{"id":19853,"date":"2018-09-08T13:03:00","date_gmt":"2018-09-08T11:03:00","guid":{"rendered":"https:\/\/webentwicklung-hess.com\/mbs2023\/en\/2018\/09\/08\/xctb-fuer-power-quality-anwendungen-bis-20-khz\/"},"modified":"2024-11-05T18:06:46","modified_gmt":"2024-11-05T17:06:46","slug":"xctb-for-power-quality-applications-up-to-20-khz","status":"publish","type":"post","link":"https:\/\/mbs-ag.com\/en\/xctb-for-power-quality-applications-up-to-20-khz\/","title":{"rendered":"XCTB \u2013 for power quality applications up to 20 kHz"},"content":{"rendered":"

At\u00a0Light & Building<\/strong>, the world\u2019s premier trade fair for lighting and building technology in Frankfurt, which is being held from\u00a018 to 23 March 2018<\/strong>, we will be showcasing our\u00a0new XCTB series of current transformers<\/strong>.

They allow high-accuracy harmonic measurements up to 20 kHz.<\/p>

New measuring requirements for inductive current transformers in the low-voltage range<\/h2>

Changes to the structure of generation and consumption<\/strong><\/p>

Over the last few years, the proportion of renewable energy in Germany has grown massively. Wind, biomass, photovoltaic and hydroelectric plants now make up approximately 30% of the country\u2019s energy mix.

Unlike in conventional nuclear or coal-fired power stations, where all synchronous generators are used to produce electricity, here inverters or frequency converters are used. As such, it is not always possible to achieve a clean sine wave.

The distortions are caused by the switching semiconductor elements in the inverter. Harmonics generated in this way are whole multiples of the first harmonic and can extend far into the single-digit kilohertz range. The total harmonic distortion (THD) factor specifies the undesirable distortion ratio of the 50 Hz sinusoidal oscillation and regularly reaches between 10 and 30%.
In addition to the harmonics produced by inverters on the generator side, there have also been changes on the consumer side in recent years. Non-linear consumers such as LED or energy-saving lamps are pushing linear ones, like traditional incandescent bulbs, out of our daily lives almost completely.

Plug-in power supply units for mobile phones and laptops are no longer made from small transformers either, but from semiconductor circuits known as switched-mode power supplies. It would not be possible to create such small, light power supply units any other way. But these benefits are set against one big disadvantage: the current is drawn from the public grid not as a sinusoidal waveform, but in pulses. The figure below illustrates this:<\/p>

\"Diagram<\/figure>

Figure 1: Bridge rectifier with pulse current draw<\/p>

The filter capacitor shown in the diagram not only smooths the required output voltage, it is also recharged in pulses by the rectifier diodes. These steep current peaks generate reactive power on the one hand, and harmonics on the other.<\/p>

Standards regulate limit values \u2013 but not always!<\/h3>

There is already a corresponding set of international norms that limits harmonic currents in end devices with a power consumption > 75 W. Devices under 75 W are not currently covered by standards. In the interests of keeping costs down, manufacturers do not usually implement filter measures or complex power factor correction. The EN 61000-3-2 set of standards does not come into play until the 25 W mark for lamps either; for example, where energy-saving lamps are concerned, THDI values of 30 to 70% and higher are not uncommon during warm-up and in continuous duty. It should also be noted that, even when they do kick in, the standards only define limit values up to 2 kHz. As a result, manufacturers have hardly taken interference suppression into account at all when developing electronic products for the frequency range > 2 kHz in the past.<\/p>

In addition, more and more electrical motors with variable-frequency drive technology are being used in the industrial sector. Today already, the percentage of electrical motors sold that have a frequency-controlled drive stands at around 40%. The majority of these motors utilise pulse width modulation technology, which can generate THDI values in the range from 100 to 120%. Clean sine waves are almost impossible to identify at these values.<\/p>

\"Diagram:<\/figure>

<\/a><\/p>

Figure 2: Flow of current for an industrial customer on the los-voltage grid<\/p>

Power electronics have so many benefits that we can categorically state there will be no return to linear consumers such as the traditional incandescent bulb. In fact, we can expect harmonic loads to increase even further in European grids, due to the development of alternative sources of energy and the growth of non-linear consumers. We should also bear in mind that having lots of consumers that are not regulated by standards could cause considerable interference overall.<\/p>

Filter systems have already had to be installed in office buildings where just computers, telephone systems and energy-efficient bulbs are used, in order to bring problems with harmonics under control.<\/p>

Effects of harmonics<\/h3>

Grid operators are primarily interested in the economic effects of harmonics. When it comes to harmonic currents, the most important phenomena are as follows :[1]<\/a>:<\/p>