Power Factor (PF) and Total Harmonic Distortion (THD) - Page 1
Forum section: electronics / beginners

author: Minerva
author_rank: Newbie
timestamp: March 08, 2024, 08:48:28 am
content: First post. I'm trying to follow the posting guidelines. Let me know if I need to improve the question or re-post to somewhere else like one of the more technical forums.Transformer losses and the impact of power factor are a weak point in my understanding. I'm trying to better understand transformers and power distribution.I have searched the forum and the internet quit a bit.Some of the reasons I've found regarding reactive power being undesirable are: 1) a requirement for larger conductors, 2) resistance losses, 3) grid stability, 4) poor ability to transmit reactive power on high voltage transmission lines, 5) noise as reactive loads are connected/disconnected.Some of the reasons I've found regarding Total Harmonic Distortion being undesirable are: 1) transformer losses, 2) noise affecting sensitive circuits, 3) RF emissions/EMI, 4) inaccuracies in power metering. I know the last point varies wildly based on the meter itself, but let's assume current transformer (CT) based meters to keep the topic focused on transformers.Is there a way of comparing the detractors of PF and THD?Is there a way of comparing different types of harmonic distortions against each other?Consider the following three scenarios:Base Scenario: an AC motor at a steady state/load will have a steady PF with an inductive componentScenario 2: if we absorb the return current from the inductance, then the drawn current will have a non-sinusoidal waveform that isasymmetricalwithin half the base frequency.Scenario 3: if we both absorb the return current and draw an extra current equal to the return current, then the drawn current will have a non-sinusoidal waveform that issymmetricalwithin half the base frequencyAnother way of describing Scenario 3 is, imagine the THD caused by a device with a capacitive-angle current draw from 0°-90°/180°-270° and a proportionate inductive-angle current draw from 90°-180°/270°-360° (and some base-level in-phase resistive draw throughout the wave).Another way of describing Scenario 2 is, imagine the THD caused by a device with an inductive-angle current draw from 90°-180°/270°-360° (and some base-level in-phase resistive draw throughout the wave).I intentionally omitted simple PF correction capacitors, because that's uninteresting for the topic at hand.In Scenario 2: we've eliminated the reactive power, but introduced harmonic distortionIn Scenario 3: I think this technically introduces more THD, but makes the waveform more symmetrical which I'm guessing is more desirable in some way?How should I be thinking about PF losses/detractors and THD losses/detractors?Are there any books or research papers you would recommend reading based on the area of interest expressed in this post?Thanks in advance.

author: jonpaul
author_rank: Super Contributor
timestamp: March 08, 2024, 11:21:40 am
content: Post has many odd impressions.see the many fine papers and seminars on PFC, for example from Dr REDL, IEEE.PFC, VARS, Watts, losses all very different forTransformer, inductive load.Classic linear DCPSSMPSSMPS plus PFC stage.Most power electronics texts have all the info.j