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PQ FAQs - Frequently Asked Questions 

Power Quality Vocabulary  More FAQs


The professionals at Power Quality Inc. have more than 20 years experience in the power quality industry. We offer engineering services and provide products worldwide.

If you have a particular problem please go to the literature request form, and detail it there or call us for assistance. For UPS/Power Conditioning Questions.


Please scroll down to find the questions and answers

1.  What is Power Quality?
2.  What are the commonly used terms that describe the parameters of electrical power that describe or measure Power Quality?
3.  What is the most common Power Quality problem?
4.  What is the second most common Power Quality problem?
5.  What type of equipment is affected by Power Quality issues.
6.  Why has Power Quality only become an issue in recent years?
7.  What are the types of Power Quality solutions available on the market today?
8.  How can Power Quality problems be detected?
9.  Are there national or international standards of Power Quality?
10. How do harmonics affect the electrical system?
11. How do harmonics affect the load?
12. How do I know what level of Power Quality protects?
13. How do I measure/characterize Power Quality?

1. What is Power Quality?

Many answers apply to this simple question. They all depend on your perspective.

From the utility perspective, Power Quality has been defined as the parameters of the voltage that affect the customers supersensitive equipment.

From the power user perspective, Power Quality may be defined as any electrical parameter or connection that affects the operation of the equipment. This included all electrical parameters, connections and grounds, whether the source from the utility, local equipment or other users.

From the Power Quality market or industry perspective, it is any product or service that is supplied to users or utilities to measure, treat, remedy, educate engineers or prevent Power Quality issues, problems and related items.

Interesting note: A survey by Georgia Power in the mid 1990's revealed that utilities perception is 1% of the Power Quality problems are caused by the utility. The users perception is the utility is 17% of the cause. The utility perspective is the customer is 25% of the cause and users perspective is the customer is 12% of the cause.

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2. What are the commonly used terms that describe the parameters of electrical power that describe or measure Power Quality?

See PQVocabulary or definitions, descriptions and details.

Voltage sags Voltage variations Interruptions Swells Brownouts
Blackouts Voltage imbalance Distortion Harmonics Harmonic resonance
Interharmonics Notching Noise Impulse Spikes (Voltage)
Ground noise Common mode noise Critical load Crest factor Electromagnetic compatibility
Dropout Fault Flicker Ground Harmonic resonance
Ground loops Voltage fluctuations Transient Interruption Momentary interruption
Clean ground Over voltage Under voltage Non-linear load THD Total Harmonic Distortion
Triplens Voltage dip Voltage regulation Blink Oscillatory transient
Outage Power surge Glitch Clean ground Bump
Raw power Surge Isolation Dirty power

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3. What is the most common Power Quality problem?

Voltage sags are considered the most common Power Quality problem. These can be caused by the utility or by customer loads. When sourced from the utility, they are most commonly caused by faults on the distribution system. These sags will be from 3 to 30 cycles and can be single or three phase. Depending on the design of the distribution system, a ground fault on 1 phase can cause a simultaneous swell on another phase.

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4. What is the second most common Power Quality problem?

A recent survey of Power Quality experts in Arizona, indicates that 50% of all Power Quality problems are related to grounding, ground bonds, neutral to ground voltages, ground loops, ground current or other ground associated issues.

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5. What type of equipment is affected by power Quality issues.

An electrically operated or connected equipment is affected by Power Quality.

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6. Why has Power Quality only become an issue in recent years?

Power Quality has been an issue since electrical power was invented. It has only become a well published issue in recent years because of the loads it affects. If your favorite TV program is interrupted by the local sewage pump operating on a Variable Speed drive interfering with it, you are aware of a Power Quality problem. When the lights blink and your PC reboots, you are aware of a Power Quality problem. The electrical loads get more sensitive.

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7. What are the types of Power Quality solutions available on the market today?

There are hundreds of manufacturers making thousands of different Power Quality solutions today.

The categories of these solutions are:

  • Utility based solutions for the substation level.
  • User based solution for whole facility protection.
  • User load level solutions for specific loads
  • Designed in solutions, built in by the equipment manufacturer to reduce the sensitivity to Power Quality problems.

Contact Power Quality Inc. for detailed solutions for specific problems

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8. How can Power Quality problems be detected?

Determining the exact problems requires sophisticated electronic test equipment. The following symptoms are indicators of Power Quality problems:

  1. A piece of equipment misoperates at the same time of day.
  2. Circuit breakers trip without being overloaded.
  3. Equipment fails during a thunderstorm.
  4. Automated systems stop for no apparent reason.
  5. Electronic systems fail or fail to operate on a frequent basis.
  6. Electronic systems work in one location but not in another location.
  7. Lights dim or blink and electronic systems misoperate.

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9. Are there national or international standards of Power Quality? Is Power Quality regulated by government standards?

There are many standards to define the parameters of Power Quality. These are listed in detail in our Power Quality Reference Library. There are no government regulations on Power Quality worldwide. Most governement regulations are related to Power Reliability.

Send us an e-mail requesting the library listing for details.

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10.  What are Harmonics?

Harmonics are distortions in the AC waveform. These distortions are caused by loads on the electrical system that use the electrical power at a different frequency than the fundamental 50 or 60 Hz. An example of such a load is the common PC, television receiver or any other electronic load.

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11. 11. How do harmonics affect the electrical system?

In general harmonics cause magnetic portions of the electrical system to overheat. Such as transformers, line reactors, magnetic relays and power factor capacitors.

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12. How do harmonics affect the load?

The affect of harmonics on loads varies a great deal and is dependent on the load itself. Most loads are not affected by moderate levels of harmonics. Exceptions to this are loads that perform electrical measurements in the frequency domain of the harmonics.

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13. How do I measure/characterize Power Quality?

It requires speciality, measurement equipment to measure, record and diagnosis harmonic problems. Because most equipment does not specify what level of power quality is required. Power Quality Inc. offers a service of characterizing all aspects of Power Quality and determining if it is acceptable to the load.

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