Harmonic currents

[Engineer54]

Whenever a square wave is introduced, there are the multiples of the fundamental frequency introduced also as a by product of the fact that the frequency components of a pure square wave are in theory infinite. Square waves are typically produced by semi-conductors used in their switching mode - hence SMPS. E.g. a transistor can be designed as a current amplifier, like an audio amp or it can be used as a switch. The very fast times these devices can switch can create a near perfect square wave but with all the associated harmonics.
VSDs also use semi-conductors in switching mode and can create similar problems.
So basically whenever we use semiconductors in switching mode we will get lots of harmonics which have to be dealt with.
If you want to read up more on it - plenty of electronics books deal with the principles of switching

The problem being, there isn't much these days that that won't cause harmonic distortion. Virtually every home appliance and audio/visual appliances will produce harmonics and or leakage currents to some degree. It's when you start to add them up over say a residential area or estate, that they start becoming a real and increasing problem. The other downside, is that nullifying these currents is an expensive business!!...

 

[plugsandsparks]

The problem being, there isn't much these days that that won't cause harmonic distortion. Virtually every home appliance and audio/visual appliances will produce harmonics and or leakage currents to some degree. It's when you start to add them up over say a residential area or estate, that they start becoming a real and increasing problem. The other downside, is that nullifying these currents is an expensive business!!...

Product of the modern age - when i was a lad, PSUs always had a transformer, diodes, a big cap, and was the cheapest way. Nowadays you can make a switching PSU for a couple of pence, also large thyristors were megabucks and only affordable by the largest of industrial users, again they are ten a penny and i keep seeing smaller and cheaper VSDs for bog standard motors. Its not going to get any better anytime soon. Oh well