Harmonic Distortion in electrical system

A pure sinusoidal voltage is a conceptual quantity produced by an ideal AC generator built with finely distributed stator and windings that operated in a uniform magnetic field. Since neither the winding distribution nor the magnetic field are uniform in a working AC machine, voltage waveform distortions are created,and the voltage- time relationship deviates from the pure sine function. The distortion at the point of generation is very small (about 1% or 2%) , but nonetheless it exists. Because this is a deviation from a pure sine wave, the deviation is in the form of a periodic function, and by definition, the voltage distortion contains harmonics.

When a sinusoidal voltage is applied to a certain type of load, the current drawn by the load is proportional to the voltage and impedance and follows the envelope of the voltage waveform. These loads are referred to as linearloads(loads where the voltage and current  follows one another without any distortion to their pure sine waves). Examples of linear loads are resistive heaters, incandescent lamps, and constant speed induction and synchronous motors.


In contrast, some loads cause the current to vary disproportionately with the voltage during each half cycle. These loads are classified as nonlinear loads, and current and voltage have waveform has numerous additional waveform superimposed upon it, creating multiple  frequencies within the normal 60 Hz sine wave. The multiple frequencies are harmonics of the fundamental frequency.

Which is more dangerous voltage or current!!!!

A common phrase heard in reference to electrical safety goes something like this "It's not voltage that kills, its current !". While there is an element of truth to this, there's more to understand about shock hazard than this simple adage. If voltage presented no danger, no one would ever print an display signs saying: DANGER -HIGH VOLTAGE!

The principle that "current kills" is essentially correct . It is electric current that burns tissue, freezes muscles, and fibrillates hearts. However , electric current doesn't just occur on its own: there must be voltage available to motivate electrons to flow through a victim. A person's body also presents resistance to current, which must be taken into account.

Taking ohm's law for voltage, current, and resistance, and expressing it in terms of current for a give n voltage and resistance , we have this equation:


I  = V/R

Current = Voltage / Resistance 


The amount of current through a body is equal to the amount of voltage applied between two points on that body, divided by the electrical resistance offered by the body between those two points. Obviously, the more voltage available to cause electrons to flow, the easier they will flow through any given amount of resistance. Hence, the danger of high voltage : high voltage means potential for large amount of current through your body, which will injure or kill you. The more resistance a body offers to current , the slower electrons will flow for any given amount of  voltage. just how much voltage is dangerous depends on how much total resistance is in the circuit to oppose the flow of electrons.


Body resistance is not fixed quantity. It varies from person to person and from time to time.
There's even a body fat measurement technique based on a measurement of electrical resistance between a person's toes and fingers. Different percentage of body fat give provide different resistance : just one variable affecting electrical resistance in human body. In order for the technique to work accurately , the person must regulate their fluid intake for several hours prior to the test, indicating that body hydration is another factor impacting the body's electrical resistance.