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Harmful harmonics

Choppy waves can quickly lead to shipwreck.

Harmonics reduce power quality, especially in a company's own network. This has negative effects on people, machines and IT. And it's not just in the event of a fire that things can get really expensive.

Harmonics are also called "Haromonics" because their frequency is an integer multiple of the 50-heart fundamental we have in our power grids. Thus, they add up to bizarre rhythms in the grid and ruin the aesthetically pleasing sine wave. This is called "pollution" of the grid.

Harmonic oscillations

Influence on operational safety

This would not be so bad if harmonics were not harmful to devices and machines and even relevant for operational safety. Wouldn't IT systems be checkmated by them and production lines go on strike as a result? Wouldn't even standardized neutral conductors be overloaded by harmonics and lead to cable fires? The extensive literature on this subject reads like a detective story, despite its lack of popularity!

But if you have harmonics in your company network, you are not alone, because every network knows the harmonics. However, there is a need for action if there are disturbances or even dangers. The only annoying thing is that the nasty things hide well and it often has to come to failures and more to take care of the matter.

"We had little transparency about energy consumption. But we were also concerned about operational safety. Current harmonics stress transformers and the N conductor and, in extreme cases, can damage equipment or cause fires."

Technician of a company in Stuttgart

From practice: Harmonics are usually measured and displayed as the total harmonic distortion in the network (THD - Total Harmonic Distortion). Here, each harmonic is represented in the magnitude of its ratio to the fundamental. The measurement below in a Stuttgart plant shows a clear conspicuousness at the fourth and sixth harmonics.

But what can you do to prevent flickering lights and humming fluorescent tubes from reducing the performance of your employees, or to prevent motors from having to be taken to the scrap heap prematurely due to constant heating? And what can you do to avoid having to justify yourself to the insurance company in the event of damage or fire? The solutions are many and should be well adapted to the situation. Knowing the cause, sources and effects is a good start. For this purpose, high-frequency measurements in the company network are important. A good analysis helps to evaluate and find solutions.

Modern consumers change the rules of the game

Who is interested in more detail: The alternating current in the German transmission grid describes an almost perfect sine wave with a frequency of 50 Herz. Neither a transformer nor a light bulb, neither a heating element nor a synchronous motor have any significant influence on the sinusoidal shape. But modern consumers are changing the rules of the game in the grid.

Harmonics deform the required fundamental vibration. The consequences are manifold, often even serious and expensive. Harmonics are also sinusoids with an integer multiple frequency of the 50-heart fundamental. Consequently, their frequency can be 100, 150, 200, 250 ...heart, thus they add up "harmonically" to each interval of the fundamental. Because of their similarity or multiplicity to the 50-heart amplitude one also speaks of the 2nd, 3rd, 4th, 5th to nth harmonics.

Distortions of the sine curve

The main cause for the pollution of the aesthetically pleasing sinusoidal shape is electronics, because it can't do anything with waves, but needs a constant DC voltage. This is generated in power supplies with capacitors and other components. For this purpose, the capacitors charge themselves with a short current pulse in each wave of the fundamental oscillation. The result is distortion of the sine wave and harmonics in any variation. Switch-on processes and starting currents of machines, as well as frequency regulators and dimmers also contribute to the contamination of the mains frequency.

Different sources of interference usually result in typical harmonics. For example, if you want to call the consultant of your choice and the telephone system is on strike again, this could be due to harmonics of the 20th to 30th harmonic, because they like to put telephone systems out of operation!

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