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Usefulness of The Various Indicators of Harmonic Distortion: From Electrical Installation Guide

THDu and THDi are indicators of voltage and current wave distortion respectively due to harmonics. THDu values of ≤5%, 5-8%, and ≥8% correspond to normal, significant distortion with possible malfunctions, and major distortion with probable malfunctions. THDi values of ≤10%, 10-50%, and ≥50% similarly correspond to normal, significant distortion with risk of overheating, and major distortion with probable malfunctions. Power factor λ and crest factor are also used to characterize installations and equipment capacity for harmonics. Harmonic spectrum provides another representation of distorted electrical signals.

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89 views2 pages

Usefulness of The Various Indicators of Harmonic Distortion: From Electrical Installation Guide

THDu and THDi are indicators of voltage and current wave distortion respectively due to harmonics. THDu values of ≤5%, 5-8%, and ≥8% correspond to normal, significant distortion with possible malfunctions, and major distortion with probable malfunctions. THDi values of ≤10%, 10-50%, and ≥50% similarly correspond to normal, significant distortion with risk of overheating, and major distortion with probable malfunctions. Power factor λ and crest factor are also used to characterize installations and equipment capacity for harmonics. Harmonic spectrum provides another representation of distorted electrical signals.

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dhruv
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© © All Rights Reserved
We take content rights seriously. If you suspect this is your content, claim it here.
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Usefulness of the various indicators of

Harmonic distortion
From Electrical Installation Guide

THDu is an indicator of the distortion of the voltage wave.

Below are given indicative values of THDu and the corresponding consequences
in an installation:
≤ 5%: normal situation, no risk of malfunctions,
5 to 8%: significant harmonic distortion, some malfunctions are possible,
≥ 8%: major harmonic distortion, malfunctions are probable. In-depth analysis and the installation of
mitigation devices are required.

THDi is an indicator of the distortion of the current wave.

The current distortion can be different in the different parts of an


installation. The origin of possible disturbances can be detected by measuring
the THDi of different circuits.

Below are given indicative values of THDi and the corresponding phenomena for
a whole installation:
≤ 10%: normal situation, no risk of malfunctions,
10 to 50%: significant harmonic distortion with a risk of temperature rise and the resulting need to
oversize cables and sources,
≥ 50%: major harmonic distortion, malfunctions are probable. In-depth analysis and the installation of
mitigation devices are required.

Power factor λ is used to determine the rating for the different devices of
the installation.

Crest factor is used to characterise the aptitude of a generator (or UPS) to


supply high instantaneous currents. For example, computer equipment draws
highly distorted current for which the crest factor can reach 3 to 5.

Harmonic spectrum provides a different representation of electrical signals


and can be used to evaluate their distortion.

Retrieved from "http://www.electrical-installation.org/enw/index.php?


title=Usefulness_of_the_various_indicators_of_Harmonic_distortion&oldid=21081"
Category: Chapter - Power harmonics management

This page was last modified on 7 December 2016, at 23:51.

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