Insymmetrical Current

Half-wave rectified DC fits that description.

Of course you can artificially generate asymmetrical load by half-wave rectification.

What I meant is, is there equipment or appliances that draw asymmetrical current in its normal operation?

Well now. If you meant something other than what you said, then I think you better clarify what you want to a finer detail than to say "equipment or appliances" in your load request. There are many pieces of "equipment or appliances" that have a low cost half wave rectified power supply inside to drive the low voltage controlling circuitry. I can think of several other things that briefly produce a non-linear load. I'm just not sure if you'd consider them "equipment or appliances" or if the brief load condition meets your unspoken criteria.

Some people use a diode to dim their light bulbs, as a first example.

Yes, but quite undesirable. I took part in a power problem of a large building having close to 1200 computers. I supplied measurements, the power guys the solutions, in steps. The 3 phases had a load imbalance, close to 30%. They reduced it to somewhere 5%. The service entrance transformer took care of the rest.

The harmonics were horrendeous. Mind it, there were no PFC correctors in those switching supplies, that came much later. Those power supplies do not conduct at low instantaneous voltages, then turn on somewhere at 50V with a very wide spread. And their turn-on is not symmetrical. The harmonic content, particularly on the ground wire got finally suppressed under 5% by the installation of a special transformer having little impedance at 60Hz, but at 400Hz full choking.

The asymmetrical turn-on, amounting to a very unwanted DC component remained. Further periodic load balancing kept it in check. The entrance transformer kept it away from the utility. But it still heated the breakers.

Utilities charge you a hefty fee, if they have to do PFC (phase factor correction) or anything extra.

By the way, any power equipment having specific anode and cathode in it, like arc lights and welders have asymmetrical power draw.

Hi Leveles,

What you are talking about is load imbalance in 3 phase supply system, NOT load current asymmetry between positive and negative cycle .

Computers power supply with no PFC will cause high harmonics, this is well known. But , the current drawn or delay turn on is still symmetrical.

Your next statement about arc welder , although they have anode and cathode, that does not mean the equipment as a whole will draw asymmetrical current, because, most likely it will have full wave rectification inside, in which case the AC current is still symmetrical, unless the arc welder has to draw half wave current for some reason, e.g. the cathode need to be tied to NEUTRAL of the AC supply. Is this the case?

My mentioning the 3 phase system was to round out the picture. The asymmetry: DC component was there with the high harmonics, overheating breakers anomalously.

As far as welders and arc lights concern, the actual devices are polarized with anode and cathode. Now, How would anybody know a particular one's internal construction? Assume it, and Murphy's law bites your behind, firmly.

Other than that, well, it is a free world.

Hi leveles,

The asymmetry: DC component was there with the high harmonics, overheating breakers anomalously.

Sorry to bug you, did you actually see the DC component /waveform on the power analyser / oscilloscope?

I am really keen to find out, in real and practical world, whether is there equipment or machine that draw asymetrical current.

Your other point: Device with polarised anode and cathode output does not in any certainly mean asymmetrical line current , unless you prove me wrong.

Please reread #11, that I do not have to bother to state his obvious, again.

The electron emissivity of metals sharply dependent on their surface temperatures. That is how radio (or power valves, obviously before your time) do their rectification, intended or not. The cathode, with a low work potential and high temperature is a good emitter. The anode, with high work potential and lower temperature is a very poor emitter. Hence, rectification, intended or not.

This is applicable to gas protected welding in general (and quicksilver and halogen based arc lamps in particular). In that welding the center electrode is molten, and provides the weld. The (frequently cooled) outside electrode is NOT an emitter. Hence, unintended rectification, unintended imbalance in waveform.

To your second claim, that you do not believe, until I prove to you, what you do not know diddly about. Sonny, this is a voluntary association. You seek enlightenment, and we - to our ability, whatever - supply guidance. It is free, considering the price. Ask for binding advice, and we will give it for a price, a good and deserving price. According to our expertise, and your ignorance.

Until then, get out of our face, and do your own research, when it does not suit you, what yo hear.. Have a good life.

Hi leveles,

Relax man ! You should be able to take a bit of challenge and vigourous discussion, I was certainly not demanding anything from anyone !

Also please see my reply to #11.

Keep sharing and posting!

Cheers !

Yes, many industrial plants could be unbalanced.

All the 3 phase items are approximately balanced but the single phase loads all come off the same phase.

I was not talking about imbalance, but asymmetrical.

Any load with an amplifier may have asymmetrical distortion, due to several different conditions, from unbalanced bias levels to frequency or phase non-linearity. The resulting output waveforms can become asymmetrical. Here is an example:

Frequency Distortion

Frequency Distortion occurs in a transistor amplifier when the level of amplification varies with frequency. Many of the input signals that a practical amplifier will amplify consist of the required signal waveform called the "Fundamental Frequency" plus a number of different frequencies called "Harmonics" superimposed onto it. Normally, the amplitude of these harmonics are a fraction of the fundamental amplitude and therefore have very little or no effect on the output waveform. However, the output waveform can become distorted if these harmonic frequencies increase in amplitude with regards to the fundamental frequency. For example, consider the waveform below:

Frequency Distortion due to Harmonics

In the example above, the input waveform consists a the fundamental frequency plus a second harmonic signal. The resultant output waveform is shown on the right hand side. The frequency distortion occurs when the fundamental frequency combines with the second harmonic to distort the output signal. Harmonics are therefore multiples of the fundamental frequency and in our simple example a second harmonic was used. Therefore, the frequency of the harmonic is 2 times the fundamental, 2 x f or 2f. Then a third harmonic would be 3f, a fourth, 4f, and so on. Frequency distortion due to harmonics is always a possibility in amplifier circuits containing reactive elements such as capacitance or inductance.

Phase Distortion

Phase Distortion or Delay Distortion occurs in a non-linear transistor amplifier when there is a time delay between the input signal and its appearance at the output. If we call the phase change between the input and the output zero at the fundamental frequency, the resultant phase angle delay will be the difference between the harmonic and the fundamental. This time delay will depend on the construction of the amplifier and will increase progressively with frequency within the bandwidth of the amplifier. For example, consider the waveform below:

Phase Distortion due to Delay

Any practical amplifier will have a combination of both "Frequency" and "Phase" distortion together with amplitude distortion but in most applications such as in audio amplifiers or power amplifiers, unless the distortion is excessive or severe it will not generally affect the operation of the system.