Article Talk Read Edit View history Search Wikipedia

Electric power quality

From Wikipedia, the free encyclopedia

Main page Electric power quality is the degree to which the voltage, frequency, and waveform of a power supply system conform to established
Contents specifications. Good power quality can be defined as a steady supply voltage that stays within the prescribed range, steady a.c.
Current events frequency close to the rated value, and smooth voltage curve waveform (resembles a sine wave). In general, it is useful to consider
Random article power quality as the compatibility between what comes out of an electric outlet and the load that is plugged into it.[1] The term is used to
About Wikipedia
describe electric power that drives an electrical load and the load's ability to function properly. Without the proper power, an electrical
Contact us
device (or load) may malfunction, fail prematurely or not operate at all. There are many ways in which electric power can be of poor
Donate
quality and many more causes of such poor quality power.
Contribute
The electric power industry comprises electricity generation (AC power), electric power transmission and ultimately electric power
Help
distribution to an electricity meter located at the premises of the end user of the electric power. The electricity then moves through the
Learn to edit
wiring system of the end user until it reaches the load. The complexity of the system to move electric energy from the point of production
Community portal
Recent changes
to the point of consumption combined with variations in weather, generation, demand and other factors provide many opportunities for the
Upload file quality of supply to be compromised.

While "power quality" is a convenient term for many, it is the quality of the voltage—rather than power or electric current—that is actually
Tools
described by the term. Power is simply the flow of energy and the current demanded by a load is largely uncontrollable.
What links here
Related changes
Contents [hide]
Special pages
Permanent link 1 Introduction
Page information 2 Power Quality Deviations
Cite this page 2.1 Voltage
Wikidata item 2.2 Frequency
2.3 Waveform
Print/export
3 Power conditioning
Download as PDF

Create PDF in your applications with the Pdfcrowd HTML to PDF API PDFCROWD
 Printable version 4 Smart grids and power quality
5 Power quality compression algorithm
Languages
5.1 Power quality challenges
‫اﻟﻌﺮﺑﯿﺔ‬
5.2 Raw data compression
Deutsch
5.3 Aggregated data compression
Español
‫ﻓﺎرﺳﯽ‬ 6 Power Quality Standards
Français 7 See also
한국어 8 References
िह दी 8.1 Literature
Italiano
Русский

6 more Introduction [ edit ]

Edit links The quality of electrical power may be described as a set of values of parameters, such as:

Continuity of service (Whether the electrical power is subject to voltage drops or overages
below or above a threshold level thereby causing blackouts or brownouts[2])
Variation in voltage magnitude (see below)
Transient voltages and currents
Harmonic content in the waveforms for AC power

It is often useful to think of power quality as a compatibility problem: is the equipment connected
to the grid compatible with the events on the grid, and is the power delivered by the grid,
including the events, compatible with the equipment that is connected? Compatibility problems
always have at least two solutions: in this case, either clean up the power, or make the
equipment tougher.

The tolerance of data-processing equipment to voltage variations is often characterized by the

CBEMA curve, which give the duration and magnitude of voltage variations that can be
tolerated.[3]

Create PDF in your applications with the Pdfcrowd HTML to PDF API PDFCROWD
 Frequency stability of some large
electrical grids

CBEMA Curve

Ideally, AC voltage is supplied by a utility as sinusoidal having an amplitude and frequency given by national standards (in the case of
mains) or system specifications (in the case of a power feed not directly attached to the mains) with an impedance of zero ohms at all
frequencies.

Power Quality Deviations [ edit ]

No real-life power source is ideal and generally can deviate in at least the following ways:

Voltage [ edit ]

Variations in the peak or RMS voltage are both important to different types of equipment.
When the RMS voltage exceeds the nominal voltage by 10 to 80% for 0.5 cycle to 1 minute, the event is called a "swell".
A "dip" (in British English) or a "sag" (in American English the two terms are equivalent) is the opposite situation: the RMS voltage is
below the nominal voltage by 10 to 90% for 0.5 cycle to 1 minute.

Create PDF in your applications with the Pdfcrowd HTML to PDF API PDFCROWD
 Random or repetitive variations in the RMS voltage between 90 and 110% of nominal can produce a phenomenon known as "flicker"
in lighting equipment. Flicker is rapid visible changes of light level. Definition of the characteristics of voltage fluctuations that produce
objectionable light flicker has been the subject of ongoing research.
Abrupt, very brief increases in voltage, called "spikes", "impulses", or "surges", generally caused by large inductive loads being turned
off, or more severely by lightning.
"Undervoltage" occurs when the nominal voltage drops below 90% for more than 1 minute.[4] The term "brownout" is an apt
description for voltage drops somewhere between full power (bright lights) and a blackout (no power – no light). It comes from the
noticeable to significant dimming of regular incandescent lights, during system faults or overloading etc., when insufficient power is
available to achieve full brightness in (usually) domestic lighting. This term is in common usage has no formal definition but is
commonly used to describe a reduction in system voltage by the utility or system operator to decrease demand or to increase system
operating margins.
"Overvoltage" occurs when the nominal voltage rises above 110% for more than 1 minute.[4]

Frequency [ edit ]

Variations in the frequency.

