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2022.01.20 05:04 PQTBlog General Reference Common Power Quality Problems and Solutions

Published by Electrotek Concepts, Inc., PQSoft Case Study: General Reference Common Power Quality Problems and Solutions, Document ID: PQS0315, July 18, 2003.
Abstract: Power quality is a frequently used term that means different things to different people. Common power quality problems include all of the issues that arise from the incompatibility between a utility’s power and the customer’s energy-using equipment that result in impaired operation. These include transients, sags and swells, harmonics, and short- and long-term voltage variations and outages. Also included under this broad area are issues of power reliability.
This document provides a brief summary of common power quality problems and solutions.
Power quality is a frequently used term that means different things to different people. Common power quality problems include all of the issues that arise from the incompatibility between a utility’s power and the customer’s energy-using equipment that result in impaired operation. These include transients, sags and swells, harmonics, and short- and long-term voltage variations and outages. Also included under this broad area are issues of power reliability.
Power quality variations occur when the voltage waveform supplied to the customer deviates from normal. These deviations may involve changes in the voltage level (rms variations), changes in the voltage sinusoidal shape (harmonics, notching, and transients), or loss of power altogether (interruptions and outages). To some extent, the power system is constantly experiencing power quality variations because the supplied voltage is never a perfect sinusoid. When these variations are so significant, however, that customer equipment is adversely affected; the quality of service supplied becomes an issue that should be investigated. In addition, the current trend toward more energy efficient electronic devices has greatly increased the sensitivity of customer load equipment. As a result, power variations that once went unnoticed now result in mis-operation of customer devices. The impact of these power quality related problems can vary significantly. For example, a VCR could miss recording a program or a semiconductor manufacturer could lose product worth hundreds of thousands of dollars during the same momentary interruption event. Events such as these adversely affect all involved parties. The customer must absorb the initial economic impact of the power quality disturbance, but the electricity supplier and the public are affected economically in the long run as well.
Characterizing the Power Quality Environment
The relative importance of a particular category of power quality phenomena for a specific customer will depend on the type of installed electrical equipment. The type of interaction between customer equipment and the power quality phenomena – equipment damage, equipment/process trip, compromised product quality, etc. – and the frequency at which it occurs or could be expected to occur are also critical factors in the evaluation process once the cause has been identified. The range of power quality phenomena is defined by IEEE Std. 1159, Recommended Practice for Monitoring Electric Power Quality.
Approaches for resolving equipment or process problems related to each category of phenomena vary widely. Causes, impacts, and appropriate solutions for this range of electrical phenomena have been analyzed in numerous research and study efforts, resulting in the development of proven solution techniques for many common power quality problems. These efforts have also contributed to a prioritization of the power quality phenomena categories. From the customer’s point of view, the problem categories that are most important are those that:

