundamental so real power will only be provided at the fundamental frequency:

On the other hand, apparent power which is equal to VrmsIrms will include all of the current harmonics, so the term in the denominator of Equation 2 will be higher than what you would expect if you are only using the current at the fundamental frequency. Taking eqn. 3 and 4 and plugging them into eqn. 2 gives:

### Distortion Factor and THD

As mentioned before, the displacement factor is due to the phase difference between voltage and current (cos(0v - 0i))

I

1_rmsI2dc+k=1I2k_rms=I1_rmsIrms

Clearly, distortion factor is due to the harmonic distortion of the current, but we need to consider how distortion factor is related to the measurement of THD, where:

With a little bit of arithmetic, distortion factor can be determined in terms of THD:

so power factor can be calculated in terms of displacement factor and THD:

### THD and Power Factor in Example Power/Power Electronic Systems

Let’s take a look at two example systems; both have harmonics in the current, but one of the systems tries to minimize the effect of the harmonics on THD. This has been examined previously, but the examination below specifically looks at the effects of the harmonics on power factor.

#### Example 1: AC/DC Converter

This first example is a simple AC/DC converter as shown in Figure 5:

##### Figure 5. A simple AC/DC Converter

This circuit produces the voltage and current waveforms that appear in Figure 6 (for an explanation of why they look like this, see this article).

##### Figure 6. Voltage and current waveforms for a linear power supply

Because of the obvious distortion in the current, you would expect the harmonic current content to be high, and this can be seen in the FFT of the current in Figure 7:

##### Figure 7. Harmonics of current flowing into a linear power supply

Clearly there is a lot of distortion in the current. Imagine a large scale power system with hundreds or thousands of AC/DC converters connected and the contribution to the harmonic distortion of all of those converters.

Let’s actually quantify the power quality and perform the measurements and calculation for determining the power factor.

To determine the power factor requires two separate measurements. The first is the THD of the current in Figure 6, and it is measured as 2.8 (yes, that means 280%). The second is the phase shift between the fundamental of the current and the voltage and it is about 10 degrees. This means power factor is

which is a very low power factor indeed, and the biggest contributor to this low power factor is the harmonic distortion of the current.

#### Example 2: AC/DC Converter with Power Factor Correction

The second example has circuitry as discussed here and shown in Figure 8  that tries to make the current track the voltage as closely as possible. The purpose of this tracking is to improve the power factor, and while this power factor correction is certainly not perfect, it is a big improvement over the first example.

##### Figure 8. Boost Power Factor Correction Circuit

This circuit produces voltage (vac) and current (iac) waveforms that look like this:

##### Figure 9. Voltage and current into boost PFC circuit

The current is obviously distorted, but not by much; the power factor correction significantly reduces the distortion. This next figure, Figure 10, gives an indication of how much the current harmonics have been reduced when compared to the harmonics in Figure 7.

##### Figure 10. Harmonics of current into boost PFC circuit

Current harmonics are low and so is the phase difference between voltage and current (about 3º). The combination of the two components, current harmonics (as measured by THD) and phase difference between voltage and current as per equation 5, gives us the power factor. The THD measured in the current signal shown in Figure 9 is 0.2 (or 20%), and the phase shift is 3º, resulting in a power factor of

P3 strives to bring you quality relevant industry related news.

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24

## Linemen Restore Power and Rebuild Infrastructure After Destructive Nebraska Storm

Thunderstorms and two tornadoes hit Omaha Public Power District's (OPPD's) service territory recently, knocking down lines, twisting transmission towers, and inflicting significant power outages. Linemen from not only OPPD, but also nationwide, came to help restore power and rebuild downed lines and damaged towers. This photo gallery shows the destruction caused by the storm as well as how linemen worked together to swiftly restore power to OPPD's customers.

Thunderstorms and two tornadoes hit Omaha Public Power District's (OPPD's) service territory recently, knocking down lines, twisting transmission towers, and inflicting significant power outages. As this video produced by OPPD shows, linemen from not only OPPD, but also nationwide, came to help restore power and rebuild downed lines and damaged towers. This photo gallery shows the destruction caused by the storm as well as how linemen worked together to swiftly restore power to OPPD's customers.

Preparing for the Big Storm

Following a severe storm or emergency, OPPD activates its storm team, which consists of field crews, damage assessment, communications, call center support, logistic, safety, IT, forestry personnel, among others.

Restoring Power

Two tornadoes touched down in Bellevue, Nebraska, causing significant damage to homes and power structures and resulting in 76,500 outages.