Nonzero low-frequency impedance (when a load draws more power, the voltage drops).
Nonzero high-frequency impedance (when a load demands a large amount of current, then suddenly stops demanding it, there will be
a dip or spike in the voltage due to the inductances in the power supply line).
Variations in the wave shape – usually described as harmonics at lower frequencies (usually less than 3 kHz) and described as
Common Mode Distortion or Interharmonics at higher frequencies.

Waveform [ edit ]

The oscillation of voltage and current ideally follows the form of a sine or cosine function, however it can alter due to imperfections in
the generators or loads.
Typically, generators cause voltage distortions and loads cause current distortions. These distortions occur as oscillations more rapid
than the nominal frequency, and are referred to as harmonics.
The relative contribution of harmonics to the distortion of the ideal waveform is called total harmonic distortion (THD).
Low harmonic content in a waveform is ideal because harmonics can cause vibrations, buzzing, equipment distortions, and losses
and overheating in transformers.

Create PDF in your applications with the Pdfcrowd HTML to PDF API PDFCROWD
 Each of these power quality problems has a different cause. Some problems are a result of the shared infrastructure. For example, a fault
on the network may cause a dip that will affect some customers; the higher the level of the fault, the greater the number affected. A
problem on one customer’s site may cause a transient that affects all other customers on the same subsystem. Problems, such as
harmonics, arise within the customer’s own installation and may propagate onto the network and affect other customers. Harmonic
problems can be dealt with by a combination of good design practice and well proven reduction equipment.

Power conditioning [ edit ]

Power conditioning is modifying the power to improve its quality.

An uninterruptible power supply can be used to switch off of mains power if there is a transient (temporary) condition on the line.
However, cheaper UPS units create poor-quality power themselves, akin to imposing a higher-frequency and lower-amplitude square
wave atop the sine wave. High-quality UPS units utilize a double conversion topology which breaks down incoming AC power into DC,
charges the batteries, then remanufactures an AC sine wave. This remanufactured sine wave is of higher quality than the original AC
power feed.[5]

A Dynamic Voltage Regulator (DVR) and static synchronous series compensator or (SSSC) are utilized for series voltage sag
compensation.

A surge protector or simple capacitor or varistor can protect against most overvoltage conditions, while a lightning arrester protects
against severe spikes.

Electronic filters can remove harmonics.

Smart grids and power quality [ edit ]

Modern systems use sensors called phasor measurement units (PMU) distributed throughout their network to monitor power quality and
in some cases respond automatically to them. Using such smart grids features of rapid sensing and automated self healing of anomalies
in the network promises to bring higher quality power and less downtime while simultaneously supporting power from intermittent power
sources and distributed generation, which would if unchecked degrade power quality.

Power quality compression algorithm [ edit ]

A power quality compression algorithm is an algorithm used in the analysis of power quality. To provide high quality electric power
service, it is essential to monitor the quality of the electric signals also termed as power quality (PQ) at different locations along an

Create PDF in your applications with the Pdfcrowd HTML to PDF API PDFCROWD
 electrical power network. Electrical utilities carefully monitor waveforms and currents at various network locations constantly, to
understand what lead up to any unforeseen events such as a power outage and blackouts. This is particularly critical at sites where the
environment and public safety are at risk (institutions such as hospitals, sewage treatment plants, mines, etc.).

Power quality challenges [ edit ]

Engineers have at their disposal many meters,[6] that are able to read and display electrical power waveforms and calculating parameters
of the waveforms. These parameters may include, for example, current and voltage RMS, phase relationship between waveforms of a
multi-phase signal, power factor, frequency, THD, active power (kW), reactive power (kVAr), apparent power (kVA) and active energy
(kWh), reactive energy (kVArh) and apparent energy (kVAh) and many more. In order to sufficiently monitor unforeseen events, Ribeiro et
al.[7] explains that it is not enough to display these parameters, but to also capture voltage waveform data at all times. This is
impracticable due to the large amount of data involved, causing what is known the “bottle effect”. For instance, at a sampling rate of 32
samples per cycle, 1,920 samples are collected per second. For three-phase meters that measure both voltage and current waveforms,
the data is 6-8 times as much. More practical solutions developed in recent years store data only when an event occurs (for example,
when high levels of power system harmonics are detected) or alternatively to store the RMS value of the electrical signals.[8] This data,
however, is not always sufficient to determine the exact nature of problems.

