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I have read in literature that nonlinear loads can impact on the operation of the so called microgrids. However, when I heard nonlinear loads I think in electronic devices such mobile phones or computers, but it seems to me that those loads are not "big" enough in terms of power demand for a grid where perhaps it is expected to be linear loads of hundreds of KW (such as industrial motors). So, what kind of "big" nonlinear loads is expected to be connected in the grid? Can you name some please?

Bur Nor
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  • If you are talking about reactive loads, the grid operators adjust the Vars to compensate. Please define what you mean by microgrid. Is this something you are setting up yourself for a small area? – SDsolar Nov 10 '17 at 17:38
  • A single computer or mobile phone [charger] is not a big load in itself, but multiply that by hundreds/thousands/millions of users and now we're talking big potatoes. Cheap switch-mode supplies that don't bother complying with any harmonics standards (e.g. CSA) may 'pollute' more. – calcium3000 Nov 10 '17 at 17:39
  • I am thinking that in factories, where there might be considerable amount of nonlinear loads, they are responsable to mitigate the harmonics produced by them so that it does not impact the grid quality. But what about offices and homes, as @calcium3000 said, if we collect many of them the result can be important. Do you guys have any idea how the distribution operator manage it? – Bur Nor Nov 13 '17 at 11:10

2 Answers2

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What kind of loads generate these kinds of waveforms? If your switching power on and off and not just a regular rectifier then you are probably a nonlinear load. Loads like LED's and diodes that only draw power from one half of the cycle are also non-linear. Anything that switches power on and of more than the cycle time is also nonlinear.

Modern industrial facilities are characterized by the widespread application of nonlinear loads. These loads can make up a significant portion of the total facility loads and inject harmonic currents into the power system, causing harmonic distortion in the voltage. This harmonic problem is compounded by the fact that these nonlinear loads have a relatively low power factor. Industrial facilities often utilize capacitor banks to improve the power factor to avoid penalty charges. The application of power factor correction capacitors can potentially magnify harmonic currents from the nonlinear loads, giving rise to resonance conditions within the facility.

Nonlinear industrial loads can generally be grouped into three categories:

1) Three-phase power converters (
2) Arcing devices
3) Saturable devices

Source: Harmonic Sources from Industrial Loads I

Three-phase electronic power converters

Three-phase electronic power converters differ from single-phase converters mainly because they do not generate third-harmonic currents. This is a great advantage because the third-harmonic current is the largest component of harmonics.

Source: Harmonic Sources from Industrial Loads I

Arcing Devices

This category includes arc furnaces, arc welders, and discharge-type lighting (fluorescent, sodium vapor, mercury vapor) with magnetic ballasts. As shown in Fig. 4.17, the arc is basically a voltage clamp in series with a reactance that limits current to a reasonable value. The voltage-current characteristics of electric arcs are nonlinear. Following arc ignition, the voltage decreases as the arc current increases, limited only by the impedance of the power system. This gives the arc the appearance of having a negative resistance for a portion of its operating cycle such as in fluorescent lighting applications. In electric arc furnace applications, the limiting impedance is primarily the furnace cable and leads with some contribution from the power system and furnace transformer. Currents in excess of 60,000 A are common.

Source:Harmonic Sources from Industrial Loads II

Saturable devices

Equipment in this category includes transformers and other electromagnetic devices with a steel core, including motors. Harmonics are generated due to the nonlinear magnetizing characteristics of the steel

Source:Harmonic Sources from Industrial Loads II

Voltage Spike
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  • *Loads like LED's and diodes that only draw power from one half of the cycle* ... wouldn't most LED's be powered by a full-wave rectifier that would draw power from both halves? – LShaver Mar 13 '19 at 16:28
  • @LShaver Most do, some don't to save on components. The ones that don't create noise. Cheap devices save money by reducing component count and using the cheapest components. \ – Voltage Spike Mar 13 '19 at 16:44
  • Hmm interesting... so is it a 50/50 chance which half of the wave a given cheapo LED draws from? – LShaver Mar 13 '19 at 18:26
  • Yep, depending on how it's built – Voltage Spike Mar 13 '19 at 19:02
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Motor control inverters, office florescent lighting, PC power supplies (Not in general negligible if you have offices in the area!).

Basically anything with a switchmode supply that does constant power, which is to say pretty much everything that is not a simple dumb heater or very old school motor drive.

Actually even a large synchronous motor is a non linear load because they are substantially constant power, dropping the voltage increases the rotor angle and causes more current to be drawn...

Dan Mills
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