Working to Turn the Lights Back On

Following the storm, which affected about 20 percent of OPPD's customers, crews worked long shifts to get everyone back online.

Twisted Towers

At its peak of the storm, 76,500 OPPD customers were out of power, making it the utility's fourth most destructive storm ever in terms of outages.

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2117 Hits
Jul
17

## Smart-UPS Online: The Next Generation

 The next generation of Scneider Electric APC Smart-UPS Online have arrived!  With higher power density, predictive battery replacement, switched outlet groups, among other game-changing advancements, these newly added 1kVA & 1.5 kVA 120V SKUs will give you the power protection they've been looking for.

1765 Hits
1765 Hits
Jul
10

## Costs and causes of downtime

The U.S. experiences more power outages than any other developed nation. And when the grid goes down, companies like yours suffer; every minute of downtime results in thousands of dollars lost in productivity. But what causes downtime? The truth is unforeseen mishaps and grid maintenance issues are often to blame. See how much downtime costs U.S. businesses and learn about all the crazy reasons the power suddenly goes out. What you discover may surprise you!

P3 strives to bring you quality relevant industry related news.

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1921 Hits
Jul
05

## Stumped by the Code? Use of Tamper-Resistant Receptacles Requirements

All questions and answers based on the 2017 NEC.

Underlined text indicates a change in the rules for the 2017 NEC.

Q. Where does the Code require the use of tamper-resistant receptacles?

A. Nonlocking-type 15A and 20A, 125V and 250V receptacles in the following areas must be listed as tamper resistant [406.12]:

(1) Dwelling unit areas specified in Sec. 210.52 and Sec. 550.13

(2) Hotel and motel guest rooms and guest suites

(3) Child care facilities (Note: A childcare facility is a building or portions thereof used for educational, supervision, or personal care services for five or more children seven years in age or less [406.2].)

(4) Preschools and elementary education facilities

(5) Business offices, corridors, waiting rooms and the like in clinics, medical and dental offices, and outpatient facilities.

(6) Places of awaiting transportation, gymnasiums, skating rinks, and auditoriums

(7) Dormitories

Informational Note: Receptacle types covered by this requirement are identified as 5‑15, 5‑20, 6‑15, and 6‑20 in NEMA WD 6, Wiring Devices—Dimensional Specifications.

Exception to (1) through (7): Receptacles in the following locations aren’t required to be tamper resistant:

(1) Receptacles located more than 5½ ft above the floor.

(2) Receptacles that are part of a luminaire or appliance.

(3) A receptacle located within dedicated space for an appliance that in normal use isn’t easily moved from one place to another.

(4) Nongrounding receptacles used for replacements as permitted in Sec. 406.4(D)(2)(a).

Q. What are the Code requirements for a dwelling unit garage branch circuit?

A. In each attached garage and each detached garage with electric power, at least one receptacle outlet, located not more than 5½ ft above the floor, is required in each vehicle bay [210.52]. At least one 20A, 120V branch circuit is required to supply the receptacle outlet(s) required by Sec. 210.52 in attached garages and detached garages with electric power. This 20A, 120V branch circuit isn’t permitted to serve any other outlet [210.11(C)(4)] (Figure).

Exception: Readily accessible outdoor receptacle outlets (not lighting outlets) can be supplied by the 20A, 120V garage receptacle branch circuit.

Q. What defines the rating of a branch circuit in the eyes of the NEC?

A. The rating of a branch circuit is determined by the rating of the branch-circuit overcurrent protection device, not the conductor ampacity [210.18]. For example, the branch-circuit rating of 10 THHN, rated 30A at 60°C, protected by a 20A circuit breaker is 20A.

Q. Does the Code allow the use of swimming pool reinforcing steel as part of the grounding electrode system?

A. Swimming pool reinforcing steel for equipotential bonding in accordance with Sec. 680.26(B)(1) and 680.26(B)(2) isn’t permitted to be used as a grounding electrode [250.52(B)(3)].

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See the origial article at: http://www.ecmweb.com/national-electrical-code/stumped-code-use-tamper-resistant-receptacles-requirements

11261 Hits
11261 Hits
Jun
26

## Beyond data center monitoring...

What if you could see data center events before they happen? Now you can. Watch this video to learn how StruxureOn takes monitoring to another level by enabling you to take action fast to prevent downtime.

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P3 features high quality products, services and software for critical facility management. Backed by superior customer service and leading industry expertise, P3 specializes in comprehensive Data Center and Power Quality solutions custom ﬁt to your needs.

#### Our Mission

Our mission is to be the industry’s trusted and respected critical power, cooling and energy solutions provider.

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