Raw data compression [ edit ]

Nisenblat et al.[9] proposes the idea of power quality compression algorithm (similar to lossy compression methods) that enables meters
to continuously store the waveform of one or more power signals, regardless whether or not an event of interest was identified. This
algorithm referred to as PQZip empowers a processor with a memory that is sufficient to store the waveform, under normal power
conditions, over a long period of time, of at least a month, two months or even a year. The compression is performed in real time, as the
signals are acquired; it calculates a compression decision before all the compressed data is received. For instance should one parameter
remain constant, and various others fluctuate, the compression decision retains only what is relevant from the constant data, and retains
all the fluctuation data. It then decomposes the waveform of the power signal of numerous components, over various periods of the
waveform. It concludes the process by compressing the values of at least some of these components over different periods, separately.
This real time compression algorithm, performed independent of the sampling, prevents data gaps and has a typical 1000:1 compression
ratio.

Aggregated data compression [ edit ]

Create PDF in your applications with the Pdfcrowd HTML to PDF API PDFCROWD
 A typical function of a power analyzer is generation of data archive aggregated over given interval. Most typically 10 minute or 1 minute
interval is used as specified by the IEC/IEEE PQ standards. A significant archive sizes are created during an operation of such
instrument. As Kraus et al.[10] have demonstrated the compression ratio on such archives using Lempel–Ziv–Markov chain algorithm,
bzip or other similar lossless compression algorithms can be significant. By using prediction and modeling on the stored time series in the
actual power quality archive the efficiency of post processing compression is usually further improved. This combination of simplistic
techniques implies savings in both data storage and data acquisition processes.

Power Quality Standards [ edit ]

The quality of electricity supplied is set forth in international standards and their local derivatives, adopted by different countries:

EN50160 is the European standard for power quality, setting the acceptable limits of distortion for the different parameters defining
voltage in AC power.

IEEE-519 is the North American guideline for power systems. It is defined as "recommended practice"[11] and, unlike EN50160, this
guideline refers to current distortion as well as voltage.

IEC 61000-4-30 is the standard defining methods for monitoring power quality. Edition 3 (2015) includes current measurements, unlike
earlier editions which related to voltage measurement alone.

See also [ edit ]

Dynamic voltage restoration

References [ edit ]

1. ^ Von Meier, Alexandra (2006). Electric power systems: a 5. ^ "Harmonic filtering in a data center? [A Power Quality discussion
conceptual introduction . John Wiley & Sons. p. 1 . on UPS design]" . DataCenterFix.com. Archived from the
2. ^ Energy Storage Association original on 2011-07-08. Retrieved 2010-12-14.
3. ^ "A utility pamphlet illustrating the CBEMA curve" (PDF). 6. ^ Galli; et al. (Oct 1996). "Exploring the power of wavelet
pge.com. analysis?". IEEE Computer Applications in Power. IEEE. 9 (4): 37–
4. ^ ab Shertukde, Hemchandra Madhusudan (2014). Distributed 41. doi:10.1109/67.539845 .[verification needed]
photovoltaic grid transformers. p. 91. ISBN 978-1482247190.
OCLC 897338163 .

Create PDF in your applications with the Pdfcrowd HTML to PDF API PDFCROWD
 7. ^ Ribeiro; et al. (2001). "An enhanced data compression method for 10. ^ Kraus, Jan; Tobiska, Tomas; Bubla, Viktor (2009). "Lossless
applications in power quality analysis?". IECON '01. Nov. 29-Dec. 2, encodings and compression algorithms applied on power quality
2001, IEEE, The 27th Annual Conference of the IEEE Industrial datasets" . CIRED 2009 - 20th International Conference and
Electronics Society. 1. pp. 676–681. Exhibition on Electricity Distribution - Part 1. 20th International
doi:10.1109/IECON.2001.976594 .[verification needed] Conference and Exhibition on Electricity Distribution, 8–11 June
8. ^ Ribeiro; et al. (Apr 2004). "An improved method for signal 2009. pp. 1–4. ISBN 978-1-84919126-5.
processing and compression in power quality evaluation?". IEEE 11. ^ "IEEE 519-2014 - IEEE Recommended Practice and
Transactions on Power Delivery. IEEE. 19 (2): 464–471. Requirements for Harmonic Control in Electric Power Systems" .
doi:10.1109/PES.2003.1270480 . ISBN 0-7803-7989- standards.ieee.org. Retrieved 2020-11-16.
6.[verification needed]
9. ^ US 7415370 , Nisenblat, Pol; Amir M. Broshi & Ofir Efrati,
"Power Quality Monitoring", published April 18, 2004, issued
September 21, 2006

