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Saturday, December 16, 2017
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   How to measure Mains Harmonic Deformation

Mains pollution is a serious problem ...... for the energy distribution network and the power plants.
NOT for your (audio) equipment at home.
The (sometimes expensive) measures such as filters, special power cables, separate end groups, etc. do not contribute to the sound quality. Waste of money and effort.


   About pollution with high frequency signals

A lot of electronic equipment uses so-called switching power supplies. (Audio amplifiers usually do not, but digital audio equipment, TVs and PCs and so usually). These types of power circuits can, in principle, cause very high frequency interference, which could hamper radio and television reception.

Such equipment must be provided with good net filters to prevent any malfunctioning from the power lines that also work as a transmitting antenna. Also, all digital devices (CD / DVD player, PC to name but a few) use very high frequency signals for internal operation. For PCs, there are several Giga Hz. These signals can "unlock the cabinet without proper facilities" and disturb the radio / TV traffic.

For a long time (short wave) radio amateurs complain that there is virtually no long-distance reception possible by the "electro smog" especially of computers. And then some computer users will be doing a lot of "case modding" again, so that the EMC shielding of the PC cabinet - in most PCs - is already very moderately eliminated. At frequencies above about 80 MHz, almost all transmission takes place by antenna operation. At (much) lower frequencies there is usually conductivity, and there is a transition area in which both conductivity and antenna operation can play a role.

(The 80 MHz limit is derived from the medical EMC standard)


   Measurements in the range 10 Hz - 48 kHz

To measure the power grid in the audio frequency range, I used a small transformer from 230 Volt to 12 Volt, and a couple of resistors to effect the signal level at about 0.6 Volt. I also used a Creative Labs USB Soundcard and the SpectrumLab analyzer software.

Both support a sample frequency of 96 kHz, so I could measure up to 48 kHz. You can download that software here (Windows zip file), it's freeware.
Please use the .INI file that accompanies the download. Put that file after installation in the program folder.



Fig. 1. The measuring probe for audio frequency signals on the mains.

I use a small printtrafo. Select the resistors so that the sound card's input is not overridden.
With 0.5 to 1 Volt, that usually goes well.

The two resistors form a voltage divider to reduce the voltage from 12 Volts to 0.57 Volts

Ua = 12V * ( 50R / (50R + 1000R) ) = 0.57 V

Both channels of the sound card get the same signal. I had a 12 volt transformer available but also a 15 Volt or 20 Volt transformer is possible.

Examples:
15 VAC Transformer = 1200R + 50R = 0.6 VAC
20 VAC Transformer = 1500R + 50R = 0.645 VAC
24 VAC Transformer = 2000R + 50R = 0.585 VAC

When using other voltages, the voltage divider must be recalculated!

You can test whether the transformer transmits the spectrum properly by setting a square wave signal.
That has to be done quite nicely. SpectrumLab has such a generator on board.



Fig. 2. The spectrum of the power grid in my house.

We see the third harmonic at -20 dB and ninth harmonics at -35 dB compared to the 230 Volt.
That's 23 Volt at the third harmonic and 4 Volts at the ninth harmonic.
Beyond 1 kHz we still have -55 dB or 0.4 volts and beyond 2 kHz it's -60 dB or 230 mV or weaker.





   About Spectrum Lab Software

Spectrum Lab is a software application designed to help users analyse the spectrum of an audio signal via the PC’s soundcard and apply audio filtering operations.

The layout is not very intuitive, so rookies may spend some time trying to understand the function of each dedicated parameter.
Spectrum Lab comes packed with several tools designed to help you analyse audio signals, such as a spectrogram, spectrum graph, amplitude bar, and correleogram.

o sum it up, Spectrum Lab bundles a handy set of tools for helping you analyse the spectrum of audio signals. To make the most out of every single built-in feature, you can check the help manual for detailed information about each audio parameter.


Download SpectrumLab Software (Windows zip file)
 

   Harmonic deformation

( This article is related to the Power Plants in the Netherlands )
We are talking about harmonic distortion when there are also frequencies in the voltage other than this basic frequency. In most cases, multiples of 50 Hz are involved; the so-called higher harmonics.
Possible effects of harmonic distortion are: additional power losses, electronic equipment failure and zero-conductor overloads. The Netcode sets limits to total harmonic distortion. A limit for the low and medium voltage network (up to 35 kV) is 8% during 95% of a week. For harmonic deformation in the streams, 25% is the maximum permissible.
Harmonic deformation is caused by non-linear loads. The main source of harmonic distortion is power electronics, such as rectifiers of computers, televisions or operating systems of electric motors. Also, energy saving lamps, LED / TL lights and solar panel converters can cause higher harmonics in the power grid.

Solutions to harmonics problems
  • To solve the problem, equipment must be installed that generates little or no harmonics. However, this is an unexpected case. Solutions can be: Magnification of vein diameter of the zero conductor.

  • In most three-phase systems with a single zero, the zero line is chosen as large as the phase conductors. However, for systems with a high non-linear load, the lineage should be wider. Use of separated zero conductors.

  • Another method may be to not combine the neutral line. Separately, an individual neutral line is drawn on each cable. Although this method contributes successfully to eliminating the harmonic current through the system, the power cable and conductors within the distribution device must still be dimensioned. Extra large transformers and generators.

  • Transformers and generators that produce loads that produce harmonics need to be extra-sized.
    Special transformers
    There are several special types of transformer circuits that can eliminate harmonics.
    For example, the traditional star / triangle transformer circuit will capture all triple harmonics (third, ninth, fifteenth, twenty-one, etc.) in the triangular circuit. Additional windings can be used to eliminate the other harmonics. These special transformers are widely used in computer spaces with taxes that create harmonics, such as mainframes. Filtering.

  • Harmonic filters can work well in eliminating harmonics. These filters can almost completely eliminate the harmonics and improve the power factor. Elimination of harmonics and improvement of the power factor reduce the electricity costs.
    The overall effect after switching on the OptiVolt MultiLiner® with harmonic filter:


  • Separation of equipment
    Until devices are available that produce little or no harmonics, the load will be distributed as much as possible across the different circuits. This separation of "dirty" and "clean" load is fundamental to today's electrotechnical design. This, however, provides more distribution circuits, distribution cabinets and panel boards. Intelligent correction as a solution for harmonic reduction From the above it can be seen that the further the harmonic tax is being implemented, the more complex and costly this measure becomes. If, in the light of thorough research, it is decided to take corrective measures, they should be implemented as close as possible to the disturbing tax. This way of correcting, as close as possible to the source, prevents the following issues:

    • Unnecessary load of the electricity grid
    • Increase in line losses by heat
    • The appeal of security devices
    • Less efficient operation of other connected machines
    • Increase in maintenance and revision to other connected machines (especially motors)
    • Danger to safety of persons and environment by overloaded zero conductors and phase conductors.

The central treatment of harmonics reduces excessive currents through the high voltage or distribution network. However, it does not solve the problems of the internal electrical infrastructure. Treatment to or at the load that causes the harmonics is the most intelligent solution to the above problems.



Consequences in costs by harmonics

Older meters measure only the current with the fundamental frequency (50 Hz). Also the traditional electromechanical kWh meters do not detect harmonics. Electricity suppliers do not place traditional kWh meters at companies. Nowadays, digital readable kWh meters are used. These modern meters measure the currents to the kilohertz range and include them in the measurement. This, in addition to the higher energy consumption caused by more heat development due to the high harmonics, increases the electricity costs by measuring high harmonics.