Using these criteria, research and case study investigations have identified the following categories of power quality phenomena to be of highest importance to customers:
This does not mean that there are never problems associated with other categories of power quality phenomena. Experience does indicate, however, that the majority of problems (especially from the custom’s perspective) are those listed above.
RMS Voltage Variations
Most customers recognize that electric power outages can never be cost-effectively eliminated. Distribution system reliability in the United States is very high, reflecting the fact that actual electric service interruptions are very infrequent, perhaps just once or twice per year. Voltage variations of short duration are not as well understood and do occur with a much higher frequency that actual service interruptions. Sometimes the duration is so short as to be almost imperceptible to the naked eye. However, modern process equipment and processes are more discerning than the naked eye, and will misoperate or even shut down in response to such voltage variations. This reaction, coupled with the relatively high rate of occurrence and the general high cost and complexity of typical solutions, make short term voltage variations one of the most, if not the most, important categories of power quality phenomena from the customer’s point of view.
IEEE Std. 1346, IEEE Recommended Practice for Evaluating Electric Power System Compatibility with Electronic Process Equipment, and IEEE Std. 1250, IEEE Guide for Service to Equipment Sensitive to Momentary Voltage Disturbances provide guidance for evaluating the impact of rms variation events on customer systems.
Figure 1 illustrates an example of a distribution system momentary interruption event. This waveform was recorded with a power quality disturbance analyzer.
Figure 1 – Example Distribution System Momentary Interruption Event
Transient overvoltages caused by switching operations or lightning strikes to electric facilities have significant potential to damage electric power equipment or disrupt operation. High-frequency transients (most impulsive transients and low- and medium-frequency oscillatory transients) have been recognized from some time as a threat to electronic equipment, and have been blamed for a wide range of failures and misoperations. Fortunately, these transients are relatively easy to protect against, and a wide range of off-the-shelf and inexpensive transient voltage surge suppressor (TVSS) products can be applied by either the customer or equipment manufacturer.
Low frequency oscillatory transients, on the other hand, are more difficult to treat. Switching (energizing) of utility shunt capacitor banks is the most common source of low-to-medium frequency transients on the electric power system. Unlike the other subcategories of transient phenomena, these are usually of modest magnitudes but contain substantial energy, so their effects can be felt quite far electrically from the point of origin. Low frequency transients have been strongly correlated with nuisance tripping of power electronic equipment, especially common types of adjustable-speed drives.
IEEE Std. 1036, Guide for the Application of Shunt Power Capacitors, provides a helpful overview to utility capacitor switching.
Figure 2 illustrates an example of a distribution bus voltage during a utility capacitor energizing event. The resulting overvoltage is approximately 1.35 per-unit (135%). Typical magnitudes for this type of event range from 1.2 to 1.8 per-unit and the resulting energizing frequencies generally fall in the range from 300 to 1000 Hz. This transient waveform was recorded with a power quality disturbance analyzer.
Figure 2 – Example Utility Capacitor Energizing Event
Harmonic Distortion
Harmonics are probably more strongly associated with power quality than any other category. It is somewhat surprising to those only casually involved in power quality that harmonics are not a chronic problem that the typical customer must deal with. Harmonics can cause equipment to misoperate, capacitor banks to fail, breakers to trip mysteriously, but in general, the electric power system has the ability to absorb substantial amounts of harmonic current with surprisingly little or no impact on connected equipment. Real problems from harmonics are usually confined to locations with high amounts of nonlinear, harmonic current-producing loads. Examples of this include a wastewater treatment plant where the entire load may be comprised of adjustable-speed motor drives powering pumps, or situations where power factor correction capacitors on the customer system or at the utility distribution level create resonances that amplify the effects of nonlinear loads. The fraction of electric power system load that produces harmonics currents has steadily increased over the past two decades.
IEEE Std. 519, IEEE Recommended Practice and Requirements for Harmonic Control in Electric Power Systems includes guidelines on establishing and using harmonic voltage and current limits on the power system. The basic philosophy of the standard is that the customer is responsible for limiting the amount of harmonic currents injected onto the overall power system and the utility is responsible for avoiding conditions on the power system that could create unacceptable voltage distortion levels (e.g., resonance).
Figure 3 illustrates an example of a dc drive current waveform. This waveform was simulated using Electrotek’s SuperHarmTM program.
Figure 3 – Example DC Drive Current Waveform
Economic Impacts of Power Quality
The ultimate reason that we are interested in power quality is economic value. There are economic impacts on utilities, their customers, and suppliers of load equipment. The quality of power can have a direct economic impact on many industrial consumers. There has recently been a great emphasis on revitalizing industry with more automation. This usually means electronically controlled, energy-efficient equipment which is often much more sensitive to deviations in the supply voltage than its electromechanical predecessors (e.g., adjustable-speed drives vs. induction motors). Thus, like the blinking clock in residences, industrial customers are now more acutely aware of minor disturbances on the power system. There can be significant costs associated with these disturbances. For example, it is conceivable for a single, commonplace, momentary utility breaker operation to result in a $10,000 loss to an average-sized industrial customer by shutting down a production line that requires four hours to restart.
The electric utility is concerned about power quality issues as well. Meeting customer expectations and maintaining customer confidence is a strong motivator. With today’s movement toward competition between utilities, it is more important than ever. The loss of a dissatisfied customer to a competing power supplier can have a very significant impact financially on a utility. Load equipment suppliers generally find themselves in a very competitive market with most customers buying on lowest cost. Thus, there is a general disincentive to add features to the equipment to withstand common disturbances unless the customer specifies otherwise. Many manufacturers are also unaware of the types of disturbances that can occur on power system.
The primary responsibility for correcting inadequacies in load equipment ultimately lies with the customers that must purchase and operate it. Specifications must include power performance criteria. Since many customers are also unaware of the pitfalls, one useful service that utilities can provide is dissemination of information on power quality and the requirements of load equipment to properly operate in the real world.
Factors that Influence Costs
Besides the obvious financial impacts on both utilities and industrial customers, there are numerous indirect and intangible costs associated with power quality problems. Residential customers typically do not suffer direct financial loss or the inability to earn income because of most power quality problems, but they can be a potent force when they perceive that the utility is providing poor service. The sheer number of complaints requires utilities to provide staffing to handle them. In addition, public interest groups frequently intervene with public service commissions, requiring the utilities to expend financial resources on lawyers, consultants, studies and the like to counter the intervention. While all of this is certainly not the result of power quality problems, a reputation for providing poor quality service does not help matters.