Literature [ edit ]

Dugan, Roger C.; Mark McGranaghan; Surya Santoso; H. Wayne Beaty (2003). Electrical Power Systems Quality. McGraw-Hill Companies, Inc.
ISBN 978-0-07-138622-7.
Meier, Alexandra von (2006). Electric Power Systems: A Conceptual Introduction. John Wiley & Sons, Inc. ISBN 978-0471178590.
Heydt, G.T. (1991). Electric Power Quality. Stars in a Circle Publications. Library Of Congress 621.3191.
Bollen, Math H.J. (2000). Understanding Power Quality Problems: Voltage Sags and Interruptions. New York: IEEE Press. ISBN 0-7803-4713-7.
Sankaran, C. (2002). Power Quality. CRC Press LLC. ISBN 978-0-8493-1040-9.
Baggini, A. (2008). Handbook of Power Quality. Wiley. ISBN 978-0-470-06561-7.
Kusko, Alex; Marc Thompson (2007). Power Quality in Electrical Systems. McGraw Hill. ISBN 978-0-07-147075-9.
Chattopadhyay, Surajit; Mitra, Madhuchhanda; Sengupta, Samarjit (2011). Electric Power Quality. Springer Science+Business. ISBN 978-94-007-
0634-7.
IEEE Standard 519 Recommended Practices and Requirements for Harmonic Control in Electrical Power Systems section 10.5 Flicker

V·T·E Electricity delivery [hide]

Automatic generation control · Backfeeding · Base load · Demand factor · Droop speed control · Economic dispatch · Electric power
· Demand management · Energy return on investment · Electrical fault · Home energy storage · Grid storage · Grid code ·
Concepts
Grid strength · Load following · Merit order · Nameplate capacity · Peak demand · Power factor · Power quality · Power-flow study ·
Repowering · Utility frequency · Variability
Sources Non-renewable Coal · Fossil fuel power station · Natural gas · Petroleum · Nuclear · Oil shale

Create PDF in your applications with the Pdfcrowd HTML to PDF API PDFCROWD
 Renewable Biomass · Biofuel · Geothermal · Hydro · Marine (Current · Osmotic · Thermal · Tidal · Wave) · Solar · Wind

AC power · Cogeneration · Combined cycle · Cooling tower · Induction generator · Micro CHP · Microgeneration · Rankine cycle ·
Generation
Three-phase electric power · Virtual power plant
Demand response · Distributed generation · Dynamic demand · Electric power distribution · Electricity retailing ·
Electrical busbar system · Electric power system · Electric power transmission · Electrical grid · Electrical interconnector ·
Transmission
and distribution High-voltage direct current · High-voltage shore connection · Load management · Mains electricity by country · Power line ·
Power station · Power storage · Pumped hydro · Smart grid · Substation · Single-wire earth return · Super grid · Transformer ·
Transmission system operator (TSO) · Transmission tower · Utility pole
Failure modes Blackout (Rolling blackout) · Brownout · Black start · Cascading failure

Protective Arc-fault circuit interrupter · Earth leakage circuit breaker · Residual-current device (GFI) · Power system protection ·
devices Protective relay · Numerical relay · Sulfur hexafluoride circuit breaker
Availability factor · Capacity factor · Carbon offset · Cost of electricity by source · Ecotax · Energy subsidies · Feed-in tariff ·
Economics
and policies Fossil fuel phase-out · Load factor · Net metering · Pigovian tax · Renewable Energy Certificates · Renewable energy payments ·
Renewable energy policy · Spark/Dark/Quark/Bark spread
Statistics and
production List of electricity sectors · Electric energy consumption

Categories: Electric power distribution · Electricity economics · Power station technology · Portals: Energy · Renewable energy

Categories: Electric power quality Electrical power control Power engineering

This page was last edited on 1 January 2021, at 10:38 (UTC).

Text is available under the Creative Commons Attribution-ShareAlike License; additional terms may apply. By using this site, you agree to the Terms of Use and
Privacy Policy. Wikipedia® is a registered trademark of the Wikimedia Foundation, Inc., a non-profit organization.

Privacy policy About Wikipedia Disclaimers Contact Wikipedia Mobile view Developers Statistics Cookie statement

Create PDF in your applications with the Pdfcrowd HTML to PDF API PDFCROWD