Harmonics

[wethery]

Can someone please describe to me the effects of harmonics on single-phase measurements, especially in circuits containing reactive components

 

[230842]

A distorded wave of a frecuency f (let' say 60 Hz) can be split in a sum of sinusoidal waves of recuencies 60, 120, 180,..60xN.. Hz. In Power Systems even order harmonics do normally not exist.
Reactances of coils and capacitors are frequency dependant. Coil reactance increases whith frecuency while capacitor reactance decreases, in sucha a way that a circuit having both types of elementes behaves diferently for every component of distorded wave.
For example: a distorded current flowing through an inductance produces a voltage drop much more distorded than current and vice versa: a coil connected to a distorded voltage source wants a less distorded current.
On the other hand capacitors have an opposite performance: current is a much more distorded than voltage.

Many of these harmonic components do not produce usefull work but increase RMS values of currents or voltages reducing the power phactor and increasing losses.


Julian

 

[avishai]

The main effect of harmonics is in the description of RMS values (current and voltages).As explained by Julian many of the devices connected to a distorted network would have higher or lower voltages/current . This is very problematic to three phases system but in single phase system the effect of harmonics is to deteriorate the way swiching power supplies are working . The distortion of the wave can make th swiching device to swich off for no visible reason , this is specially problematic with computers who are swiching off without any warning .The same can happen to TV syatems and other devices . A.Rash BScEE & PE
a_rash@bigfoot.com