As with many power quality problems, an economic evaluation is often difficult to complete since it is often very difficult to determine the cost of a particular event for an individual customer. In addition, these costs may vary drastically from customer to customer. There are a number of aspects of customer production that can be affected by a power quality event, including:
  1. Lost Production – factory costs associated with the production process being disrupted.
  2. Scrap – costs associated with product that must be scrapped and cannot be recovered by recycling the raw materials.
  3. Restart – costs associated with restarting the production process.
  4. Labor – extra labor costs associated with restarting the product line, reloading machines, cleaning up scrap, etc.
  5. Repair – costs for repair of machines and equipment damaged during the transient event.
  6. Replacement – costs for the replacement of machinery damaged during the transient event.
  7. Process Inefficiency – costs due to the process not begin able to run to its optimal efficiency.
  8. Demand Charges – increased utility charges because the customer is unable to operate equipment such as capacitors and adjustable-speed drives that might reduce demand charges.
Each event that impacts a customer’s production will include a number of these costs. Predicting the exact economic impact is nearly impossible due to the large number of system parameters that can affect the characteristics of the event. It is entirely possible, however, that a single event could generate losses sufficient to justify the additional mitigation equipment expenditure.
Common Power Quality Problems and Solutions
Customers often blame utilities for most power quality problems, but the fact is that problems may originate on either side of the meter. There are four sources for most customer-encountered problems:
  1. Natural phenomena (e.g., inclement weather)
  2. Normal utility operations (e.g., automatic protection system operations)
  3. Neighboring customers (e.g., welding equipment adjacent to an office)
  4. Customer’s own equipment and facilities (e.g., motor starting).
Within a customer’s facility, poor power quality can result from incompatible equipment interactions or from poor wiring and grounding practices. In fact, many power quality problems are associated with customers’ wiring and grounding practices. Problems such as voltage sags, however, generally originate on the utility’s side of the meter. In addition, the proliferation of harmonic (nonlinear) producing loads is resulting in power quality problems for both customers and the utilities that serve them. These loads include adjustable-speed drives, electronic ballasts for fluorescent lighting, electric arc furnaces, computers distributed throughout commercial and industrial facilities, and other electronic technologies.
Identifying Power Quality Problems
The first step is to understand how customers perceive power quality problems. Customers rarely see or understand these problems. They see symptoms of them and the resulting difficulties in their businesses and homes. Some of the more common symptoms include:
In addition to the observed symptoms, it is important to determine the customer equipment that is affected by the power quality event. Some of the most important equipment categories to consider include:
Once information regarding the symptoms and affected equipment is collected, the power quality event causing the problem can be determined. A number of common power quality issues include:
Determining Power Quality Solutions
Lessons learned from numerous research and case study projects have revealed the following fundamental steps for optimized, cost-effective solutions to power quality problems:
  1. Identify affected equipment/process.
  2. Identify nature of electrical disturbance affecting equipment.
  3. Calculate or project economic impact.
  4. Select mitigation technologies based on nature of electrical disturbance.
  5. Determine benefit/cost ratio for solution alternatives.
  6. Select appropriate solution based on technical and economic evaluation.
  7. Design solution application.
  8. Specify and procure selected solution product.
  9. Install and commission solution equipment.
  10. Evaluate/validate performance.
Not every step is necessarily mandatory or even applicable to every case. Sometimes the correct solution is more obvious, possibly even based on previous experience, and much of the problem identification/characterization effort can be bypassed. The procedure outlined does, however, illustrate the breadth and depth of knowledge required to maximize the chances of a cost-effective solution.
Challenges for the Customer
Unfortunately, the range of required expertise and background knowledge is almost never immediately available to a customer unless there has been a previous and substantial internal investment in building such capability. Outside organizations with the requisite experience and skill must often be enlisted.
When a problem is encountered, customers have an immediate feel for the impact on the bottom line, and sometimes may be able to trace the problem down to specific equipment components of the overall affected process. The urgency associated with resolving the problem and restoring production can lead to band-aid solutions, or worse, actions that result only in wasted effort and expense and do not improve the situation at all.
The solution process previously outlined is designed to prevent band-aids. Many of the steps and interim questions to answer can be beyond the skills and expertise of the customer. Examples of this include:
When a customer experiences production problems that are suspected to be related to power quality, the electric service provider (utility) and the manufacturer(s) of the affected equipment are many times the first contacts made for assistance.
Common Power Quality Solutions
The best power quality solutions are in general site-specific and potentially unique to the affected plant or process. Most problems involving one of the aforementioned power quality phenomena are difficult to resolve with off-the-shelf solution products, except for instances where the load is small in size and has no or limited interaction with other process equipment. This is, however, a trivial case, and most real problems involve a range of equipment interconnected in some fashion to constitute the process.
In applying a solution product, is it necessary to not only determine what type of technology, but also where it should be applied, in what size, and to what portions of the overall process. Sometimes determining what needs to be protected is a difficult challenge. Once determined, how and where the solution should best be applied can be a difficult proposition. The financial objective in solving power quality problems is to earn an acceptable return on investment or meet certain payback criteria.
A number of common power quality solutions include:
RMS Voltage Variations
Harmonic Distortion
IEEE Standard 100. Terms and Definitions IEEE Standard 1100. IEEE Recommended Practice for Powering and Grounding Sensitive Equipment (The Emerald Book). IEEE Standard 1159. IEEE Recommended Practice on Monitoring Electric Power Quality.
RELATED STANDARDS IEEE Standard 1159 IEEE Standard 1346 IEEE Standard 1250 IEEE Standard 1036 IEEE Standard 519
GLOSSARY AND ACRONYMS ASD: Adjustable-Speed Drive CVT: Constant Voltage Transformer GPR: Ground Potential Rise IEEE: Institute of Electrical and Electronics Engineers MOV: Metal Oxide Varistor PWM: Pulse Width Modulation TVSS: Transient Voltage Surge Suppressors UPS: Uninterruptible Power Supply VCR: Video Cassette Recorder
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So basically I met this great girl on a night out about 2-3 months ago. We instantly hit it off and she seemed really into me. We then texted eachother for a while, but it fizzled out about a month ago as I felt like we were scraping the bottom of the barrel conversation-wise, and I didn’t want to feel like I was bothering her. I would’ve asked her out somewhere but bars/ restaurants close down at like 8 now due to covid and we both have full time college courses in different colleges in the same city. I also don’t have a car or my own place as I commute to college which doesn’t help things.
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Ok I thought the change account thing would work but find out it doesn’t work consistently as now my friend is having saving issues before even quitting the game as a whole-we accidentally got booted from a friends lobby and he checks and literally the past 2 hours went poof.
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2022.01.20 05:04 anh-ion Ahri Adjustments - An Explanation

