Harmonic currents

[wethery]

The presence of non-linear electrical loads in both commercial and industrial applications has dramatically increased, generating large harmonic currents. Can someone please tell me the examples of these loads

 

[xnuke]

A couple of the most common non-linear loads include switching power supplies (for computers and other commercial electronic equipment) and variable speed drives for DC and AC motors (for industrial applications).

 

[MDom]

Non-linear magnetazing impedances of transformers,reactors,
fluorescent lamp balasts cause harmonics.The harmonic-generating devices are also static convertors,inverters,
speed controllers etc.

 

[gordonl]

Arc furnaces for the metals industry are also culprits.

 

[avishai]

In fact any device connected to the network except light bulb of the conventional type (incadescent)are generating or pumoping harmonics. The mai problem in harmonics is that they might be present in your network and you do not know it because none of you consumers are pumping them from the net. do not forget if no one is trying to input those harmonics they can not exist in the network (Ohm and Kirchoff law).So it is not so simple to know which device is creating harmonics or not .As a general rule every device connected to the network should be checked for the kind of power it is using (linear or not) . A.Rash BScEE & PE
a_rash@bigfoot.com

 

[electricpete]

A few more thoghts for what they're worth

Light bulbs are not the only linear load. Resistive heating doesn't "generate" harmonics. Likewise a motor doesn't generate harmonics unless it is operating near saturation.

In general we can characterize or analyse system by measuring or predicting the THD of both the current and the voltage.

Nonlinear loads will draw current with high THD.

The impedance in the power supply will cause that nonlinear current to produce a smaller distortion of the system voltage. (lower THDv than THDi)

That distorted system voltage also effects other components. But in a linear load, the THD of that load current will be the same as the THD of the supply voltage. In nonlinear load the THD of the current will likely exceed the THD of the supply voltage.

As you move further "upstream" within a power supply, the effect of a given non-linear load upon the system voltage decreases. Harmonic voltage drop (which causes the voltage distortion) is related to the product of harmonic current and power supply impedance.

 

[jbartos]

Suggestions:
1. Visit

http://www.pqtoday.com/downloads/pqtsum95.pdf

for some harmonics and power quality related content, including nonlinear loads.
2. Additional nonlinear loads are:
Rectifiers
Battery Chargers
Microwave Owens
Radars
Many pulse loads
Nonlinear resistors (thermistors, sensistors, thyrite, MOVs, etc.)
etc.