what is harmonics and how it is developed in UPS,Differences between Voltage THD and Current THD?

Question

in UPS voltage THD current THD having % at input side and output side what is that and how it is created

Answer 1

Harmonic distotion is found in all manners of alternating signals from power to radio waves.

power created at 60 hetze creets harmonics at 2.3.4.5.6.7 etc. so 120hertz, 180hertz. etc.

the even harmonics generally cancel eachothet out and can be ignored the odd harmonics can interfere quite a bit, esp in transmitters and motors. esp the 3rd. & 5th.

Usually the distortion is the same for current and votage unless the power factor of the circuit is lower than .95 or so or higher than 1.05... this is current leading or lagging behind the voltage waveform voltage leads in an inductive circuit, current leads in a more capacitive circuit.

A UPS normally has step up and step down transformers so usually the power coming out is slightly inductive...a good UPS will have power factor correcting capacitors to make the power factor 1.

THIS is what makes the harmonics....you creat a tank circuit inside the UPS between the transformer and the capacitor.

the third and seventh harmonic oppose the 1st and 5th, in a motor the push against the rotor as it spins creating more resistance, and more heat.

the fifth interferes more with transmitters.
you can use filters to get rid of the harmonics..shunting them to ground.

I'll chck back tomorrow if I didn't hit anything let me know in the add details section..

Answer 2

Mostly a guess. but most UPS systems, when they are on the battery supply, are making up the AC with an inverter circuit and any resemblance to a sine wave is good luck. A really quality way (and very expensive way) to do UPS is with a motor-generator system where you have both an AC motor and a DC motor on the same shaft with an AC generator. When the mains fail, the DC motor picks up the job of running the generator. The nice thing is that there is no evidence in the output of the change-over. No transient, no phase discontinuity.

Answer 3

harmonics is multiples of frequences 60,120,240,so on. On UPS input side is line frequency but output side is converted back from stored DC voltage. Harmonics are developed thru transformer action. I'm not sure on theTHD is usually a audio term total hormonic distortion. I would take that to mean in your application as the not true sine wave on the output side due to making AC from a stored DC voltage. In order to trun AC appliance depending on what it is the sinewave specs have to be meet. A tv for example has to have pretty close to true signal (ac sinewave)or else you would have a rolling picture that was hard to sync in, an iron on the other hand just needs a ac voltage to operate it can be more distorted specs would not be so tight.
Reason the specs are on UPS is so you can match it to the purpose of what your using it for.