With the adjustments to Ahri being revealed, I've noticed A LOT of people are unhappy. I'm not saying the changes are perfect, but overall these are positive changes. I'll try to explain what Riot is trying to achieve and how they do satisfy Ahri's needs.
I've been an Ahri main since her release, I've played since S1 but I've only peaked D3 playing Ahri so I'm in no way qualified, I'm speaking as an enthusiast. Also, my perspective is different from lower elo Ahri mains so maybe Riot is catering to players like me and ignoring others. The biggest issue I have with the changes is the nerf to her base stats, but I'll ignore them for now because I need to play her first.
Note: Ahri is not a carry, she never was a carry—even during her peak. In hindsight, she was an AP Assassin that fulfilled her role terribly. Ahri excels in lower skill-level environments, i.e. Season 3, when players were much worse. A true AP Assassin playstyle will require a complete overhaul, causing her to lose parts of her core identity. Ahri's current kit is that of a Mobile Mage and Riot have pushed in that direction. (I too miss the DFG glory-days but I'd rather feel reliable)

Goal 1-Lean into her mobile mage identity by allowing R to partially reset, giving her more opportunities to carry fights 
Adding a reset mechanic will give her opportunities (usually early-mid game) to carry by building small leads throughout the game, especially in scenarios she could not previously. i.e. you use all 3 R-charges to dash in and execute someone, you can now dash out to safety instead of trading 1-for-1. Or, when you would lose a kill because you don't want to trade 1-for-1 but now you've burnt ult and got nothing in return.
This buff allows her to build momentum: small but meaningful leads throughout the game. This doesn't make her a proper carry, but she isn't meant to be one, her kit just does not allow for it, she would need an overhaul.

