Service reliability and quality of power have become growing concerns for many facility managers, especially with the increasing sensitivity of electronic equipment and automated controls. There are several types of voltage fluctuations that can cause problems, including surges and spikes, sags, harmonic distortion, and momentary disruptions. Harmonics can cause sensitive equipment to malfunction and other problems, including overheating of transformers and wiring, nuisance breaker trips, and reduced power factor.
What Are Harmonics?
Harmonics are voltage and current frequencies riding on top of the normal sinusoidal voltage and current waveforms. Usually these harmonic frequencies are in multiples of the fundamental frequency, which is 60 hertz (Hz) in the US and Canada. The most common source of harmonic distortion is electronic equipment using switch-mode power supplies, such as computers, adjustable-speed drives, and high-efficiency electronic light ballasts.
服務(wù)的可靠性和電能質(zhì)量已成為越來越多設(shè)施經(jīng)理的關(guān)注，尤其是隨著電子設(shè)備和自動化控制靈敏度提高了很多。有幾種類型的電壓波動可能導(dǎo)致問題，包括浪涌和尖峰，凹陷，諧波失真，一時中斷。諧波可能導(dǎo)致敏感的設(shè)備出現(xiàn)故障和其他問題，包括變壓器、線路和斷路器過熱傳輸滋擾，并降低功率因數(shù)。
什么是諧波？
諧波電壓和電流的頻率在正常正弦電壓和電流波形時為最佳。通常，這些諧波頻率是基本頻率，這里是60赫茲，在美國和加拿大（赫茲）的倍數(shù)。諧波失真的最常見的來源是使用電子設(shè)備開關(guān)電源，如電腦，調(diào)速器，以及高效率的電子燈用鎮(zhèn)流器。
諧波也造成了這些“開關(guān)負載”（也稱為“非線性負載”，因為目前不隨電壓變化，因為它是簡單的電阻和負荷的反應(yīng)）：每次電流接通和關(guān)斷時間使電流脈沖產(chǎn)生。由此產(chǎn)生的脈沖波形組成的諧波頻率頻譜，包括60赫茲和它的倍數(shù)。從這個電壓畸變到失真，結(jié)果目前通常反應(yīng)在系統(tǒng)阻抗。（阻抗是完全對立的措施—電阻，電容和電感—交變電流。）在更高頻率的波形，統(tǒng)稱為總諧波失真（THD），不執(zhí)行任何有用的工作，也可以成為重要的滋擾。
諧波波形的特點是其振幅和諧波級次。在美國和加拿大，三次諧波為180赫茲或3 × 60赫茲和第五次諧波為300赫茲（5 × 60赫茲）。第三諧波（和它的倍數(shù)）是在單相負載電