Goal 2-Passive reworked to be more useful throughout the game Goal 3-Make her spells feel better to cast in lane 
Ahri's new passive strengthens her laning phase by allowing her to stay in lane longer, not be bullied as easily and use her abilities more effectively. This could mean bullying the enemy out of lane, killing the enemy, etc, just advantages in general. As a result, her average gold income will increase, and directly make her stronger and more useful.
How? Ahri has low base mp/mp5, and her current passive requires her to trade mana for health. It is incredibly punishing. Inefficient usage of Ahri's passive is also punishing but there may never be an opportunity for an efficient usage of it. The new passive makes her more mana-efficient, and "makes her spells feel better to cast in lane". Ahri can hold her abilities for when it matters instead.
She'll also feel like she actually has a passive throughout the game now; Triumph.

"But Ahri still lacks damage, even when I'm ahead, my entire combo doesn't 100-0 someone." 
While she won't be dealing more damage mid-late game, Ahri will be dealing more damage and overall feeling more impactful in the laning phase and early-mid game. The current state of League heavily favours early leads, as such, these changes are far more impactful than what some people might assume. You won't need to 100-0 someone to win more games.

This my interpretation of the Ahri changes, I'd love to see everyone else's perspective.
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2022.01.20 05:04 ItstheChazz Applying for IBEW when injured?

I’ve been in the application process for this years group of apprentices for my local IBEW for a little bit now and have finally gone through all the interviews. The office has mentioned that in a few months is usually when they start pulling people but I just recently got pretty badly injured and can’t do the work until I heal up all the way which will take me right into the time when my local said they would be bringing in applicants that are accepted this time around. If I get the opportunity to become apart of my local IBEW but am still not fully recovered and can’t work as of yet would I have to forfeit my place?
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2022.01.20 05:04 spirosmour Which wallets can I connect to GU

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2022.01.20 05:04 Arnold_Babar85 When Does A Gentleman In Moscow Get Good?

I read Amor Towles' "The Lincoln Highway" in less than a week including a marathon five hour session last Saturday during an epic cold weather day in Greater Boston. I found all the characters to be jumping off the page. The mid fifties America where an 18 year old kid and his 8 year old brother could walk around Manhattan and not get mugged, with no clue where they are going being from Nebraska. All the eclectic and well written people they meet along the way and of course his well meaning, long on heart but short on brains and common sense Wolley and Dutchess. It was one of my favorite books of the past ten years.
All you people told me was that it wasn't nearly as good as Towles' hit novel "A Gentleman in Moscow". Folks I am 10% through it and am wondering if I should continue. I understand the Count won't be able to leave this hotel for 30 years but I am finding this book Incredibly boring. How is it better than The Lincoln Highway? I will plow on for a couple more days and hope to find out.
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View Poll
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2022.01.20 05:04 WouldbeWanderer Florida police chief being paid to sit in jail after being arrested for domestic violence

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2022.01.20 05:04 yoxewaak Is the NFT partnership a complete scam? Any views on timing of announcment? Do we still believe the partner is GME? I am smoothbrained af

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When is the next banner of AF?
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